KR20230107792A - Polarizing film and manufacturing method of polarizing film - Google Patents

Abstract

The present invention provides a polarizing film that is excellent in appearance and can contribute to improvement of display characteristics of an image display device. A polarizing film according to an embodiment of the present invention is composed of a resin film containing iodine, has a thickness of 7 μm or less, and has a surface reflectance Rc ₆₈₀ of light having a wavelength of 680 nm in the direction of the absorption axis with respect to a wavelength of 400 nm in the direction of the absorption axis. The ratio of reflectance Rc ₄₀₀ of light (Rc ₄₀₀ /Rc ₆₈₀ ) exceeds 1.

Description

Polarizing film and manufacturing method of polarizing film

The present invention relates to a polarizing film and a method for manufacturing the polarizing film.

In a liquid crystal display device, which is a representative image display device, polarizing films are disposed on both sides of a liquid crystal cell due to the image forming method. In addition, along with the spread of thin displays, displays (OLED) equipped with organic electroluminescence (EL) panels and displays (QLED) using display panels using inorganic light emitting materials such as quantum dots have been proposed. These panels contain a highly reflective metal layer, and problems such as reflection of external light and reflection of the background tend to occur. Accordingly, it is known to prevent these problems by providing a circular polarizing plate including a polarizing film and a λ/4 plate on the viewing side. As a method for producing a polarizing film, for example, a method of obtaining a polarizing film on a resin substrate by stretching a laminate comprising a resin substrate and a polyvinyl alcohol (PVA)-based resin layer and then dyeing it has been proposed (eg, patent literature One). According to such a method, since a polarizing film having a thin thickness can be obtained, it is attracting attention as being able to contribute to thinning of recent image display devices. However, a polarizing film having a thin thickness is inferior in appearance, and sufficient display characteristics may not be obtained when used in an image display device.

Japanese Unexamined Patent Publication No. 2001-343521

The present invention has been made to solve the above problems, and its main object is to provide a polarizing film that is excellent in appearance and can contribute to improving display characteristics of an image display device.

According to an embodiment of the present invention, a polarizing film is provided. This polarizing film is composed of a resin film containing iodine, has a thickness of 7 µm or less, and has a reflectance (Rc ₄₀₀ ) of light having a wavelength of 400 nm in the direction of the absorption axis relative to a reflectance (Rc ₆₈₀ ) of light having a wavelength of 680 nm in the direction of the absorption axis of the surface. ) (Rc ₄₀₀ /Rc ₆₈₀ ) exceeds 1.

In one embodiment, the Rc ₆₈₀ of the surface is 5% or less.

In one embodiment, the Rc ₄₀₀ of the surface is greater than or equal to 4.8%.

In one embodiment, the polarizing film includes a gradient distribution region in which the amount of iodine increases from the front surface to the rear surface at an end portion on the surface side.

In one embodiment, in the polarizing film, the amount of iodine on the surface side is smaller than the amount of iodine on the back surface side.

In one embodiment, the polarizing film has a single transmittance of 42.0% or more and a polarization degree of 99.98% or more.

According to another aspect of the present invention, a method for manufacturing the polarizing film is provided. This manufacturing method includes washing the surface of a resin film containing iodine and having a moisture content of 15% by weight or less with water.

In one embodiment, the iodine concentration of the resin film is 5% by weight or more.

In one embodiment, the resin film is a resin layer formed on a resin substrate.

In one embodiment, the manufacturing method includes stretching the resin layer in water at 67° C. or lower.

In one embodiment, the manufacturing method includes heating the resin layer using a heating roll.

According to another aspect of the present invention, a polarizing plate is provided. This polarizing plate includes the polarizing film and a protective layer or a retardation layer disposed on at least one side of the polarizing film.

According to the present invention, a polarizing film having excellent appearance can be obtained by controlling the reflection characteristics of the surface. In addition, such a polarizing film can contribute to improvement of display characteristics of an image display device.

1 is a schematic cross-sectional view of a polarizing film according to one embodiment of the present invention.
2 is a schematic view showing an example of drying using a heating roll.
3 is a schematic cross-sectional view showing the schematic configuration of a polarizing plate according to the first embodiment of the present invention.
4 is a schematic cross-sectional view showing the schematic configuration of a polarizing plate according to a second embodiment of the present invention.
5 is a graph showing the ionic strength of iodine in the thickness direction of the polarizing films of Example 1, Comparative Example 1, and Reference Example 2.

EMBODIMENT OF THE INVENTION Hereinafter, although embodiment of this invention is described, this invention is not limited to these embodiment.

(Definition of Terms and Symbols)

Definitions of terms and symbols in this specification are as follows.

(1) Refractive index (nx, ny, nz)

'nx' is the refractive index in the direction in which the in-plane refractive index is maximized (ie, the slow axis direction), 'ny' is the refractive index in the direction orthogonal to the slow axis within the plane (ie, the fast axis direction), and 'nz' is is the refractive index in the thickness direction.

(2) In-plane phase difference (Re)

'Re(λ)' is an in-plane retardation measured with light having a wavelength of λ nm at 23°C. For example, 'Re(550)' is an in-plane retardation measured with light having a wavelength of 550 nm at 23°C. Re(λ) is obtained by the formula: Re(λ)=(nx-ny)×d when the thickness of the layer (film) is d(nm).

(3) Phase difference in thickness direction (Rth)

'Rth(λ)' is the phase difference in the thickness direction measured with light having a wavelength of λ nm at 23°C. For example, 'Rth(550)' is the phase difference in the thickness direction measured with light having a wavelength of 550 nm at 23°C. Rth(λ) is obtained by the formula: Rth(λ)=(nx-nz)×d when the thickness of the layer (film) is d(nm).

(4) Nz factor

The Nz coefficient is obtained by Nz=Rth/Re.

(5) Angle

When an angle is referred to in this specification, the angle includes both clockwise and counterclockwise directions with respect to the reference direction. Thus, for example, '45°' means ±45°.

A. Polarizer

1 is a schematic cross-sectional view of a polarizing film according to one embodiment of the present invention. In addition, in FIG. 1, cross-sections of the polarizing film are omitted from hatching for ease of viewing the drawing. The polarizing film 10 includes a first main surface (surface) 10a and a second main surface (back surface) 10b. The polarizing film 10 includes a gradient distribution region in which the amount of iodine increases from the front surface 10a toward the rear surface 10b at an end portion on the front surface 10a side.

The polarizing film 10 is composed of a resin film containing iodine. As the resin film, a hydrophilic polymer film such as a polyvinyl alcohol (PVA)-based film, a partially formalized PVA-based film, or an ethylene/vinyl acetate copolymer-based partially saponified film is used, for example.

The thickness of the polarizing film 10 is 7 μm or less, preferably 6 μm or less. A polarizing film of such a thickness tends to have a high iodine concentration. On the other hand, the thickness of the polarizing film is preferably 1 μm or more, more preferably 2 μm or more.

The polarizing film 10 preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The single transmittance (Ts) of the polarizing film 10 is preferably 41.0% or more, more preferably 42.0% or more, still more preferably 42.5% or more. On the other hand, the single transmittance of the polarizing film 10 is, for example, 44.2% or less. The degree of polarization P of the polarizing film 10 is preferably 99.95% or higher, more preferably 99.98% or higher, still more preferably 99.99% or higher. On the other hand, the degree of polarization of the polarization film 10 is, for example, 99.996% or less.

The single transmittance is typically a Y value measured using an ultraviolet and visible spectrophotometer and corrected for visibility. The degree of polarization is typically obtained by the following equation based on the parallel transmittance (Tp) and the orthogonal transmittance (Tc) obtained by measuring using a spectrophotometer for ultraviolet and visible light and performing visibility correction.

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

The ratio (Rc 400 /Rc 680 ) of the reflectance (Rc ₄₀₀ ) of light having a wavelength of 400 nm in the absorption axis direction to the reflectance (Rc ₆₈₀ ) of light having a wavelength of ₆₈₀ nm in the absorption axis direction of _the surface 10a of the polarizing film 10 is , greater than 1, preferably greater than or equal to 1.3, more preferably greater than or equal to 1.5. By satisfying this relationship, the reflection color can be well controlled and the appearance can be excellent. Specifically, redness can be suppressed and the appearance can be excellent. As a result, for example, an image display device with excellent visibility can be provided. Here, the polarizing film 10 may be disposed so that its surface 10a is on the viewing side of the image display device or on the opposite side to the viewing side, and the appearance can be excellent in either arrangement. By arranging the surface 10a of the polarizing film 10 to be on the viewing side of the image display device, it can be extremely excellent in appearance and display characteristics. On the other hand, Rc ₄₀₀ /Rc ₆₈₀ of the surface 10a of the polarizing film 10 is 2 or less, for example.

Rc ₄₀₀ of the surface 10a of the polarizing film 10 is, for example, 4.8% or more, preferably 4.9% or more, more preferably 5% or more, still more preferably 5.3% or more. On the other hand, Rc ₄₀₀ of the surface 10a of the polarizing film 10 is, for example, 6% or less. Rc ₆₈₀ of the surface 10a of the polarizing film 10 is, for example, 5% or less, preferably 4.9% or less, more preferably 4.5% or less, still more preferably 4% or less. On the other hand, Rc ₆₈₀ of the surface 10a of the polarizing film 10 is, for example, 3% or more.

The reflectance (Rp ₄₀₀ ) of light having a wavelength of 400 nm in the direction of the transmission axis of the surface 10a of the polarizing film 10 is, for example, 4.5% to 5%. The reflectance Rp ₆₈₀ of light having a wavelength of 680 nm in the direction of the transmission axis of the surface 10a of the polarizing film 10 is, for example, 4.3% to 4.8%.

Rc and Rp are the ratio of the reflected light intensity to the incident light intensity when light is incident on the surface of the polarizing film (resin film) at a predetermined angle and the reflected light in the direction of the absorption axis and the transmission axis is detected.

For example, in the polarizing film 10, the amount of iodine on the front surface 10a side is smaller than the amount of iodine on the back surface 10b side. Specifically, the polarizing film 10 includes, in this order, a first region 11 and a second region 12 in which iodine distribution is different from the surface side. The first region 11 is a gradient distribution region in which the amount of iodine increases from the front surface 10a toward the rear surface 10b. In the second region 12, iodine is uniformly distributed. Here, uniformity means that the intensity derived from iodine (for example, of iodine ions) detected by analysis, for example, is within the range of -20% to +20% of the average value. The thickness of the first region 11 is preferably 2% or more and 50% or less of the thickness of the polarizing film 10, more preferably 10% or more and 40% or less. The thickness of the first region 11 may be 20% or more of the thickness of the polarizing film 10 . Specifically, the thickness of the first region 11 is preferably 100 nm or more and 2.7 μm or less, more preferably 500 nm or more and 2 μm or less. The thickness of the first region 11 may be 1 μm or more. According to this range, excellent optical characteristics (the single transmittance and polarization degree) and excellent external appearance can be achieved, for example.

Although not shown, for example, the polarizing film may include, in this order, a first region, a second region, and a third region in which iodine distribution is different from the surface side. Specifically, the polarizing film may include a first region in which the amount of iodine increases from the front surface to the back surface, a second region in which iodine is uniformly distributed, and a third region in which the amount of iodine decreases from the front surface side to the back surface.

B. Manufacturing method

The polarizing film is obtained by washing the surface of a resin film containing iodine and having a predetermined moisture content. The water content of the resin film (before washing with water) is 15% by weight or less, preferably 12% by weight or less, more preferably 9% by weight or less, still more preferably 6% by weight or less. On the other hand, the moisture content of the resin film is, for example, 3% by weight or more. By washing the resin film having such a moisture content with water, the polarizing film can be produced satisfactorily. Specifically, it is possible to favorably control the reflective properties (eg reflectance, color) of the surface while maintaining excellent optical properties. For example, by lowering the reflectance in the long-wavelength region of 550 nm or more, the red color can be suppressed, and the blue color can be recognized with the naked eye.

The iodine concentration of the resin film may be, for example, 5% by weight or more, 5.5% by weight or more, or 6% by weight or more. The iodine concentration of the resin film is, for example, 8% by weight or less. The thickness of the resin film is, for example, 7 μm or less, and may be 6 μm or less. The thickness of the resin film is preferably 1 μm or more, more preferably 2 μm or more. It is one of the characteristics of the present invention that an excellent appearance can be achieved at such an iodine concentration and thickness.

B-1. resin film

For the resin film having a predetermined water content, for example, a resin layer (typically, a polyvinyl alcohol-based resin layer) is formed on a resin substrate to produce a laminate, and the laminate (resin layer) is stretched and dyed with iodine. It can be obtained by (for example, dyeing by adsorption of iodine) and then drying the layered product (resin layer).

B-1-1. laminate

In one embodiment, the laminate is produced by forming a PVA-based resin layer containing a polyvinyl alcohol (PVA)-based resin and a halide on a thermoplastic resin substrate (for example, a long image). Specifically, a laminate is produced by applying a coating liquid containing a PVA-based resin and a halide onto a thermoplastic resin base material and drying it.

The thickness of the thermoplastic resin substrate is preferably 20 μm to 300 μm, more preferably 50 μm to 200 μm. If it is less than 20 μm, there is a possibility that formation of the PVA-based resin layer becomes difficult. When it exceeds 300 µm, for example, in underwater stretching described later, time is required for the thermoplastic resin substrate to absorb water, and there is a risk that an excessive load may be required for stretching.

The water absorption of the thermoplastic resin substrate is preferably 0.2% or more, more preferably 0.3% or more. Such a thermoplastic resin substrate can absorb water and can be plasticized by the water acting as a plasticizer. As a result, the drawing stress can be greatly reduced and the drawing can be performed at a high magnification. On the other hand, the water absorption of the thermoplastic resin substrate is preferably 3.0% or less, more preferably 1.0% or less. According to such an absorption rate, problems such as significantly deteriorating the dimensional stability of the thermoplastic resin substrate during production and deterioration of the quality of the resulting polarizing film can be prevented. In addition, it is possible to prevent breakage of the thermoplastic resin substrate or peeling of the PVA-based resin layer during underwater stretching. The water absorption of the thermoplastic resin substrate can be adjusted, for example, by introducing a modifier into the constituent material. In addition, water absorption is a value calculated according to JIS K 7209.

The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120°C or less. By using such a thermoplastic resin substrate, the stretchability of the laminate can be sufficiently secured while suppressing crystallization of the PVA-based resin layer. Further, considering that plasticization of the thermoplastic resin base material with water and stretching in water are satisfactorily performed, the Tg is more preferably 100°C or less, still more preferably 90°C or less. On the other hand, the Tg of the thermoplastic resin substrate is preferably 60°C or higher. According to such Tg, problems such as deformation of the thermoplastic resin substrate (eg, occurrence of unevenness, sagging, wrinkles, etc.) can be prevented and a laminate can be produced satisfactorily when the coating liquid is applied and dried. Also, the stretching of the resin layer can be satisfactorily performed at a suitable temperature (eg, about 60° C.). The Tg of the thermoplastic resin substrate can be adjusted by, for example, heating using a crystallization material that introduces a modifier into the constituent material. In addition, the glass transition temperature (Tg) is a value obtained according to JIS K 7121.

As a constituent material of the thermoplastic resin substrate, any suitable thermoplastic resin can be employed. As the thermoplastic resin, for example, ester-based resins such as polyethylene terephthalate-based resins, cycloolefin-based resins such as norbornene-based resins, olefin-based resins such as polypropylene, polyamide-based resins, polycarbonate-based resins, and copolymer resins thereof can be heard Among these, norbornene-type resin and amorphous polyethylene terephthalate-type resin are preferable.

In one embodiment, an amorphous (non-crystallized) polyethylene terephthalate-based resin is preferably used. Among them, amorphous (hard to crystallize) polyethylene terephthalate-based resins are particularly preferably used. Specific examples of the amorphous polyethylene terephthalate-based resin include copolymers further containing isophthalic acid and/or cyclohexanedicarboxylic acid as dicarboxylic acid, and further containing cyclohexanedimethanol or diethylene glycol as glycol. A copolymer is mentioned.

In another embodiment, a polyethylene terephthalate-based resin having an isophthalic acid unit is preferably used. This is because the stretchability is extremely excellent and crystallization during stretching can be suppressed. This is considered to be due to imparting large waviness to the main chain by introducing an isophthalic acid unit. The polyethylene terephthalate-based resin has a terephthalic acid unit and an ethylene glycol unit. The content of the isophthalic acid unit is preferably 0.1 mol% or more, and more preferably 1.0 mol% or more, with respect to the total of all repeating units. This is because a thermoplastic resin substrate extremely excellent in stretchability can be obtained. On the other hand, the content of the isophthalic acid unit is preferably 20 mol% or less, more preferably 10 mol% or less, with respect to the total of all repeating units. This is because the degree of crystallinity can be favorably increased in drying described later.

The thermoplastic resin substrate may be stretched in advance (eg, before forming the PVA-based resin layer). In one embodiment, it is stretched in the transverse direction of a long thermoplastic resin base material. The transverse direction is preferably a direction orthogonal to the stretching direction of the laminate described later. In addition, in this specification, 'orthogonal' also includes the case of being substantially orthogonal. Here, 'substantially orthogonal' includes the case of 90°±5.0°, preferably 90°±3.0°, more preferably 90°±1.0°. The stretching temperature of the thermoplastic resin substrate is preferably Tg -10°C to Tg +50°C relative to the glass transition temperature (Tg) of the thermoplastic resin substrate. The draw ratio of the thermoplastic resin substrate is preferably 1.5 to 3.0 times. As a method for stretching the thermoplastic resin substrate, any suitable method may be employed. Specifically, fixed-end stretching may be used or free-end stretching may be used. The stretching method may be dry or wet. Stretching may be performed in one step or in multiple steps. In the case of performing in multiple steps, the draw ratio is the product of the draw ratios of each step.

The coating liquid is typically a solution in which a PVA-based resin and a halide are dissolved in a solvent. 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. can be heard These can be used individually or in combination of 2 or more types. Among these, water is preferable. The content of the PVA-based resin in the coating liquid is preferably 3 parts by weight to 20 parts by weight with respect to 100 parts by weight of the solvent. According to such a range, a uniform coating film adhering to the thermoplastic resin substrate can be formed. The content of the halide in the coating liquid is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

As said PVA-type resin, polyvinyl alcohol and an ethylene-vinyl alcohol copolymer are mentioned, for example. 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%, and more preferably 99.0 mol% to 99.93 mol%. By using a PVA-based resin having such a degree of saponification, a polarizing film having excellent durability can be obtained. When the degree of saponification is too high, there is a possibility of gelation. In addition, the degree of saponification can be obtained according to JIS K 6726-1994.

The average degree of polymerization of the PVA-based resin is usually 1000 to 10000, preferably 1200 to 4500, and more preferably 1500 to 4300. In addition, the average degree of polymerization can be obtained according to JIS K 6726-1994.

As the halide, any suitable halide can be employed. For example, iodides, such as potassium iodide, sodium iodide, and lithium iodide, and chlorides, such as sodium chloride, are mentioned. Among these, potassium iodide is preferable. By using a halide, a polarizing film having excellent optical properties can be obtained. Specifically, crystallization of the PVA-based resin after air-assisted stretching described later is promoted, and in subsequent wet treatment (e.g., dyeing, underwater stretching described later), disorder of orientation of polyvinyl alcohol molecules and decrease in orientation are suppressed. , a polarizing film having excellent optical properties can be obtained.

In preparation of the coating liquid, it is preferable to blend 5 parts by weight to 20 parts by weight of the halide, more preferably 10 parts by weight to 15 parts by weight, with respect to 100 parts by weight of the PVA-based resin. Specifically, the content of the halide in the obtained PVA-based resin layer is preferably 5 parts by weight to 20 parts by weight, more preferably 10 parts by weight to 15 parts by weight with respect to 100 parts by weight of the PVA-based resin. . When the amount of the halide relative to the PVA-based resin is large, the halide bleeds out, for example, and the obtained polarizing film may become cloudy.

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. These are used, for example, for the purpose of improving the uniformity, dyeability, and stretchability of the obtained PVA-based resin layer.

Examples of the coating method for applying the coating solution include a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, and a knife coating method (comma coating method etc.). can The coating/drying temperature of the coating liquid is preferably 50°C or higher.

The thickness of the PVA-based resin layer is preferably 3 μm to 40 μm, more preferably 3 μm to 20 μm.

Before forming the PVA-based resin layer, surface treatment (for example, corona treatment) may be performed on the thermoplastic resin substrate, or an easily adhesive layer may be formed on the thermoplastic resin substrate. By performing such a process, the adhesiveness of a thermoplastic resin base material and a PVA system resin layer can be improved.

B-1-2. stretching

It is preferable to carry out the above-mentioned stretching by underwater stretching after dry stretching (air assisted stretching) of the above-mentioned layered product. By auxiliary stretching, the thermoplastic resin substrate can be stretched while suppressing crystallization, and in boric acid water stretching, the problem of deterioration in stretchability due to excessive crystallization of the thermoplastic resin substrate can be solved, and the laminate can be stretched at a higher magnification. there is. In addition, in the case of using a thermoplastic resin substrate, since the application temperature can be set low, the crystallization of the PVA-based resin is relatively low, resulting in a problem that sufficient optical properties cannot be obtained. In contrast, by introducing auxiliary stretching, the crystallinity of the PVA-based resin can be enhanced even when a thermoplastic resin is used. In addition, by 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 during a subsequent wet treatment. In this way, a polarizing film having excellent optical properties can be obtained.

The method of air-assisted stretching may be fixed end stretching (eg, a method of stretching using a tenter stretching machine), or free end stretching (eg, a method of uniaxial stretching by passing a laminate between rolls having different circumferential speeds) ) may be Preferably, free end stretching is employed. For example, heating roll stretching is employed in which the laminate is stretched by a difference in circumferential speed between heating rolls while conveying the laminate in its longitudinal direction. In one embodiment, air assisted stretching includes a zone stretching process in a heat space (zone) and a heated roll stretching process. The order of the zone stretching process and the hot roll stretching process is not limited, but, for example, the zone stretching process and the hot roll stretching process are performed in this order. In another embodiment, in a tenter stretching machine, an end portion of the film is held and the film is stretched by extending the distance between tenters in the flow direction (the widening of the distance between tenters becomes the stretching ratio). At this time, the distance of the tenter in the width direction (direction perpendicular to the flow direction) is preferably set so as to be closer to free end stretching with respect to the stretching ratio in the flow direction. In the case of free end stretching, the shrinkage rate in the width direction is calculated by the formula: Shrinkage rate in the width direction = (1/stretch ratio) ^1/2 .

The draw ratio of air assisted stretching is preferably 2.0 to 3.5 times. Air assisted stretching may be performed in one step or may be performed in multiple steps. When performing in multiple steps, the draw ratio is the product of the draw ratios of each step. The stretching direction in air assisted stretching is preferably substantially the same as the stretching direction in underwater stretching described later.

The stretching temperature of the air-assisted stretching is set to any appropriate value depending on, for example, the thermoplastic resin substrate used, the stretching method, and the like. The stretching temperature is preferably equal to or higher than the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably equal to or higher than Tg +10°C, still more preferably equal to or higher than Tg +15°C. On the other hand, the upper limit of the stretching temperature is preferably 170°C. By stretching at such a temperature, rapid crystallization of the PVA-based resin can be suppressed, and defects caused by the crystallization (eg, obstruction of orientation of the PVA-based resin layer by stretching) can be suppressed.

The underwater stretching is typically performed by immersing the laminate in a stretching bath. In water stretching, stretching can be performed at a temperature lower than the glass transition temperature (typically, about 80° C.) of the thermoplastic resin substrate or the PVA-based resin layer, and the PVA-based resin layer can be stretched at a high magnification while suppressing its crystallization. can As a result, a polarizing film having excellent optical properties can be obtained.

The method of underwater stretching may be fixed-end stretching or free-end stretching (for example, a method of uniaxially stretching a laminate by passing it between rolls having different circumferential speeds). Preferably, free end stretching is employed. Stretching of the laminate may be performed in one step or may be performed in multiple steps. When performing in multiple steps, the draw ratio of the laminated body mentioned later is the product of the draw ratio of each step.

Stretching in water is preferably performed by immersing the layered product in an aqueous boric acid solution (stretching in boric acid water). By using a boric acid aqueous solution as a stretching bath, rigidity that can withstand the tension applied during stretching and water resistance that does not dissolve in water can be imparted to the PVA-based resin layer. Specifically, boric acid can generate tetrahydroxyboric acid anion in an aqueous solution and cross-link it with PVA-based resin through hydrogen bonding. As a result, rigidity and water resistance are imparted to the PVA-based resin layer, and a polarizing film that can be stretched satisfactorily and has excellent optical properties can be obtained.

The aqueous solution of boric acid is preferably obtained by dissolving boric acid and/or a boric acid salt in water as a solvent. The concentration of boric acid is preferably 1 part by weight to 10 parts by weight, more preferably 2.5 parts by weight to 6 parts by weight, still more preferably 3 parts by weight to 5 parts by weight, based on 100 parts by weight of water. By setting the boric acid concentration to 1 part by weight or more, dissolution of the PVA-based resin layer can be effectively suppressed, and a polarizing film with higher characteristics can be manufactured. In addition to boric acid or borate salts, an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde, or the like in a solvent can also be used.

Preferably, iodide is incorporated into the stretching bath (boric acid aqueous solution). By blending iodide, elution of iodine adsorbed to the PVA-based resin layer can be suppressed. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. The concentration of iodide is preferably from 0.05 parts by weight to 15 parts by weight, more preferably from 0.5 parts by weight to 8 parts by weight, based on 100 parts by weight of water.

The stretching temperature (liquid temperature of the stretching bath) is preferably 40°C or higher, and more preferably 60°C or higher. At such a temperature, it can be extended at a high magnification while suppressing dissolution of the PVA-based resin layer. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60°C or higher in relation to formation of the PVA-based resin layer. In this case, if the stretching temperature is lower than 40°C, there is a risk that satisfactory stretching may not be possible even if plasticization of the thermoplastic resin substrate by water is taken into consideration. On the other hand, the stretching temperature is, for example, 70°C or lower, preferably 67°C or lower, and more preferably 65°C or lower. The higher the stretching temperature, the higher the solubility of the PVA-based resin layer, and there is a risk that excellent optical properties cannot be obtained. In addition, according to such a stretching temperature, it is possible to suppress swelling and dissolution of the PVA-based resin layer in water washing described later, and obtain a polarizing film having excellent surface properties. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

The draw ratio by underwater stretching is preferably 1.5 times or more, and more preferably 3.0 times or more. The total stretching ratio of the laminate (stretch ratio combining air assisted stretching and underwater stretching) is preferably 5.0 times or more, more preferably 5.5 times or more, and still more preferably 5.5 times or more of the original length of the laminate. It is more than 6.0 times. By achieving such a high draw ratio, a polarizing film having extremely excellent optical properties can be manufactured. Such a high draw ratio can be achieved by adopting an underwater stretching method (boric acid underwater stretching).

B-1-3. dyeing

The dyeing is typically performed by adsorbing iodine to the PVA-based resin layer. As a method for adsorbing iodine, for example, a method of immersing a PVA-based resin layer (laminate) in a dye containing iodine, a method of coating the dye solution on a PVA-based resin layer, and a method of applying the dye solution to a PVA-based resin layer. A method of spraying may be mentioned. Preferably, it is the method of immersing a layered product in a dyeing solution (dyeing bath). This is because iodine can be favorably adsorbed.

The staining solution is preferably an iodine aqueous solution. The blending amount of iodine is preferably 0.05 to 0.5 parts by weight with respect to 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to blend iodide in an aqueous solution of iodine. Specific examples of iodide are as described above. Preferably potassium iodide is used. The blending amount of iodide is preferably from 0.1 part by weight to 10 parts by weight, more preferably from 0.3 part by weight to 5 parts by weight, based on 100 parts by weight of water. The liquid temperature at the time of dyeing of the dyeing solution is preferably 20°C to 50°C in order to suppress dissolution of the PVA-based resin. In the case of immersing the PVA-based resin layer in the dye solution, the immersion time is preferably 5 seconds to 5 minutes, more preferably 30 seconds to 90 seconds, in order to ensure the transmittance of the PVA-based resin layer.

Dyeing conditions (concentration, liquid temperature, immersion time) can be set such that, for example, the finally obtained polarizing film has a single transmittance of 42.0% or more and a polarization degree of 99.98% or more. As such a dyeing condition, for example, in an iodine aqueous solution as a dyeing solution, the ratio of the contents of iodine and potassium iodide is preferably 1:5 to 1:20, more preferably 1:5 to 1:10.

When dyeing is performed continuously after a treatment in which the laminate is immersed in a treatment bath containing boric acid (eg, insolubilization treatment described later), boric acid is mixed in the dye bath, the concentration of boric acid in the dye bath changes, and dyeability becomes unstable There are cases. In order to suppress such destabilization of dyeability, the concentration of boric acid in the dyeing bath is preferably adjusted to 4 parts by weight or less, more preferably 2 parts by weight or less with respect to 100 parts by weight of water. On the other hand, the concentration of boric acid in the dyeing bath is preferably 0.1 part by weight or more, more preferably 0.2 part by weight or more, and even more preferably 0.5 part by weight or more with respect to 100 parts by weight of water. In one embodiment, dyeing is performed using a dyeing bath containing boric acid in advance. According to such an aspect, the rate of change in boric acid concentration when boric acid is mixed in a dyeing bath can be reduced. The amount of boric acid blended in advance in the dyeing bath (content of boric acid not derived from the treatment bath) is preferably 0.1 part by weight to 2 parts by weight, more preferably 0.5 part by weight to 100 parts by weight of water. 1.5 parts by weight.

B-1-4. other processing

If necessary, insolubilization treatment is performed after the air-assisted stretching and before underwater stretching and dyeing. The insolubilization treatment is typically performed by immersing the PVA-based resin layer in boric acid aqueous solution. By performing the insolubilization treatment, water resistance can be imparted to the PVA-based resin layer, and a decrease in the orientation of PVA when immersed in water can be prevented. The concentration of the boric acid aqueous solution in the insolubilization treatment is preferably 1 part by weight to 4 parts by weight with respect to 100 parts by weight of water. The temperature of the insolubilization treatment (liquid temperature of boric acid aqueous solution) is preferably 20°C to 50°C.

If necessary, a crosslinking treatment is performed after dyeing and before stretching in water. The crosslinking treatment is typically performed by immersing the PVA-based resin layer in boric acid aqueous solution. By carrying out the crosslinking treatment, water resistance can be imparted to the PVA-based resin layer, and a decrease in orientation of the PVA can be prevented in subsequent underwater stretching. The concentration of the boric acid aqueous solution in the crosslinking treatment is preferably 1 part by weight to 5 parts by weight with respect to 100 parts by weight of water. It is preferable to blend iodide in an aqueous solution of boric acid. By blending iodide, elution of iodine adsorbed to the PVA-based resin layer can be suppressed. Specific examples of iodide are as described above. The blending amount of iodide is preferably 1 part by weight to 5 parts by weight with respect to 100 parts by weight of water. The temperature of the crosslinking treatment (liquid temperature of the boric acid aqueous solution) is preferably 20°C to 50°C.

Preferably, washing is performed after stretching in water and before drying described later. Washing is typically performed by immersing the PVA-based resin layer in an aqueous solution of potassium iodide.

B-1-5. dry

The drying may be performed in any suitable method and condition as long as a resin film having the predetermined moisture content can be obtained. Specifically, it may be performed by heating the entire zone (zone heating method) or by heating the conveying roll (heating roll method). Preferably, a heating roll system is employed, and more preferably, both are employed. By using a heating roll, heating curling of the layered product can be efficiently suppressed, and a polarizing film having excellent quality can be manufactured. Specifically, by drying in a state where the laminate is attached to a heating roll, the crystallization of the thermoplastic resin substrate can be efficiently promoted to increase the crystallinity, and even at a relatively low drying temperature, the crystallinity of the thermoplastic resin substrate can be increased satisfactorily. can make it As a result, the rigidity of the thermoplastic resin substrate is increased, and it is in a state capable of withstanding shrinkage of the PVA-based resin layer due to drying, and curl is suppressed. In addition, since the laminate can be dried while maintaining a flat state by using a heating roll, not only curling but also occurrence of wrinkles can be suppressed.

By drying, the laminate can be contracted in the width direction to improve optical properties. This is because the orientation properties of PVA and PVA/iodine complexes can be effectively increased. The shrinkage rate of the laminate in the width direction by drying is preferably 1% to 10%, more preferably 2% to 8%, still more preferably 4% to 6%. By using a heating roll, the laminate can be continuously contracted in the width direction while conveying, and high productivity can be realized.

Fig. 2 is a schematic view showing an example of drying using a heating roll. In the illustrated example, the laminate 200 is dried while being conveyed by conveyance rolls R1 to R6 and guide rolls G1 to G4 heated to a predetermined temperature. In the illustrated example, conveyance rolls R1 to R6 are arranged so that the surface of the PVA-based resin layer and the surface of the thermoplastic resin substrate are continuously heated alternately. The conveying rolls R1 to R6 may be disposed so as to continuously heat only the substrate surface).

Drying conditions can be controlled by adjusting the heating temperature of the conveyance rolls (temperature of the heating rolls), the number of heating rolls, and the contact time with the heating rolls. The temperature of the heating roll is preferably 60°C to 120°C, more preferably 65°C to 100°C, still more preferably 70°C to 80°C. According to such a temperature, while being able to suppress curl by increasing the crystallinity of a thermoplastic resin, extremely excellent durability can be provided to a laminated body. In addition, the moisture content of the resin film can be achieved satisfactorily. In addition, the temperature of a heating roll can be measured with a contact thermometer. In the illustrated example, although six conveyance rolls are provided, there is no particular restriction as long as there are a plurality of conveyance rolls. The conveyance rolls are usually provided in 2 to 40 pieces, preferably 4 to 30 pieces. The contact time (total contact time) between the laminate and the heating roll is preferably 1 second to 300 seconds, more preferably 1 to 20 seconds, still more preferably 1 to 10 seconds.

The heating roll may be provided in a heating furnace (for example, an oven) or may be provided in a normal production line (in a room temperature environment). Preferably, it is provided in a heating furnace equipped with a blowing means. By using both heating roll drying and hot air drying, rapid temperature change between the heating rolls can be suppressed, and shrinkage in the width direction can be easily controlled. The temperature of hot air drying is preferably 30°C to 100°C. In addition, the hot air drying time is preferably 1 second to 300 seconds. The wind speed of the hot air is preferably about 10 m/s to 30 m/s. In addition, the said wind speed is the wind speed in a heating furnace, and can be measured with a mini-vane type digital anemometer.

B-2. Suse

The washing with water is performed, for example, by bringing water into contact with the surface of the resin film. For example, water washing is performed by immersing the resin film in a water bath. When the resin film is immersed in a water bath, the back surface of the resin film is preferably protected with any suitable protective substrate. In one embodiment, the above resin substrate is used as the protective substrate. Specifically, the resin film is immersed in a water bath without peeling the resin substrate from the resin film (in the state of the laminate). In another embodiment, a protective layer described later is used as the protective substrate. For example, after laminating a protective layer on the surface of the resin film of the laminate, the resin substrate is separated from the resin film to produce a laminate of the protective layer and the resin film, and the laminate is immersed in a water bath. When immersed in a water bath, the resin film may be long or sheet-shaped.

The temperature of the water bath (water to be contacted) is, for example, 20°C or higher, preferably 25°C or higher, more preferably 30°C or higher, still more preferably 35°C or higher, and particularly preferably 40°C or higher. am. At such a temperature, for example, a polarizing film satisfying the above reflectance can be produced in a short time. On the other hand, the temperature of the water bath (water to be contacted) is preferably 60°C or lower, more preferably 50°C or lower. At such a temperature, for example, the obtained polarizing film has excellent surface properties and can maintain excellent optical properties.

The immersion time (contact time) in the water bath is set according to the temperature, the thickness of the resin film, and the like, for example. The immersion time in the water bath is preferably 15 seconds to 5 minutes, more preferably 30 seconds to 3 minutes.

The water bath (water to be brought into contact with) may contain additives such as boric acid.

After washing with water, the polarizing film may be subjected to a drying treatment. The drying temperature is, for example, 30°C to 60°C. The drying time is, for example, 15 seconds to 3 minutes.

C. Polarizer

A polarizing plate according to one embodiment of the present invention includes the polarizing film and a protective layer or a retardation layer disposed on at least one side of the polarizing film.

3 is a schematic cross-sectional view showing a schematic configuration of a polarizing plate according to a first embodiment of the present invention. A polarizing plate (polarizing plate with a retardation layer) 100 includes a polarizing film 10, a protective layer 20, a retardation layer 30, and an adhesive layer 40 in this order. In the polarizing plate 100, the protective layer 20 is disposed only on the back surface 10b side of the polarizing film 10, and the protective layer is not disposed on the surface 10a side (e.g., the viewer side), but practically , the surface 10a of the polarizing film 10 is protected with any suitable protective material (not shown). For example, after processing is performed on the polarizing film 10 of the polarizing plate 100, a protective material is laminated on the polarizing film 10. The retardation layer 30 may be a single layer or may include a laminated structure in which two or more layers are laminated.

4 is a schematic cross-sectional view showing a schematic configuration of a polarizing plate according to a second embodiment of the present invention. The polarizing plate (polarizing plate with a retardation layer) 110 includes the protective layer 20 disposed on the back surface 10b side of the polarizing film 10, the polarizing film 10, and the surface 10a side of the polarizing film 10. The disposed retardation layer 30 and the pressure-sensitive adhesive layer 40 are included in this order from the viewing side. In the present embodiment, the retardation layer 30 can function as a protective layer of the polarizing film 10, and the retardation layer 30 is disposed on the surface 10a side of the polarizing film 10 according to the first embodiment. different from the form

Although not shown, the polarizing plate may further contain other functional layers. The type, characteristics, number, combination, arrangement, etc. of functional layers that can be included in the polarizing plate may be appropriately set according to the purpose. For example, the polarizing plate may further contain a conductive layer or an isotropic substrate with a conductive layer. A polarizing plate (polarizing plate with a retardation layer) containing a conductive layer or an isotropic base material with a conductive layer is applied, for example, to a so-called inner touch panel type input display device in which a touch sensor is incorporated inside an image display panel. As another example, the polarizing plate may further contain other retardation layers. Other optical characteristics (eg, refractive index characteristics, in-plane retardation, Nz coefficient, photoelastic coefficient), thickness, arrangement, etc. of the retardation layer may be appropriately set depending on the purpose. As a specific example, on the viewing side of the polarizing film 10, another retardation layer (typically, a layer imparting a (other) circular polarization function) that improves visibility when viewed through polarized sunglasses, a layer imparting an ultra-high phase difference layer) may be provided. By including such a layer, excellent visibility can be realized even when the display screen is visually recognized through polarized lenses such as polarized sunglasses. Therefore, the obtained polarizing plate (polarizing plate with retardation layer) can be suitably applied also to an image display device that can be used outdoors.

Each member constituting the polarizing plate may be laminated with an arbitrary appropriate adhesive layer (not shown) interposed therebetween. As a specific example of an adhesive layer, an adhesive bond layer and an adhesive layer are mentioned. Specifically, the retardation layer 30 may be bonded to the polarizing film 10 or the protective layer 20 via an adhesive layer (preferably using an active energy ray curable adhesive), or via an adhesive layer to It may be bonded to the film 10 or the protective layer 20 . When the retardation layer 30 includes a laminated structure of two or more layers, each retardation layer is bonded through an adhesive layer (preferably, using an active energy ray curable adhesive), for example.

Although not shown, a peeling film (separator) is bonded to the surface of the pressure-sensitive adhesive layer 40 practically. The peeling film may be temporarily adhered until the polarizing plate is put into use. By using a peeling film, roll formation of a polarizing plate becomes possible while protecting an adhesive layer, for example.

The polarizing plate may be long or sheeted. In this specification, "elongated shape" refers to an elongated shape in which the length is sufficiently long relative to the width, for example, an elongated shape in which the length is 10 times or more, preferably 20 times or more, with respect to the width. A polarizing plate of the shape of a long picture can be wound in roll shape.

C-1. protective layer

The protective layer 20 may be formed of any suitable film that can be used as a protective layer of a polarizing film. Specific examples of the material serving as the main component of the film include cellulose-based resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, Transparent resins, such as cycloolefin types, such as a polysulfone type, polystyrene type, and polynorbornene type, a polyolefin type, (meth)acryl type, and an acetate type, are mentioned.

The said polarizing plate is typically arrange|positioned on the viewing side of an image display apparatus. Therefore, surface treatment such as hard coat (HC) treatment, antireflection treatment, anti-sticking treatment, antiglare treatment, etc. may be applied to the protective layer 20 as needed (for example, in the form shown in FIG. 4). .

The thickness of the protective layer 20 is preferably 5 μm to 80 μm, more preferably 10 μm to 40 μm, still more preferably 10 μm to 30 μm. In addition, when the said surface treatment is performed, the thickness of the protective layer 20 is the thickness including the thickness of the surface treatment layer.

The protective layer disposed between the polarizing film 10 and the retardation layer 30 is preferably optically isotropic in one embodiment. In this specification, 'optically isotropic' means that the in-plane retardation Re (550) is 0 nm to 10 nm and the thickness direction retardation Rth (550) is -10 nm to +10 nm.

In one embodiment, the resin substrate may be used as a protective layer of a polarizing film. For example, in the form shown in Fig. 3, the manufacturing process can be reduced by using the resin substrate as it is as a protective layer.

C-2. phase contrast layer

As the retardation layer 30, any appropriate structure can be employed. In one embodiment, as the retardation layer 30, an orientation fixation layer of liquid crystal compounds (liquid crystal orientation fixation layer) is used. By using a liquid crystal compound, the difference between nx and ny of the retardation layer obtained can be significantly increased compared to non-liquid crystal materials, so that the thickness of the retardation layer for obtaining a desired in-plane retardation can be significantly reduced. In this specification, the 'alignment fixed layer' refers to a layer in which liquid crystal compounds are aligned in a predetermined direction within the layer and the alignment state is fixed. In addition, the 'alignment hardened layer' is a concept including an alignment hardened layer obtained by curing a liquid crystal monomer as will be described later. In the retardation layer, rod-shaped liquid crystal compounds are typically aligned in a state aligned in the direction of the slow axis of the retardation layer (homogeneous orientation).

The thickness of the retardation layer depends on its structure (whether it is a single layer or a laminated structure), but is preferably 8 μm or less, and more preferably 5 μm or less. On the other hand, the thickness of the retardation layer is, for example, 1 μm or more. In addition, when the retardation layer has a laminated structure, 'the thickness of the retardation layer' means the sum of the thicknesses of each retardation layer. Specifically, the thickness of the adhesive layer is not included in the 'thickness of the retardation layer'.

The liquid-crystal alignment hardening layer performs orientation treatment on the surface of a predetermined base material, applies a coating solution containing a liquid crystal compound to the surface, aligns the liquid crystal compound in a direction corresponding to the orientation treatment, and is aligned in the orientation state. It can be formed by fixing. As the orientation treatment, any suitable orientation treatment can be employed. Specifically, a mechanical orientation treatment, a physical orientation treatment, and a chemical orientation treatment are mentioned. Specific examples of the mechanical orientation treatment include rubbing treatment and stretching treatment. Specific examples of the physical orientation treatment include magnetic field orientation treatment and electric field orientation treatment. Specific examples of the chemical orientation treatment include an oblique deposition method and an optical orientation treatment. Arbitrary appropriate conditions may be employed for the treatment conditions of various alignment treatments depending on the purpose.

The alignment of the liquid crystal compound is performed by treating at a temperature at which a liquid crystal phase is exhibited depending on the type of the liquid crystal compound. By performing such a temperature treatment, the liquid crystal compound assumes a liquid crystal state, and the liquid crystal compound is oriented along the orientation treatment direction of the surface of the substrate.

In one embodiment, the alignment state is fixed by cooling the liquid crystal compound aligned as described above. When the liquid crystal compound is a polymerizable monomer or a crosslinkable monomer, the alignment state is fixed by subjecting the liquid crystal compound aligned as described above to a polymerization treatment or a crosslinking treatment.

The specific example of a liquid crystal compound and the detail of the formation method of an alignment hardening layer are described in Unexamined-Japanese-Patent No. 2006-163343. The description of the publication is incorporated herein by reference.

When the retardation layer 30 is a single layer, the retardation layer 30 can function as a λ/4 plate, for example. Specifically, Re(550) of the retardation layer is preferably 100 nm to 180 nm, more preferably 110 nm to 170 nm, still more preferably 110 nm to 160 nm. The thickness of the retardation layer can be adjusted so that a desired in-plane retardation of the λ/4 plate is obtained. When the retardation layer is the above-mentioned liquid crystal orientation solidified layer, the thickness is, for example, 1.0 μm to 2.5 μm. In the present embodiment, the angle between the slow axis of the retardation layer and the absorption axis of the polarizing film is preferably 40° to 50°, more preferably 42° to 48°, still more preferably 44° to 46°. am. In this embodiment, the retardation layer preferably exhibits reverse dispersion wavelength characteristics in which the retardation value increases depending on the wavelength of the measurement light. Further, in this embodiment, the polarizing plate may further include a layer exhibiting a refractive index characteristic of nz>nx=ny (other retardation layers, not shown).

When the retardation layer 30 includes a laminated structure, the retardation layer 30 includes, for example, a two-layer laminated structure in which an H layer and a Q layer are sequentially disposed from the polarizing film 10 side. The H layer can typically function as a λ/2 plate, and the Q layer can typically function as a λ/4 plate. Specifically, Re(550) of the H layer is preferably 200 nm to 300 nm, more preferably 220 nm to 290 nm, still more preferably 230 nm to 280 nm; Re(550) of the Q layer is preferably 100 nm to 180 nm, more preferably 110 nm to 170 nm, still more preferably 110 nm to 150 nm. The thickness of the H layer can be adjusted so that a desired in-plane retardation of the λ/2 plate is obtained. When H layer is the above-mentioned liquid-crystal orientation hardening layer, the thickness is 2.0 micrometer - 4.0 micrometer, for example. The thickness of the Q layer can be adjusted to obtain the desired in-plane retardation of the λ/4 plate. When the Q layer is the above-mentioned liquid crystal alignment solidified layer, the thickness thereof is, for example, 1.0 μm to 2.5 μm. In the present embodiment, the angle between the slow axis of the H layer and the absorption axis of the polarizing film is preferably 10° to 20°, more preferably 12° to 18°, still more preferably 12° to 16°. ego; The angle between the slow axis of the Q layer and the absorption axis of the polarizing film is preferably 70° to 80°, more preferably 72° to 78°, still more preferably 72° to 76°. When the retardation layer 30 includes a laminated structure, each layer (e.g., H layer and Q layer) may exhibit a reverse dispersion wavelength characteristic in which the retardation value increases with the wavelength of the measurement light, and the retardation value corresponds to the wavelength of the measurement light. It may exhibit a positive wavelength dispersion characteristic that decreases with , or may exhibit a flat wavelength dispersion characteristic in which the retardation value hardly changes even with the wavelength of the measurement light.

The refractive index characteristic of the retardation layer 30 (each layer in the case of including a laminated structure) typically shows a relationship of nx>ny=nz. In addition, 'ny=nz' includes not only a case where ny and nz are completely equal, but also a case where ny and nz are substantially equal. Therefore, there may be cases where ny>nz or ny<nz is satisfied within a range that does not impair the effect of the present invention. The Nz coefficient of the retardation layer is preferably 0.9 to 1.5, more preferably 0.9 to 1.3.

As described above, the retardation layer is preferably a liquid crystal alignment solidified layer. Examples of the liquid crystal compound include a liquid crystal compound (nematic liquid crystal) in which the liquid crystal phase is a nematic phase. As such a liquid crystal compound, for example, a liquid crystal polymer or a liquid crystal monomer can be used. The liquid crystalline expression mechanism of the liquid crystal compound may be either lyotropic or thermotropic. The liquid crystal polymer and the liquid crystal monomer may be used alone or in combination.

When the liquid crystal compound is a liquid crystal monomer, the liquid crystal polymer is preferably a polymerizable monomer and a crosslinkable monomer. This is because the alignment state of the liquid crystal monomer can be fixed by polymerizing or crosslinking (ie, curing) the liquid crystal monomer. After aligning the liquid crystal monomers, for example, by polymerizing or crosslinking the liquid crystal monomers, the alignment state can be fixed. Here, a polymer is formed by polymerization and a three-dimensional network structure is formed by crosslinking, but they are non-liquid crystal. Therefore, the formed retardation layer does not undergo transition to a liquid crystal phase, a glass phase, or a crystal phase due to a temperature change peculiar to a liquid crystal compound, for example. As a result, the retardation layer becomes a very stable retardation layer that is not affected by temperature change.

The temperature range in which the liquid crystal monomer exhibits liquid crystallinity differs depending on its type. Specifically, the temperature range is preferably 40°C to 120°C, more preferably 50°C to 100°C, and most preferably 60°C to 90°C.

As the liquid crystal monomer, any suitable liquid crystal monomer can be employed. For example, the polymerizable mesogens described in Japanese Patent Application Publication Nos. 2002-533742 (WO00/37585), EP358208 (US5211877), EP66137 (US4388453), WO93/22397, EP0261712, DE19504224, DE4408171, and GB2280445. compounds and the like can be used. Specific examples of such a polymerizable mesogenic compound include, for example, BASF's trade name LC242, Merck's trade name E7, and Wacker-Chem's trade name LC-Sillicon-CC3767. As the liquid crystal monomer, a nematic liquid crystal monomer is preferable.

C-3. adhesive layer

As the pressure-sensitive adhesive layer 40, any appropriate structure can be employed. Specific examples include acrylic adhesives, rubber-based adhesives, silicone-based adhesives, polyester-based adhesives, urethane-based adhesives, epoxy-based adhesives, and polyether-based adhesives. By adjusting the type, number, combination and blending ratio of the polymers forming the base resin of the pressure-sensitive adhesive, and the blending amount, reaction temperature, reaction time, etc. of the crosslinking agent, the pressure-sensitive adhesive having desired properties according to the purpose can be prepared. The base resin of the pressure-sensitive adhesive may be used alone or in combination of two or more. The base resin is preferably an acrylic resin (specifically, the pressure-sensitive adhesive layer is preferably composed of an acrylic pressure-sensitive adhesive). The thickness of the pressure-sensitive adhesive layer is, for example, 10 μm to 20 μm.

C-4. Fabrication of polarizer

A polarizing plate can typically be obtained by laminating various layers such as a retardation layer on the polarizing film after washing with water.

In the polarizing plate 100 shown in FIG. 3, for example, the resin substrate of the laminate of the resin substrate and the polarizing film after washing with water is used as the protective layer 20 as it is, and the retardation layer 30 and the pressure-sensitive adhesive layer 40 are formed on the resin substrate. It can be obtained by sequentially stacking. Further, for example, the protective layer 20 is laminated on the resin film side of the laminate of the resin substrate and the resin film, the laminate obtained by peeling the resin substrate from the resin film is washed with water, and the retardation layer is placed on the protective layer 20 side. (30) and the pressure-sensitive adhesive layer (40) can be sequentially laminated. Further, for example, after laminating the retardation layer 30 or the retardation layer 30 and the pressure-sensitive adhesive layer 40 on the laminate of the protective layer 20 and the resin film, the polarizing plate 100 is obtained by washing with water. can also

In the polarizing plate 110 shown in FIG. 4, for example, the protective layer 20 is laminated on the resin film side of the laminate of the resin substrate and the resin film, and the laminate obtained by peeling the resin substrate from the resin film is washed with water to polarize the polarized light. It can be obtained by sequentially laminating the retardation layer 30 and the pressure-sensitive adhesive layer 40 on the film 10 side.

[Example]

Hereinafter, the present invention will be specifically described by examples, but the present invention is not limited by these examples. In addition, the thickness, the iodine concentration of the resin film, and the moisture content are values measured by the following measuring method. In addition, unless otherwise specified, 'parts' and '%' in Examples and Comparative Examples are based on weight.

1. Thickness

The thickness of 10 µm or less was measured using a scanning electron microscope (manufactured by Nippon Electronics Co., Ltd., product name 'JSM-7100F'). The thickness exceeding 10 µm was measured using a digital micrometer (manufactured by Anritz Corporation, product name 'KC-351C').

2. Iodine concentration of resin film

The fluorescence X-ray intensity (kcps) intensity of elemental iodine was measured using a fluorescence X-ray analyzer (manufactured by Rigaku, product name 'ZSX Primus IV', measurement diameter: ψ20 mm), and the iodine concentration (% by weight) was obtained by the following formula: was calculated. Here, the coefficient for calculating the iodine concentration was obtained using a calibration curve.

Iodine concentration (% by weight) = 20.5 × fluorescence X-ray intensity / thickness of resin film (kcps / μm)

3. Water content of resin film

The resin film alone (resin film peeled from the resin substrate) was dried at 120° C. for 2 hours, and the amount of moisture contained in the resin film was determined by measuring the weight change before and after drying, and the moisture content was calculated.

[Example 1]

(Production of resin film)

As the thermoplastic resin base material, an amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) was used, which was long and had a water absorption of 0.75% and a Tg of about 75°C. Corona treatment was performed on one side of the resin substrate.

Potassium iodide 13 in 100 parts by weight of a PVA-based resin obtained by mixing polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name: 'Kose Pharma Z410') at a ratio of 9:1 Part by weight was added 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 at the free end 2.4 times in the machine direction (longitudinal direction) between rolls having different circumferential speeds in a 130°C oven (air assisted stretching).

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

Next, in a dyeing bath (100 parts by weight of water, an iodine aqueous solution obtained by blending iodine and potassium iodide in a weight ratio of 1:7 with respect to 100 parts by weight of water) at a liquid temperature of 30 ° C., the finally obtained polarizing film has a single transmittance (Ts) of 43% or more It was immersed for 60 seconds while adjusting the concentration as much as possible (dyeing).

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

Thereafter, the laminate was immersed in an aqueous boric acid solution (boric acid concentration: 4.0% by weight) at a solution temperature of 64° C., and uniaxial stretching was performed between rolls having different circumferential speeds so that the total draw ratio was 5.5 times in the machine direction (longitudinal direction). (underwater stretching).

Thereafter, the laminate was immersed in a washing bath (an aqueous solution obtained by blending 4 parts by weight of potassium iodide with respect to 100 parts by weight of water) at a liquid temperature of 20°C (washing).

Thereafter, while drying in an oven maintained at 90°C, it was brought into contact with a heating roll made of SUS whose surface temperature was maintained at 75°C for about 2 seconds (drying). The shrinkage rate in the width direction of the layered product by the drying shrinkage treatment was 5.2%.

In this way, a resin film having a thickness of 5.4 μm, an iodine concentration of 6.4%, and a moisture content of 4.4% was formed on the resin substrate.

(SuSE 1)

Subsequently, an acrylic film containing a lactone ring structure having a thickness of 20 μm was bonded to one side of the obtained resin film (the side on which the resin substrate was not disposed) via an ultraviolet curable adhesive, and then the resin substrate was peeled off from the resin film, A laminate of the acrylic film and the polarizing film was obtained by immersing the laminate of the acrylic film and the resin film in a water bath at 43°C for 2 minutes, washing one side (peeling surface) of the resin film with water, and drying at 50°C.

(SuSE 2)

Subsequently, a HC-COP film having a thickness of 27 μm was bonded to one side of the obtained resin film (the side on which the resin substrate was not disposed) via an ultraviolet curable adhesive, and then the resin substrate was peeled off from the resin film, and the HC-COP film A laminate of HC-COP film and polarizing film was obtained by immersing the laminate of the resin film in a water bath at 43° C. for 2 minutes, washing one side (release side) of the resin film with water, and drying at 50° C. In addition, the HC-COP film is a film in which an HC layer (thickness of 2 μm) is formed on a cycloolefin resin (COP) film (thickness of 25 μm), and the COP film is bonded with the resin film side.

(Manufacture of phase difference layer)

10 g of a polymerizable liquid crystal exhibiting a nematic liquid crystal phase (manufactured by BASF: trade name 'Paliocolor LC242', represented by the following formula) and a photopolymerization initiator for the polymerizable liquid crystal compound (manufactured by BASF: trade name ' 3 g of Irgacure 907') was dissolved in 40 g of toluene to prepare a liquid crystal composition (coating liquid).

The surface of a polyethylene terephthalate (PET) film (thickness: 38 μm) was rubbed using a rubbing cloth to perform alignment treatment. The direction of the orientation treatment was made to be 15° direction when viewed from the visual side with respect to the direction of the absorption axis of the polarizing film when bonding to the polarizing plate. The liquid crystal compound was aligned by applying the liquid crystal coating solution to the orientation treated surface with a bar coater and heating and drying at 90°C for 2 minutes. The liquid crystal layer formed in this way was irradiated with light of 1 mJ/cm 2 using a metal halide lamp to cure the liquid crystal layer, thereby forming a liquid crystal alignment hardened layer (A) (layer H) on the PET film. The thickness of the liquid crystal alignment hardened layer (A) was 2.5 μm, and the in-plane retardation Re (550) was 270 nm. Moreover, the liquid-crystal alignment hardened layer (A) exhibited the refractive index characteristic of nx>ny=nz.

Liquid crystal alignment fixed layer (B) (Q layer) on PET film was formed. The thickness of the liquid crystal alignment fixed layer (B) was 1.5 μm, and the in-plane retardation Re (550) was 140 nm. Moreover, the liquid-crystal orientation hardening layer (B) showed the refractive index characteristic of nx>ny=nz.

(Production of polarizing plate (A))

The obtained liquid crystal alignment fixed layer (A) (H layer) and liquid crystal alignment fixed layer (B) (Q layer) were transferred in this order to the acrylic film side of the laminate of the acrylic film and the polarizing film. At this time, the angle formed by the absorption axis of the polarizing film and the slow axis of the orientation hardening layer (A) is 15 °, and the angle formed by the absorption axis of the polarizing film and the slow axis of the orientation hardening layer (B) is 75 °. ) was performed. Each transfer was performed through an ultraviolet curable adhesive (thickness: 1.0 µm). Then, a 15-micrometer-thick adhesive layer was formed on the liquid-crystal alignment hardening layer (B), and the polarizing plate (A) was obtained.

(Production of polarizing plate (B))

The obtained liquid crystal alignment fixed layer (A) (H layer) and liquid crystal alignment fixed layer (B) (Q layer) were transferred in this order to the polarizing film side of the laminate of the HC-COP film and the polarizing film. At this time, the angle formed by the absorption axis of the polarizing film and the slow axis of the orientation hardening layer (A) is 15 °, and the angle formed by the absorption axis of the polarizing film and the slow axis of the orientation hardening layer (B) is 75 °. ) was performed. Each transfer was performed through an ultraviolet curable adhesive (thickness: 1.0 µm). Then, a 15-micrometer-thick adhesive layer was formed on the liquid-crystal alignment hardening layer (B), and the polarizing plate (B) was obtained.

[Example 2]

A polarizing film and a polarizing plate were obtained in the same manner as in Example 1 except that the laminate was immersed in a 40°C water bath for 2 minutes and washed with water.

[Example 3]

A laminate was immersed in an aqueous solution of boric acid at a liquid temperature of 70°C and stretched in water to produce a resin film having a thickness of 5.4 µm, an iodine concentration of 6.6%, and a moisture content of 4.5%, and a laminate was washed with water by immersing in a water bath at 25°C for 5 minutes. Other than that, in the same manner as in Example 1, a polarizing film and a polarizing plate were obtained. In addition, the polarizing plate (B) was not produced due to the surface properties (swelling) of the polarizing film after washing with water.

[Example 4]

A laminate was immersed in an aqueous solution of boric acid at a liquid temperature of 67°C and stretched in water to produce a resin film having a thickness of 4.8 μm, an iodine concentration of 5.5%, and a moisture content of 4%, and a laminate was washed by immersing the laminate in a water bath at 43°C for 1 minute. Other than that, in the same manner as in Example 1, a polarizing film and a polarizing plate were obtained.

[Example 5]

A laminate was immersed in an aqueous solution of boric acid at a liquid temperature of 67°C and stretched in water to produce a resin film having a thickness of 4.8 μm, an iodine concentration of 5.5%, and a moisture content of 4%, and a laminate was washed with water by immersing in a water bath at 35°C for 2 minutes. Other than that, in the same manner as in Example 1, a polarizing film and a polarizing plate were obtained.

[Comparative Example 1]

A polarizing film and a polarizing plate were obtained in the same manner as in Example 1 except that the resin film was not washed with water.

[Comparative Example 2]

A polarizing film and a polarizing plate were obtained in the same manner as in Example 4 except that the resin film was not washed with water.

[Comparative Example 3]

A polarizing film and a polarizing plate were obtained in the same manner as in Example 3 except that the resin film was not washed with water.

[Reference Example 1]

(Production of resin film)

A long roll of PVA-based resin film having a thickness of 30 μm was uniaxially stretched in the longitudinal direction at 66° C. so that the total draw ratio was 6.5 times by a roll stretching machine, while simultaneously swelling, dyeing, crosslinking and washing treatment were performed, and finally A resin film having a thickness of 12 μm, an iodine concentration of 2.9%, and a moisture content of 11% was produced by performing a drying treatment with .

(SuSE 1)

To one side of the obtained resin film, an acrylic film containing a lactone ring structure having a thickness of 20 μm is bonded through an ultraviolet curable adhesive to prepare a laminate, and the laminate of the film and the resin film is immersed in a water bath at 43 ° C. for 2 minutes, A laminate of the film and the polarizing film was obtained by washing the surface (surface to which the film was not bonded) of the obtained resin film with water and drying at 50°C.

(SuSE 2)

An HC-COP film having a thickness of 27 μm was bonded to one side of the obtained resin film through an ultraviolet curing adhesive to prepare a laminate, and the laminate of the film and the resin film was immersed in a water bath at 43 ° C. for 2 minutes. A laminate of the film and the polarizing film was obtained by washing the surface (the surface to which the film was not bonded) with water and drying at 50°C.

(Production of polarizing plate (A))

The obtained liquid crystal alignment fixed layer (A) (H layer) and liquid crystal alignment fixed layer (B) (Q layer) were transferred in this order to the acrylic film side of the laminate of the acrylic film and the polarizing film. At this time, the angle formed by the absorption axis of the polarizing film and the slow axis of the orientation hardening layer (A) is 15 °, and the angle formed by the absorption axis of the polarizing film and the slow axis of the orientation hardening layer (B) is 75 °. ) was performed. Each transfer was performed through an ultraviolet curable adhesive (thickness: 1.0 µm). Then, a 15-micrometer-thick adhesive layer was formed on the liquid-crystal alignment hardening layer (B), and the polarizing plate (A) was obtained.

(Production of polarizing plate (B))

The obtained liquid crystal alignment fixed layer (A) (H layer) and liquid crystal alignment fixed layer (B) (Q layer) were transferred in this order to the polarizing film side of the laminate of the HC-COP film and the polarizing film. At this time, the angle formed by the absorption axis of the polarizing film and the slow axis of the orientation hardening layer (A) is 15 °, and the angle formed by the absorption axis of the polarizing film and the slow axis of the orientation hardening layer (B) is 75 °. ) was performed. Each transfer was performed through an ultraviolet curable adhesive (thickness: 1.0 µm). Then, a 15-micrometer-thick adhesive layer was formed on the liquid-crystal alignment hardening layer (B), and the polarizing plate (B) was obtained.

[Reference Example 2]

A polarizing film and a polarizing plate were obtained in the same manner as in Reference Example 1 except that the laminate was not washed with water.

About Examples and Comparative Examples, the following evaluation was performed. The evaluation results are summarized in Table 1 and Table 2.

<evaluation>

1. Single Transmittance and Polarization Degree

For the polarizing films (polarizing film / acrylic film or HC-COP film) of Examples and Comparative Examples, single transmittance (Ts) and parallel transmittance ( Tp) and orthogonal transmittance (Tc) were respectively taken as Ts, Tp and Tc of the polarizing film. These Ts, Tp, and Tc are Y values measured with a JIS Z8701 2-degree field of view (C light source) and corrected for visibility.

From the obtained Tp and Tc, the polarization degree (P) was calculated|required by the following formula.

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

2. Reflectance (Rc and Rp)

The reflectance of the surface (washed surface) of the polarizing film of Examples and Comparative Examples was determined by using a spectrophotometer (U-4100, manufactured by Hitachi High-Tech Co., Ltd.) to determine the reflectance (Rc) in the absorption axis direction and the reflectance (Rp) in the transmission axis direction. measured. At that time, the surface on the opposite side to the washed surface was bonded to the blackboard so that only the surface reflection could be measured. In addition, the angle of incidence of the light source (polarized light) was set to 5°, and the measurement wavelength was set to 380 nm to 780 nm.

3. Surface properties

The surface properties (presence or absence of irregularities due to swelling of the resin film) of the polarizing films of Examples and Comparative Examples were visually observed.

(Evaluation standard)

Good: No irregularities were observed

Defective: Convex and concave confirmed

4. Tint of polarizer (a ^* and b ^* )

The polarizing plates (circular polarizing plates) of Examples and Comparative Examples were bonded on an aluminum sheet, and the reflected color was measured in SCE mode with a spectrophotometer (cm-2600d manufactured by Konica Minolta Co., Ltd.).

[Table 1]

[Table 2]

Excellent optical characteristics (single transmittance and polarization degree) were obtained in both the Examples and Comparative Examples. In Examples, redness is suppressed and an excellent appearance is obtained.

For the polarizing films obtained in Example 1, Comparative Example 1, and Reference Example 2, the ionic strength of iodine in the thickness direction was measured. The measurement was performed using a time-of-flight secondary ion mass spectrometer (TOF-SIMS) (manufactured ^by ION-TOF, product name: TOF-SIMS 5) and using Bi ₃₂₊ as the primary ion. The measurement results (a graph obtained by converting the horizontal axis to the thickness of the polarizing film) are shown in FIG. 5 . As shown in Fig. 5, in the polarizing film of Example 1, it was confirmed that an inclined distribution region in which the amount of iodine increased from the front surface toward the rear surface was included at the end portion on the front surface side. In addition, the ionic strength of iodine on the horizontal axis corresponds to the iodine concentration.

A polarizing film according to one embodiment of the present invention is suitably used for image display devices such as, for example, liquid crystal display devices, organic EL display devices, and inorganic EL display devices.

10: polarizing film
20: protective layer
30: phase difference layer
40: adhesive layer
100: polarizer
110: polarizer

Claims (12)

It is composed of a resin film containing iodine,
The thickness is less than 7㎛,
The ratio (Rc ₄₀₀ /Rc ₆₈₀ ) of the reflectance Rc ₄₀₀ of light having a wavelength of 400 nm in the direction of the absorption axis to the reflectance Rc 680 of light having a wavelength of _{680 nm} in the direction of the absorption axis of the surface exceeds 1,
polarizing film. According to claim 1,
A polarizing film wherein Rc ₆₈₀ of the surface is 5% or less. The method of claim 1 or 2, wherein Rc ₄₀₀ of the surface is 4.8% or more, a polarizing film. The polarizing film according to any one of claims 1 to 3, comprising an inclined distribution region in which the amount of iodine increases from the front surface to the rear surface at an end portion on the front surface side. The polarizing film according to any one of claims 1 to 4, wherein the amount of iodine on the surface side is smaller than the amount of iodine on the back surface side. The polarizing film according to any one of claims 1 to 5, having a single transmittance of 42.0% or more and a polarization degree of 99.98% or more. The method for producing a polarizing film according to any one of claims 1 to 6, comprising washing the surface of a resin film containing iodine and having a moisture content of 15% by weight or less with water. The manufacturing method according to claim 7, wherein the iodine concentration of the resin film is 5% by weight or more. The manufacturing method according to claim 7 or 8, wherein the resin film is a resin layer formed on a resin substrate. The manufacturing method according to claim 9, comprising stretching the resin layer in water at 67°C or lower. The manufacturing method according to claim 9 or 10, comprising heating the resin layer using a heating roll. The polarizing film according to any one of claims 1 to 6;
A polarizing plate comprising a protective layer or a retardation layer disposed on at least one side of the polarizing film.