JP7475241B2 - Manufacturing method of circularly polarizing plate - Google Patents

Description

The present invention relates to a method for producing a circular polarizing plate.

Image display devices, such as liquid crystal display devices and electroluminescence (EL) display devices (e.g., organic EL display devices, inorganic EL display devices), are rapidly becoming popular. A polarizing plate and a retardation plate are typically used in image display devices. In practice, a retardation layer-attached polarizing plate (circular polarizing plate) in which a polarizing plate and a retardation plate are integrated is widely used (e.g., Patent Document 1). In recent years, the possibility of curving, bending, folding, and rolling up image display devices has been considered. Such image display devices often use a resin (e.g., polyimide) substrate instead of a glass substrate, and as a result, when a circular polarizing plate is applied to such an image display device, there is a problem that warping is likely to occur over time. In order to solve such a problem, a technique of humidifying the polarizing plate used in the circular polarizing plate has been considered. However, such a technique has a problem that the productivity is insufficient and/or the obtained circular polarizing plate (ultimately, the image display device) has a defective appearance.

Japanese Patent No. 3325560

The present invention has been made to solve the above-mentioned problems of the conventional art, and its main objective is to provide a simple and efficient method for manufacturing a circular polarizing plate that can realize an image display device that has an excellent appearance and is suppressed from warping over time.

A method for producing a circular polarizing plate according to an embodiment of the present invention is a method for producing a circular polarizing plate having a polarizing plate including a polarizer and a protective layer on at least one of the polarizers, and a retardation layer. The method includes repeating a humidification treatment and aging three or more times for the polarizing plate or the circular polarizing plate, and the cumulative humidification amount of the humidification treatment is 300 or more. Here, the cumulative humidification amount is represented by the following formula:
Accumulative humidification amount=saturated water vapor amount during humidification (g/m ³ )×humidity (%)×accumulated humidification time (minutes).
In one embodiment, the temperature in the humidification treatment is 40° C. or less, and the humidification time for each treatment is 10 minutes or less.
In one embodiment, the aging temperature is 30° C. or lower, and the aging time for one cycle is 1 hour or longer.
In one embodiment, the ratio of the thickness of the polarizer to the total thickness of the protective layer is 1:5 or less. In one embodiment, the polarizing plate includes a protective layer on both sides of the polarizer. In one embodiment, each of the protective layers is made of a triacetyl cellulose film.
In one embodiment, the retardation layer is a layer in which a liquid crystal compound is aligned and fixed.
In one embodiment, the circularly polarizing plate obtained by the above manufacturing method has an absolute value of warpage of 2 mm or less when a laminate in which the circularly polarizing plate is bonded to a polyimide film is left for 72 hours under conditions of 23°C and 55% RH.
In one embodiment, the circularly polarizing plate obtained by the above production method has an absorbance of 0.046 or more.

According to an embodiment of the present invention, in a method for manufacturing a circular polarizing plate, by repeating the humidification treatment and aging three or more times and setting the cumulative humidification amount of the humidification treatment to a predetermined amount or more, it is possible to provide a simple and efficient method for manufacturing a circular polarizing plate that can realize an image display device that has an excellent appearance and is suppressed from warping over time.

FIG. 1 is a schematic cross-sectional view illustrating an example of a circularly polarizing plate obtained by a production method according to an embodiment of the present invention.

The following describes embodiments of the present invention, but the present invention is not limited to these embodiments.

(Definition of terms and symbols)
The definitions of terms and symbols used 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 maximum (i.e., the slow axis direction), "ny" is the refractive index in the direction perpendicular to the slow axis in the plane (i.e., the fast axis direction), and "nz" is the refractive index in the thickness direction.
(2) In-plane retardation (Re)
"Re(λ)" is the in-plane retardation measured with light having a wavelength of λ nm at 23° C. For example, "Re(550)" is the in-plane retardation measured with light having a wavelength of 550 nm at 23° C. Re(λ) is calculated by the formula: Re(λ)=(nx−ny)×d, where d (nm) is the thickness of the layer (film).
(3) Retardation in the thickness direction (Rth)
"Rth(λ)" is the retardation in the thickness direction measured with light having a wavelength of λ nm at 23° C. For example, "Rth(550)" is the retardation in the thickness direction measured with light having a wavelength of 550 nm at 23° C. Rth(λ) is calculated by the formula: Rth(λ)=(nx-nz)×d, where d (nm) is the thickness of the layer (film).
(4) Nz Coefficient The Nz coefficient is calculated by Nz=Rth/Re.
(5) Angle When referring to an angle in this specification, the angle includes both clockwise and counterclockwise angles with respect to a reference direction. Thus, for example, "45°" means ±45°.

A. Outline of the structure of a circular polarizer obtained by the manufacturing method according to an embodiment of the present invention FIG. 1 is a schematic cross-sectional view showing an example of a circular polarizer obtained by the manufacturing method according to an embodiment of the present invention. The circular polarizer 100 in the illustrated example has a polarizer 10 and a retardation layer 20, typically in this order from the viewing side. The polarizer 10 typically includes a polarizer 11 and a protective layer 12 on at least one of the polarizers 11 (the viewing side in the illustrated example). The polarizer 10 preferably includes protective layers 12 and 13 on both sides of the polarizer 11, as in the illustrated example. With such a configuration, the effect according to the embodiment of the present invention may be remarkable. In practical terms, a pressure-sensitive adhesive layer 30 is provided on the opposite side of the retardation layer 20 to the polarizer 10 (i.e., as the outermost layer on the opposite side to the viewing side), and the circular polarizer can be attached to an image display cell. Furthermore, it is preferable that a release film (not shown) is temporarily attached to the surface of the pressure-sensitive adhesive layer 30 until the circular polarizer is used. By temporarily attaching the release film, the pressure-sensitive adhesive layer is protected and the circular polarizer can be rolled.

The retardation layer 20 typically has a circular polarization function or an elliptically polarizing function. Therefore, in this specification, the term "circular polarizing plate" includes not only circular polarizing plates but also elliptically polarizing plates. The retardation layer 20 may have any appropriate configuration depending on the purpose. The retardation layer 20 may be a single layer or may have a laminated structure of two or more layers.

The retardation layer 20 may be a stretched resin film (retardation film) or a liquid crystal compound alignment solidified layer (liquid crystal alignment solidified layer). The retardation layer 20 is preferably a liquid crystal alignment solidified layer. With such a configuration, the effect of the embodiment of the present invention may be remarkable. Furthermore, by using a liquid crystal compound, the difference between nx and ny of the obtained retardation layer can be significantly increased compared to non-liquid crystal materials, so that the thickness of the retardation layer to obtain the desired in-plane retardation can be significantly reduced. As a result, a circular polarizer can be significantly thinned. In this specification, the "alignment solidified layer" refers to a layer in which the liquid crystal compound is aligned in a predetermined direction within the layer and the alignment state is fixed. Note that the "alignment solidified layer" is a concept that includes an alignment hardened layer obtained by hardening a liquid crystal monomer as described later. In the retardation layer 20, typically, rod-shaped liquid crystal compounds are aligned in the slow axis direction of the retardation layer (homogeneous alignment).

In one embodiment, the circularly polarizing plate is attached to a polyimide film via the adhesive layer 30, and the absolute value of the warpage when left for 72 hours under conditions of 23° C. and 55% RH is preferably 2 mm or less, more preferably 1.5 mm or less, and even more preferably 1 mm or less. The smaller the absolute value of the warpage, the more preferable, and the lower limit may be, for example, 0.2 mm. The thickness of the polyimide film is, for example, 30 μm to 100 μm, preferably 40 μm to 80 μm. According to the manufacturing method of the embodiment of the present invention (described later), such a circularly polarizing plate can be realized. When such a circularly polarizing plate is applied to a curved image display device or an image display device that can be bent, folded, or rolled up, warpage can be significantly suppressed. Such an image display device typically employs a resin (e.g., polyimide) substrate as the substrate. The warpage is expressed by the following formula.
Warpage = (Warpage 1 - Warpage 2)
Here, "warping amount 1" is the amount of warping immediately after lamination of the laminate of the circular polarizing plate and the polyimide film, and "warping amount 2" is the amount of warping after the laminate is left for 72 hours. In this specification, the warping that is convex toward the image display cell side is represented by "positive (+)" and the warping that is convex toward the viewing side is represented by "negative (-)".

In one embodiment, the circular polarizing plate has an absorbance of preferably 0.046 or more, more preferably 0.047 or more, and even more preferably 0.048 or more. The absorbance may typically correspond to the moisture content of the polarizer in the circular polarizing plate. That is, the circular polarizing plate obtained by the manufacturing method of the embodiment of the present invention includes a polarizer with a large moisture content. This indicates that moisture can be efficiently introduced into the polarizer by repeating the humidification treatment and aging multiple times. The upper limit of the absorbance may substantially correspond to the saturated moisture content of the polarizer. In one embodiment, the upper limit of the absorbance may be, for example, 0.050. The upper limit of the absorbance may be set depending on the balance with the manufacturing efficiency, the appearance of the obtained circular polarizing plate, and the like. The absorbance may be measured, for example, using an IR moisture content meter. More specifically, the absorbance may be calculated from the difference between the 1.95 μm spectrum showing the absorption of water in IR and the baseline 1.85 μm spectrum.

The circular polarizing plate may further include other optical functional layers. The type, characteristics, number, combination, arrangement position, etc. of the optical functional layers that can be provided in the circular polarizing plate can be appropriately set according to the purpose. For example, the circular polarizing plate may further have a conductive layer or a conductive layer-attached isotropic substrate (neither is shown). The conductive layer or the conductive layer-attached isotropic substrate is typically provided on the outside of the retardation layer 20 (opposite side to the polarizing plate 10). The conductive layer or the conductive layer-attached isotropic substrate is typically an arbitrary layer that is provided as needed, and may be omitted. In addition, when the conductive layer or the conductive layer-attached isotropic substrate is provided, the circular polarizing plate can be applied to a so-called inner touch panel type input display device in which a touch sensor is incorporated between the image display cell (e.g., an organic EL cell) and the polarizing plate. In addition, for example, the circular polarizing plate may further include other retardation layers. The optical characteristics (e.g., refractive index characteristics, in-plane retardation, Nz coefficient, photoelastic coefficient), thickness, arrangement position, etc. of the other retardation layers can be appropriately set according to the purpose. As described below, the effects of the manufacturing method of the embodiment of the present invention can be achieved by subjecting the polarizing plate 10 or the circular polarizing plate (a laminate of the polarizing plate 10 and the retardation layer 20) to a specified humidification treatment and aging, so the presence or absence of other optically functional layers is not a factor that substantially affects the embodiment of the present invention.

Hereinafter, a method for manufacturing a circular polarizer as described above according to an embodiment of the present invention will be described, followed by a description of the components of the circular polarizer.

B. Manufacturing Method of Circular Polarizer The manufacturing method of the circular polarizer according to the embodiment of the present invention includes repeating humidification and aging for a polarizer or a circular polarizer three or more times. Furthermore, the cumulative humidification amount of the humidification is 300 or more. Here, the cumulative humidification amount is expressed by the following formula:
Accumulative humidification amount=saturated water vapor amount during humidification (g/m ³ )×humidity (%)×accumulated humidification time (minutes).
Hereinafter, each step in the method for producing a circularly polarizing plate will be described in order.

B-1. Preparation of Polarizing Plate The polarizing plate may be prepared by any suitable method. Specifically, the polarizing plate may include a polarizer prepared from a single-layer resin film, or may include a polarizer prepared using a laminate of two or more layers.

B-1-1. Preparation of a polarizing plate using a polarizer obtained from a single-layer resin film A method for producing a polarizer from a single-layer resin film typically includes subjecting the resin film to a dyeing treatment with a dichroic substance such as iodine or a dichroic dye, and a stretching treatment. Examples of the resin film include hydrophilic polymer films such as polyvinyl alcohol (PVA)-based films, partially formalized PVA-based films, and partially saponified ethylene-vinyl acetate copolymer-based films. The method may further include an insolubilization treatment, a swelling treatment, a crosslinking treatment, and the like. A polarizing plate can be obtained by laminating a protective layer (protective film) on at least one side of the obtained polarizer. Since such a production method is well known and commonly used in the industry, a detailed description thereof will be omitted.

B-1-2. Preparation of a polarizing plate using a polarizer obtained from a laminate When a laminate is used to manufacture a polarizer, the laminate may be a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a laminate of a resin substrate and a PVA-based resin layer formed by coating on the resin substrate. As an example, a method for manufacturing a polarizer using a laminate of a resin substrate and a PVA-based resin layer formed by coating on the resin substrate will be described. The manufacturing method typically includes: applying a PVA-based resin solution to a resin substrate and drying the substrate to form a PVA-based resin layer on the resin substrate, thereby obtaining a laminate of the resin substrate and the PVA-based resin layer; and stretching and dyeing the laminate to make the PVA-based resin layer into a polarizer. In such a manufacturing method, the stretching typically includes immersing the laminate in an aqueous solution of boric acid to stretch it. Furthermore, the stretching may further include, as necessary, stretching the laminate in air at a high temperature (e.g., 95°C or higher) before stretching in the aqueous solution of boric acid. The obtained resin substrate/polarizer laminate may be used as a polarizing plate as it is (i.e., the resin substrate may be used as a protective layer for the polarizer), or a protective layer may be further laminated on the polarizer surface of the resin substrate/polarizer laminate to form a polarizing plate. Alternatively, the resin substrate may be peeled off from the resin substrate/polarizer laminate, and any suitable protective layer according to the purpose may be laminated on the peeled surface to form a polarizing plate, or a protective layer may be further laminated on the polarizer surface of the protective layer/polarizer laminate to form a polarizing plate. Details of the manufacturing method of such a polarizing plate are described in, for example, JP-A-2012-73580 and JP Patent No. 6,470,455. The entire descriptions of these publications are incorporated herein by reference.

B-2. Preparation of a circularly polarizing plate A circularly polarizing plate can be obtained by laminating a retardation layer on the obtained polarizing plate. When the retardation layer is a stretched film of a resin film, lamination can be performed by any appropriate method. When the retardation layer is a liquid crystal alignment solidified layer, lamination can be typically performed by transferring a liquid crystal alignment solidified layer formed on a substrate. When the retardation layer has a laminated structure, each retardation layer may be laminated sequentially on the polarizing plate, or a laminate of retardation layers may be laminated on the polarizing plate. Hereinafter, a method for forming a liquid crystal alignment solidified layer will be briefly described.

The liquid crystal alignment solidified layer can be formed by performing an alignment treatment on the surface of a predetermined substrate, applying a coating liquid containing a liquid crystal compound to the surface to align the liquid crystal compound in a direction corresponding to the alignment treatment, and fixing the alignment state. Any appropriate alignment treatment can be adopted as the alignment treatment. Specific examples include mechanical alignment treatment, physical alignment treatment, and chemical alignment treatment. Specific examples of mechanical alignment treatment include rubbing treatment and stretching treatment. Specific examples of physical alignment treatment include magnetic field alignment treatment and electric field alignment treatment. Specific examples of chemical alignment treatment include oblique deposition method and photoalignment treatment. Any appropriate conditions can be adopted as the treatment conditions for various alignment treatments depending on the purpose.

The alignment of liquid crystal compounds is achieved by treating them at a temperature that exhibits a liquid crystal phase according to the type of liquid crystal compound. By carrying out such temperature treatment, the liquid crystal compounds take on a liquid crystal state, and the liquid crystal compounds are aligned according to the alignment treatment direction of the substrate surface.

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.

Specific examples of liquid crystal compounds and details of the method for forming the alignment solidification layer are described in JP 2006-163343 A. The disclosure of this publication is incorporated herein by reference.

B-3. Moisture treatment and aging In the embodiment of the present invention, as described above, the humidification treatment and aging are repeated three or more times for the polarizing plate or the circular polarizing plate. That is, the retardation layer may be laminated after the humidification treatment and aging are performed on the polarizing plate, or the retardation layer may be laminated to produce a circular polarizing plate, and then the humidification treatment and aging may be performed.

The inventors have found that by repeating the humidification treatment and aging three or more times, the moisture content of the polarizer (for example, absorbance as an index) can be significantly increased compared to the case where the humidification treatment and aging are performed only once, even if the cumulative amount of humidification is the same, and as a result, when the circular polarizing plate is applied to an image display device (particularly an image display device whose substrate is a resin substrate), warping over time can be significantly suppressed. This can be estimated as follows. However, the present invention is not bound by this estimation. Here, for ease of understanding, the explanation will be given assuming that the humidification conditions (typically, the temperature and humidity during humidification) are the same. When the polarizing plate or the circular polarizing plate is subjected to the humidification treatment, the moisture imparted by the humidification treatment is absorbed by the protective layer located on the outside of the polarizer, and then a part of it is transferred to the polarizer. Since there is a limit to the amount of moisture that the protective layer can absorb, even if the cumulative amount of humidification is increased by only one humidification treatment (for example, even if the humidification time is extended), the protective layer cannot absorb all of the moisture imparted by the humidification treatment. On the other hand, when the same cumulative humidification amount is obtained by three or more humidification processes, the amount of moisture imparted by each humidification process is smaller than that obtained by the single humidification process. For example, when the same cumulative humidification amount is obtained by three humidification processes, the amount of moisture imparted by each humidification process is one-third that obtained by the single humidification process. As a result, the protective layer can efficiently absorb the moisture imparted by the humidification process compared to the single humidification process. Furthermore, by performing aging after each humidification process, the moisture imparted to the protective layer by the humidification process can be transferred well to the polarizer. This transfer reduces the moisture in the protective layer, so that the protective layer has the capacity to absorb moisture again at the time of the next humidification process. In this way, by repeating the humidification treatment and aging three or more times (i.e., by performing the humidification treatment three or more times and performing aging after these humidification treatments), the moisture content of the polarizer can be significantly increased, and as a result, when the circular polarizing plate is used in an image display device (particularly an image display device whose substrate is a resin substrate), warping over time can be significantly suppressed.

The humidification process is typically carried out at around room temperature. The temperature in the humidification process is preferably 40°C or lower, more preferably 20°C to 35°C, and even more preferably 23°C to 30°C. If the humidification temperature is too high, problems may occur with the appearance of the resulting polarizing plate or circular polarizing plate. If the humidification temperature is too low, the humidification time required to reach the desired cumulative humidification amount may be too long.

The time for one humidification treatment in the multiple humidification treatments is preferably 10 minutes or less, more preferably 9 minutes or less, and even more preferably 8 minutes or less. According to an embodiment of the present invention, by repeating the humidification treatment and aging three or more times, the time for one humidification treatment can be relatively short. As a result, due to the synergistic effect with the effect of the humidification temperature described above, a polarizing plate and a circular polarizing plate having excellent appearance can be obtained with high manufacturing efficiency. The lower limit of the humidification time can be, for example, 4 minutes. If the humidification time is too short, the number of humidification treatments must be increased, and therefore the number of aging treatments must be increased. As a result, the manufacturing efficiency may be insufficient.

Aging is typically performed at around room temperature. The temperature during aging is preferably 30°C or less, more preferably 20°C to 30°C, and even more preferably 23°C to 27°C. If the aging temperature is too high, the moisture absorbed in the protective layer may evaporate to the outside and may not transfer well to the polarizer.

The time for one aging step in the multiple aging steps is preferably 1 hour or more, and more preferably 1 to 12 hours. With such an aging time, the total time required can be shortened compared to humidifying for a long time (only once) at low temperature, and excellent manufacturing efficiency can be ensured. The aging time can be appropriately set taking into consideration the number of humidification treatments and aging steps, the accumulated amount of humidification, manufacturing efficiency, etc.

The number of times the humidification process (and aging) is performed is three or more times as described above, and more preferably three to four times. By repeating the humidification process three or more times, the effect of performing the humidification process multiple times becomes significant. The upper limit of the number of humidification times can be appropriately set taking into consideration the humidification temperature, number of humidification times, cumulative amount of humidification, production efficiency, etc.

As described above, the cumulative humidification amount of the humidification treatment is preferably 300 or more, more preferably 350 or more, and even more preferably 380 or more. The cumulative humidification amount can be, for example, 850 or less. If the cumulative humidification amount is too small, the moisture content of the polarizer becomes insufficient, and as a result, when the circular polarizing plate is applied to an image display device, warping over time may not be sufficiently suppressed. If the cumulative humidification amount is too large, this typically corresponds to a case where the humidification temperature is too high. Therefore, in such a case, problems may occur in the appearance of the obtained polarizing plate or circular polarizing plate. The cumulative humidification amount is expressed by the following formula:
Accumulated humidification amount=saturated water vapor amount during humidification (g/m ³ )×humidity (%)×accumulated humidification time (min)
Here, the amount of saturated water vapor may correspond to the humidification temperature. As is clear from the above formula, the integrated humidification amount is a relative index of the amount of humidification and is unitless.

As is clear from the above manufacturing method, the polarizer 11 is typically a resin film containing a dichroic material (e.g., iodine). As described above, examples of the resin film include hydrophilic polymer films such as polyvinyl alcohol (PVA)-based films, partially formalized PVA-based films, and partially saponified ethylene-vinyl acetate copolymer-based films.

The thickness of the polarizer is preferably 15 μm or less, more preferably 1 μm to 12 μm, and even more preferably 3 μm to 12 μm. If the thickness of the polarizer is within this range, it is easy to set the ratio of the thickness of the polarizer to the total thickness of the protective layer to the desired range.

The polarizer preferably exhibits absorption dichroism at any wavelength between 380 nm and 780 nm. The single transmittance of the polarizer is, for example, 41.5% to 46.0%, preferably 43.0% to 46.0%, and preferably 44.5% to 46.0%. The degree of polarization of the polarizer is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more.

C-2. Protective layer The protective layer 12 and the protective layer 13 are each formed of any suitable film that can be used as a protective layer for a polarizer. Specific examples of materials that are the main components of the films include cellulose-based resins such as triacetyl cellulose (TAC), and transparent resins such as polyester, polyvinyl alcohol, polycarbonate, polyamide, polyimide, polyethersulfone, polysulfone, polystyrene, polynorbornene, polyolefin, (meth)acrylic, and acetate. Preferably, the protective layer 12 and the protective layer 13 can each be made of TAC. With such a configuration, the effects of the embodiment of the present invention can be significant.

The circular polarizing plate obtained by the manufacturing method of the embodiment of the present invention is typically placed on the viewing side of an image display device, and the protective layer 12 is typically placed on the viewing side. Therefore, the protective layer 12 may be subjected to surface treatments such as hard coat treatment, anti-reflection treatment, anti-sticking treatment, and anti-glare treatment, as necessary. Additionally/alternatively, the protective layer 12 may be subjected to treatments (typically, imparting an (elliptical) polarizing function, imparting an ultra-high phase difference) to improve visibility when viewed through polarized sunglasses, as necessary. By performing such treatments, excellent visibility can be achieved even when the display screen is viewed through polarized lenses such as polarized sunglasses. Therefore, the circular polarizing plate can be suitably applied to image display devices that can be used outdoors.

The thickness of the protective layer 12 is preferably 5 μm to 80 μm, more preferably 10 μm to 40 μm, and even more preferably 15 μm to 35 μm. If a surface treatment has been applied, the thickness of the protective layer 12 includes the thickness of the surface treatment layer.

In one embodiment, the protective layer 13 is preferably optically isotropic. In this specification, "optically isotropic" means that the in-plane retardation Re(550) is 0 nm to 10 nm, and the retardation in the thickness direction Rth(550) is -10 nm to +10 nm. The thickness of the protective layer 13 is preferably 5 μm to 80 μm, more preferably 10 μm to 40 μm, and even more preferably 10 μm to 30 μm.

The ratio of the thickness of the polarizer 11 in the polarizing plate 10 to the total thickness of the protective layers is preferably 1:5 or less, and more preferably 1:4.8 or less. With such a configuration, the effects of the embodiment of the present invention can be significant. If the ratio is too large, it means that the total thickness of the protective layers is large. In such cases, since the protective layers have a large capacity to absorb moisture, it may be possible to achieve the desired moisture content of the polarizer with only one humidification treatment. However, such a protective layer that is too thick is not practical.

D. Retardation Layer As described above, the retardation layer 20 has a circular polarization function or an elliptically polarizing function. The retardation layer 20 may be a single layer or may have a laminated structure of two or more layers, as long as it has a circular polarization function or an elliptically polarizing function.

When the retardation layer 20 is a single layer, the retardation layer can typically function as a λ/4 plate. Specifically, the Re(550) of the retardation layer is preferably 100 nm to 180 nm, more preferably 110 nm to 170 nm, and even more preferably 130 nm to 160 nm. The thickness of the retardation layer can be adjusted to obtain the desired in-plane retardation of the λ/4 plate. When the retardation layer is a liquid crystal alignment solidification layer, the thickness can be, for example, 1.0 μm to 2.5 μm. In this embodiment, the angle between the slow axis of the retardation layer and the absorption axis of the polarizer is preferably 40° to 50°, more preferably 42° to 48°, and even more preferably 44° to 46°. In this embodiment, the circularly polarizing plate may further have a retardation layer (not shown) between the retardation layer 20 and the adhesive layer 30 that exhibits a refractive index characteristic of nz>nx=ny. When the retardation layer is a single layer, the retardation layer preferably exhibits an inverse dispersion wavelength characteristic in which the retardation value increases according to the wavelength of the measurement light.

When the retardation layer 20 has a laminated structure, the retardation layer typically has a two-layer structure of an H layer and a Q layer in order from the polarizing plate side (not shown). The H layer typically functions as a λ/2 plate, and the Q layer typically functions as a λ/4 plate. Specifically, the Re(550) of the H layer is preferably 200 nm to 300 nm, more preferably 230 nm to 290 nm, and even more preferably 250 nm to 280 nm; the Re(550) of the Q layer is preferably 100 nm to 180 nm, more preferably 110 nm to 170 nm, and even more preferably 130 nm to 160 nm. The thickness of the H layer can be adjusted so that the desired in-plane retardation of the λ/2 plate is obtained. When the H layer is a liquid crystal alignment solidified layer, the thickness can be, for example, 2.0 μm to 4.0 μm. The thickness of the Q layer can be adjusted so that the desired in-plane retardation of the λ/4 plate is obtained. When the Q layer is a liquid crystal alignment solidified layer, its thickness may be, for example, 1.0 μm to 2.5 μm. In this embodiment, the angle between the slow axis of the H layer and the absorption axis of the polarizer is preferably 10° to 20°, more preferably 12° to 18°, and even more preferably 14° to 16°; the angle between the slow axis of the Q layer and the absorption axis of the polarizer is preferably 70° to 80°, more preferably 72° to 78°, and even more preferably 74° to 76°. The order of arrangement of the H layer and the Q layer may be reversed, and the angle between the slow axis of the H layer and the absorption axis of the polarizer and the angle between the slow axis of the Q layer and the absorption axis of the polarizer may be reversed. When the retardation layer has a laminated structure, each layer (e.g., the H layer and the Q layer) may exhibit an inverse dispersion wavelength characteristic in which the retardation value increases according to the wavelength of the measurement light, may exhibit a positive wavelength dispersion characteristic in which the retardation value decreases according to the wavelength of the measurement light, or may exhibit a flat wavelength dispersion characteristic in which the retardation value changes very little depending on the wavelength of the measurement light.

The retardation layer (or each layer in the case of a laminated structure) typically exhibits the following refractive index characteristic: nx>ny=nz. Note that "ny=nz" does not only include the case where ny and nz are completely equal, but also includes the case where they are substantially equal. Therefore, there may be cases where ny>nz or ny<nz, as long as the effect of the present invention is not impaired. The Nz coefficient of the retardation layer is preferably 0.9 to 1.5, and more preferably 0.9 to 1.3.

As described above, the retardation layer may be a stretched resin film or a liquid crystal alignment solidified layer. Representative examples of resins constituting the resin film include polycarbonate-based resins, polyester carbonate-based resins, polyester-based resins, polyvinyl acetal-based resins, polyarylate-based resins, cyclic olefin-based resins, cellulose-based resins, polyvinyl alcohol-based resins, polyamide-based resins, polyimide-based resins, polyether-based resins, polystyrene-based resins, and acrylic-based resins. These resins may be used alone or in combination (e.g., blended or copolymerized). When the first retardation layer is composed of a resin film exhibiting reverse dispersion wavelength characteristics, polycarbonate-based resins or polyester carbonate-based resins (hereinafter sometimes simply referred to as polycarbonate-based resins) may be suitably used.

An example of a liquid crystal compound is a liquid crystal compound whose liquid crystal phase is a nematic phase (nematic liquid crystal). For example, a liquid crystal polymer or a liquid crystal monomer can be used as such a liquid crystal compound. The mechanism by which the liquid crystallinity of the liquid crystal compound is expressed 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 monomer is preferably a polymerizable monomer and a crosslinkable monomer. This is because the orientation state of the liquid crystal monomer can be fixed by polymerizing or crosslinking (i.e., curing) the liquid crystal monomer. After the liquid crystal monomer is aligned, for example, the liquid crystal monomers can be polymerized or crosslinked with each other, thereby fixing the above-mentioned orientation state. Here, a polymer is formed by polymerization, and a three-dimensional network structure is formed by crosslinking, but these are non-liquid crystals. Therefore, the formed retardation layer does not undergo transition to a liquid crystal phase, a glass phase, or a crystalline phase due to temperature changes, which are specific to liquid crystal compounds. As a result, the retardation layer becomes a retardation layer that is not affected by temperature changes and has excellent stability.

The temperature range in which the liquid crystal monomer exhibits liquid crystallinity varies depending on the type of the monomer. 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.

Any suitable liquid crystal monomer may be used as the liquid crystal monomer. For example, the polymerizable mesogen compounds described in JP-A-2002-533742 (WO00/37585), EP358208 (US5211877), EP66137 (US4388453), WO93/22397, EP0261712, DE19504224, DE4408171, GB2280445, etc. may be used. Specific examples of such polymerizable mesogen compounds include BASF's product name LC242, Merck's product name E7, and Wacker-Chem's product name LC-Sillicon-CC3767. As the liquid crystal monomer, for example, a nematic liquid crystal monomer is preferable.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The methods for measuring each property are as follows. In the examples and comparative examples, "parts" and "%" are by weight unless otherwise specified.
(1) Thickness Thicknesses of 10 μm or less were measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name "MCPD-3000"), and thicknesses of more than 10 μm were measured using a digital micrometer (manufactured by Anritsu Co., Ltd., product name "KC-351C").
(2) Appearance The appearance of the polarizing plates used in the Examples and Comparative Examples after humidification and aging was visually observed and evaluated according to the following criteria.
Good: None of warping (curling), wrinkling, and waving was observed. Bad: One or more of warping (curling), wrinkling, and waving was observed. (3) Absorbance The absorbance of the polarizing plates used in the examples and comparative examples after humidification treatment and aging was measured using an IR moisture meter (manufactured by Kurabo Industries, Ltd., product name "RX-200").
(4) Warpage The circularly polarizing plates obtained in the examples and comparative examples were cut into a size of 140 mm x 70 mm. At this time, the polarizer was cut out so that the absorption axis direction was the long side direction. On the other hand, a polyimide film (DuPont-Toray "Kapton (registered trademark)", thickness 50 μm) was cut into a size of 140 mm x 70 mm as a substrate. The cut circularly polarizing plate and polyimide film were left under conditions of 23 ° C. and 55% RH for one day or more to condition the humidity. The humidity-conditioned circularly polarizing plate and polyimide film were bonded together via the adhesive layer of the circularly polarizing plate to obtain a test sample. The test sample was left under conditions of 23 ° C. and 55% RH for 72 hours. The amount of warpage (curl) of the test sample before and after leaving it was measured. When the test sample was placed on a flat surface, the height of the highest part from the flat surface was taken as the amount of warpage. In addition, the case where the warpage was convex toward the polyimide film side was expressed as "positive (+)", and the case where the warpage was convex toward the circularly polarizing plate side was expressed as "negative (-)". The amount of warping before standing (immediately after lamination) was defined as "amount of warping 1," and the amount of warping after standing for 72 hours was defined as "amount of warping 2." The amount of warping was calculated from the following formula, and the absolute value was used as an index for evaluation.
Warpage = (Warpage 1 - Warpage 2)
Specifically, the absolute value of the amount of warpage was evaluated according to the following criteria.
Good: absolute value of warpage is 2 mm or less. Bad: absolute value of warpage exceeds 2 mm. In Reference Example 1, a circularly polarizing plate was attached to a glass plate (thickness 0.4 mm) instead of a polyimide film as a substrate to prepare a test sample.

[Example 1]
1. Preparation of Polarizing Plate A long roll of a 30 μm thick PVA-based resin film was uniaxially stretched in the long direction by a roll stretching machine so that the total stretch ratio was 6.0 times, while simultaneously undergoing swelling, dyeing, crosslinking and washing treatments, and finally drying treatment to prepare a polarizer with a thickness of 12 μm. An HC-TAC film was bonded to one surface of the obtained polarizer as a viewing side protective layer via a PVA-based adhesive. The HC-TAC film is a film in which a hard coat (HC) layer (thickness 7 μm) is formed on a TAC film (thickness 25 μm), and the TAC film was bonded to the polarizer side. Furthermore, a TAC film (thickness 25 μm) was bonded to the other surface of the polarizer via a PVA-based adhesive to obtain a polarizing plate having a configuration of protective layer (HC-TAC film)/polarizer/protective layer (TAC film).

2. Moisture treatment and aging The obtained polarizing plate was subjected to a humidification treatment at 23°C and 80% RH for 8 minutes, and then aged for 1 hour. The aging was performed at room temperature (23°C, 55% RH). This humidification treatment and aging were repeated three times. The cumulative humidification amount in this humidification treatment was 395 [= saturated water vapor amount 20.6 (g/ ^m3 ) x humidity 80 (%) x cumulative humidification time 24 (min)]. The polarizing plate after the humidification treatment and aging was subjected to the above evaluations (2) and (3).

ポリエチレンテレフタレート（ＰＥＴ）フィルム（厚み３８μｍ）表面を、ラビング布を用いてラビングし、配向処理を施した。配向処理の方向は、偏光板に貼り合わせる際に偏光子の吸収軸の方向に対して視認側から見て１５°方向となるようにした。この配向処理表面に、上記液晶塗工液をバーコーターにより塗工し、９０℃で２分間加熱乾燥することによって液晶化合物を配向させた。このようにして形成された液晶層に、メタルハライドランプを用いて１ｍＪ/ｃｍ^２の光を照射し、当該液晶層を硬化させることによって、ＰＥＴフィルム上に液晶配向固化層Ａを形成した。液晶配向固化層Ａの厚みは２．５μｍ、面内位相差Ｒｅ（５５０）は２７０ｎｍであった。さらに、液晶配向固化層Ａは、ｎｘ＞ｎｙ＝ｎｚの屈折率特性を示した。液晶配向固化層ＡをＨ層として用いた。
塗工厚みを変更したこと、および、配向処理方向を偏光子の吸収軸の方向に対して視認側から見て７５°方向となるようにしたこと以外は上記と同様にして、ＰＥＴフィルム上に液晶配向固化層Ｂを形成した。液晶配向固化層Ｂの厚みは１．５μｍ、面内位相差Ｒｅ（５５０）は１４０ｎｍであった。さらに、液晶配向固化層Ｂは、ｎｘ＞ｎｙ＝ｎｚの屈折率特性を示した。液晶配向固化層ＢをＱ層として用いた。 3. Preparation of circularly polarizing plate 3-1. Preparation of retardation layer 10 g of polymerizable liquid crystal exhibiting a nematic liquid crystal phase (manufactured by BASF: product name "Paliocolor LC242", represented by the following formula) and 3 g of a photopolymerization initiator for the polymerizable liquid crystal compound (manufactured by BASF: product name "Irgacure 907") were 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 with a rubbing cloth and subjected to an orientation treatment. The orientation treatment direction was set to be 15° from the viewing side with respect to the direction of the absorption axis of the polarizer when it was laminated to the polarizing plate. The liquid crystal coating liquid was applied to this orientation treatment surface with a bar coater, and the liquid crystal compound was aligned by heating and drying at 90 ° C for 2 minutes. The liquid crystal layer thus formed was irradiated with light of 1 mJ / cm ² using a metal halide lamp, and the liquid crystal layer was hardened to form a liquid crystal alignment solidified layer A on the PET film. The thickness of the liquid crystal alignment solidified layer A was 2.5 μm, and the in-plane retardation Re (550) was 270 nm. Furthermore, the liquid crystal alignment solidified layer A showed a refractive index characteristic of nx > ny = nz. The liquid crystal alignment solidified layer A was used as the H layer.
A liquid crystal alignment solidified layer B was formed on a PET film in the same manner as above, except that the coating thickness was changed and the orientation treatment direction was set to a 75° direction from the viewing side with respect to the direction of the absorption axis of the polarizer. The liquid crystal alignment solidified layer B had a thickness of 1.5 μm and an in-plane retardation Re (550) of 140 nm. Furthermore, the liquid crystal alignment solidified layer B showed a refractive index characteristic of nx>ny=nz. The liquid crystal alignment solidified layer B was used as the Q layer.

3-2. Preparation of circularly polarizing plate The liquid crystal alignment solidified layer A (H layer) and liquid crystal alignment solidified layer B (Q layer) obtained in the above 3-1. were transferred in this order onto the TAC film surface of the polarizing plate subjected to the humidification treatment and aging in the above 2. At this time, the transfer (lamination) was performed so that the angle between the absorption axis of the polarizer and the slow axis of the alignment solidified layer A was 15°, and the angle between the absorption axis of the polarizer and the slow axis of the alignment solidified layer B was 75°. In addition, each transfer (lamination) was performed via an ultraviolet curing adhesive (thickness 1.0 μm). Finally, an acrylic adhesive layer (thickness 15 μm) was placed on the surface of the alignment solidified layer B (Q layer). In this way, a circularly polarizing plate having a configuration of protective layer/adhesive/polarizer/adhesive layer/retardation layer (H layer)/adhesive layer/retardation layer (Q layer)/adhesive layer was obtained. The obtained circularly polarizing plate was subjected to the above evaluation of (4). The results are shown in Table 1.

[Comparative Example 1]
A circular polarizing plate was obtained in the same manner as in Example 1, except that the polarizing plate obtained in the same manner as in Example 1 was subjected to a humidification treatment at 23°C and 80% RH for 12 minutes, and the humidification treatment and the aging in the same manner as in Example 1 were repeated twice. The cumulative humidification amount in the humidification treatment was 395 [= saturated water vapor amount 20.6 (g/ ^m3 ) x humidity 80 (%) x cumulative humidification time 24 (min)]. The obtained polarizing plate and circular polarizing plate were subjected to evaluation in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 2]
A circular polarizing plate was obtained in the same manner as in Example 1, except that the polarizing plate obtained in the same manner as in Example 1 was subjected to a humidification treatment at 23° C. and 80% RH for 24 minutes, and the humidification treatment and aging in the same manner as in Example 1 were performed only once. The cumulative humidification amount in the humidification treatment was 395 [= saturated water vapor amount 20.6 (g/m ³ ) × humidity 80 (%) × cumulative humidification time 24 (min)]. The obtained polarizing plate and circular polarizing plate were subjected to evaluation in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 3]
Except for not carrying out the humidification treatment and aging, a circular polarizing plate was obtained in the same manner as in Example 1. The obtained polarizing plate and circular polarizing plate were subjected to the same evaluations as in Example 1. The results are shown in Table 1.

[Comparative Example 4]
A circular polarizing plate was obtained in the same manner as in Example 1, except that the polarizing plate obtained in the same manner as in Example 1 was subjected to a humidification treatment at 65°C and 95% RH for 8 minutes, and the humidification treatment and aging in the same manner as in Example 1 were performed only once. The cumulative humidification amount in the humidification treatment was 1221 [= saturated water vapor amount 160.7 (g/ ^m3 ) x humidity 95 (%) x cumulative humidification time 8 (min)]. Since the appearance of the polarizing plate after the humidification treatment was poor, the evaluation of warping was not performed. The results are shown in Table 1.

[Reference Example 1]
A circularly polarizing plate was obtained in the same manner as in Example 1, except that the humidification treatment and aging were not performed. The obtained circularly polarizing plate was attached to a glass plate (thickness: 0.4 mm) to prepare a test sample, and the warpage was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[evaluation]
As is clear from Table 1, the circular polarizing plate obtained by the embodiment of the present invention can realize an image display device having an excellent appearance and suppressing warping over time. Furthermore, from the comparison between Example 1 and Comparative Examples 1 and 2, even if the cumulative humidification amount is the same, if the number of repetitions of humidification treatment and aging is small, the desired absorbance (moisture content of polarizer) cannot be obtained, and as a result, warping cannot be sufficiently suppressed. In addition, from Comparative Example 4, it can be seen that if the humidification temperature is set to a high temperature, the cumulative humidification amount can be increased in a short time, but poor appearance occurs. In addition, according to the embodiment of the present invention, since no complicated operation, special equipment, or expensive reagents are required, and the humidification time is short, the circular polarizing plate can be manufactured simply and efficiently.

The circular polarizer obtained by the manufacturing method of the embodiment of the present invention is used as a circular polarizer for an image display device, and can be particularly suitably used in curved, bent, foldable, or rollable image display devices (such image display devices typically use a resin substrate as the substrate). Representative examples of image display devices include liquid crystal display devices, organic EL display devices, and inorganic EL display devices.

REFERENCE SIGNS LIST 10 Polarizing plate 11 Polarizer 12 Protective layer 13 Protective layer 20 Retardation layer 30 Pressure-sensitive adhesive layer 100 Circularly polarizing plate

Claims (9)

A method for producing a circularly polarizing plate having a polarizing plate including a polarizer and a protective layer on at least one of the polarizers, and a retardation layer, comprising the steps of:
The method includes repeating a humidification treatment and an aging treatment for the polarizing plate or the circularly polarizing plate three to four times ;
A method for producing a circularly polarizing plate, wherein the cumulative humidification amount of the humidification treatment is 300 to 850 :
Here, the cumulative humidification amount is expressed by the following formula:
Accumulative humidification amount=saturated water vapor amount during humidification (g/m ³ )×humidity (%)×accumulated humidification time (minutes). 2. The method for producing a circularly polarizing plate according to claim 1, wherein the temperature in the humidification treatment is 20° C. to 40 ° C. , and the humidification time for each treatment is 4 minutes to 10 minutes . 3. The method for producing a circularly polarizing plate according to claim 1, wherein the aging temperature is from 20° C. to 30 ° C. , and the aging time for one cycle is from 1 hour to 12 hours . The method for producing a circularly polarizing plate according to any one of claims 1 to 3, wherein the ratio of the thickness of the polarizer to the total thickness of the protective layer is 1:5 or less. The method for producing a circular polarizing plate according to claim 4, wherein the polarizing plate includes a protective layer on both sides of the polarizer. The method for producing a circularly polarizing plate according to claim 5, wherein each of the protective layers is made of a triacetyl cellulose film. The method for producing a circularly polarizing plate according to any one of claims 1 to 6, wherein the retardation layer is a layer in which a liquid crystal compound is aligned and solidified. The method for producing a circularly polarizing plate according to any one of claims 1 to 7, wherein the obtained laminate, formed by laminating the circularly polarizing plate to a polyimide film, has an absolute value of the amount of warping of 0.2 mm to 2 mm when left for 72 hours under conditions of 23°C and 55% RH. 9. The method for producing a circularly polarizing plate according to claim 1, wherein the obtained circularly polarizing plate has an absorbance of 0.046 to 0.050 .

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