KR20240115165A - Optical laminated body and image display device using same - Google Patents

Abstract

The object of the present invention is to provide an optical laminate including a liquid crystal alignment solidification layer having high birefringence and suppressing retardation change in a high temperature environment.
The optical laminate according to an embodiment of the present invention includes a liquid crystal alignment solidification layer having a circular polarization function or an elliptical polarization function, and when the amount of the liquid crystal compound contained in the liquid crystal alignment solidification layer is 100 parts by weight, the liquid crystal The amount (X) (parts by weight) of the polymerization initiator and the amount (Y) (parts by weight) of the crosslinking agent contained in the orientation solidification layer satisfy the following formula (1) or (2):
5≤X≤20 and 0<Y≤20···(1)
5<X≤20 and 0≤Y≤20···(2).

Description

Optical laminate and image display device using the optical laminate {OPTICAL LAMINATED BODY AND IMAGE DISPLAY DEVICE USING SAME}

The present invention relates to an optical laminated body and an image display device using the optical laminated body.

In recent years, image display devices typified by liquid crystal displays and electroluminescence (EL) display devices (eg, organic EL display devices and inorganic EL display devices) are rapidly becoming popular. As an image display device, in many cases, an optical laminate containing a retardation film (for example, an anti-reflection film integrating a polarizing plate and a retardation film) is used. In recent years, as the demand for thinner image display devices has become stronger, the demand for thinner optical laminates has also become stronger. For the purpose of reducing the thickness of optical laminates, the thickness of the retardation layer (retardation film), which greatly contributes to the thickness, is being reduced. A representative example of a thin retardation film is a retardation film using a liquid crystal compound. Since the birefringence (Δn) of the liquid crystal compound is significantly greater than that of the resin, the thickness for obtaining the desired in-plane retardation can be significantly reduced compared to the stretched resin film. On the other hand, retardation films using liquid crystal compounds have large retardation changes in a high-temperature environment. As a result, when such a retardation film is used for an anti-reflection film, the anti-reflection function of the anti-reflection film may be damaged in a high temperature environment.

International Publication No. 2019/160016

The present invention was made to solve the above-described conventional problems, and its main purpose is to provide an optical laminate including a liquid crystal alignment solidification layer having high birefringence and suppressing retardation change in a high-temperature environment.

[1] The optical laminate according to an embodiment of the present invention includes a liquid crystal alignment solidification layer having a circular polarization function or an elliptical polarization function, and when the amount of the liquid crystal compound contained in the liquid crystal alignment solidification layer is 100 parts by weight , the amount (X) (part by weight) of the polymerization initiator and the amount (Y) (part by weight) of the crosslinking agent contained in the liquid crystal alignment solidification layer satisfy the following formula (1) or (2):

5≤X≤20 and 0<Y≤20···(1)

5<X≤20 and 0≤Y≤20···(2).

[2] In [1] above, the amount (X) (parts by weight) of the polymerization initiator and the amount (Y) (parts by weight) of the crosslinking agent satisfy the following formula (3):

X+Y≤35···(3).

[3] In [1] or [2] above, the amount (X) (parts by weight) of the polymerization initiator and the amount (Y) (parts by weight) of the crosslinking agent satisfy the following formula (4):

X+Y≤25···(4).

[4] In any one of [1] to [3] above, the optical laminate further includes a polarizing plate.

[5] In [4] above, the optical laminate further includes another retardation layer whose refractive index characteristic exhibits the relationship nz>nx=ny on the side opposite to the polarizing plate of the liquid crystal alignment solidification layer.

[6] In [4] above, the liquid crystal alignment solidification layer includes a first liquid crystal alignment solidification layer and a second liquid crystal alignment solidification layer; Re(550) of the first liquid crystal alignment solidification layer is 200 nm to 300 nm, and the angle between its slow axis and the absorption axis of the polarizer of the polarizing plate is 10° to 20°; Re(550) of the second liquid crystal alignment solidification layer is 100 nm to 200 nm, and the angle formed between its slow axis and the absorption axis of the polarizer of the polarizing plate is 70° to 80°.

[7] In [6] above, the optical laminate further includes another retardation layer whose refractive index characteristic exhibits the relationship nz>nx=ny on the side opposite to the polarizing plate of the liquid crystal alignment solidification layer.

[8] According to another aspect of the present invention, an image display device is provided. The image display device includes the optical laminate of any one of [1] to [7] above.

According to an embodiment of the present invention, an optical laminate containing a liquid crystal alignment solidification layer having high birefringence and suppressing phase difference change in a high temperature environment can be realized.

1 is a schematic cross-sectional view of an optical laminate according to one embodiment of the present invention.
Figure 2 is a schematic cross-sectional view of an optical laminate according to another embodiment of the present invention.

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

(Definition of terms and symbols)

The 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 where the in-plane refractive index is maximum (i.e., slow axis direction), 'ny' is the refractive index in the direction orthogonal to the slow axis in the plane (i.e., fast axis direction), and 'nz' is It is the refractive index in the thickness direction.

(2) In-plane phase difference (Re)

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

(3) Phase difference in the thickness direction (Rth)

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

(4) Nz coefficient

The Nz coefficient can be obtained by Nz=Rth/Re.

(5) angle

When referring to an angle in this specification, unless otherwise specified, the angle includes angles in both clockwise and counterclockwise directions.

A. Optical laminate

An optical laminate according to an embodiment of the present invention includes a liquid crystal alignment solidification layer having a circularly polarized light function or an elliptically polarized light function. The optical laminate may be, for example, a laminate in which a liquid crystal alignment solidification layer is formed on any suitable substrate, or may be a laminate of a liquid crystal alignment solidification layer and another optical function film (for example, a polarizing plate). The type, number, combination, lamination order, etc. of the liquid crystal alignment solidification layer and other optical function films to be laminated can be appropriately set depending on the purpose. The laminated body in which the liquid crystal alignment solidification layer was formed on the base material may be laminated with another optical function film as is, or the liquid crystal alignment solidification layer may be transferred and laminated on another optical function film. The liquid crystal alignment-fixed layer may have a circularly polarized light function or an elliptically polarized light function alone (for example, a cholesteric liquid crystal layer), or may exhibit a circularly polarized light function or an elliptically polarized light function in combination with a polarizer. The substrate preferably has an orientation regulating force. Orientation regulating force can be typically provided by rubbing orientation, stretched substrate orientation, or photo-orientation. Preferably, it is stretched substrate orientation or photo-orientation. In addition, in this specification, the term 'liquid crystal alignment solidification layer' refers to a layer in which a liquid crystal compound is oriented in a predetermined direction within the layer and the orientation state is fixed. 'Liquid crystal alignment solidification layer' is a concept including an orientation hardening layer obtained by curing a liquid crystal monomer. In one embodiment of the liquid crystal alignment solidification layer, the rod-shaped liquid crystal compounds are aligned in the slow axis direction of the liquid crystal alignment solidification layer (homogeneous orientation).

In an embodiment of the present invention, when the amount of the liquid crystal compound contained in the liquid crystal alignment solidification layer is 100 parts by weight, the amount (X) (weight part) of the polymerization initiator and the amount of the crosslinking agent (Y ) (parts by weight) satisfies the following formula (1) or (2). With such a structure, it is possible to obtain a liquid crystal alignment solidification layer that has high birefringence and excellent heating durability. As a result, it is possible to reduce the thickness of the liquid crystal alignment-fixed layer (and, as a result, the optical laminate), and also realize an optical laminate in which phase difference change in a high-temperature environment is suppressed.

5≤X≤20 and 0<Y≤20···(1)

5<X≤20 and 0≤Y≤20···(2)

In either case of formula (1) or formula (2), the amount of polymerization initiator (X) and the amount of crosslinking agent (Y) may change while being related to each other. The amount of the polymerization initiator (X) and the amount of the crosslinking agent (Y) preferably satisfy the following formula (3), and more preferably satisfy the following formula (4). With such a structure, excellent heating durability can be realized while maintaining Δn of the liquid crystal alignment solidification layer at a higher value. As a result, the thickness of the liquid crystal alignment solidification layer for obtaining the desired in-plane retardation can be reduced, contributing to thinning of the optical laminate (ultimately the image display device to which the optical laminate is applied).

X+Y≤35···(3)

X+Y≤25···(4)

'X+Y' is more preferably 20 parts by weight or less, further preferably 18 parts by weight or less, particularly preferably 15 parts by weight or less, and most preferably 13 parts by weight or less. The lower limit of 'X+Y' may be, for example, 5.5 parts by weight, or may be, for example, 7.5 parts by weight. If 'X+Y' is in this range, a liquid crystal alignment solidification layer with an excellent balance between high Δn and excellent heating durability can be realized. The amount (X) of the polymerization initiator may vary depending on the amount (Y) of the crosslinking agent. The amount (X) of the polymerization initiator may be, for example, 6 parts by weight to 18 parts by weight, for example, 7 parts by weight to 15 parts by weight, or for example, 8 parts by weight to 13 parts by weight. Likewise, the amount (X) of the crosslinking agent may vary depending on the amount (X) of the polymerization initiator. The amount (Y) of the crosslinking agent may be, for example, 2.5 parts by weight to 20 parts by weight, for example, 4 parts by weight to 15 parts by weight, or for example, 5 parts by weight to 13 parts by weight.

Hereinafter, as a representative example of an optical laminated body, an optical laminated body (polarizing plate with a retardation layer) further including a polarizing plate will be described. First, an outline of the optical laminate (polarizing plate with retardation layer) is explained, and then representative components (polarizing plate, liquid crystal alignment solidification layer, and other retardation layers) are explained in detail.

1 is a schematic cross-sectional view of an optical laminate according to one embodiment of the present invention; Figure 2 is a schematic cross-sectional view of an optical laminate according to another embodiment of the present invention. The optical laminates 100 and 102 of the illustrated example each include a polarizing plate 10 and a liquid crystal alignment solidification layer (retardation layer) 20 in this order from the top of the figure. The upper side of the drawing is the viewing side, and the lower side of the drawing is the image display panel side. The polarizer 10 includes a polarizer 11, a protective layer (visible side protective layer) 12 provided on one side of the polarizer 11, and a protective layer (inner protective layer) provided on the other side of the polarizer 11. )(13). Either of the protective layers 12 or 13 may be omitted. For example, the polarizing plate may be a so-called polarizing plate that includes a polarizer and a viewer-side protective layer.

The liquid crystal alignment-fixed layer 20 has a circularly polarized light function or an elliptically polarized light function as described above. With this configuration, an optical laminate having excellent anti-reflection properties can be obtained. The liquid crystal alignment solidified layer 20 may be a single layer as shown in FIG. 1, and has a laminated structure of the first liquid crystal alignment solidified layer 21 and the second liquid crystal alignment solidified layer 22 as shown in FIG. 2. You can stay.

In one embodiment, the optical laminate may further include another retardation layer (not shown) on the side of the liquid crystal alignment solidification layer 20 opposite to the polarizing plate 10. Another retardation layer is typically a so-called positive C plate whose refractive index characteristics exhibit the relationship nz>nx=ny. By providing such a different phase contrast layer, reflection in the oblique direction can be prevented satisfactorily, and wide viewing angle of the anti-reflection function becomes possible.

In practical terms, the optical laminate includes an adhesive layer (not shown) as the outermost layer on the image display panel side and can be attached to the image display panel. In this case, it is preferable that a release liner is temporarily attached to the surface of the adhesive layer until the optical laminate is ready for use. By temporarily attaching the release liner, the adhesive layer is protected and roll formation of the optical laminated body becomes possible.

Hereinafter, representative components of the optical laminate (polarizing plate, liquid crystal alignment solidification layer, and other retardation layers) will be described in detail.

B. Polarizer

B-1. polarizer

As the polarizer 11, any suitable polarizer can be employed. The polarizer is typically made of a polyvinyl alcohol (PVA)-based resin film containing a dichroic material (eg, iodine). Examples of PVA-based resins include polyvinyl alcohol, partially formalized polyvinyl alcohol, ethylene-vinyl alcohol copolymer, and partially saponified products of ethylene-vinyl acetate copolymer. For example, the resin film forming the polarizer may be a single-layer resin film or a laminate of two or more layers.

Specific examples of polarizers composed of a single-layer resin film include hydrophilic polymer films such as PVA-based films, partially formalized PVA-based films, and ethylene-vinyl acetate copolymer-based partially saponified films, with iodine, dichroic dyes, etc. Examples include those that have been dyed and stretched with a dichroic substance, and polyene-based oriented films such as dehydrated PVA products and dehydrochloric acid-treated polyvinyl chloride products. Preferably, a polarizer obtained by dyeing a PVA-based film with iodine and uniaxially stretching is used because it has excellent optical properties.

The dyeing with iodine is performed, for example, by immersing the PVA-based film in an aqueous iodine solution. The draw ratio of the uniaxial stretching is preferably 3 to 7 times. Stretching may be performed after dyeing treatment or may be performed while dyeing. Additionally, it may be dyed after stretching. If necessary, the PVA-based film is subjected to swelling treatment, crosslinking treatment, washing treatment, drying treatment, etc. For example, by immersing the PVA-based film in water and washing it before dyeing, it is possible to clean the surface of the PVA-based film from contamination and anti-blocking agents, as well as to prevent uneven dyeing by swelling the PVA-based film.

Specific examples of the polarizer obtained using the laminate include a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a resin substrate and a PVA-based resin layer applied to the resin substrate. A polarizer obtained using a laminated body of the following can be mentioned. A polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer formed by applying to the resin substrate is, for example, applied by applying a PVA-based resin solution to a resin substrate, drying it, and forming a PVA-based resin layer on the resin substrate, Obtaining a laminate of a resin substrate and a PVA-based resin layer; It can be produced by stretching and dyeing the laminate and using the PVA-based resin layer as a polarizer. In this embodiment, a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin is preferably formed on one side of the resin substrate. Stretching typically includes stretching the laminate by immersing it in an aqueous boric acid solution. In addition, stretching may, if necessary, further include air stretching the laminate at a high temperature (for example, 95°C or higher) before stretching in an aqueous boric acid solution. Additionally, in this embodiment, the laminate is preferably subjected to dry shrinkage treatment to shrink it by 2% or more in the width direction by heating it while conveying it in the longitudinal direction. Typically, the manufacturing method of this embodiment includes performing aerial auxiliary stretching treatment, dyeing treatment, underwater stretching treatment, and dry shrink treatment on the laminate in this order. By introducing auxiliary stretching, even when applying PVA on a thermoplastic resin, it becomes possible to increase the crystallinity of PVA and achieve high optical properties. Moreover, by simultaneously increasing the orientation of PVA in advance, problems such as a decrease in orientation or dissolution of PVA when immersed in water in the subsequent dyeing or stretching process can be prevented, making it possible to achieve high optical properties. do. Additionally, when the PVA-based resin layer is immersed in a liquid, the disruption of the orientation of polyvinyl alcohol molecules and the decrease in orientation can be suppressed compared to the case where the PVA-based resin layer does not contain a halide. Thereby, the optical properties of the polarizer obtained through a treatment process performed by immersing the laminate in a liquid, such as dyeing treatment and underwater stretching treatment, can be improved. Additionally, optical properties can be improved by shrinking the laminate in the width direction through dry shrinkage treatment. The obtained resin substrate/polarizer laminate may be used as is (i.e., the resin substrate may be used as a protective layer of the polarizer), or on the peeling surface where the resin substrate is peeled from the resin substrate/polarizer laminate, or on the peeling surface. It may be used by laminating any appropriate protective layer depending on the purpose on the side opposite to the above. Details of the manufacturing method of such a polarizer are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580 and Japanese Patent Application Publication No. 6470455. The entire descriptions of these publications are incorporated herein by reference.

The thickness of the polarizer is, for example, 12 μm or less, preferably 10 μm or less, more preferably 1 μm to 8 μm, and even more preferably 3 μm to 7 μm. By combining such a thin polarizer and a liquid crystal alignment solidification layer, significant reduction in the thickness of the optical laminated body becomes possible. Moreover, if the thickness of the polarizer is within the above range, curling during heating can be suppressed well, and good external appearance durability during heating is obtained.

The polarizer preferably exhibits absorption dichroism at any wavelength between 380 nm and 780 nm. The single transmittance of the polarizer is preferably 41.0% to 46.0%, and more preferably 42.0% to 45.0%. The polarization degree of the polarizer is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more. According to an embodiment of the present invention, even if the single transmittance is in the above range, the degree of polarization can be maintained in the above range.

B-2. protective layer

The protective layers 12 and 13 are made of any suitable resin film. Representative materials constituting the resin film include cellulose resins such as triacetylcellulose (TAC), cycloolefin resins such as polynorbornene, (meth)acrylic resins, polyethylene terephthalate (PET), and polyethylene naphthalate. Examples include polyester-based resins such as (PEN), polyolefin-based resins such as polyethylene, and polycarbonate-based resins. Representative examples of (meth)acrylic resin include (meth)acrylic resin having a lactone ring structure. (meth)acrylic resins having a lactone ring structure, for example, Japanese Patent Application Laid-Open No. 2000-230016, Japanese Patent Application Publication No. 2001-151814, Japanese Patent Application Publication No. 2002-120326, Japanese Patent Application Publication No. 2002-254544, It is described in Japanese Patent Publication No. 2005-146084. These publications are incorporated herein by reference. From the viewpoint of ease of shape release processing, etc., cellulose resin is preferable, and TAC is more preferable. From the viewpoint of obtaining a polarizing plate with low moisture permeability and excellent durability, cycloolefin-based resin and (meth)acrylic-based resin are preferable.

The optical laminate is typically placed on the viewer side of the image display device, and the protective layer 12 is typically placed on the viewer side. Therefore, the protective layer 12 may be subjected to surface treatment as needed. Examples of surface treatment include hard coat treatment, anti-reflection treatment, anti-sticking treatment, and anti-glare treatment. Additionally, the protective layer 12 may be treated, as necessary, to improve visibility when viewed through polarized sunglasses (typically, imparting an (other) circularly polarized light function or imparting an ultra-high phase difference. ) may be implemented. By performing such processing, excellent visibility can be achieved even when the display screen is viewed through polarized lenses such as polarized sunglasses. Therefore, the optical laminate can also be suitably applied to an image display device that can be used outdoors.

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 thickness direction retardation Rth(550) is -10 nm to +10 nm.

The thickness of the protective layers 12 and 13 is each preferably 10 μm to 80 μm, more preferably 12 μm to 40 μm, and still more preferably 15 μm to 35 μm. In addition, when surface treatment is performed on the protective layer 12, the thickness of the protective layer 12 is a thickness including the thickness of the surface treatment layer.

C. Liquid crystal alignment solidification layer

The liquid crystal alignment-fixed layer 20 has a circularly polarized light function or an elliptically polarized light function as described above. In addition, as mentioned above, the liquid crystal alignment solidification layer 20 may be a single layer as shown in FIG. 1, and as shown in FIG. 2, it may be comprised of the 1st liquid crystal alignment solidification layer 21 and the 2nd liquid crystal alignment solidification layer 22. ) may have a layered structure. By using the liquid crystal alignment solidification layer as a retardation layer, a desired in-plane retardation can be realized at a significantly thinner thickness compared to a stretched resin film. As a result, the optical laminate can be significantly reduced in thickness.

The birefringence (Δn) of the liquid crystal alignment solidification layer is preferably 0.06 or more, more preferably 0.08 or more, further preferably 0.09 or more, and particularly preferably 0.10 or more. The upper limit of Δn may be, for example, 0.13, and may also be, for example, 0.12. If Δn is in this range, the desired in-plane retardation can be achieved with a very thin thickness. As a result, it becomes possible to make the liquid crystal alignment solidification layer and the optical laminated body thinner, ultimately contributing to significant thinning of the image display device. According to the embodiment of the present invention, it is possible to realize a liquid crystal alignment solidification layer that has such a high Δn and has excellent heating durability.

Examples of liquid crystal compounds used in the liquid crystal alignment solidification layer include liquid crystal polymer and liquid crystal monomer. The liquid crystal compound is preferably polymerizable. If the liquid crystal compound is polymerizable, the alignment state of the liquid crystal compound can be fixed by polymerizing the liquid crystal compound after aligning it. Here, the polymer formed by polymerization is non-liquid crystalline. Therefore, the formed liquid crystal alignment solidification layer is unlikely to transition into a liquid crystal phase, a glass phase, or a crystal phase due to temperature changes peculiar to liquid crystal compounds, for example. As a result, the liquid crystal alignment solidification layer becomes a retardation layer that is unaffected by temperature changes and has extremely excellent stability.

In one embodiment, the liquid crystal alignment solidification layer can be formed using a composition containing a polymerizable liquid crystal compound (polymerizable liquid crystal compound). In this specification, the polymerizable liquid crystal compound included in the composition refers to a compound that has a polymerizable group and also has liquid crystallinity. The polymerizable group refers to a group involved in a polymerization reaction, and is preferably a photopolymerizable group. Here, the photopolymerizable group refers to a group that can participate in the polymerization reaction by active radicals or acids generated from the photopolymerization initiator.

The mechanism for expressing liquid crystallinity of the liquid crystal compound may be thermotropic or lyotropic. Additionally, the composition of the liquid crystal phase may be nematic liquid crystal or smectic liquid crystal. From the viewpoint of ease of manufacture, thermotropic nematic liquid crystal is preferable.

The temperature range where a liquid crystal monomer exhibits liquid crystallinity varies 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.

Hereinafter, each of the single layer and laminated structures will be described.

C-1. single layer

In this embodiment, the liquid crystal alignment solidification layer 20 can function as a so-called λ/4 plate. In this case, Re(550) of the liquid crystal alignment solidification layer 20 is preferably 100 nm to 200 nm. In addition, the angle formed by the slow axis of the liquid crystal alignment solidification layer 20 and the absorption axis of the polarizer 11 is preferably 40° to 50°, more preferably 42° to 48°, and even more preferably It is 44° to 46°, and is particularly preferably about 45°.

Re(550) of the liquid crystal alignment solidification layer is more preferably 110 nm to 180 nm, further preferably 120 nm to 160 nm, and particularly preferably 130 nm to 150 nm.

Since the liquid crystal alignment solidification layer has an in-plane phase difference as mentioned above, it has the relationship of nx>ny. The liquid crystal alignment solidification layer exhibits any suitable refractive index characteristic as long as it has the relationship nx>ny. The refractive index characteristics of the liquid crystal alignment solidification layer typically exhibit the relationship of nx>ny≥nz. Additionally, here, 'ny=nz' includes not only the case where ny and nz are completely the same, but also the case where they are substantially the same. Therefore, there may be cases where ny < nz, within a range that does not impair the effect according to the embodiment of the present invention. The Nz coefficient of the liquid crystal alignment solidification layer is preferably 0.9 to 2.0, more preferably 0.9 to 1.5, and still more preferably 0.9 to 1.2. By satisfying this relationship, when the optical laminate is used in an image display device, very excellent reflected color can be achieved.

The thickness of the liquid crystal alignment solidification layer can be set so that it can function most appropriately as a lambda/4 plate. In other words, the thickness can be set so that a desired in-plane retardation is obtained. Specifically, the thickness may be, for example, 1.0 μm to 5.0 μm, or for example, 1.0 μm to 3.0 μm. In this way, by using the liquid crystal alignment solidification layer as a retardation layer, a desired in-plane retardation can be realized at a significantly thinner thickness compared to a stretched film of a resin film.

C-2. Laminated structure

When the liquid crystal alignment solidified layer has a laminated structure of a first liquid crystal alignment solidified layer and a second liquid crystal alignment solidified layer from the polarizing plate side, the first liquid crystal alignment solidified layer can typically function as a λ/2 plate, and 2 The liquid crystal alignment solidification layer can typically function as a λ/4 plate. Specifically, Re(550) of the first liquid crystal alignment layer is preferably 200 nm to 300 nm, more preferably 230 nm to 290 nm, and still more preferably 250 nm to 280 nm; Re(550) of the second liquid crystal alignment layer is the same as described in Section C-1 for the single layer. The thickness of the first liquid crystal alignment solidification layer can be adjusted so that the desired in-plane retardation of the λ/2 plate is obtained. Specifically, its thickness may be, for example, 2.0 μm to 4.0 μm. The thickness of the second liquid crystal alignment solidification layer can be adjusted so that the desired in-plane retardation of the λ/4 plate is obtained. Specifically, its thickness may be, for example, 1.0 μm to 2.5 μm. In this embodiment, the angle formed by the slow axis of the first liquid crystal alignment solidification layer and the absorption axis of the polarizer is preferably 10° to 20°, more preferably 12° to 18°, and even more preferably 14°. °~16°; The angle formed by the slow axis of the second liquid crystal alignment solidification 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°. . In addition, the arrangement order of the first liquid crystal alignment solidification layer and the second liquid crystal alignment layer may be reversed, and the angle formed by the slow axis of the first liquid crystal alignment solidification layer and the absorption axis of the polarizer and the second liquid crystal alignment solidification layer The angle formed by the slow axis of and the absorption axis of the polarizer may be inverse. The first liquid crystal alignment solidification layer and the second liquid crystal alignment solidification layer may exhibit inverse dispersion wavelength characteristics in which the phase difference value increases depending on the wavelength of the measurement light, or may exhibit positive wavelength dispersion characteristics in which the phase difference value decreases depending on the wavelength of the measurement light. Alternatively, the phase difference value may exhibit flat wavelength dispersion characteristics that hardly change depending on the wavelength of the measurement light.

The liquid crystal alignment solidification layer of this embodiment is formed, for example, using a composition containing any suitable liquid crystal monomer. Liquid crystal monomers include, for example, Japanese Patent Application Publication No. 2002-533742 (WO00/37585), EP358208 (US5211877), EP66137 (US4388453), WO93/22397, EP0261712, DE19504224, DE4408171, and GB2280. Polymerizable mesogenic compounds described in 445, etc. You can use it. Specific examples of such polymerizable mesogenic compounds 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, for example, a nematic liquid crystal monomer is preferable.

C-3. Polymerization initiator and crosslinking agent

Since the liquid crystal alignment solidification layer is typically formed using a liquid crystal polymer and/or a liquid crystal monomer as described above, a polymerization initiator is contained in the liquid crystal alignment solidification layer. Additionally, since a cross-linking agent may be used to fix the alignment state of the liquid crystal compound, the liquid crystal alignment solidification layer may include a cross-linking agent. The amount of polymerization initiator (X) and the amount of crosslinking agent (Y) satisfy the formula (1) or (2), preferably the formula (3), and more preferably the formula (4) satisfies.

The polymerization initiator may be a photopolymerization initiator or a thermal polymerization initiator. Preferably, it is a photopolymerization initiator. Photopolymerization initiators have the advantage of not causing thermal cleavage and generating radicals only by light irradiation. Examples of the polymerization initiator include an alkylphenone-based photopolymerization initiator, a benzophenone-based photopolymerization initiator, an acylphosphine oxide-based photopolymerization initiator, an oxime ester-based photopolymerization initiator, and a cationic photopolymerization initiator. Specific compounds include, for example, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide. there is. The polymerization initiator may be used individually or may be used in combination of two or more types.

Examples of the crosslinking agent include an acrylic crosslinking agent and an epoxy crosslinking agent. As an acrylic crosslinking agent, for example, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, neopentyl glycol di( Meth)acrylate, 2-hydroxy-3-methacrylpropyl acrylate, 2-hydroxy-1,3-dimethacryloxypropane, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylic bifunctional (meth)acrylates such as polytetramethylene glycol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, and ethoxylated bisphenol A di(meth)acrylate; Trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, ethoxylated glycerin tri(meth)acrylate, tris-(2-acrylooxyethyl)isocyanurate, pentaerythritol Tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol poly(meth)acrylate , ethoxylated dipentaerythritol poly(meth)acrylate, and polyfunctional (meth)acrylate such as polypentaerythritol poly(meth)acrylate. Additionally, (meth)acrylate means acrylate and/or methacrylate. The crosslinking agent may be used individually or may be used in combination of two or more types.

D. Different phase contrast layers

Another retardation layer may be a so-called positive C plate whose refractive index characteristics exhibit the relationship nz>nx=ny, as described above. By using a positive C plate as another phase contrast layer, reflection in the oblique direction can be prevented well, and wide viewing angle of the anti-reflection function becomes possible. In this case, the phase difference Rth (550) in the thickness direction of the other retardation layer is preferably -50 nm to -300 nm, more preferably -70 nm to -250 nm, even more preferably -90 nm to -200 nm, especially Preferably -100nm to -180nm. Here, 'nx=ny' includes not only the case where nx and ny are strictly the same, but also the case where nx and ny are substantially the same. That is, the in-plane phase difference Re(550) of the other phase difference layer may be less than 10 nm.

The other retardation layer may be formed from any suitable material. The other retardation layer preferably comprises a film comprising a liquid crystal material fixed in homeotropic orientation. The liquid crystal material (liquid crystal compound) capable of homeotropic alignment may be a liquid crystal monomer or a liquid crystal polymer. Specific examples of the liquid crystal compound and the method for forming the retardation layer include the liquid crystal compound and the method for forming the retardation layer described in [0020] to [0028] of Japanese Patent Application Laid-Open No. 2002-333642. In this case, the thickness of the other retardation layer is preferably 0.5 μm to 10 μm, more preferably 0.5 μm to 8 μm, and still more preferably 0.5 μm to 5 μm.

E. Image display device

The optical laminated body described in items A to D above can be applied to an image display device. Accordingly, embodiments of the present invention also include an image display device using such an optical laminated body. Representative examples of image display devices include liquid crystal display devices and organic EL display devices. An image display device according to an embodiment of the present invention typically includes the optical laminated body described in paragraphs A to D above on its viewing side.

[Example]

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. The measurement and evaluation methods in the examples are as follows.

(1) Birefringence (Δn)

The liquid crystal alignment solidification layer of the optical laminated body obtained in the Example and Comparative Example was bonded to an alkali-free glass plate (45 mm x 50 mm x 0.7 mm) through an adhesive (thickness 23 μm), and then the base material was peeled. In this way, a test sample having a structure of liquid crystal alignment solidification layer/adhesive layer/glass plate was obtained. The thickness of the liquid crystal alignment solidification layer of the test sample was measured with an interference thickness meter ('MCPD9800', manufactured by Otsuka Electronics Co., Ltd.). Additionally, Re(550) of the test sample was measured using 'AXO-Scan' manufactured by AXOMETRICS. Δn was calculated by dividing the obtained Re (550) by the thickness of the liquid crystal alignment solidification layer.

(2) Phase difference change

The test sample obtained in the same manner as in (1) above was left in an oven at 85°C for 500 hours, and the phase difference change rate was determined from the following equation. In the equation below, Re(550) ₀ is the in-plane phase difference before heating, and Re(550) ₅₀₀ is the in-plane phase difference after heating.

Phase difference change rate (%)=[{Re(550) ₅₀₀ -Re(550) ₀ }/Re(550) ₀ ]×100

In addition, if the phase difference change rate is more than -3.5% (small absolute value), it is evaluated as 'good', and if it is less than -3.5% (absolute value is large), it is evaluated as 'bad'. In the vicinity of this change rate, the superiority or inferiority of anti-reflection performance may become significant.

[Example 1: Fabrication of an optical laminate having a liquid crystal alignment solidification layer/substrate configuration]

1. Preparation of coating solution for forming liquid crystal alignment solidification layer

A photopolymerizable liquid crystal compound exhibiting a nematic liquid crystal phase ('Paliocolor LC242' manufactured by BASF, chemical formula below) was dissolved in cyclopentanone to prepare a solution with a solid content concentration of 20% by weight. To this solution, a leveling agent ('Megapac F-563', manufactured by DIC), a photopolymerization initiator ('Omnirad907', manufactured by IGM Resins), and a cross-linking agent ('A-DCP', manufactured by Shinnakamura Chemical Industries, Ltd.) were added. Thus, a coating liquid for forming a liquid crystal alignment solidification layer was prepared. The addition amounts of the leveling agent, photopolymerization initiator, and crosslinking agent were 0.6 parts by weight, 7.5 parts by weight, and 2.5 parts by weight, respectively, based on 100 parts by weight of the photopolymerizable liquid crystal compound.

2. Fabrication of optical laminate

A stretched norbornene-based film (thickness: 23 μm, Re (550): 140 nm) was prepared as a substrate. On this substrate, the coating liquid for forming the liquid crystal alignment solidification layer was applied using a spin coater and heated at 100°C for 3 minutes to orient the liquid crystal compound. After cooling to room temperature, photocuring was performed by irradiating ultraviolet rays with an accumulated light amount of 600 mJ/cm ² in a nitrogen atmosphere to fix the alignment state of the liquid crystal compound. In this way, an optical laminate having a structure of a substrate/liquid crystal alignment solidification layer (Re(550): 120 nm) was produced. The thickness of the liquid crystal alignment solidification layer was 1.5㎛, and the liquid crystal alignment solidification layer showed a refractive index distribution of nx>ny=nz. In addition, the liquid crystal alignment solidification layer showed the relationship of Re(450)>Re(550). The obtained optical laminate was subjected to evaluation of (1) and (2) above. The results are shown in Table 1.

[Examples 2 to 10 and Comparative Examples 1 to 3: Production of an optical laminate having a liquid crystal alignment solidification layer/substrate structure]

In the same manner as in Example 1, except that the amount (X) (part by weight) of the photopolymerization initiator and the amount (Y) (part by weight) of the crosslinking agent relative to 100 parts by weight of the liquid crystal compound were changed as shown in Table 1, the substrate/liquid crystal was prepared. An optical laminate having an orientation-fixed layer (Re(550): 120 nm) was produced. The obtained optical laminated body was subjected to the same evaluation as Example 1. The results are shown in Table 1. Additionally, '-' in Table 1 means that the phase difference layer was not formed and measurement was impossible.

[Table 1]

[Example 11: Production of polarizer with retardation layer]

1. Production of polarizer

1-1. Fabrication of polarizer

Corona treatment was performed on one side of the resin substrate using an amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm), which is long and has a Tg of about 75°C as a thermoplastic resin substrate.

100 parts by weight of PVA-based resin, which is a 9:1 mixture of polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Japan Synthetic Chemical Industry Co., Ltd., brand name 'Gosephimer'), potassium iodide 13 The added weight was dissolved in water to prepare a PVA aqueous solution (coating solution).

The PVA aqueous solution was applied to the corona-treated surface of the resin substrate and dried at 60°C to form a PVA-based resin layer with a thickness of 13 μm, thereby producing a laminate.

The obtained laminate was uniaxially stretched 2.4 times in the longitudinal direction (longitudinal direction) in an oven at 130°C (air auxiliary stretching treatment).

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

Next, in a dyeing bath (iodine aqueous solution obtained by mixing iodine and potassium iodide at a weight ratio of 1:7 with respect to 100 parts by weight of water) at a liquid temperature of 30°C, the final single transmittance (Ts) of the polarizer obtained is the desired value. It was immersed for 60 seconds while adjusting the concentration to achieve this (dyeing treatment).

Next, it was immersed in a crosslinking bath (a boric acid aqueous solution obtained by mixing 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% by weight, potassium iodide concentration: 5% by weight) at a liquid temperature of 70°C, and the total stretch ratio was stretched in the longitudinal direction (longitudinal direction) between rolls with different circumferential speeds. Uniaxial stretching was performed to make this 5.5 times larger (underwater stretching treatment).

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

Afterwards, it was dried in an oven maintained at about 90°C and brought into contact with a heating roll made of SUS whose surface temperature was maintained at about 75°C (dry shrink treatment).

In this way, a polarizer with a thickness of about 5 μm was formed on the resin substrate, and a polarizing plate having a resin substrate/polarizer configuration was obtained. The group transmittance Ts of the polarizer was 43.3%.

1-2. Production of polarizer

The HC-TAC film was bonded to the surface of the obtained polarizer (the side opposite to the resin substrate) through an ultraviolet curing adhesive. In addition, the HC-TAC film is a film in which an HC layer (7 μm thick) was formed on a triacetylcellulose (TAC) film (25 μm thick), and the TAC film was bonded to the polarizer side. Next, the resin substrate was peeled to obtain a polarizing plate having the structure of HC layer/TAC film (protective layer)/polarizer.

2. Fabrication of different phase contrast layers

20 parts by weight of a side-chain liquid crystal polymer represented by the following formula (IV) (the numbers 65 and 35 in the formula represent the mole percent of the monomer unit, and are conveniently expressed as a block polymer: weight average molecular weight 5000), showing a nematic liquid crystalline phase. A liquid crystal coating solution was prepared by dissolving 80 parts by weight of polymerizable liquid crystal (manufactured by BASF, brand name: PaliocolorLC242) and 5 parts by weight of a photopolymerization initiator (manufactured by Chiba Specialty Chemicals, brand name: Irgacure 907) in 200 parts by weight of cyclopentanone. Then, the coating liquid was applied to the PET base material that had been vertically aligned using a bar coater, and then heated and dried at 80°C for 4 minutes to orient the liquid crystal. By irradiating ultraviolet rays to this liquid crystal layer and hardening the liquid crystal layer, another retardation layer (thickness 3 μm) exhibiting refractive index characteristics of nz>nx=ny was formed on the substrate.

3. Production of polarizer with phase contrast layer

The liquid crystal alignment solidification layer of the optical laminated body of Example 1 was bonded to the polarizer surface of the polarizing plate obtained above through an adhesive, and then the base material was peeled. That is, the liquid crystal alignment solidification layer was transferred to the polarizer surface of the polarizing plate. Additionally, the other retardation layer obtained above was transferred to the surface of the liquid crystal alignment solidification layer through an adhesive. In this way, an optical laminate (polarizing plate with a retardation layer) was obtained. When the obtained polarizing plate with a retardation layer was subjected to the same evaluation as Example 1, it was confirmed that the retardation change was small.

[Comparative Example 4: Production of polarizer with phase contrast layer]

A polarizing plate with a retardation layer was obtained in the same manner as in Example 11 except that the optical laminated body of Comparative Example 1 (substantially a liquid crystal alignment solidification layer) was used. When the obtained polarizing plate with a retardation layer was subjected to the same evaluation as Example 1, it was confirmed that the retardation change was large and exceeded the allowable range.

As is clear from the above examples and comparative examples, according to the examples of the present invention, a liquid crystal alignment solidification layer (as a result, an optical laminate) having a high Δn and excellent heating durability is obtained.

The optical laminate according to the embodiment of the present invention can be suitably used in an image display device (typically a liquid crystal display device or an organic EL display device).

10: Polarizer
11: Polarizer
12: protective layer
13: protective layer
20: Liquid crystal alignment solidification layer
21: First liquid crystal alignment solidification layer
22: Second liquid crystal alignment solidification layer
100: Optical laminate
102: Optical laminate

Claims (8)

An optical laminate comprising a liquid crystal alignment solidification layer having a circular polarization function or an elliptical polarization function,
When the amount of the liquid crystal compound contained in the liquid crystal alignment solidification layer is 100 parts by weight, the amount (X) (part by weight) of the polymerization initiator and the amount (Y) (part by weight) of the crosslinking agent contained in the liquid crystal alignment solidification layer are An optical laminate that satisfies the following formula (1) or (2):
(5≤X≤20 and 0<Y≤20···(1)
5<X≤20 and 0≤Y≤20···(2)). According to paragraph 1,
An optical laminate wherein the amount (X) (parts by weight) of the polymerization initiator and the amount (Y) (parts by weight) of the crosslinking agent satisfy the following formula (3):
(X＋Y≤35···(3)). According to paragraph 2,
An optical laminate wherein the amount (X) (parts by weight) of the polymerization initiator and the amount (Y) (parts by weight) of the crosslinking agent satisfy the following formula (4):
(X＋Y≤25···(4)). According to paragraph 1,
An optical laminate further comprising a polarizer. According to clause 4,
An optical laminate further comprising, on the side opposite to the polarizing plate of the liquid crystal alignment solidification layer, another retardation layer whose refractive index characteristics exhibit the relationship nz>nx=ny. According to clause 4,
The liquid crystal alignment solidification layer includes a first liquid crystal alignment solidification layer and a second liquid crystal alignment solidification layer,
The Re (550) of the first liquid crystal alignment solidification layer is 200 nm to 300 nm, and the angle between its slow axis and the absorption axis of the polarizer of the polarizing plate is 10 ° to 20 °,
The Re (550) of the second liquid crystal alignment solidification layer is 100 nm to 200 nm, and the angle between its slow axis and the absorption axis of the polarizer of the polarizing plate is 70 ° to 80 °,
Optical laminate. According to clause 6,
An optical laminate further comprising, on the side opposite to the polarizing plate of the liquid crystal alignment solidification layer, another retardation layer whose refractive index characteristics exhibit the relationship nz>nx=ny. An image display device comprising the optical laminated body according to any one of claims 1 to 7.