JP2003084269A - Optical film and liquid crystal display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical film having the excellent utilization factor of the light and attaining high luminance and the liquid crystal display device using the same. SOLUTION: A luminance improving film (A) having a property to separate natural light into transmitted light and reflected light and a condensing function film (B) having a projecting and recessing shaped part on a surface are laminated and integrated to yield the optical film. Lamination and integration of the luminance improving film and the condensing function film make an air interface vanish and consequently stray light is reduced and the luminance is improved owing to heightened efficiency of the luminance improving film to reflect and polarize light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical film excellent in light utilization efficiency and capable of achieving high brightness, and a liquid crystal display device using the same.

[0002]

2. Description of the Related Art Liquid crystal displays (LCD) are thin
Taking advantage of its light weight and low power consumption, it is widely used as a flat panel display essential in the advanced information and communication era, and its applications are expanding year by year. Especially in the 21st century, large LCDs such as monitors and TVs are growing rapidly. Under these circumstances, the characteristics required of LCDs in recent years include high brightness, wide viewing angle, high-speed response, and high definition. Among these,
It is highly necessary to increase the brightness of the laptop computer until a few years ago, and the brightness of the notebook computer is 70 to 100 cd / m ²
However, recently, 150 cd / m ² has become common.

With the thinning of LCDs, the flow of a one-lamp type backlight is such that the diameter of the cold cathode fluorescent lamp (CFL) is thin (generally 2 mmφ or less in a notebook computer) and the light guide plate is thin (of CFL). LCD modules, including the backlight, are now thinning to a thickness of 5 to 6 mm, and the concept of lightness and thinness and conflicting issues of securing brightness have emerged. There is. Since the LCD itself is becoming larger and brighter, in order to secure the brightness required for the LCD,
In reality, the situation is such that the improvement of the light guide plate and the back light of the CFL or the like alone cannot catch up.

As a method of increasing the brightness of the backlight, there is a method of increasing the front brightness by focusing the light emitted obliquely with respect to the traveling direction of the light of the backlight in the vicinity of the normal direction. Here, in order to focus the light in the upper, lower, left, and right directions in the normal direction, in the case of using a one-lamp type backlight, two light collecting function films are usually used. The thickness of this light-condensing function film is about 150 μm, and if two sheets are required, the LCD itself becomes considerably thick.

When a one-lamp type backlight is used, two light collecting function films (7) are required as shown in FIG. 3 in order to increase the front brightness. Assuming that the brightness of FIG. 3 using two light collecting function films is 1, the brightness enhancement film (4) as shown in FIG. 4 is used instead of the polarizing plate (5) of the lower plate.
The brightness is increased 1.2 to 1.3 times by inserting 1 sheet. When a two-lamp type backlight is used, as shown in FIG. 6, there is a case where one light-condensing function film (7) is used to increase the front brightness. If the brightness at this time is 1, the brightness is increased by 1.3 to 1.4 times by inserting one brightness improving film (4) instead of the lower plate polarizing plate (5) as shown in FIG. . Further, when the light condensing function film is not used and the brightness at that time is 1, the brightness is increased to 1.5 to 1.6 times by inserting one brightness improving film instead of the lower polarizing plate. . As described above, it has been known that the stray light is generated as the number of the light collecting function films is increased, and the light reflection / polarization efficiency of the brightness enhancement film is deteriorated.

[0006]

However, except for the condensing function film having the function of reducing the light emitted in the oblique direction to improve the front brightness, in many cases, high front brightness cannot be obtained. The need to use light collecting film has arisen.

Therefore, according to the present invention, the efficiency of light utilization is improved by integrally laminating the brightness enhancement film and the light collecting function film, that is, by reducing the number of light collecting function films and reducing the space between the films. It is an object of the present invention to provide an optical film which is excellent in high brightness and a liquid crystal display device using the optical film.

[0008]

In order to solve the above-mentioned problems, the optical film of the present invention comprises a brightness enhancement film (A) having a property of separating natural light into transmitted light and reflected light. And a light-condensing functional film (B) having an uneven portion are laminated and integrated.

In the optical film of the present invention, the light transmitted through the brightness enhancement film (A) is preferably linearly polarized light. The brightness enhancement film (A) is preferably a laminate of a cholesteric liquid crystal layer and a λ / 4 plate.

Further, in the optical film of the present invention,
It is preferable that the light collecting function film (B) has a prism portion.

In the above, preferably, a brightness enhancement film (A) having a property of separating natural light into light that transmits as linearly polarized light and reflected light composed of reusable circularly polarized light, and a prism portion on one surface. The light condensing function film (B) is integrally laminated.

In the optical film of the present invention, the brightness enhancement film (A) is preferably a film in which a cholesteric liquid crystal layer, a λ / 4 plate and an absorbing dichroic polarizing plate are sequentially laminated and integrated.

In the above, the cholesteric liquid crystal layer is preferably composed of an oriented film of a cholesteric liquid crystal polymer or a layered substrate having the oriented liquid crystal layer supported on a film substrate. In particular, two layers of liquid crystal layers having different reflection wavelengths are combined. Those having a structure in which the above are superimposed are preferable.

In the optical film of the present invention,
It is preferable that the brightness enhancement film (A) and the light collecting function film (B) are laminated and integrated via an adhesive or a pressure-sensitive adhesive.

Further, in the optical film of the present invention,
It is preferable that a resin is applied to the brightness enhancement film and a prism type is transferred to the resin to impart a light condensing function.

In the optical film of the present invention,
It is preferable that the light-condensing functional film focuses light emitted at 30 to 80 degrees with respect to the normal line in the vicinity of the normal line direction.

Further, in the optical film of the present invention,
It is preferable that the prism shape of the light condensing function film is mountain-shaped, and the apex angle thereof is in the range of 20 to 80 degrees.

Further, in the optical film of the present invention,
It is preferable that the prism shape of the light collecting function film is corrugated.

Next, the liquid crystal display device of the present invention is characterized in that the above-mentioned optical film is disposed on at least one side of a liquid crystal cell.

The liquid crystal display device of the present invention further comprises:
It is characterized by having a backlight.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The optical film of the present invention comprises a brightness enhancement film (A) having a property of separating natural light into light that transmits and reflected light, and a light-condensing functional film having an uneven portion on one surface. (B) and (B) are laminated and integrated. Among them, a brightness enhancement film (A) having a property of separating natural light into light that is transmitted as linearly polarized light and reusable circularly polarized light, and a condensing function having a prism portion on one surface. A film obtained by laminating and integrating the film (B) is preferably used.

The brightness enhancement film (A) used in the present invention can be used without any particular limitation as long as it has a property of separating natural light into light that transmits and reflected light. For example, natural light is separated into light that is transmitted as linearly polarized light and reflected light that is reusable circularly polarized light, or light that is linearly polarized with a predetermined polarization axis and is reflected by other light. Those having properties are listed.

As an example of the former, either left-handed or right-handed circularly polarized light is reflected, such as a cholesteric liquid crystal layer, particularly an oriented film of a cholesteric liquid crystal polymer or a film obtained by supporting the oriented liquid crystal layer on a film substrate. Then, a material exhibiting a property of transmitting other light can be used. Examples of the latter include those that show the property of transmitting linearly polarized light of a predetermined polarization axis and reflecting other light, such as a multilayered thin film of a dielectric or a multilayered laminate of thin film having different refractive index anisotropy. Can be mentioned.

In the brightness enhancement film of the type that transmits linearly polarized light of the above-mentioned predetermined polarization axis, the transmitted light is directly incident on the polarizing plate with the polarization axis aligned, so that absorption loss due to the polarizing plate is suppressed and the efficiency is improved. Can be transmitted. On the other hand, in a brightness enhancement film of a type that transmits circularly polarized light like a cholesteric liquid crystal layer, it can be directly incident on a polarizer, but from the viewpoint of suppressing absorption loss, the transmitted circularly polarized light is linearly polarized through a retardation plate. It is preferable that the light is incident on the polarizing plate. Λ as the retarder
By using the / 4 plate, circularly polarized light can be converted into linearly polarized light. Therefore, the brightness enhancement film includes the cholesteric liquid crystal layer, the λ / 4 plate and the absorption dichroic polarizing plate,
It is preferable that they are sequentially laminated and integrated in this order.

FIG. 1 is a schematic view showing a structural example of the brightness enhancement film 4 of the present invention. Cholesteric liquid crystal layer (3), λ / 4 plate (2) and absorbing dichroic polarizing plate (1)
However, they are sequentially laminated and integrated.

On the other hand, the light condensing function film (B) is not particularly limited as long as it has an uneven portion on one surface.
The condensing function film (B) having an uneven portion on one surface is
Any film can be used without particular limitation as long as it is a film having an uneven shape on one surface and has a high front brightness when the uneven surface is arranged so as to face the side opposite to the viewing side.
For example, in addition to those having a prism part,
Concavo-convex shapes other than prism shapes include polygonal pyramids such as triangular pyramids and quadrangular pyramids, polygonal prismatic shapes such as triangular prisms and quadrangular prisms, and various shapes such as spherical, hemispherical, and elliptical spherical shapes. It is possible to use a mold or vice versa. These uneven shapes can be constructed by directly using particles,
Further, the uneven shape formed by using particles can be indirectly used to form the uneven shape.

Further, the uneven shape may have a different refractive index, and it is also a preferable embodiment to efficiently collect light by utilizing the difference in refractive index. It is possible to change the optical path of light by changing the refractive index, and it is also possible to collect the light.

As a method for obtaining a product having a changed refractive index,
For example, it is called a two-step copolymerization method, in which a monomer that forms a low refractive index polymer is diffused in a liquid phase or a gas phase into a gel obtained by partially polymerizing a crosslinkable monomer that forms a high refractive index polymer. There is a method of using a polymer. Spherical obtained by such a method, the polymer having a changed refractive index in the shape of a cylinder, or arranged in a plane,
A light-collecting function film can also be formed by forming it on a film.

Further, in the case of the light collecting function film having the above-mentioned prism portion, in order to improve the light collecting ability, the light emitted at 30 to 80 degrees with respect to the normal line is focused in the vicinity of the normal line direction. Is preferred. The prism shape is not particularly limited, and a corrugated shape or a mountain shape can be appropriately used. However, in the mountain shape, the angle (vertical angle) formed by the two slopes of the prism part is The range is 20 to 80 degrees, preferably 30 to 70 degrees. This is because if the angle is less than 20 degrees, it is difficult to form the prism portion, and if the angle exceeds 80 degrees, the light collecting ability may be deteriorated.

The absorption dichroic polarizing plate used in the present invention, that is, the polarizing plate in which a dichroic substance is adsorbed and oriented has a basic constitution. A hydrophilic synthetic resin film is dyed by a conventional method,
Crosslinking, stretching, formed by drying, one side or both sides of the polarizer composed of a polyvinyl alcohol-based polarizing film containing a dichroic material, on the appropriate adhesive layer, for example via an adhesive layer composed of a vinyl alcohol-based polymer or the like. , A transparent protective film to be a protective layer adhered thereto.

As the polarizer (polarizing film), a hydrophilic synthetic resin film may be appropriately treated by a dyeing treatment with a dichroic substance such as iodine or a dichroic dye, a stretching treatment, a crosslinking treatment and the like. Appropriate ones that are applied in the order or method and that transmit linearly polarized light when natural light is incident can be used. In particular, those having excellent light transmittance and polarization degree are preferable. The thickness of the polarizer is not particularly limited, but is generally 1 to 80 μm, and particularly preferably 2 to 40 μm. The synthetic resin film may be swelled in a water bath or the like before being dyed.

As the hydrophilic synthetic resin film, for example, a polymer film such as polyvinyl alcohol or partially formalized polyvinyl alcohol is preferable, and a polyvinyl alcohol film is particularly preferable because it is excellent in dyeability with iodine. As the polyvinyl alcohol-based film, a polyvinyl alcohol-based resin formed by an arbitrary method such as a casting method, a casting method, an extrusion method or the like in which a stock solution of a polyvinyl alcohol resin dissolved in water or an organic solvent is cast is appropriately used. be able to.

An appropriate transparent film can be used as the protective film material which becomes the transparent protective layer provided on one side or both sides of the polarizer (polarizing film). Above all, a film made of a polymer having excellent transparency, mechanical strength, thermal stability, moisture shielding property and the like is preferably used. Examples of the polymer include acetate resin such as triacetyl cellulose, polyester resin, polyether sulfone resin, polycarbonate resin, polyamide resin, polyimide resin, polyolefin resin and acrylic resin. , But is not limited to this.

A transparent protective film which can be particularly preferably used from the viewpoint of polarization characteristics and durability is a triacetyl cellulose film whose surface is saponified with alkali or the like. The thickness of the transparent protective film is arbitrary, but generally 500 μm or less, preferably 5 to 300 μm, particularly preferably 5-1 for the purpose of thinning the polarizing plate.
It is set to 50 μm. When transparent protective films are provided on both sides of the polarizing film, transparent protective films made of different polymers may be used on the front and back sides.

The transparent protective film used for the protective layer is
As long as the object of the present invention is not impaired, a hard coat treatment, an antireflection treatment, a treatment for the purpose of preventing sticking, diffusion or antiglare, or the like may be applied. The hard coat treatment is carried out for the purpose of preventing scratches on the surface of the polarizing plate. For example, a cured coating excellent in hardness and slipperiness with a suitable ultraviolet curable resin such as silicone is used as a transparent protective film. It can be formed by a method of adding to the surface.

On the other hand, the antireflection treatment is carried out for the purpose of preventing reflection of external light on the surface of the polarizing plate, and can be achieved by forming an antireflection film or the like according to the conventional method. In addition, anti-sticking is performed for the purpose of preventing adhesion with an adjacent layer, and anti-glare treatment is performed for the purpose of preventing external light from being reflected on the surface of the polarizing plate and hindering visual recognition of light transmitted through the polarizing plate. It can be formed by imparting a fine concavo-convex structure to the surface of the transparent protective film by an appropriate method such as a surface roughening method such as a sandblasting method or an embossing method or a method of blending transparent fine particles.

The adhesive treatment between the above-mentioned polarizer (polarizing film) and the transparent protective film which is the protective layer is not particularly limited, but for example, an adhesive made of vinyl alcohol polymer, boric acid or It can be carried out through an adhesive or the like comprising at least a water-soluble cross-linking agent of a vinyl alcohol polymer such as sand, glutaraldehyde, melamine and oxalic acid. Such an adhesive layer can be formed as a coating and drying layer of an aqueous solution, etc., but when the aqueous solution is prepared, other additives and a catalyst such as an acid can be added if necessary.

Further, the retardation plate (λ / 4 used in the present invention
As the plate), for example, a birefringent film obtained by subjecting a film made of an appropriate polymer such as polycarbonate, polyvinyl alcohol, polystyrene, polymethylmethacrylate, polypropylene or other polyolefin, polyarylate, or polyamide to a stretching treatment, or a liquid crystal polymer. Examples of the oriented film, a liquid crystal polymer having an oriented layer supported by a film, and the like. The thickness of the retardation plate (λ / 4 plate) obtained by stretching the film is not particularly limited, but is generally 10 to 200 μm, and particularly 20 to
The range of 100 μm is preferable. The thickness of the retardation plate (λ / 4 plate) made of a liquid crystal polymer is not particularly limited, but is generally 0.1 to 5 μm, and particularly preferably 0.5 to 2 μm.

In the brightness enhancement film of the present invention, examples of the liquid crystals forming the liquid crystal layer include cyanobiphenyl type, cyanophenylcyclohexane type, cyanophenyl ester type, benzoic acid phenyl ester type, phenylpyrimidine type and those. Examples thereof include a low-molecular liquid crystal or a crosslinkable liquid crystal monomer that exhibits a nematic phase or a smectic phase at room temperature or high temperature, or a liquid crystal polymer that exhibits a nematic phase or a smectic phase at room temperature or high temperature. The above-mentioned crosslinkable liquid crystal monomer is usually subjected to an alignment treatment and then subjected to a crosslinking treatment by an appropriate method using heat, light or the like to obtain a polymer. Among them, the cholesteric liquid crystal layer,
In particular, such as those having an oriented film of cholesteric liquid crystal polymer or an oriented liquid crystal layer supported on a film substrate, those showing the property of reflecting either left-handed or right-handed circularly polarized light and transmitting other light, etc. Is preferred.

The cholesteric liquid crystal layer is a combination of layers having different reflection wavelengths, and has an arrangement structure in which two or more layers are superposed, so that a layer which reflects circularly polarized light in a wide wavelength range such as a visible light range can be obtained. It is possible to obtain transmission circularly polarized light having a wide wavelength range based on the obtained wavelength.

Here, the formation of the cholesteric liquid crystal polymer layer can be carried out by a method similar to the conventional alignment treatment of low-molecular liquid crystals. For example, a film of polyimide, polyvinyl alcohol, polyester, polyarylate, polyamideimide, polyetherimide or the like having a thickness of 0.1 to 5.0 μm is formed on a supporting substrate having a thickness of 10 to 100 μm, and a rayon cloth or the like is used. Liquid crystal polymer is spread on an appropriate alignment film such as an alignment film that has been rubbed and heated to a temperature above the glass transition temperature and below the isotropic phase transition temperature, and below the glass transition temperature in the state where the liquid crystal polymer molecules are Grandjean aligned. Examples of the method include a method of forming a solidified layer in which the orientation is fixed by cooling to a glass state.

Examples of the above-mentioned supporting base material include synthetic resins such as triacetyl cellulose, polyvinyl alcohol, polyimide, polyarylate, polyester, polycarbonate, polysulfone, polyether sulfone, amorphous polyolefin, modified acrylic polymer, and epoxy resin. A single layer or laminated film made of a film, a glass plate and the like can be mentioned. A synthetic resin film is preferable from the viewpoint of thinning.

The thickness of the solidified layer of the liquid crystal polymer formed on the supporting substrate is generally 0.5 to 50 μ from the viewpoints of preventing alignment disorder and lowering of transmittance and widening the wavelength range of selective reflection.
m, preferably 1 to 30 μm, particularly preferably 2 to 10
μm. The liquid crystal polymer solidified layer on the supporting base material may be used as an integral body with the supporting base material, or may be peeled and transferred from the supporting base material to another base material by using an adhesive or an adhesive. . In particular, the latter method is preferable in order to increase the peel strength of the liquid crystal layer.

Next, the light collecting function film (B) used in the present invention will be described. The optical film of the present invention is obtained by removing one sheet of the light collecting function film having the form shown in FIG. 4, adding a light collecting function to the lower side of the brightness enhancement film, and laminating both of them. This makes it possible to reduce the thickness of the entire film, and eliminates stray light due to the disappearance of the air interface. As a result, the efficiency of light reflection and polarization of the brightness enhancement film is improved, and brightness is improved. Examples of the method of adding the light collecting function to the brightness improving film by laminating and integrating the light collecting function film and the brightness improving film include the following two methods.

The first method is to prepare a prism die and heat transfer it to a transparent resin by hot pressing, and integrate it with the brightness enhancement film via an adhesive or a pressure sensitive adhesive. The second method is a method in which a transparent resin is directly coated on the lower surface of the brightness enhancement film to obtain a prism mold. Here, as the transparent resin, an acrylic resin, a polycarbonate resin, a vinyl chloride resin, or the like can be used, and an acrylic resin having a high visible light transmittance is particularly preferable.

The thickness of the optical film of the present invention (brightness improving film having a light collecting function) is 300 to 600 μm,
It is preferably 300 to 400 μm. In general, the thickness of the light collecting function film is about 150 μm, while the thickness of the acrylic resin that imparts the light collecting function to the brightness enhancement film is 5 to 50 μm. Therefore, as in the present invention, it is possible to reduce the thickness to 100 μm or more by laminating and integrating the brightness enhancement film and the light collecting function film. Further, when stacking the films, sticking causes a problem, so a space is required between the films, but it is possible to reduce the thickness further by omitting one film having a light collecting function. Become.

In the present invention, as the pressure-sensitive adhesive or adhesive used for laminating the brightness enhancement film or laminating the brightness enhancement film and the light collecting function film, for example,
It is possible to use an appropriate polymer such as an acrylic polymer, a silicone polymer, a polyester polymer, a polyurethane polymer, a polyamide polymer, or a polyether polymer, which is a base polymer.

The above-mentioned optical film of the present invention may be provided with an adhesive layer for adhering to other members such as a liquid crystal cell. The pressure-sensitive adhesive layer can be formed of a suitable pressure-sensitive adhesive such as an acrylic or urethane-based one that has been conventionally used. In particular, in terms of prevention of foaming phenomenon and peeling phenomenon due to moisture absorption, deterioration of optical characteristics due to thermal expansion difference and the like, prevention of warpage of liquid crystal cells, and further formation of a liquid crystal display device having high quality and excellent durability, the moisture absorption rate is high. The adhesive layer is preferably low and has excellent heat resistance. It is also possible to form an adhesive layer containing fine particles and exhibiting light diffusivity. The adhesive layer may be provided on a required surface as needed.

When the pressure-sensitive adhesive layer provided on the optical film is exposed on the surface, it is preferable to temporarily cover the pressure-sensitive adhesive layer with a separator for practical use until the pressure-sensitive adhesive layer is put into practical use. The separator is formed by a method in which a suitable thin sheet conforming to the above-mentioned transparent protective film or the like is provided with a release coat using a suitable release agent such as silicone-based or long-chain alkyl-based, fluorine-based or molybdenum sulfide as necessary. be able to.

Each layer such as a polarizing film or a transparent protective film, an optical layer or an adhesive layer forming the above-mentioned polarizing plate or optical member is, for example, a salicylic acid ester compound, a benzophenone compound, a benzotriazole compound, a cyanoacrylate compound. It may be one having an ultraviolet absorbing ability by an appropriate method such as a method of treating with an ultraviolet absorber such as a compound or a nickel complex salt compound.

The optical film of the present invention can be preferably used for forming various devices such as a liquid crystal display device, and particularly preferably for a transmissive liquid crystal display device having a backlight. The liquid crystal cell forming the liquid crystal display device is arbitrary, and an appropriate type such as an active matrix drive type represented by a thin film transistor type, a simple matrix drive type represented by a twist nematic type or a super twist nematic type, etc. The liquid crystal cell may be used.

The optical film of the present invention is usually used by being provided on the back side of a liquid crystal cell. When the optical film of the present invention is mounted on a liquid crystal display device, usually, the absorption dichroic polarizing plate constituting the brightness enhancement film is arranged on the liquid crystal cell side, and the light collecting function film is arranged on the backlight side. To be done. When a polarizing plate and other optical members are provided on both sides of the liquid crystal cell, they may be the same or different. Further, when forming a liquid crystal display device, appropriate components such as a prism array sheet, a lens array sheet, a reflection plate, a light diffusion plate, a light guide plate, and a backlight are arranged in one layer or two or more layers at appropriate positions. be able to.

[0053]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

Further, in this example, the brightness enhancement film was produced by the following method by sequentially superposing the cholesteric liquid crystal layer, the λ / 4 plate and the polarizing plate having the absorption dichroism.

(Production Example of Brightness Enhancement Film) Thickness 50 μm
After forming an alignment film of polyvinyl alcohol having a thickness of 0.1 μm on the triacetyl cellulose (TAC) film and performing a rubbing treatment, a cholesteric liquid crystal polymer having a selective reflection center wavelength of 700 nm, 550 nm, 40
Three layers each having a thickness of 0 nm were sequentially formed on the alignment film. The thickness of each layer was about 3 μm. A 60 μm thick polycarbonate λ / 4 plate is attached to the cholesteric liquid crystal layer via an acrylic pressure-sensitive adhesive, and an iodine-based polarizing plate (on which the acrylic pressure-sensitive adhesive is formed on both front and back surfaces) And the transmission axes were aligned and bonded to produce a brightness enhancement film.

Although not particularly mentioned in this embodiment, it is preferable that the prism shape of the condensing function film is optimized according to the distribution of emitted light of the backlight. Also,
There are two methods of setting the prism axis of the prism of the light collecting function film horizontally or orthogonally to the incident light of the backlight when two light collecting function films are used. Any of the stacking orders may be horizontal or orthogonal as long as they are arranged so as to be.

Each example will be described below with reference to the drawings. In each drawing, 5 is a polarizing plate, 6 is a liquid crystal cell, 10 is a reflector, and 11 is a light source (lamp). Not specifically mentioned in the examples.

<Backlight with one lamp type>

Example 1 A mold having a prism pattern having a tip angle of 45 degrees and a pitch of 50 μm was produced. Separately, an acrylic resin having a thickness of 8 μm was applied to the surface opposite to the multilayer film of the brightness enhancement film made of triacetyl cellulose (TAC) on which a multilayer film of cholesteric liquid crystal polymer was formed. Then, thermal transfer was carried out by hot pressing using the mold to produce a brightness enhancement film with a light collecting function.

On the light guide plate (9) made of polymethylmethacrylate, the diffusion plate (8) made of acrylic resin was placed, and on top of that, the light condensing function film (7) made of acrylic resin was placed, The brightness enhancement film (12) with a light condensing function of the present invention was superposed on it to produce a liquid crystal display having the structure shown in FIG. The prism axis of the prism of the brightness enhancement film (12) with a light collecting function was designed so as to be orthogonal to the incident light of the backlight.

Example 2 A light-collecting function film made of an acrylic film having a prism pattern having a prism tip angle of 45 degrees and a brightness enhancement film prepared by the above method were bonded together with an acrylic adhesive and dried. Then, a brightness enhancement film with a light collecting function was produced. Hereinafter, in the same manner as in Example 1, a liquid crystal display having the configuration shown in FIG. 2 was produced. The prism axis of the prism of the brightness enhancement film (12) with a light collecting function was designed so as to be orthogonal to the incident light of the backlight.

Comparative Example 1 A diffusion plate (8) was placed on a light guide plate (9), and two light-condensing functional films (7) similar to those of Example 1 were sequentially stacked on the diffusion plate (8). A liquid crystal display having the structure shown in FIG. 3 was produced in the same manner as in 1.

Comparative Example 2 A light diffusing plate (8) was placed on a light guide plate (9), and two light condensing functional films (7) similar to those of Example 1 were sequentially stacked on the diffusing plate (8), and One of the brightness enhancement films (4) produced by the method of 1 above was overlaid, and the liquid crystal display having the configuration shown in FIG. 4 was produced in the same manner as in Example 1.

<Backlight with two lamps>

Example 3 A diffusion plate (8) made of acrylic resin was placed on a light guide plate (9) made of polymethylmethacrylate, and a brightness enhancement film with a light condensing function (similar to that in Example 1) was placed thereon. 12) were overlaid to produce a liquid crystal display having the structure shown in FIG. The prism axis of the prism of the brightness enhancement film with the light collecting function was designed to be orthogonal to the incident light of the backlight.

Example 4 A light diffusion plate (8) made of acrylic resin was placed on a light guide plate (9) made of polymethylmethacrylate, and a brightness enhancement film with a light condensing function similar to that of Example 2 ( 12) were overlaid to produce a liquid crystal display having the structure shown in FIG. The prism axis of the prism of the brightness enhancement film with the light collecting function was designed to be orthogonal to the incident light of the backlight.

Comparative Example 3 A light diffusing plate (8) was placed on the light guide plate (9), and one light-collecting function film (7) similar to that of Example 1 was superposed thereon, and the same as Example 1. Then, a liquid crystal display having the structure shown in FIG. 6 was produced.

Comparative Example 4 A light diffusing plate (8) was placed on a light guide plate (9), and one light-collecting function film (7) similar to that of Example 1 was placed on it, and then the above method was used. One sheet of the produced brightness enhancement film (4) was overlaid, and in the same manner as in Example 1, a liquid crystal display having the configuration shown in FIG. 7 was produced.

(Evaluation) Examples 1 to 4 and Comparative Examples 1 to 4
Regarding the liquid crystal display (Fig. 2 to Fig. 7) manufactured in
Regarding the configuration below the liquid crystal cell 6 (that is, the configuration excluding the polarizing plate 5 and the liquid crystal cell 6), a luminance meter (TOPCOM
Manufactured by BM-7) to evaluate the brightness. The results are shown in Table 1.

[0070]

[Table 1] Backlight Brightness (cd / cm ² ) Embodiment 1 Lamp 1 lamp type 140 FIG. 2 Example 2 Lamp 1 lamp type 139 FIG. 2 Comparative example 1 Lamp 1 lamp type 100 FIG. 3 Comparative example 2 lamp 1 lamp type 125 FIG. 4 Example 3 lamp 2 lamp type 270 FIG. 5 Example 4 lamp 2 lamp type 267 FIG. 5 Comparative example 3 lamp 2 lamp type 180 FIG. 6 Comparative example 4 lamp 2 lamp type 245 FIG.

From the results shown in Table 1, when the backlight of one lamp type is used and the brightness of the configuration of FIG. 3 using two light collecting function films is 1, the lower polarizing plate and the light collecting function film are shown. By removing one sheet and inserting one sheet of the brightness enhancement film of the present invention (FIG. 2), the brightness of 1.
You can see that it goes up four times.

When a two-lamp type backlight is used, assuming that the brightness in the configuration of FIG. 6 is 1, the brightness with the light collecting function of the present invention is used instead of the lower plate polarizing plate and one light collecting function film. By inserting one enhancement film (Fig. 5),
It can be seen that the brightness is increased by 1.5 times.

As described above, the space between the films can be reduced by adding the light collecting function to the brightness enhancement film except for one light collecting function film. As a result,
While the light condensing function remains the same, the brightness can be increased by increasing the light reflection / polarization efficiency of the brightness enhancement film.

[0074]

As described above, the optical film of the present invention has a structure in which the brightness enhancement film and the light condensing function film are laminated and integrated, and in particular, they are integrated by an adhesive or a pressure-sensitive adhesive. Disappears, stray light is reduced, and the efficiency of light reflection and polarization of the brightness enhancement film is increased to improve brightness. That is, when the brightness enhancement film and the film having a light condensing function are simply installed face down with no bonding, stray light is generated due to the air interface, but via an adhesive or a pressure sensitive adhesive. By integrating the brightness enhancement film and the film having a light condensing function, the air interface disappears and stray light is reduced. As a result, when the optical film of the present invention is used in a liquid crystal display device, it is possible to provide a bright display liquid crystal display device having excellent light utilization efficiency. Therefore, its industrial value is great.

[Brief description of drawings]

FIG. 1 is a schematic view showing a configuration example of a brightness enhancement film of the present invention.

FIG. 2 is a schematic diagram showing a configuration example of a one-lamp type liquid crystal display device of the present invention.

FIG. 3 is a schematic diagram showing a configuration example of a conventional one-lamp type liquid crystal display device.

FIG. 4 is a schematic diagram showing a configuration example of a conventional one-lamp type liquid crystal display device.

FIG. 5 is a schematic diagram showing a configuration example of a two-lamp type liquid crystal display device of the present invention.

FIG. 6 is a schematic diagram showing a configuration example of a conventional two-lamp type liquid crystal display device.

FIG. 7 is a schematic diagram showing a configuration example of a conventional two-lamp type liquid crystal display device.

[Explanation of symbols]

1 Absorption dichroic polarizing plate 2 λ / 4 plate 3 Cholesteric liquid crystal layer 4 brightness enhancement film 5 Polarizer 6 Liquid crystal cell 7 Condensing function film 8 diffuser 9 Light guide plate 10 Reflector 11 Light source (lamp) 12 Brightness enhancement film with light condensing function

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G02F 1/13363 G02F 1/13363 (72) Inventor Ikuro Kawamoto 1-2-1, Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation F-term (reference) 2H042 BA04 BA12 BA14 BA20 2H049 BA02 BA03 BA05 BA07 BA42 BB03 BB62 BB63 BC22 2H091 FA10Z FA11Z FA21Z FA28Z FA41Z FB02 FC01 FD14 LA16 LA30

Claims (15)

[Claims] 1. A laminate of a brightness enhancement film (A) having a property of separating natural light into transmitted light and reflected light, and a light collecting function film (B) having an uneven portion on one surface. An optical film characterized by being made into a material. 2. The optical film according to claim 1, wherein the light transmitted through the brightness enhancement film (A) is linearly polarized light. 3. The optical film according to claim 2, wherein the brightness enhancement film (A) is a laminate of a cholesteric liquid crystal layer and a λ / 4 plate. 4. The optical film according to claim 1, wherein the light collecting function film (B) has a prism portion. 5. A brightness enhancement film (A) having a property of separating natural light into light that transmits as linearly polarized light and reflected light composed of reusable circularly polarized light, and a condensing function having a prism portion on one surface. The optical film according to claim 1, wherein the film (B) and the film (B) are integrally laminated. 6. The brightness enhancement film (A) according to claim 1, wherein a cholesteric liquid crystal layer, a λ / 4 plate and a polarizing plate with absorption dichroism are sequentially laminated and integrated. Optical film. 7. The optical film according to claim 6, wherein the cholesteric liquid crystal layer comprises an oriented film of a cholesteric liquid crystal polymer or the oriented liquid crystal layer supported on a film substrate. 8. The optical film according to claim 6, wherein the cholesteric liquid crystal layer has a structure in which two or more liquid crystal layers having different reflection wavelengths are combined and overlapped with each other. 9. The optical film according to claim 1, wherein the brightness enhancement film (A) and the light collecting function film (B) are laminated and integrated via an adhesive or a pressure sensitive adhesive. 10. The optical film according to claim 1, wherein a resin is applied to the brightness enhancement film, and a prism type is transferred to the resin to impart a light condensing function. 11. The film having a light collecting function is 3 with respect to a normal line.
The optical film according to any one of claims 1 to 10, which focuses light emitted at 0 to 80 degrees in the vicinity of the normal direction. 12. The prism shape of the condensing function film,
The optical film according to any one of claims 1 to 11, which is a mountain shape and has an apex angle in the range of 20 to 80 degrees. 13. The prism shape of the condensing function film,
The optical film according to claim 1, which is corrugated. 14. A liquid crystal display device, wherein the optical film according to claim 1 is arranged on at least one side of a liquid crystal cell. 15. The liquid crystal display device according to claim 14, further comprising a backlight.