JP2001330731A - Optical film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated optical film which comprises a polarizing layer (a) selectively reflecting visible rays and composed of a cholesteric liquid crystal layer and an optical layer (b) having an optical function different from that of (a) and composed of at least a layer of a liquid crystal layer, is excellent in durability and is capable of being thinned and a liquid crystal display device equipped with the same. SOLUTION: The optical film is manufactured by forming a PVA(polyvinyl alcohol) alignment layer with 0.1 μm thickness on a triacetyl cellulose film, by treating the layer with rubbing, subsequently by aligning an acrylic side chain nematic liquid crystal polymer with 0.5 μm thickness, having the same main component as a cholesteric liquid crystal polymer to be laminated afterwards, so as to make 1/4 phase difference layer, and by forming a layer composed of three layers of acrylic side chain cholesteric liquid crystal polymers with 700 nm, 550 nm and 400 nm central wavelengths of selective reflection respectively successively formed and aligned thereon.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical film using a brightness enhancement film and a liquid crystal display device having the same.

[0002]

2. Description of the Related Art A cholesteric liquid crystal layer that selectively reflects a specific wavelength of visible light is used in a liquid crystal display device or the like as a brightness enhancement film.

When a brightness enhancement film is used in a liquid crystal display device, the brightness enhancement film is usually used by being provided on the rear side of a liquid crystal cell of the liquid crystal display device. When natural light including visible light enters due to reflection from a backlight or the back side of a liquid crystal display device or the like, the brightness enhancement film converts linearly polarized light having a predetermined wavelength in the visible light or circularly polarized light having a predetermined rotation at a predetermined wavelength. Reflected light shows a characteristic of transmitting a predetermined light, especially the brightness enhancement film consisting of a cholesteric liquid crystal layer, when light from a light source such as a backlight, incident clockwise of a specific wavelength of visible light The circularly polarized light component of the specific wavelength is reflected, and the counterclockwise circularly polarized light component of the specific wavelength is transmitted, or vice versa. The right-handed circularly polarized light component of the wavelength has a function of transmitting, so that the transmitted light of a predetermined polarization state (for example, left-handed circularly polarized light) is obtained, and the right-handed circularly polarized light of the specific wavelength, for example, is transmitted. Without transmission Is Isa. The light reflected on the surface of the brightness enhancement film is further inverted by a reflection layer or some light reflection object or a light scattering layer provided on the back side and re-incident on the brightness enhancement plate, and a part or all of the light is reflected. The amount of light that is transmitted as light in a predetermined polarization state (for example, left-handed circularly polarized light) to increase the amount of light that passes through the brightness enhancement film, and is supplied to the polarizer to provide polarized light that is hardly absorbed, and can be used for liquid crystal image display and the like. The luminance can be improved by increasing the luminance. That is, when light is incident from the rear side of the liquid crystal cell through a polarizing plate (polarizer) with a backlight or the like without using a brightness enhancement film, the light does not coincide with the polarization axis of the polarizing plate (polarizer). Most of the light having the polarization direction is absorbed by the polarizing plate (polarizer) and does not pass through the polarizing plate (polarizer). That is, although it differs depending on the characteristics of the polarizing plate (polarizer) used, about 50% of the light is absorbed by the polarizing plate (polarizer), and the amount of light that can be used for liquid crystal image display or the like is accordingly reduced. Decreases and the image becomes darker. The brightness enhancement film is such that light having a polarization direction that is absorbed by the polarizer is once reflected by the brightness enhancement film without being incident on the polarizer, and further inverted through a reflection layer or the like provided on the rear side. The light is repeatedly incident on the brightness enhancement plate, and the polarization direction of the light reflected and inverted between the two can pass through the polarizing plate (polarizer), or the light is further polarized by intervention of a phase difference plate or the like. When polarized light that can be converted into polarized light that can pass through a plate (polarizer) is transmitted, the polarized light is transmitted and a predetermined polarized light is supplied to the polarizing plate (polarizer). The liquid crystal display device can be efficiently used for displaying an image, and the screen can be brightened.

In recent years, it has been required to add and improve various functions, and in combination with the above-mentioned visible light reflective polarizing layer using a cholesteric liquid crystal having a luminance improving function, the visible light reflective polarizing layer is used. Attempts have been made to provide or improve various functions by providing at least one optical layer having an optical function different from that of the optical layer.

For example, a cholesteric liquid crystal layer that selectively reflects visible light as described above and a quarter wave plate (also referred to as a λ / 4 plate or a quarter wavelength plate) combine to provide a reflection polarization function. Optical film having a reflective polarization function combining a cholesteric liquid crystal layer selectively reflecting visible light and a viewing angle compensation film, or a cholesteric liquid crystal layer selectively reflecting visible light and a viewing angle compensation film Combined with retarder,
Optical films having a reflective polarizing function, such as by combining with a visible light reflective polarizing layer using a cholesteric liquid crystal, by providing at least one optical layer having an optical function different from the visible light reflective polarizing layer, various Attempts have been made to add or improve functionality.

For example, an optical film having a reflective polarization function, which is a combination of a cholesteric liquid crystal layer for selectively reflecting visible light and a 位相 phase plate, has been proposed. That is, in such a laminated optical film, the visible light that has passed through the cholesteric liquid crystal layer that selectively reflects visible light is left-handed circularly polarized light as described above. However, in order to efficiently display an image using a polarizing plate in a liquid crystal display device, it is desirable that the light incident on the polarizing plate provided on the rear side of the liquid crystal cell be linearly polarized light. The ４ retardation plate has a function of converting circularly polarized light into linearly polarized light, and therefore, by stacking a cholesteric liquid crystal layer having the reflection polarization function and a ４ retardation plate,
For example, counterclockwise circularly polarized light that has passed through the cholesteric liquid crystal is converted into linearly polarized light by a 1/4 phase difference plate, and linearly polarized light whose image can be recognized by a liquid crystal display device can be efficiently extracted. Even when visible light is directly incident on a polarizing plate using a dichroic dye, desired linearly polarized light is obtained,
As described above, light rays that do not coincide with the polarization axis of the polarizer are absorbed by the polarizer, so that a considerable portion of the supplied visible light is absorbed and lost, resulting in a decrease in image brightness. is there. By using the cholesteric liquid crystal layer having the reflective polarization function, the optical film as in the present invention does not absorb the polarized light other than the polarized light that can be transmitted by the cholesteric liquid crystal layer, as in the case of the polarizing plate. As described above, while repeating reflection and reversal through a reflection layer or the like provided on the rear side and re-incident on the brightness enhancement plate made of the cholesteric liquid crystal layer, the light passes through the cholesteric liquid crystal layer. The polarized light in the obtained polarization state can be extracted. In addition, the quarter-wave plate formed on the cholesteric liquid crystal layer does not absorb, for example, left-handed circularly polarized light that has passed through the cholesteric liquid crystal layer, but converts it into linearly polarized light. have.

Accordingly, an optical film having a reflective polarization function, which is a combination of a cholesteric liquid crystal layer for selectively reflecting specific circularly polarized light of a specific wavelength out of such visible light and a quarter wave plate, has a liquid crystal structure. It is effective for application to a display device, and has been proposed so far.

[0008] However, the quarter wave plate conventionally used in this combination is a stretched and oriented transparent polymer film, and has no commonality as a compound with the cholesteric liquid crystal having the reflective polarization function. Different materials were used. That is, as the quarter wave plate, polycarbonate, polyvinyl alcohol,
A birefringent film obtained by stretching a film made of an ordinary polymer that is not an appropriate liquid crystal such as polystyrene, polymethyl methacrylate, polypropylene, other polyolefin, polyarylate, or polyamide has been used.

The reflective polarizing layer using the above-mentioned cholesteric liquid crystal having a luminance improving function can improve the front luminance when used in an actual liquid crystal display, but causes coloring in an oblique direction. There was also a problem. Therefore, in order to improve the coloring in the oblique direction, it is often adopted to bond a polymer film which is not a liquid crystal for viewing angle compensation to the viewing angle compensation layer.
Further, if necessary, a quarter-wave retarder in which a transparent polymer film is stretched and oriented as described above may be used together with the polymer film for compensating the viewing angle, so that, for example, circularly polarized light can be linearly polarized. Even when the light is converted into polarized light and incident on a polarizing plate using, for example, a dichroic dye existing thereon, desired linearly polarized light that efficiently passes through the polarizing plate is also obtained.

[0010] However, a polymer film which is not a liquid crystal for compensating viewing angle and which is conventionally used in this combination is a transparent polymer film which is stretched and oriented in a vertical, horizontal, oblique or thickness direction, and is used as a cholesteric liquid crystal. Used different materials having no common features as compounds. That is, as a polymer film for viewing angle compensation, a film made of an appropriate polymer such as polycarbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene, other polyolefin, polyarylate, or polyamide is applied in a direction perpendicular to the film plane. A birefringent film or the like oriented in the vertical and / or horizontal directions of the film in a thickness direction or a direction substantially parallel to the film plane has been used.

[0011]

Therefore, a cholesteric liquid crystal layer having a brightness improving function is provided with a 1/4 retardation plate or a polymer film for compensating viewing angle, and a polymer film for compensating viewing angle, and At least one optical layer having an optical function different from the visible light reflective polarizing layer composed of a cholesteric liquid crystal layer, such as a polymer film for a retardation plate, is attached with an adhesive or an adhesive. Deterioration of optical characteristics such as surface reflection loss due to the presence of adhesives and other refractive index interfaces, lowering of durability characteristics such as distortion and peeling due to bonding of different materials, and increase in thickness of adhesive or adhesive And so on. Further, the thickness of an optical film having an optical function such as a 1/4 retardation plate or an optical film for compensating a viewing angle by a polymer stretched film is 50 to 1
The thickness is usually 00 μm, and the intended optical film tends to become a considerably thick film by lamination.

According to the present invention, lamination can be performed without using a pressure-sensitive adhesive or an adhesive, the durability characteristics such as distortion and peeling are small, and the thickness can be considerably reduced.
A laminated optical film composed of a visible light reflective polarizing layer (a) and an optical layer (b) composed of at least one liquid crystal layer having an optical function different from that of the above (a), an optical film using the same, and It is another object of the present invention to provide a liquid crystal display device having such an optical film.

More preferably, a laminated optical film composed of a cholesteric liquid crystal layer selectively reflecting visible light and a quarter retardation layer, or a laminated optical film composed of a cholesteric liquid crystal layer selectively reflecting visible light and a viewing angle compensation layer ,
Furthermore, a laminated optical film comprising a cholesteric liquid crystal layer that selectively reflects visible light, a viewing angle compensation layer, and a 1/4 retardation layer, an optical film using the laminated optical film, and a liquid crystal display device including the optical film are provided. The purpose is to do.

The present invention comprises a visible light reflective polarizing layer (a) composed of a cholesteric liquid crystal layer and an optical layer (b) composed of at least one liquid crystal layer having an optical function different from that of the above (a). Are formed of a liquid crystal film of the same compound to solve the above problem.

[0015]

That is, the optical film and the liquid crystal display of the present invention are as follows.

[1] A visible light reflective polarizing layer (a) composed of a cholesteric liquid crystal layer that selectively reflects at least a part of the wavelength of visible light, and at least one layer of liquid crystal having an optical function different from that of (a). The optical layer (b) comprising a layer
An optical film comprising a liquid crystal layer in which the liquid crystal layers of (a) and (b) are composed of the same compound as a main component.

Since the layers (a) and (b) contain the same compound as the main component, the affinity of the interface between the two layers is improved,
Without using an adhesive or adhesive, the other layer is sequentially formed on one layer, and therefore, by using no adhesive or adhesive, surface reflection due to different refractive index interfaces is generated. It is possible to obtain an optical film having no problems such as a decrease in optical characteristics such as loss and an increase in the thickness of a pressure-sensitive adhesive or an adhesive, and in which a decrease in durability characteristics such as distortion and peeling does not easily occur.

In addition, since each of the layers is formed of a liquid crystal film, the thickness can be extremely reduced, and an optical film which is extremely effective for reducing the thickness of a liquid crystal display device or the like can be provided.

[2] In the optical film described in the above item [1], (b) is a quarter retardation layer (b1) composed of a liquid crystal layer having an optical quarter retardation function. By adopting the mode, the circularly polarized light that has passed through the cholesteric liquid crystal layer can be converted into linearly polarized light. By supplying the linearly polarized light, the absorption loss of light rays by the polarizing plate using the dichroic dye can be reduced, which is preferable.

[3] The optical film according to the above item [1], wherein (b) is a visual compensation layer (b2) composed of a vertically aligned liquid crystal layer, [4] and [1]. In the optical film according to the item, (b) is a visual compensation layer (b3) composed of a liquid crystal layer obliquely aligned, [5] In the optical film according to the item [1], (b) is Embodiment in which the helical pitch is a visual compensation layer (b4) composed of a cholesteric liquid crystal layer having a helical pitch of 250 nm or less. [6] In the optical film according to the above [1], (b) is a cholesteric liquid crystal having a helical pitch of 500 nm or more. The visual compensation layer (b5) made of a layer can improve coloring when viewed from an oblique direction when used in a liquid crystal display. It can be.

[7] Further, in the optical film according to any of the above items [3] to [6], the optical film is further optically reduced to 1/1.
A liquid crystal layer in which a 1/4 phase difference layer (b1) composed of a liquid crystal layer having a four phase difference function is laminated and integrated, and the liquid crystal layer of (b1) is mainly composed of the same compound as the liquid crystal layer other than (b1) By using the preferred embodiment of the present invention, it is possible to improve coloring when the liquid crystal display is viewed from an oblique direction when used in a liquid crystal display, and to convert circularly polarized light into linearly polarized light. Even when the light enters the used polarizing plate, by supplying the linearly polarized light that coincides with the polarization axis of the polarizing plate as described above, the absorption loss of light rays by the polarizing plate using the dichroic dye is reduced. This is preferable. Of course, different refractive index interfaces are generated by not using an adhesive or an adhesive as compared with the case where the conventional polymer stretched film is laminated as the visual compensation layer or the 1/4 retardation layer described above. Thus, there can be obtained an optical film having no problems such as a decrease in optical characteristics such as surface reflection loss, an increase in the thickness of a pressure-sensitive adhesive or an adhesive, and a decrease in durability characteristics such as distortion and peeling. In addition, since each of the layers is formed of a liquid crystal film, the thickness can be extremely reduced, and an optical film which is extremely effective for reducing the thickness of a liquid crystal display device or the like can be provided.

[8] In the optical film according to any one of the above items [1] to [7], the liquid crystal compound constituting the layers (a) and (b) is a liquid crystal polymer, and (a) Each of the layers (b) and (b) is preferably a layer having a glass state lower than the glass transition temperature of each liquid crystal polymer.

By using a liquid crystal polymer, the mechanical strength of each layer is improved, and each liquid crystal polymer is heated above its glass transition temperature, processed, laminated, and cooled below the glass transition temperature. It is preferable because it can be easily manufactured.

[9] In the optical film according to any one of the above items [1] to [7], the liquid crystal compound constituting each layer comprises a liquid crystal compound having a reactive group, and It is preferable that each of the liquid crystal compounds has a film formed by a crosslinking reaction to form each liquid crystal layer.

Since the film is formed by the cross-linking reaction, even if a relatively low-molecular liquid crystal compound is used, it can be polymerized and formed into a film, and the mechanical strength can be improved, which is preferable.

[10] In the optical film according to any one of the above items [1] to [9], the layers of the liquid crystal compound constituting each layer are laminated and integrated without any intervention of an adhesive or a pressure-sensitive adhesive. Is preferred.

Since no pressure-sensitive adhesive or adhesive is used, different refractive index interfaces are generated to lower optical characteristics such as surface reflection loss, and to lower durability characteristics such as distortion and peeling due to bonding of different materials. It is preferable because there is no problem such as an increase in the thickness of the adhesive or the adhesive.

[11] In the optical film according to any one of the above items [2] to [7], a polarizing plate using a dichroic dye is further bonded to the liquid crystal layer side of (b1). Is preferred.

Circularly polarized light transmitted through the cholesteric liquid crystal can be converted into linearly polarized light by a 1/4 phase difference plate. However, in order to extract linearly polarized light having a higher degree of polarization, the liquid crystal having the 1/4 phase difference function is used. It is preferable that a polarizing plate further using a dichroic dye is attached to the layer side.

[12] A liquid crystal display device using the optical film according to any one of the above items [1] to [11].

By providing the optical film on the back side of the liquid crystal cell of the liquid crystal display device, the above-mentioned [1] to [1]
The function described in each of [1] is exhibited, and a liquid crystal display device with improved display screen luminance can be provided. Moreover,
It can also contribute to the thinning of the liquid crystal display panel.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The liquid crystal layer (a) used in the present invention
Is used as the cholesteric liquid crystal and the liquid crystal compound of the liquid crystal layer (b) having an optical function different from the above (a).
Incidentally, a cholesteric liquid crystal is obtained by adding or copolymerizing an optically active compound to a nematic liquid crystal. For example, when the liquid crystal compound of (b) may be a nematic liquid crystal compound, the liquid crystal compound of (b) is used. When a specific nematic liquid crystal compound is used and a cholesteric liquid crystal obtained by adding an optically active compound to the nematic liquid crystal compound used for the layer (b) is used as the liquid crystal forming the layer (a), the addition of the optically active compound Only the difference in the presence or absence of the compound is preferable, because the combination of the liquid crystal compounds of the layers (a) and (b) with the same compound as the main component can be easily achieved. In the cholesteric liquid crystal, the central wavelength selectively reflected can be variously changed by adjusting the amount of the added optically active compound. Therefore, as shown in Examples and Comparative Examples, by using two or more cholesteric liquid crystal layers having different addition amounts of the optically active compound, it is possible to supply a layer (a) having a plurality of central wavelengths selectively reflected.

Further, as the layer (b), the helical pitch is 25.
In the case where the visual compensation layer (b4) made of a cholesteric liquid crystal layer having a thickness of 0 nm or less or the visual compensation layer (b5) made of a cholesteric liquid crystal layer having a helical pitch of 500 nm or more is used, the cholesteric liquid crystal contains an added optically active compound. The helical pitch can be variously changed by adjusting the addition amount of helium.

That is, in a cholesteric liquid crystal,
Assuming that the central wavelength for selective reflection is Wnm, the helical pitch of the cholesteric liquid crystal is Pnm, and the average refractive index of the cholesteric liquid crystal is N, there is a relationship of P × N = Wnm. Therefore, the average refractive index depends on the type of the cholesteric liquid crystal. Although the value of N is different, most of the cholesteric liquid crystals have an average refractive index of about 1.5 to 1.6. Therefore, the cholesteric liquid crystal layer having a helical pitch of 250 nm or less used as the visual compensation layer (b4) is not visible light. Is a region for selectively reflecting near-ultraviolet light deviating from the region, and unlike the (a) layer,
This means that the visible light is selected so as not to be selectively reflected.
Similarly, the helical pitch used as the visual compensation layer (b5) is 5
The cholesteric liquid crystal layer of 00 nm or more becomes a region for selectively reflecting near infrared light deviating from the visible light region,
Unlike the (a) layer, it is selected so as not to selectively reflect visible light. In other words, the helical pitch of the cholesteric liquid crystal used for the cholesteric liquid crystal layer (a) for selectively reflecting at least a part of the wavelength of visible light usually exists mostly in a range larger than 250 nm and smaller than 500 nm. Become. The helical pitch of the cholesteric liquid crystal can be changed to a cholesteric liquid crystal having an appropriate helical pitch by adding an added or copolymerized optically active compound or changing the copolymerization ratio.

When a liquid crystal polymer is used as the liquid crystal compound constituting the layers (a) and (b), as described above, the mechanical strength of each layer is improved, and each liquid crystal polymer is heated to the glass transition temperature or higher. Then, the layers (a) and (b) are easily laminated by heating, processing, laminating, and cooling the glass transition temperature or lower. When such a liquid crystal polymer is used, the liquid crystal in the layers (a) and (b) has the same polymer component, and the cholesteric liquid crystal in which the optically active compound is added or copolymerized is added or copolymerized with the cholesteric liquid crystal. When it is necessary to use a cholesteric liquid crystal in combination with a nematic liquid crystal that is not present, or when it is necessary to use a cholesteric liquid crystal as the layer (b), the cholesteric liquid crystals having the same polymer component but different in the ratio of addition or copolymerization of the optically active compound are different. Combinations and other than these,
The expression "having the same compound as the main component" includes a combination of cholesteric liquid crystal and nematic liquid crystal or a combination of cholesteric liquid crystals in which 50% or more of the repeating units of the polymer main chain are the same polymer.

When the liquid crystal compound is a low molecular compound,
The combination of the cholesteric liquid crystal in which the components of the liquid crystal compound are the same and the optically active compound is added, and the nematic liquid crystal having the difference that the optically active compound is not added, or the amount of the optically active compound added is different. In addition to the combination of cholesteric liquid crystals, a combination of a cholesteric liquid crystal and a nematic liquid crystal in which 50% or more of the liquid crystal compounds in the layers (a) and (b) are the same compound, or a combination of the layers (a) and (b). Also included are combinations of cholesteric liquid crystals in which 50% or more of the liquid crystal compounds are the same compound. Further, a compound which is a main component of the layers (a) and (b) is composed of a liquid crystal compound having a reactive group, and a liquid crystal having the reactive group is present in each of the layers (a) and (b). In the case of a combination in which the compound is formed into a film by a crosslinking reaction to form the liquid crystal layer of (a) and the liquid crystal layer of (b), the reactive groups of the layer liquid crystal compounds of (a) and (b) are the same. It may be a group or a different group.

The reactive group having such a reactive group in the liquid crystal compound is not particularly limited as long as it is a reactive group which causes a cross-linking reaction by polymerization or condensation reaction. Examples thereof include an acryl group, a methacryl group, an unsaturated double bond, Examples include a vinyl group, an epoxy group, and an isocyanate group.

A liquid crystal compound having such a reactive group is
It can be applied to liquid crystal compounds of relatively low molecular weight, and even if liquid crystal compounds of relatively low molecular weight are used by crosslinking reaction, it can be polymerized and formed into a film, improving mechanical strength and heat resistance. Can be.

The cholesteric liquid crystal and the nematic liquid crystal compound used in the present invention are not particularly limited as long as they satisfy the conditions of the present invention as described above. These liquid crystal compounds include a liquid crystal polymer and a liquid crystal compound having a reactive group. As the liquid crystal polymer, there is a main chain type liquid crystal polymer such as polyester, polyamide and polyurethane, or a side chain type liquid crystal polymer of acryl, methacryl and siloxane. In addition, as a liquid crystal compound having a reactive group,
It has almost the same chemical structure as ordinary liquid crystals, and has one or more reactive groups.

The cholesteric liquid crystal compound is obtained by adding an optically active compound to a nematic liquid crystal compound and copolymerizing the compound. The optically active compound is not particularly limited, but a compound having a structure similar to the liquid crystal is more preferable. . Furthermore,
The optically active compound is more preferably an optically active compound having a reactive group.

Incidentally, the 1/4 retardation layer (b) of the layer (b)
Regarding 1), the nematic liquid crystal is horizontally aligned to a predetermined thickness (homogeneous alignment), or the nematic liquid crystal is horizontally aligned to a predetermined thickness in a twisted state (twist alignment).
This can also be achieved.

The thickness d of the 1/4 retardation plate is given by:
(Birefringence) × d, the larger the value of birefringence Δn, the thinner the thickness. The birefringence Δn of the nematic liquid crystal is 0.
About 1 to 0.2, which is much larger than that of a conventional stretched polymer film.
The thickness of the / 4 retardation layer becomes extremely thin, for example, 1 μm.
m or so, and the thickness of the optical film can be reduced.

As described above, the thickness d of the 1/4 phase difference layer is determined by the phase difference = .DELTA.n.times.d.

The layer (b) other than the layer (b1) can be similarly thin, and is reduced to about 1/10 or less the thickness of a conventional stretched polymer film which is not a liquid crystal. obtain.

On the other hand, the thickness of the above-mentioned cholesteric liquid crystal layer (a) serving as the visible light reflective polarizing layer differs depending on how many cholesteric liquid crystal layers (a) having different pitches are provided. The range of the degree is preferable.

When (b) is a visual compensation layer (b2) composed of a vertically oriented liquid crystal layer or a visual compensation layer (b3) composed of an obliquely oriented liquid crystal layer, vertical orientation means a direction perpendicular to the layer plane. That is, it means that the liquid crystal is oriented substantially perpendicular to the layer plane in the thickness direction, and the angle is preferably in a range of about 90 ° ± 10 ° with respect to the layer plane.

The term "oblique orientation" means that the liquid crystal is oriented obliquely to the layer plane, that is, obliquely to the layer plane in the thickness direction. A range of about 5 ° is preferable.

There is no particular limitation on the manner in which the liquid crystal is vertically or obliquely aligned. For example, in the case of a liquid crystal polymer, the liquid crystal compound is converted to an isotropic phase having no liquid crystallinity. After heating to a temperature equal to or higher than the temperature at which the target layer is heated, the temperature of the target layer is kept several degrees lower (about 4 to 8 ° C.) than the isotropic phase transition temperature (that is, the temperature at which the liquid crystal transitions from the isotropic phase). This can be achieved by applying a voltage in the thickness direction (that is, with an electric field applied) and cooling to room temperature. The same applies to the case where a voltage is applied by appropriately adding a solvent or the like to the liquid crystal. The solvent is eventually removed by evaporation or the like (for example, when the solvent is heated to a temperature higher than the isotropic phase, the solvent is removed by evaporation). Voltage) may be applied with the solvent removed. Since the applied voltage and frequency are different depending on the type of liquid crystal, the range cannot be limited by numerical values. However, for example, around 50 V and 50 Hz is a standard. Then, in order to perform the oblique alignment, it is possible to perform the oblique alignment by making the applied voltage or the like smaller than in the case of performing the vertical alignment. In the case of a liquid crystal compound having a reactive group, the alignment can be performed in substantially the same manner as described above. A voltage is applied while maintaining the liquid crystal temperature, and the reactive group is reacted by irradiation of ultraviolet light or other light in that state. To fix the alignment state. The applied voltage at that time is, for example, 10 V, 50 Hz.
Around is a guide.

The optical film of the present invention can be produced by, for example, but not limited to, the following method.

In order to align the liquid crystal, the liquid crystal is applied on the rubbed alignment film. Of course, a triacetyl cellulose (hereinafter sometimes abbreviated as TAC) film or the like is provided below the alignment film. It is preferable to use an alignment film having an appropriate protective layer. In order to form a cholesteric liquid crystal layer (a) serving as a visible light reflective polarizing layer and an optical layer (b) composed of a liquid crystal layer having an optical function different from the above (a) on the alignment film, a liquid crystal is usually used. Is diluted with an appropriate solvent, for example, cyclohexanone or ethyl acetate, and then coated with a diluted predetermined liquid crystal on an appropriate rubbed alignment film such as polyvinyl alcohol (hereinafter sometimes abbreviated as PVA). Then, after the solvent is volatilized and removed, the liquid crystal is oriented by heating to a temperature showing liquid crystallinity,
Alternatively, if necessary, a voltage is applied as described above to cause vertical or oblique alignment, and when the liquid crystal is a polymer, the liquid crystal is cooled to a temperature lower than its glass transition temperature. The same applies to the case where a plurality of liquid crystal layers are formed. However, in this case, select the type of the solvent to be diluted, or apply it and then blow it and dry it quickly to remove the solvent, so that the existing lower layer is not affected much. Is preferred. Then, a necessary liquid crystal layer can be formed in substantially the same manner.

When using a liquid crystal of a type in which a liquid crystal layer is formed by forming a liquid crystal layer by a cross-linking reaction using a relatively low molecular weight liquid crystal compound having a reactive group, an appropriate solvent is applied onto the alignment film. After the diluted predetermined liquid crystal is applied and the solvent is volatilized and removed, the liquid crystal is aligned by heating to a temperature exhibiting liquid crystallinity, and then cross-linked by ultraviolet irradiation or the like. When a next liquid crystal layer is further formed thereon, it can be performed in substantially the same manner.

Although there is no particular limitation, when a liquid crystal polymer is used, the glass transition temperature is 70 to 150 ° C.
A liquid crystal polymer exhibiting liquid crystallinity in the vicinity of a temperature range of 100 to 200 ° C. (usually, the temperature exhibiting liquid crystallinity is slightly higher than the glass transition temperature) is preferably used. If the glass transition temperature is too low, the formed liquid crystal layer may be in a liquid crystal state and may change.If it is too high, alignment by heating becomes difficult, or liquid crystallinity is exhibited in the manufacturing process. When heating to temperature,
It becomes necessary to consider the problem such as thermal degradation to other materials such as other protective layers and alignment films.

In the case of using a liquid crystal of a type in which a liquid crystal compound having a reactive group and having a relatively low molecular weight is formed into a film by a crosslinking reaction to form a liquid crystal layer, a crystallization temperature of 0 to 120 is used. C. is preferable, and a liquid crystal exhibiting liquid crystallinity in the vicinity of this temperature range (normally, the temperature exhibiting liquid crystallinity is slightly higher than the crystallization temperature) is suitably used. As described above, even when the crystallization temperature is low, when the liquid crystal layer is formed by forming a film by a crosslinking reaction, heat resistance is improved, and
It can be used even in a high temperature atmosphere exceeding ℃.

As the visual compensation layer, a visual compensation layer (b2) composed of a vertically oriented liquid crystal layer, a visual compensation layer (b3) composed of an obliquely oriented liquid crystal layer, a cholesteric liquid crystal having a helical pitch of 250 nm or less, depending on the purpose. A visual compensation layer (b4) composed of a layer, a visual compensation layer (b5) composed of a cholesteric liquid crystal layer having a helical pitch of 500 nm or more can be appropriately selected and used.

When applied to a liquid crystal display, there are several methods for improving the coloring that occurs when the liquid crystal screen is viewed from an oblique direction, as a liquid crystal layer (viewing angle compensation layer) for improving coloring. Suitable ones also differ depending on the type of the cholesteric liquid crystal layer a). For example, when the liquid crystal is vertically aligned (positive phase difference plate), there is almost no front phase difference, but a phase difference occurs in an oblique direction. Alternatively, when the liquid crystal is obliquely aligned, a slight front phase difference occurs, but the oblique phase difference also varies depending on the direction. In the case of a cholesteric liquid crystal whose selective reflection is not visible light (a near-ultraviolet light is selectively reflected when the helical pitch is 250 nm or less and a near-infrared light is selectively reflected when the helical pitch is 500 nm or more), the front phase difference is low. A phase difference is generated in the oblique direction, and functions like a negative phase difference plate. Since various phase differences occur in all of these oblique directions, they exhibit an effective function for improving oblique coloring of the reflective polarizing plate.

These viewing angle compensation layers (b2), (b3),
The arrangement position of the liquid crystal layer as (b4) or (b5) is as follows.
When the cholesteric layer (a), which is a visible light reflective polarizing layer, is composed of multiple cholesteric layers (a), it may be between the multiple cholesteric layers (a), or may be located between the cholesteric liquid crystal layer (a) and the cholesteric liquid crystal layer. Even with the 問 phase difference function layer (b1), the １ ／ phase difference function layer (b
It may be between 1) and a dichroic polarizing plate.

Also, an optical film in which the above-mentioned cholesteric liquid crystal layer (a) of the present invention and a liquid crystal layer (b1) having an optically 1/4 phase difference function are laminated and integrated, or
A cholesteric liquid crystal layer (a) and a viewing angle compensation layer (b2),
In an optical film in which (b3), (b4) or (b5) and a liquid crystal layer (b1) having an optically 1/4 retardation function are laminated and integrated, a polarizing plate further using a dichroic dye An optical film bonded to the side where the liquid crystal layer (b1) having a １ ／ retardation function is present is also useful. This does not mean that the polarizing plate is directly adhered to the liquid crystal layer (b1). For example, the optical film of the present invention comprises (a) and (b1) and a viewing angle compensation layer (b2).
To (b5), (a) and (b5)
In the case of the optical film laminated in the order of 1) and the viewing angle compensation layer, the polarizing plate exists on the side where (b1) exists, that is, above the viewing angle compensation layer. Of course (a)
In the case of the optical film laminated in the order of (b1) and the viewing angle compensation layer, the polarizing plate exists on the upper side of (b1).

The predetermined circularly polarized light transmitted through the cholesteric liquid crystal of the layer (a) can be converted into linearly polarized light by the ４ retardation layer (b1). However, in recent years, it has been required in liquid crystal display devices such as personal computers. In order to extract linearly polarized light having a higher degree of polarization, a polarizing plate further using a dichroic dye may be bonded to the side where the liquid crystal layer (b1) having the ４ phase difference function is present. It is preferred.

The polarizing plate using a dichroic dye is not particularly limited, but a polarizing plate effectively used in this field is used. For example, specifically, a polyvinyl alcohol film (hereinafter referred to as a polyvinyl alcohol film) is used. , PVA film). Iodine having dichroism or 2
A dyeing step of dyeing with a color dye, a crosslinking step of crosslinking with boric acid or borax, and a stretching step of uniaxial stretching (dying,
The steps of cross-linking and stretching need not be performed separately but may be performed simultaneously, and the order of each step is not particularly limited. ), Dried, and appropriately bonded to a protective layer such as a triacetyl cellulose film (hereinafter sometimes abbreviated as a TAC film). For bonding, an appropriate pressure-sensitive adhesive or adhesive is used.

[0060]

The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

Comparative Example 1 An alignment film of PVA having a thickness of 0.1 μm was formed on a 50 μm-thick triacetyl cellulose (TAC) film.
After forming a thickness of m and rubbing, the temperature at which the liquid crystal
Acrylic side chain type cholesteric liquid crystal polymer of 90 to 200 ° C. (glass transition temperature: 90 ° C.) having a selective reflection center wavelength of 700 nm, 550 nm, and 400 nm is sequentially formed on an alignment film in three layers, and then aligned. It became thin. The thickness of each layer was 3 μm. The cholesteric liquid crystal layer is formed by applying the cholesteric liquid crystal diluted with a solvent to a concentration of about 25% by mass, evaporating and removing the solvent,
The liquid crystal was aligned by heating to 160 ° C., and was cooled to room temperature so as to be lower than its glass transition temperature to form a liquid crystal. In this case, cyclohexanone was used as a solvent. Immediately after the application of the second and third layers, air was blown at 25 ° C. (room temperature) to quickly evaporate the solvent, thereby minimizing the mixing with the lower layer.

Next, on this third cholesteric liquid crystal layer, a 1/4 retardation plate of polycarbonate having a thickness of 60 μm with an acrylic adhesive of 25 μm thickness (front retardation 130 n
m) was laminated to obtain a comparative optical film.

Comparative Example 2 An alignment film of PVA was formed on a triacetyl cellulose (TAC) film having a thickness of 50 μm.
After forming a thickness of μm and performing a rubbing treatment, a temperature at which liquid crystallinity having a bifunctional acrylic group (two acrylic groups) as a UV (ultraviolet) crosslinkable reactive group is 40 to 150 ° C. (crystallization temperature: 40 ° C.) ) Acrylic cholesteric liquid crystal with selective reflection center wavelength of 700 nm, 590 nm, 500 n
Four layers having a thickness of 430 nm were sequentially formed on an alignment film, aligned, and cross-linked by ultraviolet rays to form a cholesteric liquid crystal layer. The thickness of each layer was 4 μm. The cholesteric liquid crystal layer is formed by coating the cholesteric liquid crystal diluted with a solvent to a concentration of about 25% by mass sequentially for each layer, evaporating and removing the solvent, and then heating the mixture to 100 ° C. to align the liquid crystal. Cool to room temperature, perform UV crosslinking,
Formed. In this case, ethyl acetate was used as a solvent. Further, the selective reflection center wavelengths of the first to fourth cholesteric liquid crystal layers are 700 nm and 590 n, respectively.
m, 500 nm and 430 nm, the amount of the acrylic optically active compound added was 8.4% by mass for the first layer, 10.0% by mass for the second layer, and 10.0% by mass for the third layer. It adjusted so that an eye might be 11.8 mass% and a 4th layer might be 13.7 mass%.

Next, on the fourth cholesteric liquid crystal layer, a 1/4 retardation plate (front retardation: 130 n) of polycarbonate having a thickness of 60 μm with an acrylic adhesive having a thickness of 25 μm was used.
m) was laminated to obtain a comparative optical film.

Example 1 An alignment film of PVA 0.1 was formed on a 50 μm-thick triacetyl cellulose (TAC) film.
After forming a thickness of μm and rubbing, an acrylic side chain type nematic whose main component is the same as that of the cholesteric liquid crystal polymer of Comparative Example 1 and whose liquid crystallinity is 90 to 250 ° C. (glass transition temperature: 90 ° C.) A 0.5 μm thick liquid crystal polymer (having no cholesteric liquid crystal polymer optically active compound of Comparative Example 1 copolymerized) (front retardation: 130
nm) and align the nematic liquid crystal polymer layer (1/4
A retardation layer) was formed thereon, and three cholesteric liquid crystal polymer layers (visible light reflective polarizing layers) (thickness: 3 μm each) were formed and aligned on Comparative Example 1 to form an optical film of the present invention. [Example of combination of layer (b1) and layer (a)].

The nematic liquid crystal polymer layer was formed by applying the above nematic liquid crystal diluted to a concentration of about 25% by mass using cyclohexanone as a solvent.
After the solvent was removed by volatilization, the mixture was heated to 160 ° C. to align the liquid crystal, and then cooled to room temperature so as to have a glass transition temperature or lower, thereby forming a liquid crystal. The same three cholesteric liquid crystal polymer solid layers as in Comparative Example 1 were formed in the same manner as in Comparative Example 1.

Example 2 An alignment film of PVA having a thickness of 0.1 μm was formed on a 50 μm-thick triacetyl cellulose (TAC) film.
After the rubbing treatment, a main component is the same as that of the UV (ultraviolet) crosslinkable cholesteric liquid crystal of Comparative Example 2,
Acrylic nematic liquid crystal having a bifunctional acrylic group as a V (ultraviolet) crosslinkable reactive group and having a liquid crystallinity of 40 to 160 ° C. (crystallization temperature: 40 ° C.) is 0.7 μm.
UV (ultraviolet) with m thickness (front phase difference 130nm)
Cross-linking is performed to form a nematic liquid crystal layer (1/4 retardation layer), and on top of this, four UV (ultraviolet) crosslinkable cholesteric liquid crystal layers as in Comparative Example 2 (each having a thickness of 4 μm) are formed and aligned. UV crosslinking was carried out to form a cholesteric liquid crystal layer (a visible light reflective polarizing layer), thereby producing an optical film of the present invention. [Example of combination of layer (b1) and layer (a)].

The formation of the crosslinked nematic liquid crystal layer is as follows.
After coating the nematic liquid crystal diluted with a solvent to a concentration of about 25% by mass and evaporating and removing the solvent, the liquid crystal was aligned by heating to 100 ° C., cooled to room temperature, and subjected to ultraviolet crosslinking to form. . The same four cholesteric liquid crystal layers as in Comparative Example 2 were formed in the same manner as in Comparative Example 2.

Thickness of the optical films obtained in Comparative Examples 1 and 2 and Examples 1 and 2, durability at 80 ° C. for 1000 hours,
Table 1 shows the luminance improvement ratios when installed in the liquid crystal display device.

[0070]

[Table 1]

As is clear from the above, the optical films of the present invention of Examples 1 and 2 did not peel off as compared with the conventional optical films shown in Comparative Examples 1 and 2, respectively.
In addition to having excellent durability, the thickness can be reduced to less than half the thickness of a conventional product, which can contribute to a reduction in the thickness of a liquid crystal display device. Moreover, since no adhesive or pressure-sensitive adhesive was present at the lamination interface, it was recognized that the surface reflection loss was reduced by that amount and the luminance improvement rate was also improved.

(Example 3) By a similar operation to that of Example 1, a 0.1 μm thick PVA alignment film was formed on a 50 μm thick triacetyl cellulose (TAC) film. The main component is the same as the cholesteric liquid crystal polymer, and the temperature at which liquid crystallinity is exhibited is 90 to 250 ° C.
(Glass transition temperature: 90 ° C.) Acrylic side chain type nematic liquid crystal polymer (having no cholesteric liquid crystal polymer optically active compound of Comparative Example 1 copolymerized) is oriented by 0.5 μm thickness (front retardation: 130 nm). To form a nematic liquid crystal polymer layer (1/4 retardation layer),
Next, the same acrylic side chain type nematic liquid crystal polymer having a thickness of 0.8 μm is applied thereon, and vertically aligned by an electric field to form a visual compensation layer (a retardation in the thickness direction of 210 nm). 3 cholesteric liquid crystal polymer layers (visible light reflective polarizing layer) (3 μm thick each)
Formed and oriented to make the optical film of the present invention.
[Example of combination of layers (b1), (b2) and (a)].

(Example 4) In a similar manner to Example 3, a 0.1 μm thick PVA alignment film was formed on a 50 μm thick triacetyl cellulose (TAC) film. The main component is the same as the cholesteric liquid crystal polymer, and the temperature at which liquid crystallinity is exhibited is 90 to 250 ° C.
(Glass transition temperature: 90 ° C.) Acrylic side chain type nematic liquid crystal polymer (a cholesteric liquid crystal polymer of Comparative Example 1 in which the optically active compound is not copolymerized) is oriented to a thickness of 0.3 μm (front retardation: 80 nm). To form a nematic liquid crystal polymer layer (1/4 retardation layer), then apply the same acrylic side chain type nematic liquid crystal polymer 0.3 μm thick on top of this, and align it obliquely 45 ° by an electric field to compensate for visual Forming a layer (front retardation 50 nm),
Next, the same cholesteric liquid crystal polymer layer (visible light reflective polarizing layer) as in Comparative Example 1 was formed thereon (thickness: 3 μm each) and oriented to prepare an optical film of the present invention.
[Example of combination of layers (b1), (b3) and (a)].

Example 5 An alignment film of PVA having a thickness of 0.1 μm was formed on a 50 μm-thick triacetyl cellulose (TAC) film.
After the rubbing treatment, a main component is the same as that of the UV (ultraviolet) crosslinkable cholesteric liquid crystal of Comparative Example 2,
Acrylic nematic liquid crystal having a bifunctional acrylic group as a V (ultraviolet) crosslinkable reactive group and having a liquid crystallinity of 40 to 160 ° C. (crystallization temperature: 40 ° C.) is 0.7 μm.
UV (ultraviolet) with m thickness (front phase difference 130nm)
Crosslinking was performed to form a nematic liquid crystal layer (1/4 retardation layer), and four UV (ultraviolet) crosslinkable cholesteric liquid crystal layers (each having a thickness of 4 μm) as in Comparative Example 2 were formed thereon.
(Ultraviolet) Second layer for cross-linking (selective reflection center wavelength 5
90 nm) and the third layer (selective reflection center wavelength 500 nm) and the same UV (ultraviolet) crosslinkable cholesteric liquid crystal having a helical pitch of 200 nm (selective reflection center wavelength 32).
0 nm) liquid crystal layer (visual compensation layer) 2 μm thick and UV
(Ultraviolet) crosslinking was performed to prepare an optical film of the present invention. [Example of combination of layer (b1), layer (b4), and layer (a)]. The same kind of UV (ultraviolet) crosslinkable cholesteric liquid crystal having a helical pitch of 200 nm can be adjusted by increasing the amount of the optically active compound.

Example 6 An alignment film of PVA having a thickness of 0.1 μm was formed on a 50 μm-thick triacetyl cellulose (TAC) film.
After the rubbing treatment, a main component is the same as that of the UV (ultraviolet) crosslinkable cholesteric liquid crystal of Comparative Example 2,
Acrylic nematic liquid crystal having a bifunctional acrylic group as a V (ultraviolet) crosslinkable reactive group and having a liquid crystallinity of 40 to 160 ° C. (crystallization temperature: 40 ° C.) is 0.7 μm.
UV (ultraviolet) with m thickness (front phase difference 130nm)
Crosslinking was performed to form a nematic liquid crystal layer (1/4 retardation layer), and four UV (ultraviolet) crosslinkable cholesteric liquid crystal layers (each having a thickness of 4 μm) as in Comparative Example 2 were formed thereon.
(Ultraviolet) First layer for cross-linking (selective reflection center wavelength 7
00 nm) and the second layer (selective reflection center wavelength 590 nm), the same cholesteric liquid crystal of UV (ultraviolet) cross-linking with a helical pitch of 600 nm (selective reflection center wavelength 96).
0 nm) liquid crystal layer (visual compensation layer) 3 μm thick and UV
(Ultraviolet) crosslinking was performed to prepare an optical film of the present invention. [Example of combination of layer (b1), layer (b5), and layer (a)]. A UV (ultraviolet) crosslinkable cholesteric liquid crystal of the same kind having a helical pitch of 600 nm can be adjusted by reducing the amount of the optically active compound.

The thicknesses of the reflective polarizers of Comparative Examples 1 and 2 and Examples 4 to 6, the durability at 80 ° C. for 1000 hours, the rate of improvement in brightness when installed in a liquid crystal display, and the oblique view at 45 °. Table 2 shows the coloring conditions.

[0077]

[Table 2]

[0078]

The optical film of the present invention can be laminated without using a pressure-sensitive adhesive or an adhesive, has little deterioration in durability characteristics such as distortion and peeling, and has a different refractive index interface. The cholesteric liquid crystal layer that selectively reflects visible light and the cholesteric liquid crystal layer that selectively reflects the visible light have optical functions different from those of the cholesteric liquid crystal layer, which can reduce the reduction of optical characteristics such as surface reflection loss and can be considerably reduced in thickness. An optical layer comprising at least one liquid crystal layer, for example, a 1/4 retardation layer, a visual compensation layer, or a laminated optical film composed of both of them, an optical film to which the laminated optical film is applied, and such an optical film are provided. A liquid crystal display device can be provided. Therefore, it is possible to contribute to a reduction in thickness and durability of a liquid crystal display device and the like. In addition, when the optical film of the present invention of the type in which the visual compensation layer is laminated is used for a liquid crystal display, it is possible to improve coloring when viewing a liquid crystal display image from an oblique direction.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02F 1/13363 G02F 1/13363 1/1347 1/1347 (72) Inventor Miki Shirahaogawa Shimohozumi, Ibaraki-shi, Osaka 1-1-2, Nitto Denko Corporation F-term (reference) 2H049 BA02 BA05 BA07 BA26 BA42 BA43 BB03 BB33 BB43 BC02 BC22 2H089 HA04 HA22 HA25 KA08 NA22 QA11 SA02 SA08 TA04 TA14 TA15 2H091 FA09X FA09Z FA11X FA11Z04 JA02 LA11 LA12 LA20 4F100 AJ05 AK01A AK01B AK21 AK25 AR00A AR00B BA02 CA13A GB41 HB00A JA11B JL10A JN10A JN30B 4H027 BA01 BA02 BA11 BE06

Claims (12)

[Claims] 1. A visible light reflection / polarization layer (a) comprising a cholesteric liquid crystal layer for selectively reflecting at least a part of the wavelength of visible light, and at least one liquid crystal layer having an optical function different from that of (a). An optical film comprising a liquid crystal layer in which a liquid crystal layer of (a) and (b) is mainly composed of the same compound. 2. The optical film according to claim 1, wherein (b) is a quarter retardation layer (b1) comprising a liquid crystal layer having an optical quarter retardation function. 3. The optical film according to claim 1, wherein (b) is a visual compensation layer (b2) comprising a vertically aligned liquid crystal layer. 4. The optical film according to claim 1, wherein (b) is a visual compensation layer (b3) composed of an obliquely oriented liquid crystal layer. 5. The optical film according to claim 1, wherein (b) is a visual compensation layer (b4) composed of a cholesteric liquid crystal layer having a helical pitch of 250 nm or less. 6. The optical film according to claim 1, wherein (b) is a visual compensation layer (b5) composed of a cholesteric liquid crystal layer having a helical pitch of 500 nm or more. 7. A 1/4 retardation layer (b1) composed of a liquid crystal layer having an optically 1/4 retardation function is laminated and integrated, and the liquid crystal layer of (b1) is a liquid crystal other than (b1). 4. A liquid crystal layer containing the same compound as a main component as a layer.
7. The optical film according to any one of 6. 8. The optical film according to claim 1, wherein the liquid crystal compound constituting each layer is a liquid crystal polymer, and each layer is a layer having a glass state at or below the glass transition temperature of the liquid crystal polymer. 9. A liquid crystal compound constituting each layer is formed of a liquid crystal compound having a reactive group, and the liquid crystal compound having the reactive group is formed into a film by a crosslinking reaction to form each liquid crystal layer. The optical film according to claim 1. 10. The optical film according to claim 1, wherein the layers of the liquid crystal compound constituting each layer are laminated and integrated without interposition of an adhesive or a pressure-sensitive adhesive. 11. The optical film according to claim 2, wherein a polarizing plate using a dichroic dye is bonded to the side where the liquid crystal layer of (b1) exists. 12. A liquid crystal display device using the optical film according to claim 1.