WO2016194890A1 - Manufacturing method for half mirror used in image display surface of image display device, half mirror, and mirror with image display function - Google Patents

Abstract

The present invention provides a manufacturing method for a half mirror, said manufacturing method comprising preparing a transfer material that includes a circularly polarized light reflection layer, laminating a transparent substrate and the surface of the circularly polarized light reflection layer of the transfer material by means of a curing adhesive, and curing the curing adhesive to form an adhesion layer having a thickness of 1.0-5.0 μm, inclusive, wherein the surface of the transfer material which is laminated to the transparent substrate has a pencil hardness of HB or lower. By using a half mirror manufactured by the manufacturing method according to the present invention, it is possible to provide a mirror with an image display function that enables bright, clear image display and mirror-reflected image display.

Description

Method for manufacturing half mirror used for image display surface of image display device, half mirror, and mirror with image display function

The present invention relates to a method of manufacturing a half mirror used on the surface of an image display unit of an image display device, a half mirror manufactured by this method, and a mirror with an image display function.

By arranging a half mirror composed of a reflective polarizing plate or the like on the surface of the image display unit of the image display device, an image is displayed when the image is displayed on the image display unit, while an image is displayed on the image display unit. When is not displayed, a configuration that acts as a mirror surface can be obtained. For example, in Patent Document 1, a configuration in which a reflective polarizer formed on a transparent substrate on the front surface of an image display unit of an image display device is arranged in order of a reflective polarizer and a transparent substrate from the image display unit side. Is disclosed.

JP 2011-45427 A

An object of the present invention is to provide a method of manufacturing a half mirror that enables bright and clear image display and mirror reflection image display as a half mirror used on the surface of an image display unit of an image display device. Another object of the present invention is to provide a novel half mirror and to provide a mirror with an image display function capable of displaying a bright and clear image display and a mirror reflection image display.

The present inventors tried to produce a half mirror using a layer in which a cholesteric liquid crystal phase is fixed (hereinafter referred to as a cholesteric liquid crystal layer) as the reflective polarizing plate, and repeated studies. A cholesteric liquid crystal layer is known to exhibit selective reflection at a specific wavelength, and a film including the cholesteric liquid crystal layer is applied to various uses as a reflecting member. A cholesteric liquid crystal layer is generally formed by coating a liquid crystal composition containing a polymerizable liquid crystal compound on a support material, forming a cholesteric liquid crystal phase in the coating film, and then curing the coating film by ultraviolet irradiation. Formed with fixed phases.

The inventors tried to directly form a cholesteric liquid crystal layer on the transparent substrate surface by the above procedure using a transparent substrate as a support as described in Patent Document 1, and desired a polymerizable liquid crystal compound. In some cases, it is difficult to align the cholesteric liquid crystal phase as described above. Therefore, the present inventors performed film formation in which a cholesteric liquid crystal layer formed on a temporary support is adhered to a transparent substrate and transferred.

However, distortion was visually confirmed in the mirror reflection image obtained by observing the half mirror including the transparent substrate and the cholesteric liquid crystal layer thus produced from the transparent substrate side. Thereafter, the present inventors have found that the above-described distortion is caused by the orange-peel-shaped unevenness of the highly transparent adhesive transfer tape (OCA tape) used for adhesion. The OCA tape is widely used as an adhesive used on the surface of the image display unit of the image display device.

Therefore, the present inventors tried to transfer using a curable adhesive instead of a highly transparent adhesive transfer tape, but a distortion different from the distortion caused by the unevenness of the orange peel was used as a mirror surface. This was confirmed in the mirror reflection image. In order to make the cholesteric liquid crystal layer and the transparent substrate sufficiently adhere to each other, the curable adhesive layer needs to have a thickness of about 20 to 30 μm. This is thought to be due to unevenness in thickness.
Based on the above findings, the present inventors have further studied and completed the present invention.

That is, the present invention provides the following [1] to [19].
[1] A method of manufacturing a half mirror used on the image display unit surface of an image display device,
The half mirror includes a circularly polarized light reflection layer, an adhesive layer, and a transparent substrate in this order,
The circularly polarized light reflection layer includes a cholesteric liquid crystal layer,
The above manufacturing method is
Preparing a transfer material including the circularly polarized reflective layer;
The surface of the circularly polarized light reflecting layer of the transfer material and the transparent substrate are bonded with a curable adhesive, and the curable adhesive is cured to have a thickness of 1.0 μm or more and 5.0 μm or less. Forming an adhesive layer,
The manufacturing method whose pencil hardness of the surface bonded with the said transparent substrate of the said transcription | transfer material is below HB.

[2] The transfer material includes a temporary support,
The circularly polarized light reflecting layer in the transfer material,
Forming a liquid crystal composition containing a polymerizable liquid crystal compound on the temporary support to obtain a coating film, and forming the coating film by a method including curing the coating film to obtain the cholesteric liquid crystal layer. [1] The production method according to [1].
[3] The manufacturing method according to [2], wherein the manufacturing method includes peeling the temporary support after the formation of the adhesive layer.
[4] The manufacturing method according to any one of [1] to [3], wherein the transfer material includes a quarter-wave plate.

[5] The transfer material includes a temporary support,
The quarter-wave plate in the transfer material is
The production method according to [4], comprising: forming a coating film by applying on the temporary support and forming the coating film by a method including curing the coating film.
[6] The production method according to [5], including applying the liquid crystal composition containing a polymerizable liquid crystal compound to the surface of the quarter-wave plate to obtain the cholesteric liquid crystal layer.
[7] A half mirror used on the image display unit surface of the image display device,
Manufactured by the manufacturing method according to any one of [1] to [6],
The circularly polarized light reflecting layer and the adhesive layer are in direct contact with each other,
The adhesive layer and the transparent substrate are in direct contact,
The half mirror, wherein the adhesive layer has a thickness of 1.0 μm or more and 5.0 μm or less.

[8] A half mirror used on the image display unit surface of the image display device,
Including a circularly polarized light reflecting layer, an adhesive layer and a transparent substrate in this order,
The circularly polarized light reflection layer includes a cholesteric liquid crystal layer,
The circularly polarized light reflecting layer and the adhesive layer are in direct contact with each other,
The adhesive layer and the transparent substrate are in direct contact,
The adhesive layer is a layer obtained by curing a curable adhesive,
The adhesive layer has a thickness of 1.0 μm or more and 5.0 μm or less,
The said half mirror whose pencil hardness of the surface of the said half mirror in the said circularly polarized light reflection layer side is HB or less with respect to the said transparent substrate.
[9] The half mirror according to [7] or [8], wherein the circularly polarizing reflection layer includes two or more cholesteric liquid crystal layers, and the two or more cholesteric liquid crystal layers have different selective reflection center wavelengths.
[10] The half mirror according to [9], wherein two or more cholesteric liquid crystal layers are in direct contact with each other.
[11] The half mirror according to [9] or [10], wherein the circularly polarizing reflection layer includes three or more cholesteric liquid crystal layers, and the three or more cholesteric liquid crystal layers have different selective reflection center wavelengths.

[12] The circularly polarizing reflection layer includes a cholesteric liquid crystal layer having a central wavelength of selective reflection at 400 nm to 500 nm, a cholesteric liquid crystal layer having a central wavelength of selective reflection at 500 nm to 580 nm, and a center of selective reflection at 580 nm to 700 nm. The half mirror according to [11], including a cholesteric liquid crystal layer having a wavelength.
[13] In any one of [9] to [12], in the circularly polarized light reflecting layer, a cholesteric liquid crystal layer having a shorter central wavelength of selective reflection is disposed closer to the adhesive layer. Half mirror.
[14] The half mirror according to any one of [7] to [13], wherein the circularly polarized light reflecting layer includes a cholesteric liquid crystal layer having a central wavelength of selective reflection in an infrared light region.
[15] The half mirror according to any one of [7] to [14], wherein the circularly polarized light reflecting layer has a thickness of 25 μm or less.
[16] The half mirror according to any one of [7] to [15], wherein the transparent substrate is a glass plate or a plastic film having a front phase difference of less than 10 nm.
[17] including a quarter-wave plate,
The half mirror according to any one of [7] to [16], including the quarter-wave plate, the circularly polarizing reflection layer, the adhesive layer, and the transparent substrate in this order.
[18] The half mirror according to any one of [7] to [17],
A mirror with an image display function including the image display device, the circularly polarized light reflection layer, the adhesive layer, and the transparent substrate in this order.
[19] The mirror with an image display function according to [18], in which the image display device and the half mirror are directly bonded via an adhesive layer.

According to the present invention, there is provided a method of manufacturing a half mirror that enables bright and clear image display and mirror reflection image display. The present invention also provides a novel half mirror as a half mirror used on the image display unit surface of the image display device. By using the half mirror of the present invention, a mirror with an image display function capable of displaying a bright and clear image and a mirror reflection image can be provided. The mirror with an image display function of the present invention has an advantage that a display image and a mirror reflection image can be observed even through polarized sunglasses.

Hereinafter, the present invention will be described in detail.
In the present specification, “˜” is used to mean that the numerical values described before and after it are included as a lower limit value and an upper limit value. In the present specification, for example, an angle such as “45 °”, “parallel”, “vertical”, or “orthogonal”, unless otherwise specified, has a difference from an exact angle within a range of less than 5 degrees. Means. The difference from the exact angle is preferably less than 4 degrees, and more preferably less than 3 degrees.
In this specification, “(meth) acrylate” is used to mean “one or both of acrylate and methacrylate”.

In this specification, “selective” for circularly polarized light means that either the right circularly polarized light component or the left circularly polarized light component has more light than the other circularly polarized light component. Specifically, when referred to as “selective”, the degree of circular polarization of light is preferably 0.3 or more, more preferably 0.6 or more, and even more preferably 0.8 or more. More preferably, it is substantially 1.0. Table In _{/ (I R + I L)} | Here, the degree of circular polarization, the intensity of the right circularly polarized light component of the light I _R, when the strength of the left-handed circularly polarized light component and I _L, | I _R -I _L Is the value to be

In this specification, “sense” for circularly polarized light means right circularly polarized light or left circularly polarized light. The sense of circularly polarized light is right-handed circularly polarized light when the electric field vector tip turns clockwise as time increases when viewed as the light travels toward you, and left when it turns counterclockwise. Defined as being circularly polarized.

In this specification, the term “sense” is sometimes used for the twist direction of the spiral of the cholesteric liquid crystal. When the twist direction (sense) of the spiral of the cholesteric liquid crystal is right, it reflects right circularly polarized light and transmits left circularly polarized light. When the sense is left, it reflects left circularly polarized light and transmits right circularly polarized light.

Visible light is light having a wavelength that can be seen by human eyes among electromagnetic waves, and indicates light having a wavelength range of 380 nm to 780 nm. Infrared rays (infrared light) are electromagnetic waves in the wavelength range that are longer than visible rays and shorter than radio waves. Among infrared rays, near infrared light is an electromagnetic wave having a wavelength range of 780 nm to 2500 nm.

In this specification, when an image display function mirror or half mirror is referred to as an “image”, an image is displayed on the image display unit when used as a mirror with an image display function or incorporated in a mirror with an image display function. This means an image that can be observed by visually observing the half mirror from the transparent substrate side. Further, in this specification, when a mirror or half mirror with an image display function is referred to as a “mirror reflection image”, the image display unit is used as a mirror with an image display function or when incorporated in a mirror with an image display function. When an image is not displayed, it means an image that can be visually observed from the transparent substrate side.

<Half mirror>
The half mirror manufactured by the manufacturing method of the present invention (hereinafter referred to as the half mirror of the present invention) is a half mirror used on the surface of the image display unit of the image display device as will be described later. The half mirror of the present invention is a half mirror that is used so that the surfaces thereof face each other particularly on the surface of the image display unit of the image display device, and is used as a mirror surface when no image is displayed on the image display unit. It is preferable to be a half mirror.

The present inventors have noticed that there is distortion in the mirror reflection image obtained by observing the half mirror including the transparent substrate and the cholesteric liquid crystal layer from the transparent substrate side as described above. This distortion is considered to be based on the orange peel-like irregularities generated on the surface of the cholesteric liquid crystal layer, in which the reflected light in the visible light region is scattered. On the other hand, it is difficult to visually recognize orange peel-like irregularities when laminating films used inside the image display device. Moreover, even if it is used on the surface of the image display unit of the image display device, orange peel-like irregularities are difficult to visually recognize in a film having a low visible light reflectance. The present inventors provide a half mirror including a cholesteric liquid crystal layer as a visible light reflective half mirror for use on the surface of an image display unit of an image display device, and the unevenness is easily visible with such a half mirror. I found out. Further, the inventors have further studied and found a manufacturing method capable of reducing orange peel-like irregularities on the surface of the cholesteric liquid crystal layer, which causes distortion of the mirror reflection image.

The degree of the orange-peeled irregularities on the surface of the cholesteric liquid crystal layer is determined based on the degree to which the image of the object seen through the half mirror looks clear and undistorted (the sharpness of the image). can do. Specifically, it can be considered that the higher the sharpness of the image, the fewer orange peel-like irregularities. The image sharpness can be measured in accordance with JIS K 7374 as shown in the examples. The sharpness of the image may be obtained by using ICM-IT manufactured by Suga Test Instruments Co., Ltd. as used in the examples.
The image sharpness is preferably 70% or more and 80% or more when the incident light angle is 0 ° (perpendicular to the sample surface) in a transmission method and a 0.05 mm optical comb is employed. More preferably, it is more preferably 85% or more.

The half mirror of the present invention includes a circularly polarized light reflection layer, an adhesive layer, and a transparent substrate in this order. In the half mirror of the present invention, the circularly polarized light reflecting layer and the adhesive layer may be in direct contact, and the adhesive layer and the transparent substrate may be in direct contact.

<Method for manufacturing half mirror>
The half mirror can be formed by bonding a circularly polarized light reflection layer and a transparent substrate. Specifically, a transfer material including a circularly polarized reflective layer is prepared, the surface of the circularly polarized reflective layer of the transfer material and the transparent substrate are bonded with a curable adhesive, and then the curable adhesive is cured. Can be formed.

[Transparent substrate]
The material for the transparent substrate is not particularly limited. As the transparent substrate, a glass plate or a plastic plate used for producing a normal mirror can be used. The transparent substrate is preferably transparent in the visible light region and has a small birefringence. Examples of the plastic film include polyester such as polyethylene terephthalate (PET), polycarbonate, acrylic resin, epoxy resin, polyurethane, polyamide, polyolefin, cellulose derivative, and silicone.
The thickness of the transparent substrate may be about 100 μm to 10 mm, preferably 200 μm to 5.0 mm, and more preferably 500 μm to 3.0 mm.

The area of the main surface of the transparent substrate may be larger, the same or smaller than the area of the main surface of the circularly polarized light reflection layer. In this specification, the “main surface” refers to the surface (front surface or back surface) of a plate-like or film-like member. The circularly polarized light reflecting layer may be bonded to a part of the main surface of the transparent substrate, and another type of reflecting layer such as a metal foil may be bonded or formed at other portions. With such a configuration, an image can be displayed on a part of the mirror. On the other hand, it may be a half mirror in which a circularly polarized reflective layer is adhered to the entire main surface of the transparent substrate, and the half mirror further has an image display unit having the same area as the main surface of the circularly polarized reflective layer. You may adhere | attach with the image display part of an apparatus. With such a configuration, image display on the entire mirror surface is possible.

[Adhesive layer]
In the production method of the present invention, when the circularly polarized light reflecting layer and the transparent substrate are bonded, an adhesive layer having a thickness of 1.0 μm or more and 5.0 μm or less is used. That is, in the manufactured half mirror, the adhesive layer may be 1.0 μm or more and 5.0 μm or less. By controlling the thickness of the adhesive layer in the range of 1.0 μm or more and 5.0 μm or less, the inventors of the present invention have an orange peel-like shape on the surface of the circularly polarized reflective layer, that is, the surface of the cholesteric liquid crystal layer. It was found that unevenness can be reduced.
The thickness of the adhesive layer is more preferably 2.0 μm or more and 4.0 μm or less.

As the adhesive layer for bonding the circularly polarized light reflecting layer and the transparent substrate, a layer obtained by curing a curable adhesive is used. There are two types of curable adhesives: thermosetting type, photocuring type, and reactive curing type from the viewpoint of curing method. Materials are acrylate, urethane, urethane acrylate, epoxy, epoxy acrylate, polyolefin, modified. Olefin, polypropylene, ethylene vinyl alcohol, vinyl chloride, chloroprene rubber, cyanoacrylate, polyamide, polyimide, polystyrene, polyvinyl butyral, and the like can be used. From the viewpoint of workability and productivity, the photocuring type is preferable as the curing method, and from the viewpoint of optical transparency and heat resistance, it is preferable to use an acrylate, urethane acrylate, epoxy acrylate, or the like material.

[Transfer material]
The circularly polarized light reflecting layer is prepared as a transfer material, and may be bonded to the transparent substrate on the surface of the circularly polarized light reflecting layer. The transfer material may include a temporary support. As described later, a half mirror is manufactured by using a transfer material formed with a circularly polarized reflective layer formed on a temporary support, and transferring the circularly polarized reflective layer to a transparent substrate using this transfer material. Can do. Further, the transfer material may have a circularly polarized light reflection layer and a quarter wavelength plate. For example, the transfer material may have a temporary support, a quarter-wave plate, and a circularly polarized light reflection layer in this order.
When a transfer material having a temporary support is used, the temporary support may be peeled off after the circularly polarized light reflection layer is bonded to the transparent substrate. The temporary support may be peeled off when the circularly polarized light reflection layer is bonded to the image display device, and may be bonded to the image display device with the obtained peeled surface. The temporary support may function as a protective film, for example.

The transfer material may be a quarter wave plate and a circularly polarized light reflecting layer. For example, a plurality of cholesteric liquid crystal layers are sequentially formed on the surface of a quarter-wave plate such as a stretched film to form a circularly polarized reflective layer, and this half polarized mirror is adhered to the transparent substrate on the surface of the circularly polarized reflective layer. You can also get
When bonding the circularly polarized reflective layer to the transparent substrate, the circularly polarized reflective layer in the transfer material and the transparent substrate are bonded with a curable adhesive. Preferably, a curable adhesive is applied to the surface of the circularly polarized light reflecting layer, and the coated surface is bonded to a transparent substrate. Thereafter, curing may be performed according to the used curable adhesive.

As described above, it has been difficult in the past to secure sufficient adhesion for use on the surface of the image display unit of the image display device with a thin adhesive layer thickness of 1 μm or more and 5 μm or less. It was found that the adhesiveness can be ensured by setting the pencil hardness of the surface of the transfer material to be bonded with a curable adhesive (the surface of the transfer material to be bonded to the transparent substrate) to HB or less. The surface of the transfer material to be bonded with the curable adhesive may be a circularly polarized light reflecting layer. That is, the outermost surface of the transfer material when bonded to the transparent substrate may be a circularly polarized light reflection layer.
Without being bound by any theory, the reason why sufficient adhesion is obtained is that the adhesive surface of the transfer material has become soft, so that minute bubbles can be easily removed when bonded to the adhesive layer. Adhesive layer components due to the fact that the adhesive layer of the transfer material has become soft, the adhesive surface of the transfer material has become soft, and the transfer material surface has become somewhat sticky, or the adhesive surface of the transfer material has become softer It is conceivable that the ink easily penetrates into the vicinity of the adhesive surface of the transfer material.

The pencil hardness of the surface of the transfer material to be bonded to the transparent substrate is preferably HB, B, 2B, 3B, or 4B, and more preferably B, 2B, or 3B. In this specification, pencil hardness means the value obtained by evaluating the layer surface based on JIS K5400 (pencil scratch test method).
The pencil hardness of the transfer material can be adjusted by adjusting the amount of the cross-linking agent in the liquid crystal composition for forming the outermost layer of the adhesive, that is, the circularly polarized light reflecting layer. Or it can adjust by adjusting the light irradiation conditions at the time of hardening a liquid-crystal composition, and forming a layer, or heating conditions.

In the transfer material, a part of the cholesteric liquid crystal layer including the cholesteric liquid crystal layer closest to the adhesive layer may have a pencil hardness of HB or less on the surface at the time of manufacture. Each liquid crystal layer may have a pencil hardness of not more than the above HB at the time of manufacture on the surface, but the latter is preferred. When the transfer material includes a ¼ wavelength plate, it is preferable that the ¼ wavelength plate has a pencil hardness equal to or lower than the above HB on the surface thereof when manufactured. In particular, when the transfer material includes a quarter-wave plate formed from a liquid crystal composition, it is preferable that the quarter-wave plate also has a pencil hardness of not more than the above HB on the surface at the time of manufacture.

In the half mirror obtained by adhering to the transparent substrate with the pencil hardness of the surface of the transfer material to be bonded being HB or less, the inventors of the half mirror on the side opposite to the transparent substrate as viewed from the circularly polarized reflective layer. It was found that the pencil hardness of the surface was H or less. On the other hand, when the pencil hardness of the surface of the transfer material to be bonded in the manufacturing method is higher than HB, sufficient adhesion cannot be obtained. In such an example, it is opposite to the transparent substrate as viewed from the circularly polarized light reflecting layer. An example in which the pencil hardness of the surface of the side half mirror is H was also included. In the study by the present inventors, in the case of the half mirror in which the pencil hardness of the surface of the half mirror opposite to the transparent substrate as viewed from the circularly polarized light reflection layer is HB or less, the pencil hardness of the transfer material surface to be bonded in the manufacturing method No higher than HB was found. Therefore, such a half mirror is considered to be a half mirror manufactured with the pencil hardness of the transfer material surface to be bonded being HB or less. In addition, as described above, the pencil hardness of the surface of the circularly polarized reflective layer to be bonded is also improved in the half mirror where the pencil hardness of the surface of the half mirror opposite to the transparent substrate is H as seen from the circularly polarized reflective layer. There is a possibility that it is a half mirror manufactured as HB or less.
The surface of the half mirror on the side of the circularly polarized light reflecting layer with respect to the transparent substrate may be a circularly polarized light reflecting layer or a quarter wavelength plate.

[Circularly polarized reflective layer]
The circularly polarized light reflection layer includes at least one cholesteric liquid crystal layer exhibiting selective reflection in the visible light region. The circularly polarized light reflecting layer may include two or more cholesteric liquid crystal layers, and may include other layers such as an alignment layer. The circularly polarized light reflecting layer is preferably composed only of a cholesteric liquid crystal layer. Further, when the circularly polarized light reflection layer includes a plurality of cholesteric liquid crystal layers, it is preferable that they are in direct contact with adjacent cholesteric liquid crystal layers. The circularly polarized light reflection layer preferably includes three or more cholesteric liquid crystal layers such as three layers and four layers.

The thickness of the circularly polarized light reflecting layer is preferably 2.0 μm to 30 μm, more preferably 4.0 μm to 25 μm, and even more preferably 5.0 μm to 20 μm.
In the half mirror, orange peel is more likely to occur as the thickness of the layer bonded to the transparent substrate is smaller. Therefore, when the thickness of the circularly polarized light reflecting layer or the total thickness of the laminate of the circularly polarized light reflecting layer and the quarter-wave plate described below is 25 μm or less, particularly when it is 20 μm or less, the orange peel of the present invention is reduced. The effect of is remarkable.

(Cholesteric liquid crystal layer)
In this specification, a cholesteric liquid crystal layer means a layer in which a cholesteric liquid crystal phase is fixed. The cholesteric liquid crystal layer is sometimes simply referred to as a liquid crystal layer.
The cholesteric liquid crystal phase selectively reflects the circularly polarized light of either the right circularly polarized light or the left circularly polarized light in a specific wavelength range and exhibits circularly polarized light selective reflection that transmits the circularly polarized light of the other sense. Are known. In this specification, the circularly polarized light selective reflection is sometimes simply referred to as selective reflection.
Many films formed from a composition containing a polymerizable liquid crystal compound have been known as a film containing a layer in which a cholesteric liquid crystal phase exhibiting circularly polarized light selectively is fixed. You can refer to the technology.

The cholesteric liquid crystal layer may be a layer in which the orientation of the liquid crystal compound in the cholesteric liquid crystal phase is maintained. Typically, the polymerizable liquid crystal compound is placed in the orientation state of the cholesteric liquid crystal phase and then irradiated with ultraviolet rays. Any layer may be used as long as it is polymerized and cured by heating or the like to form a layer having no fluidity, and at the same time, the layer is changed to a state in which the orientation is not changed by an external field or an external force. In the cholesteric liquid crystal layer, it is sufficient that the optical properties of the cholesteric liquid crystal phase are maintained in the layer, and the liquid crystal compound in the layer may no longer exhibit liquid crystallinity. For example, the polymerizable liquid crystal compound may have a high molecular weight due to a curing reaction and may no longer have liquid crystallinity.

The central wavelength λ of selective reflection of the cholesteric liquid crystal layer depends on the pitch P (= helical period) of the helical structure in the cholesteric phase, and follows the relationship between the average refractive index n of the cholesteric liquid crystal layer and λ = n × P. In this specification, the central wavelength λ of selective reflection of the cholesteric liquid crystal layer means a wavelength at the center of gravity of the reflection peak of the circularly polarized reflection spectrum measured from the normal direction of the cholesteric liquid crystal layer. In the present specification, the center wavelength of selective reflection means the center wavelength when measured from the normal direction of the cholesteric liquid crystal layer.
As can be seen from the above equation, the center wavelength of selective reflection can be adjusted by adjusting the pitch of the helical structure. The center wavelength λ can be adjusted in order to selectively reflect either the right circularly polarized light or the left circularly polarized light with respect to light of a desired wavelength by adjusting the n value and the P value.

When light is incident on the cholesteric liquid crystal layer at an angle, the center wavelength of selective reflection is shifted to the short wavelength side. Therefore, it is preferable to adjust n × P so that λ calculated according to the above formula λ = n × P becomes a long wavelength with respect to the wavelength of selective reflection required for image display. In the cholesteric liquid crystal layer having a refractive index n ₂ , the center wavelength of selective reflection when a light beam passes at an angle of θ ₂ with respect to the normal direction of the cholesteric liquid crystal layer (helical axis direction of the cholesteric liquid crystal layer) is λ _d . Λ _d is expressed by the following equation.
λ _d = n ₂ × P × cos θ ₂

Considering the above, by designing the central wavelength of selective reflection of the cholesteric liquid crystal layer included in the circularly polarized light reflection layer, it is possible to prevent the visibility of the image from being obliquely viewed. In addition, visibility of the image from an oblique direction can be reduced. This is useful because, for example, it is possible to prevent peeping in a smartphone or a personal computer.

Further, due to the selective reflection property described above, in the mirror with an image display function using the half mirror of the present invention, the display image and the mirror reflection image viewed from an oblique direction may be colored. By including a cholesteric liquid crystal layer having a center wavelength of selective reflection in the infrared light region in the circularly polarized light reflecting layer, it is possible to prevent this color. In this case, the center wavelength of selective reflection in the infrared region is specifically 780 to 900 nm, preferably 780 to 850 nm.

Since the pitch of the cholesteric liquid crystal phase depends on the type of chiral agent used together with the polymerizable liquid crystal compound or the concentration of the chiral agent, a desired pitch can be obtained by adjusting these. For the method of measuring spiral sense and pitch, use the methods described in “Introduction to Liquid Crystal Chemistry Experiments” edited by the Japanese Liquid Crystal Society, Sigma Publishing 2007, page 46, and “Liquid Crystal Handbook”, Liquid Crystal Handbook Editorial Committee, Maruzen, page 196. be able to.

In the half mirror of the present invention, the circularly polarized light reflecting layer includes a cholesteric liquid crystal layer having a central wavelength of selective reflection in a red light wavelength region, a cholesteric liquid crystal layer having a central wavelength of selective reflection in a wavelength region of green light, and blue It is preferable to include a cholesteric liquid crystal layer having a central wavelength of selective reflection in the wavelength region of light. The reflective layer is, for example, a cholesteric liquid crystal layer having a central wavelength of selective reflection in 400 nm to 500 nm, a cholesteric liquid crystal layer having a central wavelength of selective reflection in 500 nm to 580 nm, and a cholesteric liquid crystal having a central wavelength of selective reflection in 580 nm to 700 nm. It is preferable to include a layer.

In the half mirror of the present invention, the central wavelength of selective reflection of the cholesteric liquid crystal layer may be adjusted as follows based on the emission peak of the image display device used in combination. That is, the central wavelength of selective reflection of the cholesteric liquid crystal layer may differ from the wavelength of the light emission peak of the image display device by 5 nm or more, preferably 10 nm or more. In particular, it is preferable to perform the above adjustment in the half mirror of the present invention that does not include a quarter-wave plate described later. By shifting the center wavelength of selective reflection and the wavelength of the emission peak for image display of the image display device, the light for image display is not reflected by the cholesteric liquid crystal layer, and the display image can be brightened. The wavelength of the emission peak of the image display device can be confirmed by the emission spectrum when the image display device displays white. The peak wavelength may be any peak wavelength in the visible light region of the emission spectrum. For example, the above-described red light emission peak wavelength λR, green light emission peak wavelength λG, and blue light emission peak wavelength λB of the image display device. Any one or more selected from the group consisting of: The central wavelength of selective reflection of the cholesteric liquid crystal layer is 5 nm or more for any of the above-described red light emission peak wavelength λR, green light emission peak wavelength λG, and blue light emission peak wavelength λB of the image display device, preferably It is preferably different by 10 nm or more. When the circularly polarized light reflection layer includes a plurality of cholesteric liquid crystal layers, the central wavelength of selective reflection of all the cholesteric liquid crystal layers is different from the wavelength of the peak of light emitted from the image display device by 5 nm or more, preferably 10 nm or more. do it. For example, when the image display device is a full-color display device showing an emission peak wavelength λR of red light, an emission peak wavelength λG of green light, and an emission peak wavelength λB of blue light in the emission spectrum during white display, All of the central wavelengths of selective reflection of the cholesteric liquid crystal layer may be different from each of λR, λG, and λB by 5 nm or more, preferably 10 nm or more.

Further, when the circularly polarized light reflecting layer includes a plurality of cholesteric liquid crystal layers, it is preferable that the cholesteric liquid crystal layer closer to the image display device has a longer selective reflection center wavelength. With such a configuration, it is possible to suppress oblique color in the image and the mirror reflection image.

By adjusting the central wavelength of selective reflection of the cholesteric liquid crystal layer to be used according to the emission wavelength range of the image display device and the usage mode of the circularly polarized light reflection layer, a bright image can be displayed with high light utilization efficiency. Examples of the usage of the circularly polarized light reflecting layer include an incident angle of light to the circularly polarized light reflecting layer, an image observation direction, and the like.

As each cholesteric liquid crystal layer, a cholesteric liquid crystal layer whose spiral sense is either right or left is used. The sense of reflected circularly polarized light in the cholesteric liquid crystal layer coincides with the sense of a spiral. When a plurality of cholesteric liquid crystal layers are included in the circularly polarized light reflection layer, all of the spiral senses may be the same or different. Each of the cholesteric liquid crystal layers having a specific selective reflection center wavelength may include either the right or left sense cholesteric liquid crystal layer, or both the right and left sense cholesteric liquid crystal layers. May be.

In a half mirror including a quarter-wave plate, which will be described later, depending on the sense of circularly polarized light of the sense that is obtained from the image display device and transmitted through the quarter-wave plate, the sense of the spiral is right or A cholesteric liquid crystal layer which is one of the left side may be used. Specifically, a cholesteric liquid crystal layer having a spiral sense that transmits the circularly polarized light of the sense obtained from the image display device and transmitted through the quarter wavelength plate may be used. When a plurality of cholesteric liquid crystal layers are included in the circularly polarized light reflecting layer, it is preferable that the senses of the spirals are all the same.

The full width at half maximum Δλ (nm) of the selective reflection band showing selective reflection depends on the relationship of Δλ = Δn × P, where Δλ depends on the birefringence Δn of the liquid crystal compound and the pitch P. Therefore, the width of the selective reflection band can be controlled by adjusting Δn. Δn can be adjusted by adjusting the kind of the polymerizable liquid crystal compound and the mixing ratio thereof, or by controlling the temperature at the time of fixing the alignment.
In order to form one type of cholesteric liquid crystal layer having the same central wavelength of selective reflection, a plurality of cholesteric liquid crystal layers having the same period P and the same spiral sense may be stacked. By laminating cholesteric liquid crystal layers having the same period P and the same spiral sense, the circularly polarized light selectivity can be increased at a specific wavelength.

[¼ wave plate]
The half mirror of the present invention may include a quarter wavelength plate. Further, the transfer material may include a quarter wavelength plate. When the half mirror of the present invention is used in a mirror with an image display function, the circularly polarized light reflecting layer allows light from the image display device to be disposed by arranging a quarter wave plate between the image displaying device and the circularly polarized light reflecting layer. It can be converted into circularly polarized light of sense to be transmitted and incident on the circularly polarized light reflecting layer. Therefore, the light reflected by the circularly polarized light reflection layer and returning to the image display device side can be greatly reduced, and a bright image can be displayed.

The quarter wave plate may be a retardation layer that functions as a quarter wave plate in the visible light region. Examples of the quarter-wave plate include a single-layer quarter-wave plate, a broadband quarter-wave plate in which a quarter-wave plate and a half-wave retardation plate are stacked, and the like.
The front phase difference of the former ¼ wavelength plate may be a length that is ¼ of the emission wavelength of the image display device. Therefore, for example, when the emission wavelength of the image display device is 450 nm, 530 nm, and 640 nm, the wavelength of 450 nm is 112.5 nm ± 10 nm, preferably 112.5 nm ± 5 nm, more preferably 112.5 nm, and 530 nm. Inverse dispersion phase difference such that the phase difference is 5 nm ± 10 nm, preferably 132.5 nm ± 5 nm, more preferably 132.5 nm, 160 nm ± 10 nm, preferably 160 nm ± 5 nm, more preferably 160 nm at a wavelength of 640 nm A layer is most preferable as a quarter-wave plate, but a retardation plate having a small retardation wavelength dispersion or a forward dispersion retardation plate can also be used. The reverse dispersion means a property that the absolute value of the phase difference becomes larger as the wavelength becomes longer, and the forward dispersion means a property that the absolute value of the phase difference becomes larger as the wavelength becomes shorter.

The laminated quarter-wave plate is formed by laminating a quarter-wave plate and a half-wave retardation plate at an angle of 60 ° with the slow axis, and the side of the half-wave retardation plate is linearly polarized. It is arranged on the incident side, and the slow axis of the half-wave retardation plate is used so as to cross 15 ° or 75 ° with respect to the plane of polarization of the incident linearly polarized light. Since it is favorable, it can be suitably used.
In the present specification, the phase difference means frontal retardation. The phase difference can be measured using a polarization phase difference analyzer AxoScan manufactured by AXOMETRICS. Alternatively, measurement may be performed by making light of a specific wavelength incident in the normal direction of the film in KOBRA 21ADH or WR (manufactured by Oji Scientific Instruments).

There is no restriction | limiting in particular as a quarter wavelength plate, According to the objective, it can select suitably. For example, quartz plate, stretched polycarbonate film, stretched norbornene polymer film, transparent film containing inorganic particles exhibiting birefringence such as strontium carbonate, and oblique deposition of inorganic dielectric on support Thin films and the like.

Examples of the quarter-wave plate include (1) a birefringent film having a large retardation and a birefringence having a small retardation described in JP-A-5-27118 and JP-A-5-27119. A retardation film obtained by laminating the optical films so that their optical axes are orthogonal to each other, (2) a polymer film having a λ / 4 wavelength at a specific wavelength described in JP-A-10-68816 And a retardation film which can be obtained by laminating a polymer film made of the same material and having a λ / 2 wavelength at the same wavelength to obtain a λ / 4 wavelength in a wide wavelength region, (3) JP-A-10-90521 A retardation plate capable of achieving a λ / 4 wavelength in a wide wavelength range by laminating two polymer films described in (4) WO 00/26705 pamphlet A retardation plate capable of achieving a λ / 4 wavelength in a wide wavelength range using the modified polycarbonate film described in (5), (5) a wide wavelength range using a cellulose acetate film described in International Publication No. 00/65384 pamphlet And a retardation plate capable of achieving a λ / 4 wavelength.
A commercial item can also be used as a quarter wavelength plate, As a commercial item, brand name: Pure Ace (trademark) WR (Teijin Ltd. make, polycarbonate film) etc. are mentioned, for example.

The quarter wavelength plate may be formed by arranging and fixing a polymerizable liquid crystal compound or a polymer liquid crystal compound. For example, for a quarter-wave plate, a liquid crystal composition is applied to a temporary support or an alignment film, and a polymerizable liquid crystal compound in the liquid crystal composition is formed into a nematic alignment in a liquid crystal state, and then subjected to photocrosslinking or thermal crosslinking. It can be formed by immobilization. The quarter-wave plate fixes the alignment by cooling the composition containing the polymer liquid crystal compound after applying the liquid crystal composition to the temporary support or the alignment film surface to form a nematic alignment in the liquid crystal state. It may be a layer obtained in this way.

[Method for producing quarter-wave plate and cholesteric liquid crystal layer]
Hereinafter, a preparation material and a preparation method of a quarter-wave plate formed from a cholesteric liquid crystal layer and a liquid crystal composition will be described.
Examples of the material used for forming the quarter wavelength plate include a liquid crystal composition containing a polymerizable liquid crystal compound. The material used for forming the cholesteric liquid crystal layer preferably further contains a chiral agent (optically active compound). If necessary, apply the above liquid crystal composition, which is further mixed with a surfactant or polymerization initiator and dissolved in a solvent, to a temporary support, alignment film, quarter wavelength plate, underlying cholesteric liquid crystal layer, etc. Then, after the alignment and ripening, the liquid crystal composition is fixed by curing to form a quarter-wave plate or a cholesteric liquid crystal layer.

(Polymerizable liquid crystal compound)
A rod-like liquid crystal compound may be used as the polymerizable liquid crystal compound.
Examples of the rod-like polymerizable liquid crystal compound include a rod-like nematic liquid crystal compound. Examples of rod-like nematic liquid crystal compounds include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines. , Phenyldioxanes, tolanes and alkenylcyclohexylbenzonitriles are preferably used. Not only low-molecular liquid crystal compounds but also high-molecular liquid crystal compounds can be used.

The polymerizable liquid crystal compound can be obtained by introducing a polymerizable group into the liquid crystal compound. Examples of the polymerizable group include an unsaturated polymerizable group, an epoxy group, and an aziridinyl group, preferably an unsaturated polymerizable group, and particularly preferably an ethylenically unsaturated polymerizable group. The polymerizable group can be introduced into the molecule of the liquid crystal compound by various methods. The number of polymerizable groups possessed by the polymerizable liquid crystal compound is preferably 1 to 6, more preferably 1 to 3. Examples of polymerizable liquid crystal compounds are described in Makromol. Chem. 190, 2255 (1989), Advanced Materials 5, 107 (1993), US Pat. No. 4,683,327, US Pat. No. 5,622,648, US Pat. No. 5,770,107, International Publication WO 95/22586, WO 95 / 24455, WO 97/00600, WO 98/23580, WO 98/52905, JP-A-1-272551, JP-A-6-16616, JP-A-7-110469, JP-A-11-80081, and JP-A-2001. The compounds described in Japanese Patent Publication No. 328873 are included. Two or more kinds of polymerizable liquid crystal compounds may be used in combination. When two or more kinds of polymerizable liquid crystal compounds are used in combination, the alignment temperature can be lowered.

The addition amount of the polymerizable liquid crystal compound in the liquid crystal composition is preferably 80 to 99.9% by mass with respect to the solid content mass (mass excluding the solvent) of the liquid crystal composition, and is preferably 85 to 99. It is more preferably 5% by mass, particularly preferably 90 to 99% by mass.

(Chiral agent: optically active compound)
The material used for forming the cholesteric liquid crystal layer preferably contains a chiral agent. The chiral agent has a function of inducing a helical structure of a cholesteric liquid crystal phase. The chiral compound may be selected according to the purpose because the helical sense or helical pitch induced by the compound is different.
There is no restriction | limiting in particular as a chiral agent, A well-known compound can be used. Examples of chiral agents include liquid crystal device handbook (Chapter 3, Section 4-3, TN, chiral agent for STN, 199 pages, edited by Japan Society for the Promotion of Science, 142th Committee, 1989), JP-A 2003-287623, Examples thereof include compounds described in JP-A No. 2002-302487, JP-A No. 2002-80478, JP-A No. 2002-80851, JP-A No. 2010-181852 or JP-A No. 2014-034581.

A chiral agent generally contains an asymmetric carbon atom, but an axially asymmetric compound or a planar asymmetric compound containing no asymmetric carbon atom can also be used as the chiral agent. Examples of the axial asymmetric compound or the planar asymmetric compound include binaphthyl, helicene, paracyclophane, and derivatives thereof. The chiral agent may have a polymerizable group. When both the chiral agent and the liquid crystal compound have a polymerizable group, they are derived from the repeating unit derived from the polymerizable liquid crystal compound and the chiral agent by a polymerization reaction between the polymerizable chiral agent and the polymerizable liquid crystal compound. A polymer having repeating units can be formed. In this aspect, the polymerizable group possessed by the polymerizable chiral agent is preferably the same group as the polymerizable group possessed by the polymerizable liquid crystal compound. Therefore, the polymerizable group of the chiral agent is also preferably an unsaturated polymerizable group, an epoxy group or an aziridinyl group, more preferably an unsaturated polymerizable group, and an ethylenically unsaturated polymerizable group. Particularly preferred.
The chiral agent may be a liquid crystal compound.

As the chiral agent, an isosorbide derivative, an isomannide derivative, or a binaphthyl derivative can be preferably used. As the isosorbide derivative, a commercial product such as LC-756 manufactured by BASF may be used.
The content of the chiral agent in the liquid crystal composition is preferably 0.01 mol% to 200 mol%, more preferably 1 mol% to 30 mol%, based on the total molar amount of the polymerizable liquid crystal compound.

(Polymerization initiator)
The liquid crystal composition preferably contains a polymerization initiator. In the embodiment in which the polymerization reaction is advanced by ultraviolet irradiation, the polymerization initiator to be used is preferably a photopolymerization initiator that can start the polymerization reaction by ultraviolet irradiation. Examples of photopolymerization initiators include α-carbonyl compounds (described in US Pat. Nos. 2,367,661 and 2,367,670), acyloin ether (described in US Pat. No. 2,448,828), α-hydrocarbon substituted aromatics. Group acyloin compounds (described in US Pat. No. 2,722,512), polynuclear quinone compounds (described in US Pat. Nos. 3,046,127 and 2,951,758), a combination of triarylimidazole dimer and p-aminophenyl ketone (US patent) No. 3549367), acridine and phenazine compounds (JP-A-60-105667, US Pat. No. 4,239,850), acylphosphine oxide compounds (JP-B 63-40799, JP-B-5) No. 29234, Japanese Patent Laid-Open No. 10-95788 JP, 10-29997, JP 2001-233842, JP 2000-80068, JP 2006-342166, JP 2013-114249, JP 2014-137466, JP 4223071, JP 2010-262028, described in JP-T-2014-500852), oxime compounds (described in JP 2000-66385 A, Japanese Patent No. 4,454,067), and oxadiazole compounds (described in US Pat. No. 4,221,970). Etc. For example, the description in paragraphs 0500 to 0547 of JP2012-208494A can be considered.

As the polymerization initiator, it is also preferable to use an acyl phosphine oxide compound or an oxime compound.
As the acylphosphine oxide compound, for example, IRGACURE819 (compound name: bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide) manufactured by BASF Japan Ltd. can be used. Examples of the oxime compounds include IRGACURE OXE01 (manufactured by BASF), IRGACURE OXE02 (manufactured by BASF), TR-PBG-304 (manufactured by Changzhou Strong Electronic New Materials Co., Ltd.), Adeka Arcles NCI-831, Adeka Arcles NCI-930 Commercial products such as (ADEKA) and Adeka Arcles NCI-831 (ADEKA) can be used.
Only one type of polymerization initiator may be used, or two or more types may be used in combination.
The content of the photopolymerization initiator in the liquid crystal composition is preferably 0.1 to 20% by mass, and preferably 0.5 to 5% by mass with respect to the content of the polymerizable liquid crystal compound. Further preferred.

(Crosslinking agent)
The liquid crystal composition may optionally contain a crosslinking agent in order to improve the film strength after curing and improve the durability. As the cross-linking agent, one that can be cured by ultraviolet rays, heat, moisture, or the like can be suitably used.
The crosslinking agent is not particularly limited and may be appropriately selected depending on the intended purpose. For example, polyfunctionality such as trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, etc. Acrylate compounds; Epoxy compounds such as glycidyl (meth) acrylate and ethylene glycol diglycidyl ether; 2,2-bishydroxymethylbutanol-tris [3- (1-aziridinyl) propionate], 4,4-bis (ethyleneiminocarbonylamino) ) Aziridine compounds such as diphenylmethane; isocyanate compounds such as hexamethylene diisocyanate and biuret type isocyanate; polyoxazoline compounds having an oxazoline group in the side chain; vinyltrimethoxysila And N-(2-aminoethyl) 3-aminopropyltrimethoxysilane alkoxysilane compounds may be mentioned. Of these, polyfunctional acrylate compounds are preferred. The polyfunctional acrylate compound is preferably a 3-6 functional acrylate compound, and more preferably a 4-6 functional acrylate compound. Moreover, a well-known catalyst can be used according to the reactivity of a crosslinking agent, and productivity can be improved in addition to membrane strength and durability improvement. These may be used individually by 1 type and may use 2 or more types together.

The content of the cross-linking agent in the liquid crystal composition is preferably 0 to 8.0 parts by mass, and 0.1 to 7.0 parts by mass with respect to 100 parts by mass of the polymerizable liquid crystal compound in the liquid crystal composition. Is more preferable, and 0.2 to 5.5 parts by mass is even more preferable. By adjusting the content of the crosslinking agent within the above range, the pencil hardness of the formed cholesteric liquid crystal layer surface can be adjusted to HB or less.

(Orientation control agent)
An alignment control agent that contributes to stable or rapid planar alignment may be added to the liquid crystal composition. Examples of the alignment control agent include fluorine (meth) acrylate polymers described in paragraphs [0018] to [0043] of JP-A-2007-272185, and paragraphs [0031] to [0034] of JP-A-2012-203237. And compounds represented by the formulas (I) to (IV) as described above.
In addition, as an orientation control agent, 1 type may be used independently and 2 or more types may be used together.

The addition amount of the alignment control agent in the liquid crystal composition is preferably 0.01% by mass to 10% by mass and more preferably 0.01% by mass to 5.0% by mass with respect to the total mass of the polymerizable liquid crystal compound. 0.02% by mass to 1.0% by mass is particularly preferable.

(Other additives)
In addition, the liquid crystal composition may contain at least one selected from a surfactant for adjusting the surface tension of the coating film to make the film thickness uniform, and various additives such as a polymerizable monomer. . Further, in the liquid crystal composition, if necessary, a polymerization inhibitor, an antioxidant, an ultraviolet absorber, a light stabilizer, a colorant, metal oxide fine particles, and the like may be added as long as the optical performance is not deteriorated. Can be added.

(solvent)
There is no restriction | limiting in particular as a solvent used for preparation of a liquid-crystal composition, Although it can select suitably according to the objective, An organic solvent is used preferably.
The organic solvent is not particularly limited and may be appropriately selected depending on the intended purpose. For example, ketones, alkyl halides, amides, sulfoxides, heterocyclic compounds, hydrocarbons, esters, ethers, etc. Is mentioned. These may be used individually by 1 type and may use 2 or more types together. Among these, ketones are particularly preferable in consideration of environmental load.

(Coating, orientation, polymerization)
The method for applying the liquid crystal composition to the temporary support, the alignment film, the quarter wavelength plate, the underlying cholesteric liquid crystal layer, and the like is not particularly limited and can be appropriately selected according to the purpose. Examples of the coating method include curtain coating method, extrusion coating method, direct gravure coating method, reverse gravure coating method, die coating method, spin coating method, dip coating method, spray coating method, and slide coating method. It can also be carried out by transferring a liquid crystal composition separately coated on a support. The liquid crystal molecules are aligned by heating the applied liquid crystal composition. In forming the cholesteric liquid crystal layer, cholesteric alignment may be performed, and in forming the quarter-wave plate, nematic alignment is preferable. In the cholesteric orientation, the heating temperature is preferably 200 ° C. or lower, and more preferably 130 ° C. or lower. By this alignment treatment, an optical thin film in which the polymerizable liquid crystal compound is twisted and aligned so as to have a helical axis in a direction substantially perpendicular to the film surface is obtained.
In the nematic orientation, the heating temperature is preferably 50 ° C. to 120 ° C., more preferably 60 ° C. to 100 ° C.

The aligned liquid crystal compound can be further polymerized to cure the liquid crystal composition. The polymerization may be either thermal polymerization or photopolymerization utilizing light irradiation, but photopolymerization is preferred. It is preferable to use ultraviolet rays for light irradiation. The irradiation energy is preferably ^{20mJ / cm 2 ~ 50J / cm} 2, 100mJ / cm 2 ~ 1,500mJ / cm 2 is more preferable. In order to accelerate the photopolymerization reaction, light irradiation may be performed under heating conditions or in a nitrogen atmosphere. The irradiation ultraviolet wavelength is preferably 350 nm to 430 nm. The polymerization reaction rate is preferably high from the viewpoint of stability, preferably 70% or more, and more preferably 80% or more. The polymerization reaction rate can be determined by measuring the consumption ratio of the polymerizable functional group using an IR absorption spectrum.

The thickness of each cholesteric liquid crystal layer is not particularly limited as long as it exhibits the above characteristics, but is preferably in the range of 1.0 to 20 μm, more preferably in the range of 2.0 to 10 μm.
The thickness of the quarter-wave plate formed from the liquid crystal composition is not particularly limited, but is preferably 0.2 μm to 10 μm, more preferably 0.5 μm to 2.0 μm.

[Temporary support]
The liquid crystal composition may be applied and formed on the surface of the temporary support or the alignment layer formed on the surface of the temporary support. The temporary support or the temporary support and the alignment layer may be peeled off after forming the layer. For example, the transfer material may be peeled off after being bonded to the transparent substrate. Examples of the temporary support include polyester such as polyethylene terephthalate (PET), polycarbonate, acrylic resin, epoxy resin, polyurethane, polyamide, polyolefin, cellulose derivative, silicone, or glass plate.
The thickness of the temporary support may be about 5 μm to 1000 μm, preferably 10 μm to 250 μm, more preferably 15 μm to 120 μm.

The alignment layer has a rubbing treatment of organic compounds such as polymers (resins such as polyimide, polyvinyl alcohol, polyester, polyarylate, polyamideimide, polyetherimide, polyamide, modified polyamide), oblique deposition of inorganic compounds, and microgrooves. It can be provided by means such as formation of a layer or accumulation of an organic compound (for example, ω-tricosanoic acid, dioctadecylmethylammonium chloride, methyl stearylate) using the Langmuir-Blodgett method (LB film). Further, an alignment layer that generates an alignment function by application of an electric field, application of a magnetic field, or light irradiation may be used.
In particular, the alignment layer made of a polymer is preferably subjected to a rubbing treatment and a liquid crystal composition is applied to the rubbing treatment surface. The rubbing treatment can be performed by rubbing the surface of the polymer layer several times in a certain direction with paper or cloth.
The liquid crystal composition may be applied to the surface of the temporary support without providing the alignment layer, or the surface obtained by rubbing the temporary support.
The thickness of the alignment layer is preferably 0.01 μm to 5.0 μm, and more preferably 0.05 μm to 2.0 μm.

[Laminated film of quarter wave plate and cholesteric liquid crystal layer]
As described above, a cholesteric liquid crystal layer or a quarter wave plate is a liquid crystal composition in which a polymerizable liquid crystal compound and a polymerization initiator, a chiral agent added as necessary, a surfactant, and the like are dissolved in a solvent. , A temporary support, an alignment layer, a quarter-wave plate, or a cholesteric liquid crystal layer prepared in advance, and dried to obtain a coating film. A polymerizable liquid crystal compound is applied to the coating film in a desired form. It can be formed by orientation and then polymerizing the polymerizable compound to fix the orientation.
A laminate of layers formed from a polymerizable liquid crystal compound can be formed by repeating the above steps. A part of the layers or a part of the laminated films may be separately manufactured, and they may be bonded together with an adhesive layer.

When forming a laminated film composed of a plurality of cholesteric liquid crystal layers, a laminated film composed of a quarter wavelength plate and a cholesteric liquid crystal layer, or a laminated film composed of a quarter wavelength plate and a plurality of cholesteric liquid crystal layers, A liquid crystal composition containing a polymerizable liquid crystal compound or the like may be applied directly to the surface of the wave plate or the previous cholesteric liquid crystal layer, and the alignment and fixing steps may be repeated. A separately prepared cholesteric liquid crystal layer and quarter wave plate Alternatively, these laminates may be laminated using an adhesive or the like, but the former is preferred. This is because uneven interference due to uneven thickness of the adhesive layer is difficult to be observed. In the laminated film of the cholesteric liquid crystal layer, the liquid crystal on the air interface side of the cholesteric liquid crystal layer formed earlier is formed by forming the next cholesteric liquid crystal layer so as to be in direct contact with the surface of the cholesteric liquid crystal layer formed earlier. This is because the orientation direction of the molecules matches the orientation direction of the liquid crystal molecules below the cholesteric liquid crystal layer formed thereon, and the polarization property of the laminate of the cholesteric liquid crystal layer is improved.

For example, a plurality of cholesteric liquid crystal layers may be sequentially formed on a temporary support to form a circularly polarized light reflection layer, which may be used as a transfer material. The half-mirror can be obtained by adhering to the transparent substrate on the surface of the circularly polarized light reflecting layer and then peeling the temporary support as necessary. Alternatively, a quarter-wave plate and a cholesteric liquid crystal layer may be sequentially formed on the temporary support to form a laminate of the quarter-wave plate and the circularly polarized light reflection layer, which may be used as a transfer material. The half-mirror having a quarter-wave plate can be obtained by adhering to the transparent substrate on the surface of the circularly polarized light reflecting layer and then peeling the temporary support as necessary.

[Other adhesive layers]
The half mirror of the present invention may include an adhesive layer for adhering each layer in addition to the adhesive layer for adhering the circularly polarized light reflecting layer and the transparent substrate. As the adhesive layer at that time, a layer obtained by curing the above curable adhesive, or a layer made of a hot-melt type adhesive or a pressure-sensitive adhesive that does not require curing can be used. . The thickness is not particularly limited and may be, for example, 1.0 μm or more and 5.0 μm or less, preferably 2.0 μm or more and 4.0 μm or less. Even when the half mirror is bonded to an image display device described later, a layer obtained by curing the curable adhesive may be used. The thickness in that case should just be 10 micrometers or more and 200 micrometers or less, and 20 micrometers or more and 100 micrometers or less are preferable. When adhering the half mirror to an image display device described later, it is preferable to use a highly transparent adhesive transfer tape (OCA tape) or the like generally used on the surface of the image display unit of the image display device.

<Mirror with image display function>
The half mirror of the present invention is used on the surface of an image display unit of an image display device. For example, the half mirror of the present invention can be combined with an image display device to be a mirror with an image display function. At this time, a half mirror may be disposed or adhered to the surface of the image display unit of the image display device. The mirror with an image display function includes an image display device, a circularly polarized light reflection layer, an adhesive layer, and a transparent substrate in this order. When a quarter wavelength plate is included, the image display device, the quarter wavelength plate, the circularly polarized reflection layer, the adhesive layer, and the transparent substrate may be included in this order.

Other layers such as an adhesive layer may be included between the image display device and the half mirror, but it is preferable that no other layers other than the adhesive layer are included. That is, it is preferable that the image display device and the half mirror are directly bonded. The image display device may be bonded to the half mirror at least at a part of the image display unit. The area of the surface of the half mirror to be bonded may be smaller than, equal to, or larger than the area of the image display unit.

In a mirror with an image display function including a ¼ wavelength plate, the angle of the ¼ wavelength plate and the image display device is preferably adjusted so that the image is brightest. That is, the relationship between the polarization direction of the linearly polarized light (transmission axis) and the slow axis of the quarter-wave plate so that the linearly polarized light is transmitted best, particularly for an image display device displaying an image by linearly polarized light. Is preferably adjusted. For example, in the case of a single layer type quarter wave plate, it is preferable that the transmission axis and the slow axis form an angle of 45 °. The light emitted from the image display device displaying an image by linearly polarized light is circularly polarized light of either right or left sense after passing through the quarter wavelength plate. The circularly polarized light reflecting layer described later is preferably composed of a cholesteric liquid crystal layer having a twist direction that transmits the circularly polarized light of the sense.

[Image display device]
The image display device is not particularly limited. The image display device is preferably an image display device that emits (emits light) linearly polarized light to form an image, and more preferably a liquid crystal display device or an organic EL device.
The liquid crystal display device may be a transmission type or a reflection type, and is particularly preferably a transmission type. The liquid crystal display device includes an IPS (In Plane Switching) mode, an FFS (Fringe Field Switching) mode, a VA (Vertical Alignment) mode, an ECB (Electrically Controlled Birefringence) mode, an STN (Super Twisted Nematic) mode, and a TN (Twisted Nematic) mode. Any liquid crystal display device such as an OCB (Optically Compensated Bend) mode may be used.

The image displayed on the image display unit of the image display device may be a still image, a moving image, or simply text information. Further, it may be a monochrome display such as black and white, a multi-color display, or a full-color display.
It is also preferable that the image display device shows a red light emission peak wavelength λR, a green light emission peak wavelength λG, and a blue light emission peak wavelength λB in an emission spectrum during white display. By having such an emission peak wavelength, full-color image display is possible. λR may be 580 to 700 nm, preferably 610 to 680 nm. λG may be 500-580, preferably 510-550 nm. λB may be 400-500 nm, preferably 440-480 nm.

[Use of mirror with image display function]
The use of the mirror with an image display function is not particularly limited. For example, it can be used as a security mirror, a beauty salon or a barber mirror, and can display images such as character information, still images, and moving images. The mirror with an image display function may be a vehicle rearview mirror, and may be used as a television, a personal computer, a smartphone, or a mobile phone.

The present invention will be described more specifically with reference to the following examples. The materials, reagents, amounts and ratios of substances, operations, and the like shown in the following examples can be appropriately changed without departing from the gist of the present invention. Therefore, the scope of the present invention is not limited to the following examples.

(1) The coating liquid 1, the coating liquid 2, the coating liquid 3, and the coating liquid 4 for 1/4 wavelength plate for cholesteric liquid crystal layer formation were prepared with the composition shown in the following Table 1. Furthermore, the pencil hardness of the film | membrane of each coating liquid was changed by changing the addition amount of a crosslinking agent.

化合物２は特開２００５－９９２４８号公報に記載の方法で製造した。

Compound 2 was produced by the method described in JP-A-2005-99248.

(2) (Preparation of transfer material A)
The temporary support (100 mm × 150 mm) uses a PET film (Cosmo Shine A4100, thickness: 100 μm) manufactured by Toyobo Co., Ltd., and is rubbed (rayon cloth, pressure: 0.1 kgf (0.98 N), rotation speed: 1000 rpm. , Transport speed: 10 m / min, number of times: 1 reciprocation).
(3) Coating solution 1 (without adding A-TMMT) was applied to the rubbed surface of the PET film using a wire bar, then dried and placed on a hot plate at 30 ° C., electrodeless manufactured by Fusion UV Systems Co., Ltd. UV irradiation was performed with a lamp “D bulb” (60 mW / cm ² ) for 6 seconds to fix the cholesteric liquid crystal phase to obtain a cholesteric liquid crystal layer having a thickness of 3.5 μm. The same process is repeated using coating solution 2 and coating solution 3 (both without addition of A-TMMT) on the surface of the obtained layer, and a transfer material A for three cholesteric liquid crystal layers (layer of coating solution 2: 3 0.0 μm, coating solution 3 layer: 2.7 μm). When the transmission spectrum of the transfer material A was measured with a spectrophotometer (manufactured by JASCO Corporation, V-670), transmission spectra having reflection peaks at 630 nm, 540 nm, and 450 nm were obtained.

The temporary support (100 mm × 150 mm) uses a PET film (Cosmo Shine A4100, thickness: 100 μm) manufactured by Toyobo Co., Ltd., and is rubbed (rayon cloth, pressure: 0.1 kgf (0.98 N), rotation speed: 1000 rpm. , Transport speed: 10 m / min, number of times: 1 reciprocation).
(3) (Preparation of transfer material B)
Coating solution 4 (without addition of A-TMMT) was applied to the rubbed surface of the PET film using a wire bar, dried and placed on a 30 ° C. hot plate, and the electrodeless lamp “D” manufactured by Fusion UV Systems Co., Ltd. With a “bulb” (60 mW / cm ² ), UV irradiation was performed for 6 seconds to fix the liquid crystal phase, thereby obtaining a quarter-wave plate having a thickness of 0.8 μm. The same process was repeated using coating solution 1, coating solution 2 and coating solution 3 (all without A-TMMT addition) on the surface of the obtained layer, and three cholesteric liquid crystal layers were formed on the quarter-wave plate. A transfer material B (a layer of coating solution 1: 3.5 μm, a layer of coating solution 2: 3 μm, a layer of coating solution 3: 2.7 μm) was obtained. When the transmission spectrum of the transfer material B was measured at V-670, transmission spectra having reflection peaks at 630 nm, 540 nm, and 450 nm were obtained.

Transfer materials C to G were prepared in the same manner as transfer material A by changing the amount of A-TMMT (crosslinking agent) added to coating solutions 1 to 3 and the hot plate temperature during UV irradiation. The pencil hardness of the cholesteric liquid crystal layer side surface of each transfer material is as follows. The pencil hardness was measured according to JIS K5400 (pencil scratch test method).

(4-1) An adhesive LCR0631 manufactured by Toagosei Co., Ltd. was applied to the surface of the cholesteric liquid crystal layer with a wire bar, and then adhered to a glass plate (50 mm × 50 mm) having a thickness of 1.8 mm using a laminator. At this time, the wire bar count and the nip roll pressure of the laminator were adjusted to adjust the thickness of the adhesive layer. Then, it was placed on a hot plate at 50 ° C., irradiated with UV for 30 seconds with an electrodeless lamp “D bulb” (60 mW / cm ² ) manufactured by Fusion UV Systems, and then the PET film was peeled off.
(4-3) An optical adhesive film (Panaclean (registered trademark) PD-S1) manufactured by Panac Co., Ltd. was used and bonded to a glass plate (50 mm × 50 mm) having a thickness of 1.8 mm using a laminator. Thereafter, the PET film was peeled off.

(5) The adhesion between the film and glass was evaluated by a cross-cut test (according to JIS K5600, but with a lattice pattern consisting of 100 film pieces). Nitto tape was used as the tape. A film having more than 90 pieces remained as A. What remained less than 90 film pieces was defined as B. The cross-cut (adhesion) is preferably as the number of peeled film pieces is smaller, and A is a practical range.
(6) The degree of the orange-peeled unevenness was evaluated by evaluating the sharpness of the image using ICM-IT manufactured by Suga Test Instruments Co., Ltd. according to JIS K 7374. The measurement was performed by a transmission method at an incident light angle of 0 ° (perpendicular to the sample surface), and an optical comb of 0.05 mm was adopted. 70% or more was designated as A, and less than 70% was designated as B. A is a practical range.
(7) The pencil hardness of the surface (PET interface side surface) obtained after peeling the PET film was measured according to JIS K5400 (pencil scratch test method).

Claims (19)

A method of manufacturing a half mirror used on the image display unit surface of an image display device,
The half mirror includes a circularly polarized light reflection layer, an adhesive layer, and a transparent substrate in this order,
The circularly polarized light reflection layer includes a cholesteric liquid crystal layer,
The manufacturing method includes:
Preparing a transfer material including the circularly polarized light reflection layer;
The surface of the circularly polarizing reflective layer of the transfer material and the transparent substrate are bonded with a curable adhesive, and the curable adhesive is cured to have a thickness of 1.0 μm or more and 5.0 μm or less. Forming an adhesive layer,
The manufacturing method whose pencil hardness of the surface bonded with the said transparent substrate of the said transfer material is HB or less. The transfer material comprises a temporary support;
The circularly polarized reflective layer in the transfer material;
Forming a liquid crystal composition containing a polymerizable liquid crystal compound on the temporary support to obtain a coating, and forming the coating by curing the coating to obtain the cholesteric liquid crystal layer. The manufacturing method according to claim 1. The manufacturing method according to claim 2, wherein the manufacturing method includes peeling the temporary support after the formation of the adhesive layer. The manufacturing method according to any one of claims 1 to 3, wherein the transfer material includes a quarter-wave plate. The transfer material comprises a temporary support;
The quarter-wave plate in the transfer material,
The manufacturing method of Claim 4 including forming by the method including apply | coating on the said temporary support body, obtaining a coating film, and hardening | curing the said coating film. The manufacturing method of Claim 5 including apply | coating the liquid crystal composition containing a polymeric liquid crystal compound to the surface of the said 1/4 wavelength plate, and obtaining the said cholesteric liquid crystal layer. A half mirror used on the image display unit surface of the image display device,
It is produced by the production method according to any one of claims 1 to 6,
The circularly polarized light reflecting layer and the adhesive layer are in direct contact with each other,
The adhesive layer and the transparent substrate are in direct contact,
The half mirror, wherein the adhesive layer has a thickness of 1.0 μm or more and 5.0 μm or less. A half mirror used on the image display unit surface of the image display device,
Including a circularly polarized light reflecting layer, an adhesive layer and a transparent substrate in this order,
The circularly polarized light reflection layer includes a cholesteric liquid crystal layer,
The circularly polarized light reflecting layer and the adhesive layer are in direct contact with each other,
The adhesive layer and the transparent substrate are in direct contact,
The adhesive layer is a layer obtained by curing a curable adhesive,
The adhesive layer has a thickness of 1.0 μm or more and 5.0 μm or less,
The said half mirror whose pencil hardness of the surface of the said half mirror of the said circularly polarized light reflection layer side with respect to the said transparent substrate is below HB. The half mirror according to claim 7 or 8, wherein the circularly polarized light reflection layer includes two or more cholesteric liquid crystal layers, and the two or more cholesteric liquid crystal layers have different selective reflection center wavelengths. The half mirror according to claim 9, wherein the two or more cholesteric liquid crystal layers are in direct contact with each other. The half mirror according to claim 9 or 10, wherein the circularly polarized light reflection layer includes three or more cholesteric liquid crystal layers, and the three or more cholesteric liquid crystal layers have different selective reflection center wavelengths. The circularly polarized light reflection layer has a cholesteric liquid crystal layer having a central wavelength of selective reflection at 400 nm to 500 nm, a cholesteric liquid crystal layer having a central wavelength of selective reflection at 500 nm to 580 nm, and a central wavelength of selective reflection at 580 nm to 700 nm. The half mirror according to claim 11, comprising a cholesteric liquid crystal layer. The half mirror according to any one of claims 9 to 12, wherein in the circularly polarized light reflection layer, a cholesteric liquid crystal layer having a shorter central wavelength of selective reflection is disposed at a position closer to the adhesive layer. The half mirror according to any one of claims 7 to 13, wherein the circularly polarized light reflection layer includes a cholesteric liquid crystal layer having a central wavelength of selective reflection in an infrared light region. The half mirror according to any one of claims 7 to 14, wherein a thickness of the circularly polarized light reflection layer is 25 μm or less. The half mirror according to any one of claims 7 to 15, wherein the transparent substrate is a glass plate or a plastic film having a front phase difference of less than 10 nm. Including a quarter wave plate,
The half mirror according to any one of claims 7 to 16, comprising the quarter-wave plate, the circularly polarized light reflecting layer, the adhesive layer, and the transparent substrate in this order. A half mirror according to any one of claims 7 to 17,
A mirror with an image display function including the image display device, the circularly polarized light reflection layer, the adhesive layer, and the transparent substrate in this order. The mirror with an image display function according to claim 18, wherein the image display device and the half mirror are directly bonded via an adhesive layer.