JP6972543B2 - Depolarization element - Google Patents

Description

The present invention relates to a depolarizing element that eliminates the polarized light of polarized light and converts it into unpolarized light as a whole.

Light with the same phase state (polarized light) has strong regularity, which may cause interference, or it may not be able to pass through a polarizing plate such as polarized sunglasses, causing problems. Therefore, the state of the same phase (polarized state). Need to be resolved.

As a means for that, for example, a technique of applying a film having a high phase difference as described in Patent Document 1 and a technique of applying an element having a plurality of regions having different film thicknesses as described in Patent Document 2 are used. be.

Further, as described in Patent Document 3, there is also a technique of randomly refracting inorganic particles having birefringence in a transparent resin to eliminate the polarized state.

Japanese Patent No. 3105374 Japanese Unexamined Patent Publication No. 2014-2286 Japanese Unexamined Patent Publication No. 2012-88507

However, since the transmittance of a film having a high phase difference as described in Patent Document 1 greatly differs depending on the wavelength, the color may change due to the transmission depending on the incident light. Further, in an element as described in Patent Document 2, the thickness of the element becomes thick, and if there are a plurality of regions having different phase differences, the function as a depolarizing element is exhibited, but the transmittance depending on the wavelength can be biased. , There was a problem that the color was added.

Further, in the technique of dispersing the inorganic particles having birefringence in the transparent resin as in Patent Document 3, since the particles having different refractive indexes are dispersed, the transparency is impaired and the haze becomes high.

Therefore, in view of the above problems, the present invention provides a depolarizing element capable of reducing the change in color due to transmission while maintaining high transparency and suppressing the thickening. Make it an issue.

Hereinafter, the present invention will be described.

One aspect of the present invention is a depolarizing element that emits light with a plurality of phase differences applied to the incident light, and the regions having at least two different phase difference states are mixed so as to form a mottled pattern. It is a depolarizing element provided with a liquid crystal layer.

Such a liquid crystal layer may have a uniform thickness.

Further, in the above-mentioned depolarizing element, when the front phase difference is Re and the thickness phase difference is Rth,
Nz = (Rth / Re) +0.5
With respect to the Nz coefficient represented by, when the Nz coefficient at a wavelength of 450 nm is N ₄₅₀ and the Nz coefficient at a wavelength of 550 nm is N ₅₅₀ .
N ₄₅₀ <N ₅₅₀
Can be configured to hold.

Further, regarding the liquid crystal of the liquid crystal layer, when the birefringence at a wavelength of 450 nm is Δn ₄₅₀ , the birefringence at a wavelength of 550 nm is Δn ₅₅₀ , and the birefringence at a wavelength of 650 nm is Δn ₆₅₀ .
Δn ₄₅₀ <Δn ₅₅₀ <Δn ₆₅₀
Can be considered to be a relationship of.

Further, in the above-mentioned depolarizing element, the transmittance can be 0.2 or more and 0.8 or less at any wavelength in the wavelength range of 380 nm or more and 780 nm or less.

At that time, when the depolarizing element is arranged between the two polarizing plates having parallel absorption axes so that the optical axis is tilted at 45 ° in plan view with respect to the absorption axis, the wavelength range is 380 nm or more and 780 nm or less. , The transmittance may be 0.2 or more and 0.8 or less at any wavelength.

The thickness of the depolarizing element can be 20 μm or less.

Further, it is possible to provide a display device including an image display unit that emits an image and the above-mentioned depolarization element arranged on the image emission side of the image display unit.

According to the present invention, a plurality of different retardation regions are mixed in the liquid crystal layer, and the polarized state of transmitted light can be eliminated as a whole. In that case, since the difference in transmittance depending on the visible light wavelength can be reduced, it is possible to suppress the change in color due to transmission. And since it is composed of a liquid crystal layer, the layer can be made thin.

It is a perspective view of the depolarization element 10. It is a figure explaining the phase difference region of the liquid crystal layer 12. It is a graph explaining the operation of the polarization elimination element 10 with respect to the transmittance. It is an exploded perspective view which shows the image forming apparatus 1 conceptually.

Hereinafter, the present invention will be described based on the embodiments shown in the drawings. However, the present invention is not limited to these forms.

FIG. 1 is a diagram illustrating the first embodiment, and is a perspective view of the depolarizing element 10. As can be seen from FIG. 1, the depolarization element 10 of the present embodiment includes a base material 11 and a liquid crystal layer 12 laminated on the base material 11.

The base material 11 is a transparent layer that serves as a base material for laminating the liquid crystal layer 12 on one surface thereof. As the material forming the base material 11, various materials can be used. However, a material that is widely used as a material for a member constituting an optical element, has excellent mechanical properties, optical properties, stability, processability, and the like, and can be obtained at low cost can be used. This includes, for example, a polymer resin having an alicyclic structure, a methacrylic resin, a polycarbonate resin, a polystyrene resin, an acrylonitrile-styrene copolymer, a methyl methacrylate-styrene copolymer, an ABS resin, a thermoplastic resin such as polyether sulfone, and the like. Examples thereof include epoxy acrylate, urethane acrylate-based reactive resin (ionized radiation curable resin, etc.), triacetyl cellol roll resin, polyethylene terephthalate resin (PET), glass, and the like.
The thickness thereof can be configured to be 10 μm to 1000 μm.

The liquid crystal layer 12 is a layer made of a liquid crystal material laminated on the base material 11. In the present embodiment, the surface of the liquid crystal layer 12 opposite to the base material 11 side is a smooth surface. Therefore, in the present embodiment, the liquid crystal layer 12 is composed of a liquid crystal layer whose front and back surfaces are smooth and whose thickness is constant.

As shown in FIG. 2, the liquid crystal layer 12 has at least two different phase differences having regions in the plane along the layer plane, and is mixed so as to form a mottled pattern. In this embodiment, as can be seen from FIG. 2, the region of the first phase difference state A shown by hatching and the region of the second phase difference state B shown by white outline form a mottled pattern. It is mixed in.
That is, in the liquid crystal layer 12, the phase difference region of 1 and the other phase difference regions are mixed without having a specific period and are mixed so as to be uneven.
According to such a liquid crystal layer 12, the polarized light of the incident light in a predetermined polarized state can be converted and emitted as a non-polarized state, and the basic function of the depolarizing element can be exhibited. .. More details will be described later.

The liquid crystal layer 12 is configured by containing and mixing a liquid crystal material having a positive A characteristic and a liquid crystal material having a positive C characteristic.

Here, the characteristics of positive A are Nx for the refractive index in the X-axis direction along the layer surface, Ny for the refractive index in the Y-axis direction orthogonal to the X-axis in the direction along the layer surface, and Nz for the refractive index in the layer thickness direction. When, the relationship is Nx> Ny≈Nz, and the optical axis is in the Nx direction.

Examples of the polymerizable rod-shaped liquid crystal material that can form the liquid crystal layer having such a positive A characteristic include materials represented by the following chemical formulas (1) to (17).

The characteristics of positive C are Nx for the refractive index in the X-axis direction along the layer surface, Ny for the refractive index in the Y-axis direction orthogonal to the X-axis in the direction along the layer surface, and Nz for the refractive index in the layer thickness direction. When, Nz> Nx≈Ny, and the optical axis is in the Nz direction.

The liquid crystal material having such positive C characteristics is a liquid crystal material that is vertically oriented due to the orientation restricting force in the vertical direction (thickness direction of the alignment layer), and various rod-shaped liquid crystal compounds having a polymerizable functional group in the molecule. Can be applied. Specifically, for example, the configuration disclosed in JP-A-2015-191143 can be applied. More specifically, RMM28B manufactured by Merck Group, UCL-018 manufactured by DIC Corporation, and the like can be applied.

With respect to the liquid crystal constituting the liquid crystal layer 12, when the birefringence at a wavelength of 450 nm is Δn ₄₅₀ , the birefringence at a wavelength of 550 nm is Δn ₅₅₀ , and the birefringence at a wavelength of 650 nm is Δn ₆₅₀ .
Δn ₄₅₀ <Δn ₅₅₀ <Δn ₆₅₀
It can also be a relationship of. That is, it is possible to obtain a liquid crystal layer having a wavelength dispersibility (reverse dispersibility) in which the phase difference increases from the short wavelength side to the long wavelength side in the visible light region.
Conventionally, a polycarbonate copolymer resin using fluorene is known as a back-dispersible material, but if this is used, the member becomes thick.
As for the liquid crystal material, a polymerizable liquid crystal compound having a reverse dispersibility can be mentioned. However, although such a polymerizable liquid crystal compound can be thinned, it is more costly than a positively dispersible material and has a problem from the viewpoint of widely supplying products. On the other hand, by adopting the above configuration, if a liquid crystal material having a reverse dispersibility is used, it is possible to obtain a thinner depolarizing element without color tint while suppressing the cost.

According to the liquid crystal layer 12 constituting the depolarizing element 10, the phase difference region of 1 and the other phase difference regions, which are the above-mentioned characteristics, are mixed with each other without having a specific period. This makes it possible to impart completely different characteristics to the liquid crystal layer that does not have such characteristics as a whole.
For example, when the front phase difference is Re and the thickness phase difference is Rth, the Nz coefficient is
Nz = (Rth / Re) +0.5
In the depolarization element of this embodiment, the Nz coefficient N _{450 at a wavelength of 450 nm and the Nz coefficient N 550} at a wavelength of 550 nm are represented by
N ₄₅₀ <N ₅₅₀
It is also possible to.
As described above, in the depolarization element, it is possible to control the phase difference beyond the range of the characteristics of the conventional liquid crystal layer, and the depolarization element has a high degree of freedom in design.

Since the liquid crystal layer is used in this embodiment, the polarized state can be eliminated by a very thin element. For example, the thickness of the depolarizing element 10 can be 20 μm or less.
Further, since it can be made of a flexible material, it is possible to give flexibility to the element and flexibly correspond to the shape of the object to which the polarizing optical element 10 is applied.

Further, in the present invention, since liquid crystal is used to convert light into a plurality of lights having different phase differences, there is no increase in haze that occurs when inorganic particles are dispersed, and light is transmitted in a state where the increase in haze is suppressed to a low level. It is possible to make it. Specifically, it is also possible to form a depolarizing element having a haze value of 5% or less.

The depolarizing element 10 having the above configuration operates as follows, for example.
Light having the same phase (in a predetermined polarized state) is incident on the depolarizing element 10. At that time, this light passes through the liquid crystal layer 12.
Here, in the depolarization element 10 of the present embodiment, as shown in FIG. 2, regions having at least two different phase differences, region A and region B, are mixed in the liquid crystal layer 12. Therefore, in the depolarization element 10 of the present embodiment, as a result of the light having the same phase (in a predetermined polarization state) passing through the depolarization element 10, the light has two kinds of phase differences, and a single phase difference (single phase difference). The polarized light) state can be eliminated.

Further, in that case, as described below, the depolarizing element 10 can suppress the difference in transmittance depending on the wavelength, and can transmit light while suppressing the change in color. FIG. 3 shows a diagram for explanation. FIG. 3 is a graph in which the horizontal axis is the wavelength and the vertical axis is the transmittance.
As can be seen from FIG. 3, the transmittance obtained by combining the transmittance characteristic in the region A and the transmittance characteristic in the region B is the total transmittance of the depolarizing element 10, so that the transmittance for each wavelength is high. By adjusting the transmittance so that it is constant (for example, around 0.5), it is possible to obtain an element having a transmittance characteristic that suppresses the deviation of the transmittance depending on the wavelength.
As a result, the depolarizing element 10 can suppress the difference in transmittance depending on the wavelength in the visible light region, and can transmit light while suppressing the change in color. That is, even when the depolarizing element 10 is used in an image display device, sunglasses, or the like, it is possible to suppress the change in color from the color of the original image and provide it to the observer. Therefore, in the conventional depolarization element, the color change in the transmitted light may be a problem, but such a problem can be solved by the present invention.

Similarly, when the light source of the image display device has a steep emission spectrum, in the conventional depolarizing element, the transmittance of a predetermined color is determined in relation to the emission spectrum and the wavelength transmittance characteristic of the depolarizing element. There was a problem that the color changed significantly when it became extremely low and passed through the depolarizing element. According to the present invention, even for such a problem, it is possible to suppress the change in the color of the light source light and transmit it, and it is possible to eliminate the polarized state regardless of the type of the light source.

In the wavelength range of 380 nm or more and 780 nm or less, which is a visible light region, the transmittance is preferably 0.2 or more and 0.8 or less at any wavelength. More preferably, the transmittance is 0.3 or more and 0.7 or less, and most preferably 0.4 or more and 0.6 or less at any wavelength. This transmittance is transmitted when a depolarizing element is inserted between two polarizing plates (a state in which the transmission axes are parallel or orthogonal to each other) with the optical axis tilted 45 degrees with respect to the absorption axis of the polarizing plate. It can be defined by the rate.

Further, the depolarizing element 10 is thin as described above, and by configuring the liquid crystal layer 12 as described above, the light traveling in the depolarizing element in the oblique direction is parallel to the inside of the depolarizing element in the thickness direction. It is difficult to make a big difference with the light that travels in the direction of polarized light. As a result, even if there is light traveling diagonally in the depolarizing element, it is easy to obtain the desired performance of the depolarizing state and the color as designed.
In the conventional technique, the light traveling diagonally in the element travels over other phase difference regions, so that the planned phase difference state cannot be obtained or the color changes. Therefore, the depolarization element of the present invention can solve the problem of accurately realizing the phase difference state and the color change as designed.

The depolarizing element 10 as described above can be manufactured, for example, as follows.

First, a material constituting the liquid crystal layer 12 of the depolarizing element 10 is prepared. The liquid crystal layer 12 is manufactured by using a liquid crystal material having a positive A characteristic and a liquid crystal material having a positive C characteristic. The properties of Positive A and Positive C, and examples of the material are as described above.

Next, both of the above liquid crystal materials and, for example, a polymerization initiator, a surfactant, and a solvent are mixed to obtain a composition. As a specific example, the liquid crystal of the above chemical formula (11) and the chemical formula (17) is used as the liquid crystal for positive A, and the RMM28B manufactured by Merck Group is used as the liquid crystal for positive C, and these are 0.11. : The ratio is 0.11: 0.78. Then, use Irgacure 907 manufactured by BASF Corporation as a polymerization initiator, Megafuck F477 manufactured by DIC Corporation as a surfactant, and a 1: 1 mixed solvent of methyl ethyl ketone (MEK) and methyl isobutyl ketone (MIBK) as a solvent. Can be done. Then, it is possible to use a composition containing 25% by mass of the liquid crystal material.

The type of liquid crystal material to be selected and the mixing ratio determine the phase difference of each region and the ratio of each region, whereby a depolarizing element having desired performance can be obtained.

The composition obtained as described above is applied to the surface of the base material 11. The coating method is not particularly limited, but the coating can be performed by, for example, a bar coater.
An alignment film may be laminated on the surface of the base material 11 and the above composition may be applied thereto. Known materials can be applied as the material constituting the alignment film.

Next, temperature control is performed on the above-mentioned composition in order to form a state (mottled pattern structure) in which regions having different phase differences as described with reference to FIG. 2 are mixed. Specifically, it is slowly cooled from a high temperature, rapidly cooled to a temperature at which a desired mixed state (mottled pattern) is obtained, and cured. For example, it is cooled by first heating at 90 ° C. for 1 minute and then heating at 60 ° C. for 1 minute. However, the initial heating temperature, time, and cooling heating temperature, time can be appropriately adjusted in order to obtain a desired mixed state (mottled pattern).

By manufacturing the depolarizing element by each of the above processes, the liquid crystal layer 12 having the above-mentioned structure can be obtained. More specifically, it is as follows.
That is, by mixing and cooling a plurality of types of liquid crystal materials having different orientation temperatures (in this embodiment, a liquid crystal material having a positive A characteristic and a liquid crystal material having a positive C characteristic), it becomes a starting point for changing the orientation state. A site is created and the change in orientation begins from here. Then, the site that becomes the starting point where the orientation state changes is randomly generated.
For example, this orientation state can be controlled by the temperature history of the cooling process or the like.
It is also possible to change the rate of change in the orientation state by changing the blending ratio of a plurality of types of liquid crystal materials.
Further, by changing the cooling rate, it is possible to control the number of sites that are the starting points where the orientation state changes. By increasing the cooling rate, it is possible to increase the number of starting points.
In this way, by controlling the temperature for cooling and controlling the blending ratio of the plurality of types of liquid crystal materials, regions having different phase differences can be obtained like the mottled pattern.

An alignment film may be provided between the base material layer 11 and the liquid crystal layer 12 with respect to the depolarization element 10 described above. A known alignment film can be used. By using the alignment film, the optical axis can be set to an arbitrary direction determined by the polarization exposure, and the optical axis can be controlled accurately and easily.

Further, the depolarization element can be configured only by the liquid crystal layer 12 having no base material 11 with respect to the depolarization element 10. According to such a depolarizing element, the element can be further made thinner.
Such a depolarizing element is provided with a treatment (for example, coating of a mold release material) on the surface of the base material 11 on which the liquid phase layer 12 is laminated to facilitate peeling, and the base material 11 is coated with a liquid crystal layer. It can be produced by peeling off the base material 11 after coating 12 and curing it.

By arranging the above-mentioned depolarizing element 10 in a display device such as a liquid crystal display device, it is possible to eliminate problems caused by light in a polarized state. As one embodiment, as shown in FIG. 4, the display device 1 includes an image display unit 2 that emits an image, and a depolarization element 10 that is arranged on the image emission side of the image display unit 2, which is necessary for the other. It is configured by being housed in a housing (not shown) in combination with various devices.

A liquid crystal display device 1 is mentioned as a specific example of the display device 1, in which case the image display unit 2 is a liquid crystal display unit 2, which is arranged on the front and back of a layer made of liquid crystal as an image source. A liquid crystal panel provided with a polarizing plate is included. The liquid crystal display unit 2 may be a known one, and an existing form can be used.
In a normal liquid crystal display device, the light emitted from the liquid crystal display device is in a predetermined polarized state due to the nature of the liquid crystal panel. The image may be barely visible. On the other hand, if the liquid crystal display device 1 is formed by arranging the depolarizing element 10 on the emission side of the liquid crystal display unit 2, the observer can see the image light in which the depolarized state is depolarized. Therefore, for example, polarized sunglasses. You can see the image even when wearing sunglasses.

When the display device is a liquid crystal display device, it is preferable that the depolarizing element provided therein has the following configuration.
As is known, the liquid crystal display unit 2 is provided with a layer made of liquid crystal and polarizing plates on the front and back sides (light source side and observer side) of the layer made of liquid crystal. Of these polarizing plates, a polarizing plate arranged on the observer side is prepared (polarizing plate a), and another polarizing plate having a transmission axis parallel to the polarizing plate a is prepared (polarizing plate b), and polarized light is obtained. The depolarizing element 10 is arranged between the plate a and the polarizing plate b. At this time, the optical axis of the depolarizing element 10 is installed so as to be 45 degrees with respect to the absorption axis of the polarizing plate a when viewed from the front.
When the laminated body of the polarizing plate a, the depolarizing element 10, and the polarizing plate b is irradiated with light from the polarizing plate a side and measured by a spectrophotometer on the light emitting side, the wavelength is in the visible light region. In the range of 380 nm or more and 780 nm or less, the transmittance is preferably 0.2 or more and 0.8 or less at any wavelength. More preferably, the transmittance is 0.3 or more and 0.7 or less, and most preferably 0.4 or more and 0.6 or less at any wavelength.

Although the case of the liquid crystal display unit has been described here, other types of display units provided with a polarizing plate can be similarly configured. This includes, for example, an organic EL display unit. That is, a polarizing plate provided in the display unit is prepared (polarizing plate a), another polarizing plate having a transmission axis parallel to the polarizing plate a is prepared (polarizing plate b), and the polarizing plate a and the polarizing plate b are prepared. The depolarizing element 10 is arranged between the and. At this time, the optical axis of the depolarizing element 10 is installed so as to be 45 degrees with respect to the absorption axis of the polarizing plate a when viewed from the front.
When the laminated body of the polarizing plate a, the depolarizing element 10, and the polarizing plate b is irradiated with light from the polarizing plate a side and measured by a spectrophotometer on the light emitting side, the wavelength is in the visible light region. In the range of 380 nm or more and 780 nm or less, the transmittance is preferably 0.2 or more and 0.8 or less at any wavelength. More preferably, the transmittance is 0.3 or more and 0.7 or less, and most preferably 0.4 or more and 0.6 or less at any wavelength.

10 Depolarization element 11 Base material 12 Liquid crystal layer

Claims (8)

It is a depolarizing element that emits light by giving multiple phase differences to the incident light.
It comprises a liquid crystal layer in which a liquid crystal material having a positive A characteristic and a liquid crystal material having a positive C characteristic are contained and mixed, and at least two kinds of regions having different phase differences are mixed so as to form a mottled pattern. A depolarizing element having a constant phase difference within the region of 1. The depolarizing element according to claim 1, wherein the liquid crystal layer has a uniform thickness. When the front phase difference is Re and the thickness phase difference is Rth,
Nz = (Rth / Re) +0.5
With respect to the Nz coefficient represented by, when the Nz coefficient at a wavelength of 450 nm is N ₄₅₀ and the Nz coefficient at a wavelength of 550 nm is N ₅₅₀ .
N ₄₅₀ <N ₅₅₀
The depolarizing element according to claim 1 or 2, wherein the above is satisfied. With respect to the liquid crystal of the liquid crystal layer, when the birefringence at a wavelength of 450 nm is Δn ₄₅₀ , the birefringence at a wavelength of 550 nm is Δn ₅₅₀ , and the birefringence at a wavelength of 650 nm is Δn ₆₅₀ .
Δn ₄₅₀ <Δn ₅₅₀ <Δn ₆₅₀
The depolarizing element according to any one of claims 1 to 3, which is related to the above. The depolarizing element according to any one of claims 1 to 4, wherein the transmittance is 0.2 or more and 0.8 or less at any wavelength in the wavelength range of 380 nm or more and 780 nm or less. In the wavelength range of 380 nm or more and 780 nm or less when the depolarizing element is arranged so that the optical axis is tilted at 45 ° in plan view with respect to the absorption axis between two polarizing plates having parallel absorption axes. The depolarizing element according to claim 5, wherein the transmittance is 0.2 or more and 0.8 or less at any wavelength. The depolarizing element according to any one of claims 1 to 6, wherein the thickness is 20 μm or less. An image display unit that emits an image and
A display device including the depolarization element according to any one of claims 1 to 7, which is arranged on the image emitting side of the image display unit.

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