JP2021043313A - λ/2-RETARDATION PLATE, OPTICAL ARTICLE AND REFLECTION TYPE PROJECTION SYSTEM - Google Patents

Abstract

To provide a λ/2-retardation plate that can give a preferable conversion ratio of linearly polarized light in a wide wavelength region.SOLUTION: The λ/2-retardation plate has a first positive A-layer and a second positive A-layer, in which the slow axis of the first positive A-layer and the slow axis of the second positive A-layer intersect, and the λ/2-retardation plate satisfies the following condition 1. Condition 1: a spectral transmittance of linearly polarized light in any wavelength region of 120 nm width or more of linearly polarized light incident at an incidence angle α degrees with respect to the λ/2-retardation plate is 2.0% or less in at least one 10-degree width region selected within the range from 30 to 60 degrees of the incident angle α.SELECTED DRAWING: Figure 1

Description

The present invention relates to λ / 2 retardation plates, optics and reflective projection systems.

Some optical products such as optical pickup devices and liquid crystal projectors include linearly polarized light conversion elements. Examples of the linearly polarized light conversion element include a λ / 2 retardation plate that rotates the vibration direction of linearly polarized light by 90 degrees. When the linearly polarized light passes through the λ / 2 retardation plate, the P-polarized light is converted into S-polarized light, and the S-polarized light is converted into P-polarized light.

Since the λ / 2 retardation plate has a wavelength dependence in which the phase difference changes as the wavelength changes, the function deteriorates for wavelengths deviating from the center wavelength (usually 550 nm), and the conversion ratio of linearly polarized light increases. descend.
Therefore, as a wave plate that functions as a λ / 2 phase difference plate in a wide wavelength range, the λ / 2 phase difference plate of Patent Documents 1 and 2 has been proposed.

Japanese Unexamined Patent Publication No. 5-100114 Japanese Unexamined Patent Publication No. 2004-170853

The λ / 2 retardation plates of Patent Documents 1 and 2 are formed by laminating two wave plates at a predetermined angle. However, in the λ / 2 retardation plates of Patent Documents 1 and 2, the conversion ratio of linearly polarized light often decreases extremely depending on the usage conditions.

The present inventors have diligently investigated the cause of the decrease in the conversion ratio of linearly polarized light even when the wave plates of Patent Documents 1 and 2 are used. As a result, the present inventors assume that "Patent Documents 1 and 2 exclusively assume a condition in which linearly polarized light is incident substantially perpendicular to the λ / 2 retardation plate" and "Patent Documents. In 1 and 2, the condition that the linearly polarized light is obliquely incident on the λ / 2 retardation plate is not assumed, and under the condition, the conversion ratio of the linearly polarized light deviating from the center wavelength is extremely reduced. " I found.
As a result of further studies, the present inventors can improve the conversion ratio of the linearly polarized light in a wide wavelength range even under the usage condition in which the linearly polarized light is obliquely incident on the λ / 2 retardation plate. We have completed a two-phase difference plate.

That is, the present invention provides the following [1] to [10].
[1] A λ / 2 retardation plate, wherein the λ / 2 retardation plate has a first positive A layer and a second positive A layer, and has a slow phase of the first positive A layer. A λ / 2 retardation plate in which the shaft and the slow phase shaft of the second positive A layer intersect and satisfy the following condition 1.
<Condition 1>
The spectral transmittance of the linearly polarized light in the wavelength range of any width of 120 nm or more of the linearly polarized light incident on the λ / 2 retardation plate at an incident angle α degree is within the range of an incident angle α of 30 to 60 degrees. Shows 2.0% or less in at least one 10 degree wide region selected from.
[2] The central wavelength of an arbitrary wavelength region having a width of 120 nm or more satisfying the above condition 1 is λc [nm], and the in-plane phase difference at the wavelength λc [nm] of the first positive A layer is Re1 (λc). Λ / 2 according to [1], where Re1 (λc)> Re2 (λc) when the in-plane phase difference at the wavelength λc [nm] of the second positive A layer is defined as Re2 (λc). Phase difference plate.
[3] The λ / 2 retardation plate according to [1] or [2], wherein the central wavelength λc in an arbitrary wavelength region having a width of 120 nm or more that satisfies the above condition 1 is located within a wavelength of 500 to 600 nm.
[4] When the in-plane phase difference of the first positive A layer at a wavelength of 550 nm is defined as Re1 (550), and the in-plane phase difference of the second positive A layer at a wavelength of 550 nm is defined as Re2 (550). Λ according to any one of [1] to [3], wherein Re1 (550) is 280 to 320 nm, Re2 (550) is 230 to 270 nm, and Re1 (550)> Re2 (550). / 2 phase difference plate.
[5] The horizontal direction in the plane of the λ / 2 retardation plate is defined as D1, the direction orthogonal to the horizontal direction in the plane of the λ / 2 retardation plate is defined as D2, and further, the first positive When the angle formed by the slow axis of the A layer and D2 is defined as θ1, and the angle formed by the slow axis of the second positive layer A and D2 is defined as θ2, θ1 and θ2 meet the following conditions 2-1. The λ / 2 retardation plate according to any one of [1] to [4], which satisfies any combination of (A1) to (A4) shown.
<Condition 2-1>
(A1) θ1 is 12.5 to 27.5 degrees, θ2 is 57.5 to 72.5 degrees, and (A2) θ1 is 57.5 to 72.5 degrees, and θ2 is 12.5 to 27. 5 degrees (A3) θ1 is -12.5 to -27.5 degrees, θ2 is -57.5 to -72.5 degrees (A4) θ1 is -57.5 to -72.5 degrees, and θ2 is -12.5 to −27.5 degrees [6] The first positive A layer and the second positive A layer are provided between the first transparent base material and the second transparent base material. , The λ / 2 retardation plate according to any one of [1] to [5].
[7] The λ / 2 retardation plate according to any one of [1] to [6], wherein the linearly polarized light under the condition 1 is S-polarized light.
[8] An optical product including the λ / 2 retardation plate according to any one of [1] to [7].
[9] The optical article according to [8], which is a reflective screen.
[10] A reflective projection system including a reflective screen including the λ / 2 retardation plate according to any one of [1] to [7] and a light source.

The λ / 2 retardation plate of the present invention, and the optical equipment and the reflection type projection system using the same, can improve the conversion ratio of linearly polarized light in a wide wavelength range.

It is sectional drawing which shows one Embodiment of the λ / 2 retardation plate of this invention. The figure which shows the spectral transmittance of the S polarized light when the S polarized light is incident on the λ / 2 retardation plate of Examples 1 and 2 and the comparative example 1 and 2 at an incident angle of 55 degrees. The figure which shows the spectral transmittance of the S polarized light when the S polarized light is incident on the λ / 2 retardation plate of Examples 1 and 2 and the comparative example 1 and 2 at an incident angle of 45 degrees. The figure which shows the spectral transmittance of the S polarized light when the S polarized light is incident on the λ / 2 retardation plate of Examples 1 and 2 and the comparative example 1 and 2 at an incident angle of 35 degrees. The figure which shows the spectral transmittance of the S polarized light when the S polarized light is incident on the λ / 2 retardation plate of Examples 1 and 2 and the comparative example 1 and 2 at an incident angle of 25 degrees. The figure which shows the spectral transmittance of the S polarized light when the S polarized light is incident on the λ / 2 retardation plate of Examples 1 and 2 and the comparative example 1 and 2 at an incident angle of 15 degrees. The figure which shows the spectral transmittance of the S polarized light when the S polarized light is incident on the λ / 2 retardation plate of Examples 1 and 2 and the comparative example 1 and 2 at an incident angle of 5 degrees. It is the schematic explaining the evaluation method of the double image of an Example.

Hereinafter, embodiments of the present invention will be described.
[Λ / 2 phase difference plate]
The λ / 2 retardation plate of the present invention has a first positive A layer and a second positive A layer, and has a slow axis of the first positive A layer and a delay of the second positive A layer. It intersects with the phase axis and satisfies the following condition 1.
<Condition 1>
The spectral transmittance of the linearly polarized light in the wavelength range of any width of 120 nm or more of the linearly polarized light incident on the λ / 2 retardation plate at an incident angle α degree is within the range of an incident angle α of 30 to 60 degrees. Shows 2.0% or less in at least one 10 degree wide region selected from.

FIG. 1 is a cross-sectional view showing an embodiment of the λ / 2 retardation plate of the present invention. The λ / 2 retardation plate 100 of FIG. 1 has a first positive A layer 10 and a second positive A layer 20. Further, in the λ / 2 retardation plate 100 of FIG. 1, a first positive A layer 10 and a second positive A layer 20 are formed between the first transparent base material 50 and the second transparent base material 60. Is placed. Further, the λ / 2 retardation plate 100 of FIG. 1 is formed between the first transparent base material 50 and the first positive A layer 10 and between the second transparent base material 60 and the second positive A layer 20. It has an adhesive layer (30, 40) between the two.

In the present specification, "linearly polarized light incident on XX at an incident angle of YY degrees" means "linearly polarized light incident on a direction deviated by YY degrees from the normal direction of XX".
Further, in the present specification, the "region having a width of 10 degrees" means a region of "x to x + 10 degrees" when the reference angle is x degrees. For example, when the reference angle is 40 degrees, it means a region of 40 to 50 degrees.
Further, in the present specification, "the incident angle α satisfies" xxx "in at least one region having a width of 10 degrees selected from the range of 30 to 60 degrees" means that the incident angle α is 30 to 60 degrees. The condition may be satisfied if "xxx" is satisfied in at least one 10-degree width region within the range of degrees, and "xxx" may or may not be satisfied in the other 10-degree width regions. Means. For example, if "xxx" is satisfied in a 10 degree width of an incident angle of 40 to 50 degrees, it is not necessary to satisfy "xxx" in a 10 degree width of an incident angle of 30 to 40 degrees. In addition, "xxx" means various conditions related to the incident angle α in this specification.
As used herein, the term "positive A layer" refers to Nx as the refractive index in the slow axis direction in the plane, Ny as the refractive index in the direction orthogonal to the slow axis direction in the plane, and Ny as the refractive index in the thickness direction. When Nz is set, the relationship is Nx> Ny≈Nz.
In the present specification, the in-plane retardation (Re) has an in-plane refractive index in the slow axis direction as Nx, an in-plane refractive index in the direction orthogonal to Nx as Ny, and a film thickness as d (nm). In this case, it can be expressed by the following formula, and the unit is nm. Further, in the present specification, the in-plane phase difference (Re) means an in-plane phase difference in the front direction (an in-plane phase difference when light is vertically incident on the positive A layer) unless otherwise specified.
In-plane phase difference (Re) = (Nx-Ny) x d

<Condition 1>
Condition 1 is the spectral transmittance (incident light) of linearly polarized light in a wavelength range of any width of 120 nm or more of linearly polarized light (P-polarized light or S-polarized light) incident on a λ / 2 retardation plate at an incident angle of α degrees. In the case of P-polarized light, it is the spectral transmittance of P-polarized light, and when the incident light is S-polarized light, it is the spectral transmittance of S-polarized light.) It is stipulated that 2.0% or less is shown in one region having a width of 10 degrees.

Condition 1 stipulates that "the spectral transmittance of the linearly polarized light in an arbitrary wavelength range of 120 nm or more is 2.0% or less". This indicates that the conversion ratio of linearly polarized light by the λ / 2 retardation plate is good. That is, under condition 1, it means that when the incident light is S-polarized light, most of it is converted to P-polarized light, and when the incident light is P-polarized light, most of it is converted to S-polarized light. ..

Condition 1 defines the spectral transmittance of linearly polarized light in "a wavelength range having an arbitrary width of 120 nm or more". By improving the conversion ratio of linearly polarized light in such a wide wavelength range, performance can be improved and the degree of freedom in product design can be increased in various optical applications (reflective screens, sensors, etc.) described later. It can be done easily.
The wavelength region having an arbitrary width of 120 nm or more under Condition 1 may be located in the visible light region (380 to 780 nm) or may be located outside the visible light region. When condition 1 is satisfied in the wavelength range of visible light, it is preferable in that the color reproducibility of the reflection screen using the λ / 2 retardation plate can be improved.

As for the incident angle of linearly polarized light with respect to the λ / 2 retardation plate, there is an ideal incident angle according to the purpose of use of the λ / 2 retardation plate and the like. However, even if the incident angle of linearly polarized light with respect to the λ / 2 retardation plate is completely matched to the ideal angle, the incident angle may fluctuate due to environmental factors such as vibration. Further, if the ideal incident angle is too narrow, it is necessary to have a specific arrangement relationship between the λ / 2 retardation plate and the light source, which limits the degree of freedom in product design. That is, in condition 1, "the incident angle α is selected from the range of 30 to 60 degrees as" at least one region having a width of 10 degrees "" is defined as the incident angle due to the influence of the above-mentioned environmental factors. It means that there is no problem even if it goes back and forth a little, and that the degree of freedom in product design is not restricted. In order to make the effect better, it is preferable to satisfy the same conditions as the condition 1 in the "at least one 15 degree wide region", and the same as the condition 1 in the "at least one 20 degree wide region". It is more preferable to satisfy the conditions.

The wider the "wavelength range having an arbitrary width of 120 nm or more" satisfying the condition 1, the more preferable. Specifically, the width of an arbitrary wavelength region satisfying condition 1 is preferably 130 nm or more, more preferably 150 nm or more, and even more preferably 160 nm or more. However, it is difficult to satisfy Condition 1 over a wide range. The upper limit of the width of an arbitrary wavelength range satisfying condition 1 is about 300 nm or less, preferably 250 nm or less, and more preferably 200 nm or less.

The spectral transmittance defined in Condition 1 is preferably 1.7% or less, and more preferably 1.5% or less. The lower the spectral transmittance defined in Condition 1, the more preferable.

The λ / 2 retardation plate may satisfy condition 1 when the incident light is at least one of P-polarized light and S-polarized light.
Considering a reflective screen, which is an example of the use of the λ / 2 retardation plate, it is preferable that condition 1 is satisfied when the incident light is S-polarized light. When S-polarized light is projected as incident light on a λ / 2 retardation plate (reflection screen) that satisfies condition 1 when the incident light is S-polarized light, it is reflected on the surface of the λ / 2 retardation plate (reflection screen). The image can be visually recognized by the S-polarized light, and the S-polarized light that has entered the inside without being reflected on the surface of the λ / 2 retardation plate (reflection screen) is converted to P-polarized light and the interfacial reflectance is lowered. Therefore, the double image can be suppressed.
In the λ / 2 retardation plate, P-polarized light is converted to S-polarized light, and S-polarized light is converted to P-polarized light. From the viewpoint of Brewster's angle, P-polarized light is less likely to be reflected at the interface and more easily transmitted than S-polarized light, but since linearly polarized light is converted as described above, when the same λ / 2 retardation plate is used, , The difference in spectral transmittance is a slight difference regardless of the type of linearly polarized light of the incident light. Therefore, when the same λ / 2 retardation plate is used, either straight can be obtained by arranging the λ / 2 retardation plate at an appropriate angle according to the type of incident linearly polarized light (P-polarized light or S-polarized light). If the polarized light satisfies the condition 1, the other linearly polarized light often satisfies the condition 1.

In order to easily satisfy the condition 1, it is preferable that the slow axis of the first positive A layer and the slow axis of the second positive A layer are arranged so as to intersect with each other. Further, the slow axis of the first positive A layer preferably forms a predetermined angle (θ1) with a direction (D2) orthogonal to the horizontal direction in the plane of the λ / 2 retardation plate, and similarly. The slow axis of the second positive A layer preferably forms a predetermined angle (θ2) with D2. The preferable angles of θ1 and θ2 will be described later.
Further, in order to easily satisfy the condition 1, it is preferable that the phase difference of the first positive A layer and the phase difference of the second positive A layer are different. For example, it is preferable to satisfy the relationship of "Re1 (λc)> Re2 (λc)" or "Re1 (550)> Re2 (550)" described later.
Further, in order to easily satisfy the condition 1, it is preferable to reduce the difference in refractive index between the layers adjacent to each other constituting the λ / 2 retardation plate.

The conversion ratio of linearly polarized light that has penetrated into the λ / 2 retardation plate for each wavelength can be simulated by the following steps (1) and (2).
(1) The in-plane phase difference Re1 (α) of the first positive A layer at the incident angle α degree and the in-plane phase difference Re2 (α) of the second positive A layer at the incident angle α degree are set for each wavelength. calculate.
(2) Linearly polarized light that has passed through the first positive A layer and the second positive A layer in consideration of Re1 (α) and Re2 (α) calculated in (1) above and θ1 and θ2 described later. Verify which coordinates of the Poincare sphere are converted to.

In the above step (1), the in-plane phase difference Re (α) of the positive A layer at the incident angle α degree can be calculated by the following formula (i). In the following equation, Re (0) means the in-plane phase difference of the positive A layer having an incident angle of 0 degrees. Further, θ means any of θ1 and θ2 described later.

FIG. 2 is a diagram showing the spectral transmittance of S-polarized light when S-polarized light is incident on the λ / 2 retardation plates of Examples 1 and 2 and Comparative Examples 1 and 2 at an incident angle of 55 degrees. FIG. 3 is a diagram showing the spectral transmittance of S-polarized light when S-polarized light is incident on the λ / 2 retardation plates of Examples 1 and 2 and Comparative Examples 1 and 2 at an incident angle of 45 degrees. In FIGS. 2 and 3, the solid line indicates Example 1, the alternate long and short dash line indicates Example 2, the dashed line with a wide pitch indicates Comparative Example 1, and the dashed line with a narrow pitch indicates Comparative Example 2.
From FIGS. 2 and 3, the λ / 2 retardation plate of Examples 1 and 2 has a wavelength width of an arbitrary width of 120 nm or more in a region having a width of 10 degrees from an incident angle of 45 degrees to an incident angle of 55 degrees. (Common to FIGS. 2 and 3, in the example, the spectral transmittance is 2.0% or less in the wavelength range from 430 nm to 580 nm. There is.)

In one embodiment of the λ / 2 retardation plate of the present invention, the central wavelength of an arbitrary wavelength region having a width of 120 nm or more satisfying the above condition 1 is λc [nm], and the wavelength λc [nm] of the first positive A layer is set. ], The in-plane phase difference at the wavelength λc [nm] of the second positive A layer is defined as Re1 (λc), and Re1 (λc)> Re2 (λc). Is preferable.
By setting Re1 (λc)> Re2 (λc), the condition 1 can be easily satisfied. The preferable range of "Re1 (λc) -Re2 (λc)" cannot be unequivocally determined because it depends on the value of λc [nm].
When λc is located in the wavelength of 500 to 600 nm, “Re1 (λc) −Re2 (λc)” is preferably 20 to 80 nm, more preferably 40 to 60 nm.
The values of Re1 (λc) and Re2 (λc) can be adjusted by values before and after 1/2 of λc [nm].

As one embodiment of the λ / 2 retardation plate of the present invention, it is preferable that the central wavelength λc of an arbitrary wavelength region having a width of 120 nm or more that satisfies the above condition 1 is located within the wavelength of 500 to 600 nm, and the wavelength 505. It is more preferably located in the wavelength range of ~ 570 nm, and further preferably located in the wavelength range of 510 to 560 nm.
The fact that λc is located in the wavelength range of 500 to 600 nm means that λc is located in the wavelength range where human visual sensitivity is high. For example, when condition 1 is satisfied when the incident light is S-polarized light, a λ / 2 retardation plate in which λc is located in a wavelength of 500 to 600 nm is used as the reflection screen, and S-polarized light is used as the incident light, λ / The image can be visually recognized by the S-polarized light reflected on the surface of the two-phase difference plate (reflection screen), and the S-polarized light that has penetrated into the λ / 2 retardation plate (reflection screen) is converted to P-polarized light and interfacially reflected. Since the rate is reduced, the double image can be suppressed.

As one embodiment of the λ / 2 retardation plate of the present invention, the in-plane retardation of the first positive A layer at a wavelength of 550 nm is set to Re1 (550), and the in-plane position of the second positive A layer at a wavelength of 550 nm. When the phase difference is defined as Re2 (550), it is preferable that Re1 (550) is 280 to 320 nm, Re2 (550) is 230 to 270 nm, and Re1 (550)> Re2 (550). ..
By having this configuration, it is possible to easily satisfy the condition 1 in the wavelength region where the human visual sensitivity is high. With this configuration, either the first positive A layer or the second positive A layer may be located on the light incident surface side.
In this configuration, Re1 (550) is more preferably 285-310 nm, further preferably 290-300 nm. Further, in the configuration, Re2 (550) is more preferably 235 to 260 nm, and further preferably 240 to 250 nm. Further, in the configuration, "Re1 (550) -Re2 (550)" is more preferably 20 to 80 nm, and further preferably 30 to 70 nm.

Conventionally, in order to increase the conversion ratio of linearly polarized light in the wavelength region where human visual sensitivity is high, a λ / 2 retardation plate in which two positive A layers having an in-plane retardation of 270 nm of 550 nm are laminated has been used. However, in the conventional λ / 2 retardation plate, the conversion ratio of linearly polarized light is significantly reduced when the incident light is oblique (see Comparative Example 2). By setting Re1 (550) and Re1 (550) to different values as in the above-described embodiment of the λ / 2 retardation plate of the present invention, the condition 1 can be set in the wavelength range where human visual sensitivity is high. It can be made easier to fill. The same applies when increasing the conversion ratio of linearly polarized light in other wavelength regions. In the case of other wavelength ranges, it is preferable that Re1 (λc) and Re1 (λc) have different values.

As one embodiment of the λ / 2 retardation plate of the present invention, the horizontal direction in the plane of the λ / 2 retardation plate is D1, and the direction orthogonal to the horizontal direction in the plane of the λ / 2 retardation plate is defined as D1. When defined as D2, the angle formed by the slow axis of the first positive A layer and D2 is defined as θ1, and the angle formed by the slow axis of the second positive A layer and D2 is defined as θ2. In addition, it is preferable that θ1 and θ2 satisfy any combination of (A1) to (A4) shown in the following condition 2-1.
<Condition 2-1>
(A1) θ1 is 12.5 to 27.5 degrees, θ2 is 57.5 to 72.5 degrees, and (A2) θ1 is 57.5 to 72.5 degrees, and θ2 is 12.5 to 27. 5 degrees (A3) θ1 is -12.5 to -27.5 degrees, θ2 is -57.5 to -72.5 degrees (A4) θ1 is -57.5 to -72.5 degrees, and θ2 is -12.5 to -27.5 degrees

The horizontal direction means a direction orthogonal to the direction of the azimuth angle of the incident light when the λ / 2 retardation plate is used as a reference. In the embodiment described later, when the direction parallel to the ground is set to an azimuth angle of 0 degrees, light is incident on the λ / 2 retardation plate from the direction of the azimuth angle of 90 degrees. That is, in the examples described later, the horizontal direction is a direction parallel to the ground.
In condition 2-1 which of the first positive A layer and the second positive A layer may be located on the light incident surface side.
In condition 2-1, when the slow axis exists in the clockwise direction with respect to D2, the angle formed is "+", and when the slow axis exists in the counterclockwise direction with respect to D2, the angle is formed. The angle formed is "-".

By satisfying the condition 2-1, it is possible to easily satisfy the condition 1. As a premise of condition 2-1 the first positive A layer and the second positive A layer satisfy the relationship of Re1 (λc)> Re2 (λc) or Re1 (550)> Re2 (550). Is preferable.
With respect to condition 2-1 it is more preferable that θ1 and θ2 satisfy any combination of (A5) to (A8).
(A5) θ1 is 15.5 to 17.5 degrees, θ2 is 59.0 to 61.0 degrees, and (A6) θ1 is 59.0 to 61.0 degrees, and θ2 is 15.5 to 17. 5 degrees (A7) θ1 is -15.55 to -17.5 degrees, θ2 is -59.0 to -61.0 degrees (A8) θ1 is -59.0 to -61.0 degrees, and θ2 is -15.5--17.5 degrees

<Positive A layer>
In the positive A layer, when the refractive index in the slow-phase axial direction in the plane is Nx, the refractive index in the in-plane direction orthogonal to the slow-phase axial direction is Ny, and the refractive index in the thickness direction is Nz, Nx> Ny. The relationship is ≈Nz.

From the viewpoint of versatility, it is preferable to use a positive A layer that exhibits positive dispersibility.
The positive dispersibility is a wavelength dispersion characteristic in which the phase difference in transmitted light is larger toward the shorter wavelength side.

The main component of the positive A layer is preferably a structural unit derived from a liquid crystal compound. Therefore, it is preferable that both the first positive A layer and the second positive A layer contain a structural unit derived from a liquid crystal compound. The main component means that the total solid content of the positive A layer is 50% by mass or more, and preferably 70% by mass or more.

The liquid crystal compound forming the positive A layer preferably contains a polymerizable liquid crystal compound having a polymerizable functional group in the molecule. By having a polymerizable functional group, it becomes possible to polymerize and fix the liquid crystal compound, so that the arrangement stability is excellent and the phase difference property with time is less likely to change. Further, it is more preferable that the polymerizable liquid crystal compound has two or more polymerizable functional groups in the molecule. By having two or more polymerizable functional groups, the three-dimensional orientation of the liquid crystal compound can be made more stable.
Examples of the polymerizable functional group include those that polymerize by the action of ultraviolet rays, ionizing radiation such as an electron beam, or heat. Examples of these polymerizable functional groups include radically polymerizable functional groups. Representative examples of the radically polymerizable functional group include a functional group having at least one addition-polymerizable ethylenically unsaturated double bond, and specific examples thereof include a vinyl group and an acrylate group having or not having a substituent. (A generic term including an acryloyl group, a methacryloyl group, an acryloyloxy group, and a methacryloyloxy group) and the like.
Further, as the polymerizable functional group, a generally known cationically polymerizable functional group may be used, and specifically, an alicyclic ether group (epoxy group, oxetanyl group, etc.), a cyclic acetal group, etc. Examples thereof include a cyclic lactone group, a cyclic iminoether group, a cyclic thioether group, a spirolethoester group, a vinyloxy group and the like. Among these, an alicyclic ether group and a vinyloxy group are preferable, and an epoxy group, an oxetanyl group and a vinyloxy group are more preferable.

Further, the liquid crystal compound is particularly preferably one having a polymerizable functional group at the terminal. By using such a liquid crystal compound, for example, the ends of the liquid crystal compound can be polymerized with each other to form a three-dimensionally oriented state, so that the liquid crystal compound has stability and exhibits optical characteristics. It can be an excellent retardation layer. The liquid crystal compound may be used alone or in combination of two or more.

The liquid crystal compound may be used alone or in combination of two or more. In the case of one type alone, the one type of liquid crystal compound is preferably a polymerizable liquid crystal compound. When two or more kinds are used in combination, it is preferable that at least one kind is a polymerizable liquid crystal compound, and it is more preferable that all of them are polymerizable liquid crystal compounds.

For the positive A layer, it is preferable to form the positive A layer using a liquid crystal compound that is homogenically oriented. The molecular orientation means a state in which the molecular major axis of the liquid crystal compound is oriented in the horizontal direction. The positive A layer preferably exhibits a smectic phase. Here, the smectic phase refers to a state in which molecules aligned in one direction have a phase structure.

Examples of the positive A layer liquid crystal compound include a disk-shaped liquid crystal material (discotic liquid crystal material) and a rod-shaped liquid crystal material.
As the liquid crystal compound of the positive A layer, a general-purpose material can be used. For example, a compound represented by the general formula (I) described in JP-A-2008-297210, and a compound represented by the general formula (I) described in JP-A-2010-84032 can be used. Examples thereof include the compound represented by the formula (1), the liquid crystal compound A0 described in JP-A-2016-53709, and the like. As the liquid crystal compound of the positive A layer, the compounds represented by the following formulas (1) to (17) can also be used.

The positive A layer can be formed, for example, by applying, drying, curing, or the like, an ink for forming a positive A layer containing a component and a solvent constituting the positive A layer on a transparent base material.
The content of the liquid crystal compound in the positive A layer forming ink is not particularly limited, but is preferably contained in the ink in a proportion of 5% by mass or more and 40% by mass or less, and 10% by mass or more and 30% by mass or more. It is more preferable that it is contained in a proportion of% or less. If the amount of the liquid crystal compound is less than 5% by mass, it is necessary to apply a large amount of ink on the transparent base material, which makes it difficult to manufacture and requires removal of a large amount of solvent. Deterioration is likely to occur. On the other hand, if it exceeds 40% by mass, the viscosity of the polymerizable liquid crystal composition becomes too high, so that the workability of producing the positive A layer deteriorates.
The content of the liquid crystal compound with respect to the solid content mass (mass excluding the solvent) of the positive A layer forming ink is preferably 75 to 99.9% by mass, more preferably 80 to 99% by mass, and further preferably 85. ~ 98% by mass.

The positive A layer forming ink may contain a polymerization initiator, a leveling agent, an orientation accelerator and the like.
The thickness of the first positive A layer and the second positive A layer can be appropriately adjusted in consideration of the applied retardation value, and is usually about 0.1 to 10 μm.

<Transparent base material>
One embodiment of the λ / 2 retardation plate of the present invention preferably has a transparent substrate. Further, in one embodiment of the λ / 2 retardation plate of the present invention, the first positive A layer and the second positive A layer are sandwiched between the first transparent base material and the second transparent base material. It is more preferable to have.
The transparent base material has a role as a support when forming the positive A layer or the like, a role of protecting the positive A layer or the like, or the like.

The transparent substrate may be formed of a polymer or glass.
Examples of the polymer include cellulose acylate, polycarbonate polymer, polyester polymer such as polyethylene terephthalate and polyethylene naphthalate, acrylic polymer such as polymethyl methacrylate, and styrene polymer such as polystyrene and acrylonitrile / styrene copolymer (AS resin). Etc. can be used. Further, polyolefins such as polyethylene and polypropylene, polyolefin polymers such as ethylene / propylene copolymers, vinyl chloride polymers, amide polymers such as nylon and aromatic polyamides, imide polymers, sulfone polymers, and polyether sulfone polymers. , Polyether ether ketone polymer, polyphenylene sulfide polymer, vinylidene chloride polymer, vinyl alcohol polymer, vinyl butyral polymer, allylate polymer, polyoxymethylene polymer, epoxy polymer, or a mixture of these polymers. Be done.
Examples of the glass include soda-lime glass, borosilicate glass and quartz glass.

The transparent substrate is preferably optically isotropic. In the present specification, the optical isotropic property means that the in-plane phase difference at 550 nm is 5 nm or less.

In one embodiment of the λ / 2 retardation plate of the present invention, as described above, between the first transparent base material and the second transparent base material, the first positive A layer and the second transparent base material It is preferable to have a positive A layer. At that time, the first transparent base material and the second transparent base material may be the same or different. For example, when the refractive index of the first transparent base material is n1 and the refractive index of the second transparent base material is n2, the relationship may be n1 = n2 or n1 ≠ n2. Good. Further, in the case of the relationship of n1 ≠ n2, the light incident is performed by using the one having the higher refractive index among the first transparent base material and the second transparent base material so as to be on the light incident surface side of linearly polarized light. While increasing the reflectance on the surface side, the reflectance on the exit side interface can be lowered, and the visibility of the reflective screen can be improved.

When a λ / 2 retardation plate having a first positive A layer and a second positive A layer between the first transparent base material and the second transparent base material is used as a reflection screen, the light incident surface side. The refractive index of the transparent substrate of No. 1 is preferably 1.1 to 1.9, more preferably 1.3 to 1.7. Further, in this case, the refractive index of the transparent base material on the light emitting surface side may be the same as the refractive index of the transparent base material on the light incident surface side, but is less than the refractive index of the transparent base material on the light incident surface side. Is preferable.

The thickness of the transparent base material is usually about 25 to 125 μm in the case of a transparent base material formed of a polymer, and usually about 100 μm to 5 mm in the case of a transparent base material formed of glass.

<Other layers>
One embodiment of the λ / 2 retardation plate of the present invention may have other layers.
Examples of other layers include an alignment film for facilitating the orientation of the positive A layer, an ultraviolet absorbing layer, an intermediate film, an adhesive layer, and the like. The interlayer film is a layer formed to impart impact resistance, anti-scattering property, etc. to the λ / 2 retardation plate, and can be formed from, for example, polyvinyl butyral or the like.
In order to easily satisfy the condition 1, it is preferable to reduce the difference in refractive index between the layers adjacent to each other constituting the λ / 2 retardation plate. The other layers are preferably optically isotropic.

<Optical characteristics>
In one embodiment of the λ / 2 retardation plate of the present invention, the total light transmittance measured in accordance with JIS K7361-1: 1997 is preferably 60% or more, and more preferably 70% or more. It is preferably 80% or more, and more preferably 80% or more. Therefore, it is preferable that the λ / 2 retardation plate of the present invention does not have a polarizer.
Further, in one embodiment of the λ / 2 retardation plate of the present invention, the haze measured in accordance with JIS K7136: 2000 is preferably 2.0% or less, and preferably 1.0% or less. More preferred.

The λ / 2 retardation plate of the present invention is, for example, a laminate 1 formed by forming a first positive A layer on a first transparent base material and a second positive A on a second transparent base material. It can be manufactured by laminating the laminated body 2 formed with a layer via an adhesive layer.

<Use>
The λ / 2 retardation plate of the present invention can be used, for example, as various optical products.
Examples of optical supplies include parts (linearly polarized light conversion members) incorporated in optical sensors, optical measuring instruments, optical pickup devices, liquid crystal projectors, and the like.
Another optical fixture is a reflective screen. When S-polarized light is projected as incident light on a λ / 2 retardation plate that satisfies condition 1 when the incident light is S-polarized light, the S-polarized light reflected on the surface of the λ / 2 retardation plate (reflection screen) The image can be visually recognized, and the S-polarized light that is not reflected by the surface of the λ / 2 retardation plate (reflection screen) and penetrates inside is converted to P-polarized light, which reduces the interfacial reflectance, resulting in a double image. Can be suppressed. When the λ / 2 retardation plate is used as the reflection screen, it is preferable that λc is located in the wavelength of 500 to 600 nm. A more specific example of a reflective screen is a head-up display.
Other optical supplies include polarizing filters such as polarized sunglasses and filters for cameras. The polarizing filter has a λ / 2 retardation plate of the present invention and a polarizer. Most of the reflected light incident on a polarizing filter such as polarized sunglasses is incident on the polarizing filter from an oblique direction, and the reflected light has a large proportion of S-polarized light. Therefore, the polarizing filter having the λ / 2 retardation plate of the present invention and the polarizer that cuts P-polarized light converts S-polarized light, which is abundantly contained in the reflected light, into P-polarized light by the λ / 2 retardation plate. While the P-polarized light is absorbed by the polarizer, the P-polarized light in the reflected light is converted into S-polarized light by the λ / 2 retardation plate and transmitted, so that the reflected light is cut off.

[Reflective projection system]
The reflection type projection system of the present invention comprises the above-mentioned λ / 2 retardation plate of the present invention and a light source.

The light source is not particularly limited. Examples of the light projected from the light source include non-polarized light, linearly polarized light, and circularly polarized light.
Examples of the light source capable of projecting linearly polarized light include a light source in which a polarizer is arranged on a display element such as an organic EL, and a liquid crystal projector. Examples of the light source capable of projecting circularly polarized light include a light source capable of projecting linearly polarized light with a retardation layer added.
When the light projected from the light source is other than linearly polarized light, a polarizer may be arranged between the λ / 2 retardation plate and the light source, converted to linearly polarized light, and then incident on the λ / 2 retardation plate.

Next, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" and "%" are based on mass.

1. 1. Fabrication of Laminated Body with Positive A Layer <Laminated Body 1>
An alignment film-forming composition (solid content 4%, propylene glycol monomethyl ether dilution) containing a polycinnamate compound was applied onto a PET film having a thickness of 80 μm to form a coating film. The obtained coating film was dried at 120 ° C. for 1 minute and ^{irradiated with polarized light exposure of 20 mJ / cm 2} (310 nm) to form an alignment film having a film thickness of 200 nm.
Next, an ink for forming a positive A layer having the following composition is applied on the alignment film with a bar coater, dried, and cured, and a PET film, an alignment film, and a positive A layer (first positive A layer) are laminated in this order. I got body 1. The drying conditions were a temperature of 120 ° C. and a time of 60 seconds. The curing condition (ultraviolet irradiation amount) was 200 mJ / cm ² . The thickness of the positive A layer (first positive A layer) of the laminated body 1 was adjusted so that Re (550) was 295 nm. The positive A layer (first positive A layer) showed positive dispersibility, and Re (450) / Re (550) was 1.09.
<Ink for forming positive A layer>
25% by mass of the liquid crystal compound represented by the above formula (11), 5% by mass of the photopolymerization initiator (manufactured by BASF, trade name: Irgacure 907), fluorine-based surfactant (manufactured by DIC, trade name: mega). A composition containing 0.4% by mass of Fuck F554) and the balance being a solvent (MEK: MIBK = 1: 1 mixed solvent).

<Laminated body 2>
The PET film, the alignment film, and the positive A layer (similar to the laminated body 1) except that the thickness of the positive A layer was changed and the Re (550) of the positive A layer (second positive A layer) was set to 245 nm. A laminated body 2 provided with the first positive A layer) in this order was obtained.

<Laminated body 3>
A laminate 3 having a PET film, an alignment film, and a positive A layer in this order was obtained in the same manner as the laminate 1 except that the thickness of the positive A layer was changed and Re (550) was set to 270 nm.

2. Fabrication of λ / 2 Phase Difference Plate [Example 1]
An acrylic pressure-sensitive adhesive layer (thickness 25 μm) having optical isotropic property is formed on a glass plate (refractive index 1.51) having a thickness of 1 mm having optical isotropic property, and further, an acrylic pressure-sensitive adhesive layer (thickness 25 μm) having optical isotropic property is formed on the pressure-sensitive adhesive layer. The surfaces of the laminate 1 on the positive A layer (first positive A layer) side were bonded together to obtain a laminate A.
The PET film and the alignment film of the laminate A were peeled off, and an acrylic pressure-sensitive adhesive layer (thickness 25 μm) having optical isotropic properties was formed on the peeled surface. Next, the surface of the laminate 2 on the positive A layer (second positive A layer) side was bonded onto the acrylic pressure-sensitive adhesive layer to obtain a laminate B.
The PET film and alignment film of the laminate B are peeled off, and on the peeled surface, an acrylic adhesive layer (thickness 25 μm) having optical isotropic property and a TAC film having optical isotropic property (sacination-treated product, A thickness of 80 μm) was laminated.
Through the above steps, a glass plate, an acrylic pressure-sensitive adhesive layer, a positive A layer (first positive A layer), an acrylic pressure-sensitive adhesive layer, a positive A layer (second positive A layer), an acrylic pressure-sensitive adhesive layer, A λ / 2 retardation plate (length 50 mm, width (horizontal direction) 50 mm) of Example 1 having a TAC film in this order was obtained. At this time, in the λ / 2 retardation plate of Example 1, θ1 was set to 16.5 degrees and θ2 was set to 60.0 degrees. When the horizontal direction in the plane of the λ / 2 retardation plate is defined as D1 and the direction orthogonal to the horizontal direction in the plane of the λ / 2 retardation plate is defined as D2, θ1 is the first positive. It means the angle formed by the slow axis of the A layer and D2, and θ2 means the angle formed by the slow axis of the second positive A layer and D2.

[Example 2]
A λ / 2 retardation plate of Example 2 was obtained in the same manner as in Example 1 except that θ1 was changed to 22.5 degrees and θ2 was changed to 67.5 degrees.

[Comparative Example 1]
An acrylic pressure-sensitive adhesive layer (thickness 25 μm) having optical isotropic property is formed on a glass plate (refractive index 1.51) having a thickness of 1 mm having optical isotropic property, and further, an acrylic pressure-sensitive adhesive layer (thickness 25 μm) having optical isotropic property is formed on the pressure-sensitive adhesive layer. The surfaces of the laminate 3 on the positive A layer side were bonded together to obtain a laminate C.
The PET film and alignment film of the laminate C are peeled off, and on the peeled surface, an acrylic adhesive layer (thickness 25 μm) having optical isotropic property and a TAC film having optical isotropic property (sacination-treated product, A thickness of 80 μm) was laminated.
By the above steps, the λ / 2 retardation plate of Comparative Example 1 having a glass plate, an acrylic pressure-sensitive adhesive layer, a positive A layer, an acrylic pressure-sensitive adhesive layer, and a TAC film in this order (length 50 mm, width (horizontal direction)) 50 mm) was obtained. At this time, the λ / 2 retardation plate of Comparative Example 1 has an angle formed by the slow axis of the positive A layer and D2 (the direction orthogonal to the horizontal direction in the plane of the λ / 2 retardation plate) of 45. It was set to 0 degrees.

[Comparative Example 2]
Two of the above laminated bodies 3 were prepared. One laminated body 3 is referred to as a laminated body 3i, and the other laminated body 3 is referred to as a laminated body 3ii. Further, the layer structure of the laminated body 3i is PET film i, the alignment film i and the positive A layer i, and the layer structure of the laminated body 3ii is the PET film ii, the alignment film ii and the positive A layer ii.
An acrylic pressure-sensitive adhesive layer (thickness 25 μm) having optical isotropic property is formed on a glass plate (refractive index 1.51) having a thickness of 1 mm having optical isotropic property, and further, an acrylic pressure-sensitive adhesive layer (thickness 25 μm) having optical isotropic property is formed on the pressure-sensitive adhesive layer. The surfaces of the laminated body 3i on the positive A layer i side were bonded together to obtain a laminated body A.
The PET film i and the alignment film i of the laminate A were peeled off, and an acrylic pressure-sensitive adhesive layer (thickness 25 μm) having optical isotropic properties was formed on the peeled surface. Next, the surface of the laminated body 3ii on the positive A layer ii side was bonded onto the acrylic pressure-sensitive adhesive layer to obtain a laminated body B.
The PET film ii and the alignment film ii of the laminate B are peeled off, and an acrylic pressure-sensitive adhesive layer (thickness 25 μm) having optical isotropic property and a TAC film having optical isotropic property (sacination treatment) are peeled off on the peeled surface. The product, thickness 80 μm) was laminated.
By the above steps, λ / 2 of Comparative Example 1 having a glass plate, an acrylic pressure-sensitive adhesive layer, a positive A layer i, an acrylic pressure-sensitive adhesive layer, a positive A layer ii, an acrylic pressure-sensitive adhesive layer, and a TAC film in this order. A retardation plate (length 50 mm, width (horizontal direction) 50 mm) was obtained. At this time, the λ / 2 retardation plate of Comparative Example 2 has an angle formed by the slow axis of the positive A layer i and D2 (the direction orthogonal to the horizontal direction in the plane of the λ / 2 retardation plate) of 22. At 5.5 degrees, the angle formed by the slow axis of the positive A layer ii and D2 (the direction orthogonal to the horizontal direction in the plane of the λ / 2 retardation plate) was set to 67.5 degrees.

3. 3. Measurement and evaluation 3-1. Spectral Transmittance S-polarized light was incident on the λ / 2 retardation plates of Examples and Comparative Examples at a predetermined angle of incidence, and the spectral transmittance of S-polarized light was measured. The λ / 2 retardation plate was arranged so that the lateral direction (horizontal direction) of the λ / 2 retardation plate was parallel to the ground. The spectral transmittance was measured using V7100 manufactured by JASCO Corporation. The angle of incidence was changed every 10 degrees in the range of 5 to 55 degrees. The results are shown in FIGS. 2-7. Table 1 shows the wavelength widths at which the spectral transmittance is 2.0% or less at each incident angle.

3-2. The total light transmittance (JISK7361-1: 1997) of the λ / 2 retardation plates of Examples and Comparative Examples was measured using a total light transmittance haze meter (HM-150, manufactured by Murakami Color Technology Research Institute). Those having a total light transmittance of 60% or more were designated as "A", and those having a total light transmittance of less than 60% were designated as "C".

3-3. Duplex image Image light using S-polarized light as a light source was incident on the λ / 2 retardation plates of Examples and Comparative Examples at an incident angle of 45 degrees, and was visually observed from the positional relationship shown in FIG. The one that does not bother the double image is designated as "A", and the one that does not care about the double image is designated as "C". The results are shown in Table 1.

From the results of FIGS. 2 to 7 and Table 1, the λ / 2 retardation plate of the embodiment has a wide wavelength range of 120 nm or more in at least one 10-degree width region in which the incident angle of 30 to 60 degrees is large. It can be confirmed that the conversion ratio of linearly polarized light can be improved. Further, since the λ / 2 retardation plate of the embodiment exerts the above-mentioned effect in the wavelength range of visible light, the reflection screen using the λ / 2 retardation plate of the embodiment can improve the color reproducibility. is there. Further, from the results of FIGS. 2 to 7 and Table 1, the λ / 2 retardation plate of the embodiment produces a double image at an incident angle of 45 degrees, which is the center of the incident angle of 30 to 60 degrees, which exerts the above-mentioned effect. It can be confirmed that this can be suppressed.

10: First positive A layer 20: Second positive A layer 30, 40: Adhesive layer 50: First transparent base material 60: Second transparent base material 100: λ / 2 retardation plate 200: Light source

Claims (10)

λ / 2 retardation plate
The λ / 2 retardation plate has a first positive A layer and a second positive A layer, and has a slow axis of the first positive A layer and a slow axis of the second positive A layer. Crossed with
A λ / 2 retardation plate that satisfies the following condition 1.
<Condition 1>
The spectral transmittance of the linearly polarized light in the wavelength range of any width of 120 nm or more of the linearly polarized light incident on the λ / 2 retardation plate at an incident angle α degree is within the range of an incident angle α of 30 to 60 degrees. Shows 2.0% or less in at least one 10 degree wide region selected from. The central wavelength of an arbitrary wavelength region having a width of 120 nm or more satisfying the above condition 1 is λc [nm], the in-plane phase difference at the wavelength λc [nm] of the first positive A layer is Re1 (λc), and the second. The λ / 2 retardation plate according to claim 1, wherein Re1 (λc)> Re2 (λc) when the in-plane phase difference at the wavelength λc [nm] of the positive A layer is defined as Re2 (λc). .. The λ / 2 retardation plate according to claim 1 or 2, wherein the central wavelength λc in an arbitrary wavelength region having a width of 120 nm or more that satisfies the above condition 1 is located within a wavelength of 500 to 600 nm. When the in-plane retardation of the first positive A layer at a wavelength of 550 nm is defined as Re1 (550) and the in-plane retardation of the second positive A layer at a wavelength of 550 nm is defined as Re2 (550), the Re1 ( The λ / 2 position according to any one of claims 1 to 3, wherein 550) is 280 to 320 nm, Re2 (550) is 230 to 270 nm, and Re1 (550)> Re2 (550). Phase difference plate. The horizontal direction in the plane of the λ / 2 retardation plate is defined as D1, the direction orthogonal to the horizontal direction in the plane of the λ / 2 retardation plate is defined as D2, and further, the first positive A layer. When the angle formed by the slow axis and D2 is defined as θ1 and the angle formed by the slow axis of the second positive A layer and D2 is defined as θ2, θ1 and θ2 are shown in the following condition 2-1 (A1). ) To (A4), the λ / 2 retardation plate according to any one of claims 1 to 4.
<Condition 2-1>
(A1) θ1 is 12.5 to 27.5 degrees, θ2 is 57.5 to 72.5 degrees, and (A2) θ1 is 57.5 to 72.5 degrees, and θ2 is 12.5 to 27. 5 degrees (A3) θ1 is -12.5 to -27.5 degrees, θ2 is -57.5 to -72.5 degrees (A4) θ1 is -57.5 to -72.5 degrees, and θ2 is -12.5 to -27.5 degrees The λ according to any one of claims 1 to 5, which has the first positive A layer and the second positive A layer between the first transparent base material and the second transparent base material. / 2 phase difference plate. The λ / 2 retardation plate according to any one of claims 1 to 6, wherein the linearly polarized light of the condition 1 is S-polarized light. An optical product comprising the λ / 2 retardation plate according to any one of claims 1 to 7. The optical article according to claim 8, which is a reflective screen. A reflection type projection system including a reflection screen including the λ / 2 retardation plate according to any one of claims 1 to 7 and a light source.