JP2003307622A - Polarizing element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarizing element having excellent optical characteristics and capable of enhancing contrast and securing satisfactory visibility when assembled in a liquid crystal display device and the like. <P>SOLUTION: When refractive indices of a cholesteric liquid crystal layer 11, a quarter-wave retardation plate 12 and an adhesive layer 13 are defined as n<SB>1</SB>, n<SB>2</SB>and n<SB>3</SB>, respectively, n<SB>1</SB>, n<SB>2</SB>and n<SB>3</SB>satisfy a relation n<SB>1</SB>≤n<SB>3</SB>≤n<SB>2</SB>or n<SB>2</SB>≤n<SB>3</SB>≤n<SB>1</SB>. Both the values of the refractive indices n<SB>2</SB>and n<SB>3</SB>are the values of average refractive indices. The value of the refractive index n<SB>1</SB>is obtained from an equation n<SB>1</SB>=n<SB>4</SB>×sinθ/sin(θ×b) based on θ×b and θ determined so that an equation λ=a×cos(θ×b) (wherein a and b are constants) is satisfied between θ and λ when an incident angle θ of light in changed, in measurement for detecting wavelength λ of reflected light when light made incident in the cholesteric liquid crystal layer 11 with the incident angle θ under an atmosphere of a refractive index n<SB>4</SB>is selectively reflected by the cholesteric liquid crystal layer 11, and the refractive index n<SB>4</SB>. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element used in a polarized light source device, a liquid crystal display device, etc.
The present invention relates to a polarizing element including a liquid crystal layer having a cholesteric phase (also referred to as “cholesteric liquid crystal layer”). Note that in this specification, the term “liquid crystal layer” is used to mean a layer having an optical property of liquid crystal, and the state of the layer includes a state of a liquid crystal phase having fluidity and a state of a liquid crystal phase. It also includes a solid phase state in which the molecular sequence is maintained and solidified.

[0002]

2. Description of the Related Art Most optical elements have a multilayer structure composed of a plurality of optical members, and interface reflection occurs due to the difference in refractive index between the optical members forming the optical member. Such interface reflection is effectively used in an antireflection film or the like incorporated in a display or the like, but in many cases, it causes a loss of light use efficiency and is not preferable. In particular, in the case of a polarizing element among optical elements, the polarization state of light transmitted or reflected by the polarizing element often changes due to interface reflection, and the deterioration of optical characteristics has been a problem.

Among such polarizing elements, a polarizing element having a cholesteric liquid crystal layer reflects one of right-handed and left-handed circularly polarized light components having a wavelength corresponding to the helical pitch of liquid crystal molecules and transmits the other. It has a selective reflection function.

However, such a polarizing element has a special characteristic that selective reflection is realized by Bragg reflection inside the cholesteric liquid crystal layer, and interface reflection of light incident on the cholesteric liquid crystal layer is realized. The impact was not fully considered.

In this regard, for example, Japanese Patent Laid-Open No. 9-189
Japanese Patent No. 811 describes that a cholesteric liquid crystal layer and a light guide plate are laminated via an adhesive layer to prevent reflection loss at each interface. In addition, JP-A-11-
In Japanese Patent No. 125717, 1 is formed on a cholesteric liquid crystal layer.
Regarding the refractive index of the adhesive layer used when laminating the / 4 wavelength plate, the brightness is improved and the unevenness of color is prevented by setting the refractive index of the adhesive layer to n ± 0.2 based on the average refractive index n of the cholesteric liquid crystal layer. It is described that prevention etc. can be achieved.

[0006]

However, in the polarizing element described in JP-A-9-189811, the relationship of the refractive index between the cholesteric liquid crystal layer and the adhesive layer is not sufficiently taken into consideration, It is difficult to sufficiently solve the above-mentioned problem of interface reflection.

Further, although the above-mentioned Japanese Patent Laid-Open No. 11-125717 describes the relationship of the refractive index between the cholesteric liquid crystal layer and the adhesive layer, the above-mentioned interface reflection can be achieved only by satisfying such a relationship. It has been empirically revealed that the above problem cannot be solved sufficiently.

Against this background, the present inventor has conducted earnest research on the relationship of the refractive index between the cholesteric liquid crystal layer, other optical layers adjacent to the cholesteric liquid crystal layer, and the adhesive layer for adhering them to each other. We have found an optimum method for obtaining the refractive index of the cholesteric liquid crystal layer, which is the basis of the conditions for suppressing the interface reflection that occurs between the liquid crystal layer and the optical layer adjacent to it, and we also found the cholesteric liquid crystal obtained by such a method. Based on the refractive index of the layer, by optimizing the refractive index relationship between the cholesteric liquid crystal layer, the adjacent optical layer and the adhesive layer provided between them, the above-mentioned problem of interface reflection It has been found that can be effectively suppressed.

The present invention has been made on the basis of such findings, and has excellent optical characteristics, and when incorporated into a liquid crystal display device or the like, it is possible to improve contrast and ensure good visibility. The purpose is to provide a device.

[0010]

In order to suppress interfacial reflection that occurs between a cholesteric liquid crystal layer and an optical layer such as a retardation layer adjacent to the cholesteric liquid crystal layer in a polarizing element provided with a cholesteric liquid crystal layer, which is a prerequisite of the present invention, , It is necessary to optimize the refractive index relationship between the cholesteric liquid crystal layer, the optical layers adjacent to the cholesteric liquid crystal layer, and the adhesive layer provided between them, if necessary.

At that time, the refractive index of the cholesteric liquid crystal layer, the optical layer such as a retardation layer adjacent to the cholesteric liquid crystal layer, and the adhesive layer is generally the average refractive index. According to such an idea, the refractive index of the optical layer such as the retardation layer and the adhesive layer has no problem, and the refractive index of the cholesteric liquid crystal layer has been conventionally considered to have no problem.

That is, since liquid crystal molecules generally have a helical structure in the cholesteric liquid crystal layer, its refractive index was considered to be equal to the average refractive index of the isotropic phase of the liquid crystal molecules when averaged in the thickness direction. . Note that the “average refractive index” referred to here is in the three-dimensional Cartesian coordinate system xyz,
It is represented by (n _x + n _y + n _z ) / 3.

However, according to the research conducted by the present inventor,
It has been clarified that the refractive index of the cholesteric liquid crystal layer actually has a value considerably different from that of the average refractive index.

FIG. 6 is a plot diagram showing the result of simulation for confirming the refractive index of the cholesteric liquid crystal layer. Here, the following simulation was performed using LCDMaster (manufactured by Shintech Co., Ltd.), which is general-purpose simulation software. That is,
Right circularly polarized light of a perfect circle having a central wavelength of 520 nm is vertically incident on a semi-transparent cholesteric liquid crystal layer having a central selective reflection wavelength of 520 nm with respect to right circularly polarized light, and transmitted through the cholesteric liquid crystal layer. A simulation was conducted to investigate the ellipticity of the circularly polarized light coming in. Here, of the right circularly polarized light incident on the cholesteric liquid crystal layer,
Part of the light is reflected inside the cholesteric liquid crystal layer and emerges from the surface on the incident side, while the rest passes through the cholesteric liquid crystal layer and emerges from the surface on the emission side. At this time, if the interface reflection does not occur on the incident side surface, the light emitted from the incident side surface is directly emitted to the outside. However, if interface reflection occurs on the incident-side surface, the interface-reflected light is output with the optical rotation direction reversed (that is, right circularly polarized light converted to left circularly polarized light). The light is transmitted through the cholesteric liquid crystal layer and is emitted to the outside together with the right circularly polarized light emitted from the surface on the emission side. Therefore, the light that finally emerges from the surface on the output side becomes right elliptically polarized light in which right circularly polarized light and left circularly polarized light are mixed, and its ellipticity depends on the ratio of the light reflected at the interface (left circularly polarized light). It will change.

The horizontal axis of FIG. 6 is the refractive index of the atmosphere in which the cholesteric liquid crystal layer is placed, and the vertical axis is the ellipticity of circularly polarized light that passes through the cholesteric liquid crystal layer. Here, as is clear from the above description, the large ellipticity of circularly polarized light means that the circularly polarized light is close to a perfect circle. Here, the fact that circularly polarized light is close to a perfect circle means that the effect of interfacial reflection is small, that is, that the refractive index of the cholesteric liquid crystal layer and the refractive index of the atmosphere are closer to each other. It is estimated that the refractive index of the atmosphere when the ellipticity of is largest is equal to the refractive index of the cholesteric liquid crystal layer. According to the results shown in FIG. 6, the value of the refractive index of the atmosphere is 1.585 when the ellipticity of the circularly polarized light that passes through the cholesteric liquid crystal layer is closest to 1.
The value of the refractive index of the cholesteric liquid crystal layer is also estimated to be 1.585. On the other hand, the value of the average refractive index of the cholesteric liquid crystal layer having the central selective reflection wavelength of 520 nm is 1.563.

Although the above description is based on the result of the simulation, when an actual experiment was performed using a cholesteric polymer film having the same characteristics as the cholesteric liquid crystal layer set in the above-mentioned simulation, the same result was obtained. Results were obtained.

Solution to Problem Under the above-mentioned premise, the present invention provides, as a first solution, a cholesteric liquid crystal layer having a cholesteric regularity having a spiral axis in the thickness direction and a cholesteric liquid crystal layer adjacent to the cholesteric liquid crystal layer. An optical layer arranged as described above, and an adhesive layer that is disposed between the cholesteric liquid crystal layer and the optical layer, and that adheres the cholesteric liquid crystal layer and the optical layer to each other, the cholesteric liquid crystal layer, the optical layer And the refractive index of the adhesive layer is n ₁ , n ₂ and n ₃ , respectively, these are n ₁ ≦ n ₃ ≦ n ₂ or n
₂ ≦ n ₃ ≦ n ₁ (1) is satisfied, and the refractive index n _{2 of the} optical layer and the refractive index n ₃ of the adhesive layer are both values of the average refractive index and the refractive index of the cholesteric liquid crystal layer. n ₁ is a value obtained by the following method, that is, when light incident on the cholesteric liquid crystal layer at an incident angle θ in an atmosphere having a refractive index n ₄ is selectively reflected by the cholesteric liquid crystal layer. In the measurement for detecting the wavelength λ of the reflected light, λ = a × cos (θ × b) (where a and b are constants) is between θ and λ when the incident angle θ of the light is changed. Based on θ × b, θ determined so as to hold and n ₄ above, n ₁ = n ₄ × sin θ / sin (θ ×
There is provided a polarizing element having the value obtained in b).

In the above first solution,
Refractive index n of the adhesive layer_ThreeThe value of is (n ₁+ N_Two) / 2 based
It is preferable that the range is ± 0.05. Well
Further, the cholesteric liquid crystal layer has a circular polarization in one optical rotation direction.
A semi-transmissive layer that reflects part of the light component and transmits the rest
And the optical layer and the adhesive layer are the cholesteric
It is preferably located on the light incident side with respect to the liquid crystal layer.
Good The term "semi-transmissive" as used in the present specification refers to one of
To partially reflect / transmit the circularly polarized light component in the optical rotation direction
Yes, the reflection / transmission ratio can be any value (eg reflection
The ratio of light can be 1% to 99.5%).
Wear.

Further, in the above-mentioned first solving means,
The optical layer is preferably a retardation layer, and more preferably an absorption type linear polarization layer is laminated on the retardation layer. Here, the retardation layer is a ¼ wavelength retardation layer disposed adjacent to the cholesteric liquid crystal layer, and a ½ wavelength retardation layer laminated on the ¼ wavelength retardation layer.
It is preferable that the refractive index of the cholesteric liquid crystal layer, the quarter-wave retardation layer and the adhesive layer adjacent to the cholesteric liquid crystal layer including the wavelength retardation layer satisfy the relationship of the above expression (1). The retardation layer includes a ½ wavelength retardation layer disposed adjacent to the cholesteric liquid crystal layer, and a ¼ wavelength retardation layer laminated on the ½ wavelength retardation layer. The refractive index of the cholesteric liquid crystal layer, the half-wave retardation layer and the adhesive layer adjacent to the cholesteric liquid crystal layer may satisfy the relationship of the above expression (1). The optical layer is preferably a transparent member.

As a second means for solving the problems, the present invention comprises a cholesteric liquid crystal layer having a cholesteric regularity having a spiral axis in the thickness direction, and an optical layer arranged so as to be in direct contact with the cholesteric liquid crystal layer. , The refractive index n ₁ of the cholesteric liquid crystal layer and the refractive index n _{2 of the} optical layer
Are substantially equal to each other, the refractive index n ₂ of the optical layer is a value of an average refractive index, and the refractive index n ₂ of the cholesteric liquid crystal layer is
₁ is a value obtained by the following method, that is, reflection when light incident on the cholesteric liquid crystal layer at an incident angle θ in an atmosphere having a refractive index n ₄ is selectively reflected by the cholesteric liquid crystal layer. In the measurement for detecting the wavelength λ of light, λ = a × cos (θ × b) (where a and b are constants) is established between θ and λ when the incident angle θ of light is changed. Based on θ × b, θ determined as above, and n ₄ above, n ₁ = n ₄ × sin θ / sin (θ ×
There is provided a polarizing element having the value obtained in b).

In the above-mentioned second solving means,
The cholesteric liquid crystal layer is a semi-transmissive layer that reflects a part of the circularly polarized light component in one optical rotation direction and transmits the rest, and the optical layer is arranged on the light incident side with respect to the cholesteric liquid crystal layer. It is preferable.

Further, in the above-mentioned second solving means,
The optical layer is preferably a retardation layer, and more preferably an absorption type linear polarization layer is laminated on the retardation layer. Here, the retardation layer is a ¼ wavelength retardation layer disposed adjacent to the cholesteric liquid crystal layer, and a ½ wavelength retardation layer laminated on the ¼ wavelength retardation layer.
It is preferable to include a wavelength retardation layer so that the refractive index of the cholesteric liquid crystal layer and the refractive index of the quarter wavelength retardation layer adjacent thereto are substantially equal to each other. The retardation layer includes a ½ wavelength retardation layer disposed adjacent to the cholesteric liquid crystal layer, and a ¼ wavelength retardation layer laminated on the ½ wavelength retardation layer. May be included so that the refractive index of the cholesteric liquid crystal layer and the refractive index of the half-wave retardation layer adjacent thereto are substantially equal to each other.
The optical layer is preferably a transparent member.

According to the first solution of the present invention,
The refractive index of the liquid crystal layer was calculated by the following method.
Value, that is, refractive index n_FourCholestery under the atmosphere of
Light incident on the liquid crystal layer at an incident angle θ is
Wave of reflected light when selectively reflected by the resteric liquid crystal layer
In the measurement to detect the long λ, change the incident angle θ of the light.
Between θ and λ when λ = a × cos (θ × b)
Θ (where a and b are constants)
Xb, θ, and the above n_FourBased on n₁= N _FourXs
The value obtained by inθ / sin (θ × b)
Refractive Index of Cholesteric Liquid Crystal Layer Obtained as
n₁Refractive index of cholesteric liquid crystal layer
n₁Placed next to the cholesteric liquid crystal layer
Refractive index n of the optical layer_Two, And placed between them
Refractive index n of adhesive layer_ThreeBut n₁≤n_Three≤n _TwoOr n_Two≤
n_Three≤n₁Since it is optimized to satisfy the relationship of
Between the cholesteric liquid crystal layer and the adjacent optical layer
Effectively suppress the interface reflection caused by the difference in refractive index,
Excellent optical characteristics when incorporated in liquid crystal display devices, etc.
(Contrast and good visibility)
You can

According to the second solution of the present invention, the refractive index n ₁ of the cholesteric liquid crystal layer is set to a value obtained by the same method as the method according to the first solution described above, and in this way Based on the calculated refractive index n ₁ of the cholesteric liquid crystal layer, the refractive index n ₁ of the cholesteric liquid crystal layer
And the refractive index n ₂ of the optical layer that is directly adhered and laminated on the cholesteric liquid crystal layer are optimized to be substantially equal to each other, so that the refractive index between the cholesteric liquid crystal layer and the optical layer adjacent thereto is It is possible to more effectively suppress the interface reflection caused by the difference, and to exhibit excellent optical characteristics (contrast and good visibility) when incorporated in a liquid crystal display device or the like.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the polarizing element 10 according to the present embodiment is arranged so as to be adjacent to the cholesteric liquid crystal layer 11 having a cholesteric regularity having a helical axis in the thickness direction and the cholesteric liquid crystal layer 11. 1/4 done
The wavelength retardation layer (optical layer) 12 is provided. Further, an adhesive layer 13 is arranged between the cholesteric liquid crystal layer 11 and the quarter-wave retardation layer 12, and the cholesteric liquid crystal layer 1 is provided.
The 1 and the quarter-wave retardation layer 12 can be brought into close contact with each other. The quarter-wave retardation layer 12 and the adhesive layer 13, which are optical members, are preferably transparent members.

Here, the cholesteric liquid crystal layer 11 has a spiral structure in which the direction of the director of the liquid crystal molecules is continuously rotated in the thickness direction of the cholesteric liquid crystal layer 11 as the physical molecular arrangement of the liquid crystal molecules. Therefore, it has a polarization splitting property of splitting a circularly polarized light component in one direction and a circularly polarized light component in the opposite direction based on such a physical molecular arrangement of liquid crystal molecules. That is, in the cholesteric liquid crystal layer 11, natural light incident along the spiral axis is separated into two circularly polarized components of right-handed and left-handed, one of which is transmitted and the other of which is reflected. This phenomenon is known as circular dichroism, and when the spiral winding direction in the spiral structure of liquid crystal molecules is appropriately selected, the circular polarization component having the same optical rotation direction as the spiral winding direction is selectively reflected.

Incidentally, such a cholesteric liquid crystal layer 1
In No. 1, the ratio of reflected light to incident light can be determined by appropriately selecting the thickness. For example, if the cholesteric liquid crystal layer 11 is made sufficiently thick,
That is, if the number of spiral pitches is sufficiently large, one circularly polarized light component having the same optical rotation direction as the spiral winding direction out of the unpolarized light that is incident light is almost 100% (when viewed from the entire incident light, The other circularly polarized light component is transmitted at a rate of almost 100% (similarly, when viewed from the entire incident light, an intensity of 50%). On the other hand, if the cholesteric liquid crystal layer 11 is made thin to some extent, it exhibits semi-transparency, and a part of one circularly polarized light component included in the incident light is reflected and the rest is transmitted. Specifically, for example, when non-polarized light is incident on the cholesteric liquid crystal layer 11 that reflects 50% of the right circularly polarized light, when the intensity of the incident light is 100%, the right circularity ideally has an intensity of 25%. Polarized light is reflected, 2
Right circularly polarized light having an intensity of 5% and left circularly polarized light having an intensity of 50% are transmitted. Further, when only right-handed circularly polarized light is incident, ideally, right-handed circularly polarized light having an intensity of 50% is reflected and right-handed circularly polarized light having an intensity of 50% is transmitted. This reflection / transmission ratio depends on the number of spiral pitches, and the smaller the number of spiral pitches, the smaller the reflectance. Generally, in order to saturate the selective reflection (ideally 100% selective reflection, but in fact, it saturates at 90% or more and the reflectance does not become higher than that), one specific wavelength is used. About 8 pitches are necessary for the area. Therefore, when the cholesteric liquid crystal layer 11 is a semi-transmissive layer, the thickness is adjusted so that the number of spiral pitches is 8 pitches or less.

Here, the circularly polarized light component separated by the cholesteric liquid crystal layer 11 as described above is ideally circularly polarized light, but is a semi-transmissive cholesteric liquid crystal layer 11.
The polarization state of the light transmitted through may deviate from true circular polarization and become elliptically polarized light. Such a deviation of the polarization state causes an unexpected deviation of the polarization state when used by being incorporated in, for example, a liquid crystal display device, resulting in deterioration of optical characteristics such as contrast.

The main cause of such a deviation of the polarization state is the effect of interface reflection inside the polarizing element 10. Here, taking as an example the case where right circularly polarized light is incident on the cholesteric liquid crystal layer 11 that reflects 50% of the right circularly polarized light from the ¼ wavelength phase difference layer 12 side, as shown in FIG. Bragg reflection occurs inside the liquid crystal layer 11, and a part of right circularly polarized light (in this case, ideally 50% of the intensity of incident light) is reflected and emerges from the surface on the incident side, while the rest remains. The right circularly polarized light of is transmitted (see the optical path indicated by the solid line in FIG. 1). At this time, when the light reflected inside the cholesteric liquid crystal layer 11 exits from the cholesteric liquid crystal layer 11, interface reflection occurs due to the difference in refractive index between the cholesteric liquid crystal layer 11 and the adhesive layer 13. The light reflected at the interface comes out from the surface on the emission side in a state where the optical rotation direction is reversed (that is, in the state where the right circularly polarized light is converted to the left circularly polarized light), and the light is reflected by the cholesteric liquid crystal layer 11. It is transmitted and emitted to the outside together with the right-handed circularly polarized light emitted from the surface on the emission side (see the optical path indicated by the dotted line in FIG. 1). Therefore, the light finally emitted from the surface on the emission side becomes right elliptical polarized light in which left circularly polarized light is mixed with right circularly polarized light.

In order to suppress such a phenomenon, it is necessary to optimize the relationship of the refractive index among the cholesteric liquid crystal layer 11, the 1/4 wavelength retardation layer 12 and the adhesive layer 13 which constitute the polarizing element 10. . Ideally, it is desirable to make the refractive indexes of all the optical members constituting the polarizing element 10 uniform, but the materials of the optical members are actually different, and the refractive indexes are also different accordingly. For example, the liquid crystal material forming the cholesteric liquid crystal layer 11 has a high refractive index of 1.5 to 1.7, and the retardation film forming the quarter-wave retardation layer 12 has a refractive index of 1.4 to 1. As low as 5.

Therefore, in this embodiment, the refractive index of the adhesive layer 13 disposed between the cholesteric liquid crystal layer 11 and the quarter-wave retardation layer 12 is set as follows.

That is, the cholesteric liquid crystal layers 11 and 1
When the refractive indices of the / 4 wavelength retardation layer 12 and the adhesive layer 13 are n ₁ , n ₂ and n ₃ , respectively, n ₁ ≤n ₃ ≤n ₂ or n ₂ ≤n ₃ ≤n ₁ (1) Make sure the relationship is met.

At this time, more preferably, n ₃ = (n ₁ + n ₂ ) / 2 ± Δn (2) Note that Δn in the above equation (2) can be appropriately determined according to the allowable contrast. For example, when the contrast is suppressed within the range of fluctuation of about 10%, Δn is set to about 0.05.

Specifically, for example, the refractive index of the cholesteric liquid crystal layer 11 is n ₁ = 1.58, and the quarter-wave retardation layer 1 is used.
When the refractive index of ₂ is n ₂ = 1.47, the refractive index n ₃ of the adhesive layer 13 provided between them is 1.47 ≦
It is preferable that n ₃ ≦ 1.58, and further,
n ₃ = (1.47 + 1.58) /2±Δn=1.53±
More preferably, Δn.

In the above equations (1) and (2), 1/4
Refractive index n ₃ of the refractive index n ₂ and the adhesive layer 13 of the wavelength retardation layer 12 are both mean refractive index.

On the other hand, the refractive index n ₁ of the cholesteric liquid crystal layer 11 is a value obtained by the following method. That is, the cholesteric liquid crystal layer 11 is formed under the atmosphere of the refractive index n _4.
In the measurement to detect the wavelength (center selective reflection wavelength) λ of the reflected light when the light incident at a certain incident angle θ is selectively reflected by the cholesteric liquid crystal layer, the incident angle θ of the light is detected.
Between θ and λ when is changed, λ = a × cos (θ × b) (where a and b are constants) (3) is determined so that θ × b, θ, and N ₄ above
Based on, n ₁ = n ₄ × sin θ / sin (θ × b) (4)

Details of such a calculation method will be described below with reference to FIGS. 7 and 8.

As shown in FIG. 7, unpolarized light (or light including circularly polarized light in one optical rotation direction which is selectively reflected) is made incident on the cholesteric liquid crystal layer 11 at an incident angle θ in an atmosphere having a refractive index n _4. Then, at that time, the cholesteric liquid crystal layer 1
The relationship between the central selective reflection wavelength λ of the circularly polarized light reflected at 1 and the incident angle θ at that time is measured.

Here, the center selective reflection wavelength λ of the circularly polarized light reflected by the cholesteric liquid crystal layer 11 changes according to the incident angle of light according to the incident angle dependence of the cholesteric liquid crystal layer 11. The incident angle serving as a reference at this time is an incident angle θ ₂ inside the cholesteric liquid crystal layer 11 as shown in FIG. 7, and the central selective reflection wavelength λ is based on the incident angle θ ₂ Shift according to 5).

Λ = λ ₀ × cos (θ ₂ ) ... (5) In the above equation (5), λ ₀ is such that light is perpendicular to the cholesteric liquid crystal layer 11 (the thickness direction of the cholesteric liquid crystal layer 11). It is the central selective reflection wavelength when incident.
The central selective reflection wavelength λ ₀ is given by spiral pitch × refractive index.

From the above, λ and θ obtained by the above measurement can be fitted by the following equation (6).

Λ = a × cos (θ × b) (6) Here, a and b are both constants, and a = λ ₀ , b
= Θ ₂ / θ.

Therefore, if the measured data for λ and θ are fitted by the method of least squares or the like according to the above equation (6), the constants a and b can be obtained respectively.

On the other hand, according to Snell's law, n ₁ × sin
Since θ ₂ = n ₄ × sin θ holds, in consideration of θ ₂ = θ × b, n ₁ = n ₄ × sin θ / sin (θ × b) (7)

Therefore, θ determined by the above-mentioned method
The refractive index n ₁ of the cholesteric liquid crystal layer 11 can be obtained by substituting n ₄ together with the values of × b and θ into the above equation (7).

FIG. 8 is a plot diagram showing measured data (λ and θ) obtained in an actual experiment. By fitting this measurement data to the above equation (6), a = 575.
7, b = 0.63154 is obtained.

Here, when θ approaches 0, s is approximated.
Since in θ = θ, from the above formula (7), n ₁ = n ₄ × θ / (θ × b) = n ₄ / b, and the refractive index of the cholesteric liquid crystal layer 11 is n ₁
= 1 / 0.63154 = 1.583 is obtained. In addition,
It can be seen that the above experimental results are in good agreement with the above-mentioned simulation results (n ₁ = 1.585) in which the data of the cholesteric liquid crystal used in the experiment are the same.

As a measuring device used for the above-mentioned measurement of λ and θ, a light source for emitting the measurement light toward the cholesteric liquid crystal layer 11 and the cholesteric liquid crystal layer 1 are used.
There is no particular limitation as long as it has a detector for detecting the reflected light reflected by No. 1 and can change the incident angle of the measurement light emitted from the light source to the cholesteric liquid crystal layer 11. As the light source, a white light source is preferable, and a halogen light source, a xenon light source and the like which are widely used can be used. The measurement light is preferably parallel light to some extent. On the other hand, the detector is not particularly limited as long as it can measure the spectral characteristics of the reflected light (wavelength dispersion of the reflected light), and other than the method of using polychromatic light as the measuring light, It is also possible to use a method of measuring the intensity distribution of each monochromatic light by using different monochromatic lights and sequentially using each monochromatic light as the measurement light. As the measuring device, for example, a UV3100PC manufactured by Shimadzu or a goniophotometer manufactured by Apex can be used. In the measuring device as described above, in order to measure the incident angle dependency of the cholesteric liquid crystal layer 11, it is preferable that the positions, angles, etc. of the sample setting part, the light source, the detector, etc. can be arbitrarily set.

Next, details of each optical member constituting the polarizing element 10 shown in FIG. 1 will be described.

The cholesteric liquid crystal layer 11 can be formed by using one having a conjugated linear molecule that imparts liquid crystal orientation, and any of a monomer, an oligomer and a polymer may be used. However, in the case of stably forming a film without using a supporting substrate or the like, it is preferable to use an oligomer or a polymer. As the cholesteric liquid crystal, for example, those having a mesogen group-bonded structure such as polyester, polyamide, and polyacrylate can be used, and if necessary, a compound having a chiral component called a chiral agent is mixed. Good.

The cholesteric liquid crystal layer 11 may have an optional selective reflection wavelength band. However, when the cholesteric liquid crystal layer 11 has a wide selective reflection wavelength band, the central selective reflection wavelengths are different (that is, the spiral selective reflection wavelength band is different). The cholesteric liquid crystal layer 1 is formed by a method of stacking a plurality of liquid crystal layers (having different pitches) or a method of changing the spiral pitch in a single liquid crystal layer.
1 should be configured. In addition, the cholesteric liquid crystal layer 11
Can be used alone, or can be used together with the supporting base material used in the layer formation. Such a supporting substrate can be used without particular limitation as long as it is optically isotropic, and for example, a glass substrate or the like can be used. An anisotropic material such as a stretched film is generally not preferable because it changes the polarization state when light passes through the supporting base material itself, but the retardation amount of the supporting base material itself is appropriately designed. If so, it can be used without problems.
In addition, in general, when forming a cholesteric liquid crystal layer on a supporting substrate such as a glass substrate, an alignment film or the like obtained by subjecting a polyimide film to rubbing treatment is provided, and a slight phase difference is provided by the alignment film or the like. In some cases, there is no problem in most cases because it has no optical influence. The thickness of the cholesteric liquid crystal layer 11 is not particularly limited, but when the cholesteric liquid crystal layer 11 is a semi-transmissive layer, it is generally 0.01 although it depends on the liquid crystal material.
˜50 μm, particularly preferably 0.05 to 20 μm. In addition, when the selective reflection wavelength band is wide, a thickness of about 1 to 10 times the above-mentioned thickness is required.

The quarter-wave retardation layer 12 can be formed by using a polymer film, and the polymer film is stretched uniaxially or biaxially, or the liquid crystal material is regularly arranged. Can be formed. As the polymer film, for example, a film made of polycarbonate, polyester, polyvinyl alcohol, polystyrene, polysulfone, polymethylmethacrylate, polypropylene, cellulose acetate polymer polyamide or the like can be used.

The quarter-wave retardation layer 12 is preferably transparent and has a uniform retardation amount in the plane. In general, the retardation layer has wavelength dependence, and even if it is designed according to the amount of retardation required in a certain wavelength range, it often deviates in other wavelength ranges. For example, in the 1/4 wavelength retardation layer, when converting circularly polarized light into linearly polarized light, it is necessary to give a phase difference of 1/4 wavelength to the wavelength to be converted, but when it is applied over the entire visible light range. It is necessary to combine the compensation layer with the usual 1/4 wavelength retardation layer. Generally, when forming a wideband quarter-wave retardation layer, a quarter-wave retardation layer and a half-wave retardation layer are used in combination. Depending on the material, it is possible to realize a quarter-wave retardation layer having a wide band by itself.

The adhesive layer 13 can be formed by using a transparent adhesive such as an acrylic polymer, a silicone polymer, polyester, polyurethane or polyether. Acrylic adhesives are generally widely used. In this case, for example, acrylic acid ester or methacrylic acid having an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a hexyl group, or a cyclohexyl group. The thing which copolymerized the ester etc. can be used. The adhesive layer 13 is preferably made of an optical adhesive that has excellent adhesive strength to glass, plastic, etc., is colorless and transparent, and has a wide range of refractive index selection.

The adhesive layer 13 is formed in a sheet shape in advance and used, or a liquid adhesive is applied onto the optical member to be adhered, and the optical member is bonded through the adhesive and then cured. You may make it process. In addition,
As the adhesive in this case, an arbitrary one such as a radiation curable type such as an ultraviolet curable type, a thermosetting type and a two-liquid mixed type can be used. The thickness of the adhesive layer 13 is not particularly limited, but it is preferably 1 to 500 μm, and more preferably 5 to 100 μm in terms of adhesive strength, tint and the like.

Here, 1/4 of the polarizing element 10 shown in FIG.
Other optical members can be further laminated on the wavelength retardation layer 12 depending on the required optical function. Specifically, like the polarizing element 10 'shown in FIG.
1/2 on the 1/4 wavelength retardation layer 12 with the adhesive layer 15 interposed
The wavelength retardation layer 14 is laminated or the polarizing element 1 shown in FIG.
As in the case of 0 ″, in the polarizing element 10 ′ shown in FIG. 2, the absorption type linear polarizing layer 16 can be further laminated on the ½ wavelength retardation layer 14 via the adhesive layer 17.
Further, other optional optical members such as a color filter may be used in combination, if necessary.

In the case of the polarizing elements 10 'and 10 "as shown in FIGS. 2 and 3, ideally, all the optical members (cholesteric liquid crystal layer 11, quarter wavelength retardation layer 1) are used.
2, 1/2 wavelength retardation layer 14, absorption type linear polarization layer 16)
The adhesive layers 13, 15, 17 disposed between the
Alternatively, it is preferable to satisfy the relationship of (2). However,
When the polarizing elements 10 ′ and 10 ″ are used by being incorporated in a liquid crystal display device or the like, it is the cholesteric liquid crystal layer 11 and the ¼ wavelength retardation layer 12 that is most adjacent to the cholesteric liquid crystal layer 11 that contributes most to the deterioration of optical characteristics. Because of the interfacial reflection between the cholesteric liquid crystal layer 11, the ¼ wavelength retardation layer 12 and the adhesive layer 13 adjacent to the cholesteric liquid crystal layer 11, at least satisfy the relationship of the above formula (1) or (2). To do so.

The cholesteric liquid crystal layer 11 is a semi-transmissive layer, and the optical members 11, 12, 14, 16 and the adhesive layers 13, 15, 17 are on the light incident side (backlight side) with respect to the cholesteric liquid crystal layer 11. When the observer observes the cholesteric liquid crystal layer 11 from the light emission side (liquid crystal cell side), the cholesteric liquid crystal layer 11 and the incident side (backlight side) adjacent to the cholesteric liquid crystal layer 11 are It suffices that the refractive indices of the four-wavelength phase difference layer 12 and the adhesive layer 13 satisfy the relationship of the above expression (1) or (2).

In relation to this point, the behavior of light when the polarizing element 10 ″ shown in FIG. 3 is incorporated in a liquid crystal display device will be described below with reference to FIGS. 4 (a) and 4 (b).

First, taking the case where the right circularly polarized light is incident on the semi-transmissive cholesteric liquid crystal layer 11 which reflects 50% of the right circularly polarized light from the backlight side, as shown in FIG. 4 (a). In addition, Bragg reflection occurs inside the cholesteric liquid crystal layer 11, and a part of the right circularly polarized light is reflected and emerges from the surface on the backlight side, while the remaining right circularly polarized light is transmitted (see FIG. 4 (a ) See the solid optical path). At this time, when the light reflected inside the cholesteric liquid crystal layer 11 exits from the cholesteric liquid crystal layer 11, interface reflection occurs due to the difference in refractive index between the cholesteric liquid crystal layer 11 and the adhesive layer 13. The light reflected by the interface comes out from the surface on the liquid crystal cell side in the state where the optical rotation direction is reversed (that is, in the state where the right circularly polarized light is converted to the left circularly polarized light), and the cholesteric liquid crystal layer 11 And is emitted to the outside together with the right-handed circularly polarized light emitted from the surface on the liquid crystal cell side (see the optical path indicated by the dotted line in FIG. 4 (a)). Therefore, the light finally emitted from the surface of the cholesteric liquid crystal layer 11 on the liquid crystal cell side becomes right elliptical polarized light in which right circularly polarized light and left circularly polarized light are mixed, and further, the light reflected by the interface (left circularly polarized light) is Since the ellipticity changes depending on the ratio, the interface reflection at the incident side interface of the cholesteric liquid crystal layer 11 becomes a serious problem.

On the other hand, when right-handed circularly polarized light is incident on the cholesteric liquid crystal layer 11 from the liquid crystal cell side, Bragg reflection occurs inside the cholesteric liquid crystal layer 11 as shown in FIG. 4B. Part of the right circularly polarized light is reflected and emerges from the surface on the liquid crystal cell side, while the remaining right circularly polarized light is transmitted (see the optical path indicated by the solid line in FIG. 4B). At this time, when the light reflected inside the cholesteric liquid crystal layer 11 exits from the cholesteric liquid crystal layer 11,
Interface reflection occurs at the interface of the cholesteric liquid crystal layer 11 on the liquid crystal cell side, but the light reflected by the interface is emitted to the outside from the surface of the cholesteric liquid crystal layer 11 on the backlight side (the optical path indicated by the dotted line in FIG. 4B). reference). Therefore, the light finally emitted from the surface of the cholesteric liquid crystal layer 11 on the liquid crystal cell side is only right-handed circularly polarized light, and the cholesteric liquid crystal layer 11
The interface reflection at the interface on the incident side of is not a problem of deterioration of optical characteristics.

The polarizing element 1 shown in FIG. 2 and FIG.
In 0 ′ and 10 ″, the ½ wavelength retardation layer 14 can be formed in the same manner as the ¼ wavelength retardation layer 12 described above, and the adhesive layers 15 and 17 can also be formed in the same manner as the adhesive layer 13 described above.
Can be formed in the same manner as.

In the polarizing element 10 ″ shown in FIG. 3, the absorption type linear polarizing layer 16 is formed by adding iodine to a hydrophilic polymer film such as a polyvinyl alcohol film or an ethylene / vinyl acetate copolymer partially saponified film. And 2
It can be formed by using a film or the like which is made to adsorb and draw a color dye or the like.

When the absorption type linear polarization layer 16 is used by being incorporated in a liquid crystal display device or the like, it is preferable that it has a high light transmittance and a high degree of polarization. In particular, the light transmittance is preferably 40% or more. On the other hand, the degree of polarization is 99% or more,
More preferably, it is 99.5% or more. The degree of polarization as used herein is defined by the following equation (8).

SQR [(Tp-Tc) / (Tp + Tc)] (8) Here, in the above formula (8), SQR [x] means the square root of x, and Tp arranges the polarizing layers in parallel Nicols. The light transmittance, Tc, means the light transmittance when the polarizing layers are arranged in crossed Nicols.

There is no particular limitation on the thickness of the absorption type linear polarization layer 16, and it may be, for example, about 10 to 80 μm.

As described above, according to the present embodiment, the refractive index n ₁ of the cholesteric liquid crystal layer 11 is set to the value obtained by the following method, that is, the refractive index n ₁ of the cholesteric liquid crystal layer 11 is set in the atmosphere. In the measurement for detecting the wavelength λ of the reflected light when the light incident at a certain incident angle θ is selectively reflected by the cholesteric liquid crystal layer 11, the relationship between θ and λ when the incident angle θ of the light is changed is detected. Between λ = a × c
Based on θ × b, θ determined so that os (θ × b) (where a and b are constants) and n ₄ above,
n ₁ = _{n 4} × a value determined by sinθ / sin (θ × b) , reference to the refractive index _{n 1} of the cholesteric liquid crystal layer 11 obtained in this manner, the refractive index _{n 1} of the cholesteric liquid crystal layer 11 , The refractive index n _{2 of} the quarter-wave retardation layer 12 arranged adjacent to the cholesteric liquid crystal layer 11 and the refractive index n ₃ of the adhesive layer 13 arranged between them are n ₁ ≦ n ₃ ≤n ₂ or n ₂ ≤n ₃ ≤n
Since it is optimized so as to satisfy the relationship of ₁ , the interface reflection generated due to the difference in the refractive index between the cholesteric liquid crystal layer 11 and the quarter-wave retardation layer 12 is effectively suppressed, and the liquid crystal display device or the like can be obtained. When incorporated, it can exhibit excellent optical characteristics (contrast and good visibility).

In the above-described embodiment, in the polarizing elements 10, 10 ', 10 "shown in FIGS. 1 to 3, the quarter-wave retardation layer 12 is used as the optical layer adjacent to the cholesteric liquid crystal layer 11. However, the present invention is not limited to this, and any optical member can be used according to the required optical function.

Further, in the above-described embodiment, in the polarizing elements 10 'and 10 "shown in FIGS. 2 and 3,
1/4 wavelength retardation layer 12 on cholesteric liquid crystal layer 11
And the half-wave retardation layer 14 are laminated in this order,
The ½ wavelength retardation layer and the ¼ wavelength retardation layer may be laminated in this order.

Further, in the above-mentioned embodiment,
In the polarizing elements 10, 10 ′ and 10 ″ shown in FIGS. 1 to 3, the quarter-wave retardation layer 12 is laminated on the cholesteric liquid crystal layer 11 via the adhesive layer 13, but the present invention is not limited to this. 5, the quarter-wave retardation layer 12 may be directly adhered and laminated on the cholesteric liquid crystal layer 11. In this case, the refractive index n of the cholesteric liquid crystal layer is n. ₁ and 1/4 wavelength retardation layer 12
It is preferable that the refractive index n ₂ is substantially equal to the refractive index n ₂ . The term “substantially equal” as used herein means that the difference between the refractive indices n ₁ and n ₂ is within ± 0.05. The refractive index n ₂ of the quarter-wave retardation layer 12 is a value of the average refractive index, and the refractive index n ₁ of the cholesteric liquid crystal layer is obtained by the same method as the method according to the above-described embodiment. It is a value.

According to the polarizing element 20 shown in FIG. 5, the refractive index n ₁ of the cholesteric liquid crystal layer 11 is set to a value obtained by the same method as the method according to the above-described embodiment, and thus obtained. With reference to the refractive index n ₁ of the cholesteric liquid crystal layer 11, the refractive index n ₁ of the cholesteric liquid crystal layer 11 and the refractive index n of the ¼ wavelength retardation layer 12 that is directly adhered on the cholesteric liquid crystal layer 11. _{Since 2} is optimized so as to be substantially equal to each other, the interface reflection caused by the difference in refractive index between the cholesteric liquid crystal layer 11 and the quarter-wave retardation layer 12 is more effectively suppressed,
When incorporated in a liquid crystal display device or the like, it is possible to exhibit excellent optical characteristics (contrast and good visibility).

[0073]

EXAMPLES Next, specific examples of the above-described embodiment will be described.

Example A polyimide film having a thickness of 0.07 μm was formed on a glass substrate, and then the polyimide film was rubbed to prepare a support.

On the other hand, a monomer-mixed liquid crystal prepared by adding a chiral agent to a main component composed of an ultraviolet-curable nematic liquid crystal was dissolved in toluene to prepare a cholesteric liquid crystal solution. A photopolymerization initiator was added to the cholesteric liquid crystal solution.

Then, the cholesteric liquid crystal solution prepared as described above is applied onto the support prepared as described above, and the solvent is removed at a predetermined temperature (80 ° C.) and then a predetermined strength ( A cholesteric liquid crystal layer was formed in a thickness of 2.2 μm by irradiating with ultraviolet rays of 5 mW / cm ² ) for a predetermined time (1 minute) to cure. The cholesteric liquid crystal layer thus formed has a thickness of 56
It had a central selective reflection wavelength at 0 nm, a half width of about 57 nm, and a right circularly polarized light transmittance of 25%.

After that, the refractive index n ₁ of the cholesteric liquid crystal layer thus formed was calculated by the following method.

That is, a halogen lamp is used as a light source for emitting the measurement light toward the cholesteric liquid crystal layer, and a goniometer manufactured by Apex Co. is used as a detector for detecting the reflected light reflected by the cholesteric liquid crystal layer. The apparatus was prepared, and the relationship between the incident angle θ of the measurement light and the central selective reflection wavelength λ of the reflected light was measured using the measurement apparatus as described below. The measuring light emitted from the halogen lamp, which is a light source, was collimated using a lens and a slit.

With the normal direction to the surface of the cholesteric liquid crystal layer being 0 °, the incident angle θ of the measuring light with respect to the cholesteric liquid crystal layer was changed in 1 ° steps within a range of 10 ° to the left and right, and the center at each incident angle θ was changed. The selective reflection wavelength λ was measured. The measurement data obtained in this way, the central selective reflection wavelength λ on the vertical axis, the incident angle θ of the measurement light on the horizontal axis,
By plotting and fitting by the least squares method, the coefficients a and b of the above equation (3) were determined. The obtained values were a = 560.7 and b = 0.63154. From this, n = 1.583 was obtained from the above equation (4). As a reference, the average refractive index of this liquid crystal material at 560 nm was measured and found to be about 1.56.

Next, for light having a wavelength of 560 nm, 1 /
A retardation film that gives a retardation of 4 wavelengths and an absorption type linearly polarizing film having a light transmittance of 38% and a polarization degree of 99% or more were prepared, and 1 was formed on the cholesteric liquid crystal layer produced as described above. The / 4 wavelength retardation film and the absorption type linear polarization film were laminated in this order. In addition, the bonding angle of these optical members is such that the right circularly polarizing film is constituted by both of the absorption type linear polarizing film and the 1/4 wavelength retardation film, and the 1/4 wavelength An arbitrary angle was set between the retardation film and the cholesteric liquid crystal layer.

Here, as the quarter-wave retardation film, a film in which polyvinyl alcohol was sandwiched between cellulose acetobutyrate (average refractive index was 1.50) was used. As the absorption type linearly polarizing film, a film obtained by sandwiching a stretched film dyed with an iodine dye with cellulose acetoacetate (average refractive index 1.50) was used. An optical adhesive (NOA series) manufactured by Norland was used as the adhesive that adheres the respective interfaces of the optical members. Here, the refractive index of the cholesteric liquid crystal layer is 1.583, 1
Since the refractive index of the / 4 wavelength retardation film is 1.50, and the optimum refractive index of the adhesive layer is 1.542 from the above formula (2), the NOA68 having the refractive index of 1.54 is used. The cholesteric liquid crystal layer and the quarter-wave retardation film were adhered to each other to manufacture a polarizing element according to an example.

(Comparative Example) Similar to the above-described example, a plurality of cholesteric liquid crystal layers and 1/4 wavelength retardation films, which are optical members, were prepared, and different types of adhesives were used to adjust the cholesteric liquid crystal layer and 1/4 wavelength positions. A plurality of types of polarizing elements (Comparative Examples 1 to 4) bonded with a retardation film were produced. Table 1 below summarizes the adhesives used in each of Comparative Examples 1 to 4 and their refractive indexes. In addition, the following Table 1
At NOA65 (refractive index 1.52) and NOA
61 (refractive index 1.56) is the above-mentioned NOA series NOA series adhesive, VTC-2 (refractive index 1.50) is an adhesive manufactured by Summers Lab, HV16 (refractive index 1.60). Is an adhesive made by Optocrepe.

[0083]

[Table 1] (Evaluation Results) Next, the optical characteristics of the polarizing elements according to the examples and Comparative Examples 1 to 4 were evaluated.

A right circular polarizing film and a left circular polarizing film are prepared corresponding to the polarizing elements according to the examples and the comparative examples 1 to 4, respectively, and are used in the polarizing elements according to the examples and the comparative examples 1 to 4. The corresponding polarizing element was adhered to different portions (A, B) on the glass substrate side via the adhesive. In each of the samples produced in this manner, the light is vertically incident from the absorption type linear polarizing film side of the polarizing element, and the intensity of the transmitted light is measured with respect to the portion A to which the right circular polarizing film is bonded, The comparison was made with the part B to which the left circularly polarizing film is adhered. In such a measurement, the light intensity at the A portion corresponds to the bright display when incorporated in the liquid crystal display device, and the light intensity at the B portion corresponds to the dark display. The contrast can be evaluated in a pseudo manner. As for the evaluation, the higher the contrast, the better the performance.

Table 2 below shows the contrast of the samples corresponding to the polarizing elements according to the example and the comparative examples 1 to 4 when the wavelength of light is 560 nm. As is clear from Table 2 below, in the polarizing element according to Example 4, which is out of the range between the refractive index 1.50 of the quarter-wave retardation film and the refractive index 1.583 of the cholesteric liquid crystal layer, Although the contrast is greatly reduced, the contrast is improved as the refractive index of 1.542 obtained from the above formula (2) is approached, and it can be confirmed that the polarizing element according to the example has the highest contrast.

[0086]

[Table 2]

[0087]

As described above, according to the present invention, the optical characteristics are excellent, and it is possible to improve the contrast and secure good visibility when incorporated in a liquid crystal display device or the like.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a polarizing element according to the present invention.

FIG. 2 is a sectional view showing a modification of the polarizing element shown in FIG.

FIG. 3 is a sectional view showing another modification of the polarizing element shown in FIG.

FIG. 4 is a diagram for explaining the behavior of light when the polarizing element shown in FIG. 3 is incorporated in a liquid crystal display device.

FIG. 5 is a sectional view showing another embodiment of the polarizing element according to the present invention.

FIG. 6 is a plot diagram showing a result of a simulation for confirming the refractive index of the cholesteric liquid crystal layer (relationship between ellipticity of circularly polarized light passing through the cholesteric liquid crystal layer and refractive index of atmosphere).

FIG. 7 is a diagram for explaining how light is reflected by a cholesteric liquid crystal layer.

FIG. 8 is a plot diagram showing a relationship between a central selective reflection wavelength of reflected light reflected by a cholesteric liquid crystal layer and an incident angle.

[Explanation of symbols]

10, 10 ', 10 ", 20 Polarizing element 11 Cholesteric liquid crystal layer 12 1/4 wavelength retardation layer 13 Adhesive layer 14 1/2 wavelength retardation layer 15 Adhesive layer 16 Absorption type linear polarization layer 17 Adhesive layer

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H049 BA02 BA03 BA06 BA07 BA43                       BB03 BB42 BB43 BC03 BC22                 2H088 EA47 GA03 HA04 HA18 JA14                       KA05 MA02 MA16                 2H091 FA08 FA11 FC29 FC30 FD09                       FD10 GA07 GA17 HA11 LA03                       LA11 LA12 LA13 LA17

Claims (13)

[Claims] 1. A cholesteric liquid crystal layer having a cholesteric regularity having a spiral axis in a thickness direction, an optical layer arranged adjacent to the cholesteric liquid crystal layer, and between the cholesteric liquid crystal layer and the optical layer. And an adhesive layer for adhering the cholesteric liquid crystal layer and the optical layer to each other, wherein the refractive indices of the cholesteric liquid crystal layer, the optical layer and the adhesive layer are n ₁ , n ₂ and n ₃ , respectively. , These satisfy the relationship of n ₁ ≦ n ₃ ≦ n ₂ or n ₂ ≦ n ₃ ≦ n ₁ (1), and the refractive index n _{2 of the} optical layer and the refractive index n _{3 of the} adhesive layer are satisfied.
Are both values of the average refractive index, and the refractive index n ₁ of the cholesteric liquid crystal layer is a value obtained by the following method, that is, an incident angle with respect to the cholesteric liquid crystal layer under an atmosphere of the refractive index n _4. In the measurement for detecting the wavelength λ of the reflected light when the light incident at θ is selectively reflected by the cholesteric liquid crystal layer, λ = a between θ and λ when the incident angle θ of the light is changed. Θ cos (θ × b) (where a and b are constants), and θ × b and θ, and the above n ₄
A polarizing element characterized by having a value obtained by the following formula: n ₁ = n ₄ × sin θ / sin (θ × b). 2. The value of the refractive index n ₃ of the adhesive layer is (n ₁ + n
The polarizing element according to claim 1, wherein the polarizing element has a range of ± 0.05 with respect to ₂ ) / 2. 3. The cholesteric liquid crystal layer is a semi-transmissive layer that reflects a part of the circularly polarized light component in one optical rotation direction and transmits the rest, and the optical layer and the adhesive layer are different from the cholesteric liquid crystal layer. The polarizing element according to claim 1 or 2, wherein the polarizing element is arranged on a light incident side. 4. The polarizing element according to claim 1, wherein the optical layer is a retardation layer. 5. The polarizing element according to claim 4, wherein an absorption type linear polarizing layer is laminated on the retardation layer. 6. The retardation layer, a quarter-wave retardation layer disposed adjacent to the cholesteric liquid crystal layer,
And a ½ wavelength retardation layer laminated on the ¼ wavelength retardation layer, the cholesteric liquid crystal layer, the ¼ wavelength retardation layer and the adhesive layer adjacent to the cholesteric liquid crystal layer having the above-described refractive index. The polarizing element according to claim 4 or 5, which satisfies the relationship (1). 7. The polarizing element according to claim 1, wherein the optical layer is a transparent member. 8. A refractive index n of the cholesteric liquid crystal layer, comprising: a cholesteric liquid crystal layer having a cholesteric regularity having a spiral axis in a thickness direction; and an optical layer arranged so as to be in direct contact with the cholesteric liquid crystal layer. ₁ and the refractive index n _{2 of the} optical layer are substantially equal to each other, the refractive index n ₂ of the optical layer is a value of an average refractive index, and the refractive index n ₁ of the cholesteric liquid crystal layer is obtained by the following method. In the measurement for detecting the value λ, that is, the wavelength λ of the reflected light when the light incident on the cholesteric liquid crystal layer at an incident angle θ under the atmosphere of the refractive index n ₄ is selectively reflected by the cholesteric liquid crystal layer, Incident angle of light θ
Between θ and λ when V is changed, θ × b and θ determined so that λ = a × cos (θ × b) (where a and b are constants), and the above n ₄
A polarizing element characterized by having a value obtained by the following formula: n ₁ = n ₄ × sin θ / sin (θ × b). 9. The cholesteric liquid crystal layer is a semi-transmissive layer that reflects a part of the circularly polarized light component in one optical rotation direction and transmits the rest, and the optical layer is a light incident side with respect to the cholesteric liquid crystal layer. 9. The polarizing element according to claim 8, wherein the polarizing element is arranged in. 10. The polarizing element according to claim 8, wherein the optical layer is a retardation layer. 11. The polarizing element according to claim 10, wherein an absorption type linear polarizing layer is laminated on the retardation layer. 12. The retardation layer comprises a quarter-wave retardation layer arranged adjacent to the cholesteric liquid crystal layer, and a half-wavelength layer laminated on the quarter-wave retardation layer. The polarizing element according to claim 10, further comprising a retardation layer, wherein the refractive index of the cholesteric liquid crystal layer and the refractive index of the ¼ wavelength retardation layer adjacent thereto are substantially equal to each other. 13. The polarizing element according to claim 8, wherein the optical layer is a transparent member.