JP2018045135A - Light control film, light control device using the same, and screen - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light control film with a transmission/scattering type light control layer, which suppresses rainbow irregularity and irregularity accompanying color changes and prevents blackout even when viewed through a polarizing filter.SOLUTION: A light control film comprises a light control layer, and a transparent electrode and transparent film substrate provided on each side of the light control layer in the described order, and is capable of switchably providing two or more types of haze (cloudiness) by means of voltage applicable to the light control layer via the transparent electrodes. Each transparent film substrate has a thickness in a range of 20-100 μm, inclusive, and exhibits retardation in a range of 100-1000 nm, inclusive, when light having a wavelength of 586.4 nm enters the transparent film substrate at an angle in a range of 0-50°, where a difference between maximum and minimum values of retardation is no greater than 500 nm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a light control film provided with a light control layer using liquid crystal, a light control device using the light control film, and a screen.

  LCD light control film is a film that uses liquid crystal and instantly switches between “transparent” and “white turbidity” by turning the power on and off, and controls the light that passes through. Also, it has a function as a video projection screen. In addition, the white turbidity (cloudiness) of the light control film is usually called haze.

  There are two types of liquid crystal light control films (hereinafter referred to as light control films): normal mode and reverse mode. As shown in FIG. 1, the former uses a polymer liquid crystal composite film in which liquid crystal molecules are wrapped in a polymer as a light control layer (3A or 3B), and the light control layer is formed of transparent electrodes 2a and 2b made of a transparent conductive film from both sides. It has a structure sandwiched by the film bases 1a and 1b. In the reverse mode, as shown in FIG. 2, alignment films 9a and 9b are further provided between the light control layer (3A or 3B) and the transparent electrodes 2a and 2b.

  There are several types of polymer liquid crystals used for the polymer liquid crystal composite film, but a typical type is called a polymer network liquid crystal (PNLC) (Patent Document 1), a high type A type called a molecular dispersed liquid crystal (PDLC: Polymer Dispersed Liquid Crystal) has been proposed (Patent Document 2).

  FIG. 3 is a schematic cross-sectional view showing the structure and behavior of a normal mode light control film 10A including a PNLC light control layer 3A. In the PNLC type, the liquid crystal molecules 5 are arranged in voids formed inside a three-dimensional network structure called a polymer network 4. FIG. 4 is a schematic cross-sectional view showing the structure and behavior of a normal mode light control film 10B including a PDLC type light control layer 3B. In the PDLC type, the liquid crystal material 7 including the liquid crystal molecules 8 is dispersedly arranged in the polymer matrix 6.

  FIGS. 3 (a) and 4 (a) show the PNLC type and PDLC type, respectively, when the AC power supply 11 is turned off. Since the liquid crystal molecules 5 and 8 are randomly arranged, the incident light 21 is high. Multiple scattering occurs at the interface between the molecule and the liquid crystal, and the scattered light 22 becomes noticeable and becomes in a high haze state and becomes white turbid. 3 (b) and 4 (b) are PNLC type and PDLC type, respectively, when the AC power supply 11 is on. The liquid crystal molecules 5 and 8 are aligned along the electric field, so there is no light scattering, and the transparent It becomes a low haze state.

  FIG. 5 is a schematic cross-sectional view showing the structure and behavior of a reverse mode light control film 20A including a PNLC light control layer 3A. The reverse mode light control film 20A includes alignment films 9a and 9b between the light control layer 3A and the transparent electrodes 2a and 2b on both sides of the light control layer 3A. The alignment films 9a and 9b are so-called vertical alignment films, and when no voltage is applied to the light control layer 3A (FIG. 5A), the longitudinal direction of the liquid crystal molecules 5 is in the normal direction of the alignment films 9a and 9b. The liquid crystal molecules 5 are aligned so as to be along. For this reason, when a voltage is not applied to the light control layer 3A, it becomes a low haze state and transparency becomes high. On the other hand, when a voltage is applied to the light control layer 3A (FIG. 5 (b)), the orientation of the liquid crystal molecules 5 becomes irregular and becomes a high haze state and becomes clouded.

The structure and behavior of the reverse mode light control film 20B (FIG. 2) including the PDLC type light control layer 3B are also the same as those in FIG.

US Pat. No. 5,304,323 US Pat. No. 4,688,900

As the film substrate of the light control film, a biaxially stretched polyethylene terephthalate (PET) film, a polycarbonate (PC) film, and the like are particularly preferable from the viewpoints of transparency, heat resistance, ease of handling, strength, and cost. However, since these materials have so-called birefringence (refractive index anisotropy), the following phenomena (1) and (2) occur, which may impair the visual quality of the light control film. It was.
(1) A phenomenon in which interference color called “rainbow unevenness” or unevenness accompanied by color change occurs particularly when the light control film is observed obliquely.
(2) A phenomenon called “blackout” caused by the relationship between the polarization axes, particularly when viewed through a polarizing filter such as polarized sunglasses.

  The present invention has been made in order to solve the above-mentioned problems, and in a light control film using a transmission-scattering light control layer such as a PNLC type or a PDLC type, the occurrence of rainbow unevenness and unevenness accompanied by a color change. And a light control film that can prevent blackout even when viewed through a polarizing filter such as polarized sunglasses, a light control device using the light control film, and a screen. To do.

In order to solve the above-mentioned problem, the invention according to claim 1 includes a light control layer, a transparent electrode and a transparent film base material in this order on both sides of the light control layer, and the transparent A light control film capable of switching between two or more types of haze (white turbidity) by a voltage that can be applied to the light control layer through an electrode;
The film thickness of the transparent film substrate is 20 μm or more and 100 μm or less,
The light control film has a retardation of 100 nm or more and 1000 nm or less when light having a wavelength of 586.4 nm is incident on the transparent film substrate at an angle of 0 to 50 °.

  In the invention according to claim 2, the difference between the maximum value and the minimum value of retardation when light having a wavelength of 586.4 nm is incident on the transparent film substrate at an angle of 0 to 50 ° is 500 nm or less. It is set as the light control film of Claim 1 characterized by these.

  The invention according to claim 3 is the light control film according to claim 1 or 2, further comprising an alignment film between the light control layer and the transparent electrode.

  According to a fourth aspect of the present invention, the dimming layer is a liquid crystal molecule disposed in a void formed inside a polymer network having a three-dimensional network structure, or a liquid crystal dispersed in a polymer matrix. The light control film according to claim 1, comprising liquid crystal molecules contained in the material.

  The invention according to claim 5 is the light control film according to any one of claims 1 to 4, wherein the light control layer has a thickness of 5 μm or more and 50 μm or less.

  Invention of Claim 6 is equipped with the light control film in any one of Claims 1-5, The alternating current power supply which can apply a voltage to the said transparent electrode in this light control film, and the said alternating current to the said transparent electrode The light control device includes a switch for switching whether to apply a voltage of a power supply.

  Invention of Claim 7 is equipped with the light control apparatus of Claim 6, and is transparent on the said transparent film base material of the at least one surface of this light control apparatus through a transparent contact bonding layer. The screen is characterized by comprising glass.

  According to the present invention, the transparency when the thickness of the transparent film substrate is 20 μm or more and 100 μm or less and light with a wavelength of 586.4 nm is incident at an angle of 0 to 50 ° is 100 nm or more and 1000 nm or less. Since the film substrate is used, a light control film capable of suppressing the occurrence of rainbow unevenness and unevenness with color change, and preventing blackout even when viewed through a polarizing filter such as polarized sunglasses, and the light control film A light control device and a screen can be obtained.

It is a schematic cross section which shows the layer structure of the light control film of a normal mode. It is a schematic cross section which shows the layer structure of the light control film of a reverse mode. It is a schematic cross section which shows the structure and behavior of a normal mode light control film provided with a PNLC type light control layer. (A) When power is off (b) When power is on. It is a schematic cross section which shows the structure and behavior of a normal mode light control film provided with a PDLC type light control layer. (A) When power is off (b) When power is on. It is a schematic cross section which shows the structure and behavior of a reverse mode light control film provided with a PNLC type light control layer. (A) When power is off (b) When power is on. It is a perspective view for demonstrating the incident angle to the transparent film base material prescribed | regulated by this invention, and the retardation of a transparent film base material. It is a model side view which shows the structural example of the screen using the light modulation apparatus of this invention.

  Hereinafter, the light control film which concerns on embodiment of this invention is demonstrated in detail. In addition, the same code | symbol is attached | subjected about the same component unless there is a reason for convenience, and the overlapping description is abbreviate | omitted. Also, in the drawings used in the following description, in order to make the features easy to understand, the portions that become the features may be shown in an enlarged manner, and the dimensional ratios of the respective constituent elements are not the same as the actual ones.

  Among the light control films according to the embodiment of the present invention, the normal mode light control film (10A or 10B) has the layer structure shown in FIG. 1 and is the same as the layer structure of the conventional light control film. In this configuration, a voltage can be applied to the light control layer (3A or 3B) through the transparent electrodes 2a and 2b, and the haze (white turbidity) of the light control film (10A or 10B) can be switched between two or more types. . Here, the two types of “more than” are that by changing the effective voltage in addition to turning on / off the AC power supply, the degree of light transmission / scattering can be changed, and the haze can be changed in various ways. Because.

  The film base (hereinafter abbreviated as film base) in the light control film of the present invention is chemically and physically strong, has sufficient hardness and durability, and maintains high transparency. Therefore, the thickness is preferably 20 μm or more and 100 μm or less.

Biaxially stretched polyethylene terephthalate film, polycarbonate film, and the like that are particularly preferable as the film base material of the light control film of the present invention have birefringence, so that when light passes through the film, the retardation (phase difference) is usually obtained. Arise. This causes the above-mentioned rainbow unevenness and blackout phenomenon.

Retardation (Re) is the refractive index (Nx) in the direction having the highest refractive index (slow axis direction) in the plane of the film substrate having birefringence and the direction (fast axis) perpendicular to the slow axis direction. (Direction) and the thickness (d) of the film substrate are represented by the following formula (1).
Retardation (Re) = (Nx−Ny) × d (1)

  In the film base material in the light control film of the present invention, the retardation when light having a wavelength of 586.4 nm is incident on the film base material at an angle of 0 to 50 ° is 100 nm or more and 1000 nm or less.

  FIG. 6 is a perspective view for explaining the incident angle θ to the film base and the retardation of the film base defined in the present invention. Measurement light 31a and 31b wavelength-selected by a band-pass filter (not shown) passes through polarizers 32a and 32b, respectively, on the slow axis (Nx) and fast axis (Ny) of the film substrate 1. The polarized light oscillates in a parallel direction, passes through the film substrate 1 and the analyzers 33a and 33b, and enters the light receiving elements 34a and 34b. Polarized light corresponding to the Nx and Ny directions incident on the light receiving elements 34a and 34b is sent to the retardation measuring unit 35 to obtain retardation. The measurement lights 31a and 31b are preferably lights emitted from the same light source and branched by a beam splitter.

  The film base in the light control film of the present invention is not only when the light having a wavelength of 586.4 nm is normally incident on the film base (incidence angle 0 °), but is also incident obliquely at an incident angle of 0 to 50 °. Defined by retardation. FIG. 6 illustrates a case where the film substrate 1 is inclined and incident obliquely. Here, the incident angle θ is equal to the tilt angle T of the film substrate 1.

  In the expression (1) representing retardation, d represents the distance that light travels in the film, and when the film substrate 1 is tilted by T (= θ), it becomes d / Cos θ, which is more than in the case of normal incidence. become longer. Therefore, if Nx and Ny are constant, the retardation increases as the tilt angle of the film substrate 1 is increased. However, since Nx actually changes depending on the incident angle, the retardation does not increase monotonously with the tilt angle. .

In the film substrate in the light control film of the present invention, it is preferable that the difference between the maximum and minimum retardation values measured under the above measurement conditions is 500 nm or less.
The effectiveness of the retardation value under the measurement conditions defined by the film substrate in the light control film of the present invention is shown in the Examples.

  The light control layer in the light control film of the present invention is a liquid crystal molecule disposed in a void formed inside a polymer network having a three-dimensional network structure, or a liquid crystal material dispersed in a polymer matrix. It is preferable that the liquid crystal molecule contained is included. Therefore, a PNLC-type and PDLC-type polymer liquid crystal composite film can be used as the light control layer.

  The thickness of the light control layer in the light control film of the present invention is preferably 5 μm or more and 50 μm or less, and more preferably 10 μm or more and 25 μm or less. When the thickness of the light control layer is less than 5 μm, there is a tendency that a short circuit is likely to occur, and the lamination with the transparent electrode tends to be difficult. When the thickness exceeds 50 μm, the responsiveness decreases.

A light control device of the present invention includes a light control film of the present invention, and includes a power source capable of applying a voltage to a transparent electrode and a switch for switching whether to apply a voltage from the AC power source to the transparent electrode. It is an optical device. Therefore, the basic form is equivalent to the form which connected the light control film and AC power supply shown in FIGS. 3-5 via a switch. The AC power source is preferably a variable power source that can change its effective voltage. This is because the degree of light transmission / scattering can be controlled and the haze can be varied in various ways as described above.

  The screen of the present invention includes the light control device of the present invention, and is a screen including transparent glass on a film substrate on at least one surface of the light control device via a transparent adhesive layer. FIG. 7 shows a mode in which transparent glasses 42a and 42b are provided on the film bases 1a and 1b on both sides of the light control device 30 via transparent adhesive layers 41a and 41b.

  In the screen of the present invention, when the light control film becomes transparent by switching the power source, it becomes transparent glass and the other side of the glass can be visually recognized. In addition, when it becomes cloudy and opaque, it functions as a screen for visually recognizing the image projected on the glass. Moreover, by using a variable power source, an intermediate state between them can be created.

Examples of the present invention will be described below, but the present invention is not limited to these examples.
First, materials and production methods of the light control films produced in Examples 1 to 4 and Comparative Examples 1 to 2 will be described.

<Example 1>
A PET film 1 (film thickness of 40 μm) is prepared as the film bases 1a and 1b, and a 0.1 μm-thick ITO (indium tin oxide) film is formed as a transparent electrode on one surface thereof by sputtering. A sheet conductive film was prepared. Next, a PNLC type light control layer is laminated on one ITO film side of the two sheets of conductive film, and the other conductive film is laminated with the ITO film side as the light control layer side. A light control film was obtained.

  The PET form 1 had a retardation of 150 to 566 nm when incident at an angle of 0 to 50 ° when the vertical direction was 0 °. Retardation was measured by using KOBRA-WR (manufactured by Oji Scientific Instruments Co., Ltd.) with light having a wavelength of 586.4 nm.

<Example 2>
In addition to the layer configuration of Example 1, polyimide was inserted as an alignment film between the light control layer and the transparent electrode to obtain a light control film of Example 2. The thickness of the alignment layer was 0.1 μm.

<Example 3>
The light control film of Example 3 was obtained by replacing the PET film 1 with the PC film 1 (film thickness 100 μm) instead of the PET film 1 in the layer configuration of Example 1. The retardation from 0 to 50 ° of the PC film 1 measured in the same manner as in Example 1 was 138 to 544 nm.

<Example 4>
In addition to the layer configuration of Example 3, polyimide was inserted as an alignment film between the light control layer and the transparent electrode to obtain a light control film of Example 4. The thickness of the alignment layer was 0.1 μm.

<Comparative Example 1>
In the layer configuration of Example 1, the PET film 1 was replaced with a PET film 2 having a large retardation value instead of the PET film 1. The retardation from 0 to 50 ° of the PET film 2 measured in the same manner as in Example 1 was 3105 to 7173 nm.

<Comparative example 2>
The light control film of the comparative example 2 was obtained by substituting with the PC film 2 (film thickness of 100 micrometers) with a small retardation value instead of the PET film 1 by the layer structure of Example 1. FIG. The retardation from 0 to 50 ° of the PC film 2 measured in the same manner as in Example 1 was 562 to 1855 nm.

<Rainbow unevenness, unevenness measurement with color change, evaluation method>
The light control film of Example or Comparative Example is observed from the front and oblique directions through the light of the three-wavelength type fluorescent tube, and the film is observed to be bent to an extent that it is not bent. The occurrence of unevenness was determined as follows.
○: Neither rainbow unevenness nor unevenness accompanied by color change is observed from any direction.
X: Depending on the direction of observation, rainbow unevenness and unevenness with color change are observed.

<Blackout measurement and evaluation method>
The light control film of an Example or a comparative example was bonded to the display, and visual observation was performed through the polarizing plate from 0 degree and 40 degree directions. During visual observation, the polarizing plate was rotated 0 to 360 °, and the occurrence of blackout was determined as follows.
○: No blackout is observed even when the polarizing plate is rotated by 0 to 360 °.
X: Generation | occurrence | production of blackout is seen at a certain angle when a polarizing plate is rotated 0-360 degrees.

<Evaluation results>
Table 1 shows the evaluation results. Example 1 and Example 3 are forms of the normal mode of FIG. 3, and Examples 2 and 4 are forms of the reverse mode of FIG. 5 using polyimide as an alignment film, but the film base material is PET or PC. Regardless of whether or not there is, the range of retardation and the difference are within the range defined by the present invention, so that rainbow unevenness did not occur, blackout did not occur, and unevenness accompanied by color change was small. On the other hand, in the comparative examples 1 and 2 in which the retardation range and the difference deviated from the range defined in the present invention, the three evaluation items were inferior.

  The present invention is useful for use as an image projection screen in order to improve the visual quality of the light control film. For example, it can be used as a screen capable of blocking the field of view, such as a building window or a partition. It can also be applied to display applications such as notice boards, show windows, and projections.

1, 1a, 1b ... Film base 2a, 2b ... Transparent electrode 3A ... Light control layer (PNLC type)
3B ... Light control layer (PDLC type)
4 ..... Polymer network 5, 8 .... Liquid crystal molecule 6 ..... Polymer matrix 7 ..... Liquid crystal material 9a, 9b ... Alignment film 10A: Light control film (PNLC type, normal mode)
10B: Light control film (PDLC type, normal mode)
11: AC power supply 12: Switch 20A: Light control film (PNLC type, reverse mode)
20B ... ・ Light control film (PDLC type, reverse mode)
21... Incident light 22... Scattered light 23... Transmitted light 30... Dimmers 31 a and 31 b ... Measuring light 32 a and 32 b. , 33b... Analyzer 34a, 34b... Light receiving element 35... Retardation measurement unit Nx... Refractive index in the slow axis direction Ny. θ ··· incident angle T ··· film substrate tilt angle d ··· film substrate thickness 40 ··· screen 41a, 41b ··· transparency Adhesive layers 42a, 42b ... Transparent glass 43 ... Projector 44 ... Projection light

Claims (7)

A dimming layer, a transparent electrode and a transparent film base material are provided in this order on both sides of the dimming layer, and haze (white turbidity) is applied by a voltage that can be applied to the dimming layer through the transparent electrode. A light control film that can be switched between two or more types,
The film thickness of the transparent film substrate is 20 μm or more and 100 μm or less,
A light control film having a retardation of 100 nm or more and 1000 nm or less when light having a wavelength of 586.4 nm is incident on the transparent film substrate at an angle of 0 to 50 °.   The difference between the maximum value and the minimum value of retardation when light having a wavelength of 586.4 nm is incident on the transparent film substrate at an angle of 0 to 50 ° is 500 nm or less. Light control film.   The light control film according to claim 1, further comprising an alignment film between the light control layer and the transparent electrode.   The light control layer includes liquid crystal molecules arranged in voids formed inside a polymer network having a three-dimensional network structure, or liquid crystal molecules contained in a liquid crystal material dispersed in a polymer matrix. The light control film in any one of Claims 1-3 characterized by the above-mentioned.   The thickness of the said light control layer is 5 micrometers or more and 50 micrometers or less, The light control film in any one of Claims 1-4 characterized by the above-mentioned.   An AC power supply comprising the light control film according to claim 1 and capable of applying a voltage to the transparent electrode in the light control film, and whether to apply the voltage of the AC power supply to the transparent electrode. A dimming device comprising a switch for switching between.   A screen comprising the light control device according to claim 6, wherein a transparent glass is provided on the transparent film substrate on at least one surface of the light control device through a transparent adhesive layer. .

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