JP6844164B2 - Dimming film, dimming device and screen using it - Google Patents

Description

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

The liquid crystal dimming film is a film that uses liquid crystal to instantly switch between "transparent" and "white turbidity" when the power is turned on / off to control the transmitted light, and has a light-shielding function, infrared cut, and ultraviolet cut function. It also has a function as a video projection screen. The white turbidity (cloudiness) of the light control film is usually called haze.

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

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

FIG. 3 is a schematic cross-sectional view showing the structure and behavior of the normal mode dimming film 10A including the PNLC type dimming 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 the normal mode dimming film 10B including the PDLC type dimming layer 3B. In the PDLC type, the liquid crystal material 7 containing the liquid crystal molecules 8 is dispersed and arranged in the polymer matrix 6.

3 (a) and 4 (a) show the states of the PNLC type and the PDLC type when the AC power supply 11 is off, respectively. Since the liquid crystal molecules 5 and 8 are randomly arranged, the incident light 21 is high. Multiple scattering is performed at the interface between the molecule and the liquid crystal, and the scattered light 22 becomes prominent, becomes a high haze state, and becomes cloudy. 3 (b) and 4 (b) are PNLC type and PDLC type, respectively, in the state when the AC power supply is turned on. Since the liquid crystal molecules 5 and 8 are arranged along the electric field, light scattering is eliminated and the liquid crystal molecules are transparent. It becomes a low haze state.

FIG. 5 is a schematic cross-sectional view showing the structure and behavior of the reverse mode dimming film 20A including the PNLC type dimming 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 molecule 5 is oriented along the line. Therefore, when no voltage is applied to the dimming layer 3A, the haze is low and the transparency is high. On the other hand, when a voltage is applied to the dimming layer 3A (FIG. 5B), the orientation of the liquid crystal molecules 5 becomes irregular, resulting in a high haze state and cloudiness.

Since the structure and behavior of the reverse mode dimming film 20B (FIG. 2) including the PDLC type dimming layer 3B are the same as in FIG. 5, the description thereof will be omitted.

U.S. Pat. No. 5,304,323 U.S. Pat. No. 4,688,900 Japanese Unexamined Patent Publication No. 2015-197637

As the film base material of the light control film, biaxially stretched polyethylene terephthalate (PET) film, polycarbonate (PC) film and the like are particularly preferable from the viewpoint 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) may occur, which may impair the visual quality of the light control film. It was.
(1) A phenomenon in which unevenness accompanied by interference color or color change called "rainbow unevenness" occurs especially when the light control film is observed from an angle.
(2) A phenomenon in which the screen disappears, which is called "blackout" due to the relationship between the polarization axes, especially when viewed through a polarizing filter such as polarized sunglasses.

Further, Patent Document 3 discloses a PDLC type dimming layer having excellent transparency and scattering contrast, but there is a problem that rainbow unevenness occurs when the PDLC type dimming layer is attached to a curved surface.

The present invention has been made to solve the above problems, and in a light control film using a transmission-scattering type light control layer such as a PNLC type or a PDLC type, unevenness accompanied by rainbow unevenness and color change. Provided are a dimming film capable of suppressing the occurrence of light, and further preventing blackout even when viewed through a polarizing filter such as polarized sunglasses, and a dimming device and a screen using the dimming film. It is the purpose.

In order to solve the above-mentioned problem, the invention according to claim 1 is provided with a light control layer and transparent electrodes and a transparent film base material on both side surfaces of the light control layer in this order, and the transparency is provided. A light control film capable of switching between two or more types of haze (white turbidity) depending on the voltage that can be applied to the light control layer through an electrode.
The film thickness of the transparent film base material is 20 μm or more and 100 μm or less.
When the angle of incidence when vertically incident on the transparent film substrate is 0 °, the 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 4000 nm. The light control film is characterized by having a wavelength of 20000 nm or less.

According to the second aspect of the present invention, 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 5000 nm or less. The light control film according to claim 1, wherein the light control film is characterized by the above.

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

The invention according to claim 4 is the dimming film according to any one of claims 1 to 3, wherein the transparent film base material is made of polyester containing a polyether component as a copolymerization component. It is a thing.

The invention according to claim 5 is the light control film according to claim 4, wherein the polyester contains the polyether component as a copolymerization component in an amount of 0.1 mol% or more and less than 5 mol%. is there.

The invention according to claim 6 is the light control film according to claim 4 or 5, wherein the number average molecular weight of the polyether component is 500 or more and 10000 or less.

According to the invention of claim 7, the dimming layer is a liquid crystal molecule arranged in a void formed inside a polymer network having a three-dimensional network structure, or a liquid crystal dispersedly arranged in a polymer matrix. The light control film according to any one of claims 1 to 6, wherein the material contains liquid crystal molecules contained in the material.

The invention according to claim 8 is the light control film according to any one of claims 1 to 7, wherein the thickness of the light control layer is 5 μm or more and 20 μm or less.

The invention according to claim 9 includes the light control film according to any one of claims 1 to 8, an AC power source capable of applying a voltage to the transparent electrode in the light control film, and the AC to the transparent electrode. It is a dimming device characterized by being provided with a switch for switching whether or not to apply a voltage of a power source.

The invention according to claim 10 comprises the dimming device according to claim 9, and is transparent on the transparent film substrate on at least one surface of the dimming device via a transparent adhesive layer. It is a screen characterized by being provided with glass.

According to the present invention, the thickness of the transparent film substrate is 20 μm or more and 100 μm or less, and the retardation when light having a wavelength of 586.4 nm is incident at an angle of 0 to 50 ° is 4000 nm or more and 20000 nm or less. Since it is a film base material, it is possible to suppress the occurrence of rainbow unevenness and unevenness accompanied by color change, and further, a light control film that prevents blackout even when viewed through a polarizing filter such as polarized sunglasses, and the light control film. A dimmer and a screen using the above can be obtained.

It is a schematic cross-sectional view which shows the layer structure of the light control film of a normal mode. It is a schematic cross-sectional view which shows the layer structure of the light control film of a reverse mode. It is a schematic cross-sectional view which shows the structure and behavior of the light control film of the normal mode including a PNLC type light control layer. (A) When the power is off (b) When the power is on. It is a schematic cross-sectional view which shows the structure and behavior of the light control film of the normal mode including a PDLC type light control layer. (A) When the power is off (b) When the power is on. It is a schematic cross-sectional view which shows the structure and behavior of the light control film of the reverse mode including a PNLC type light control layer. (A) When the power is off (b) When the power is on. It is a perspective view for demonstrating the angle of incidence on the transparent film base material and the retardation of a transparent film base material defined in this invention. It is a schematic side view which shows the structural example of the screen which uses the dimmer of this invention.

Hereinafter, the light control film according to the embodiment of the present invention will be described in detail. The same components are designated by the same reference numerals unless there is a reason for convenience, and duplicate description will be omitted. Further, in the drawings used in the following description, in order to make the features easy to understand, the featured portions may be enlarged and shown, and the dimensional ratio of each component is not the same as the actual one.

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, which 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 to two or more types. .. Here, the two types of "or more" are that the degree of light transmission / scattering can be changed and the haze can be changed in various ways by making the effective voltage variable in addition to turning on / off the AC power supply. Because.

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

Biaxially stretched polyethylene terephthalate film, polycarbonate film, etc., which are particularly preferable as the film base material of the light control film of the present invention, have birefringence, and therefore, usually, retardation (phase difference) occurs when light passes through the film. Occurs. Due to this, the above-mentioned rainbow unevenness and blackout phenomenon occur.

The retardation (Re) is the refractive index (Nx) in the direction having the largest refractive index in the plane of the film substrate having birefringence (slow-phase axis direction) and the direction orthogonal to the slow-phase axis direction (phase-advance axis). It is represented by the following formula (1) by the refractive index (Ny) of the direction) and the thickness (d) of the film base material.
Reference (Re) = (Nx-Ny) x d ... Equation (1)

In the film base material of 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 4000 nm or more and 20000 nm or less.

FIG. 6 is a perspective view for explaining the angle of incidence θ on the film substrate and the retardation of the film substrate defined in the present invention. The measurement lights 31a and 31b whose wavelengths are selected by a bandpass filter (not shown) pass through the polarizers 32a and 32b, respectively, and become the slow axis (Nx) and the phase advance axis (Ny) of the film substrate 1. It becomes polarized light that oscillates in a parallel direction, passes through the film substrate 1, further the detectors 33a and 33b, and is incident on the light receiving elements 34a and 34b. The 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, and retardation is required. The measurement lights 31a and 31b are preferably light emitted from the same light source and separated by a beam splitter.

The film substrate in the light control film of the present invention is not only vertically incident on the film substrate with light having a wavelength of 586.4 nm (incident angle 0 °), but also when obliquely incident at an incident angle of 0 to 50 °. Specified by retardation. FIG. 6 shows a case where the film base material 1 is tilted and obliquely incident. Here, the incident angle θ is equal to the inclination angle T of the film base material 1.

In the equation (1) expressing 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 / Cosθ, which is higher than that in the case of vertical incident. become longer. Therefore, if Nx and Ny are constant, the retardation increases as the tilt angle of the film substrate 1 increases. However, since Nx actually changes depending on the incident angle, the retardation does not increase monotonically with the tilt angle. ..

In the film substrate of the light control film of the present invention, the difference between the maximum value and the minimum value of retardation measured under the above measurement conditions is preferably 5000 nm or less.
The effectiveness of the retardation value under the measurement conditions specified by the film substrate in the light control film of the present invention is shown in Examples.

The film base material in the light control film of the present invention is preferably made of polyester containing a polyether component as a copolymerization component. As a result, it is possible to avoid a situation in which stress is generated during stretching of the film production, Ny becomes large, and the retardation becomes too small outside the range specified in the present invention.

When the total acid component is 100 mol%, the polyester preferably contains a polyether component of 0.1 mol% or more and less than 5 mol% as a copolymerization component. If it is less than 0.1 mol%, the effect of containing the above-mentioned polyether component is lost. On the other hand, if it is 5 mol% or more, it becomes difficult to produce a stable stretched film.

The number average molecular weight of the polyether component is preferably 500 or more and 10000 or less. If the number average molecular weight is less than 500, the effect of containing the above-mentioned polyether component becomes small. On the other hand, if it is 10,000 or more, it becomes difficult to produce a stable stretched film, and it is disadvantageous in terms of cost.

The light control layer in the light control film of the present invention is a liquid crystal molecule arranged 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 preferably contains the liquid crystal molecules contained. Therefore, PNLC type and PDLC type polymer liquid crystal composite films 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, a short circuit tends to occur, and it tends to be difficult to laminate the light control layer with the transparent electrode. If the thickness exceeds 50 μm, the responsiveness decreases.

The dimming device of the present invention includes the dimming film of the present invention, and includes an AC power source capable of applying a voltage to the transparent electrode and a switch for switching whether or not 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 in which the dimming film and the AC power supply are connected via a switch as shown in FIGS. 3 to 5. The AC power supply is preferably a variable power supply whose effective voltage can be changed. This is because, as described above, the degree of light transmission / scattering can be controlled and the haze can be changed in various ways.

The screen of the present invention is a screen provided with the dimming device of the present invention, and the transparent glass is provided on a film substrate on at least one surface of the dimming device via a transparent adhesive layer. FIG. 7 shows a form in which transparent glasses 42a and 42b are provided on film substrates 1a and 1b on both side surfaces of the dimming 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 supply, 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 that allows the image projected on the glass to be visually recognized. Also, by using a variable power supply, an intermediate state between them can be created.

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

<Example 1>
PET film 1 (thickness 40 μm) was prepared as the film substrates 1a and 1b, and ITO (indium tin oxide) having a thickness of 0.1 μm was formed on one surface of the PET film 1a and 1b by a sputtering method. A conductive film of the sheet was produced. Next, the PNLC type dimming layer is laminated on one ITO film side of the two sheets of the conductive film, and the other conductive film is further laminated with the ITO film side as the dimming layer side. A dimming film was obtained. As the PET film, it is preferable to use a lineup product of Cosmo Shine (registered trademark) manufactured by Toyobo Co., Ltd.

The PET form 1 had a retardation of 5101 to 7732 nm when incident at an angle of 0 to 50 ° when the vertical direction was 0 °. The retardation was measured by KOBRA-WR (manufactured by Oji Measuring Instruments Co., Ltd.) using light having a wavelength of 586.4 nm.

<Example 2>
In addition to the layer structure 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.

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

<Comparative example 2>
In the layer structure of Example 1, the PET film 1 was replaced with a PC film having a small retardation value. The retardation of the PC film measured in the same manner as in Example 1 from 0 to 50 ° was 562 to 1855 nm.

<Measurement and evaluation method of rainbow unevenness and unevenness accompanied by color change>
The dimming film of the example or the comparative example is observed through the light of a three-wavelength fluorescent tube from the front and diagonally in a straight state or curved to the extent that it does not bend, accompanied by rainbow unevenness and color change. The occurrence of unevenness was determined as follows.
◯: No rainbow unevenness or unevenness accompanied by color change was observed when observing from any direction.
X: Occurrence of rainbow unevenness and unevenness accompanied by color change is observed depending on the observation direction.

<Blackout measurement and evaluation method>
A light control film of Example or Comparative Example was attached to the display, and visual observation was performed from 0 ° and 40 ° directions through a polarizing plate. The polarizing plate was rotated by 0 to 360 ° during visual observation, 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: When the polarizing plate is rotated by 0 to 360 °, blackout occurs at a certain angle.

<Evaluation result>
Table 1 shows the evaluation results. Example 1 is a form of the normal mode of FIG. 3, and Example 2 is a form of the reverse mode of FIG. 5 in which a polyimide is used as an alignment film, but the range and difference of the retardation are within the range specified in the present invention. , Rainbow unevenness did not occur, blackout did not occur, and unevenness accompanied by color change was small. On the other hand, in Comparative Examples 1 and 2 in which the range of retardation was out of the range specified in the present invention, all the above three evaluation items gave poor results.

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

1, 1a, 1b ... Film substrate 2a, 2b ... Transparent electrode 3A ... Dimming layer (PNLC type)
3B ・ ・ ・ ・ ・ ・ Dimming layer (PDLC type)
4 ... Polymer network 5, 8 ... Liquid crystal molecules 6 ... Polymer matrix 7 ... Liquid crystal materials 9a, 9b ... Alignment film 10A ・ ・ ・ ・ ・ Dimming film (PNLC type, normal mode)
10B: Dimming film (PDLC type, normal mode)
11 ・ ・ ・ ・ ・ AC power supply 12 ・ ・ ・ ・ ・ Switch 20A ・ ・ ・ ・ Dimming film (PNLC type, reverse mode)
20B ... Dimming film (PDLC type, reverse mode)
21 ... Incident light 22 ... Scattered light 23 ... Transmitted light 30 ... Dimmer 31a, 31b ... Measurement light 32a, 32b ... Polarizer 33a , 33b ... Detector 34a, 34b ... Light receiving element 35 ... Polarization measuring unit Nx ... Refractive coefficient in the slow axis direction Ny ... Refractive coefficient in the phase advance axis direction θ ・ ・ ・ ・ ・ ・ Incident angle T ・ ・ ・ ・ ・ ・ Tilt angle of film base material d ・ ・ ・ ・ ・ ・ Thickness of film base material 40 ・ ・ ・ ・ ・ Screens 41a, 41b ・ ・ ・ Transparency Adhesive layers 42a, 42b ... Transparent glass 43 ... Projector 44 ... Projected light

Claims (10)

A transparent electrode and a transparent film base material are provided in this order on the light control layer and both side surfaces of the light control layer, and haze (white turbidity) is caused by a voltage that can be applied to the light control 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 base material is 20 μm or more and 100 μm or less.
When the angle of incidence when vertically incident on the transparent film substrate is 0 °, the 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 4000 nm. A light control film having a wavelength of 20000 nm or less. The first aspect of claim 1, wherein 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 5000 nm or less. Dimming film. The light control film according to claim 1 or 2, further comprising an alignment film between the light control layer and the transparent electrode. The light control film according to any one of claims 1 to 3, wherein the transparent film base material is made of polyester containing a polyether component as a copolymerization component. The light control film according to claim 4, wherein the polyester contains the polyether component as a copolymerization component in an amount of 0.1 mol% or more and less than 5 mol%. The light control film according to claim 4 or 5, wherein the number average molecular weight of the polyether component is 500 or more and 10000 or less. The dimming layer contains 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 dispersedly arranged in a polymer matrix. The dimming film according to any one of claims 1 to 6, wherein the light control film is characterized by this. The light control film according to any one of claims 1 to 7, wherein the thickness of the light control layer is 5 μm or more and 50 μm or less. Whether the AC power supply provided with the light control film according to any one of claims 1 to 8 and capable of applying a voltage to the transparent electrode of the light control film and the voltage of the AC power supply to the transparent electrode are applied. A dimming device characterized by having a switch for switching between on and off. A screen comprising the dimming device according to claim 9, wherein transparent glass is provided on the transparent film substrate on at least one surface of the dimming device via a transparent adhesive layer. ..

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