Light control film and transparent conductive film

Abstract

The purpose of the present invention is to provide a reverse type light control film that has excellent appearance quality by reducing the occurrence of white spots, and a transparent conductive film.　A light control film according to the present invention is characterized by comprising: a pair of transparent substrates (1); a transparent electrode layer (2) disposed inside the transparent substrates (1); an alignment layer (3) disposed inside the transparent electrode layer (2); and a light control layer (4) disposed inside the alignment layer (3) and including liquid crystal molecules (6), wherein the arithmetic average roughness Sa value of the surface of the transparent electrode layer (2) on the side facing the alignment layer (3) is 2.5 nm or less. It is preferable that, on the surface of the transparent electrode layer (2), the maximum height Peek value between adjacent valleys and peaks be 140 nm or less.

Description

Light-controlling film and transparent conductive film

[0001] The present invention relates to a light control film and a transparent conductive film.

[0002] Patent Document 1 discloses a display device having a pair of substrates, a pair of electrodes formed on opposing surfaces of the pair of substrates, and an electrolyte layer sandwiched between the pair of electrodes and containing an electrochromic material containing silver and a mediator. One of the pair of electrodes is a transparent electrode with projections and recesses, and the difference between the maximum height and the minimum height is preferably 50 nm or more and 400 nm or less.

[0003] Patent No. 6256881

[0004] Reverse-type light-control films have a problem in which white spots appear due to the disordered alignment of liquid crystal molecules.

[0005] However, the display device of Patent Document 1 uses a light control method that enables multicolor display by providing relatively large irregularities on the electrode surface, and is different in structure and purpose from the reverse-type light control film.

[0006] The present invention has been made in view of the above points, and aims to provide a reverse-type light control film and a transparent conductive film that reduce the occurrence of white spots and have excellent appearance quality.

[0007] The light control film of this embodiment comprises a pair of transparent substrates, a transparent electrode layer disposed inside the transparent substrates, an alignment layer disposed inside the transparent electrode layer, and a light control layer disposed inside the alignment layer and containing liquid crystal molecules, and is characterized in that the arithmetic mean roughness Sa value of the surface of the transparent electrode layer facing the alignment layer is 2.5 nm or less.

[0008] Alternatively, the light control film of this embodiment has a pair of transparent substrates, a transparent electrode layer arranged inside the transparent substrates, an alignment layer arranged inside the transparent electrode layer, and a light control layer arranged inside the alignment layer and containing liquid crystal molecules, and is characterized in that the height of the protrusions formed on the surface of the transparent electrode layer facing the alignment layer is smaller than the film thickness of the alignment layer.

[0009] Furthermore, the transparent conductive film of this embodiment is a transparent conductive film that is applied to a reverse-type light-control film in which a transparent electrode layer is formed on the surface of a transparent substrate, and is characterized in that the arithmetic mean roughness Sa value of the surface of the transparent electrode layer is 2.5 nm or less.

[0010] According to the present invention, it is possible to provide a reverse light control film that can reduce the occurrence of white spots and has good appearance quality, and a transparent conductive film used therefor.

[0011] FIG. 1 is a cross-sectional schematic diagram of a light control film according to the present embodiment; FIG. 2 is a partially enlarged schematic diagram for explaining the cause of white spots; (a) is a photograph of white spots, and (b) is a schematic diagram; FIG. 3 is a partially enlarged schematic diagram for explaining a characteristic configuration of the light control film according to the present embodiment; FIG. 4 is a graph showing the relationship between the arithmetic mean roughness Sa value of the surface of the transparent electrode layer and the number of white spots; and FIG. 5 is a graph showing the relationship between the PEEK value of the surface of the transparent electrode layer and the number of white spots.

[0012] The following describes in detail an embodiment of the present invention, but the following description is an example (typical example) of the embodiment of the present description, and the present invention is not limited to these details as long as it does not deviate from the gist of the present invention. In addition, the expression "to" includes a lower limit value and an upper limit value.

[0013] <Configuration of light control film 10> Figure 1 is a cross-sectional schematic diagram of a light control film 10 of a first embodiment. As shown in Figure 1, the light control film 10 has a laminated structure including a pair of transparent substrates 1, transparent electrode layers 2 formed on the inside of each transparent substrate 1, alignment layers 3 formed on the inside of each transparent electrode layer 2, and light control layers 4 formed on the inside of each alignment layer. The "inside" refers to the opposing side.

[0014] In other words, the light-controlling film 10 is laminated in the following order from the bottom: transparent substrate 1 (first transparent substrate), transparent electrode layer 2 (first transparent electrode layer), alignment layer 3 (first alignment layer), light-controlling layer 4, alignment layer 3 (second alignment layer), transparent electrode layer 2 (second transparent electrode layer), and transparent substrate (second transparent substrate).

[0015] (Transparent conductive film 5) The transparent substrate 1 and transparent electrode layer 2 shown in Fig. 1 constitute a transparent conductive film 5. Here, "film" refers to a planar shape whose planar width and length are much greater than its thickness, but it can also be read as "sheet." Note that in this embodiment, "film" and "sheet" are not distinguished by the thickness defined in the JIS standard.

[0016] Although the material of the transparent substrate 1 is not limited, a PET (Polyethylene Terephthalate) film is preferably used.

[0017] The transparent electrode layer 2 is a transparent layer having electrical conductivity, and although the material is not limited, examples thereof include indium tin oxide (ITO), fluorine-doped tin oxide (FTO), tin oxide, zinc oxide, carbon nanotubes (CNT), polymers containing poly(3,4-ethylenedioxythiophene) (PEDOT), and multilayer films containing Ag alloy thin films. Of these, it is preferable to use ITO or an Ag alloy for the transparent electrode layer 2. Furthermore, although the film thickness is not limited, the transparent substrate 1 is approximately 50 μm to 200 μm, and the transparent electrode layer 2 is approximately 10 nm to 100 nm.

[0018] The transparent conductive film 5 may also have a functional layer provided between the transparent substrate 1 and the transparent electrode layer 2 or on at least one of the outer surfaces 1a (surfaces opposite to the side facing the transparent electrode layer 2) of the transparent substrate 1. The functional layer preferably includes at least one of a hard coat layer, an anti-blocking layer, a primer layer, a protective layer, and an index matching layer, for example.

[0019] (Alignment layer 3) The alignment layer 3 is a layer that controls the alignment of the liquid crystal molecules contained in the light control layer 4. The light control film 10 of this embodiment is a reverse-type light control film, which is transparent when no driving voltage is applied, with the liquid crystal molecules oriented along the normal direction of the alignment layer 3 (vertical alignment), and becomes opaque when a driving voltage is applied.

[0020] There is no limitation on the material constituting the alignment layer 3, but examples thereof include polyamide, polyimide, polycarbonate, polystyrene, polysiloxane, polyesters such as polyethylene terephthalate and polyethylene naphthalate, and polyacrylates such as polymethyl methacrylate. Of these, it is preferable to use a polyimide-based resin.

[0021] Although there are no limitations on the film thickness of the alignment layer 3, it is about 50 nm to 250 nm, preferably about 70 nm to 220 nm, and more preferably about 100 nm to 200 nm, which allows for excellent alignment control power for liquid crystal molecules.

[0022] (Light-modulating layer 4) The light-modulating layer 4 contains liquid crystal molecules. The liquid crystal molecules have, for example, a positive dielectric anisotropy, and the dielectric constant in the long axis direction of the liquid crystal molecules is greater than the dielectric constant in the short axis direction of the liquid crystal molecules. The liquid crystal molecules are not limited to, but examples thereof include Schiff base, azo, azoxy, biphenyl, terphenyl, benzoate ester, tolan, pyrimidine, cyclohexane carboxylic acid ester, phenylcyclohexane, and dioxane liquid crystal molecules.

[0023] The light-controlling layer 4 is preferably made of a polymer network liquid crystal (PNLC). The polymer network liquid crystal has a polymer network with a three-dimensional mesh structure, and holds liquid crystal molecules in the voids of the polymer network.

[0024] The PNLC layer in this embodiment preferably contains liquid crystal molecules, a photocurable resin, and spacers.

[0025] <How the light-control film 10 of this embodiment was developed> Figure 2 is a partially enlarged schematic diagram illustrating the problem of white spots occurring in the prior art. Figure 2 shows only the layers below the light-control layer 4 of the light-control film 10 shown in Figure 1 . Note that, in the prior art, the same problem also occurs in the layers above the light-control layer 4, but since this is the same as the lower layer, a description thereof will be omitted. In Figure 2 , the transparent substrate is designated by the symbol 11, the transparent electrode layer by the symbol 12, the alignment layer by the symbol 13, and the light-control layer by the symbol 14.

[0026] As shown in Figure 2, the surface 12a of the transparent electrode layer 12 is not flat but has protrusions 12b. In other words, the surface 12a is uneven. As shown in Figure 2, large protrusions 12b are present and vary greatly. As a result, the flatness of the surface 13a of the alignment layer 13 formed on the surface 12a of the transparent electrode layer 12 is reduced, disrupting the vertical alignment of the crystalline molecules 15. As a result, white spots appear in the normally transparent state when the power is turned off. Figure 3(a) is a photograph of the white spots, and (b) is a schematic diagram. The whitish circular area in the center of Figure 3 is a white spot, and the diameter of the white spot is 1 mm or more. This is visible, resulting in a decrease in appearance quality.

[0027] In particular, as shown in Figure 2, in areas where the height t1 of the protrusions 12b formed on the surface 12a of the transparent electrode layer 12 is greater than the film thickness t2 of the alignment layer 13, the unevenness of the surface 13a of the alignment layer 13 becomes more pronounced, making the vertical alignment of the crystalline molecules 15 more likely to be disturbed.

[0028] Therefore, the inventors have conducted extensive research and have come up with the invention of a reverse-type light control film 10 that can adjust the surface roughness of the transparent electrode layer, smooth the surface of the alignment layer, and reduce the occurrence of white spots.

[0029] <Characteristics of the light control film 10 of this embodiment> This embodiment is characterized in that the arithmetic mean roughness Sa of the surface of the transparent electrode layer 2 facing the alignment layer 3 is 2.5 nm or less.

[0030] The arithmetic mean roughness Sa value (international standard for three-dimensional surface texture, ISO 25178) is a parameter that expands the arithmetic mean roughness Ra of a line to a surface, and indicates the average of the absolute values ​​of the height differences at multiple points on the measurement surface.２ The size is, but is not limited to, a size per square meter, and for example, measurement can be performed on a measurement surface with one side greater than 0.5 mm and equal to or less than 5 mm. The Sa value can be measured together with the PEEK value (to be described later) using a VertScan R3300G Lite from Ryoka Systems Co., Ltd.

[0031] In this embodiment, it is preferable that the maximum height PEEK value of adjacent valleys (which can also be called depressions) and peaks (which can also be called protrusions or convex portions) on the surface of the transparent electrode layer 2 facing the alignment layer 3 is 140 nm or less.

[0032] In this embodiment, by adjusting the arithmetic mean roughness Sa value, and preferably adjusting the PEEK value together with the arithmetic mean roughness Sa value, the flatness of the surface 3a of the alignment layer 3 can be improved compared to conventional methods, as shown in Figure 4, and therefore, disturbance of the vertical alignment of the liquid crystal molecules 6 contained in the light-controlling layer 4 can be suppressed, and the occurrence of white spots can be reduced.

[0033] As shown in Figure 4, the protrusions 2b formed on the surface 2a of the transparent electrode layer 2 are smaller than those shown in Figure 2, and the height t3 of the protrusions 2b is smaller than the film thickness t4 of the alignment layer 3. Here, the height t3 of the protrusions 2b is the dimension from the flat surface 2a (the bottom surface of the recess) of the transparent electrode layer 2, and the film thickness t4 of the alignment layer 3 is shown as the dimension from the surface 2a of the transparent electrode layer 2 to the surface 3a of the alignment layer 3. In this way, when a liquid alignment material is applied to the surface 2a of the transparent electrode layer 2 and cured so that the relationship of height t3 of the protrusions 2b < film thickness t4 of the alignment layer 3 is satisfied, the surface 3a of the alignment layer 3 is made flat, and the number and size of the protrusions formed on the surface 3a of the alignment layer 3 can be reduced.

[0034] Therefore, the alignment layer 3 can exert an excellent alignment control force on the liquid crystal molecules 6, and can properly align the liquid crystal molecules 6 vertically when the power is off. As a result, it is possible to reduce white spots and provide a reverse-type light-control film with good appearance quality. ２ The number of white spots having a diameter of 1 mm or more can be reduced to 1 or less, preferably 0.7 or less.

[0035] In this embodiment, the arithmetic mean roughness Sa value of the surface 2a of the transparent electrode layer 2 is more preferably 2.0 nm or less, and even more preferably 1.5 nm or less. The PEEK value of the surface 2a of the transparent electrode layer 2 is more preferably 100 nm or less, more preferably 70 nm or less, and even more preferably 50 nm or less. ２ The number of white spots having a diameter of 1 mm or more can be reduced to 0.6 or less, preferably 0.5 or less.

[0036] The present invention will be described in detail below with reference to examples carried out to clarify the effects of the present invention, but the present invention is not limited to the following examples.

[0037] <Surface Roughness Measurement> Using a plurality of samples with different surface roughness of the transparent electrode layer of the conductive film, the Sa value and PEEK value of each sample were measured as the surface quality (surface roughness measurement) according to ISO 25178 using a VertScan R3300G Lite from Ryoka Systems Co., Ltd.

[0038] The Sa value indicates the three-dimensional arithmetic mean roughness, and the PEEK value indicates the maximum height of adjacent valleys and peaks.

[0039] <Production of reverse-type light-controlling film and measurement of the number of white spots> Using each conductive film, a reverse-type light-controlling film was produced. At this time, the film thickness of the alignment layer was set to about 100 nm to 200 nm. ２ The number of white spots with a diameter of 1 mm or more was calculated. The experimental results are shown in Table 1 below.

[0040]

[0041] FIG. 5 is a graph showing the relationship between the arithmetic mean roughness Sa value of the surface of the transparent electrode layer and the number of white spots, and FIG. 6 is a graph showing the relationship between the PEEK value of the surface of the transparent electrode layer and the number of white spots.

[0042] As shown in Table 1 and FIG. 5, when the Sa value is 2.5 nm or less, ２ It was found that the number of white spots with a diameter of 1 mm or more can be reduced to one or less.２ It was found that the number of white spots with a diameter of 1 mm or more could be reduced to 0.5 or less.

[0043] Furthermore, as shown in Table 1 and FIG. 6, by making the PEEK value 140 nm or less, ２ It was found that the number of white spots with a diameter of 1 mm or more in the whole area can be kept to one or less. It is preferable that the PEEK value is 100 nm or less, and in particular, by making it 50 nm or less, it is possible to keep the number of white spots with a diameter of 1 mm or more within 1 mm. ２ It was found that the number of white spots with a diameter of 1 mm or more could be reduced to 0.5 or less.

[0044] This application is based on Japanese Patent Application No. 2024-086016, filed May 28, 2024, the contents of which are incorporated herein in their entirety.

Claims

1. A light control film comprising a pair of transparent substrates, a transparent electrode layer disposed on the inside of the transparent substrates, an alignment layer disposed on the inside of the transparent electrode layer, and a light control layer disposed on the inside of the alignment layer and containing liquid crystal molecules, wherein the arithmetic mean roughness Sa of the surface of the transparent electrode layer facing the alignment layer is 2.5 nm or less.

2. The light-control film according to claim 1, wherein the maximum height (PEEK) of adjacent peaks and valleys on the surface of the transparent electrode layer is 140 nm or less.

3. A light control film comprising a pair of transparent substrates, a transparent electrode layer disposed on the inside of the transparent substrates, an alignment layer disposed on the inside of the transparent electrode layer, and a light control layer disposed on the inside of the alignment layer and containing liquid crystal molecules, wherein the height of protrusions formed on the surface of the transparent electrode layer facing the alignment layer is smaller than the film thickness of the alignment layer.

4. The light control film according to claim 1 or 3, wherein the transparent electrode layer is made of ITO or an Ag alloy.

5. The light control film according to claim 1 or 3, characterized in that the alignment layer is formed from a polyimide resin.

6. The light control film according to claim 1 or 3, characterized in that the transparent substrate is a PET substrate.

7. A light-controlling film according to claim 1 or claim 3, characterized in that it has a functional layer between the transparent substrate and the transparent electrode layer, and / or on the outer surface of the transparent substrate opposite to the side facing the transparent electrode layer.

8. The light control film according to claim 7, wherein the functional layer includes at least one of a hard coat layer, an anti-blocking layer, a primer layer, a protective layer, and an index matching layer.

9. The light-controlling film according to claim 1 or 3, characterized in that the light-controlling layer contains liquid crystal molecules, a photocurable resin, and spacers.

10. A transparent conductive film applied to a reverse-type light-control film in which a transparent electrode layer is formed on the surface of a transparent substrate, characterized in that the arithmetic mean roughness Sa value of the surface of the transparent electrode layer is 2.5 nm or less.

11. The transparent conductive film according to claim 10, wherein the maximum height (PEEK value) of adjacent peaks and valleys on the surface of the transparent electrode layer is 140 nm or less.

Images