Barrier film for electronic paper, and electronic paper using the same

Abstract

The present invention provides a barrier film for electronic paper that exhibits good barrier properties and can suppress the deterioration of the display quality of electronic paper. [Solution] A barrier film 100 for electronic paper having a first coating layer 11, a first inorganic oxide layer 12, and a first substrate 13 in this order, wherein the average thickness of the first coating layer 11 is 100 nm or more and 600 nm or less, and the standard deviation σ of the thickness of the first coating layer 11 is 3 nm or more and 60 nm or less.

Description

[Technical Field]

[0001] This disclosure relates to a barrier film for electronic paper and electronic paper using the same. [Background technology]

[0002] Electronic paper consumes power only when rewriting information and can maintain its display even after the power supply is cut off, thus reducing power consumption compared to liquid crystal displays and organic EL displays. In addition, electronic paper has excellent characteristics such as "excellent flexibility" and "thin and lightweight."

[0003] Electronic paper is composed of, for example, a back electrode substrate having a back substrate and back electrodes, a transparent electrode substrate having a transparent substrate and transparent electrodes, and a display medium layer disposed between the back electrode substrate and the transparent electrode substrate.

[0004] The display medium layer of electronic paper has a configuration in which dyes are dispersed in a filler liquid, for example. Electronic paper can rewrite the information displayed on it by controlling the voltage to position the desired dyes in the display medium layer towards the observer. The information rewriting performance of the display medium layer is prone to deterioration if the filler liquid evaporates or if moisture from the outside air enters. In addition, to make electronic paper thinner, lighter, and more flexible, a plastic film is often used for at least one of the back substrate and the transparent substrate. Plastic films have inferior barrier properties compared to glass. Therefore, there is a need for plastic films for electronic paper with good barrier properties.

[0005] For example, Patent Documents 1 and 2 have proposed barrier films for electronic paper. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2017 / 130617 [Patent Document 2] Japanese Patent Publication No. 2011-240668 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Barrier films for electronic paper require high levels of barrier properties and optical properties. In particular, as the transition from monochrome to color displays has progressed, the requirements for optical properties have become increasingly stringent in recent years. To achieve high levels of barrier properties, the inventors considered forming an inorganic oxide layer on a substrate by vapor deposition or the like, and then providing a coating layer on top of the inorganic oxide layer.

[0008] However, when a coating layer is applied on top of an inorganic oxide layer, while barrier properties are improved, striped color unevenness can sometimes be seen within the surface of the barrier film. This striped color unevenness degrades the display quality of display devices such as electronic paper. In particular, the striped color unevenness becomes extremely noticeable in monochrome two-color electronic paper. Patent documents 1 and 2 do not address the above-mentioned problems that arise when a coating layer is provided on an inorganic oxide layer.

[0009] This disclosure aims to provide a barrier film for electronic paper that has good barrier properties and can suppress a deterioration in the display quality of electronic paper. Furthermore, this disclosure aims to provide electronic paper using the aforementioned barrier film. [Means for solving the problem]

[0010] This disclosure is as follows: <1> ~ <2> To provide. <1> A barrier film for electronic paper having a first coating layer, a first inorganic oxide layer, and a first substrate in this order, A barrier film for electronic paper, wherein the average thickness of the first coating layer calculated in Measurement 1 below is 100 nm or more and 600 nm or less, and the standard deviation σ of the thickness of the first coating layer calculated in Measurement 1 below is 3 nm or more and 60 nm or less. <Measurement 1> Cut out a rectangular sample with a short side of 3 cm and a long side of 6 cm from the barrier film for electronic paper. Draw a first line that trisects the short side direction of the sample and a second line that sextuples the long side direction of the sample. Measure the thickness of the first coating layer at 10 intersection points of the first line and the second line. Based on the thicknesses of the first coating layer at the 10 points, calculate the "average thickness of the first coating layer", the "standard deviation σ of the thickness of the first coating layer", the "difference between the maximum value and the minimum value of the thickness of the first coating layer", and the "maximum value of the differences in the thicknesses of the first coating layer at adjacent measurement points". <2> An electronic paper including an electronic paper display element and the barrier film described in <1>.

Advantages of the Invention

[0011] The barrier film for electronic paper and the electronic paper using the same according to the present disclosure have good barrier properties and can suppress deterioration of the display quality of the electronic paper.

Brief Description of the Drawings

[0012] [Figure 1] It is a cross-sectional view showing an embodiment of the barrier film for electronic paper according to the present disclosure. [Figure 2] It is a cross-sectional view showing another embodiment of the barrier film for electronic paper according to the present disclosure. [Figure 3] It is a cross-sectional view showing an embodiment of the electronic paper according to the present disclosure. [Figure 4] It is a diagram for explaining measurement locations of the thickness of the first coating layer.

Modes for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present disclosure will be described. In this specification, the notation "AA to BB" means AA or more and BB or less. In this specification, the "barrier film for electronic paper" may be abbreviated as "barrier film".

[0014] [Barrier film for electronic paper] The barrier film for electronic paper disclosed herein is The coating layer, the inorganic oxide layer, and the first substrate are in this order. The average thickness of the coating layer calculated in Measurement 1 below is between 100 nm and 600 nm, and the standard deviation σ of the thickness of the coating layer calculated in Measurement 1 below is between 3 nm and 60 nm. <Measurement 1> A rectangular sample measuring 3 cm on the short side and 6 cm on the long side is cut from the barrier film for electronic paper. A first line is drawn dividing the short side of the sample into three equal parts, and a second line is drawn dividing the long side of the sample into six equal parts. The thickness of the first coating layer is measured at 10 intersection points of the first and second lines. Based on the thickness of the first coating layer at 10 locations, the "average thickness of the first coating layer," the "standard deviation σ of the thickness of the first coating layer," the "difference between the maximum and minimum thickness of the first coating layer," and the "maximum difference in the thickness of the first coating layer at adjacent measurement points" are calculated.

[0015] Figures 1 and 2 are cross-sectional views showing embodiments of the barrier film 100 for electronic paper according to the present disclosure. The barrier film 100 in Figures 1 and 2 has a first coating layer 11, a first inorganic oxide layer 12, and a first substrate 13 in that order. The barrier film 100 in Figure 2 further has an adhesive layer 14 and a second substrate 15, and thus has a first coating layer 11, a first inorganic oxide layer 12, a first substrate 13, an adhesive layer 14, and a second substrate 15 in that order. Figures 1 and 2 are schematic cross-sectional views. That is, the scales of each layer constituting the barrier film 100 in Figures 1 and 2 are schematic for illustrative purposes and do not reflect the actual scales. The same applies to Figure 3.

[0016] <First base material> The first base material is a resin film containing one or more resins selected from polyester, triacetylcellulose, cellulose diacetate, cellulose acetate butyrate, polyamide, polyimide, polyethersulfone, polysulfone, polypropylene, polymethylpentene, polyvinyl chloride, polyvinyl acetal, polyetherketone, acrylic, polycarbonate, polyurethane, and amorphous olefin. Among these resin films, stretched polyester film is preferred from the viewpoint of mechanical strength, dimensional stability, and heat resistance, and biaxially stretched polyester film is more preferred. Examples of polyester films include polyethylene terephthalate film and polyethylene naphthalate film.

[0017] The thickness of the first substrate is preferably 5.0 μm or more, more preferably 8.0 μm or more, and even more preferably 10.0 μm or more. The thickness of the first substrate is preferably 100.0 μm or less, more preferably 75.0 μm or less, and even more preferably 50.0 μm or less. By setting the thickness of the first substrate within the above range, the handling properties of the barrier film can be improved, and the barrier film can be made thinner.

[0018] In the constituent elements shown herein, if multiple options are provided for both the upper and lower limits of a numerical value, the description shall include embodiments of a range combining one selected from the upper limit options and one selected from the lower limit options. For example, embodiments of the thickness range of the first substrate described above include 5.0 μm to 100.0 μm, 5.0 μm to 75.0 μm, 5.0 μm to 50.0 μm, 8.0 μm to 100.0 μm, 8.0 μm to 75.0 μm, 8.0 μm to 50.0 μm, 10.0 μm to 100.0 μm, 10.0 μm to 75.0 μm, and 10.0 μm to 50.0 μm.

[0019] In this specification, the thickness of the first substrate and the second substrate (described later) shall be the average of the thicknesses at any 10 locations. The thicknesses of the first and second substrates shall be measured using a general-purpose film thickness measuring instrument. Examples of film thickness measuring instruments include Mitutoyo's Digimatic Standard Outside Micrometer (model number: MDC-25SX).

[0020] In this specification, the thickness of the layer, haze, and b * When measuring various parameters such as values, measurements shall be taken in an atmosphere of 23°C ± 5°C and a relative humidity of 40% to 65%, unless otherwise specified. Furthermore, before measuring various parameters, the sample shall be exposed to the aforementioned atmosphere for 30 to 60 minutes.

[0021] The first substrate may have an anti-blocking layer containing a matting agent on one side to suppress blocking. General-purpose inorganic particles and organic particles can be used as the matting agent. It is preferable that the anti-blocking layer be placed on the side of the first substrate opposite to the side having the first inorganic oxide layer.

[0022] The surface of the first substrate having the first inorganic oxide layer may be surface-treated to improve adhesion and other properties. Examples of surface treatments include corona discharge treatment, ozone treatment, low-temperature plasma treatment, glow discharge treatment, and oxidation treatment. Furthermore, an anchor coat layer may be formed on the side of the first substrate having the first inorganic oxide layer to improve adhesion.

[0023] <First Inorganic Oxide Layer> The first inorganic oxide layer preferably contains one or more inorganic oxides selected from aluminum oxide, silicon oxide, and magnesium oxide. To facilitate good barrier properties and to increase the production efficiency of the barrier film, silicon oxide or aluminum oxide is preferred among the inorganic oxides. In other words, the first inorganic oxide layer preferably contains silicon oxide or aluminum oxide.

[0024] The first inorganic oxide layer can be formed by physical vapor deposition (PVD) methods such as vacuum deposition, sputtering, and ion plating, or by chemical vapor deposition (CVD) methods such as plasma chemical vapor deposition, thermochemical vapor deposition, and photochemical vapor deposition. Among these, vacuum deposition is preferred due to its good productivity (deposition rate). The PVD method is preferred over the CVD method because it is less likely to result in carbon contamination in the inorganic oxide layer.

[0025] When the first inorganic oxide layer contains silicon and oxygen, the total content of silicon and oxygen is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, based on the total solid content of the first inorganic oxide layer. Examples of inorganic oxides containing silicon and oxygen include silicon dioxide and other silicon oxides (SiOx). When the first inorganic oxide layer contains aluminum and oxygen, the total content of aluminum and oxygen is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, based on the total solid content of the first inorganic oxide layer. Examples of inorganic oxides containing aluminum and oxygen include aluminum oxide (AlOx) such as Al2O3. A small amount of aluminum hydroxide may also be included as an inorganic oxide containing aluminum and oxygen, to the extent that it does not hinder the effects of this disclosure.

[0026] The preferred thickness of the first inorganic oxide layer varies depending on the type of inorganic oxide, so it cannot be stated definitively. When the first inorganic oxide layer contains silicon and oxygen, the thickness of the first inorganic oxide layer is preferably 30 nm or more, more preferably 40 nm or more, and even more preferably 50 nm or more, in order to improve barrier properties. When the first inorganic oxide layer contains silicon and oxygen, the thickness of the first inorganic oxide layer is preferably 200 nm or less, more preferably 150 nm or less, and even more preferably 120 nm or less. By setting the thickness to 200 nm or less, it is possible to suppress the occurrence of scratches and cracks in the first inorganic oxide layer, and the barrier film b * It makes it easier to lower the value.

[0027] When the first inorganic oxide layer contains aluminum and oxygen, the thickness of the first inorganic oxide layer is preferably 6 nm or more, and more preferably 7 nm or more, in order to improve barrier properties. Furthermore, when the first inorganic oxide layer contains aluminum and oxygen, the thickness of the first inorganic oxide layer is preferably 50 nm or less, more preferably 45 nm or less, and even more preferably 40 nm or less. By setting the thickness to 50 nm or less, it is easier to suppress the occurrence of scratches and cracks in the first inorganic oxide layer.

[0028] In this specification, the thickness of the first inorganic oxide layer and the adhesive layer described later can be calculated, for example, by measuring the thickness at 10 locations on a vertical cross-sectional image taken using a scanning transmission electron microscope (STEM) and taking the average value of the 10 values.

[0029] <First coating layer> The barrier film of this disclosure requires that the first coating layer be located on the side of the first inorganic oxide layer opposite to the first substrate. By providing the first coating layer in addition to the first inorganic oxide layer, the barrier properties of the barrier film can be easily enhanced. Preferably, the first coating layer is located on the outermost surface of the barrier film.

[0030] The barrier film of this disclosure is required to have an average thickness of the first coating layer calculated in Measurement 1 below that is between 100 nm and 600 nm, and a standard deviation σ of the thickness of the first coating layer calculated in Measurement 1 below that is between 3 nm and 60 nm. <Measurement 1> A rectangular sample measuring 3 cm on the short side and 6 cm on the long side is cut from the barrier film for electronic paper. A first line is drawn dividing the short side of the sample into three equal parts, and a second line is drawn dividing the long side of the sample into six equal parts. The thickness of the first coating layer is measured at 10 intersection points of the first and second lines. Based on the thickness of the first coating layer at 10 locations, the "average thickness of the first coating layer," the "standard deviation σ of the thickness of the first coating layer," the "difference between the maximum and minimum thickness of the first coating layer," and the "maximum difference in the thickness of the first coating layer at adjacent measurement points" are calculated.

[0031] Figure 4 is a diagram illustrating the measurement locations for the thickness of the first coating layer in Measurement 1. In Figure 4, reference numeral 100A indicates a rectangular sample with a short side of 3 cm and a long side of 6 cm. In Figure 4, the dashed line represents the first line, the dashed line represents the second line, and the black circles with reference numerals X1 to X10 correspond to the intersections of the first and second lines.

[0032] In Measurement 1, the thickness of the first coating layer is measured at 10 points at the intersections of the first and second lines. In Measurement 1, the thickness of the first coating layer at each point is measured from the image of the vertical cross-section of the barrier film captured by a scanning transmission electron microscope. Specifically, the thickness of the first coating layer at each point is measured according to the following procedure A1 to A3.

[0033] A1: Cut out 10 small samples from a rectangular sample measuring 3 cm on the short side and 6 cm on the long side. Each small sample should be a rectangle measuring 3 mm on the short side and 6 mm on the long side. The direction of the short and long sides of the small samples should be aligned with the direction of the short and long sides of the original 3 cm x 6 cm sample. Each small sample should have the intersection point located in the center of its plane. A2: From each small sample, prepare an imaging sample in which the vertical cross-section of the barrier film is exposed. Prepare the imaging sample so that the width direction of the vertical cross-section is in the direction of the longer side of the small sample. "Vertical cross-section of the barrier film" means a cross-section perpendicular to the XY plane, assuming that the plane of the barrier film is the XY plane. A3: The sample for imaging is imaged using a scanning transmission electron microscope to obtain an image of the vertical cross-section of the barrier film. The image is adjusted so that the width of the image area, excluding the scale bar, is 1200 nm. The thickness of the first coating layer in the image is measured at three locations every 200 nm in the width direction, and the average of these three measurements is taken as the thickness of the first coating layer for each small sample. Then, the thickness of the first coating layer for each small sample is taken as the thickness of the first coating layer at each measurement location.

[0034] The samples for imaging A2 and A3 are prepared, for example, by the following steps B1 and B2. The acceleration voltage for the A3 scanning transmission electron microscope is preferably 100V to 30kV.

[0035] B1: Prepare an embedded sample by embedding a small sample in resin. B2: Prepare an imaging sample by vertically cutting the embedded sample, exposing the vertical cross-section of the barrier film. Cut the embedded sample so that the width direction of the vertical cross-section is aligned with the longer side of the smaller sample. Cut the embedded sample with a microtome using a diamond knife.

[0036] In B1 above, epoxy resin is preferred for embedding. An embedded sample can be obtained, for example, by placing a small sample in a silicone embedding plate, pouring in embedding resin, allowing the embedding resin to harden, and then removing the small sample and the surrounding embedding resin from the silicone embedding plate. The embedded sample is block-shaped. The silicone embedding plate is sometimes referred to as a silicone capsule.

[0037] In step B2 above, when cutting the embedded sample, it is preferable to cut it so that it passes through the center of the small sample. When cutting embedded samples with a microchromatome, it is preferable to initially cut the embedded sample roughly, and then finally trim it precisely under the conditions of "SPEED: 1.00 mm / s" and "FEED: 70 nm".

[0038] The barrier film of this disclosure is required to have an average thickness of the first coating layer calculated in Measurement 1 of 100 nm or more and 600 nm or less, and a standard deviation σ of the thickness of the first coating layer calculated in Measurement 1 of 3 nm or more and 60 nm or less. The barrier film of this disclosure has good barrier properties and can suppress a decrease in the display quality of electronic paper by setting the average thickness of the first coating layer and the standard deviation σ of the thickness of the first coating layer within the above range. The reason why the barrier film of this disclosure can have good barrier properties and suppress a decrease in the display quality of electronic paper will be explained below.

[0039] First, the barrier film of this disclosure can be made easier to improve barrier properties by setting the average thickness of the first coating layer to 100 nm or more. Furthermore, the barrier film of this disclosure can be made easier to suppress crack formation in the first coating layer by setting the average thickness of the first coating layer to 600 nm or less, thereby making it easier to suppress a decrease in barrier properties. However, when the average thickness of the first coating layer was set to between 100 nm and 600 nm, cases of striped color unevenness occurring within the surface of the barrier film frequently occurred. The inventors investigated the cause of striped color unevenness within the surface of a barrier film having a coating layer on an inorganic oxide layer. As a result, the inventors found that "when the average thickness of the first coating layer is between 100 nm and 600 nm, interference is more likely to occur because the thickness approaches the wavelength of light," "if the first coating layer has thickness unevenness within the surface, interference unevenness occurs within the surface," and "striped color unevenness is visible due to interference unevenness within the surface." The inventors then found that striped color unevenness can be suppressed by reducing the thickness unevenness of the first coating layer. In other words, the inventors found that the deterioration of the display quality of electronic paper can be suppressed by reducing the thickness unevenness of the first coating layer. However, simply reducing the thickness variation of the first coating layer sometimes resulted in the first coating layer adhering to other components, reducing the manufacturing efficiency of the barrier film. Other components include the first substrate and the conveyor rolls of the coating apparatus. Furthermore, when the first coating layer was peeled off from a state in which it was adhering to other components, a part of the first coating layer was sometimes damaged, reducing its barrier properties. As a result of diligent research, the inventors have discovered that the above-mentioned problems can be suppressed by setting the standard deviation σ of the thickness of the first coating layer to a predetermined value or higher. As described above, the barrier film of this disclosure has good barrier properties and can suppress a decrease in the display quality of electronic paper by setting the average thickness of the first coating layer and the standard deviation σ of the thickness of the first coating layer within the above range.

[0040] The average thickness of the first coating layer is preferably 120 nm to 570 nm, and more preferably 150 nm to 550 nm. The standard deviation σ of the thickness of the first coating layer is preferably 3 nm or more and 55 nm or less, and more preferably 4 nm or more and 50 nm or less.

[0041] The difference between the maximum and minimum thickness of the first coating layer calculated in measurement 1 is preferably 10 nm or more and 200 nm or less, more preferably 15 nm or more and 180 nm or less, and even more preferably 20 nm or more and 150 nm or less. By setting the difference between the maximum and minimum values ​​to 10 nm or more, it becomes easier to suppress the first coating layer from adhering to other components. By setting the difference between the maximum and minimum values ​​to 200 nm or less, it becomes easier to suppress the deterioration of the display quality of the electronic paper. Furthermore, by setting the difference between the maximum and minimum values ​​to 200 nm or less, it becomes easier to suppress the localized deterioration of barrier properties in thin areas.

[0042] The maximum value of the difference in thickness of the first coating layer between adjacent measurement locations calculated in Measurement 1 is preferably 5 nm or more and 100 nm or less, more preferably 8 nm or more and 90 nm or less, and even more preferably 10 nm or more and 80 nm or less. By setting the maximum difference in thickness between adjacent measurement points to 5 nm or more, it becomes easier to suppress the first coating layer from adhering to other components. By setting the maximum difference to 100 nm or less, it becomes easier to suppress the deterioration of the display quality of the electronic paper. Furthermore, by setting the maximum difference to 100 nm or less, it becomes easier to suppress the localized deterioration of barrier properties in thin areas. Adjacent measurement points refer to measurement points adjacent in the direction of the long side and / or the short side. For example, if the reference point is X1 in Figure 4, the adjacent measurement points are X2 and X6 (2 points). If the reference point is X3 in Figure 4, the adjacent measurement points are X2, X4, and X8 (3 points).

[0043] Barrier films can take the form of a single sheet or a roll. When multiple rectangular samples measuring 3 cm on the short side and 6 cm on the long side can be cut from a sheet of barrier film, the percentage of samples in which the "average thickness of the first coating layer" and the "standard deviation σ of the thickness of the first coating layer" satisfy the above-mentioned range is preferably 50% or more, more preferably 70% or more, even more preferably 90% or more, and most preferably 100%. Similarly, the percentage of samples in which the "difference between the maximum and minimum thickness of the first coating layer" and the "difference in the thickness of the first coating layer at adjacent measurement points" satisfy the above-mentioned range is preferably 50% or more, more preferably 70% or more, even more preferably 90% or more, and most preferably 100%.

[0044] In the case of a roll of barrier film, a rectangular sample measuring 3 cm on the short side and 6 cm on the long side is cut out with the long side of the sample aligned with the width direction of the roll. If multiple rectangular samples measuring 3 cm on the short side and 6 cm on the long side can be cut out in the width direction of the roll, the percentage of samples in which the "average thickness of the first coating layer" and the "standard deviation σ of the thickness of the first coating layer" satisfy the above-mentioned range is preferably 50% or more, more preferably 70% or more, even more preferably 90% or more, and most preferably 100%. Similarly, the percentage of samples in which the "difference between the maximum and minimum thickness of the first coating layer" and the "difference in the thickness of the first coating layer at adjacent measurement points" satisfy the above-mentioned range is preferably 50% or more, more preferably 70% or more, even more preferably 90% or more, and most preferably 100%. The physical properties of the coating film tend to fluctuate in the width direction of the roll, but less so in the flow direction of the roll. Therefore, the process of cutting multiple rectangular samples of 3 cm x 6 cm in the width direction of the roll only needs to be performed at predetermined positions in the flow direction of the roll, and does not need to be performed at all positions in the flow direction of the roll. However, the physical properties of the coating film may fluctuate near the start and end points of the roll. Therefore, the process of cutting multiple samples in the width direction of the roll should be performed, for example, at positions at 10%, 50%, and 90% of the total length of the roll.

[0045] The first coating layer preferably contains one or more selected from water-soluble polymers and metal alkoxide compounds. The coating layer more preferably contains one or more selected from water-soluble polymers and metal alkoxide compounds, and even more preferably contains one or more selected from water-soluble polymers and one or more selected from metal alkoxide compounds.

[0046] Examples of water-soluble polymers include polyvinyl alcohol, polyvinylpyrrolidone, and ethylene-vinyl alcohol copolymers. Among these, polyvinyl alcohol and ethylene-vinyl alcohol copolymers are preferred due to their barrier properties, and polyvinyl alcohol is more preferred. In other words, the coating layer preferably contains one or more selected from polyvinyl alcohol and ethylene-vinyl alcohol copolymers, and more preferably contains polyvinyl alcohol.

[0047] When the first coating layer contains a water-soluble polymer and a metal alkoxide compound, the content of the water-soluble polymer relative to 100 parts by mass of the total amount of the metal alkoxide compound is preferably 5 parts by mass or more and 500 parts by mass or less, more preferably 7 parts by mass or more and 100 parts by mass or less, and even more preferably 8 parts by mass or more and 50 parts by mass or less.

[0048] Examples of metal alkoxide compounds include metal alkoxides, metal alkoxide hydrolysates, and metal alkoxide polymers. Metal alkoxides are M(OR) n It is a compound represented by the general formula , where M represents a metal such as Si, Ti, Al, and Zr, and R represents an alkyl group such as a methyl group and an ethyl group. Specific examples of metal alkoxides include tetramethoxysilane, tetraethoxysilane, and isopropoxyaluminum.

[0049] It is preferable that the first coating layer is substantially free of particles. This is because the presence of particles may result in differences in barrier properties between areas with and without particles. "Substantially absent" means that the amount is 0.1% by mass or less of the total solid content of the first coating layer, preferably 0.01% by mass or less, and most preferably 0% by mass.

[0050] The first coating layer can be formed, for example, by applying and drying a coating solution for the first coating layer, which contains the components constituting the first coating layer, onto an inorganic oxide layer. The coating solution may contain additives such as a silane coupling agent, a curing agent, and a dispersant.

[0051] The average thickness of the first coating layer can be adjusted, for example, by the amount of solid content adhering to the coating solution for the first coating layer. The standard deviation σ of the thickness of the first coating layer can be adjusted, for example, by the methods C1 to C2 described below. C1: Viscosity of the coating solution. Lower viscosity tends to decrease the standard deviation, while higher viscosity tends to increase it. Viscosity can be adjusted, for example, by the solid content of the coating solution. C2: Change in drying temperature. Lower drying temperatures tend to decrease the standard deviation, while higher drying temperatures tend to increase it.

[0052] <Other layers> The barrier film of this disclosure may have layers other than the first coating layer, the first inorganic oxide layer, and the first substrate. For example, the barrier film of this disclosure may have an anchor coat layer between the first inorganic oxide layer and the first substrate.

[0053] The barrier film of this disclosure further comprises a second coating layer and a second inorganic oxide layer, and may have the first coating layer, the first inorganic oxide layer, the second coating layer, the second inorganic oxide layer and the first substrate in this order. The embodiment of the second coating layer can be the same as the embodiment of the first coating layer. However, since the second coating layer is located inside the barrier film, the range of the standard deviation σ of the thickness, the range of the difference between the maximum and minimum thickness values, and the range of the thickness difference between adjacent measurement points may be different from those of the first coating layer. The embodiment of the second inorganic oxide layer can be the same as the embodiment of the first inorganic oxide layer.

[0054] The barrier film of this disclosure further comprises an adhesive layer and a second substrate, and the coating layer, the inorganic oxide layer, the first substrate, the adhesive layer, and the second substrate may be arranged in this order. The presence of an adhesive layer and a second substrate in the barrier film makes it easier to handle the barrier film.

[0055] <Second base material> The second base material is a resin film containing one or more resins selected from polyester, triacetylcellulose, cellulose diacetate, cellulose acetate butyrate, polyamide, polyimide, polyethersulfone, polysulfone, polypropylene, polymethylpentene, polyvinyl chloride, polyvinyl acetal, polyetherketone, acrylic, polycarbonate, polyurethane, and amorphous olefin. Among these resin films, stretched polyester film is preferred from the viewpoint of mechanical strength, dimensional stability, and heat resistance, and biaxially stretched polyester film is more preferred. Examples of polyester films include polyethylene terephthalate film and polyethylene naphthalate film.

[0056] The second substrate may have a blocking prevention layer containing a matting agent on at least one side of the resin film to suppress blocking. General-purpose inorganic particles and organic particles can be used as the matting agent.

[0057] The thickness of the second substrate is preferably 20.0 μm or more, more preferably 30.0 μm or more, and even more preferably 45.0 μm or more. The thickness of the second substrate is preferably 120.0 μm or less, more preferably 100.0 μm or less, and even more preferably 80.0 μm or less. By setting the thickness of the second substrate within the above range, the handling properties of the barrier film can be improved, and the barrier film can be made thinner.

[0058] <Adhesive layer> Examples of adhesives that can be used to form the adhesive layer include moisture-curing adhesives, thermosetting adhesives, UV-curing adhesives, heat-sensitive adhesives (e.g., hot-melt adhesives), and pressure-sensitive adhesives. General-purpose adhesives can be used for these various types of adhesives.

[0059] The adhesive layer is preferably formed from a curing adhesive to ensure good adhesion over the long term. Examples of curing adhesives include moisture-curing adhesives, thermosetting adhesives, and UV-curing adhesives, with thermosetting adhesives and UV-curing adhesives being preferred, and thermosetting adhesives being more preferred.

[0060] Examples of thermosetting adhesives include general-purpose one-component curing adhesives and two-component curing adhesives. Among these, two-component curing polyurethane adhesives are preferred. Two-component curing polyurethane adhesives are adhesives containing a polyol compound and an isocyanate compound.

[0061] The thickness of the adhesive layer is preferably 2 μm to 30 μm, more preferably 3 μm to 20 μm, and even more preferably 4 μm to 10 μm. By making the thickness 2 μm or more, it is easier to improve the adhesion to the second substrate. By making the thickness 30 μm or less, it is easier to make the barrier film thinner and it is easier to suppress the stress generated due to curing shrinkage of the adhesive.

[0062] <Physical properties> The barrier film has a water vapor transmission value of 0.02 g / m² according to JIS K7129-2:2019. 2 It is preferable that it be less than or equal to 0.01 g / m². 2 It is preferable that it be less than or equal to one day. The temperature and humidity conditions for measuring water vapor transmission shall be 40°C and 90% relative humidity. Furthermore, before measuring water vapor transmission, the sample shall be exposed to an atmosphere of 23°C ± 5°C and a relative humidity of 40% to 65% for 30 to 60 minutes. In this specification, water vapor transmission refers to the average value of three measured values.

[0063] The barrier film has an oxygen permeability value of 0.5 cc / m² according to JIS K7126-2:2006. 2 It is preferable that it is less than or equal to day·atm. The temperature and humidity conditions for measuring oxygen permeability shall be 23°C and 90% relative humidity. Furthermore, before measuring oxygen permeability, the sample to be measured shall be exposed to an atmosphere of 23°C ± 5°C and a relative humidity of 40% to 65% for 30 to 60 minutes. In this specification, oxygen permeability refers to the average value of three measured values.

[0064] The barrier film preferably has a total light transmittance of 85% or higher, more preferably 87% or higher, and even more preferably 89% or higher, according to JIS K7361-1:1997. The upper limit of the total light transmittance is approximately 95%. In this specification, total light transmittance refers to the average value of three measurements.

[0065] The barrier film preferably has a haze of 20% or less, more preferably 15% or less, and even more preferably 10% or less, according to JIS K7136:2000. The lower limit of the haze is not particularly limited, but is usually 0.1% or more. By keeping the haze below 20%, it becomes easier to suppress the blurring and visibility of the electronic paper display element. In this specification, haze refers to the average value of three measurements. The light incident surface when measuring total light transmittance and haze is the surface on the first substrate side.

[0066] The barrier film is based on the reflected light when the first substrate side is the light incident surface with respect to the first inorganic oxide layer. * a * b* The b value of the color system * is preferably -1.0 or more and 5.0 or less. b * is more preferably -0.5 or more and 4.0 or less, and even more preferably -0.1 or more and 3.0 or less. In this specification, b * value means the average value of three measured values. b * By setting the b value to 5.0 or less, the yellowness of the barrier film can be suppressed. b * By setting the b value to -1.0 or more, it is easy to suppress the disruption of the white balance of the background of the electronic paper. In this specification, b * the reflected light from which the b value is calculated shall be measured so as to include the specular reflection component based on the geometric condition d of JIS Z8722:2009. <Geometric condition d of JIS Z8722:2009> The sample is irradiated with a single light beam whose optical axis does not exceed 10° with respect to the normal of the sample surface, and the light reflected in all directions is collected and received. Also, in this case, the irradiation light beam shall not include a light beam having an inclination of 5° or more with respect to its center line.

[0067] The b value of the barrier film described above * is the b value of the reflected light. Also, the light transmitted through the barrier film is reflected by the display element. For example, in the case of a barrier film for an electronic paper, the light transmitted through the barrier film is reflected by the electronic paper display element. Therefore, when measuring the b value of the barrier film * it is measured taking into account the reflection of the display element. Specifically, a sample is prepared by placing a standard white reflecting plate of perfect diffusion on the surface opposite to the light incident surface of the barrier film, and the b value of the barrier film is measured using the sample. * it is measured taking into account the reflection of the display element. Specifically, a sample is prepared by placing a standard white reflecting plate of perfect diffusion on the surface opposite to the light incident surface of the barrier film, and the b value of the barrier film is measured using the sample. * value is measured. L * a * b * The color system is the L * a * b *It is based on a color system and is adopted in JIS Z8781-4:2013.

[0068] [Electronic paper] The electronic paper of this disclosure includes an electronic paper display element and the barrier film of this disclosure described above.

[0069] Figure 3 is a cross-sectional view showing one embodiment of the electronic paper 300 of the present disclosure. The electronic paper 300 in Figure 3 includes an electronic paper display element 200 and a barrier film 100 of the present disclosure. In the electronic paper 300 of Figure 3, the surface of the barrier film 100 facing the first coating layer 11 faces the electronic paper display element 200. In this specification, "the side of the barrier film facing the first coating layer" means the side of the barrier film having the first coating layer, with respect to the first inorganic oxide layer.

[0070] A general-purpose electronic paper display element can be used as the electronic paper display element. The electronic paper display element includes, for example, a back electrode substrate having a back substrate and a back electrode, a transparent electrode substrate having a transparent substrate and a transparent electrode, and a display medium layer disposed between the back electrode substrate and the transparent electrode substrate.

[0071] General-purpose back electrode substrates, transparent electrode substrates, and display media layers can be used as the back electrode substrate, transparent electrode substrate, and display media layer. For example, the display medium layer can be appropriately selected according to the electronic paper display method. Examples of electronic paper display methods include electrophoresis, twist ball method, powder transfer method, liquid crystal display method, and electrochromic method.

[0072] Preferably, the electronic paper display element and the barrier film of this disclosure are laminated with an adhesive layer in between. The adhesive constituting the adhesive layer can be a general-purpose adhesive.

[0073] The electronic paper of this disclosure may have components other than the electronic paper display element and the barrier film of this disclosure. Examples of components other than the electronic paper display element and the barrier film of this disclosure include a touch panel, an anti-reflective film, an anti-glare film, etc. The touch panel is preferably placed between the electronic paper display element and the barrier film of this disclosure. The anti-reflective film and the anti-glare film are preferably placed on the opposite side of the barrier film of this disclosure from the electronic paper display element.

[0074] This disclosure is as follows: <1> ~ <8> Includes. <1> A barrier film for electronic paper having a first coating layer, a first inorganic oxide layer, and a first substrate in this order, A barrier film for electronic paper, wherein the average thickness of the first coating layer calculated in Measurement 1 below is 100 nm or more and 600 nm or less, and the standard deviation σ of the thickness of the first coating layer calculated in Measurement 1 below is 3 nm or more and 60 nm or less. <Measurement 1> A rectangular sample measuring 3 cm on the short side and 6 cm on the long side is cut from the barrier film for electronic paper. A first line is drawn dividing the short side of the sample into three equal parts, and a second line is drawn dividing the long side of the sample into six equal parts. The thickness of the first coating layer is measured at 10 intersection points of the first and second lines. Based on the thickness of the first coating layer at 10 locations, the "average thickness of the first coating layer," the "standard deviation σ of the thickness of the first coating layer," the "difference between the maximum and minimum thickness of the first coating layer," and the "maximum difference in the thickness of the first coating layer at adjacent measurement points" are calculated. <2> The difference between the maximum and minimum values ​​of the thickness of the first coating layer calculated in the measurement 1 is 10 nm or more and 200 nm or less. <1> The barrier film for electronic paper described above. <3> The maximum difference in the thickness of the first coating layer at adjacent measurement locations, calculated in the above measurement 1, is 5 nm or more and 100 nm or less. <1> or <2> The barrier film for electronic paper described above. <4> The first coating layer comprises one or more selected from water-soluble polymers and metal alkoxide compounds. <1> ~ <3> A barrier film for electronic paper as described in any of the following. <5> The first inorganic oxide layer contains silicon dioxide or aluminum oxide. <1> ~ <4> A barrier film for electronic paper as described in any of the following. <6> Furthermore, it has an adhesive layer and a second substrate, and the first coating layer, the first inorganic oxide layer, the first substrate, the adhesive layer and the second substrate are in this order. <1> ~ <5> A barrier film for electronic paper as described in any of the following. <7> With the first inorganic oxide layer as the reference and the first substrate side as the light incident surface, L based on reflected light * a * b * color system b * The value is between -1.0 and 5.0. <1> ~ <6> A barrier film for electronic paper as described in any of the following. <8> Electronic paper display element, <1> ~ <7> Electronic paper comprising a barrier film as described in any of the above. [Examples]

[0075] Next, the present disclosure will be described in more detail by examples, but the present disclosure is not limited in any way by these examples. Unless otherwise specified, "parts" and "%" are based on mass.

[0076] 1. Measurement and Evaluation The following measurements and evaluations were performed on the barrier films for electronic paper in the examples and comparative examples. The evaluations or measurements in 1-1 to 1-5 were carried out in an atmosphere with a temperature of 23°C ± 5°C and a relative humidity of 40% to 65%. In addition, the samples were exposed to the above atmosphere for 30 to 60 minutes before evaluation or measurement.

[0077] 1-1. Thickness of the first coating layer A rectangular sample measuring 3 cm on the short side and 6 cm on the long side was cut from near the center of the barrier film of the examples and comparative examples. The thickness of the first coating layer was measured at 10 locations on the sample according to the procedures A1 to A3 in the main text of the specification. Based on the thickness of the first coating layer at 10 locations, the "average thickness of the first coating layer," the "standard deviation σ of the thickness of the first coating layer," the "difference between the maximum and minimum thickness of the first coating layer," and the "difference in the thickness of the first coating layer at adjacent measurement locations" were calculated.

[0078] 1-2. Total light transmittance and haze The total light transmittance and haze of the barrier films in the examples and comparative examples were measured using a haze meter (manufactured by Murakami Color Technology Laboratory, part number: HM-150). The light incident surface was the surface on the first substrate side.

[0079] 1-3.b * value Samples were prepared by placing a fully diffusing standard white reflector on the first coating layer side of the barrier film of the examples and comparative examples. The first substrate side of the sample was used as the light incident surface, and L based on the reflected light of the sample was measured. * a * b * color system b * The values ​​were measured. The measuring instrument used was a spectrophotometer manufactured by JASCO Corporation (product name: V670), and the following accessories were used. • Included unit: Integrating sphere unit (manufactured by JASCO Corporation, part number: ISN-723) • Light source: Deuterium lamp (190-350nm), halogen lamp (330-2700nm) • Measurement spot diameter: 2mm

[0080] 1-4. Striped color unevenness Samples were prepared by laminating the first substrate side of the barrier films of the examples and comparative examples to a black board (Kuraray Co., Ltd., product name: Comoglass DFA2CG 502K (black), thickness 2 mm) measuring 3 cm on the short side and 6 cm on the long side, via an optically transparent adhesive sheet (product name: Panaclean PD-S1) from Panac Co., Ltd. The sample was placed on a horizontal table with the first coating layer facing the surface. The presence of striped color unevenness was evaluated in a brightly lit room environment where the illuminance on the sample surface was between 500 lux and 1000 lux. Twenty adults evaluated the samples and ranked them according to the following criteria. A: Two or fewer people answered that they could clearly perceive striped color unevenness. B: More than 2 people but less than 5 people answered that they could clearly perceive striped color unevenness. C: More than 5 people but less than 10 people answered that they could clearly perceive striped color unevenness. D: More than 10 people answered that they could clearly see striped color unevenness.

[0081] 1-5. Adhesion between the first coating layer and other components Ten barrier films of the examples and comparative examples were stacked. A 1000g weight was then placed on top, and the stacks were left for 24 hours in an atmosphere of 23°C ± 5°C and a relative humidity of 40% to 65%. After removing the weight, the presence or absence of a first coating layer adhering to an adjacent first substrate was evaluated when separating the ten barrier films. Films without a first coating layer adhering to an adjacent first substrate were designated as "A," and films with a first coating layer adhering to an adjacent first substrate were designated as "C."

[0082] 1-6. Water vapor transmission For the barrier films for electronic paper in the examples and comparative examples, the water vapor transmission rate was measured according to JIS K7129-2:2019. The measuring device used was the MOCON ultra-high sensitivity water vapor transmission rate measuring device (product name: AQUATRAN 3) from Hitachi High-Tech Science Co., Ltd. The temperature and humidity conditions for measuring water vapor transmission rate were 40°C and 90% relative humidity. Prior to measuring water vapor transmission rate, the sample was exposed to an atmosphere of 23°C ± 5°C and a relative humidity of 40% to 65% for 30 minutes. The water vapor transmission rate was 0.02 g / m³. 2 • A score of 1 day or less is considered a passing level.

[0083] 2. Fabrication of barrier film for electronic paper [Example 1] As the first substrate, a sheet-like biaxially oriented PET film with a thickness of 23 μm was prepared (sheet size: 20 cm x 30 cm). Silicon oxide (SiO2) was deposited onto the first substrate by vacuum deposition to form the first inorganic oxide layer (thickness: 70 nm). Next, the following coating solution for the first coating layer was applied to the first inorganic oxide layer by gravure printing, and the mixture was heated at 180°C for 60 seconds to form a first coating layer with an average thickness of 300 nm, thereby obtaining the barrier film for electronic paper of Example 1.

[0084] <Preparation of coating solution for the first coating layer> Solution A was prepared by mixing tetraethoxysilane with a solution (pH 2.2) of water, isopropyl alcohol, and 0.5N hydrochloric acid while cooling to 10°C. Separately, Solution B was prepared by mixing polyvinyl alcohol with a saponification value of 99% or more and isopropyl alcohol. Solution A and Solution B were mixed to prepare the coating solution for the first coating layer (solid content: 8% by mass). In the coating solution for the first coating layer, the mass ratio of tetraethoxysilane to polyvinyl alcohol was 29:4.

[0085] [Examples 2-5], [Comparative Examples 1-4] Barrier films for electronic paper of Examples 2-5 and Comparative Examples 1-4 were obtained in the same manner as in Example 1, except that the solid content of the coating solution for the first coating layer, the drying temperature of the coating solution for the first coating layer, and the average thickness of the first coating layer were changed to the values ​​in Table 1.

[0086] [Table 1]

[0087] From the results in Table 1, it can be confirmed that the barrier film of the example has good barrier properties because it has a low water vapor permeability. Furthermore, from the results in Table 1, it can be confirmed that the barrier film of the example can suppress striped color unevenness, thus suppressing the deterioration of the display quality of the electronic paper. Furthermore, from the results in Table 1, it can be confirmed that the barrier film of the example can suppress adhesion between the first coating layer and other components. For this reason, the barrier film of the example can suppress the deterioration of the display quality of the electronic paper caused by adhesion between the first coating layer and other components. On the other hand, the barrier film of Comparative Example 1 did not have sufficient barrier properties because the average thickness of the first coating layer was less than 100 nm. The barrier film of Comparative Example 2 did not have sufficient barrier properties because the average thickness of the first coating layer exceeded 600 nm, making it prone to cracking in the first coating layer. The barrier film of Comparative Example 3 could not suppress adhesion between the first coating layer and other components because the standard deviation σ of the thickness of the first coating layer was less than 3 nm. The barrier film of Comparative Example 4 could not suppress striped color unevenness because the standard deviation σ of the thickness of the first coating layer exceeded 60 nm. Multiple rectangular samples measuring 3 cm on the short side and 6 cm on the long side can be cut from the barrier films of the examples and comparative examples. The thickness of the first coating layer in Table 1 is the value for samples cut from near the center of the barrier films of the examples and comparative examples. Although not shown in Table 1, the thickness of the first coating layer of samples cut from other parts of the barrier films of the examples and comparative examples was equivalent to the value in Table 1. [Explanation of symbols]

[0088] 11:First coating layer 12: First inorganic oxide layer 13: First base material 14: Adhesive layer 15:Second base material 100: Barrier film for electronic paper 200: Electronic paper display elements 300: Electronic paper

Claims

1. A barrier film for electronic paper having a first coating layer, a first inorganic oxide layer, and a first substrate in this order, A barrier film for electronic paper, wherein the average thickness of the first coating layer calculated in Measurement 1 below is 100 nm or more and 600 nm or less, and the standard deviation σ of the thickness of the first coating layer calculated in Measurement 1 below is 3 nm or more and 60 nm or less. <Measurement 1> A rectangular sample measuring 3 cm on the short side and 6 cm on the long side is cut from the aforementioned barrier film for electronic paper. A first line divides the short side of the sample into three equal parts, and a second line divides the long side of the sample into six equal parts. The thickness of the first coating layer is measured at 10 intersection points of the first line and the second line. Based on the thickness of the first coating layer at 10 locations, the "average thickness of the first coating layer," the "standard deviation σ of the thickness of the first coating layer," the "difference between the maximum and minimum thicknesses of the first coating layer," and the "maximum difference in the thickness of the first coating layer at adjacent measurement points" are calculated.

2. The barrier film for electronic paper according to claim 1, wherein the difference between the maximum and minimum values ​​of the thickness of the first coating layer calculated in the measurement 1 is 10 nm or more and 200 nm or less.

3. The barrier film for electronic paper according to claim 1, wherein the maximum value of the difference in thickness of the first coating layer at adjacent measurement locations calculated in the measurement 1 is 5 nm or more and 100 nm or less.

4. The barrier film for electronic paper according to claim 1, wherein the first coating layer comprises one or more selected from water-soluble polymers and metal alkoxide compounds.

5. The barrier film for electronic paper according to claim 1, wherein the first inorganic oxide layer comprises silicon oxide or aluminum oxide.

6. The barrier film for electronic paper according to claim 1, further comprising an adhesive layer and a second substrate, wherein the first coating layer, the first inorganic oxide layer, the first substrate, the adhesive layer, and the second substrate are arranged in this order.

7. With the first inorganic oxide layer as the reference and the first substrate side as the light incident surface, L based on reflected light ＊ a ＊ b ＊ color system b ＊ A barrier film for electronic paper according to claim 1, wherein the value is between -1.0 and 5.

0.

8. Electronic paper comprising an electronic paper display element and a barrier film according to any one of claims 1 to 7.

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