Protective film for electronic paper and electronic paper using the same

Abstract

To provide a protective film for an electronic paper that can suppress reduction in the display quality of an electronic paper when barrier properties are enhanced by using silicon oxides.SOLUTION: A protective film for an electronic paper includes: a barrier film including an inorganic oxide layer on a first substrate; and a second substrate. The first substrate side of the barrier film and the second substrate are laminated together via an adhesive layer. The inorganic oxide layer contains silicon oxides, has a thickness of 30nm or more, and satisfies the relations: (a haze of the second substrate)≤(a haze of the barrier film) and (a thickness of the barrier film)≤(a thickness of the second substrate).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a protective film for electronic paper, and electronic paper using the same. [Background technology]

[0002] Electronic paper consumes power only when information is rewritten and can maintain display even after the power supply is stopped, so it consumes less power than liquid crystal display devices and organic electroluminescence display devices. Electronic paper also has excellent properties such as being "highly flexible" and "thin and light."

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

[0004] The display medium layer of electronic paper is a mechanism for rewriting display information by dispersing pigments in a filling liquid and arranging the desired pigments on the viewer side by controlling the voltage. If the filling liquid evaporates or moisture from the outside air invades the display medium layer, the desired voltage is not applied, and the rewriting performance of the display information is likely to deteriorate. Electronic paper often uses a plastic film instead of glass for at least one of the back substrate and the transparent substrate in order to make it thinner, lighter, or more flexible. Since plastic films have a lower barrier property than glass, it is necessary to improve the barrier property.

[0005] As barrier films or protective films for electronic paper, for example, Patent Documents 1 to 4 have been proposed. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2019-89311 A [Patent Document 2] JP 2018-180212 A [Patent Document 3] International Publication No. WO2017 / 130617 [Patent Document 4] JP 2014-148584 A Summary of the Invention [Problem to be solved by the invention]

[0007] Protective films for electronic paper are required to have high barrier properties and optical properties. In particular, as the trend away from black and white to color progresses, the requirements for optical properties have become stricter in recent years. As a means for achieving high barrier properties and optical properties, the present inventors have investigated using silicon oxide as a material for the barrier layer of protective films for electronic paper and increasing the thickness of the barrier layer containing silicon oxide.

[0008] However, when the thickness of the barrier layer containing silicon oxide was increased, minute black dots were sometimes visible within the surface of the protective film. If the minute black dots were clearly visible, the display quality of the electronic paper would be reduced. Patent Documents 1 to 4 do not consider at all the above problems that arise when the barrier property is improved by using silicon oxide.

[0009] The present disclosure aims to provide a protective film for electronic paper that can suppress deterioration in the display quality of electronic paper when the barrier property is improved by using silicon oxide. The present disclosure also aims to provide electronic paper using the protective film for electronic paper. [Means for solving the problem]

[0010] The present disclosure provides the following [1] to [2]. [1] A protective film for electronic paper, The protective film includes a barrier film having an inorganic oxide layer on a first substrate, and a second substrate; the first substrate side of the barrier film and the second substrate are laminated via an adhesive layer, The inorganic oxide layer contains silicon oxide and has a thickness of 30 nm or more; the haze of the second substrate is less than or equal to the haze of the barrier film; A protective film for electronic paper, wherein the thickness of the barrier film is less than or equal to the thickness of the second substrate. [2] An electronic paper comprising an electronic paper display element and the protective film described in [1] above, the surface of the protective film on the barrier film side being arranged on the electronic paper display element side. Effect of the Invention

[0011] The protective film for electronic paper of the present disclosure and electronic paper using the same can suppress deterioration in display quality. [Brief description of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view showing one embodiment of a protective film for electronic paper according to the present disclosure. [Diagram 2] FIG. 1 is a cross-sectional view showing an embodiment of electronic paper according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, embodiments of the present disclosure will be described. In this specification, haze refers to the haze defined by JIS K7136:2000. In this specification, the notation "AA to BB" means AA or more and BB or less. In this specification, the "protective film for electronic paper" may be abbreviated to "protective film".

[0014] [Protective film for electronic paper] The protective film for electronic paper according to the present disclosure comprises: A barrier film having an inorganic oxide layer on a first substrate, and a second substrate, the first substrate side of the barrier film and the second substrate are laminated via an adhesive layer, The inorganic oxide layer contains silicon oxide and has a thickness of 30 nm or more; the haze of the second substrate is less than or equal to the haze of the barrier film; The thickness of the barrier film is less than or equal to the thickness of the second substrate.

[0015] Fig. 1 is a cross-sectional view showing one embodiment of a protective film for electronic paper 100 of the present disclosure. The protective film 100 in Fig. 1 has a barrier film 10 having an inorganic oxide layer 12 on a first substrate 11, and a second substrate 30. In the protective film 100 in Fig. 1, the first substrate side 11 of the barrier film 10 and the second substrate 30 are laminated via an adhesive layer 20. In Fig. 1, the barrier film 10 has an inorganic oxide layer 12 on the first substrate 11, and further has a coating layer 13 on the inorganic oxide layer 12. Fig. 1 is a schematic cross-sectional view. In other words, in Fig. 1, the scale of each layer constituting the protective film 100 is schematic for ease of illustration and differs from the actual scale. The same is true for Fig. 2.

[0016] <Features of the protective film for electronic paper disclosed herein> The main features of the protective film for electronic paper of the present disclosure are that it has the following configurations (1) to (3). (1) The inorganic oxide layer contains silicon oxide and has a thickness of 30 nm or more. (2) The haze of the second substrate≦the haze of the barrier film is satisfied. (3) The relationship: thickness of the barrier film≦thickness of the second substrate is satisfied.

[0017] Hereinafter, the technical concept that makes it possible to suppress deterioration in the display quality of electronic paper by the above configurations (1) to (3) will be described. As described above in (1), the inorganic oxide layer of the electronic paper protective film of the present disclosure contains silicon oxide and has a thickness of 30 nm or more. By using silicon oxide as the inorganic oxide constituting the inorganic oxide layer, the price of the protective film can be prevented from increasing. In addition, by making the thickness of the inorganic oxide 30 nm or more, the protective film can be provided with high barrier properties. However, when the thickness of the inorganic oxide layer containing silicon oxide is increased, the L of the inorganic oxide layer originates from silicon oxide. * a * b * Color space b * The value tends to be high. In addition, when the inorganic oxide layer is formed by a vacuum deposition method or the like, black minute dots may be visible on the inorganic oxide layer. For example, in an inorganic oxide layer formed by a vacuum deposition method, black minute dots are formed due to a splash phenomenon. Since black minute dots are partial defects during film formation, the longer the film formation time, the more likely they are to occur within the surface of the protective film. In other words, the thicker the inorganic oxide layer, the more likely black minute dots are to occur within the surface of the protective film. It is difficult to completely eliminate black minute dots. For example, reduction of the splash phenomenon of vacuum deposition has been studied in the past, but even at the time of filing the present application, the splash phenomenon cannot be completely eliminated. On the other hand, even if tiny black dots occur on the protective film, the barrier properties may be able to maintain an acceptable level (since the inorganic oxide layer has a thickness of 30 nm or more, it is considered that a predetermined barrier property may be able to be maintained even if defects occur in a portion of the thickness direction. Alternatively, it is considered that a predetermined barrier property may be able to be maintained by filling in the defective areas with a coating layer formed on the inorganic oxide layer). In order to improve the yield, it is considered to use the protective film having tiny black dots as a non-defective product. However, as mentioned above, when the thickness of the inorganic oxide layer containing silicon oxide is increased, the L originating from silicon oxide may become a problem. * a * b * Color space b *The higher values ​​give the protective film a yellowish tinge, and the tiny black dots stand out more against the white of the electronic paper display and the yellowish background of the silicon oxide. As described above, the above-mentioned (1) configuration is excellent in that it is easy to realize low cost and high barrier properties, but the presence of small black dots is a factor that reduces the display quality of electronic paper. However, the protective film of the present disclosure suppresses the deterioration of the display quality of electronic paper by the above-mentioned (2) and (3) configurations. Below, we will further explain why the above-mentioned (2) and (3) configurations can suppress the deterioration of the display quality of electronic paper.

[0018] In the electronic paper, it is preferable to arrange the barrier layer such as the inorganic oxide layer near the electronic paper display element. That is, it is preferable to arrange the protective film of the present disclosure so that the barrier film is closer to the electronic paper display element than the second substrate. When the protective film of the present disclosure is arranged as described above, the barrier film is farther away from the viewer than the second substrate. The haze of the second substrate and the haze of the barrier film both have the effect of making minute black dots difficult to see, but the effect is stronger in the member located farther away from the viewer. Therefore, in order to make minute black dots difficult to see, the above configuration (2) is important. The inorganic oxide layer and the coating layer described later have extremely low haze values. Therefore, it can be said that the haze of the barrier film is essentially the haze of the first substrate. The light diffused by the haze of the barrier film is further diffused according to the thickness of the second substrate. Therefore, by satisfying the above configuration (2) and the above configuration (3), it is possible to make the black tiny dots less visible. On the other hand, even if the above configuration (2) is satisfied, if the above configuration (3) is not satisfied, the light diffusion according to the thickness of the second substrate becomes insufficient, and the black tiny dots become easily visible. As described above, the configurations (2) and (3) above can make minute black dots less visible, making it easier to prevent degradation of the display quality of the electronic paper. In order to more easily prevent deterioration in the display quality of the electronic paper by the above configurations (1) to (3), it is preferable to further include the following configurations (2') and (3'). (2') The relationship of haze of the second substrate < haze of the barrier film is satisfied. (3') The relationship of thickness of the barrier film < thickness of the second substrate is satisfied.

[0019] <Barrier film> The barrier film is required to have an inorganic oxide layer on a first substrate, and preferably further has a coating layer on the inorganic oxide layer.

[0020] 《First base material》 The first substrate may be a resin film containing one or more resins selected from polyester, triacetyl cellulose, cellulose diacetate, cellulose acetate butyrate, polyamide, polyimide, polyethersulfone, polysulfone, polypropylene, polymethylpentene, polyvinyl chloride, polyvinyl acetal, polyether ketone, acrylic, polycarbonate, polyurethane, and amorphous olefin. Among these resin films, from the viewpoints of mechanical strength, dimensional stability, and heat resistance, stretched polyester films are preferred, and biaxially stretched polyester films are more preferred. Examples of polyester films include polyethylene terephthalate films and polyethylene naphthalate films.

[0021] The thickness of the first substrate is preferably 5.0 μm or more, more preferably 8.0 μm or more, and even more preferably 12.0 μm or more. The thickness of the first substrate is preferably 75.0 μm or less, more preferably 50.0 μm or less, and even more preferably 40.0 μm or less.

[0022] In the configuration requirements shown in this specification, when multiple options for the upper limit and the lower limit of the numerical value are shown, it is assumed that an embodiment is described that combines one selected from the upper limit and one selected from the lower limit. For example, the embodiment of the range of the thickness of the first base material described above includes 5.0 μm to 75.0 μm, 5.0 μm to 50.0 μm, 5.0 μm to 40.0 μm, 8.0 μm to 75.0 μm, 8.0 μm to 50.0 μm, 8.0 μm to 40.0 μm, 12.0 μm to 75.0 μm, 12.0 μm to 50.0 μm, and 12.0 μm to 40.0 μm.

[0023] In this specification, the layer thickness, haze, b * Unless otherwise specified, the measurement of various parameters such as the value of the resin should be performed in an atmosphere having a temperature of 23°C ± 5°C and a relative humidity of 40% to 65%. Furthermore, before measuring the various parameters, the sample should be exposed to the above atmosphere for 30 minutes to 60 minutes.

[0024] In order to easily satisfy the relationship of "haze of the second substrate≦haze of the barrier film," the first substrate is preferably one having a layer containing a matting agent on at least one surface of the resin film. Alternatively, in order to easily satisfy the relationship, the first substrate is preferably one containing an internal diffusing agent in the resin film. As the matting agent and the internal diffusing agent, general-purpose inorganic particles and organic particles can be used. The haze of the barrier film can be increased by increasing the content of the matting agent or internal diffusing agent, by increasing the difference in refractive index between the matting agent or internal diffusing agent and the binder resin, or by increasing the thickness of the layer containing the matting agent or internal diffusing agent.

[0025] The surface of the first base material on which the inorganic oxide layer is formed may be subjected to a surface treatment in order to improve adhesion, etc. Examples of the surface treatment include corona discharge treatment, ozone treatment, low-temperature plasma treatment, glow discharge treatment, and oxidation treatment.

[0026] <Inorganic oxide layer> The inorganic oxide layer must contain silicon oxide. Furthermore, the inorganic oxide layer must have a thickness of 30 nm or more. By containing silicon oxide as an inorganic oxide constituting the inorganic oxide layer, it is possible to suppress an increase in the price of the protective film. By making the thickness of the inorganic oxide 30 nm or more, it is possible to impart a high level of barrier property to the protective film. Silicon oxide is an oxide containing silicon. A typical example of silicon oxide is silicon oxide (SiOx), such as silicon dioxide.

[0027] The total content of silicon and oxygen in the inorganic oxide layer is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more. The inorganic oxide layer may contain elements other than silicon and oxygen as long as they do not impair the effects of the present invention.

[0028] In order to improve the barrier property, the thickness of the inorganic oxide is preferably 40 nm or more, more preferably 50 nm or more, and further preferably 55 nm or more. If the inorganic oxide layer is too thick, it is easy for cracks to occur in the inorganic oxide layer. Also, when the inorganic oxide layer reaches a certain thickness, the barrier property tends to saturate. Therefore, the thickness of the inorganic oxide layer is preferably 200 nm or less, more preferably 150 nm or less, and even more preferably 120 nm or less.

[0029] The inorganic oxide layer can be formed by, for example, a physical vapor deposition method (PVD method) such as a vacuum deposition method, a sputtering method, and an ion plating method, or a chemical vapor deposition method (CVD method) such as a plasma chemical vapor deposition method, a thermal chemical vapor deposition method, and a photochemical vapor deposition method. Among these, the vacuum deposition method is preferred because of its good productivity (deposition rate). The PVD method is preferred because carbon is less likely to be mixed into the inorganic oxide layer than the CVD method.

[0030] 《Coating layer》 The barrier film preferably has a coating layer on the inorganic oxide layer to improve the barrier property.

[0031] The coating layer preferably contains one or more selected from a water-soluble polymer and a metal alkoxide-based compound. Of the water-soluble polymer and the metal alkoxide-based compound, the coating layer more preferably contains one or more selected from the water-soluble polymer, and further preferably contains one or more selected from the water-soluble polymer and one or more selected from the metal alkoxide-based compound.

[0032] Examples of the water-soluble polymer include polyvinyl alcohol, polyvinylpyrrolidone, and ethylene-vinyl alcohol copolymer, and among these, polyvinyl alcohol and ethylene-vinyl alcohol copolymer are preferred for their barrier properties, and polyvinyl alcohol is more preferred. That is, the coating layer preferably contains one or more selected from polyvinyl alcohol and ethylene-vinyl alcohol copolymer, and more preferably contains polyvinyl alcohol.

[0033] When the coating layer contains a water-soluble polymer and a metal alkoxide-based compound, the content of the water-soluble polymer per 100 parts by mass of the total amount of the metal alkoxide-based compounds 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.

[0034] Examples of the metal alkoxide-based compound include metal alkoxides, metal alkoxide hydrolysates, and metal alkoxide polymers. Metal alkoxides are M(OR) nIt is a compound represented by the general formula: In the formula, M represents a metal such as Si, Ti, Al, or Zr, and R represents an alkyl group such as a methyl group or an ethyl group. Specific examples of metal alkoxides include tetramethoxysilane, tetraethoxysilane, and isopropoxyaluminum.

[0035] The coating layer can be formed, for example, by applying a coating liquid containing components constituting the coating layer onto the inorganic oxide layer and drying the coating liquid. The coating liquid may contain additives such as a silane coupling agent, a curing agent, and a dispersing agent.

[0036] In order to provide good barrier properties, the thickness of the coating layer is preferably 70 nm or more, more preferably 100 nm or more, and even more preferably 150 nm or more. The thickness of the coating layer is preferably 600 nm or less, more preferably 480 nm or less, more preferably 370 nm or less, and even more preferably 300 nm or less. By making the thickness 600 nm or less, the protective film can be made thinner and the occurrence of cracks in the coating layer can be easily suppressed.

[0037] The lower limit of the haze of the barrier film is preferably 0.3% or more, more preferably 0.5% or more, and the upper limit is preferably 8.0% or less, more preferably 5.0% or less. The light incident surface when measuring the haze of the barrier film is the surface having the inorganic oxide layer with respect to the first substrate. By setting the haze of the barrier film to 0.3% or more, minute black dots can be made less visible, making it easier to prevent degradation of the display quality of the electronic paper. If the haze of the barrier film is too high, the display of the electronic paper display element may become blurred and difficult to see. Therefore, by setting the haze of the barrier film to 8.0% or less, it becomes easier to suppress the deterioration of the display quality of the electronic paper.

[0038] The barrier film preferably has a total light transmittance according to JIS K7361-1:1997 of 80% or more, more preferably 85% or more, and even more preferably 87% or more.

[0039] The thickness of the barrier film is preferably 5.0 μm or more, more preferably 8.0 μm or more, and even more preferably 12.0 μm or more. The thickness of the barrier film is preferably 75.0 μm or less, more preferably 50.0 μm or less, and even more preferably 40.0 μm or less. By setting the thickness of the barrier film to 5.0 μm or more, the barrier film can be easily handled with ease, and by setting the thickness of the barrier film to 75.0 μm or less, the electronic paper can be easily made thinner.

[0040] The barrier film is a type of barrier film that reduces the L caused by reflected light when the first substrate side is the light incident surface. * a * b * Color space b * It is preferable that the value is 0.1 or more and 5.0 or less. * The value is more preferably 0.2 or more and 3.0 or less, and even more preferably 0.3 or more and 2.0 or less. Barrier film b * The larger the value, the thicker the inorganic oxide layer containing silicon oxide tends to be. * By setting the value to 0.1 or more, it is easy to improve the barrier property. * If the value is too large, tiny black dots become more noticeable. * By setting the value to 5.0 or less, minute black dots can be made less visible, making it easier to prevent degradation of the display quality of the electronic paper.

[0041] The above-mentioned barrier film b * The value is the b * Therefore, the b value of the barrier film *When measuring the value, the reflection on the surface opposite to the light incident surface of the barrier film is prevented. For example, a sample is prepared by attaching a black film to the surface opposite to the light incident surface of the barrier film via a pressure-sensitive adhesive layer, and the b value of the barrier film is measured using the sample. * Measure the value. L * a * b * The color system is the L color system standardized by the International Commission on Illumination (CIE) in 1976. * a * b * It is based on a color space system and is adopted in JIS Z8781-4:2013.

[0042] <Second base material> The second substrate may be a resin film containing one or more resins selected from polyester, triacetyl cellulose, cellulose diacetate, cellulose acetate butyrate, polyamide, polyimide, polyethersulfone, polysulfone, polypropylene, polymethylpentene, polyvinyl chloride, polyvinyl acetal, polyether ketone, acrylic, polycarbonate, polyurethane, and amorphous olefin. Among these resin films, from the viewpoints of mechanical strength, dimensional stability, and heat resistance, stretched polyester films are preferred, and biaxially stretched polyester films are more preferred. Examples of polyester films include polyethylene terephthalate films and polyethylene naphthalate films. In addition, the resin film as the second substrate is preferably one that can reduce haze.

[0043] In order to suppress blocking, the second substrate may have an anti-blocking layer containing a matting agent on at least one surface of the resin film. As the matting agent, general-purpose inorganic particles and organic particles can be used.

[0044] If the haze of the second substrate is too high, the display of the electronic paper display element may become blurred and difficult to see, so the haze of the second substrate is preferably 5.0% or less, and more preferably 3.0% or less. The lower limit of the haze of the second substrate is not particularly limited. In order to use a general-purpose resin film as the second substrate, the haze of the second substrate is preferably 0.1% or more, and more preferably 0.2% or more.

[0045] The haze of the barrier film / the haze of the second substrate is preferably 1.05 or more and 5.0 or less, and more preferably 1.10 or more and 3.0 or less. By setting the ratio to 1.05 or more, minute black dots can be made less visible, making it easier to prevent deterioration of the display quality of the electronic paper. By setting the ratio to 5.0 or less, it is easier to prevent the display of the electronic paper display element from becoming blurred, making it easier to prevent deterioration of the display quality of the electronic paper.

[0046] 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 making the thickness of the second substrate 20.0 μm or more, it is possible to make the minute black dots less visible, and therefore it is easier to suppress the deterioration of the display quality of the electronic paper. By making the thickness of the second substrate 120.0 μm or less, it is easier to suppress the display of the electronic paper display element from becoming blurred, and therefore it is easier to suppress the deterioration of the display quality of the electronic paper. In addition, by making the thickness of the second substrate 120.0 μm or less, it is easier to make the electronic paper thinner.

[0047] The ratio of the thickness of the second substrate to the thickness of the barrier film is preferably 1.2 or more and 10.0 or less, and more preferably 1.5 or more and 8.0 or less. By setting the ratio to 1.2 or more, minute black dots can be made less visible, making it easier to prevent deterioration of the display quality of the electronic paper. By setting the ratio to 10.0 or less, it is easier to prevent the display of the electronic paper display element from becoming blurred, making it easier to prevent deterioration of the display quality of the electronic paper.

[0048] In this specification, the thickness of the second substrate and the barrier film is the average value of the thicknesses at any 10 points. The thickness of the second substrate and the barrier film can be measured with a film thickness measuring device. Examples of the film thickness measuring device include Mitutoyo's Digimatic Standard Outside Micrometer (product number: MDC-25SX).

[0049] <Adhesive layer> The adhesive layer is located between the barrier film and the second substrate, and serves to integrate the barrier film, the adhesive layer, and the second substrate.

[0050] Examples of adhesives constituting the adhesive layer include moisture-curing adhesives, heat-curing adhesives, ultraviolet-curing adhesives, heat-sensitive adhesives (e.g., hot-melt adhesives), pressure-sensitive adhesives, etc. As these various adhesives, general-purpose adhesives can be used.

[0051] The adhesive layer is preferably a layer formed from a curing adhesive in order to maintain good adhesion for a long period of time. Examples of the curing adhesive include moisture-curing adhesives, heat-curing adhesives, and ultraviolet-curing adhesives, among which heat-curing adhesives and ultraviolet-curing adhesives are preferred, and heat-curing adhesives are more preferred.

[0052] Examples of the thermosetting adhesive include general-purpose one-component curing adhesives and two-component curing adhesives. Among these, two-component curing polyurethane adhesives are preferred. The two-component curing polyurethane adhesive is an adhesive containing a polyol compound and an isocyanate compound.

[0053] The thickness of the adhesive layer is preferably from 2 μm to 30 μm, more preferably from 3 μm to 20 μm, and even more preferably from 4 μm to 10 μm. A thickness of 2 μm or more can improve adhesion between the barrier film and the second substrate, while a thickness of 30 μm or less can facilitate thinning of the electronic paper and suppression of stress caused by cure shrinkage of the adhesive.

[0054] The adhesive layer preferably has a high total light transmittance and a low haze, and therefore preferably does not contain an internal scattering agent or a visible light absorbing agent.

[0055] <Physical Properties> Water vapor permeability The protective film has a water vapor permeability of 0.02 g / m according to JIS K7129-2:2019. 2 ·day or less, and 0.01 g / m 2 It is preferable that the time is 10-24 hours or less. The temperature and humidity conditions for measuring water vapor permeability are 40°C and 90% relative humidity. In addition, before measuring water vapor permeability, the sample to be measured is exposed to an atmosphere with a temperature of 23°C ± 5°C and a relative humidity of 40% to 65% for 30 minutes or more. The water vapor transmission rate can be measured, for example, by a MOCON ultra-sensitive water vapor transmission rate measuring device (product name: AQUATRAN 3) manufactured by Hitachi High-Tech Science Corporation.

[0056] Oxygen permeability The protective film has an oxygen permeability of 0.5cc / m according to JIS K7126-2:2006. 2 It is preferable that the temperature be less than 100°C / day atm. The temperature and humidity conditions for measuring oxygen permeability are 23°C and 90% relative humidity. In addition, before measuring oxygen permeability, the sample to be measured is exposed to an atmosphere with a temperature of 23°C ± 5°C and a relative humidity of 40% to 65% for 30 minutes or more. The oxygen permeability can be measured, for example, by an oxygen permeability measuring device (product name: OX-TRAN) manufactured by MOCON (MOCON method).

[0057] 《Total light transmittance》 The protective film preferably has a total light transmittance according to JIS K7361-1:1997 of 85% or more, more preferably 87% or more, and even more preferably 89% or more.

[0058] <Layer structure> Examples of the laminate structure of the protective film for electronic paper of the present disclosure include the following (1) and (2): In the following (1) and (2), " / " indicates the interface between layers. (1) Inorganic oxide layer / first base material / adhesive layer / second base material (2) Covering layer / inorganic oxide layer / first base material / adhesive layer / second base material

[0059] The protective film for electronic paper may have layers other than those described above, as long as the effects of the present disclosure are not impaired.

[0060] [Electronic Paper] The electronic paper of the present disclosure includes an electronic paper display element and the protective film of the present disclosure described above, with the surface of the protective film facing the barrier film facing the electronic paper display element.

[0061] Fig. 2 is a cross-sectional view showing one embodiment of electronic paper 300 of the present disclosure. The electronic paper 300 of Fig. 2 includes an electronic paper display element 200 and a protective film 100 of the present disclosure. The electronic paper 300 of Fig. 2 is arranged such that the surface of the protective film 100 on the barrier film 10 side faces the electronic paper display element 100. In this specification, "the surface of the protective film facing the barrier film" means the surface of the protective film having the barrier film when the adhesive layer is used as the reference.

[0062] A general-purpose electronic paper display element can be used as the electronic paper display element. The electronic paper display element has, for example, a rear electrode substrate having a rear substrate and a rear electrode, a transparent electrode substrate having a transparent substrate and a transparent electrode, and a display medium layer disposed between the rear electrode substrate and the transparent electrode substrate.

[0063] As the back electrode substrate, the transparent electrode substrate and the display medium layer, general-purpose back electrode substrate, transparent electrode substrate and display medium layer can be used. For example, the display medium layer can be appropriately selected depending on the display type of the electronic paper, such as an electrophoretic type, a twist ball type, a powder movement type, a liquid crystal display type, an electrochromic type, and the like.

[0064] It is preferable that the electronic paper display element and the protective film of the present disclosure are laminated via an adhesive layer. The adhesive constituting the adhesive layer may be a general-purpose adhesive.

[0065] The electronic paper of the present disclosure may have a member other than the electronic paper display element and the protective film of the present disclosure. Examples of the member other than the electronic paper display element and the protective film of the present disclosure include a touch panel, an anti-reflection film, an anti-glare film, etc. The touch panel is preferably disposed between the electronic paper display element and the protective film of the present disclosure. The anti-reflection film and the anti-glare film are preferably disposed on the opposite side of the protective film of the present disclosure to the electronic paper display element.

[0066] This disclosure includes the following [1] to [8]. [1] A protective film for electronic paper, The protective film includes a barrier film having an inorganic oxide layer on a first substrate, and a second substrate; the first substrate side of the barrier film and the second substrate are laminated via an adhesive layer, The inorganic oxide layer contains silicon oxide and has a thickness of 30 nm or more; the haze of the second substrate is less than or equal to the haze of the barrier film; A protective film for electronic paper, wherein the thickness of the barrier film is less than or equal to the thickness of the second substrate. [2] The protective film for electronic paper described in [1], wherein the haze of the barrier film is 0.3% or more and 8.0% or less. [3] The protective film for electronic paper described in [1] or [2], wherein the haze of the second substrate is 0.1% or more and 5.0% or less. [4] The protective film for electronic paper according to any one of [1] to [3], wherein the barrier film has a thickness of 5.0 μm or more and 75.0 μm or less. [5] The protective film for electronic paper according to any one of [1] to [4], wherein the second base has a thickness of 20.0 μm or more and 120.0 μm or less. [6] The protective film for electronic paper according to any one of [1] to [5], wherein the barrier film has a coating layer on the inorganic oxide layer. [7] The barrier film has an L based on reflected light when the first substrate side is a light incident surface. * a * b * Color space b * The protective film for electronic paper according to any one of [1] to [6], wherein the value is 0.1 or more and 5.0 or less. [8] An electronic paper comprising an electronic paper display element and the protective film according to any one of [1] to [7], wherein the surface of the protective film on the barrier film side faces the electronic paper display element. EXAMPLES

[0067] Next, the present disclosure will be described in more detail with reference to examples, but the present disclosure is not limited to these examples. "Parts" and "%" are based on mass unless otherwise specified.

[0068] 1. Measurement and Evaluation The following measurements and evaluations were carried out on the protective films for electronic paper of the Examples and Comparative Examples, and on the barrier film and second substrate constituting the protective films. The results are shown in Table 1. The evaluation or measurement of 1-1 to 1-4 was performed in an atmosphere with a temperature of 23° C.±5° C. and a relative humidity of 40% to 65%. Furthermore, the sample was exposed to the above atmosphere for 30 minutes or more before the evaluation or measurement.

[0069] 1-1. Display quality of electronic paper A white film (haze: 30.0%) was prepared as a pseudo electronic paper display element. A black dot with a diameter of about 100 μm was drawn with a black pen on the barrier film side of the electronic paper protective film of the examples and comparative examples. The black dot was considered to be a black dot generated in the inorganic oxide layer. A protective film with black dots drawn thereon was placed on the white film to prepare a sample for evaluation. The protective film was placed so that the barrier film side faced the white film. The sample was visually observed from a distance of 30 cm in a bright room environment, and evaluated whether black dots were clearly visible or not. The evaluators were 20 healthy people in their 20s and 30s, and they ranked the samples according to the following criteria. <Rank criteria> A: Fewer than two people answered that the black dots were clearly visible. B: 3 to 5 people answered that the black dots were clearly visible. C: 6 to 10 people answered that the black dots were clearly visible. D: 11 or more people answered that the black dots were clearly visible.

[0070] 1-2. Hayes The haze of the barrier film and the second substrate constituting the protective film for electronic paper in the examples and comparative examples was measured using a haze meter (manufactured by Murakami Color Research Laboratory, product number: HM-150). The light incident surface when measuring the haze of the barrier film was the surface on the coating layer side.

[0071] 1-3.b * value A sample was prepared by attaching a black film to the surface of the barrier film on the coating layer side of the protective film for electronic paper of the examples and comparative examples via a pressure-sensitive adhesive layer. The surface of the sample on the first substrate side was used as the light incident surface, and the L based on the reflected light of the sample was measured. * a * b * Color space b * The measurement device used was a spectrophotometer manufactured by JASCO Corporation (product name: V670), and the following accessories were used: Accessory unit: Integrating sphere unit (JASCO Corporation, product number: ISN-723) Light source: Deuterium lamp (190~350nm), halogen lamp (330~2700nm) Measurement spot diameter: 2mm

[0072] 1-4.Total light transmittance The total light transmittance was measured for the electronic paper protective films of the examples and comparative examples. A haze meter (HM-150, manufactured by Murakami Color Research Laboratory) was used as the measuring device. A total light transmittance of 85% or more is considered to be at the pass level.

[0073] 1-5.Water vapor permeability The water vapor permeability values ​​according to JIS K7129-2:2019 were measured for the electronic paper protective films of the examples and comparative examples. The measurement device used was a MOCON ultra-high sensitivity water vapor permeability measuring device (product name: AQUATRAN 3) manufactured by Hitachi High-Tech Science Corporation. The temperature and humidity conditions for measuring the water vapor permeability were 40°C and a relative humidity of 90%. In addition, before measuring the water vapor permeability, the measurement sample was exposed to an atmosphere with a temperature of 23°C ± 5°C and a relative humidity of 40% to 65% for 30 minutes or more. When the water vapor permeability was 0.02 g / m 2 The passing level is less than 100 days.

[0074] 2. Preparation of protective film for electronic paper [Example 1] A substrate was prepared as the first substrate, which was a biaxially stretched PET film having a layer containing a matting agent formed on one side thereof. The first substrate had a total thickness of 23 μm, with the biaxially stretched PET film having a thickness of 22 μm and the layer containing a matting agent having a thickness of 1 μm. The haze of the first substrate was 1.5%. Silicon oxide (SiO2) was deposited by vacuum deposition on the surface of the first substrate that did not have the layer containing a matting agent, to form an inorganic oxide layer (thickness: 70 nm). Next, the following coating solution for forming a coating layer was applied onto the inorganic oxide layer by gravure printing, and heat-treated at 180° C. for 60 seconds to form a coating layer with a thickness of 300 nm, thereby obtaining a barrier film used in Example 1. Next, a two-component curing polyurethane adhesive was applied by gravure printing to one side of a second substrate (material: biaxially oriented PET film, thickness: 75 μm, haze: 0.8%) and dried to form an adhesive layer with a thickness of 7 μm, thereby obtaining a laminate having an adhesive layer on a second substrate. Next, the adhesive layer side of the laminate was opposed to the first substrate side side of the barrier film, and then the laminate and the barrier film were dry laminated to obtain a protective film for electronic paper of Example 1.

[0075] <Preparation of Coating Solution for Forming Covering Layer> Tetraethoxysilane was mixed into a solution (pH 2.2) of water, isopropyl alcohol, and 0.5N hydrochloric acid while cooling to 10°C to prepare solution A. 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 a coating liquid for forming a coating layer (solid content: 5% by mass). In the coating liquid for forming a coating layer, the mass ratio of tetraethoxysilane to polyvinyl alcohol was 29:4.

[0076] [Comparative Example 1] The first substrate was changed to a biaxially stretched PET film (thickness: 75 μm, haze: 0.8%; second substrate of Example 1). The second substrate was changed to a biaxially stretched PET film (thickness: 25 μm, haze: 1.5%; first substrate of Example 1). A protective film for electronic paper of Comparative Example 1 was obtained in the same manner as in Example 1, except for the above-mentioned changes. The thicknesses of the inorganic oxide layer and the coating layer of the barrier films of Comparative Examples 1 to 6 are the same as the thicknesses of the inorganic oxide layer and the coating layer of the barrier film of Example 1.

[0077] [Example 2] As the first substrate, a substrate was prepared in which a layer containing a matting agent was formed on one side of a biaxially stretched PET film. The first substrate had a biaxially stretched PET film thickness of 22 μm, a layer containing a matting agent thickness of 3 μm, and a total thickness of 25 μm. The haze of the first substrate was 2.6%. The first substrate of Example 2 had a larger haze than the first substrate of Example 1 because the surface unevenness of the matting layer was large. In addition, a biaxially stretched PET film (thickness: 75 μm, haze: 0.9%) was prepared as the second substrate. A protective film for electronic paper of Example 2 was obtained in the same manner as in Example 1, except that the above-mentioned materials were used as the first substrate and the second substrate. The thicknesses of the inorganic oxide layer and the coating layer in Examples 2 and 3 are the same as those of the inorganic oxide layer and the coating layer of the barrier film in Example 1.

[0078] [Example 3] A biaxially stretched PET film (thickness: 50 μm, haze: 1.0%) was prepared as the first substrate. A biaxially stretched PET film (thickness: 75 μm, haze: 0.9%) was prepared as the second substrate. A protective film for electronic paper of Example 3 was obtained in the same manner as in Example 1, except that the above-mentioned materials were used as the first substrate and the second substrate.

[0079] [Comparative Example 2] A biaxially stretched PET film (thickness: 23 μm, haze: 0.3%) was prepared as the first substrate. A biaxially stretched PET film (thickness: 75 μm, haze: 1.2%) was prepared as the second substrate. A protective film for electronic paper of Comparative Example 2 was obtained in the same manner as in Example 1, except that the above-mentioned materials were used as the first substrate and the second substrate.

[0080] [Comparative Example 3] A biaxially stretched PET film (thickness: 23 μm, haze: 0.9%) was prepared as the first substrate. A biaxially stretched PET film (thickness: 50 μm, haze: 1.0%) was prepared as the second substrate. A protective film for electronic paper of Comparative Example 3 was obtained in the same manner as in Example 1, except that the above-mentioned materials were used as the first substrate and the second substrate.

[0081] [Comparative Example 4] A biaxially stretched PET film (thickness: 23 μm, haze: 0.9%) was prepared as the first substrate. A biaxially stretched PET film (thickness: 50 μm, haze: 2.8%) containing particles was prepared as the second substrate. A protective film for electronic paper of Comparative Example 4 was obtained in the same manner as in Example 1, except that the above-mentioned materials were used as the first substrate and the second substrate.

[0082] [Comparative Example 5] A biaxially stretched PET film (thickness: 50 μm, haze: 1.0%) was prepared as the first substrate. A biaxially stretched PET film (thickness: 23 μm, haze: 1.1%) was prepared as the second substrate. A protective film for electronic paper of Comparative Example 5 was obtained in the same manner as in Example 1, except that the above-mentioned materials were used as the first substrate and the second substrate.

[0083] [Comparative Example 6] A biaxially stretched PET film (thickness: 23 μm, haze: 0.3%) was prepared as the first substrate. A biaxially stretched PET film (thickness: 23 μm, haze: 1.1%) was prepared as the second substrate. A protective film for electronic paper of Comparative Example 6 was obtained in the same manner as in Example 1, except that the above-mentioned materials were used as the first substrate and the second substrate.

[0084] [Table 1]

[0085] From the results in Table 1, it can be seen that the protective films for electronic paper of the examples have good barrier properties and can suppress deterioration of display quality. [Explanation of symbols]

[0086] 10: Barrier film 11: First base material 12: Inorganic oxide layer 13: Covering layer 20: Adhesive layer 30:Second base material 100: Protective film for electronic paper 200: Electronic paper display element 300: Electronic paper

Claims

1. A protective film for electronic paper, The protective film includes a barrier film having an inorganic oxide layer on a first substrate, and a second substrate; the first substrate side of the barrier film and the second substrate are laminated via an adhesive layer, The inorganic oxide layer contains silicon oxide and has a thickness of 30 nm or more; the haze of the second substrate is less than or equal to the haze of the barrier film; A protective film for electronic paper, wherein the thickness of the barrier film is less than or equal to the thickness of the second substrate.

2. The protective film for electronic paper according to claim 1 , wherein the haze of the barrier film is 0.3% or more and 8.0% or less.

3. The protective film for electronic paper according to claim 1 , wherein the haze of the second substrate is 0.1% or more and 5.0% or less.

4. The protective film for electronic paper according to claim 1 , wherein the barrier film has a thickness of 5.0 μm or more and 75.0 μm or less.

5. The protective film for electronic paper according to claim 1 , wherein the second substrate has a thickness of 20.0 μm or more and 120.0 μm or less.

6. The protective film for electronic paper according to claim 1 , wherein the barrier film has a coating layer on the inorganic oxide layer.

7. The barrier film is a barrier film that is formed by a barrier layer ... ＊ a ＊ b ＊ Color space b ＊ The protective film for electronic paper according to claim 1 , wherein the value is 0.1 or more and 5.0 or less.

8. 8. An electronic paper comprising an electronic paper display element and the protective film according to claim 1, the protective film being disposed so that the surface of the protective film facing the barrier film faces the electronic paper display element.

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