Optical laminate for electronic paper and electronic paper using same

Abstract

The present invention provides an optical laminate for electronic paper, the optical laminate having suppressed degradation in barrier property over time. An optical laminate 200 for electronic paper has a first surface P1 and a second surface P2 on the reverse side from the first surface. The optical laminate has a first base material 11 and a barrier film 100 having an inorganic oxide layer 21 on a second base material 12. The first base material 11 is located closer to the first surface P1 side than the second base material 12, the inorganic oxide layer 21 is located on the second surface P2 side of the second base material 12. The first base material 11 is a triacetyl cellulose film, and the second base material 12 is a polyester film.

Description

Optical laminate for electronic paper, and electronic paper using the same

[0001] This disclosure relates to an optical laminate for electronic paper and electronic paper using the same.

[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 allows for the rewriting of 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 barrier films for electronic paper with good barrier properties.

[0005] For example, Patent Documents 1 to 3 have proposed barrier films for electronic paper.

[0006] Japanese Patent Publication No. 2023-050695, Japanese Patent Publication No. 2022-152150, International Publication No. 2017 / 130617

[0007] The barrier films for electronic paper described in Patent Documents 1 to 3 have predetermined barrier properties. On the other hand, in order to more adequately protect the display medium layer of the electronic paper or to increase the strength of the barrier film, an optical laminate in which a plastic film is laminated to the barrier film may be used.

[0008] However, optical laminates formed by laminating a plastic film onto a barrier film sometimes experienced a decrease in barrier properties over time. Patent documents 1 to 3 do not address the aforementioned problem at all.

[0009] This disclosure aims to provide an optical laminate for electronic paper that suppresses the deterioration of barrier properties over time. Furthermore, this disclosure aims to provide electronic paper using the aforementioned optical laminate for electronic paper.

[0010] The inventors investigated the cause of the deterioration of barrier properties over time in an optical laminate formed by laminating a plastic film onto a barrier film. As a result, they found that when a triacetylcellulose film, which has excellent optical isotropy, is used as the plastic film to be laminated to the barrier film, the barrier properties tend to deteriorate over time. Further research by the inventors revealed that the barrier properties of the optical laminate deteriorate over time due to the following factors: "the triacetylcellulose film has high hygroscopicity," "when the highly hygroscopic triacetylcellulose film absorbs moisture, the optical laminate curls in a direction that is convex towards the triacetylcellulose film," and "if there are fine scratches on the surface of the inorganic oxide layer, the scratches are widened by the curling of the optical laminate." The inventors have now completed an optical laminate that can suppress the deterioration of barrier properties over time, even when using a triacetylcellulose film.

[0011] This disclosure provides the following <1> to <2>: <1> An optical laminate for electronic paper having a first surface and a second surface opposite to the first surface, wherein the optical laminate comprises a first substrate and a barrier film having an inorganic oxide layer on a second substrate, the first substrate being located on the first surface side of the second substrate, the inorganic oxide layer being located on the second surface side of the second substrate, the first substrate being a triacetylcellulose film, and the second substrate being a polyester film. <2> Electronic paper comprising an electronic paper display element and the barrier film described in [1], wherein the surface of the optical laminate on the second surface side is arranged to face the electronic paper display element.

[0012] The optical laminate for electronic paper and the electronic paper using the same according to this disclosure can suppress the deterioration of barrier properties over time.

[0013] This is a cross-sectional view showing one embodiment of an optical laminate for electronic paper according to the present disclosure. This is a cross-sectional view showing one embodiment of electronic paper according to the present disclosure.

[0014] Embodiments of this disclosure are described below. In this specification, the notation "AA to BB" means AA or greater and BB or less. In this specification, "optical laminate for electronic paper" may be abbreviated as "optical laminate".

[0015] [Optical Laminate for Electronic Paper] An optical laminate for electronic paper according to the present disclosure is, for example, the following: An optical laminate for electronic paper having a first surface and a second surface opposite to the first surface, wherein the optical laminate comprises a first substrate and a barrier film having an inorganic oxide layer on a second substrate, the first substrate being located on the first surface side of the second substrate, the inorganic oxide layer being located on the second surface side of the second substrate, the first substrate being a triacetylcellulose film, and the second substrate being a polyester film.

[0016] Figure 1 is a cross-sectional view showing an embodiment of an optical laminate 200 for electronic paper according to the present disclosure. In Figure 1, the optical laminate 200 has a first surface P1 and a second surface P2 opposite to the first surface. In Figure 1, the optical laminate 200 has a first substrate 11 and a barrier film 100 having an inorganic oxide layer 21 on a second substrate 12. In Figure 1, the first substrate 11 is located on the first surface P1 side of the second substrate 12. In Figure 1, the inorganic oxide layer 21 is located on the second surface P2 side of the second substrate 12. In Figure 1, the barrier film 100 further has a coating layer 22 on the inorganic oxide layer 21. In Figure 1, the optical laminate 200 further has a first adhesive layer 31, a third substrate 13, and a second adhesive layer 32 between the first substrate 11 and the barrier film 100. Figure 1 is a schematic cross-sectional view. In other words, in Figure 1, the scales of each layer constituting the optical laminate 200 are schematic representations for ease of illustration and differ from the actual scales. The same applies to Figure 2.

[0017] <Laminated Structure of Optical Laminate> Examples of laminated structures of the optical laminate of this disclosure include (1) to (6) below. In the laminated structures of (1) to (6) below, the left side is the first surface side and the right side is the second surface side. In (1) to (6) below, the "first substrate" is a "triacetylcellulose film" and the "second substrate" is a "polyester film". In (1) to (6) below, " / " means the interface of the layers. To the extent that it does not impede the effects of this disclosure, the optical laminate of this disclosure may have other layers other than the first substrate, the first adhesive layer, the third substrate, the second adhesive layer, the coating layer, the inorganic oxide layer and the second substrate. Examples of other layers include functional layers described later. (1) First base material / first adhesive layer / second base material / inorganic oxide layer (2) first base material / first adhesive layer / second base material / inorganic oxide layer / coating layer (3) first base material / first adhesive layer / third base material / second adhesive layer / second base material / inorganic oxide layer (4) First base material / first adhesive layer / third base material / second adhesive layer / second base material / inorganic oxide layer / covering layer (5) first base material / first adhesive layer / second base material / inorganic oxide layer / second adhesive layer / third base material (6) first base material / first adhesive layer / second base material / inorganic oxide layer / covering layer / second adhesive layer / third base material

[0018] When arranging the optical laminate of this disclosure on an electronic paper, it is preferable to arrange it so that the second surface of the optical laminate faces the electronic paper display element.

[0019] <First Substrate> The first substrate is a triacetylcellulose film. Triacetylcellulose film has excellent optical isotropy due to its low in-plane retardation. Therefore, by using a triacetylcellulose film as the first substrate, it is easier to suppress the deterioration of the display characteristics of the electronic paper caused by in-plane retardation. In addition, triacetylcellulose film has higher hygroscopicity than other plastic films. Therefore, by using a triacetylcellulose film as the first substrate, the first substrate can be made hygroscopic. By the first substrate absorbing moisture, it is easier to suppress the advance of moisture to the second surface side of the optical laminate. Furthermore, in electronic paper, the first surface side of the optical laminate is located on the side farther from the electronic paper display element. Therefore, by using a triacetylcellulose film as the first substrate, it is easier to suppress the advance of moisture to the electronic paper display element.

[0020] On the other hand, when a highly hygroscopic triacetylcellulose film absorbs moisture, the optical laminate curls in a direction that is convex toward the triacetylcellulose film side. When the optical laminate curls, a load is placed on the inorganic oxide layer. Furthermore, since the absorption and release of moisture by the triacetylcellulose film is repeated over time, the inorganic oxide layer is repeatedly subjected to load. For this reason, when a triacetylcellulose film is used as the first substrate, the barrier properties of the optical laminate sometimes deteriorate over time. The inventors have diligently researched and discovered that by configuring the barrier film within the optical laminate in a specific way, the deterioration of barrier properties over time when a triacetylcellulose film is used as the first substrate can be suppressed. Specifically, the inventors have discovered that by using a barrier film having an inorganic oxide layer on a polyester film as the second substrate, and by arranging the barrier film so that the inorganic oxide layer is located on the second surface side of the second substrate, the deterioration of barrier properties over time can be suppressed. An optical laminate using a triacetylcellulose film as the first substrate curls in a direction that is convex toward the first surface side when the triacetylcellulose film absorbs moisture. The inorganic oxide layer of the barrier film constituting the optical laminate may have minute scratches on its surface. If minute scratches are present on the surface of the inorganic oxide layer, and the optical laminate curls in a direction where the inorganic oxide layer side of the barrier film becomes convex, the scratches in the inorganic oxide layer will spread, causing the barrier performance to deteriorate over time. On the other hand, even if minute scratches are present on the surface of the inorganic oxide layer, if the optical laminate curls in a direction where the inorganic oxide layer side of the barrier film becomes concave, the scratches in the inorganic oxide layer will not spread, thus suppressing the deterioration of the barrier performance over time. Therefore, by arranging the barrier film so that the inorganic oxide layer is located on the second surface side of the second substrate, even if the optical laminate curls in a direction where it becomes convex towards the first surface side due to moisture absorption by the triacetylcellulose film, the deterioration of the barrier performance of the optical laminate over time can be suppressed. Furthermore, polyester film has good rigidity. Therefore, by using polyester film as the second substrate, it is easier to reduce the curl that occurs when the triacetylcellulose film absorbs moisture.Therefore, by using a polyester film as the second substrate of the barrier film, it is easier to suppress the deterioration of the barrier properties of the optical laminate over time.

[0021] The in-plane retardation of the first substrate is preferably 30 nm or less, more preferably 20 nm or less, even more preferably 10 nm or less, and even more preferably 3 nm or less. The in-plane retardation of the first substrate is expressed by the following formula, where nx is the refractive index in the direction of the slow axis, which is the direction of the highest refractive index in the plane of the first substrate, ny is the refractive index in the direction perpendicular to the slow axis in the plane of the first substrate, and T [nm] is the thickness of the first substrate. In this specification, the refractive index means the refractive index at a wavelength of 550 nm. In-plane retardation = (nx - ny) × T [nm]

[0022] The thickness of the first substrate is preferably 40 μm or more, more preferably 55 μm or more, and even more preferably 70 μm or more, in order to increase the strength of the optical laminate and to increase the moisture absorption of the first substrate. The thickness of the first substrate is preferably 150 μm or less, more preferably 130 μm or less, and even more preferably 100 μm or less, in order to thin the electronic paper.

[0023] In the constituent elements shown in this specification, if multiple options are given for both the upper and lower limits of a numerical value, the description shall be limited to an embodiment within a range that combines one selected from the upper limit options and one selected from the lower limit options. As a first example, we will consider the statement, "Parameter B may be A1 or greater, A2 or greater, or A3 or greater. Parameter B may be A4 or less, A5 or less, or A6 or less." In the first example, the numerical range of parameter B may be A1 or greater and A4 or less, A1 or greater and A5 or less, A1 or greater and A6 or less, A2 or greater and A4 or less, A2 or greater and A5 or less, A2 or greater and A6 or less, A3 or greater and A4 or less, A3 or greater and A5 or less, or A3 or greater and A6 or less. As a second example, we will consider the statement, "Parameter C may be A1 or greater and A4 or less, A2 or greater and A5 or less, or A3 or greater and A6 or less." In the second example, the numerical range of parameter C may be A1 or more and A4 or less, A1 or more and A5 or less, A1 or more and A6 or less, A2 or more and A4 or less, A2 or more and A5 or less, A2 or more and A6 or less, A3 or more and A4 or less, A3 or more and A5 or less, or A3 or more and A6 or less. Furthermore, embodiments of the thickness range of the first substrate described above include 40 μm or more and 150 μm or less, 40 μm or more and 130 μm or less, 40 μm or more and 100 μm or less, 55 μm or more and 150 μm or less, 55 μm or more and 130 μm or less, 55 μm or more and 100 μm or less, 70 μm or more and 150 μm or less, 70 μm or more and 130 μm or less, and 70 μm or more and 100 μm or less.

[0024] In this specification, the thicknesses of the first, second, and third substrates are the average of the thicknesses at any 10 locations. The thicknesses of the first, second, and third substrates are 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).

[0025] In this specification, the thickness of the layer, haze, and b ＊When measuring various parameters such as values, unless otherwise specified, the measurement shall be made in an atmosphere with a temperature of 23°C ± 5°C and a relative humidity of 40% or more and 65% or less. Further, before measuring various parameters, the sample shall be exposed to the above atmosphere for 30 minutes or more and 60 minutes or less.

[0026] The optical laminate of the present disclosure may have functional layers such as an antiglare layer and a hard coat layer on the first surface side of the first substrate. By having an antiglare layer on the first surface side of the first substrate, it is easy to suppress the reflection of backgrounds and the like on the surface of the electronic paper. By having a hard coat layer on the first surface side of the first substrate, it is easy to suppress the occurrence of scratches on the surface of the electronic paper. The functional layer may contain an ultraviolet absorber in order to improve the weather resistance of the electronic paper. The ultraviolet absorber may be contained in a layer other than the functional layer.

[0027] The antiglare layer contains, for example, particles such as inorganic particles and organic particles, and a binder resin. General-purpose materials can be used for the particles and the binder resin. The hard coat layer contains, for example, a cured product of a curable resin composition. Examples of the curable resin composition include a thermosetting resin composition and an ionizing radiation curable resin composition. General-purpose materials can be used for the thermosetting resin composition and the ionizing radiation curable resin composition.

[0028] <Barrier film> The barrier film has an inorganic oxide layer on the second substrate. The barrier film preferably has an inorganic oxide layer and a coating layer.

[0029] 《Second substrate》 The second substrate is a polyester film. In order to enhance rigidity, a stretched polyester film is preferable as the polyester film, and a biaxially stretched polyester film is more preferable. Examples of the polyester film include a polyethylene terephthalate film and a polyethylene naphthalate film. Among the polyester films, a biaxially stretched polyethylene terephthalate film is most preferable.

[0030] For enhancing rigidity, the thickness of the second substrate is preferably 10 μm or more, more preferably 12 μm or more, and even more preferably 20 μm or more. For thinning the electronic paper, the thickness of the second substrate is preferably 130 μm or less, more preferably 80 μm or less, and even more preferably 50 μm or less.

[0031] When not having the third substrate described later, the ratio of the thickness of the second substrate to the thickness of the first substrate (thickness of the second substrate / thickness of the first substrate) is preferably 0.5 or more and 1.5 or less, more preferably 0.6 or more and 1.4 or less, and even more preferably 0.7 or more and 1.3 or less. When having the third substrate described later, the ratio of the thickness of the second substrate to the thickness of the first substrate (thickness of the second substrate / thickness of the first substrate) is preferably 0.05 or more and 0.50 or less, more preferably 0.10 or more and 0.45 or less, and even more preferably 0.15 or more and 0.40 or less. By setting the thickness of the second substrate / the thickness of the first substrate within the above range, it is easy to suppress the curl of the optical laminate while thinning the electronic paper.

[0032] The surface on the side of the second substrate having the inorganic oxide layer may be subjected to surface treatment to improve adhesion and the like. Examples of the surface treatment include corona discharge treatment, ozone treatment, low-temperature plasma treatment, glow discharge treatment, oxidation treatment, and the like. Further, an anchor coat layer for improving adhesion may be formed on the side of the second substrate having the inorganic oxide layer.

[0033] 《Inorganic Oxide Layer》 The inorganic oxide layer preferably contains one or more inorganic oxides selected from aluminum oxide, silicon oxide, and magnesium oxide. Among the inorganic oxides, silicon oxide or aluminum oxide is preferable in order to easily improve the barrier property and increase the production efficiency of the barrier film. That is, the inorganic oxide layer preferably contains silicon oxide or aluminum oxide.

[0034] The 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 because it offers excellent productivity due to its high 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.

[0035] When the inorganic oxide layer contains silicon and oxygen, the total content of silicon and oxygen is preferably 60% by mass or more, more 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 mass basis of the total solid content of the inorganic oxide layer. Examples of inorganic oxides containing silicon and oxygen include silicon oxide (SiOx), such as silicon dioxide. The inorganic oxide layer containing silicon and oxygen may also contain other elements such as carbon, to the extent that it does not hinder the effect of the optical laminate of this disclosure. When the 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 mass basis of the total solid content of the inorganic oxide layer. Examples of inorganic oxides containing aluminum and oxygen include Al ２ O ３ Examples include aluminum oxide (AlOx). A small amount of aluminum hydroxide may be included as an inorganic oxide containing aluminum and oxygen, to the extent that it does not impair the effects of this disclosure.

[0036] The preferred thickness of the inorganic oxide layer varies depending on the type of inorganic oxide and cannot be stated in general terms. When the inorganic oxide layer contains silicon and oxygen, the thickness of the 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 inorganic oxide layer contains silicon and oxygen, 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. By setting the thickness to 200 nm or less, it is easier to suppress the occurrence of scratches and cracks in the inorganic oxide layer, and the b of the optical laminate ＊ It's easy to lower the value.

[0037] When the inorganic oxide layer contains aluminum and oxygen, the thickness of the 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 inorganic oxide layer contains aluminum and oxygen, the thickness of the inorganic oxide layer is preferably 25 nm or less, more preferably 20 nm or less, more preferably 15 nm or less, more preferably 12 nm or less, and more preferably 10 nm or less. By setting the thickness to 25 nm or less, it is easier to suppress the occurrence of scratches and cracks in the inorganic oxide layer.

[0038] In this specification, the thickness of layers other than the substrate, such as the inorganic oxide layer, the first adhesive layer, and the second adhesive layer, is calculated by measuring the thickness at 10 locations on a vertical cross-sectional image taken using a scanning transmission electron microscope (STEM), and averaging the values ​​of the 10 locations.

[0039] <Coating Layer> It is preferable that the barrier film has a coating layer on top of the inorganic oxide layer. In other words, it is preferable that the barrier film has an inorganic oxide layer and a coating layer on a second substrate in that order. It is preferable that the coating layer is in contact with the inorganic oxide layer. By providing a coating layer on top of the inorganic oxide layer, the barrier properties of the barrier film can be more easily enhanced.

[0040] The coating layer preferably contains one or more selected from water-soluble polymers and metal alkoxide compounds. More preferably, the coating layer contains one or more selected from water-soluble polymers and metal alkoxide compounds, and even more preferably, it contains one or more selected from water-soluble polymers and one or more selected from metal alkoxide compounds.

[0041] 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.

[0042] When the 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.

[0043] 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.

[0044] 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, in order to improve barrier properties. Furthermore, 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 setting the thickness to 600 nm or less, the barrier film can be made thinner, and the occurrence of cracks in the coating layer is easily suppressed.

[0045] The coating layer can be formed, for example, by applying and drying a coating solution containing the components that make up the 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.

[0046] <Third Substrate> The optical laminate of the present disclosure may further have a third substrate. The third substrate is positioned between the first substrate and the barrier film, or on the side of the barrier film away from the first substrate.

[0047] Examples of the third base material include resin films 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 olefins. From the viewpoint of mechanical strength, dimensional stability, and heat resistance, polyester films are preferred as the third base material, stretched polyester films are more preferred, and biaxially oriented polyester films are even more preferred. Examples of polyester films include polyethylene terephthalate films and polyethylene naphthalate films. Biaxially oriented polyethylene terephthalate film is most preferred as the third base material.

[0048] The thickness of the third substrate is preferably 25 μm or more, more preferably 40 μm or more, and even more preferably 55 μm or more. The thickness of the third substrate is preferably 120 μm or less, more preferably 100 μm or less, and even more preferably 80 μm or less. By setting the thickness of the third substrate within the above range, it is easier to thin the electronic paper while suppressing curling of the optical laminate.

[0049] The ratio of the sum of the thicknesses of the second and third substrates to the thickness of the first substrate [(thickness of the second substrate + thickness of the third substrate) / thickness of the first substrate] is preferably 0.50 or more and 1.50 or less, more preferably 0.60 or more and 1.40 or less, and even more preferably 0.70 or more and 1.30 or less. By setting (thickness of the second substrate + thickness of the third substrate) / thickness of the first substrate within the above range, it is easier to thin the electronic paper while suppressing curling of the optical laminate.

[0050] <Adhesive Layer> Preferably, the first substrate and the barrier film are laminated with an adhesive layer in between. If the optical laminate further has a third substrate, preferably the first substrate, the barrier film and the third substrate are each laminated with an adhesive layer in between.

[0051] Stress is generated when the first substrate absorbs moisture and expands. By laminating the first substrate and the barrier film with an adhesive layer in between, the stress can be less likely to be transmitted to the inorganic oxide layer due to the relaxing effect of the adhesive layer. Furthermore, if the optical laminate has a third substrate, by laminating the first substrate, the barrier film, and the third substrate with adhesive layers in between, the stress can be less likely to be transmitted to the inorganic oxide layer due to the relaxing effect of the adhesive layer.

[0052] In this specification, the adhesive layer that adheres the first substrate to the barrier film or the third substrate is referred to as the first adhesive layer, and the adhesive layer that adheres the barrier film to the third substrate is referred to as the second adhesive layer.

[0053] The optical laminate of this disclosure has a first adhesive layer, and may have a first substrate, a first adhesive layer, and a barrier film in this order. The optical laminate of this disclosure has a first adhesive layer, a third substrate, and a second adhesive layer, and may have a first substrate, a first adhesive layer, a third substrate, a second adhesive layer, and a barrier film in this order. The optical laminate of this disclosure has a first adhesive layer, a third substrate, and a second adhesive layer, and may have a first substrate, a first adhesive layer, a barrier film, a second adhesive layer, and a third substrate in this order.

[0054] Examples of adhesives that constitute the adhesive layers, such as the first adhesive layer and the second adhesive layer, include moisture-curing adhesives, thermosetting adhesives, ultraviolet-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.

[0055] The adhesive constituting the first adhesive layer is preferably a pressure-sensitive adhesive. In other words, the first adhesive layer is preferably a pressure-sensitive adhesive layer. Pressure-sensitive adhesives relieve stress more easily than curing adhesives. Therefore, by making the first adhesive layer a pressure-sensitive adhesive layer, it is easier to mitigate the transmission of stress generated when the first substrate absorbs moisture and expands to the barrier film. Since the first adhesive layer is in contact with the first substrate, which is the source of stress, a pressure-sensitive adhesive layer that easily relieves stress is preferred. The pressure-sensitive adhesive layer preferably contains an acrylic-based pressure-sensitive adhesive with excellent transparency.

[0056] The adhesive constituting the second adhesive layer is preferably a curing type adhesive in order to ensure good adhesion between the barrier film and the third substrate over a long period of time. Examples of curing type adhesives include moisture-curing adhesives, thermosetting adhesives, and ultraviolet-curing adhesives, of which thermosetting adhesives and ultraviolet-curing adhesives are preferred, and thermosetting adhesives are more preferred. In other words, the second adhesive layer is preferably a curing type adhesive layer, more preferably a thermosetting adhesive layer or an ultraviolet-curing adhesive layer, and even more preferably a thermosetting adhesive layer.

[0057] 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 polyol compounds and isocyanate compounds.

[0058] The thickness of the first adhesive layer is preferably 5 μm to 80 μm, more preferably 10 μm to 70 μm, even more preferably 15 μm to 60 μm, and still more preferably 25 μm to 40 μm. By making the thickness of the first adhesive layer 5 μm or more, it is easier to mitigate the transmission of stress generated when the first substrate absorbs moisture and expands to the barrier film. By making the thickness of the first adhesive layer 80 μm or less, it is easier to make the optical laminate into a thin film.

[0059] The ratio of the thickness of the first adhesive layer to the thickness of the first substrate (thickness of the first adhesive layer / thickness of the first substrate) is preferably 0.10 or more and 0.50 or less, more preferably 0.15 or more and 0.45 or less, and even more preferably 0.23 or more and 0.40 or less. By setting the ratio to 0.10 or more, it is easier to mitigate the transmission of stress generated in the first substrate to the barrier film, thereby more easily suppressing the deterioration of barrier properties over time. By setting the ratio to 0.50 or less, it is possible to suppress the optical laminate from becoming thick due to the first adhesive layer being too thick, and to suppress the deterioration of the strength of the optical laminate due to the first substrate being too thin.

[0060] The thickness of the second 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. A thickness of 2 μm or more for the second adhesive layer makes it easier to improve adhesion between the barrier film and the third substrate. A thickness of 30 μm or less for the second adhesive layer makes it easier to thin the optical laminate.

[0061] <Total Thickness> The total thickness of the optical laminate is preferably 50 μm or more and 300 μm or less, more preferably 75 μm or more and 275 μm or less, and even more preferably 100 μm or more and 250 μm or less. A total thickness of 50 μm or more makes it easier to increase the strength of the optical laminate. A total thickness of 300 μm or less makes it easier to thin the electronic paper.

[0062] <Physical Properties> The optical laminate has a water vapor transmission rate of 0.02 g / m³ according to JIS K7129-2:2019. ２ - Preferably less than or equal to 0.01 g / m² ２ - It is more preferable that it be less than or equal to 1 day. The temperature and humidity conditions for measuring water vapor transmission shall be 40°C and 90% relative humidity. In addition, before measuring water vapor transmission, 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, water vapor transmission means the average value of three measured values.

[0063] The optical laminate has an oxygen permeability value of 0.5 cc / m³ according to JIS K7126-2:2006. ２ - Preferably, the temperature is 1 / day·atm or less. The temperature and humidity conditions for measuring oxygen permeability shall be 23°C and 90% relative humidity. In addition, before measuring oxygen permeability, the sample to be measured shall be exposed to an atmosphere of 23°C ± 5°C and 40% to 65% relative humidity for 30 to 60 minutes. In this specification, oxygen permeability means the average value of three measured values.

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

[0065] The optical laminate preferably has a haze of 20% or less, more preferably 15% or less, and even more preferably 10% or less in accordance with JIS K7136:2000. The lower limit of the haze is not particularly limited, but is usually 0.1% or more. By setting the haze to 20% or less, it is easy to suppress the display of the electronic paper display element from being blurred and visible. In this specification, the haze means the average value of three measurement values. The light incident surface when measuring the total light transmittance and the haze is the surface on the second surface side.

[0066] When the light incident surface of the optical laminate is the surface on the first surface side, L based on the reflected light ＊ a ＊ b ＊ the b value of the colorimetric system ＊ is preferably −1.0 or more and 5.0 or less. The b ＊ value 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, the b ＊ value means the average value of three measurement values. By setting the b ＊ value to 5.0 or less, the yellowness of the optical laminate can be suppressed. By setting the b ＊ value to −1.0 or more, it is easy to suppress the white balance of the background of the electronic paper from being lost. The reflected light used as the basis for calculating the b ＊ value 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 integrated 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 the center line thereof.

[0067] The b ＊ value of the above-described optical laminate is the b ＊ value of the reflected light. Also, the light transmitted through the optical laminate is reflected by the electronic paper display element. Therefore, the b ＊When measuring the value, the reflection of the electronic paper display element is taken into consideration. Specifically, a sample is prepared in which a perfectly diffusive standard white reflector is placed on the side of the optical laminate opposite to the light incident surface, and the b of the optical laminate is measured using this sample. ＊ Measure the value. L ＊ a ＊ b ＊ The color system was standardized by the International Commission on Illumination (CIE) in 1976. ＊ 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 optical laminate of this disclosure described above, wherein the second surface of the optical laminate is arranged to face the electronic paper display element.

[0069] Figure 2 is a cross-sectional view showing one embodiment of the electronic paper 400 of the present disclosure. The electronic paper 400 in Figure 2 includes an electronic paper display element 300 and an optical laminate 200 of the present disclosure. In the electronic paper 400 of Figure 2, the surface of the optical laminate 200 on the second surface P2 side faces the electronic paper display element 300 side.

[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 media layer can be appropriately selected according to the display method of the electronic paper. Examples of electronic paper display methods include electrophoresis, twist ball, powder transfer, liquid crystal display, and electrochromic methods.

[0072] Preferably, the electronic paper display element and the optical laminate 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 optical laminate of this disclosure. Examples of components other than the electronic paper display element and the optical laminate of this disclosure include touch panels. It is preferable to place the touch panel between the electronic paper display element and the optical laminate of this disclosure.

[0074] This disclosure includes the following <1> to <9>. <1> An optical laminate for electronic paper having a first surface and a second surface opposite to the first surface, wherein the optical laminate comprises a first substrate and a barrier film having an inorganic oxide layer on a second substrate, the first substrate being located on the first surface side of the second substrate, the inorganic oxide layer being located on the second surface side of the second substrate, the first substrate being a triacetylcellulose film, and the second substrate being a polyester film. <2> The optical laminate for electronic paper according to <1>, further comprising a first adhesive layer, wherein the first substrate, the first adhesive layer, and the barrier film are in this order. <3> The optical laminate for electronic paper according to <1>, further comprising a first adhesive layer, a third substrate, and a second adhesive layer, wherein the first substrate, the first adhesive layer, the third substrate, the second adhesive layer, and the barrier film are in this order. <4> The optical laminate for electronic paper according to <3>, wherein the third substrate is a polyester film. <5> An optical laminate for electronic paper according to any one of <2> to <4>, wherein the first adhesive layer is a pressure-sensitive adhesive layer. <6> An optical laminate for electronic paper according to any one of <1> to <5>, wherein the total thickness is 50 μm or more and 300 μm or less. <7> An optical laminate for electronic paper according to any one of <1> to <6>, wherein the barrier film has a coating layer on the inorganic oxide layer. <8> An optical laminate for electronic paper according to any one of <1> to <7>, wherein the first substrate has an anti-glare layer or a hard coat layer on the first surface side. <9> Electronic paper comprising an electronic paper display element and an optical laminate for electronic paper according to any one of <1> to <8>, wherein the second surface side of the optical laminate is arranged to face the electronic paper display element.

[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 optical laminates of the examples and comparative examples were measured and evaluated as follows. The evaluations or measurements in 1-1 and 1-2 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 the evaluations or measurements in 1-1 and 1-2.

[0077] 1-1. Total Light Transmittance and Haze The optical laminates of the examples and comparative examples were cut to a size of 5 cm x 5 cm to prepare measurement samples. The total light transmittance and haze of the samples were measured using a haze meter (Murakami Color Technology Laboratory, part number: HM-150). The light incident surface was the second surface side.

[0078] 1-2. b ＊ Samples were prepared by placing a perfectly diffusive standard white reflector on the second surface of the optical laminate of the example and comparative example. The size of the sample was 5 cm x 5 cm. The surface of the sample opposite to the standard white reflector was used as the light incident surface, and L was calculated based on the reflected light of the sample. ＊ 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: • Accessories: Integrating sphere unit (manufactured by JASCO Corporation, part number: ISN-723) • Light source: Deuterium lamp (190-350 nm), halogen lamp (330-2700 nm) • Measurement spot diameter: 2 mm

[0079] 1-3. The optical laminates of the initial water vapor transmission examples and comparative examples were cut to a size of 20 cm x 20 cm to prepare measurement samples. The cutting direction was aligned with the direction of the four sides of the rectangle of the second substrate. For the said samples, the water vapor transmission value was measured according to JIS K7129-2:2019. The measuring device used was Hitachi High-Tech Science's MOCON ultra-high sensitivity water vapor transmission rate measuring device (product name: AQUATRAN 3). The temperature and humidity conditions for measuring water vapor transmission were 40°C and 90% relative humidity. In addition, before measuring water vapor transmission, the measurement samples were exposed to an atmosphere of 23°C ± 5°C and relative humidity of 40% to 65% for 30 minutes. The water vapor transmission value was 0.02 g / m³.２ - A score of 7 or less is considered a passing level.

[0080] 1-4. Time-dependent changes in barrier properties. Optical laminates of the examples and comparative examples were cut to a size of 20 cm x 20 cm to prepare measurement samples. The cutting direction was aligned with the direction of the four sides of the rectangle of the second substrate. A moist heat treatment was performed by exposing the samples to an atmosphere of 60°C and 90% relative humidity for 72 hours. Paper (manufactured by Sakurai Co., Ltd., product name: EX Clean Paper) was placed on a plain weave wire mesh, and the sample was placed on the paper while the moist heat treatment was performed. The sample was placed on the paper so that the second side of the sample faced the paper. The water vapor transmission rate was measured using the optical laminate after the moist heat treatment in the same manner as in 1-3 above. Samples with a ratio of water vapor transmission rate after moist heat treatment to initial water vapor transmission rate (water vapor transmission rate after moist heat treatment / initial water vapor transmission rate) of 1.0 or more and less than 1.3 were classified as "A ＋ ", those with a ratio of 1.3 or more and less than 1.5 are designated as "A", those with a ratio of 1.5 or more and less than 1.8 are designated as "B", and those with a ratio of 1.8 or more and less than 2.0 are designated as "B － " and those with a ratio of 2.0 or higher were designated as "C".

[0081] 2. Fabrication of optical laminates for electronic paper [Example 1] A rectangular sheet of biaxially oriented PET film with a thickness of 23 μm was prepared as the second substrate. Silicon oxide (SiO₂) was deposited on the second substrate by vacuum deposition. ２A 50 nm thick inorganic oxide layer was formed by depositing a 50 nm thick inorganic oxide layer. Next, the following coating solution for the coating layer was applied to the inorganic oxide layer by gravure printing and heated at 180°C for 60 seconds to form a 300 nm thick coating layer and obtain a barrier film. Next, a two-component curing polyurethane adhesive was applied to one side of a third substrate (biaxially oriented PET film, 75 μm thick) by gravure printing and dried to form a 7 μm thick second adhesive layer, obtaining a first laminate having the second adhesive layer on the third substrate. Next, the second adhesive layer side of the first laminate was superimposed on the second substrate side of the barrier film and the barrier film and the first laminate were dry laminated to obtain a second laminate. Next, the first substrate (a 100 μm thick triacetylcellulose film, with an in-plane phase difference of 3 nm or less) and the third substrate side of the second laminate were bonded together via a pressure-sensitive adhesive layer, the first adhesive layer (manufactured by Panac Co., Ltd., product name "Panaclean PD-S1", 25 μm thick, type of pressure-sensitive adhesive: acrylic-based pressure-sensitive adhesive), to obtain the optical laminate for electronic paper of Example 1. The optical laminate for electronic paper of Example 1 has the first substrate, the first adhesive layer, the third substrate, the second adhesive layer, the second substrate, an inorganic oxide layer, and a coating layer in this order.

[0082] <Preparation of coating solution for the 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 a coating solution for the coating layer (solid content: 5% by mass). In the coating solution for the coating layer, the mass ratio of tetraethoxysilane to polyvinyl alcohol was 29:4.

[0083] [Example 2] A barrier film and a first laminate were prepared in the same manner as in Example 1. Next, the side of the first laminate facing the second adhesive layer was superimposed on the side of the barrier film facing the coating layer, and the barrier film and the first laminate were dry-laminated to obtain a third laminate. Next, the first substrate (a triacetylcellulose film with a thickness of 100 μm, in-plane phase difference: 3 nm or less) and the second substrate side of the third laminate were bonded together via a pressure-sensitive adhesive layer, the first adhesive layer (manufactured by Panac Co., Ltd., product name "Panaclean PD-S1", thickness of 25 μm), to obtain the optical laminate for electronic paper of Example 2. The optical laminate for electronic paper of Example 2 has the first substrate, the first adhesive layer, the second substrate, an inorganic oxide layer, a coating layer, the second adhesive layer, and the third substrate in this order. In the optical laminate for electronic paper of Example 2, the materials constituting the optical laminate are the same as in Example 1, but the positions of the third substrate and the second adhesive layer in the thickness direction of the optical laminate are different from those of Example 1.

[0084] [Example 3] A barrier film was obtained in the same manner as in Example 1, except that a rectangular sheet-shaped biaxially oriented PET film with a thickness of 50 μm was used as the second substrate. Next, the first substrate (a triacetylcellulose film with a thickness of 100 μm, in-plane phase difference: 3 nm or less) and the second substrate side of the barrier film were bonded together via a pressure-sensitive adhesive layer, the first adhesive layer (manufactured by Panac Co., Ltd., product name "Panaclean PD-S1", thickness 25 μm), to obtain the optical laminate for electronic paper of Example 3. The optical laminate for electronic paper of Example 3 has the first substrate, the first adhesive layer, the second substrate, an inorganic oxide layer, and a coating layer in this order.

[0085] [Example 4] An optical laminate for electronic paper of Example 4 was obtained in the same manner as in Example 1, except that the first adhesive layer was changed to a pressure-sensitive adhesive layer with a thickness of 15 μm (type of pressure-sensitive adhesive: acrylic-based pressure-sensitive adhesive).

[0086] [Example 5] An optical laminate for electronic paper of Example 5 was obtained in the same manner as in Example 1, except that the first adhesive layer was changed to a pressure-sensitive adhesive layer with a thickness of 35 μm (type of pressure-sensitive adhesive: acrylic-based pressure-sensitive adhesive).

[0087] [Example 6] An optical laminate for electronic paper of Example 6 was obtained in the same manner as in Example 1, except that the first substrate was changed to a triacetylcellulose film with a thickness of 80 μm (in-plane phase difference: 3 nm or less).

[0088] [Example 7] An optical laminate for electronic paper of Example 7 was obtained in the same manner as in Example 1, except that the first substrate was changed to a triacetylcellulose film with a thickness of 125 μm (in-plane phase difference: 3 nm or less).

[0089] [Example 8] An optical laminate for electronic paper of Example 8 was obtained in the same manner as in Example 1, except that the first adhesive layer was changed to a pressure-sensitive adhesive layer with a thickness of 9 μm (type of pressure-sensitive adhesive: acrylic-based pressure-sensitive adhesive).

[0090] [Example 9] A barrier film, a first laminate, and a second laminate were prepared in the same manner as in Example 1. Next, a two-component curing polyurethane adhesive (a mixture of Mitsui Chemicals' product names "Takelac" and "Takenate") was applied to the third substrate side of the second laminate by gravure printing and dried to form a first adhesive layer with a thickness of 25 μm, thereby preparing a fourth laminate. Product name "Takelac" is the polyol component, which is the main agent, and product name "Takenate" is the isocyanate component, which is the curing agent. The first adhesive layer in Example 9 is a thermosetting adhesive layer. Next, the first substrate (a triacetylcellulose film with a thickness of 100 μm, in-plane phase difference: 3 nm or less) and the first adhesive layer side of the fourth laminate were dry-laminated to obtain the optical laminate for electronic paper of Example 9. The optical laminate for electronic paper in Example 9 comprises a first substrate, a first adhesive layer, a third substrate, a second adhesive layer, a second substrate, an inorganic oxide layer, and a coating layer in this order.

[0091] [Comparative Example 1] A barrier film and a first laminate were prepared in the same manner as in Example 1. A third laminate was also prepared in the same manner as in Example 2. Next, the first substrate (triacetylcellulose film with a thickness of 100 μm, in-plane phase difference: 3 nm or less) and the third substrate side of the third laminate were bonded together via a pressure-sensitive adhesive layer, the first adhesive layer (manufactured by Panac Co., Ltd., product name "Panaclean PD-S1", thickness of 25 μm), to obtain the optical laminate for electronic paper of Comparative Example 1. The optical laminate for electronic paper of Comparative Example 1 has the following components in this order: first substrate, first adhesive layer, third substrate, second adhesive layer, coating layer, inorganic oxide layer, and second substrate.

[0092] [Comparative Example 2] A barrier film was prepared in the same manner as in Example 1. Next, the first substrate (a triacetylcellulose film with a thickness of 100 μm, in-plane phase difference: 3 nm or less) and the coating layer side of the barrier film were bonded together via a pressure-sensitive adhesive layer, the first adhesive layer (manufactured by Panac Co., Ltd., product name "Panaclean PD-S1", thickness of 25 μm), to obtain the optical laminate for electronic paper of Comparative Example 2. The optical laminate for electronic paper of Comparative Example 2 has the first substrate, the first adhesive layer, the second substrate, the coating layer, the inorganic oxide layer, and the second substrate in this order.

[0093]

[0094] The results in Table 1 confirm that the barrier film of the example can suppress changes in barrier properties over time.

[0095] 11: First substrate 12: Second substrate 13: Third substrate 31: First adhesive layer 32: Second adhesive layer 21: Inorganic oxide layer 22: Coating layer 100: Barrier film 200: Optical laminate for electronic paper 300: Electronic paper display element 400: Electronic paper

Claims

1. An optical laminate for electronic paper having a first surface and a second surface opposite to the first surface, wherein the optical laminate comprises a first substrate and a barrier film having an inorganic oxide layer on a second substrate, the first substrate being located on the first surface side of the second substrate, the inorganic oxide layer being located on the second surface side of the second substrate, the first substrate being a triacetylcellulose film, and the second substrate being a polyester film.

2. The optical laminate for electronic paper according to claim 1, further comprising a first adhesive layer, wherein the first substrate, the first adhesive layer, and the barrier film are arranged in this order.

3. The optical laminate for electronic paper according to claim 1, further comprising a first adhesive layer, a third substrate, and a second adhesive layer, wherein the first substrate, the first adhesive layer, the third substrate, the second adhesive layer, and the barrier film are arranged in this order.

4. The optical laminate for electronic paper according to claim 3, wherein the third substrate is a polyester film.

5. The optical laminate for electronic paper according to claim 2, wherein the first adhesive layer is a pressure-sensitive adhesive layer.

6. The optical laminate for electronic paper according to claim 1, wherein the total thickness is 50 μm or more and 300 μm or less.

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

8. The optical laminate for electronic paper according to claim 1, wherein the first substrate has an anti-glare layer or a hard coat layer on the first surface side.

9. An electronic paper comprising an electronic paper display element and an optical laminate for electronic paper according to any one of claims 1 to 8, wherein the second surface of the optical laminate is arranged to face the electronic paper display element.

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