Flexible display device and method for manufacturing flexible display device

Abstract

The present invention addresses the problem of providing a flexible display device having both impact resistance and folding endurance, as well as a method for manufacturing such a flexible display device.　A flexible display device according to the present invention, which at least includes a cover member, a color filter, and a light-emitting element, is characterized in that: the cover member at least includes a first film and a second film; the second film is disposed on the light-emitting element side relative to the first film; the first film contains cellulose acetate and a filler made of a metal oxide or a metal salt; the aspect ratio of the filler made of the metal oxide or the metal salt is within the range of 110-2000; and when the tensile modulus of the first film is signified by E1 [GPa] and the tensile modulus of the second film is signified by E2 [GPa], the modular ratio (E1 / E2) satisfies formula (1).

Description

Flexible display device and method for manufacturing the same

[0001] The present invention relates to a flexible display device and a manufacturing method for the flexible display device, and more particularly to a display device that is both impact resistant and fold resistant.

[0002] Recently, there has been active development of flexible display devices that can be folded or rolled up. Display devices with an internal metal substrate tend to have difficulty in obtaining sufficient visibility due to the tendency for light to be reflected from the surface of the metal substrate. For this reason, a technique for improving visibility by incorporating a circular polarizer into the display device is known. However, in recent years, there has been a demand for further thinning of display devices, and methods that do not require a circular polarizer, such as replacing the anti-reflection function of the circular polarizer with other components, are being investigated.

[0003] One known method is to use a color filter to replace the function of a circular polarizer. This method allows display devices to be made thinner. However, thinner display devices are more susceptible to shocks caused by bending and other operations. Therefore, it is necessary to attach a cover member to protect the display device (module) to improve the display device's shock resistance. Furthermore, thinner display devices are more easily bent, and therefore the cover member is required to have higher folding resistance.

[0004] Thin film glass is known as a substrate for a cover member. Thin film glass has high transparency and high folding resistance, but on the other hand, it has poor impact resistance. Patent Document 1 discloses a technology for an optical laminate including a first film, a first adhesive layer, a glass plate, a second adhesive layer, and a second film. In this technology, the impact resistance of a cover member having a glass substrate is improved by providing films on both sides of the glass plate. However, providing films on both sides of the glass plate results in a relatively thick cover member. Therefore, it is difficult for a cover member having a glass substrate to achieve both impact resistance and thinness.

[0005] Polyimide is also known as a base material for the cover member, but polyimide has problems such as lower transparency and lower folding resistance compared to thin film glass.

[0006] Patent No. 7036889

[0007] The present invention has been made in consideration of the above problems and circumstances, and the problem to be solved is to provide a flexible display device that is both impact-resistant and fold-resistant, and a method for manufacturing a flexible display device.

[0008] The present inventors have investigated the causes of the above problems in order to solve the above problems. The flexible display device of the present invention has a cover member, a color filter, and a light-emitting element. The cover member has a first film and a second film. The first film contains a specific resin and a specific filler. The first film and the second film satisfy specific conditions in terms of their tensile modulus of elasticity E. The present inventors have found that by satisfying these conditions, a flexible display device can achieve both impact resistance and folding resistance, and have arrived at the present invention. That is, the above problems of the present invention are solved by the following means.

[0009] 1. A flexible display device having at least a cover member, a color filter, and a light-emitting element, wherein the cover member has at least a first film and a second film, the second film is disposed closer to the light-emitting element than the first film, the first film contains acetyl cellulose and a filler of a metal oxide or a metal salt, the aspect ratio of the filler of the metal oxide or the metal salt is within a range of 110 to 2000, and the tensile modulus of the first film is E １ [GPa], the tensile modulus of the second film is E ２ [GPa], the elastic modulus ratio (E １ / E ２ ) satisfies the following formula (1): 1.5≦E １ / E ２ ≦15.0.

[0010] 2. The flexible display device according to item 1, wherein the degree of substitution of the acetyl group in the acetyl cellulose is within a range of 2.3 to 3.0.

[0011] 3. Tensile modulus E of the first film １ 3. The flexible display device according to claim 1 or 2, wherein the modulus of elasticity is in the range of 5.0 to 8.0 GPa.

[0012] 4. The flexible display device according to claim 1 or 2, wherein the metal oxide is alumina.

[0013] 5. The flexible display device according to item 1 or 2, wherein the content of the metal oxide or metal salt filler is within a range of 1 to 30 mass % with respect to the total mass of the first film.

[0014] 6. The flexible display device according to item 1 or 2, wherein the first film is a stretched film, and the stretching ratio of the first film in the width direction is within a range of 1 to 50%.

[0015] 7. The flexible display device according to claim 1 or 2, wherein the thickness of the first film is in the range of 30 to 80 μm.

[0016] 8. The refractive index of the first film is n １ , the refractive index of the second film is n ２ When the refractive index difference (|n １ -n ２ |) satisfies the following formula (2): 0.00≦|n １ -n ２ 3. The flexible display device according to claim 1 or 2, wherein |≦0.02.

[0017] 9. The flexible display device according to item 1 or 2, wherein the second film contains an acrylic resin.

[0018] 10. The flexible display device according to claim 1 or 2, wherein the second film contains rubber particles.

[0019] 11. The flexible display device according to item 10, wherein the content of the rubber particles is in the range of 20 to 90 mass % with respect to the total mass of the second film.

[0020] 12. The flexible display device according to item 1 or 2, wherein the cover member has a hard coat layer, and the hard coat layer is disposed closer to the viewing side than the first film.

[0021] 13. The flexible display device according to claim 1 or 2, wherein the light-emitting element is an organic electroluminescence element.

[0022] 14. The flexible display device according to item 13, wherein the color filter has a function of preventing reflection of light incident from the outside.

[0023] 15. A manufacturing method for a flexible display device according to claim 1, comprising the step of manufacturing the first film, wherein the manufacturing method for the first film comprises the steps of: preparing a dope containing the acetyl cellulose and the filler of a metal oxide or a metal salt; casting the dope on a support to form a cast film; peeling the cast film from the support; and drying the peeled cast film.

[0024] 16. The method for producing a flexible display device according to item 15, wherein the casting film is dried by heating.

[0025] 17. A manufacturing method for a flexible display device according to claim 1, comprising the step of manufacturing the first film, wherein the manufacturing method for the first film comprises the steps of: preparing a dope containing the acetyl cellulose and the metal oxide or metal salt filler; applying the dope onto a support to form a coating film; drying the coating film on the support; and peeling off the dried coating film from the support.

[0026] According to the above-described means of the present invention, it is possible to provide a flexible display device that is both impact-resistant and folding-resistant, and a method for manufacturing the flexible display device.

[0027] The mechanism by which the effects of the present invention are manifested or the mechanism of action is not clear, but is speculated as follows.

[0028] As described above, in a flexible display device having a color filter, the film applied to the cover member is required to have particularly high impact resistance and folding resistance.

[0029] The film used in the cover member according to the present invention is composed of two films, a relatively hard first film and a relatively soft second film, which satisfy a specific elastic modulus ratio. Of these, the second film is disposed on the light-emitting element side.

[0030] By placing the relatively hard first film on the viewing side, it is possible to make it difficult for external impacts to be transmitted to the internal light-emitting element (module), thereby improving impact resistance. By placing the relatively soft second film on the light-emitting element side, even if a portion of the impact is transmitted to the interior, the impact can be dispersed and the impact transmitted to the light-emitting element can be reduced. Furthermore, bending the relatively hard first film generates relatively large stress. However, by placing the relatively soft second film on the light-emitting element side, it is thought that the stress can be alleviated, improving folding resistance.

[0031] The first film according to the present invention contains acetyl cellulose. By substituting the hydrogen atoms of the hydroxyl groups in cellulose with substituents (functional or characteristic groups) such as acyl groups, the reactivity of the cellulose and the interactions between cellulose molecules can be changed. In the present invention, the hydrogen atoms of the hydroxyl groups are esterified by substituting acetyl groups. This is believed to provide a network formed between acetyl cellulose molecules with moderate flexibility and moderate rigidity. It is also believed to enable the added filler to be dispersed appropriately.

[0032] The film according to the present invention also contains a filler having an aspect ratio within a specific range. It is believed that the combination of the acetyl cellulose and the filler can impart appropriate hardness to the film while maintaining appropriate flexibility.

[0033] 1 is a cross-sectional view of a basic layer structure of a flexible display device according to the present embodiment; 2 is a cross-sectional view of a basic layer structure of a flexible display device according to the present embodiment when an adhesive layer is provided; 3 is a cross-sectional view of a basic layer structure of a flexible display device according to the present embodiment when an adhesive layer and a hard coat layer are provided; 4 is a schematic view of an example of a method for manufacturing a second film according to the present embodiment; 5 is a schematic view of an example of a color display method preferably used in the present embodiment; 6 is a schematic view of an example of a color display method preferably used in the present embodiment;

[0034] The flexible display device of the present invention is a flexible display device having at least a cover member, a color filter, and a light-emitting element, wherein the cover member has at least a first film and a second film, the second film is disposed closer to the light-emitting element than the first film, the first film contains acetyl cellulose and a filler of a metal oxide or a metal salt, the aspect ratio of the filler of the metal oxide or the metal salt is in the range of 110 to 2000, and the tensile modulus of elasticity of the first film is E １ [GPa], the tensile modulus of the second film is E ２ [GPa], the elastic modulus ratio (E １ / E ２ ) satisfies the above formula (1). This feature is a technical feature common to or corresponding to the following embodiments.

[0035] In this embodiment, from the viewpoint of achieving both impact resistance and folding resistance, the degree of substitution of acetyl groups in the acetyl cellulose is preferably within the range of 2.3 to 3.0.

[0036] In this embodiment, from the viewpoint of impact resistance, the tensile modulus E １is preferably in the range of 5.0 to 8.0 GPa.

[0037] In this embodiment, from the viewpoint of impact resistance, the metal oxide is preferably alumina.

[0038] In this embodiment, from the viewpoint of achieving both impact resistance and folding resistance, it is preferable that the content of the metal oxide or metal salt filler is within the range of 1 to 30 mass % relative to the total mass of the first film.

[0039] In this embodiment, from the viewpoint of obtaining a desired tensile modulus, it is preferable that the first film is a stretched film, and that the stretch ratios of the first film in the longitudinal direction and width direction are each within the range of 5 to 30%.

[0040] In this embodiment, from the viewpoint of simultaneously achieving impact resistance, folding resistance, and thinness, the thickness of the first film is preferably within the range of 30 to 80 μm.

[0041] In this embodiment, from the viewpoint of visibility, the refractive index of the first film is set to n １ , the refractive index of the second film is n ２ When the refractive index difference (|n １ -n ２ |) preferably satisfies the above formula (2).

[0042] In this embodiment, from the viewpoint of achieving both impact resistance and folding resistance, the second film preferably contains an acrylic resin.

[0043] In this embodiment, from the viewpoint of folding endurance, it is preferable that the second film contains rubber particles.

[0044] In this embodiment, from the viewpoint of folding endurance, it is preferable that the content of the rubber particles is within a range of 20 to 90 mass % with respect to the total mass of the second film.

[0045] In the present embodiment, from the viewpoint of impact resistance, it is preferable that the cover member has a hard coat layer, and that the hard coat layer is disposed closer to the viewer than the first film.

[0046] In this embodiment, from the viewpoint of achieving a thinner device, the light-emitting element is preferably an organic electroluminescence element.

[0047] In this embodiment, from the viewpoint of visibility, it is preferable that the color filter has a function of preventing reflection of light incident from the outside.

[0048] The manufacturing method of a flexible display device of the present invention is a manufacturing method of a flexible display device for manufacturing the flexible display device, comprising a step of manufacturing the first film, wherein the step of manufacturing the first film comprises a step of preparing a dope containing the acetyl cellulose and the metal oxide or metal salt filler, a step of casting the dope onto a support to form a casting film, a step of peeling the casting film from the support, and a step of drying the peeled casting film.

[0049] In this embodiment, it is preferable to dry the casting film by heating in view of uneven distribution of the filler.

[0050] The manufacturing method of a flexible display device of the present invention is a manufacturing method of a flexible display device for manufacturing the flexible display device, which includes a step of manufacturing the first film, and is characterized in that the step of manufacturing the first film includes a step of preparing a dope containing the acetyl cellulose and the metal oxide or metal salt filler, a step of applying the dope to a support to form a coating film, a step of drying the coating film on the support, and a step of peeling off the dried coating film from the support.

[0051] Hereinafter, one or more embodiments of the present invention will be described with reference to the drawings. However, the scope of the present invention is not limited to the disclosed embodiments. In this application, the symbol "to" is used to mean that the numerical values ​​before and after it are included as the lower and upper limits.

[0052] 1. Overview of Flexible Display Device The flexible display device of the present invention is a flexible display device having at least a cover member, a color filter, and a light-emitting element, wherein the cover member has at least a first film and a second film, the second film is disposed closer to the light-emitting element than the first film, the first film contains acetyl cellulose and a filler of a metal oxide or a metal salt, the aspect ratio of the filler of the metal oxide or the metal salt is within a range of 110 to 2000, and the tensile modulus of elasticity of the first film is E １ [GPa], the tensile modulus of the second film is E ２ [GPa], the elastic modulus ratio (E １ / E ２ ) satisfies the following formula (1): 1.5≦E １ / E ２ ≦15.0

[0053] The flexible display device may have other components or an adhesive layer or a adhesive layer for attaching each component, as necessary. The first film may also have a hard coat layer on the viewing side. Hereinafter, the "flexible display device" may also be simply referred to as a "display device."

[0054] 1 to 3 show cross-sectional views of the basic layer structure of a flexible display device. The flexible display device 10 has, from the viewing side, a first film 1, a second film 2, a color filter 3, and a light-emitting element 4, in this order. As shown in FIG. 2, the flexible display device 10 may have an adhesive layer 5 between each layer. As shown in FIG. 3, the flexible display device 10 may have a hard coat layer 6 on the viewing side of the first film 1.

[0055] In this embodiment, the "cover member" refers to a laminate disposed on the viewing side of the color filter. The cover member may be composed of only the first film and the second film, or may include other members as necessary.

[0056] The display device has a tensile elastic modulus E to elastic modulus ratio (E １ / E２ In this specification, the unit of the tensile modulus E is [GPa]. １ / E ２ ≦15.0 E １ : Tensile modulus of first film [GPa] E ２ : tensile modulus of second film [GPa]

[0057] By combining the first film and the second film, the display device can achieve both visibility (impact resistance) after a keystroke test and folding resistance even when the display device is thin. In particular, when the light-emitting element is an organic EL element and the function of the circular polarizer is replaced by a color filter, the display device can be even thinner. Even in such cases, both impact resistance and folding resistance can be achieved.

[0058] The first film, the second film, the color filter, and the light-emitting element will be described below.

[0059] 2. First Film The first film according to this embodiment contains acetyl cellulose and a filler of a metal oxide or a metal salt, the aspect ratio of which is in the range of 110 to 2000.

[0060] (1) Structure of the First Film The first film contains acetyl cellulose and a filler of a metal oxide or a metal salt, and may contain additives as needed. The acetyl cellulose, the filler of a metal oxide or a metal salt, and the additives will be described below.

[0061] (1.1) Acetyl cellulose The first film contains acetyl cellulose as a resin. It is believed that the use of acetyl cellulose facilitates the formation of a network between resin molecules, thereby imparting rigidity to the film.

[0062] Cellulose is a polymer in which β-glucose units are linked in a linear chain via β-1,4-glycosidic bonds. Cellulose ester is cellulose in which some or all of the hydrogen atoms in the hydroxyl groups (-OH) at the 2-, 3-, and 6-positions in one glucose unit are substituted with acyl groups. Cellulose ester in which the acyl groups are acetyl groups is called "acetyl cellulose."

[0063] (Degree of substitution of acetyl group) The degree of substitution of acetyl group represents the average number of acetyl groups per glucose unit. In other words, it represents how many of the hydrogen atoms of the hydroxy groups at the 2-, 3-, and 6-positions in one glucose unit are substituted with acetyl groups. Therefore, the maximum degree of substitution of acetyl group is 3.0, which means that all of the hydrogen atoms of the hydroxy groups at the 2-, 3-, and 6-positions are substituted with acetyl groups.

[0064] The acetyl groups may be substituted evenly at the 2-, 3-, and 6-positions of one glucose unit, or may be substituted with a distribution. The degree of acetyl substitution is determined by the method specified in ASTM-D817-96.

[0065] When the degree of substitution of the acetyl group of the acetyl cellulose is within the range of 2.3 to 3.0, the film can be given an appropriate rigidity, and an appropriate network can be formed between the resin molecules.

[0066] In order to obtain desired optical properties, acetyl celluloses having different degrees of substitution may be mixed and used. The mixing ratio of acetyl celluloses having different degrees of substitution is not particularly limited.

[0067] From the viewpoint of mechanical strength, the number average molecular weight (Mn) of acetyl cellulose is 2 × 10 ４ ~3 x 10 ５ It is preferable that the range is 2×10 ４ ~1.2 × 10 ５ More preferably, it is within the range of 4×10 ４ ~8 x 10 ４ It is more preferable that the range is within the range of

[0068] From the viewpoint of mechanical strength, the weight average molecular weight (Mw) of acetyl cellulose is 2 × 10 ４ ~1 x 10 ６ It is preferable that the range is 2×10 ４ ~1.2 × 10 ５ More preferably, it is within the range of 4×10 ４ ~8 x 10 ４ The number average molecular weight (Mn) and weight average molecular weight (Mw) of acetyl cellulose can be measured by the following method.

[0069] <Gel Permeation Chromatography> Solvent: methylene chloride Column: three columns, "Shodex K806, K805, K803G" (all manufactured by Showa Denko K.K.), were connected and used. Column temperature: 25°C Sample concentration: 0.1% by mass Detector: "RI Model 504" (manufactured by GL Science Co., Ltd.) Pump: "L6000" (manufactured by Hitachi, Ltd.) Flow rate: 1.0 mL / min Calibration curve: A calibration curve was used using 13 samples of standard polystyrene STK standard polystyrene (manufactured by Tosoh Corporation) with Mw = 500 to 2,800,000. It is preferable to use the 13 samples at approximately equal intervals.

[0070] Acetyl cellulose can be synthesized by a known method.

[0071] The raw cellulose for acetyl cellulose is not particularly limited, but examples include cotton linter, wood pulp, and kenaf. The raw cellulose, acetic acid, acetic anhydride, and a catalyst (such as sulfuric acid) are mixed together to esterify the cellulose. The reaction is continued until a cellulose triester is produced. In the triester, all three hydrogen atoms of the hydroxyl groups in one glucose unit are substituted with acetyl groups.

[0072] Next, the cellulose triester is hydrolyzed to obtain acetyl cellulose having the desired degree of acetyl substitution. After that, acetyl cellulose is finally obtained through steps such as filtration, precipitation, washing with water, dehydration, and drying. Specifically, it can be synthesized with reference to the method described in JP-A-10-45804.

[0073] (1.2) Metal Oxide or Metal Salt Filler The first film contains a metal oxide or metal salt filler having an aspect ratio in the range of 110 to 2000. By using this filler, the mechanical strength of the first film can be improved. Specifically, the tensile modulus of elasticity of the first film can be improved. Furthermore, by using this filler, sufficient visibility (transparency) of the first film can be obtained, and therefore sufficient visibility can be obtained even when used in a display device.

[0074] The metal oxide or metal salt filler is an acicular particle of a metal oxide or a metal salt, and it is preferable that the surface of the particle is modified. In this specification, the "metal oxide or metal salt filler" is also simply referred to as "filler."

[0075] The content of the filler is preferably in the range of 1 to 30% by mass, and more preferably in the range of 1 to 10% by mass, based on the total mass of the first film.

[0076] (1.2.1) Metal Oxide or Metal Salt Filler Materials The metal oxide is not particularly limited. Examples of metal oxides include alumina (aluminum oxide), silica (silicon dioxide), magnesium oxide, zinc oxide, lead oxide, boehmite, pseudo-boehmite, tantalum oxide, indium oxide, bismuth oxide, yttrium oxide, cobalt oxide, copper oxide, manganese oxide, selenium oxide, iron oxide, zirconia (zirconium oxide), germanium oxide, tin oxide, titanium oxide, niobium oxide, molybdenum oxide, and vanadium oxide. These may be used alone or in combination of two or more.

[0077] The metal salt is not particularly limited. Examples of the metal salt include strontium carbonate, calcium carbonate, magnesium carbonate, cobalt carbonate, manganese carbonate, barium carbonate, and potassium carbonate. These may be used alone or in combination of two or more.

[0078] Among these, from the viewpoint of achieving both mechanical strength and visibility of the first film, the metal oxide is preferably alumina, and the metal salt is preferably strontium carbonate.

[0079] (1.2.2) Aspect Ratio of Metal Oxide or Metal Salt Filler The aspect ratio of the metal oxide or metal salt filler according to the present invention is within the range of 110 to 2000. By ensuring that the aspect ratio is within this range, the mechanical strength of the first film can be improved. Specifically, the tensile modulus of elasticity of the first film can be improved.

[0080] In the present invention, the aspect ratio of the filler and the filler precursor described below can be measured by the following method.

[0081] A cross section of the first film is directly photographed using a scanning electron microscope (SEM). At least 100 fillers are randomly selected from the resulting image (SEM image). The major axis (x) and minor axis (y) of each filler are measured. The major axis (x) is divided by the minor axis (y) to calculate the value (x / y), and the average value of these is defined as the "aspect ratio."

[0082] When a circumscribing rectangle (circumscribed rectangle) is drawn for each filler, the length of the short side of the circumscribing rectangle is the minor axis, and the length of the long side is the major axis. Usually, the major axis (x) and minor axis (y) of the filler correspond to the average length and average diameter, respectively.

[0083] In order to achieve both good mechanical strength and good visibility for the first film, the aspect ratio of the filler is preferably in the range of 200 to 1,500, and more preferably in the range of 500 to 1,200.

[0084] The average diameter of the filler is not particularly limited, but is preferably 1 to 10 nm. An average diameter of 1 nm or more can impart sufficient mechanical strength to the film. Furthermore, a diameter of 10 nm or less can suppress a decrease in the visibility of the film. The average diameter of the filler is more preferably within the range of 4 to 8 nm. Note that this average diameter corresponds to the minor axis (y) in the above-mentioned "aspect ratio."

[0085] (1.2.3) Surface Modifier From the viewpoint of dispersibility of the filler in the first film, it is preferable that the filler is surface-modified. By surface-modifying the filler, a sulfonic acid group (—SO ３ H), a carboxy group (—COOH), or a phosphate group (—P(═O)(OH) ３－ｎ ) It is preferable that n in the phosphate group is 1 or 2. Preferred embodiments of the surface modifying agent will be described below, but the present invention is not limited thereto.

[0086] Sulfonic acid group (-SO ３ The compound having H) is not particularly limited, and examples thereof include alkylsulfonic acids such as methanesulfonic acid and ethanesulfonic acid; aromatic sulfonic acids such as alkylbenzenesulfonic acids such as benzenesulfonic acid, p-toluenesulfonic acid, styrenesulfonic acid and dodecylbenzenesulfonic acid; and alkali metal salts and ammonium salts of these sulfonic acids, and esters of these sulfonic acids with lower alcohols.

[0087] The compound having a carboxy group (—COOH) is not particularly limited, and examples thereof include monocarboxylic acids such as formic acid, acetic acid, and propionic acid; dicarboxylic acids such as oxalic acid, fumaric acid, and maleic acid; hydroxycarboxylic acids such as lactic acid, malic acid, and citric acid; aromatic carboxylic acids such as benzoic acid and salicylic acid; and salts thereof.

[0088] Phosphate group (-P(=O)(OH) ３－ｎ) is not particularly limited. Note that n is 1 or 2. Examples of the phosphate group include ethyl acid phosphate, butyl acid phosphate, butyl pyrophosphate, butoxyethyl acid phosphate, 2-ethylhexyl acid phosphate, oleyl acid phosphate, tetracosyl acid phosphate, phenyl acid phosphate, diphenyl acid phosphate, benzyl acid phosphate, n-octyl acid phosphate, (2-hydroxyethyl) methacrylate acid phosphate, dibutyl phosphate, bis(2-ethylhexyl) phosphate, lauryl acid phosphate, stearyl acid phosphate, ethylene glycol monoethyl ether acid phosphate, triethylene glycol monoethyl ether acid phosphate, and triethylene glycol monobutyl ether acid phosphate.

[0089] The surface modifier preferably has an aryl group. Examples of surface modifiers having an aryl group include aromatic sulfonic acids such as benzenesulfonic acid, p-toluenesulfonic acid, styrenesulfonic acid, and dodecylbenzenesulfonic acid. Other examples include alkali metal salts and ammonium salts of these aromatic sulfonic acids, and esters of these aromatic sulfonic acids with lower alcohols. Further examples include aromatic carboxylic acids such as benzoic acid and salicylic acid, or salts of aromatic carboxylic acids.

[0090] (1.2.4) Method for Producing Metal Oxide or Metal Salt Filler (1.2.4.1) Method for Producing Metal Oxide Filler The method for producing a metal oxide filler is not particularly limited, and it can be produced by a method similar to a known method such as the method described in JP 2016-44114 A. For example, a metal oxide raw material is hydrolyzed in an acid aqueous solution to form a hydrated oxide. The resulting alcohol is distilled off, and then peptized to obtain a metal oxide filler precursor (aqueous metal oxide sol). The metal oxide filler precursor is then treated with a surface modifier (dehydration treatment). The above method is described in detail below. However, the present invention is not limited thereto.

[0091] First, a metal oxide raw material is hydrolyzed in an acidic aqueous solution to obtain a hydrated oxide. The metal oxide raw material is not particularly limited. Examples of the metal oxide raw material that can be used include alkoxides, oligomers, and acetoacetates of the metals that make up the metal oxides.

[0092] Examples of the metal oxide raw material include metal alkoxides such as aluminum ethoxide, aluminum isopropoxide, aluminum n-butoxide, aluminum sec-butoxide, tetraethoxysilane, tetrapropoxysilane, tetraisopropoxysilane, tetrasec-butoxysilane, tetra-n-butoxysilane, tetraisopropoxytitanium, tetra-n-butoxytitanium, tetra-t-butoxytitanium, tetra-n-butoxyzirconium, and zirconium alkoxide; cyclic aluminum oligomer, diisopropoxy(ethylacetoacetato)aluminum, and tris(ethylacetoacetato)aluminum.

[0093] These metal oxide raw materials may be used alone or in combination of two or more. Among these metal oxide raw materials, alkoxides of aluminum, silicon, or zirconium are preferably used. Furthermore, alkoxides of aluminum, silicon, or zirconium having a carbon number of 2 to 4 are more preferred.

[0094] The acid used for hydrolysis is not particularly limited, and examples thereof include hydrochloric acid, nitric acid, formic acid, acetic acid, propionic acid, butyric acid, etc. Among these, from the viewpoint of ease of handling, formic acid, acetic acid, propionic acid, or butyric acid is preferred, and acetic acid is more preferred.

[0095] The amount of acid used is not particularly limited, and for example, it is preferably in the range of 0.2 to 2.0 mol, and more preferably in the range of 0.3 to 1.8 mol, per mol of the metal oxide raw material. By using an amount within this range, the metal oxide raw material can be efficiently hydrolyzed, and a filler having the desired shape (aspect ratio, diameter) can be produced. The acid may be used in the form of an aqueous solution. The concentration of the acid in the aqueous solution is not particularly limited, and for example, it is preferably in the range of 10 to 50 mass %, and more preferably in the range of 15 to 30 mass %.

[0096] The hydrolysis conditions are not particularly limited as long as they allow the metal oxide raw material to be hydrolyzed, and can be appropriately selected depending on the type of metal oxide raw material, the amount of acid used, and the like. For example, the hydrolysis temperature is preferably within a range of 50 to 100°C. The hydrolysis time is preferably within a range of 10 minutes to 3 hours. Under these conditions, the metal oxide raw material can be efficiently hydrolyzed, and a filler having the desired shape (aspect ratio, diameter) can be produced.

[0097] The resulting hydrated oxide is peptized while distilling off the produced alcohol, to obtain an aqueous metal oxide sol. Here, the hydrated oxide is in the form of a solution (e.g., an aqueous solution). The hydrated oxide concentration (solids concentration) at this time is not particularly limited, and is preferably within the range of, for example, 2 to 15% by mass, and more preferably within the range of 3 to 10% by mass. By ensuring that the concentration is within the above range, the hydrated oxide can be efficiently peptized.

[0098] The deflocculation conditions are not particularly limited as long as they are conditions that can deflocculate the hydrated oxide. For example, the deflocculation temperature is preferably within the range of 100 to 200°C, and more preferably within the range of 110 to 180°C. The deflocculation time is preferably within the range of 1 to 20 hours, and more preferably within the range of 2 to 15 hours. By keeping the deflocculation time within the above ranges, the hydrated oxide can be efficiently deflocculated, and a filler having the desired shape (aspect ratio, diameter) can be produced.

[0099] The above method produces a metal oxide filler precursor (aqueous metal oxide sol). The shape of the metal oxide filler precursor is not particularly limited, provided that it has substantially the same shape as the final metal oxide filler. That is, the average diameter of the metal oxide filler precursor is preferably within the range of 1 to 10 nm, more preferably within the range of 4 to 8 nm. The aspect ratio of the metal oxide filler precursor is within the range of 110 to 2000, preferably within the range of 120 to 1000.

[0100] Next, the precursor of the metal oxide filler (aqueous metal oxide sol) is treated with a surface modifier. Specifically, an organic solvent and a surface modifier are added to the precursor of the metal oxide filler (aqueous metal oxide sol) obtained above and mixed. Then, solvent substitution is performed. The method of solvent substitution is not particularly limited, and for example, a method using an ultrafiltration membrane or a dehydration method utilizing the boiling point difference between water and an organic solvent can be used. The surface modifier is the same as the surface modifier described above.

[0101] The amount of surface modifier used is not particularly limited as long as it is an amount that can surface-modify the precursor of the metal oxide filler. Note that "surface-modifying the precursor of the metal oxide filler" refers to disposing the surface modifier on the surface of the metal oxide filler. Specifically, the amount of surface modifier used is preferably in the range of 1 to 100 mass % relative to the precursor of the metal oxide filler, and more preferably in the range of 10 to 20 mass %. By being within the above range, the precursor of the metal oxide filler can be surface-modified to the desired degree. In other words, the surface modifier can be disposed to the desired degree on the surface of the metal oxide filler.

[0102] The organic solvent that can be used for surface modification is not particularly limited and can be appropriately selected depending on the type of metal oxide filler precursor and surface modifier. Specific examples of the organic solvent include benzene, toluene, xylene, ethylbenzene, diethylbenzene, trimethylbenzene, triethylbenzene, cyclohexane, cyclohexene, decahydronaphthalene, dipentene, pentane, hexane, heptane, octane, nonane, decane, ethylcyclohexane, methylcyclohexane, p-menthane, dipropyl ether, dibutyl ether, anisole, butyl acetate, amyl acetate, and methyl isobutyl ketone. These solvents may be used alone or in combination.

[0103] The amount of the organic solvent used is not particularly limited, but it is preferable to select the amount of the organic solvent used so that the total concentration of the metal oxide filler precursor and the surface modifier is, for example, in the range of 1 to 20 mass %, preferably in the range of 2 to 10 mass %.

[0104] The surface modification (dehydration treatment) conditions are not particularly limited as long as the conditions are such that the metal oxide filler precursor can be surface-modified to the desired extent, and under such conditions, the metal oxide filler precursor can be treated with a surface modifier to produce a filler having the desired shape (aspect ratio, diameter).

[0105] (1.2.4.2) Method for Producing Metal Salt Filler The method for producing the metal salt filler is not particularly limited, and it can be produced by a method similar to a known method. As an example, a method for producing a strontium carbonate filler will be described below. However, the present invention is not limited to this.

[0106] Acicular strontium carbonate particles can be produced, for example, by heating fine spherical strontium carbonate particles in water to cause particle growth, while spherical strontium carbonate particles can be produced, for example, by carbonating strontium hydroxide.

[0107] Specifically, carbon dioxide gas is introduced into an aqueous solution or suspension of strontium hydroxide in the presence of an organic acid while the solution or suspension is being stirred. The concentration of strontium hydroxide in the aqueous solution or suspension is preferably within a range of 1 to 20% by mass, more preferably within a range of 2 to 15% by mass, and even more preferably within a range of 3 to 8% by mass.

[0108] The organic acid preferably has at least one hydroxy group and one carboxy group, and at least three in total. Examples of organic acids include tartaric acid, malic acid, and gluconic acid. The amount of organic acid used is preferably within a range of 0.1 to 20% by mass, more preferably within a range of 1 to 10% by mass, based on the total mass of strontium hydroxide.

[0109] The flow rate of the carbon dioxide gas is preferably in the range of 0.5 to 200 mL / min, and more preferably in the range of 0.5 to 100 mL / min, per 1 g of strontium hydroxide. The spherical strontium carbonate particles can be prepared by the method described in WO 2011 / 052680.

[0110] The surface of the needle-shaped strontium carbonate particles can be modified by the same method as that used to modify the surface of the precursor of the metal oxide filler.

[0111] (1.3) Additives The first film may further contain other additives. The other additives are not particularly limited, and conventionally used additives can be used. Examples include plasticizers, matting agents, UV absorbers, antioxidants, retardation control agents, and peel promoters. In addition to these additives, additives typically used in films constituting the cover member can be used as needed.

[0112] (1.3.1) Plasticizer The first film can improve the flexibility and processability of the film by containing a plasticizer. For example, polyester can be used as the plasticizer. Polyester can be obtained by polymerizing a dicarboxylic acid and a diol. It is preferable that 70% or more of the dicarboxylic acid structural units (structural units derived from dicarboxylic acids) are derived from aromatic dicarboxylic acids, and 70% or more of the diol structural units (structural units derived from diols) are derived from aliphatic diols.

[0113] The proportion of structural units derived from aromatic dicarboxylic acids is preferably 70% or more, more preferably 80% or more, and even more preferably 90% or more. The proportion of structural units derived from aliphatic diols is preferably 70% or more, more preferably 80% or more, and even more preferably 90% or more. The polyesters may be used alone or in combination of two or more.

[0114] Examples of aromatic dicarboxylic acids include terephthalic acid; isophthalic acid; naphthalenedicarboxylic acids such as 2,6-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic acid; 4,4'-biphenyldicarboxylic acid; 3,4'-biphenyldicarboxylic acid; and ester-forming derivatives thereof.

[0115] For the polyester, aliphatic dicarboxylic acids (adipic acid, azelaic acid, sebacic acid, etc.) or monocarboxylic acids (benzoic acid, propionic acid, butyric acid, etc.) can be used as long as the object of the present invention is not impaired.

[0116] Examples of the aliphatic diol include ethylene glycol, 1,3-propylene diol, 1,4-butanediol, 1,4-cyclohexanedimethanol, 1,6-hexanediol, and ester-forming derivatives thereof.

[0117] For the polyester, monoalcohols (butyl alcohol, hexyl alcohol, octyl alcohol, etc.) or polyhydric alcohols (trimethylolpropane, glycerin, pentaerythritol, etc.) can also be used within the scope of the present invention.

[0118] The polyester can be synthesized by a known method such as a direct esterification method or a transesterification method. Examples of polycondensation catalysts used in the synthesis of polyesters include known antimony compounds (antimony trioxide, antimony pentoxide, etc.), germanium compounds (germanium oxide, etc.), titanium compounds (titanium acetate, etc.), and aluminum compounds (aluminum chloride, etc.). However, the polycondensation catalyst is not limited to these.

[0119] Preferred polyesters include polyethylene terephthalate, polyethylene terephthalate-isophthalate copolymer, polyethylene-1,4-cyclohexanedimethylene-terephthalate copolymer, polyethylene-2,6-naphthalene dicarboxylate, polyethylene-2,6-naphthalene dicarboxylate-terephthalate copolymer, polyethylene-terephthalate-4,4'-biphenyldicarboxylate, poly-1,3-propylene-terephthalate, polybutylene terephthalate, polybutylene-2,6-naphthalene dicarboxylate, and the like.

[0120] More preferred polyesters include polyethylene terephthalate, polyethylene terephthalate-isophthalate copolymer, polyethylene-1,4-cyclohexanedimethylene-terephthalate copolymer, polybutylene terephthalate, and polyethylene-2,6-naphthalenedicarboxylate.

[0121] (1.3.2) Matting Agent The first film can be made easier to handle by containing a matting agent. Examples of matting agents include inorganic fine particles (silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, kaolin, talc, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, calcium phosphate, etc.), crosslinked polymers, etc. Among these, silicon dioxide is preferred as the matting agent from the viewpoint of reducing the haze of the film, etc. These matting agents may be used alone or in combination of two or more.

[0122] When the matting agent is in the form of fine particles, the average primary particle diameter of the fine particles is not particularly limited, and is preferably in the range of 1 to 20 nm, more preferably in the range of 5 to 16 nm, and even more preferably in the range of 5 to 12 nm.

[0123] Furthermore, the fine particles are preferably contained in the film in a state in which secondary particles are formed. The average secondary particle diameter is preferably within the range of 0.1 to 5 μm, more preferably within the range of 0.1 to 2 μm, and even more preferably within the range of 0.2 to 0.6 μm. This allows unevenness with a height within the range of 0.1 to 1.0 μm to be formed on the surface of the film, thereby imparting appropriate slip properties to the surface of the film. The average primary particle diameter of the fine particles is measured by observing the particles with a transmission electron microscope at a magnification within the range of 500,000 to 2,000,000 times. 100 particles are observed, the particle diameters are measured, and the average value is taken as the average primary particle diameter.

[0124] (1.3.3) Ultraviolet absorber The first film can improve its lightfastness by containing an ultraviolet absorber. The ultraviolet absorber aims to improve lightfastness by absorbing ultraviolet light with a wavelength of 400 nm or less. The ultraviolet absorber preferably has a transmittance, particularly at a wavelength of 370 nm, in the range of 0.1 to 30%, more preferably in the range of 1 to 20%, and even more preferably in the range of 2 to 10%.

[0125] Examples of the ultraviolet absorber include a benzotriazole-based ultraviolet absorber, a benzophenone-based ultraviolet absorber, a triazine-based ultraviolet absorber, etc. Among these, the ultraviolet absorber is preferably a benzotriazole-based ultraviolet absorber or a benzophenone-based ultraviolet absorber.

[0126] Examples of benzotriazole-based ultraviolet absorbers and benzophenone-based ultraviolet absorbers include 5-chloro-2-(3,5-di-sec-butyl-2-hydroxylphenyl)-2H-benzotriazole, (2-2H-benzotriazol-2-yl)-6-(linear and branched chain dodecyl)-4-methylphenol, 2-hydroxy-4-benzyloxybenzophenone, and 2,4-benzyloxybenzophenone.

[0127] Other examples include "Tinuvin (registered trademark)" products such as "Tinuvin (registered trademark) 109," "Tinuvin (registered trademark) 171," "Tinuvin (registered trademark) 234," "Tinuvin (registered trademark) 326," "Tinuvin (registered trademark) 327," "Tinuvin (registered trademark) 328," and "Tinuvin (registered trademark) 928." All of these are commercially available products manufactured by BASF Japan Ltd. and can be preferably used. Of these, it is preferable that the "Tinuvin (registered trademark)" products do not have a halogen group.

[0128] In addition, discotic compounds such as compounds having a 1,3,5-triazine ring are also preferably used as ultraviolet absorbers. Examples include "Tinuvin (registered trademark) 400" and "Tinuvin (registered trademark) 405" (both manufactured by BASF Japan Ltd.), and "LA-46" (manufactured by ADEKA Corporation). These ultraviolet absorbers may be used alone or in combination of two or more.

[0129] Polymeric ultraviolet absorbers are also preferably used as the ultraviolet absorber. In particular, the polymeric ultraviolet absorbers described in JP-A-6-148430 are preferably used. Furthermore, it is preferable that the ultraviolet absorber does not have a halogen group.

[0130] The UV absorber can be added by dissolving it in a solvent and then adding the solution to the dope, or by directly adding the UV absorber during the preparation of the dope. Examples of the solvent include organic solvents such as alcohol (methanol, ethanol, butanol, etc.), methylene chloride, methyl acetate, acetone, and dioxolane. The solvent may also be a mixture of these organic solvents. UV absorbers that are insoluble in organic solvents, such as inorganic powders, can be added to the dope by dispersing them in an organic solvent using a dissolver or sand mill.

[0131] The content of the ultraviolet absorber is preferably selected appropriately depending on the type of ultraviolet absorber, the conditions of use, etc. The content of the ultraviolet absorber is preferably within a range of 0.5 to 10 parts by mass, and more preferably within a range of 0.6 to 4 parts by mass, per 100 parts by mass of acetyl cellulose.

[0132] (1.3.4) Antioxidant The first film contains an antioxidant, which can prevent deterioration in a high-temperature, high-humidity environment.

[0133] As the antioxidant, a hindered phenol compound is preferably used. Examples of the hindered phenol compound include 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate], 1,6-hexanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)- Examples of such an amine include 1,3,5-triazine, 2,2-thio-diethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, N,N'-hexamethylenebis(3,5-di-t-butyl-4-hydroxy-hydrocinnamamide), 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, and tris-(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate.

[0134] Among these, the hindered phenol compound is preferably 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], or triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate].

[0135] In addition, for example, a hydrazine-based metal deactivator (N,N'-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyl]hydrazine, a phosphorus-based processing stabilizer (tris(2,4-di-t-butylphenyl)phosphite, etc.) may be used in combination. These antioxidants may be used alone or in combination of two or more.

[0136] The content of the antioxidant is not particularly limited, but is preferably in the range of 0.0001 to 1 part by mass, and more preferably in the range of 0.001 to 0.1 part by mass, per 100 parts by mass of acetyl cellulose.

[0137] (1.3.5) Retardation Control Agent The first film can improve the display quality of the display device by containing a retardation control agent. Examples of retardation control agents include aromatic compounds having two or more aromatic rings, such as those described in European Patent No. 911656A2, and rod-shaped compounds, such as those described in Japanese Patent Laid-Open No. 2006-2025. Two or more aromatic compounds may also be used in combination.

[0138] The aromatic ring of the aromatic compound preferably contains an aromatic heterocycle in addition to an aromatic hydrocarbon ring. The aromatic heterocycle is generally an unsaturated heterocycle. In particular, the aromatic compound containing an aromatic heterocycle is preferably a 1,3,5-triazine ring as described in JP-A-2006-2026.

[0139] The content of the retardation control agent is preferably in the range of 0.5 to 20 parts by mass, and more preferably in the range of 1 to 10 parts by mass, based on 100 parts by mass of acetyl cellulose.

[0140] (1.3.6) Release Accelerator The first film may contain a release accelerator to reduce the peel resistance of the film. The release accelerator is preferably a surfactant.

[0141] Examples of the peeling accelerator include phosphate ester surfactants, carboxylic acid or carboxylate surfactants, sulfonic acid or sulfonate surfactants, and sulfate ester surfactants.

[0142] Further, examples of the release promoter include fluorine-based surfactants in which some of the hydrogen atoms bonded to the hydrocarbon chain of the above surfactants are substituted with fluorine atoms. Examples of release promoters are shown below.

[0143] RZ-1:C ８ H １７ OP(=O)-(OH) ２ RZ-2:C１２ H ２５ O-P(=O)-(OK) ２ RZ-3:C １２ H ２５ OCH ２ HH ２ O-P(=O)-(OK) ２ RZ-4:C １５ H ３１ (OCH) ２ HH ２ ) ５ O-P(=O)-(OK) ２ RZ-5:{C １２ H ２５ O(EH ２ HH ２ O) ５} ２ -P(=O)-OH RZ-6:{C １８ H ３５ (OCH) ２ HH ２ ) ８ O} ２ -P(=O)-ONH ４ RZ-7:(t-C ４ H ９ ) ３ -C ６ H ２ -OCH ２ HH ２ O-P(=O)-(OK) ２ RZ-8:(iso-C ９ H １９ -C ６ H ４ -O-(EH ２ HH ２ O) ５ -P(=O)-(OK)(OH) RZ-9:C １２ H ２５ SO ３ Na RZ-10:C １２ H ２５ OSA ３ Na RZ-11:C １７ H ３３ COOH RZ-12:C １７ H ３３ CO2・N(CO2 ２ HH ２ (O) ３ RZ-13:iso-C８ H １７ -C ６ H ４ -O-(CH ２ CH ２ O) ３ - (CH ２ ) ２ SO ３ Na RZ-14: (iso-C ９ H １９ ) ２ -C ６ H ３ -O-(CH ２ CH ２ O) ３ - (CH ２ ) ４ SO ３ Na RZ-15: Sodium triisopropylnaphthalenesulfonate RZ-16: Sodium tri-t-butylnaphthalenesulfonate RZ-17: C １７ H ３３ CON (CH ３ ) CH ２ CH ２ SO ３ Na RZ-18:C １２ H ２５ -C ６ H ４ SO ３ ・NH ４

[0144] The content of the peel promoter is preferably in the range of 0.05 to 5 parts by mass, more preferably in the range of 0.1 to 2 parts by mass, and even more preferably in the range of 0.1 to 0.5 parts by mass, relative to 100 parts by mass of acetyl cellulose.

[0145] (2) Physical Properties of First Film (2.1) Tensile Modulus E １ Tensile modulus E of the first film １ is preferably in the range of 5.0 to 8.0 GPa, more preferably in the range of 6.0 to 8.0 GPa, and even more preferably in the range of 6.5 to 8.0 GPa.

[0146] Tensile modulus E of the first film １can be measured in the machine direction (MD) by the following method in accordance with JIS K7127 (1999). The tensile modulus is determined by linear regression between strains of 0.05 and 0.25%.

[0147] 1) The first film is cut into a size of 100 mm (MD) x 10 mm (TD) to prepare a test piece. 2) This test piece is measured using a Tensilon universal material testing machine "RTC-1225A" (manufactured by Orientec Co., Ltd.). The chuck distance is set to 50 mm, and the test piece is pulled in the longitudinal (MD) direction at a pulling rate of 50 mm / min. The tensile modulus E in the MD direction is measured. １ The measurement is carried out at 23°C and 55% RH.

[0148] (2.2) Refractive index n １ Refractive index n of the first film １ is preferably in the range of 1.47 to 1.51, and more preferably in the range of 1.48 to 1.50.

[0149] The refractive index of the first film can be measured using, for example, an Abbe refractometer. Examples of Abbe refractometers include the multi-wavelength Abbe refractometer "DR-M2 / 1550" (manufactured by Atago Co., Ltd.). The refractive index is measured at any five points on the surface of the first film, and the arithmetic average value is used. The measurement is performed at 23°C and 55% RH.

[0150] (2.3) Thickness The thickness of the first film is not particularly limited. However, from the viewpoint of achieving both impact resistance and folding resistance, the thickness of the first film is preferably in the range of 30 to 80 μm, and more preferably in the range of 40 to 60 μm.

[0151] (3) Manufacturing Method of First Film The manufacturing method of the first film is not particularly limited, but from the viewpoint of obtaining a desired film, it is preferable to manufacture the first film by a solution casting method or a solution coating method. In these methods, first, a dope containing a resin, a solvent, and any other components is prepared. The dope is applied to a substrate by casting or coating, and then the cast film or coated film is dried to obtain a film. In the solution casting method, it is preferable to peel the cast film from the support and then dry the cast film. On the other hand, in the solution coating method, it is preferable to dry the coated film on the support and then peel the coated film from the support.

[0152] The form of the first film is not particularly limited and may be, for example, a strip-like form. That is, the first film is preferably wound into a roll in a direction perpendicular to its width direction to form a roll body.

[0153] The method for producing the first film by the solution casting method preferably includes the steps of preparing a dope containing acetyl cellulose and a filler of a metal oxide or a metal salt, casting the dope onto a support to form a casting film, peeling the casting film from the support, and drying the casting film.

[0154] The method for producing the first film by the solution coating method preferably includes the steps of preparing a dope containing acetyl cellulose and a filler of a metal oxide or metal salt, coating the dope on a support to form a coating film, drying the coating film on the support, and peeling the dried coating film from the support.

[0155] In this embodiment, both the first film and the second film are preferably manufactured by a solution casting method or a solution coating method. Therefore, the method for manufacturing the first film will mainly describe a procedure for forming the film by the solution casting method, and the method for manufacturing the second film will mainly describe a procedure for forming the film by the solution coating method. When the first film is formed by the solution coating method, the method for manufacturing the second film can be applied, and when the second film is formed by the solution casting method, the method for manufacturing the first film can be applied. Note that detailed manufacturing conditions, etc., may be changed as appropriate depending on the materials contained in each film. Below, the method for manufacturing the first film by the solution casting method will be described.

[0156] (3.1) Dope Preparation Process The dope preparation process will be described. A higher concentration of acetyl cellulose in the dope is preferable because it reduces the drying load after casting onto the metal support. However, if the acetyl cellulose concentration is too high, the load during filtration increases, resulting in poor filtration accuracy. A concentration that satisfies both of these requirements is preferably within the range of 10 to 35% by mass, and more preferably within the range of 15 to 25% by mass.

[0157] The solvent used in the dope may be used alone or in combination of two or more. It is preferable to use a mixture of a good solvent and a poor solvent for acetyl cellulose from the viewpoint of production efficiency. Examples of the good solvent include methylene chloride and methyl acetate. Examples of the poor solvent include methanol, ethanol, n-butanol, cyclohexane, and cyclohexanone.

[0158] The dope preferably contains water in the range of 0.01 to 2% by mass. In the film-forming step described below, the solvent removed from the film by drying may be recovered and reused for dissolving acetyl cellulose.

[0159] A general method can be used to dissolve acetyl cellulose when preparing the dope. By combining heating and pressure, it is possible to heat the dope to a temperature above the boiling point at normal pressure. A general method can be used to disperse the filler when preparing the dope.

[0160] Next, the acetyl cellulose solution is filtered using a suitable filter material such as filter paper, etc. The filter material preferably has an absolute filtration accuracy of 0.008 mm or less, more preferably in the range of 0.001 to 0.008 mm, and even more preferably in the range of 0.003 to 0.006 mm.

[0161] The filter material is not particularly limited, and a common filter material can be used. The filter material is preferably made of a plastic material such as polypropylene or Teflon (registered trademark), or a metal material such as stainless steel, in order to prevent fibers from falling off.

[0162] The dope can be filtered by a conventional method. For example, the filtration temperature is preferably equal to or higher than the boiling point of the solvent at normal pressure, and is within a range in which the solvent does not boil under pressure. By filtering while heating, the increase in the difference in filtration pressure (differential pressure) before and after filtration can be reduced. The filtration temperature is preferably within a range of 45 to 120°C, more preferably within a range of 45 to 70°C, and even more preferably within a range of 45 to 55°C.

[0163] The filtration pressure is preferably small, and is preferably 1.6 MPa or less, more preferably 1.2 MPa or less, and even more preferably 1.0 MPa or less.

[0164] (3.2) Step of casting the dope onto a support to form a cast film Next, the casting of the dope will be described.

[0165] The metal support used in the casting step preferably has a mirror-finished surface. Examples of the metal support include a stainless steel belt or a cast drum with a plated surface. The casting width is preferably within the range of 1 to 4 m.

[0166] The surface temperature of the metal support in the casting step is preferably -50°C or higher and lower than the boiling point of the solvent, more preferably in the range of 0 to 40°C, and even more preferably in the range of 5 to 30°C.

[0167] From the viewpoint of providing the first film with good planarity, the residual solvent amount when the web is peeled from the metal support is preferably in the range of 10 to 150% by mass, more preferably in the range of 20 to 40% by mass or in the range of 60 to 130% by mass, and even more preferably in the range of 20 to 30% by mass or in the range of 70 to 120% by mass.

[0168] In the present invention, the amount of residual solvent is defined by the following formula:

[0169] Residual solvent amount (mass%) = {(M - N) / N} × 100 (Formula) where M is the mass of a sample taken at any time during or after the production of the web or film, and N is the mass of M after heating at 115°C for 1 hour.

[0170] (3.3) Step of Peeling the Cast Film from the Support The web is peeled off from the metal support. A known method can be used to peel the web off from the metal support.

[0171] (3.4) Step of drying the peeled cast film In the step of drying the first film, the web peeled from the metal support is further dried. The residual solvent content is preferably 1% by mass or less, more preferably 0.1% by mass or less, and further preferably in the range of 0 to 0.01% by mass.

[0172] The drying process of the first film generally uses a roll drying method or a tenter method in which the web is dried while being transported. In the roll drying method, the web is dried by passing it alternately through multiple rolls arranged above and below.

[0173] The first film is preferably stretched in the machine direction (MD) immediately after peeling from the metal support, at a portion of the web where the residual solvent is large, and is preferably stretched in the transverse direction (TD) using a tenter system in which both ends of the web are held with clips or the like.

[0174] The means for drying the web is not particularly limited, and generally includes hot air, infrared rays, a heated roll, microwaves, etc. From the viewpoint of simplicity, hot air is preferred.

[0175] The drying temperature in the web drying step is preferably in the range of 90° C. to 200° C., more preferably in the range of 110° C. to 190° C. It is preferable to increase the drying temperature in stages.

[0176] The preferred drying time, although it depends on the drying temperature, is preferably within the range of 5 to 60 minutes, and more preferably within the range of 10 to 30 minutes.

[0177] The thickness of the film is not particularly limited, but is preferably in the range of 10 to 200 μm, more preferably in the range of 10 to 100 μm, and more preferably in the range of 20 to 60 μm.

[0178] The width of the film is preferably in the range of 1 to 4 m. From the viewpoint of productivity, the width is preferably in the range of 1.6 to 4 m, and more preferably in the range of 1.8 to 3.6 m.

[0179] (3.5) Step of Stretching the First Film The stretching operation can be performed in both the longitudinal direction (MD direction) and the width direction (TD direction) of the first film. Stretching in the TD direction is particularly preferred. The stretching ratio in the TD direction is preferably within the range of 1 to 50%, more preferably within the range of 5 to 30%. Further stretching in the production of the first film can change the molecular orientation of the acetyl cellulose, thereby adjusting the tensile modulus of the first film.

[0180] For example, a method of stretching in the MD direction by using the difference in peripheral speeds between multiple rolls can be used. Other examples include a method of fixing both ends of the web with clips or pins, widening the gap between the clips or pins in the direction of travel to stretch in the MD direction, and a method of similarly widening the web laterally to stretch in the TD direction. Another example includes a method of simultaneously widening the web in both the MD and TD directions to stretch in both the MD and TD directions.

[0181] In the film-forming process, the width is preferably maintained or the film is stretched in the width direction by a tenter, and either a pin tenter or a clip tenter may be used.

[0182] The first film conveying tension in the film-forming process in a tenter or the like, although it depends on the temperature, is preferably in the range of 120 to 200 N / m, more preferably in the range of 140 to 200 N / m, and even more preferably in the range of 140 to 160 N / m.

[0183] When the glass transition temperature of the first film is Tg, the temperature of the first film during stretching is preferably within the range of (Tg-30) to (Tg+100)°C, more preferably within the range of (Tg-20) to (Tg+80)°C, and even more preferably within the range of (Tg-5) to (Tg+20)°C.

[0184] The Tg of the first film can be controlled by the types of materials constituting the first film and the ratio of the materials. The Tg of the first film when dried is preferably 110° C. or higher, and more preferably 120° C. or higher.

[0185] The dry Tg of the first film is preferably not more than 190° C., and more preferably not more than 170° C. The Tg of the first film can be determined by the method described in JIS K7121, for example.

[0186] By setting the stretching temperature to 150°C or higher and the stretching ratio to 15% or higher, it is possible to impart appropriate roughness to the surface of the film. By imparting appropriate roughness to the surface of the first film, not only can the slipperiness be improved, but also the surface processability and adhesion to adjacent layers can be improved. The average surface roughness Ra of the first film is preferably in the range of 2.0 to 4.0 nm, and more preferably in the range of 2.5 to 3.5 nm.

[0187] It is preferable that the average surface roughness Ra (nm) of the first film and the polarity of the first film itself with respect to the solvent satisfy the following relational expression: where "log P" represents the octanol / water partition coefficient of the first film.

[0188] (Formula) Ra≧3.5×logP-25.4

[0189] After stretching, the first film is preferably heat-set. The temperature during heat-setting is preferably higher than the temperature during the final stretching in the TD direction. Heat-setting is preferably carried out at a temperature of (Tg-20°C) or lower, usually for 0.5 to 300 seconds. In this case, heat-setting is preferably carried out while sequentially increasing the temperature in two or more divided regions so that the temperature difference is in the range of 1 to 100°C.

[0190] The heat-set first film is usually cooled to below Tg, and the clipped portions at both ends of the first film are cut and wound up. At this time, it is preferable to relax the film by 0.1 to 10% in the TD direction within a temperature range below the final heat-setting temperature and above Tg. In addition, it is also preferable to relax the film by 0.1 to 10% in the MD direction.

[0191] The cooling is preferably performed by slowly cooling from the final heat setting temperature to Tg at a cooling rate of 100°C per second or less. The method for the cooling and relaxation treatment is not particularly limited, and any conventionally known method can be used. In particular, from the viewpoint of improving the dimensional stability of the first film, it is preferable to perform these treatments while sequentially cooling in multiple temperature ranges.

[0192] The cooling rate is calculated by (T1-Tg) / t, where T1 is the final heat setting temperature and t is the time it takes for the first film to reach Tg from the final heat setting temperature.

[0193] The optimal conditions for these heat setting conditions and cooling and relaxation treatment conditions vary depending on the types of additives constituting the first film, such as acetyl cellulose, filler, plasticizer, etc. The physical properties of the resulting biaxially stretched first film can be measured, and the constituent materials of the first film can be appropriately selected so that the first film has desirable properties.

[0194] Whether the first film is stretched or not can be confirmed, for example, by checking whether or not there is an in-plane slow axis (an axis extending in the direction in which the refractive index is maximized).

[0195] 3. Second Film The second film according to this embodiment has a tensile modulus E ２In the above formula (1), the structure of the film is not particularly limited as long as it satisfies the formula (1). An example of a film that satisfies the formula (1) is a resin film. The tensile modulus E of the second film varies depending on the type of resin contained in the resin film. ２ The tensile modulus E of the second film can be adjusted by changing the type and content of the additive contained in the resin film. ２ In addition, the tensile modulus E can also be adjusted by adjusting the stretching ratio in the manufacturing process of the second film. ２ can be adjusted.

[0196] (1) Structure of the Second Film The resin used for the second film is not particularly limited, and examples thereof include cellulose ester resin, cycloolefin resin, fumaric acid diester resin, polypropylene, (meth)acrylic resin, polyester, polyarylate, polyimide, and styrene resin. Also included are composite resins thereof. Among these, the resin is preferably a linear polymer material having a carbonyl group in the side chain, or a polymer material having a cyclic structure in the main chain. Furthermore, from the viewpoint of achieving both physical properties such as folding endurance and optical properties, the resin is preferably a (meth)acrylic resin, a styrene-(meth)acrylate copolymer, a cycloolefin resin, or a polyimide.

[0197] In this specification, "(meth)acrylic" is a general term for "acrylic" and "methacrylic" and means one or both of them. For example, "methyl (meth)acrylate" means one or both of "methyl acrylate" and "methyl methacrylate".

[0198] The second film may contain additives as needed in addition to the resins described above. The additives may include rubber particles and fine particles described below, as well as the additives contained in the first film described above.

[0199] (1.1) (Meth)acrylic Resin The (meth)acrylic resin preferably contains at least a structural unit (U1) derived from methyl methacrylate and a structural unit (U2) derived from phenylmaleimide. By containing the structural unit (U2) derived from phenylmaleimide, the photoelastic coefficient of the second film can be reduced, and the occurrence of unevenness can be suppressed even when the second film expands due to moisture absorption.

[0200] The (meth)acrylic resin may further contain structural units other than those described above. Examples of such structural units include structural units derived from (meth)acrylic acid alkyl esters (adamantyl acrylate, etc.), (meth)acrylic acid cycloalkyl esters (2-ethylhexyl acrylate, etc.), etc. Among these, from the viewpoint of reducing the deterioration of brittleness due to the inclusion of the structural unit (U2) derived from phenylmaleimide, it is preferable that the (meth)acrylic resin further contains a structural unit (U3) derived from an acrylic acid alkyl ester as the other structural unit.

[0201] That is, the (meth)acrylic resin more preferably contains a structural unit (U1) derived from methyl methacrylate, a structural unit (U2) derived from phenylmaleimide, and a structural unit (U3) derived from an alkyl acrylate.

[0202] The content of the structural unit (U1) derived from methyl methacrylate is preferably within a range of 50 to 95 mass %, and more preferably within a range of 70 to 90 mass %, based on all structural units constituting the (meth)acrylic resin.

[0203] The structural unit (U2) derived from phenylmaleimide has a relatively rigid structure, thereby improving the mechanical strength of the second film. Furthermore, the structural unit (U2) derived from phenylmaleimide has a relatively bulky structure. Therefore, when rubber particles are added to the second film, the structural unit (U2) derived from phenylmaleimide has microvoids that facilitate the movement of the rubber particles in the resin matrix. As a result, the rubber particles can be easily distributed unevenly in the surface layer portion of the second film.

[0204] The content of the structural unit (U2) derived from phenylmaleimide is preferably within a range of 1 to 25% by mass relative to all structural units constituting the (meth)acrylic resin. When the content of the structural unit (U2) derived from phenylmaleimide is 1% by mass or more, the second film has excellent storage stability in a high-humidity environment. When the content is 25% by mass or less, the brittleness of the second film is less likely to be excessively impaired. From the above viewpoints, the content of the structural unit (U2) derived from phenylmaleimide is more preferably within a range of 7 to 15% by mass.

[0205] The structural unit (U3) derived from an alkyl acrylate can impart appropriate flexibility to the (meth)acrylic resin, and can therefore improve the brittleness caused by including the structural unit (U2) derived from, for example, phenylmaleimide.

[0206] The number of carbon atoms in the alkyl moiety of the acrylic acid alkyl ester is preferably in the range of 1 to 7, and more preferably in the range of 1 to 5. Examples of the acrylic acid alkyl ester include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-hydroxyethyl acrylate, hexyl acrylate, and 2-ethylhexyl acrylate.

[0207] The content of the structural unit (U3) derived from an acrylic acid alkyl ester is preferably within the range of 1 to 25% by mass relative to all structural units constituting the (meth)acrylic resin. When the content of the structural unit (U3) derived from an acrylic acid alkyl ester is 1% by mass or more, the (meth)acrylic resin can be imparted with appropriate flexibility, so that the second film does not become too brittle and is less likely to break. When the content of the structural unit (U3) derived from an acrylic acid alkyl ester is 25% by mass or less, the Tg of the second film does not become too low, and the second film has excellent storage stability in high-humidity environments. From the above viewpoints, the content of the structural unit (U3) derived from an acrylic acid alkyl ester is more preferably within the range of 5 to 15% by mass.

[0208] The content of the structural unit (U2) derived from phenylmaleimide is preferably 20 to 70 parts by mass relative to 100 parts by mass of the total content of the structural unit (U2) derived from phenylmaleimide and the structural unit (U3) derived from an alkyl acrylate. When the content is 20 parts by mass or more, the elastic modulus of the second film can be increased, and when the content is 70 parts by mass or less, the brittleness of the second film is less likely to be impaired.

[0209] The glass transition temperature (Tg) of the (meth)acrylic resin is preferably 100°C or higher, and more preferably within the range of 120 to 150°C. When the Tg of the (meth)acrylic resin is within the above range, the heat resistance of the second film can be improved. In order to adjust the Tg of the (meth)acrylic resin, it is preferable to adjust the content of, for example, the structural unit (U2) derived from phenylmaleimide or the structural unit (U3) derived from an alkyl acrylate.

[0210] The weight-average molecular weight (Mw) of the (meth)acrylic resin is not particularly limited and can be adjusted according to the purpose. The weight-average molecular weight of the (meth)acrylic resin is preferably 100,000 or more, more preferably 1,000,000 or more. A weight-average molecular weight of 100,000 or more can, for example, promote entanglement of resin molecules with each other, thereby increasing the toughness of the second film and making it less susceptible to breakage. Furthermore, a weight-average molecular weight of 100,000 or more can appropriately increase the coefficient of moisture absorption expansion, allowing the curl amount to be adjusted to a level suitable for adhesion.

[0211] By ensuring that the weight-average molecular weight of the (meth)acrylic resin is 1,000,000 or more, the toughness of the second film can be increased. This can prevent the second film from breaking due to conveying tension when conveyed as a laminated film in the manufacturing process, thereby improving conveying stability. From the above viewpoints, it is more preferable that the weight-average molecular weight of the (meth)acrylic resin is in the range of 1,500,000 to 3,000,000. The method for measuring the weight-average molecular weight is as follows.

[0212] <Gel Permeation Chromatography> Solvent: methylene chloride Column: three columns of "Shodex (registered trademark) K806, K805, K803G" (manufactured by Showa Denko K.K.) were connected and used. Column temperature: 25°C Sample concentration: 0.1% by mass Detector: "RI Model 504" (manufactured by GL Science Co., Ltd.) Pump: "L6000" (manufactured by Hitachi, Ltd.) Flow rate: 1.0 mL / min Calibration curve: A calibration curve was used using 13 samples of standard polystyrene STK standard polystyrene (manufactured by Tosoh Corporation) in the range of Mw = 500 to 2,800,000. It is preferable to use the 13 samples at approximately equal intervals.

[0213] The content of the (meth)acrylic resin is preferably 50% by mass or more, and more preferably 70% by mass or more, based on the total mass of the second film.

[0214] (1.2) Styrene-(meth)acrylate copolymer Hereinafter, the "styrene-(meth)acrylate copolymer" is also referred to as "styrene-acrylic resin." Styrene-acrylic resin has excellent transparency. In addition, since the coefficient of moisture absorption expansion can be adjusted by the copolymerization ratio of the styrene portion, curling of the second film can be controlled by changing these ratios.

[0215] The styrene-acrylic resin is synthesized by addition polymerization of at least a styrene monomer and a (meth)acrylic acid ester monomer.

[0216] Styrene monomers include styrene, represented by the structural formula CH2=CH-C6H5, as well as styrene derivatives having known side chains or functional groups in the styrene structure. (Meth)acrylic acid ester monomers include acrylic acid esters and methacrylic acid esters represented by CH(R1)=CHCOOR2, as well as acrylic acid ester derivatives and methacrylic acid ester derivatives having known side chains or functional groups in the ester structure. Here, R1 represents a hydrogen atom or a methyl group, and R2 represents an alkyl group having 1 to 24 carbon atoms.

[0217] Examples of styrene monomers include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-phenylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-tert-butylstyrene, p-n-hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene, and p-n-dodecylstyrene.

[0218] Examples of acrylic acid ester monomers include methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, isobutyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate (2EHA), stearyl acrylate, lauryl acrylate, and phenyl acrylate.

[0219] Examples of methacrylic acid ester monomers include methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, lauryl methacrylate, phenyl methacrylate, diethylaminoethyl methacrylate, and dimethylaminoethyl methacrylate.

[0220] The (meth)acrylic acid ester monomer may be used alone or in combination of two or more. For example, a copolymer may be synthesized using a styrene monomer and two or more acrylic acid ester monomers. A copolymer may be synthesized using a styrene monomer and two or more methacrylic acid ester monomers. A copolymer may be synthesized using a styrene monomer, an acrylic acid ester monomer, and a methacrylic acid ester monomer.

[0221] The weight average molecular weight (Mw) of the styrene-acrylic resin is preferably in the range of 5,000 to 150,000, more preferably in the range of 30,000 to 120,000, from the viewpoint of easy control of plasticity.

[0222] The styrene-acrylic resin may be a commercially available product, such as MS resin "TX320XL" (manufactured by Denka Co., Ltd.).

[0223] The content of the styrene-acrylic resin is preferably 50% by mass or more, and more preferably 70% by mass or more, based on the total mass of the second film.

[0224] <Rubber Particles> The second film preferably contains rubber particles from the viewpoint of imparting toughness (suppleness) and folding endurance. In particular, when the second film uses a (meth)acrylic resin or a styrene-acrylic resin as the resin, it preferably contains rubber particles. Hereinafter, the rubber particles contained when the second film uses a (meth)acrylic resin or a styrene-acrylic resin as the resin will be described.

[0225] The rubber particles are particles containing a rubbery polymer. The rubbery polymer is a soft crosslinked polymer having a glass transition temperature of 20°C or lower. Examples of such crosslinked polymers include butadiene-based crosslinked polymers, (meth)acrylic crosslinked polymers, and organosiloxane-based crosslinked polymers. Among these, (meth)acrylic crosslinked polymers are preferred, and acrylic crosslinked polymers (acrylic rubbery polymers) are more preferred. By using a (meth)acrylic crosslinked polymer, the difference in refractive index between the (meth)acrylic resin or styrene-acrylic resin can be reduced, and the transparency of the second film is less likely to be impaired.

[0226] That is, the rubber particles are preferably particles containing the acrylic rubber-like polymer (a). The acrylic rubber-like polymer (a) will now be described.

[0227] The acrylic rubber-like polymer (a) is a crosslinked polymer containing structural units derived from an acrylic acid ester. The acrylic rubber-like polymer (a) preferably contains structural units derived from an acrylic acid ester, structural units derived from another monomer copolymerizable therewith, and structural units derived from a polyfunctional monomer having two or more radically polymerizable groups (non-conjugated reactive double bonds) per molecule.

[0228] The acrylic acid ester preferably has an alkyl group having a carbon number in the range of 1 to 12. Examples of acrylic acid esters having an alkyl group having a carbon number in the range of 1 to 12 include methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, sec-butyl acrylate, isobutyl acrylate, benzyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, and n-octyl acrylate. The acrylic acid esters may be used alone or in combination of two or more.

[0229] The content of the structural units derived from the acrylic acid ester is preferably within a range of 40 to 80 mass %, more preferably within a range of 50 to 80 mass %, based on all structural units constituting the acrylic rubber-like polymer (a). By having the content of the acrylic acid ester within the above range, sufficient toughness can be imparted to the second film.

[0230] The copolymerizable other monomer is a monomer copolymerizable with an acrylic acid ester other than a polyfunctional monomer. That is, the copolymerizable monomer does not have two or more radically polymerizable groups. Examples of the copolymerizable monomer include methacrylic acid esters (methyl methacrylate, etc.); styrenes (styrene, methylstyrene, etc.); (meth)acrylonitriles; (meth)acrylamides; (meth)acrylic acid, etc. Among them, the copolymerizable other monomer is preferably a styrene. The copolymerizable other monomer may be used alone or in combination of two or more.

[0231] The content of structural units derived from other copolymerizable monomers is preferably within a range of 5 to 55 mass %, more preferably within a range of 10 to 45 mass %, based on all structural units constituting the acrylic rubber-like polymer (a).

[0232] Examples of polyfunctional monomers include allyl (meth)acrylate, triallyl cyanurate, triallyl isocyanurate, diallyl phthalate, diallyl maleate, divinyl adipate, divinyl benzene, ethylene glycol di(meth)acrylate, diethylene glycol (meth)acrylate, triethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tetra(meth)acrylate, dipropylene glycol di(meth)acrylate, and polyethylene glycol di(meth)acrylate.

[0233] The content of the structural units derived from the polyfunctional monomer is preferably within a range of 0.05 to 10% by mass, and more preferably within a range of 0.1 to 5% by mass, relative to all structural units constituting the acrylic rubber-like polymer (a). When the content of the polyfunctional monomer is 0.05% by mass or more, the degree of crosslinking of the acrylic rubber-like polymer (a) can be increased, and the hardness and rigidity of the second film are not impaired. When the content is 10% by mass or less, the toughness of the second film is less likely to be impaired.

[0234] The monomer composition of the acrylic rubber-like polymer (a) can be measured, for example, by the peak area ratio detected by pyrolysis gas chromatography (GC-MS).

[0235] The glass transition temperature (Tg) of the acrylic rubber-like polymer (a) is preferably 0° C. or lower, more preferably −10° C. or lower. When the glass transition temperature (Tg) of the acrylic rubber-like polymer (a) is 0° C. or lower, the film can be imparted with appropriate toughness. The glass transition temperature (Tg) of the acrylic rubber-like polymer (a) can be measured by the same method as described above.

[0236] The glass transition temperature (Tg) of the acrylic rubber-like polymer (a) can be adjusted by the composition of the acrylic rubber-like polymer (a). The glass transition temperature (Tg) can be lowered by adjusting the mass ratio represented by the following formula (formula) to 3 or more, preferably within the range of 4 to 10. (Formula) Mass ratio = A / B A: Content of structural units derived from acrylic acid esters having alkyl groups with 4 or more carbon atoms B: Content of structural units derived from other copolymerizable monomers

[0237] The particles containing the acrylic rubbery polymer (a) may be any of the following: Particles made of the acrylic rubbery polymer (a) Particles having a hard layer made of a hard crosslinked polymer (c) having a glass transition temperature of 20°C or higher and a soft layer made of the acrylic rubbery polymer (a) arranged around the hard layer Particles made of an acrylic graft copolymer obtained by polymerizing a mixture of monomers such as a methacrylic acid ester in at least one stage in the presence of the acrylic rubbery polymer (a)

[0238] The particles made of the acrylic graft copolymer may be core-shell type particles having a core containing the acrylic rubbery polymer (a) and a shell covering the core. Hereinafter, the core-shell type rubber particles containing the acrylic rubbery polymer (a) will be described.

[0239] (Core) The core contains an acrylic rubber-like polymer (a) and may further contain a hard crosslinked polymer (c) as needed. That is, the core may have a soft layer made of the acrylic rubber-like polymer (a) and a hard layer made of the hard crosslinked polymer (c) disposed inside the soft layer.

[0240] The crosslinked polymer (c) is not particularly limited, but is preferably a crosslinked polymer containing a methacrylic acid ester as a main component, i.e., the crosslinked polymer (c) is preferably a crosslinked polymer containing a structural unit derived from a methacrylic acid alkyl ester, a structural unit derived from another monomer copolymerizable therewith, and a structural unit derived from a polyfunctional monomer.

[0241] The methacrylic acid alkyl ester may be any of the methacrylic acid alkyl esters exemplified above for the styrene-acrylic resin. The copolymerizable other monomer may be any of the styrenes, acrylic acid esters, etc. exemplified above. The polyfunctional monomer may be any of the polyfunctional monomers exemplified above.

[0242] The content of structural units derived from methacrylic acid alkyl esters is preferably within a range of 40 to 100% by mass relative to all structural units constituting the crosslinked polymer (c). The content of structural units derived from other copolymerizable monomers is preferably within a range of 60 to 0% by mass relative to all structural units constituting the crosslinked polymer (c). The content of structural units derived from polyfunctional monomers is preferably within a range of 0.01 to 10% by mass relative to all structural units constituting the crosslinked polymer (c).

[0243] (Shell Portion) The shell portion contains a methacrylic polymer (b) containing structural units derived from a methacrylic acid ester, and the methacrylic polymer (b) is graft-bonded to the acrylic rubber-like polymer (a).

[0244] The methacrylic acid ester constituting the methacrylic polymer (b) is preferably a methacrylic acid alkyl ester (e.g., methyl methacrylate) in which the alkyl group has 1 to 12 carbon atoms. The methacrylic acid ester may be used alone or in combination of two or more kinds.

[0245] The content of the methacrylic acid ester is preferably 50% by mass or more relative to all structural units constituting the methacrylic polymer (b). By having a content of the methacrylic acid ester of 50% by mass or more, compatibility with a methacrylic resin containing structural units derived from methyl methacrylate as a main component is easily obtained. From the above viewpoint, the content of the methacrylic acid ester is more preferably 70% by mass or more relative to all structural units constituting the methacrylic polymer (b).

[0246] The methacrylic polymer (b) may further contain a structural unit derived from another monomer copolymerizable with the methacrylic acid ester. Examples of the other copolymerizable monomer include acrylic acid esters (methyl acrylate, ethyl acrylate, n-butyl acrylate, etc.). Examples of the other copolymerizable monomer include (meth)acrylic monomers having an alicyclic ring, a heterocyclic ring, or an aromatic ring (ring-containing (meth)acrylic monomers). Examples of ring-containing (meth)acrylic monomers include benzyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and phenoxyethyl (meth)acrylate.

[0247] The content of structural units derived from copolymerizable monomers is preferably 50% by mass or less, and more preferably 30% by mass or less, based on the total structural units constituting the methacrylic polymer (b).

[0248] In the present embodiment, when the second film is not stretched, the shape of the rubber particles is preferably close to a perfect sphere, i.e., when observing the cross section or surface of the second film, the aspect ratio of the rubber particles is preferably about 1 to 2.

[0249] The average particle size of the rubber particles is preferably within the range of 100 to 400 nm. When the average particle size of the rubber particles is 100 nm or more, sufficient toughness and stress relaxation properties can be imparted to the second film. Furthermore, when the average particle size of the rubber particles is 400 nm or less, the transparency of the second film is less likely to be impaired. From the same viewpoint, the average particle size of the rubber particles is more preferably within the range of 150 to 300 nm.

[0250] The average particle size of the rubber particles can be measured and calculated by the following method.

[0251] The average particle size of the rubber particles can be measured as the average of the circle-equivalent diameters of 100 particles obtained by SEM or TEM photography of the surface or slice of the second film. The circle-equivalent diameter is determined by converting the projected area of ​​the particles obtained by photography into the diameter of a circle having the same area. In this case, rubber particles observed by SEM or TEM observation at a magnification of 5000 times are used to calculate the average particle size.

[0252] The content of the rubber particles is not particularly limited, but is preferably in the range of 20 to 90 mass% relative to the total mass of the second film, more preferably in the range of 40 to 85 mass%, and even more preferably in the range of 45 to 75 mass%.

[0253] (1.3) Cycloolefin Resin The cycloolefin resin is preferably a polymer of a cycloolefin monomer or a copolymer of a cycloolefin monomer and another copolymerizable monomer.

[0254] The cycloolefin monomer is preferably a cycloolefin monomer having a norbornene skeleton, and more preferably has a structure represented by the following general formula (A-1) or (A-2).

[0255]

[0256] In general formula (A-1), R 1 ~R 4 each independently represents a hydrogen atom, a hydrocarbon group having 1 to 30 carbon atoms, or a polar group, and p represents an integer of 0 to 2. 1 ~R 4 do not all represent hydrogen atoms at the same time, and R 1 and R 2 does not simultaneously represent a hydrogen atom, and R 3 and R 4 does not simultaneously represent a hydrogen atom.

[0257] R 1 ~R 4 The hydrocarbon group having 1 to 30 carbon atoms represented by the formula (I) is preferably a hydrocarbon group having 1 to 10 carbon atoms, and more preferably a hydrocarbon group having 1 to 5 carbon atoms. The hydrocarbon group having 1 to 30 carbon atoms may further have a linking group containing, for example, a halogen atom, an oxygen atom, a nitrogen atom, a sulfur atom, or a silicon atom. Examples of such linking groups include divalent polar groups such as a carbonyl group, an imino group, an ether bond, a silyl ether bond, and a thioether bond. Examples of hydrocarbon groups having 1 to 30 carbon atoms include a methyl group, an ethyl group, a propyl group, and a butyl group.

[0258] R 1 ~R 4 Examples of the polar group represented by the formula (I) include a carboxy group, a hydroxy group, an alkoxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, an amino group, an amide group, and a cyano group. Among these, the polar group is preferably a carboxy group, a hydroxy group, an alkoxycarbonyl group, or an aryloxycarbonyl group. Furthermore, from the viewpoint of ensuring solubility during solution casting, the polar group is preferably an alkoxycarbonyl group or an aryloxycarbonyl group.

[0259] In general formula (A-1), p is preferably 1 or 2 from the viewpoint of enhancing the heat resistance of the second film. When p is 1 or 2, the resulting polymer becomes bulky and the glass transition temperature is likely to be increased. Furthermore, when p is 1 or 2, the hygroscopic expansion coefficient can be adjusted, and curling of the second film can be controlled.

[0260]

[0261] In general formula (A-2), R 5 represents a hydrogen atom, a hydrocarbon group having 1 to 5 carbon atoms, or an alkylsilyl group having an alkyl group having 1 to 5 carbon atoms. 6 represents a carboxy group, a hydroxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, an amino group, an amido group, a cyano group, or a halogen atom. A halogen atom represents a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom. p represents an integer of 0 to 2.

[0262] R in general formula (A-2) 5 is preferably a hydrocarbon group having 1 to 5 carbon atoms, and more preferably a hydrocarbon group having 1 to 3 carbon atoms.

[0263] R in general formula (A-2) 6 is preferably a carboxy group, a hydroxy group, an alkoxycarbonyl group, or an aryloxycarbonyl group. 6 is more preferably an alkoxycarbonyl group or an aryloxycarbonyl group.

[0264] In terms of improving the heat resistance of the second film, p in general formula (A-2) is preferably 1 or 2. When p is 1 or 2, the obtained polymer becomes bulky and the glass transition temperature is likely to be improved.

[0265] A cycloolefin monomer having a structure represented by general formula (A-2) can improve the solubility in organic solvents. In general, by breaking the symmetry of an organic compound, the crystallinity decreases and the solubility in organic solvents improves. 5 and R 6 is substituted only on one ring carbon atom with respect to the axis of symmetry of the molecule, and therefore has low molecular symmetry. In other words, a cycloolefin monomer having a structure represented by general formula (A-2) has high solubility and is therefore suitable when the second film is produced by a solution casting method.

[0266] The content of the cycloolefin monomer having the structure represented by general formula (A-2) is preferably 70 mol% or more, more preferably 80 mol% or more, and even more preferably 100 mol% relative to the total amount of all cycloolefin monomers constituting the cycloolefin resin. By including a certain amount or more of the cycloolefin monomer having the structure represented by general formula (A-2), the orientation of the resin is improved, and therefore the phase difference (retardation) value is likely to increase.

[0267] Specific examples of cycloolefin monomers having a structure represented by general formula (A-1) are shown below as Exemplary Compounds 1 to 14, and specific examples of cycloolefin monomers having a structure represented by general formula (A-2) are shown below as Exemplary Compounds 15 to 34.

[0268]

[0269] Examples of copolymerizable monomers copolymerizable with cycloolefin monomers include copolymerizable monomers capable of ring-opening copolymerization with cycloolefin monomers, and copolymerizable monomers capable of addition copolymerization with cycloolefin monomers.

[0270] Examples of copolymerizable monomers capable of ring-opening copolymerization include cycloolefins such as cyclobutene, cyclopentene, cycloheptene, cyclooctene, and dicyclopentadiene.

[0271] Examples of copolymerizable monomers capable of addition copolymerization include unsaturated double bond-containing compounds, vinyl cyclic hydrocarbon monomers, (meth)acrylates, etc. Examples of unsaturated double bond-containing compounds include olefins having 2 to 12 carbon atoms, preferably 2 to 8 carbon atoms. Examples of olefins include ethylene, propylene, and butene. Examples of vinyl cyclic hydrocarbon monomers include vinylcyclopentene-based monomers such as 4-vinylcyclopentene and 2-methyl-4-isopropenylcyclopentene. Examples of (meth)acrylates include alkyl (meth)acrylates having 1 to 20 carbon atoms, such as methyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate.

[0272] The content of the cycloolefin monomer is preferably within a range of 20 to 80 mol %, more preferably within a range of 30 to 70 mol %, based on the total amount of all monomers constituting the copolymer.

[0273] As described above, the cycloolefin resin is a polymer obtained by polymerizing or copolymerizing a cycloolefin monomer having a norbornene skeleton, preferably a cycloolefin monomer having a structure represented by general formula (A-1) or (A-2). Examples of the cycloolefin resin include the following:

[0274] 1) Ring-opening polymer of cycloolefin monomer; 2) Ring-opening copolymer of cycloolefin monomer and copolymerizable monomer capable of ring-opening copolymerization therewith; 3) Hydrogenated product of ring-opening (co)polymer of 1) or 2) above; 4) Ring-opening (co)polymer of 1) or 2) above, cyclized by Friedel-Crafts reaction, followed by hydrogenation; 5) Saturated copolymer of cycloolefin monomer and unsaturated double bond-containing compound; 6) Addition copolymer of cycloolefin monomer with vinyl cyclic hydrocarbon monomer, and hydrogenated product thereof; 7) Alternating copolymer of cycloolefin monomer and (meth)acrylate

[0275] The polymers 1) to 7) above can all be obtained by known methods, such as those described in JP-A-2008-107534 or JP-A-2005-227606. For example, the catalyst and solvent used in the ring-opening copolymerization 2) above can be those described in paragraphs 0019 to 0024 of JP-A-2008-107534. The catalyst used in the hydrogenation 3) and 6) above can be those described in paragraphs 0025 to 0028 of JP-A-2008-107534. The acidic compound used in the Friedel-Crafts reaction 4) above can be those described in paragraph 0029 of JP-A-2008-107534. The catalyst used in the addition polymerization 5) to 7) above can be those described in paragraphs 0058 to 0063 of JP-A-2005-227606. The alternating copolymerization reaction of 7) above can be carried out, for example, by the method described in paragraphs 0071 and 0072 of JP-A No. 2005-227606.

[0276] Among these, the cycloolefin resin is preferably a polymer of the above 1) to 3) or 5), and more preferably a polymer of the above 3) or 5). That is, from the viewpoint of increasing the glass transition temperature and increasing the light transmittance, the cycloolefin resin preferably contains at least one of a structural unit represented by the following general formula (B-1) and a structural unit represented by the following general formula (B-2). Among these, it is more preferable that the cycloolefin resin contains only a structural unit represented by the general formula (B-2), or contains both a structural unit represented by the general formula (B-1) and a structural unit represented by the general formula (B-2). The structural unit represented by the general formula (B-1) is a structural unit derived from the cycloolefin monomer represented by the above general formula (A-1), and the structural unit represented by the general formula (B-2) is a structural unit derived from the cycloolefin monomer represented by the above general formula (A-2).

[0277]

[0278] In general formula (B-1), X represents -CH=CH- or -CH2CH2-. 1 ~R 4 and p are R in general formula (A-1), 1 ~R 4 and p.

[0279]

[0280] In general formula (B-2), X represents -CH=CH- or -CH2CH2-. 5 ~R 6 and p are R in general formula (A-2), 5 ~R 6 and p.

[0281] The cycloolefin resin may be a commercially available product. Examples of commercially available cycloolefin resins include "Arton (registered trademark) G (e.g., G7810, etc.)," ​​"Arton F," "Arton R (e.g., R4500, R4900, and R5000, etc.)," ​​and "Arton RX (e.g., RX4500, etc.)" (all manufactured by JSR Corporation).

[0282] The intrinsic viscosity [η]inh of the cycloolefin resin is 0.2 to 5 cm when measured at 30°C.3 / g, and 0.3 to 3 cm 3 / g, and more preferably in the range of 0.4 to 1.5 cm 3 It is more preferable that the range is 1 / g.

[0283] The number average molecular weight (Mn) of the cycloolefin resin is preferably within the range of 8,000 to 100,000, more preferably within the range of 10,000 to 80,000, and even more preferably within the range of 12,000 to 50,000. The weight average molecular weight (Mw) of the cycloolefin resin is preferably within the range of 20,000 to 300,000, more preferably within the range of 30,000 to 250,000, and even more preferably within the range of 40,000 to 200,000. The number average molecular weight and weight average molecular weight of the cycloolefin resin can be measured in polystyrene equivalent terms using the aforementioned gel permeation chromatography (GPC).

[0284] When the intrinsic viscosity [η]inh, number average molecular weight, and weight average molecular weight are within the above ranges, the cycloolefin resin has good heat resistance, water resistance, chemical resistance, mechanical properties, and moldability as a second film.

[0285] The glass transition temperature (Tg) of the cycloolefin resin is preferably 110°C or higher, more preferably in the range of 110 to 350°C, even more preferably in the range of 120 to 250°C, and particularly preferably in the range of 120 to 220°C. A Tg of 110°C or higher can suppress deformation of the second film under high temperature conditions. A Tg of 350°C or lower can facilitate molding of the second film and suppress deterioration of the cycloolefin resin due to heat during molding.

[0286] The content of the cycloolefin resin is preferably 70% by mass or more, and more preferably 80% by mass or more, based on the total mass of the second film.

[0287] <Fine Particles> When a cycloolefin resin is used as the resin for the second film, fine particles may be further contained. The fine particles may be an inorganic compound or an organic compound.

[0288] Examples of inorganic compounds include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, calcium phosphate, and the like.

[0289] Examples of organic compounds include polytetrafluoroethylene, cellulose acetate, polystyrene, polymethyl methacrylate, polypropyl methacrylate, polymethyl acrylate, polyethylene carbonate, styrene-acrylic resin, silicone resin, polycarbonate, benzoguanamine resin, melamine resin, polyolefin powder, polyester, polyamide, polyimide, polyethylene fluoride, etc. In addition, pulverized fractions of organic polymer compounds such as starch, polymer compounds synthesized by suspension polymerization, etc. may also be used.

[0290] From the viewpoint of reducing turbidity, it is preferable that the fine particles contain silicon, and it is particularly preferable that they contain silicon dioxide. Commercially available fine particles may be used. Examples of commercially available fine particles containing silicon dioxide include "Aerosil (registered trademark) R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600" (all manufactured by Nippon Aerosil Co., Ltd.).

[0291] (1.4) Polyimide Polyimide is a polymerization reaction product of tetracarboxylic dianhydride and diamine.

[0292] The tetracarboxylic dianhydride may be any of aromatic tetracarboxylic dianhydride, aliphatic tetracarboxylic dianhydride, and alicyclic tetracarboxylic dianhydride. Of these, the tetracarboxylic dianhydride is preferably aromatic tetracarboxylic dianhydride. The diamine may be any of aromatic diamine, aliphatic diamine, and alicyclic diamine. Of these, the diamine is preferably aromatic diamine.

[0293] The weight-average molecular weight (Mw) of the polyimide is not particularly limited. From the viewpoint of increasing the toughness of the second film and making it less likely to break due to conveying tension, the weight-average molecular weight is preferably in the range of 100,000 to 300,000, and more preferably in the range of 130,000 to 250,000. The method for measuring the weight-average molecular weight (Mw) of the polyimide is the same as that described above.

[0294] The content of polyimide is preferably 60% by mass or more, and more preferably 70% by mass or more, based on the total mass of the second film.

[0295] (2) Physical Properties of Second Film (2.1) Tensile Modulus of Elasticity Tensile modulus of elasticity E of second film ２ is not particularly limited as long as it satisfies the relationship of the above formula (1). ２ The tensile modulus E of the second film is preferably in the range of 0.5 to 3.0 GPa, more preferably in the range of 0.5 to 2.5 GPa, and even more preferably in the range of 1.0 to 2.5 GPa. ２ is the tensile modulus E of the first film １ can be measured in the same way.

[0296] (2.2) Refractive index n ２ Refractive index n of the second film ２ is preferably in the range of 1.47 to 1.51, and more preferably in the range of 1.48 to 1.50. ２ is the refractive index of the first film, n １ can be measured in the same way.

[0297] (2.3) Retardation Ro and Rt The second film may function as a retardation film.

[0298] The second film can be used, for example, as a retardation film for an IPS mode. In this case, the in-plane retardation Ro measured at a wavelength of 590 nm, at 23°C, and at 55% RH is preferably in the range of 0 to 10 nm, more preferably 0 to 5 nm. The thickness-direction retardation Rt of the second film is preferably in the range of −40 to 40 nm, more preferably −25 to 25 nm.

[0299] Ro and Rt are defined by the following formulas (a) and (b), respectively.

[0300] Formula (a): Ro = (n x -n y )×d Formula (b): Rt=((n x +n y ) / 2-n z )×d (in the formula, n x represents the refractive index in the in-plane slow axis direction of the second film (the direction in which the refractive index is maximum). y represents the refractive index in the direction perpendicular to the in-plane slow axis of the second film. z represents the refractive index in the thickness direction of the second film, and d represents the film thickness (nm) of the second film.

[0301] The in-plane slow axis of the second film can be confirmed by an automatic birefringence meter, Axo Scan Mueller Matrix Polarimeter (manufactured by Axometrics Co., Ltd.).

[0302] Ro and Rt can be measured by the following method.

[0303] 1) The second film is conditioned for 24 hours in an environment of 23° C. and 55% RH. The average refractive index of this film is measured with an Abbe refractometer, and the film thickness d is measured with a commercially available micrometer.

[0304] 2) After humidity conditioning, the retardation Ro and Rt of the film are measured at a wavelength of 590 nm under an environment of 23°C and 55% RH using an automatic birefringence meter, Axo Scan "Axo Scan Mueller Matrix Polarimeter" (manufactured by Axometrics Co., Ltd.).

[0305] The retardation Ro and Rt of the second film can be adjusted by, for example, the type of resin, stretching conditions, drying conditions, etc. For example, Rt can be reduced by increasing the drying temperature.

[0306] (2.4) Thickness The thickness of the second film is not particularly limited. However, from the viewpoint of achieving both impact resistance and folding resistance, the thickness of the second film is preferably within a range of 40 to 60 μm, and more preferably within a range of 40 to 50 μm.

[0307] (3) Method for Producing Second Film The method for producing the second film is not particularly limited, but from the viewpoint of obtaining a desired film, it is preferable to produce the second film by a solution casting method or a solution coating method. In these methods, a dope containing a resin, a solvent, and any other components is first prepared. The dope is applied to a substrate by casting or coating, and then the cast film or coated film is dried to obtain a film.

[0308] The shape of the second film is not particularly limited and may be, for example, a strip shape. That is, the second film is preferably wound into a roll in a direction perpendicular to its width direction to form a roll body.

[0309] The method for producing the second film by the solution coating method is described below. The method for producing the second film by the solution coating method preferably includes the steps of preparing a dope, applying the dope to a support to form a coating film, drying the coating film on the support, and peeling the dried coating film from the support.

[0310] (3.1) Step of Preparing Dope In this step, a dope (solution for the second film) containing the above-mentioned resin, a solvent, and, if necessary, additives (such as the above-mentioned rubber particles and fine particles) is prepared.

[0311] The solvent used for the dope is not particularly limited as long as it can disperse or dissolve the resin well. Examples of organic solvents include alcohols (e.g., methanol, ethanol, diols, triols, tetrafluoropropanol), glycols, cellosolves, ketones (e.g., acetone, methyl ethyl ketone), carboxylic acids (e.g., formic acid, acetic acid), carbonates (e.g., ethylene carbonate, propylene carbonate), esters (e.g., ethyl acetate, propyl acetate), ethers (e.g., isopropyl ether, THF), amides (e.g., dimethyl sulfoxide), hydrocarbons (e.g., heptane), nitriles (e.g., acetonitrile), aromatics (e.g., cyclohexylbenzene, toluene, xylene, chlorobenzene), alkyl halides (e.g., dichloromethane (also referred to as "methylene chloride")), amines (e.g., 1,4-diazabicyclo[2.2.2]octane, diazabicycloundecene), and lactones.

[0312] Among these, the solvent is preferably a chlorine-based solvent having a boiling point of 100° C. or less under atmospheric pressure, and more specifically, dichloromethane (methylene chloride) is more preferable. Dichloromethane has high solubility in various resins and a fast drying rate, so by using it as a solvent, the film quality of the coating film can be easily adjusted and it is easy to handle.

[0313] A hydrophilic solvent may be further added to the solvent. Examples of the hydrophilic solvent include ketones and alcohols, and among these, the hydrophilic solvent is preferably an alcohol. The hydrophilic solvent is more preferably isopropanol, ethanol, methanol, etc., and most preferably methanol. The amount of the hydrophilic solvent added is preferably within a range of 1 to 20% by mass, more preferably within a range of 3 to 10% by mass, based on the total mass of the solvent.

[0314] The resin concentration of the dope is preferably in the range of 1.0 to 20% by mass, for example, from the viewpoint of easily adjusting the viscosity to the range described below. Furthermore, from the viewpoint of reducing the amount of shrinkage of the coating film during drying, the resin concentration of the dope is preferably moderately high, more preferably in the range of 5 to 20% by mass, and even more preferably in the range of 5 to 15% by mass. Adjusting the resin concentration shortens the time required to form the second film, and the drying time of the coating film can also be used as a means for controlling the surface condition of the second film. To increase the concentration of the dope, a mixed solvent may be used as appropriate.

[0315] The viscosity of the dope is not particularly limited as long as it can form a second film with a desired thickness. In particular, the viscosity of the dope is preferably in the range of 5 to 5,000 mPa·s. A viscosity of 5 mPa·s or more makes it easier to form a second film with an appropriate thickness. A viscosity of 5,000 mPa·s or less can prevent unevenness in film thickness due to an increase in the viscosity of the solution. From the same viewpoint, the viscosity of the dope is more preferably in the range of 100 to 1,000 mPa·s. The viscosity of the dope can be measured at 25°C using an E-type viscometer.

[0316] (3.2) Step of applying the dope to the support to form a coating film In this step, the dope is applied to the surface of the support. Specifically, the obtained dope is applied to the surface of the support to form a coating film. The first film described above may be used as the support. In this case, there is no need to provide an adhesive layer between the first film and the second film, and the cover member can be made thinner.

[0317] The support supports the second film during the formation of the second film, and examples of the support include a resin film. The thickness of the support is not particularly limited. From the viewpoint that the support is a thin film and needs a certain degree of strength (flexibility, rigidity, etc.), the thickness is preferably 50 μm or less, more preferably in the range of 15 to 45 μm, and even more preferably in the range of 20 to 40 μm.

[0318] Examples of resins used for the support include cellulose ester resins, cycloolefin resins, polypropylene, acrylic resins, polyesters, polyarylates, and styrene resins, or composite resins thereof. Among these, polyesters are preferred from the viewpoint of excellent storage stability in high humidity environments.

[0319] Examples of polyesters include polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), etc. Among these, from the viewpoint of ease of handling, the resin is preferably polyethylene terephthalate (PET) or polyethylene naphthalate (PEN).

[0320] The resin film may be one that has been heat-treated (heat-relaxed) or stretched.

[0321] The heat treatment is carried out to reduce residual stress in the resin film (e.g., residual stress due to stretching). The treatment temperature is not particularly limited, and is preferably within the range of (Tg + 60) to (Tg + 180)°C, where Tg is the glass transition temperature of the resin constituting the resin film.

[0322] The stretching treatment is carried out to increase the residual stress of the resin film. The stretching treatment is preferably carried out, for example, in the biaxial direction of the resin film. The stretching treatment can be carried out under any conditions. The stretching ratio is not particularly limited, and is preferably in the range of 120 to 900%. Whether the resin film is stretched can be confirmed, for example, by whether there is an in-plane slow axis (an axis extending in the direction in which the refractive index is maximized).

[0323] Commercially available polyester films can be used, such as polyethylene terephthalate film "TN100" (manufactured by Toyobo Co., Ltd.) and "MELINEX (registered trademark) ST504" (manufactured by Teijin DuPont Films Japan Ltd.).

[0324] The support may further have a release layer on the surface of the resin film, which makes it easier to peel the second film from the support.

[0325] The release layer may contain any known release agent, and is not particularly limited. The release agents contained in the release layer are broadly divided into silicone-based release agents and non-silicone-based release agents.

[0326] Examples of silicone-based release agents include known silicone resins. Examples of non-silicone-based release agents include long-chain alkyl pendant polymers obtained by reacting polyvinyl alcohol or ethylene-vinyl alcohol copolymer with long-chain alkyl isocyanate. Examples of non-silicone-based release agents include olefin resins (e.g., copolymerized polyethylene, cyclic polyolefin, polymethylpentene, etc.), polyarylate resins (e.g., polycondensates of aromatic dicarboxylic acid components and dihydric phenol components), fluororesins (e.g., polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), PFA (copolymers of tetrafluoroethylene and perfluoroalkoxyethylene, etc.), FEP (copolymers of tetrafluoroethylene and hexafluoropropylene), ETFE (copolymers of tetrafluoroethylene and ethylene)), and the like.

[0327] The thickness of the release layer is not particularly limited as long as it can exhibit the desired releasability, and the thickness of the release layer is preferably in the range of 0.1 to 1.0 μm.

[0328] The support may contain an additive. The support may contain a plasticizer. The plasticizer is not particularly limited, and examples thereof include polyhydric alcohol ester plasticizers, phthalate ester plasticizers, citric acid plasticizers, fatty acid ester plasticizers, phosphate ester plasticizers, polycarboxylic acid ester plasticizers, and polyester plasticizers.

[0329] The support may contain an ultraviolet absorber. Examples of ultraviolet absorbers include benzotriazoles, 2-hydroxybenzophenones, and salicylic acid phenyl esters. Specific examples of triazoles include 2-(5-methyl-2-hydroxyphenyl)benzotriazole, 2-[2-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]-2H-benzotriazole, and 2-(3,5-di-t-butyl-2-hydroxyphenyl)benzotriazole. Examples of benzophenones include 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, and 2,2'-dihydroxy-4-methoxybenzophenone.

[0330] The support may contain fine particles from the viewpoint of improving transportability. The fine particles may be the same as those that may be contained in the second film when a cycloolefin resin is used as the resin for the second film.

[0331] Examples of methods for forming a film from the support include melt extrusion (such as inflation and T-die methods), calendaring, cutting, casting, emulsion, and hot pressing. Among these, the melt extrusion method is preferred. Since the melt extrusion method does not require dissolving the material in a solvent, it is possible to use a material with low solubility in a solvent. Furthermore, by preparing the support from a material with low solubility in a solvent, dissolution of the support components into the dope can be suppressed even when the dope is applied to the support.

[0332] When the support is formed by melt extrusion, the method for producing the support preferably includes 1) an extrusion step, 2) a molding step, and 3) a winding step. In the extrusion step, the resin and additives are fed into an extruder and melt-extruded through a die (mold). It is preferable that the resin is pre-mixed and pelletized. In the molding step, the molten resin extruded from the die is cooled and molded into a film. In the winding step, the finished film is wound into a roll.

[0333] The second film is preferably formed by the following method using the produced support.

[0334] (3.3) Step of drying the coating film on the support In this step, the coating film applied to the support is dried to form a second film.

[0335] Drying can be performed by, for example, blowing air or heating. Among these, drying by blowing air is preferred from the viewpoint of easily suppressing curling of the second film. Furthermore, from the viewpoint of controlling the film thickness deviation, it is preferred to provide a difference in air speed between the first half and the second half of drying. Specifically, the higher the air speed in the initial stage of drying, the larger the film thickness deviation, and the lower the initial air speed, the smaller the film thickness deviation.

[0336] The density of the second film can be controlled by adjusting the drying conditions (e.g., drying temperature, drying air volume, drying time, etc.). By adjusting the drying conditions, it is preferable to adjust the thickness of the second film so as to satisfy the following (equation):

[0337] (Formula) 5<|Average film thickness (B) of three randomly selected points in the width direction - average film thickness (A)| / average film thickness (A) x 100<20(%) Here, "average film thickness (A)" is the average film thickness of 10 points randomly selected from the film.

[0338] When the value represented by the above formula exceeds 5%, the second film has a moderate unevenness on its surface, which improves adhesion to the upper layer. When the value represented by the above formula is less than 20%, the second film has a surface unevenness that is not too large, which is unlikely to affect the coatability and smoothness of the upper layer.

[0339] The film thickness can be measured using a commercially available film thickness measuring device, for example, the film thickness measuring system "F20-UV" (manufactured by Filmetrics Inc.).

[0340] The deviation in the thickness of the second film is preferably adjusted to within a range of 0.5±0.2 μm. The film quality is preferably adjusted to be coarser in order to improve adhesion to the upper layer. Specifically, it is preferable to increase the drying speed, and the observed speed is 0.0015 to 0.05 kg / hr m. 2 It is preferable that the range is 0.002 to 0.05 kg / hr m 2It is more preferable that the range is within the range of

[0341] The drying rate is expressed as the mass of solvent evaporated per unit time and unit area. The drying rate can usually be adjusted by the drying temperature. The drying temperature depends on the type of solvent used, but is preferably in the range of 50 to 200°C. Furthermore, the drying temperature is preferably in the range of (Tb-50) to (Tb+50)°C, where Tb is the boiling point of the solvent used. Temperature control may be performed in multiple stages. After drying has progressed to a certain extent, the drying rate and film quality can be controlled by drying at a higher temperature.

[0342] (3.4) Step of Peeling the Dried Coating Film from the Support In this step, the dried coating film (the formed second film) is peeled from the support. As described above, when the formed second film is strip-shaped and is wound up into a roll, the second film may be peeled from the support before being wound up, or may be wound up together with the support without being peeled from the support. When the second film is wound up together with the support, the second film is peeled from the support during the manufacture of the display device (particularly when it is bonded to the first film).

[0343] (3.5) Step of Winding the Second Film to Obtain a Roll In this step, the obtained strip-shaped second film is wound into a roll in a direction perpendicular to its width direction to obtain a roll.

[0344] The length of the strip-shaped second film is not particularly limited, but is preferably in the range of 100 to 10,000 m. The width of the strip-shaped second film is preferably 1 m or more, more preferably in the range of 1.1 to 4 m. From the viewpoint of improving the uniformity of the second film, the width is further preferably in the range of 1.3 to 2.5 m.

[0345] (3.6) Manufacturing Apparatus The manufacturing method for the second film can be carried out by, for example, a manufacturing apparatus shown in FIG.

[0346] 4 is a schematic diagram of a manufacturing apparatus B200 for carrying out the method for manufacturing the second film. The manufacturing apparatus B200 has a supply section B210, a coating section B220, a drying section B230, a cooling section B240, and a winding section B250. Ba to Bd indicate transport rolls that transport the support B110.

[0347] The supply section B210 has a payout device (not shown) that pays out a roll B201 of the belt-shaped support B110 wound around a core.

[0348] The coating section B220 is a coating device that includes a backup roll B221 that holds the support B110, a coating head B222 that applies dope to the support B110 held by the backup roll B221, and a reduced pressure chamber B223 that is provided upstream of the coating head B222.

[0349] The flow rate of the dope discharged from the coating head B222 can be adjusted by a pump (not shown) and is set to an amount that allows a coating layer of a predetermined thickness to be stably formed when the dope is continuously coated under the conditions of the coating head B222 that have been adjusted in advance.

[0350] The decompression chamber B223 is a mechanism for stabilizing a bead (a pool of coating liquid) formed between the dope from the coating head B222 and the support B110 during coating. The degree of decompression in the decompression chamber B223 is adjustable. The decompression chamber B223 is connected to a decompression blower (not shown) to reduce the pressure inside. The decompression chamber B223 is air-tight and the gap between the decompression chamber B223 and the backup roll is adjusted to be narrow, allowing for the formation of a stable bead of coating liquid.

[0351] The drying section B230 is a drying device that dries the coating film applied to the surface of the support B110, and includes a drying chamber B231, a drying gas inlet B232, and an outlet B233. The temperature and volume of the drying air are determined appropriately depending on the type of coating film and the type of support B110. By setting conditions such as the temperature and volume of the drying air and the drying time in the drying section B230, the amount of residual solvent in the coating film after drying can be adjusted. The amount of residual solvent in the coating film after drying can be measured by comparing the mass of the coating film after drying with the mass of the coating film after further thorough drying.

[0352] (Amount of Residual Solvent) Since the second film is obtained by coating a dope, the solvent derived from the solution may remain. The amount of residual solvent can be controlled by the solvent, the concentration of the solution (dope), the air speed to dry the second film, the drying temperature, the drying time, the conditions of the drying chamber (open air or internal air circulation), the heating temperature of the back roll during coating, etc. As mentioned above, high-speed drying makes the film sparse, allowing the surface condition to be controlled.

[0353] From the viewpoint of curl balance, it is preferable that the residual solvent amount of the second film satisfies the following formula, where S1 is the residual solvent amount of the second film: 10<S1<1000 (ppm).

[0354] From the viewpoint of curl balance, the residual solvent amount in the second film is preferably less than 800 ppm, and more preferably in the range of 500 to 700 ppm. Furthermore, from the viewpoint of improving adhesion between the support and the second film, it is preferable that the solvent remains in both the support and the second film, and it is preferable to select the type of solvent and the coating process appropriately. The residual solvent amount in the support is preferably in the range of 10 to 100 ppm.

[0355] The residual solvent amount in the support and the second film can be measured by headspace gas chromatography. In headspace gas chromatography, a sample is first sealed in a container and heated. Then, with the container filled with volatile components, the gas in the container is quickly injected into a gas chromatograph, and mass spectrometry is performed to identify the compounds and quantify the volatile components. In the headspace method, all peaks of volatile components can be observed using a gas chromatograph. In addition, by using an analytical method utilizing electromagnetic interactions, high accuracy is achieved and volatile substances, monomers, etc. can also be quantified.

[0356] The cooling section B240 cools the support B110 having the coating film (second film) obtained by drying in the drying section B230, and adjusts the temperature to an appropriate level. The cooling section B240 has a cooling chamber B241, a cooling air inlet B242, and a cooling air outlet B243. The temperature and volume of the cooling air can be determined appropriately depending on the type of coating film and the type of support B110. Furthermore, if an appropriate cooling temperature can be achieved without providing the cooling section B240, the cooling section B240 may not be provided.

[0357] The winding section B250 is a winding device (not shown) that winds up the support B110 on which the second film is formed to obtain a roll body B251.

[0358] 4. Interaction between the first film and the second film The tensile modulus of the first film is E １ [GPa], the tensile modulus of the second film is E ２ [GPa], the elastic modulus ratio (E １ / E ２ ) satisfies the following formula (1): 1.5≦E １ / E ２ ≦15.0

[0359] It is believed that by using a combination of a relatively hard first film and a relatively soft second film, a synergistic effect can be obtained in addition to the advantages of each film.

[0360] (Impact resistance) Even if part of the impact penetrates the first film and is transmitted further inside, it is believed that the second film can disperse the impact and reduce the impact transmitted to the light-emitting element. In particular, when inputting to a display device with a pen or finger, a high load is applied to a narrow area, but by combining the second film, it is believed that the high load (impact) transmitted to the narrow area can be dispersed over a wide area within the second film.

[0361] (Folding Resistance) The first film is relatively hard, and therefore generates a relatively large stress when folded. However, it is believed that by combining the first film with a relatively soft second film, the stress can be alleviated, and folding resistance can be improved.

[0362] (Transmittance) The refractive index of the first film is n １ , the refractive index of the second film is n ２ When the refractive index difference (|n １ -n ２ It is preferable that |n satisfies the following formula (2): 0.00≦|n １ -n ２ |≦0.02 By satisfying the above relationship of the refractive index difference, that is, by reducing the refractive index difference, the transparency of the cover member can be increased, and visibility can be improved.

[0363] Generally, the more multilayered the structure, the more likely it is that transparency will decrease due to differences in the refractive index of each layer, the structure of the interface, etc. However, by combining the first film and the second film, it is possible to satisfy the above-mentioned relationship of refractive index difference, and it is thought that high transparency can be obtained.

[0364] 5. Color Filter The display device of this embodiment has a color filter, which allows it to display a desired color image.

[0365] The color display method of the display device of this embodiment is not particularly limited. Furthermore, as will be described in detail later, it is preferable to use organic electroluminescence (EL) elements as the light-emitting elements according to the present invention. Any of the following color display methods using organic EL elements may be used. Schematic diagrams of examples of color display methods suitable for use in the present invention are shown in FIGS. 5 to 8. However, the light-emitting elements are not limited to organic EL elements, and the present invention can also be applied to other light-emitting elements when a color filter is used.

[0366] The present invention can be applied to the following methods 2) and 3), since color filters are essential for their use. The type of light-emitting element is not particularly limited. Furthermore, the present invention can be applied to the following methods 1) and 4), if color filters are used to improve color purity. 1) A method in which light-emitting layers 42 emitting R (red), G (green), and B (blue) light respectively are arranged horizontally (FIG. 5). 2) A method in which white light 45 is arranged on the rear surface and passes through an RGB color filter 46 (FIG. 6). 3) A method in which blue light 47 is arranged on the rear surface and is absorbed by a phosphor through a color filter (wavelength conversion film) 48, resulting in the emission of red light (R) and green light (FIG. 7). 4) A method in which light-emitting layers emitting R, G, and B light respectively are vertically stacked (FIG. 8).

[0367] In this embodiment, the term "color filter" refers to a filter that transmits visible light in a specific wavelength range and has the function of changing the transmitted light to a desired hue. By including a color filter, the display device of the present invention can express a desired color and can improve color reproducibility.

[0368] The "aperture ratio" refers to the ratio of the area of ​​the area (excluding the black matrix) through which visible light transmits to the area of ​​the entire area on the surface of a color filter through which visible light of a specific wavelength range is irradiated. Each area through which visible light transmits corresponds to a pixel.

[0369] 9 is a schematic diagram of a color filter. The color filter 60 is composed of a black matrix 51 that does not transmit visible light and a transmissive region 52 that transmits visible light. Colored pixels are arranged in the transmissive region 52 as needed so that the transmitted light has a desired hue. The region of the color filter 60 that is irradiated with visible light in a specific wavelength region is indicated by the irradiation region 53 (inside the dotted line). The aperture ratio is expressed as the ratio of the area of ​​the transmissive region 52 to the area of ​​the irradiation region 53.

[0370] By appropriately adjusting the aperture ratio of the color filter, it is possible to impart an anti-reflection function to light incident from the outside. Furthermore, a display device with excellent visibility can be obtained without the need to introduce a new circular polarizer. Furthermore, since there is no need to introduce a circular polarizer, the display device can be made thinner.

[0371] The aperture ratio of the color filter is preferably in the range of 65 to 90%, and more preferably in the range of 65 to 80%. By keeping the aperture ratio within this range, it is possible to reduce the reflectance of light incident from the outside and improve color reproducibility.

[0372] Furthermore, even in the above methods 1) and 4), in which a color filter is not usually essential, a display device with excellent visibility can be obtained without the need for a circular polarizer by deliberately using a color filter and adjusting the aperture ratio. That is, the display device can be made thinner and the color reproducibility can be improved.

[0373] The color filter may be a conventionally known color filter. The color filter has a colored layer consisting of a black matrix and colored pixels on one surface of a transparent substrate. The black matrix is ​​preferably formed in a lattice or stripe pattern between the colored pixels. If necessary, the color filter may also have fixed spacers or an overcoat layer.

[0374] The colored layer is preferably formed from a colored resin composition. The colored resin composition is prepared by mixing, for example, a colorant, a binder resin, a photopolymerizable monomer, a photopolymerization initiator, an additive, an organic solvent, and the like. As the colorant, a conventionally known red pigment, green pigment, yellow pigment, blue pigment, purple pigment, black pigment, and the like can be used. Furthermore, a color conversion material (inorganic fluorescent material or organic fluorescent material) may be used as needed. As the additive, for example, a surfactant, a chain transfer agent, a storage stabilizer, and the like can be used.

[0375] The colored resin composition is preferably prepared in the form of a gravure offset printing ink, a waterless offset printing ink, an inkjet ink, a silk screen printing ink, or a solvent-developable or alkali-developable colored resist.

[0376] The content of the colorant is preferably in the range of 5 to 70% by mass, more preferably in the range of 20 to 50% by mass, based on the total mass of the solid content of the colored resin composition.

[0377] It is preferable to remove coarse particles of 5 μm or more, preferably coarse particles of 1 μm or more, more preferably coarse particles of 0.5 μm or more, and mixed dust from the colored resin composition using centrifugation, a sintered filter, a membrane filter, or the like.

[0378] The method for forming the colored pixels is preferably photolithography. A colored resin composition is prepared as a solvent-developable or alkali-developable colored resist. The resulting resist is then preferably applied to an array substrate by a coating method such as spray coating, spin coating, slit coating, or roll coating so that the resulting thickness after drying is within the range of 0.2 to 10 μm.

[0379] Methods for drying the coating film include a vacuum dryer, a convection oven, an IR oven, and a hot plate. The dried coating film is then exposed to ultraviolet light through a mask having a predetermined pattern, which is placed in contact with the film or not. When checking the alignment mark with the mask, infrared light with a wavelength in the range of 750 to 1000 nm is used.

[0380] The uncured portions are then removed by immersion in an organic solvent or alkaline developer, or by spraying the developer onto the film, to form the desired pattern. The same process is then repeated for the other colors to form colored pixels for the color filter.

[0381] In the development, an aqueous solution of sodium carbonate, sodium hydroxide, or the like can be used as an alkaline developer. Also, organic alkalis such as dimethylbenzylamine and triethanolamine can be used. Furthermore, an antifoaming agent or a surfactant can be added to the developer. Examples of development methods include shower development, spray development, dip (immersion) development, and puddle (liquid puddle) development.

[0382] The thickness of the color filter is preferably in the range of 1 to 5 μm. When the thickness is 1 μm or more, color purity can be further improved, and when the thickness is 5 μm or less, brightness can be improved.

[0383] 6. Light-emitting element The display device of this embodiment has a light-emitting element. Note that "light-emitting element" is a general term for an electronic component that converts an electrical signal into an optical signal. In the present invention, the light-emitting element is not particularly limited, and examples thereof include an organic electroluminescence (EL) element, an inorganic electroluminescence (EL) element, and a quantum dot light-emitting element.

[0384] Among these, an organic EL element is preferable from the viewpoint of flexibility and thinning. Conventionally known organic EL elements can be used. For example, the organic EL element is composed of an electrode / electron transport layer / light-emitting layer / hole transport layer / transparent electrode.

[0385] 7. Manufacturing Method of Display Device The display device of this embodiment can be manufactured by bonding a cover member, a color filter, and a light-emitting element together via an adhesive, etc. The cover member can be manufactured by bonding the first film, the second film, etc. together via an adhesive, etc. The manufacturing method is not particularly limited, and a conventionally known method can be used.

[0386] The pressure-sensitive adhesive is not particularly limited, and examples thereof include rubber-based pressure-sensitive adhesives, acrylic pressure-sensitive adhesives, silicone-based pressure-sensitive adhesives, urethane-based pressure-sensitive adhesives, vinyl alkyl ether-based pressure-sensitive adhesives, polyvinyl alcohol-based pressure-sensitive adhesives, polyvinylpyrrolidone-based pressure-sensitive adhesives, polyacrylamide-based pressure-sensitive adhesives, and cellulose-based pressure-sensitive adhesives. Among these, acrylic pressure-sensitive adhesives are preferred. Acrylic pressure-sensitive adhesives have excellent transparency and excellent adhesive properties (adhesion, cohesion, and adhesion). They also have excellent weather resistance, heat resistance, and the like. Here, "acrylic pressure-sensitive adhesive" refers to a pressure-sensitive adhesive containing an acrylic polymer as a base polymer.

[0387] 8. Product Example of Flexible Display Device The flexible display device of this embodiment is characterized by having at least the above-described cover member, a color filter, and a light-emitting element. In the present invention, the term "display device" refers to a device having a display mechanism.

[0388] Examples of display devices include liquid crystal display devices, organic electroluminescence (EL) display devices, inorganic electroluminescence (EL) display devices, touch panel display devices, electron emission display devices (field emission displays (FEDs), surface field emission displays (SEDs)), electronic paper (display devices using electronic ink or electrophoretic elements), plasma display devices, projection display devices (grating light valve (GLV) display devices, display devices having digital micromirror devices (DMDs), etc.), piezoelectric ceramic displays, etc.

[0389] Furthermore, examples of the liquid crystal display device include a transmission type liquid crystal display device, a semi-transmission type liquid crystal display device, a reflection type liquid crystal display device, a direct-view type liquid crystal display device, and a projection type liquid crystal display device.

[0390] These display devices may be display devices that display two-dimensional images or stereoscopic display devices that display three-dimensional images. Among these, the display device of the present invention is preferably an organic electroluminescence (EL) display device from the viewpoints of flexibility and thinning. Furthermore, a touch panel display device is preferably used from the viewpoint of having a cover member with excellent impact resistance.

[0391] An example of a flexible display device (flexible display) is a foldable display. A foldable display preferably has a structure in which a single continuous display can be folded in half when carried, thereby reducing the size by half and improving portability. Furthermore, a foldable display is preferably thin and lightweight.

[0392] The term "flexible" means that the display can be bent or curved, and "flexible or curved" includes the state of being bent or curved. Specifically, the radius of curvature that can be bent or curved is preferably 10 mm or less, and more preferably 3 mm or less. In particular, if the radius of curvature is 3 mm or less, the display can be folded and used.

[0393] The display device of this embodiment has excellent impact resistance due to the cover member. Furthermore, the display device of this embodiment can obtain sufficient visibility without using a circular polarizer. In other words, the display device of this embodiment is thin and has excellent visibility.

[0394] Furthermore, the display device of this embodiment has excellent visibility even after the display is repeatedly folded. Specifically, image distortion is unlikely to occur at the folding point of the display. Therefore, for example, a mobile terminal device equipped with a foldable display can provide beautiful images, is highly functional, and is convenient in terms of portability and other factors.

[0395] The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. In the examples, the terms "parts" and "%" are used, but they represent "parts by mass" or "% by mass" unless otherwise specified. In the following examples, operations were carried out at room temperature (25°C) unless otherwise specified.

[0396] 1. Preparation of Flexible Display Device (1) Preparation of First Film (1.1) Preparation of Acetylcellulose Acetylcelluloses having degrees of substitution of 2.45 and 2.90 were prepared by known methods.

[0397] (1.2) Preparation of Filler (1.2.1) Preparation of Filler 1 A 500 mL four-neck flask was charged with 130 g of ion-exchanged water and 8.8 g (0.146 mol) of acetic acid. The mixture was heated to 30°C (liquid temperature) while stirring. 27 g (0.132 mol) of aluminum isopropoxide was added dropwise to the mixture over 30 minutes. Then, while distilling off isopropyl alcohol from the mixture, the mixture was heated to 95°C (liquid temperature) and hydrolysis was carried out at 95°C for 30 minutes.

[0398] Next, this mixture was reacted in an autoclave with stirring at 150°C for 6 hours. After the reaction was carried out for the predetermined time, the reaction solution was cooled to room temperature (25°C) to obtain a solution (solid content: approximately 5 mass%) containing alumina filler precursor 1. Here, the average diameter and average length of alumina filler precursor 1 were 4 nm and 3000 nm (aspect ratio = 750), respectively.

[0399] 50 g of a solution containing alumina filler precursor 1, 50 g of methyl isobutyl ketone, and 0.4 g of dodecylbenzenesulfonic acid were mixed. The mixture was then dehydrated using a Dean-Stark apparatus. A methyl isobutyl ketone dispersion of alumina filler precursor 1 surface-modified with dodecylbenzenesulfonic acid was obtained. The alumina filler obtained in this manner was designated Filler 1.

[0400] The minor axis (y) and major axis (x) of the obtained Filler 1 were 4 nm and 3,000 nm, respectively (aspect ratio (x / y) = 750). In this example, the minor axis and major axis of Filler 1 corresponded to the average diameter and average length, respectively.

[0401] (1.2.2) Preparation of Fillers 2 to 5 Fillers 2 to 5 were prepared in the same manner as in the preparation of Filler 1, except that the amount of acetic acid added was changed. The aspect ratios of each filler were as shown in Tables I and II.

[0402] (1.2.3) Preparation of Filler 6 Alumina filler precursor 1 was prepared using the same procedure as in the preparation of Filler 1 above. Next, 50 g of alumina filler precursor 1, 50 g of methyl isobutyl ketone, and 0.4 g of benzoic acid were mixed. The mixture was dehydrated using a distillation apparatus. Then, a methyl isobutyl ketone dispersion of alumina filler precursor 1 surface-modified with benzoic acid was obtained. The alumina filler obtained in this manner was designated Filler 6.

[0403] The minor axis (y) and major axis (x) of the obtained filler 6 were 4 nm and 3,000 nm, respectively (aspect ratio (x / y) = 750). In this example, the minor axis and major axis of the filler 6 corresponded to the average diameter and average length, respectively.

[0404] (1.2.4) Preparation of Filler 7 Alumina filler precursor 1 was prepared in the same procedure as in the preparation of Filler 1 above. Next, 50 g of alumina filler precursor 1, 50 g of cyclohexanone, and 0.4 g of "JP-506H" (manufactured by Johoku Chemical Industry Co., Ltd.) were mixed. The mixture was dehydrated using a Dean-Stark apparatus. Then, a cyclohexanone dispersion of alumina filler precursor 1 surface-modified with butoxyethyl acid phosphate was obtained. Butoxyethyl acid phosphate was "JP-506H" (manufactured by Johoku Chemical Industry Co., Ltd., structural formula: (C ４ H ９ OCH ２ CH ２ O)n-P(=O)-(OH) ３－ｎ ) where n is 1 or 2. The alumina filler obtained in this manner was designated as Filler 7.

[0405] The minor axis (y) and major axis (x) of the obtained filler 7 were 4 nm and 3,000 nm, respectively (aspect ratio (x / y) = 750). In this example, the minor axis and major axis of the filler 7 corresponded to the average diameter and average length, respectively.

[0406] (1.2.5) Preparation of Filler 8 130 g of ion-exchanged water and 8.8 g (0.146 mol) of acetic acid were charged into a 500 mL four-neck flask. The mixture was heated to 30°C (liquid temperature) while stirring. 30 g (0.142 mol) of tetraethyl orthosilicate was added dropwise to the mixture over 30 minutes. Then, while distilling off ethanol from the mixture, the mixture was heated to 95°C (liquid temperature) and hydrolysis was carried out at 95°C for 30 minutes.

[0407] Next, this mixture was reacted in an autoclave at 150°C for 6 hours while stirring. After the reaction was carried out for the predetermined time, the reaction solution was cooled to room temperature (25°C) to obtain a solution containing a silica filler precursor (solid content: approximately 5% by mass). Here, the average diameter and average length of the silica filler precursor were 4 nm and 3,000 nm (aspect ratio = 750), respectively.

[0408] 50 g of a solution containing a silica filler precursor, 50 g of methyl isobutyl ketone, and 0.4 g of dodecylbenzenesulfonic acid were mixed. The mixture was dehydrated using a Dean-Stark apparatus. A methyl isobutyl ketone dispersion of a silica filler precursor surface-modified with dodecylbenzenesulfonic acid was obtained. The silica filler obtained in this manner was designated Filler 8.

[0409] The minor axis (y) and major axis (x) of the obtained filler 8 were 4 nm and 3,000 nm, respectively (aspect ratio (x / y) = 750). In this example, the minor axis and major axis of the filler 8 corresponded to the average diameter and average length, respectively.

[0410] (1.2.6) Preparation of Filler 9 130 g of ion-exchanged water and 8.8 g (0.146 mol) of acetic acid were charged into a 500 mL four-neck flask. The mixture was heated to 30°C (liquid temperature) while stirring. 30 g (0.142 mol) of orthotitanium tetraethyl was added dropwise to the mixture over 30 minutes. Then, while distilling off ethanol from the mixture, the mixture was heated to 95°C (liquid temperature) and hydrolysis was carried out at 95°C for 30 minutes.

[0411] Next, this mixture was reacted in an autoclave at 150°C for 6 hours while stirring. After the reaction for the predetermined time, the reaction solution was cooled to room temperature (25°C) to obtain a solution containing a titania filler precursor (solid content: approximately 5% by mass). Here, the average diameter and average length of the titania filler precursor were 4 nm and 3,000 nm (aspect ratio = 750), respectively.

[0412] 50 g of a solution containing a titania filler precursor, 50 g of methyl isobutyl ketone, and 0.4 g of dodecylbenzenesulfonic acid were mixed. The mixture was dehydrated using a Dean-Stark apparatus. A methyl isobutyl ketone dispersion of a titania filler precursor surface-modified with dodecylbenzenesulfonic acid was obtained. The titania filler thus obtained was designated Filler 9.

[0413] The minor axis (y) and major axis (x) of the obtained filler 9 were 4 nm and 3,000 nm, respectively (aspect ratio (x / y) = 750). In this example, the minor axis and major axis of the filler 9 corresponded to the average diameter and average length, respectively.

[0414] (1.2.7) Preparation of Fillers 10 and 11 Using a known method, a strontium carbonate filler precursor and a barium carbonate filler precursor having an average diameter and an average length of 4 nm and 3,000 nm (aspect ratio = 750), respectively, were prepared.

[0415] Next, 50 g of each filler precursor was mixed with 50 g of methyl isobutyl ketone and 0.4 g of glycerin stearate. The mixture was dehydrated using a distillation apparatus. A methyl isobutyl ketone dispersion of each filler precursor 1 surface-modified with glycerin stearate was obtained. The strontium carbonate filler thus obtained was designated Filler 10, and the barium carbonate filler was designated Filler 11.

[0416] The minor axis (y) and major axis (x) of the obtained fillers 10 and 11 were 4 nm and 3,000 nm, respectively (aspect ratio (x / y) = 750). In this example, the minor axis and major axis of fillers 10 and 11 corresponded to the average diameter and average length, respectively.

[0417] (1.3) Preparation of Dope (1.3.1) Preparation of Dope 1 Dope 1 for the first film 1 was prepared by the following procedure. (Silicon dioxide dispersion) "Aerosil (registered trademark) R812" (manufactured by Nippon Aerosil Co., Ltd., average primary particle size 7 nm) 10.000 parts by mass Ethanol 90.000 parts by mass The above components were stirred and mixed in a dissolver for 30 minutes, and then dispersed using a Manton-Gaulin to prepare a silicon dioxide dispersion. The silicon dioxide dispersion was filtered through a polypropylene wound cartridge filter "TCW-PPS-1N" (manufactured by Advantec Toyo Co., Ltd.).

[0418] Dichloromethane 80.960 parts by mass Ethanol 7.040 parts by mass Silicon dioxide dispersion (10% by mass dispersion) 0.120 parts by mass Filler 1 (5% by mass dispersion) 12.000 parts by mass The above components were stirred at 23°C for 1 hour, and then 12.000 parts by mass of acetyl cellulose was added and stirred at 23°C for 4 hours. Then, the mixture was filtered using "Azumi Filter Paper No. 24" (manufactured by Azumi Filter Paper Co., Ltd.) to prepare Dope 1. The content of silicon dioxide was 0.1% by mass based on the total mass of acetyl cellulose. The content of Filler 1 was 5.0% by mass based on the total mass of acetyl cellulose.

[0419] (1.3.2) Preparation of Dopes 2 to 19 Dopes 2 to 19 for the first films 2 to 19 were prepared in the same manner as in the preparation of Dope 1, except that the resins and fillers were changed as shown in Tables I and II. Note that no filler was added to Dopes 2 and 7.

[0420] (1.4) Formation of First Film (1.4.1) Formation of First Film 1 Using a belt casting apparatus, the dope 1 was uniformly cast onto a stainless steel band support to form a cast film. The solvent was evaporated on the stainless steel band support until the residual solvent amount in the cast film reached 100%, and the cast film was peeled off from the stainless steel band support. The cast film was heated at 35°C to evaporate the solvent. The cast film from which the solvent had evaporated was slit into a width of 1.65 m, held in a tenter, and dried at a drying temperature of 160°C. The drying temperature here was also the heat treatment temperature and the stretching temperature. The stretching ratio in the transverse direction (TD) was 5%.

[0421] The residual solvent content at the start of drying was 20%. The film was then dried for 15 minutes while being transported by multiple rolls in a drying apparatus at 120°C, after which knurling was performed on both ends of the film to a width of 15 mm and a height of 10 μm. The film was wound around a core to obtain a first film 1. The residual solvent content of the first film 1 was 0.2% by mass, the thickness was 50 μm, and the number of windings was 6,000 m.

[0422] (1.4.2) Preparation of First Films 2 to 19 First films 2 to 19 were obtained in the same manner as above except that dope 1 was replaced with dopes 2 to 19.

[0423] Tables I and II show the constructions of First Films 1 to 19. Regarding the fillers, alumina, silica, and titania are metal oxides, and strontium carbonate and barium carbonate are metal salts. "-" in the tables indicates not applicable.

[0424] In the table, "acrylic resin" refers to a thermoplastic (meth)acrylic resin, namely, MMA (methyl methacrylate) / PMI (phenylmaleimide) / MA (methyl acrylate) copolymer (85 / 10 / 5 mass ratio, Mw: 2,000,000, Tg: 122°C). In the table, "AC" stands for acetyl cellulose, and "PET" stands for polyethylene terephthalate.

[0425]

[0426]

[0427] Tables III and IV show the physical properties of the first films 1-19.

[0428]

[0429]

[0430] (2) Preparation of Second Film (2.1) Preparation of Support A polyethylene terephthalate (PET) film "TN100" (manufactured by Toyobo Co., Ltd., with a release layer containing a non-silicone release agent, film thickness 38 μm) was prepared as a support.

[0431] (2.2) Preparation of Dope (2.2.1) Preparation of Dope 1 The following components were mixed to obtain Dope 1. Methylene chloride (boiling point 41°C) 800.000 parts by mass Acrylic resin 80.000 parts by mass Rubber particles R1 20.000 parts by mass Dispersant (polyoxyethylene lauryl ether sodium phosphate: molecular weight 332) Added in an amount that would give 0.006% by mass in the second film.

[0432] <Preparation of Rubber Particles R1> Rubber particles R1 prepared by the following method were used.

[0433] The following components were charged into an 8 L polymerization reactor equipped with a stirrer: Deionized water 180.00000 parts by mass Polyoxyethylene lauryl ether phosphate 0.00200 parts by mass Boric acid 0.47250 parts by mass Sodium carbonate 0.04725 parts by mass Sodium hydroxide 0.00760 parts by mass

[0434] After thoroughly replacing the atmosphere inside the polymerization reactor with nitrogen gas, the internal temperature was raised to 80°C, and the following components were added to prepare reaction liquid (I): 0.021 parts by mass of potassium persulfate (added as a 2% by mass aqueous solution)

[0435] Next, a monomer mixture (c') having the following mixing ratio was prepared: methyl methacrylate 84.6% by mass, butyl acrylate 5.9% by mass, styrene 7.9% by mass, allyl methacrylate 0.5% by mass, and n-octyl mercaptan 1.1% by mass.

[0436] The mixture obtained by mixing the following components was continuously added to the reaction solution (I) over 63 minutes. The polymerization reaction was then continued for 60 minutes to obtain the innermost rigid polymer (c): Monomer mixture (c') 21.000 parts by mass Polyoxyethylene lauryl ether phosphate 0.070 parts by mass

[0437] Thereafter, the following components were added to prepare a reaction solution (II): 0.021 parts by mass of sodium hydroxide (added as a 2% by mass aqueous solution) 0.062 parts by mass of potassium persulfate (added as a 2% by mass aqueous solution)

[0438] Next, a monomer mixture (a') having the following mixing ratio was prepared: butyl acrylate 80.0% by mass, styrene 18.5% by mass, and allyl methacrylate 1.5% by mass.

[0439] A mixture obtained by mixing the following components was continuously added to the reaction liquid (II) over 117 minutes: Monomer mixture (a') 39.000 parts by mass Polyoxyethylene lauryl ether phosphate 0.025 parts by mass

[0440] After the addition was completed, the following components were added and the polymerization reaction was continued for 120 minutes to obtain a soft layer (a layer made of an acrylic rubber-like polymer (a)): Potassium persulfate: 0.012 parts by mass (added as a 2% by mass aqueous solution)

[0441] The glass transition temperature (Tg) of the soft layer was −30° C. The glass transition temperature of the soft layer was calculated by averaging the glass transition temperatures of the homopolymers of the monomers constituting the acrylic rubber-like polymer (a) according to the composition ratio.

[0442] Thereafter, the following components were added to prepare a reaction solution (III): 0.040 parts by mass of potassium persulfate (added as a 2% by mass aqueous solution)

[0443] Next, a monomer mixture (b') having the following mixing ratio was prepared: 97.5% by mass of methyl methacrylate, 2.5% by mass of butyl acrylate.

[0444] The following components were continuously added to the reaction solution (III) over 78 minutes. The polymerization reaction was continued for an additional 30 minutes to obtain a polymer (b): Monomer mixture (b'): 26.100 parts by mass

[0445] The resulting polymer (b) was poured into a warm 3% by mass aqueous solution of sodium sulfate and salted out or coagulated. The polymer (b) was then repeatedly dehydrated and washed, and then dried to obtain three-layer structure acrylic graft copolymer particles (rubber particles R1). The average particle size of the resulting rubber particles R1 was 200 nm.

[0446] The average particle size of the rubber particles was measured by the following method. (Average Particle Size) The dispersed particle size of the rubber particles in the obtained dispersion was measured using a zeta potential / particle size measuring system "ELSZ-2000ZS" (manufactured by Otsuka Electronics Co., Ltd.).

[0447] (2.2.2) Preparation of Dopes 2 to 3 and 5 to 8 Dopes 2 to 3 and 5 to 8 for the second films 2 to 3 and 5 to 8 were prepared in the same manner as in the preparation of Dope 1, except that the type of resin and the content of rubber particles were changed as shown in Tables V and VI.

[0448] (2.3) Formation of Second Film (2.3.1) Formation of Second Film 1 Dope 1 was applied onto the release layer of the support by a back coating method using a die. Then, the dope 1 on the support was dried in the following drying step to obtain a second film 1 with a thickness of 50 μm.

[0449] (Initial drying) 1st step: 1 minute at 40°C 2nd step: 1 minute at 70°C 3rd step: 1 minute at 100°C 4th step: 2 minutes at 130°C (Post-drying) 5th step: 15 minutes at 110°C

[0450] (2.3.2) Preparation of Second Films 2 to 3 and 5 to 8 Second films 2 to 3 and 5 to 8 were obtained in the same manner as above, except that dope 1 was replaced with dopes 2 to 3 and 5 to 8.

[0451] Tables V and VI show the structures of Second Films 1 to 8. In the tables, "acrylic" refers to a (meth)acrylic resin (MMA (methyl methacrylate) / PMI (phenylmaleimide) / MADA (adamantyl acrylate) copolymer (60 / 20 / 20 mass ratio), Mw: 1.5 million, Tg: 137°C). In the tables, "glass" refers to thin-film glass "Dynorex (registered trademark) T2X-1" (manufactured by Nippon Electric Glass Co., Ltd.). In the tables, "COP" refers to a cycloolefin resin "Arton (registered trademark) G7810" (manufactured by JSR Corporation). In the tables, "CPI" refers to a colorless and transparent polyimide obtained by synthesizing the following acid anhydride 1 and diamine 1. The rubber particles used were the rubber particles R1, and the content was varied. In the tables, a "-" next to the rubber particles indicates that they were not contained. In the tables, a "-" next to the glass indicates that the physical properties were not measured.

[0452]

[0453]

[0454]

[0455] (3) Preparation of Adhesive Layer 1 (3.1) Preparation of UV-Curable Acrylic Adhesive Composition (a-1) A monomer mixture consisting of the following components was prepared: 2-Ethylhexyl acrylate (2EHA) 78.000 parts by mass N-Vinyl-2-pyrrolidone (NVP) 18.000 parts by mass 2-Hydroxyethyl acrylate (HEA) 4.000 parts by mass

[0456] The following components were added as photopolymerization initiators: 1-hydroxycyclohexyl phenyl ketone 0.035 parts by mass 2,2-dimethoxy-1,2-diphenylethan-1-one 0.035 parts by mass The following commercially available photopolymerization initiators were used: 1-hydroxycyclohexyl phenyl ketone: "Omnirad (registered trademark) 184" (having an absorption band in the wavelength range of 200 to 370 nm, manufactured by IGM Resins B.V.) 2,2-dimethoxy-1,2-diphenylethan-1-one: "Omnirad (registered trademark) 651" (having an absorption band in the wavelength range of 200 to 380 nm, manufactured by IGM Resins B.V.)

[0457] Thereafter, the mixture was irradiated with ultraviolet light until the viscosity (measurement conditions: BH viscometer No. 5 rotor, 10 rpm, measurement temperature 30°C) reached approximately 20 Pa s. As a result, a prepolymer composition (polymerization rate: 8%) in which a portion of the monomer components was polymerized was obtained.

[0458] Next, the following components were added to the prepolymer composition and mixed to obtain an acrylic pressure-sensitive adhesive composition: 0.150 parts by mass of hexanediol diacrylate (HDDA) 0.300 parts by mass of silane coupling agent "KBM-403" (manufactured by Shin-Etsu Chemical Co., Ltd.)

[0459] The following components were added to the obtained acrylic pressure-sensitive adhesive composition and stirred to obtain an ultraviolet-curable acrylic pressure-sensitive adhesive composition (a-1): 2,4-bis-[{4-(4-ethylhexyloxy)-4-hydroxy}-phenyl]-6-(4-methoxyphenyl)-1,3,5-triazine (dissolved in n-butyl acrylate to give a solids concentration of 15% by mass and added) 1.400 parts by mass Bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide 0.200 parts by mass The following commercially available products were used. 2,4-bis-[{4-(4-ethylhexyloxy)-4-hydroxy}-phenyl]-6-(4-methoxyphenyl)-1,3,5-triazine: "Tinosorb (registered trademark) S" (manufactured by BASF Japan Ltd.) Bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide: "Omnirad (registered trademark) 819" (having an absorption band in the wavelength range of 200 to 450 nm, manufactured by IGM Resins B.V.)

[0460] (3.2) Formation of Adhesive Layer 1 The obtained ultraviolet-curable acrylic adhesive composition (a-1) was applied onto the surface of a release film so that the thickness after curing would be 30 μm, and further, a release film was attached to the surface. Thereafter, illuminance: 6.5 mW / cm ２ , cumulative light amount: 1500 mJ / cm ２ The composition was cured by irradiating it with ultraviolet light under the conditions of (a) and (b), and the release film was peeled off to form an adhesive layer 1.

[0461] (4) Preparation of cover member (4.1) Preparation of cover member 1 The various films obtained above were bonded together in the order of first film 1, adhesive layer 1, second film 1, adhesive layer 1 to obtain cover member 1.

[0462] (4.2) Preparation of cover members 2 to 30 Various films were changed as shown in Tables I to VI, and the films were laminated in the order of the first film, adhesive layer 1, second film, and adhesive layer 1 to obtain cover members 2 to 30.

[0463] (5) Preparation of Color Filters (5.1) Preparation of Resin Solutions (A-1) and (A-2) 800.000 parts by mass of cyclohexanone was placed in a reaction vessel, and the vessel was heated while nitrogen gas was injected into it. A mixture of the following monomers and a thermal polymerization initiator was added dropwise to carry out a polymerization reaction. 60.000 parts by mass of styrene, 60.000 parts by mass of methacrylic acid, 65.000 parts by mass of methyl methacrylate, 65.000 parts by mass of butyl methacrylate, 10.000 parts by mass of thermal polymerization initiator, and 3.000 parts by mass of chain transfer agent. After sufficient heating after the dropwise addition, a solution of 2.000 parts by mass of the thermal polymerization initiator in 50.000 parts by mass of cyclohexanone was added, and the reaction was continued to obtain an acrylic resin solution. Cyclohexanone was added to this resin solution so that the non-volatile content was 20% by mass to prepare an acrylic resin solution, designated resin solution (A-1). The weight average molecular weight of the acrylic resin was about 30,000.

[0464] 800.000 parts by mass of cyclohexanone was placed in a reaction vessel, and the vessel was heated while injecting nitrogen gas. A mixture of the following monomers and thermal polymerization initiator was added dropwise to carry out a polymerization reaction. Styrene 55.000 parts by mass Methacrylic acid 65.000 parts by mass Methyl methacrylate 65.000 parts by mass Benzyl methacrylate 60.000 parts by mass Thermal polymerization initiator 15.000 parts by mass Chain transfer agent 3.000 parts by mass After sufficient heating after the dropwise addition, a solution of 2.000 parts by mass of thermal polymerization initiator dissolved in 500.000 parts by mass of cyclohexanone was added, and the reaction was continued to obtain an acrylic resin solution. Cyclohexanone was added to this resin solution so that the solids content was 30% by mass to prepare an acrylic resin solution, designated resin solution (A-2). The weight average molecular weight of the acrylic resin was approximately 20,000.

[0465] (5.2) Preparation of Pigment-Containing Resin Composition <Red Resin Composition> A mixture of the following components was stirred and mixed to become uniform, and then filtered through a 5 μm filter to obtain a red resin composition. Red pigment: 39.990 parts by mass of C.I. Pigment Red 254 Red pigment: 4.500 parts by mass of C.I. Pigment Red 177 Yellow pigment: 4.500 parts by mass of C.I. Pigment Red 177 Pigment Yellow 150 5.400 parts by mass Dispersant: "Disperbyk-303" (manufactured by BYK-Chemie Co., Ltd.) 1.000 parts by mass Resin solution (A-1) 10.130 parts by mass Polyfunctional polymerizable monomer 1.900 parts by mass Photopolymerization initiator: "Irgacure-OXE02" (manufactured by Ciba-Geigy Co., Ltd.) 0.200 parts by mass Sensitizer 0.290 parts by mass Cyclohexanone 36.590 parts by mass

[0466] <Green Resin Composition> Thereafter, a mixture of the following components was stirred and mixed to become uniform, and then filtered through a 5 μm filter to obtain a green resin composition. Green pigment: C.I. Pigment Green 58 40.900 parts by mass Yellow pigment: C.I. Pigment Yellow 150 8.370 parts by mass Dispersant 1.000 parts by mass Resin solution (A-1) 4.110 parts by mass Resin solution (A-2) 4.110 parts by mass Polyfunctional polymerizable monomer 2.000 parts by mass Photopolymerization initiator 0.200 parts by mass Photosensitizer 0.290 parts by mass Cyclohexanone 39.020 parts by mass

[0467] <Blue Resin Composition> A mixture of the following components was stirred and mixed to become uniform, and then filtered through a 5 μm filter to obtain a blue resin composition. Blue pigment: C.I. Pigment Blue 15 20.000 parts by mass Dispersant 1.000 parts by mass Resin solution (A-1) 2.820 parts by mass Resin solution (A-2) 1.720 parts by mass Polyfunctional polymerizable monomer 7.730 parts by mass Photopolymerization initiator 0.940 parts by mass Photosensitizer 0.460 parts by mass Cyclohexanone 33.760 parts by mass

[0468] <Black Resin Composition> A mixture of the following components was stirred and mixed to become uniform, and then filtered through a 5 μm filter to obtain a black resin composition: Photopolymerization initiator 5.300 parts by mass, Acrylic resin 10.700 parts by mass, Monomer having an ethylenically unsaturated double bond 4.400 parts by mass, Black pigment dispersion 23.400 parts by mass, Propylene glycol monomethyl ether acetate 56.200 parts by mass.

[0469] The black pigment dispersion was prepared by the following method. A mixture of the following composition was stirred and mixed for 30 minutes using a dissolver, and then dispersed for 30 minutes using an ultrasonic disperser to prepare a dispersion. The obtained dispersion was filtered through a polypropylene wound cartridge filter "TCW-1N-PPS" (manufactured by Advantec Toyo Kaisha, Ltd.) to obtain a black pigment dispersion. Carbon black "#950" (manufactured by Mitsubishi Chemical Corporation) 10.000 parts by mass Methyl ethyl ketone 90.000 parts by mass

[0470] (5.3) Formation of Black Matrix The black colored composition was uniformly applied onto a glass substrate by spray coating and dried. Next, the substrate was exposed to ultraviolet light through a photomask having a desired light-shielding pattern by photolithography. The unexposed portions were then washed away by shower development using a developer containing sodium carbonate to form a desired pattern. After development, the substrate was thoroughly washed with water and dried, and then heat-treated at 230°C for 60 minutes to harden the pattern, forming a black matrix.

[0471] (5.4) Formation of Colored Pixels and Colored Pixel Stack Spacers The red resin composition was uniformly applied by spray coating onto a glass substrate on which a black matrix had been formed, and then dried. Next, by photolithography, the regions where red pixels were to be formed and the regions where colored pixel stack spacers were to be formed were exposed to ultraviolet light through a photomask having a desired light-shielding pattern. The unexposed portions were then washed away by shower development using a developer consisting of sodium carbonate, forming the desired pattern. After development, the substrate was thoroughly rinsed with water and dried, and then heat-treated at 230°C for 20 minutes to harden the pattern.

[0472] Using the above green resin composition, a green pattern was formed in the region where a green pixel was to be formed and in the region where a colored pixel stack spacer was to be formed, in the same process as in the formation of the red pattern.

[0473] Using the above blue resin composition, a blue pattern was formed in the area where blue pixels were to be formed and in the area where colored pixel stack spacers were to be formed, using the same process as for forming the red pattern. In this case, the blue color at the top of the colored pixel stack spacer covered and integrated the red color of the first stacked layer and the green color of the second stacked layer, thereby forming a colored layer and colored pixel stack spacer consisting of three colors: red (R), green (G), and blue (B). The aperture ratio of the resulting color filter was 77%.

[0474] (6) Fabrication of Light-Emitting Element (Organic Electroluminescence Element) A bottom-emission type organic EL element was fabricated according to the following method.

[0475] (6.1) Preparation of a first substrate with a gas barrier layer: A 50 μm thick varnish was spin-coated onto a carrier glass with a thickness of 0.7 mm. Then, post-baking was performed at 200° C. for 20 minutes to obtain a first substrate as a flexible film substrate with a size of 30 cm × 40 cm.

[0476] The following polysilazane-containing coating solution was applied onto a varnish substrate using a wire bar so that the average film thickness after drying would be 300 nm, and the coating was dried by heat treatment in an atmosphere of a temperature of 85°C and a humidity of 55% RH for 1 minute. Subsequently, the coating was held in an atmosphere of a temperature of 25°C and a humidity of 10% RH (dew point temperature -8°C) for 10 minutes for dehumidification treatment, thereby forming a polysilazane-containing layer on the varnish substrate.

[0477] Next, the varnish substrate on which the polysilazane-containing layer was formed was fixed on the moving stage of an excimer irradiation device "MECL-M-1-200" (manufactured by MDCOM Co., Ltd.) and then subjected to a modification treatment under the following conditions to form a polysilazane-modified layer with a thickness of 300 nm as a gas barrier layer, thereby obtaining a first substrate with a gas barrier layer.

[0478] (Polysilazane-Containing Coating Liquid) As a polysilazane-containing coating liquid, a 10% by mass dibutyl ether solution of perhydropolysilazane "AQUAMICA (registered trademark) NN120-10, catalyst-free type" (manufactured by Merck Ltd.) was prepared.

[0479] (Modification treatment conditions) Irradiation wavelength: 172 nm Lamp gas: Xe Excimer lamp light intensity: 130 mW / cm ２ (172 nm) Distance between polysilazane-containing layer and light source: 1 mm Stage heating temperature: 70°C Oxygen concentration in irradiation device: 0.5% by volume Excimer lamp irradiation time: 5 seconds

[0480] The resulting first substrate with the gas barrier layer was cleaned by a wet cleaning method. A detergent solution in which an alkaline detergent was diluted to 5.0% by mass was heated to 60°C, and the first substrate was immersed in the 60°C detergent solution. The first substrate was then scrubbed to remove any foreign matter adhering to the first substrate. The first substrate was then subjected to ultrasonic cleaning, rinsing with pure water, nitrogen gas blowing, and IR (Infra Red) drying, in that order. The first substrate was then irradiated with UV (Ultra Violet) to remove any organic matter adhering to the surface of the first substrate, and then dried in an oven.

[0481] (6.2) Fabrication of TFT unit First, a SiO film was formed as a base layer by CVD, and then a gate electrode was formed. Then, a gate insulating film, an a-Si:H film as a channel layer, and an n+a-Si:H film were sequentially formed by CVD. Then, they were processed into the desired shape pattern by dry etching.

[0482] Next, a source electrode and a drain electrode were formed, followed by the formation of a passivation film. An a-Si TFT with an electrode width of 100 μm, a thickness of 200 nm, a channel width W of 3 mm, and a channel length L of 20 μm was then formed in a position corresponding to the color filter. At the same time, an extraction electrode for the first electrode was formed using ITO, completing the TFT unit.

[0483] (6.3) Preparation of Organic EL Device Next, a white tandem organic EL device was formed on the first substrate and the TFT unit.

[0484] In the fabrication of the TFT unit, ITO was used as an extraction electrode for the organic EL element, and the organic EL element (OLED) was fabricated using the same ITO as a first electrode (anode).

[0485] Next, according to the method (Example) described in paragraphs (0201) to (0219) of JP-A-2015-201508, an organic functional layer group (7) consisting of a first hole transport layer / a first light-emitting layer / a first electron transport layer / an intermediate connector layer / a second hole transport layer / a second light-emitting layer / a second electron transport layer was formed.

[0486] Next, aluminum was vapor-deposited to a thickness of 150 nm to form a second electrode (cathode). The emitting layer of the fabricated organic EL device was appropriately adjusted so that the CIE chromaticity of the emitting layer under conditions of emission without the color filter according to the present invention was the same as that under the D65 standard light source. The layers constituting the organic EL device were formed using an inkjet printing method.

[0487] Next, silane gas and ammonia gas were supplied onto the second electrode under a deposition pressure of 50 Pa, and a silicon nitride film having a thickness of 500 nm was deposited by plasma CVD. This film was used as a first sealing layer.

[0488] Specifically, the first base material formed up to the second electrode was 1×10 －４ The temperature of the first substrate was adjusted to about 70°C, and the reaction gas was SiH ４ Gas and NH ３ Gas, H ２ The gases were introduced into a vacuum chamber at a ratio of 2:1:4. The film was formed by plasma CVD using a 13.56 MHz high-frequency power source under a reduced pressure of 50 Pa. The film was formed while cooling the first substrate so that the temperature of the first substrate was 70°C. This resulted in the formation of a first sealing layer made of SiN and having a thickness of 500 nm.

[0489] Next, a second sealing layer was formed. AlPET coated with a thermosetting adhesive was attached to the first sealing layer formed above. The AlPET was used to prevent moisture from attacking the SiN film constituting the first sealing layer. During the attachment process, a heat treatment at 100°C was performed for 30 minutes to harden the thermosetting adhesive, thereby producing an organic EL device.

[0490] (7) Fabrication of Display Device (7.1) Fabrication of Display Device 1 An adhesive layer was formed on the color filter using the same thermosetting adhesive used in forming the second sealing layer of the organic EL element. Next, the carrier glass of the first substrate of the organic EL element was peeled off by laser irradiation. Then, the color filter was placed on the first substrate surface of the organic EL element where the varnish surface was exposed, and heat treatment was performed at 100°C for 30 minutes to bond the color filter and the organic EL element.

[0491] A cover member 1 was attached to the surface of the color filter opposite to the surface to which the organic EL element was attached, via the adhesive layer 1, to obtain a display device 1. The arrangement order of the films in the display device 1 was, from the viewing side, the first film, the adhesive layer 1, the second film, the adhesive layer 1, the color filter, the adhesive layer, and the organic EL element.

[0492] (7.2) Preparation of Display Devices 2 to 30 Display Devices 2 to 30 were obtained in the same manner as in the preparation of Display Device 1 above, except that the films were changed as shown in Tables V and VI.

[0493] 2. Evaluation The tensile modulus of elasticity of the obtained first film and second film was measured. In addition, the following evaluation was performed for each display device.

[0494] (1) Measurement of tensile modulus of elasticity of first film and second film The tensile modulus of elasticity E of each film was measured in the machine direction (MD) by the following method in accordance with JIS K7127 (1999). The tensile modulus was determined by linear regression between strains of 0.05 and 0.25%.

[0495] 1) Each film was cut into a size of 100 mm (MD) x 10 mm (TD) to prepare a test specimen. 2) This test specimen was measured using a Tensilon universal material testing machine "RTC-1225A" (manufactured by Orientec Co., Ltd.). The chuck distance was set to 50 mm, and the test specimen was pulled in the longitudinal (MD) direction at a pulling rate of 50 mm / min to measure the tensile modulus E in the MD direction. The measurement was carried out at 23°C and 55% RH.

[0496] (2) Visibility after keystroke test (impact resistance) For each of the display devices obtained above, a keystroke test was carried out using a keystroke tester with a silicone rubber keystroke (φ25 mm) at a load of 2.5 N, 150,000 keystrokes, and a keystroke speed of 150 times / min.

[0497] After the keystroke test, a black image was displayed on each display device. Then, the front reflectance was measured using a spectrophotometer "CM-2600d" (manufactured by Konica Minolta, Inc.) and evaluated according to the following criteria. Note that if the evaluation is B or higher (A to B), it is usable. A: Less than 1.7. B: 1.7 or higher but less than 1.8. C: 1.8 or higher.

[0498] (3) Folding Endurance Each display device obtained above was cut to a size of 20 mm in the transverse direction (TD) × 110 mm in the longitudinal direction (MD). Using a no-load U-shaped stretch tester "DLDMLH-FS" (manufactured by Yuasa System Co., Ltd.), a bending radius of 1 mm was set, and the sample was bent 100 times at a rate of 1 bend / second. The sample was fixed at both ends 10 mm apart in the MD, and the bent portion was 20 mm × 90 mm. After the bending process, the sample was placed on a flat surface with the bent inside facing down, and the haze of the bent portion was measured using a haze meter "NDH4000" (manufactured by Nippon Denshoku Industries Co., Ltd.). The haze value before the bending test was designated as a, and the haze value after the bending test was designated as b. The difference (b-a) between these values ​​was calculated and evaluated according to the following criteria. A rating of B or higher (AA to B) indicates practical use. AA: Less than 0.1. A: 0.1 or higher, less than 0.5. B: 0.5 or more and less than 1.1. C: 1.1 or more.

[0499] (4) Evaluation Results Ratio of tensile modulus of elasticity of each cover member (E １ / E ２ ) and the difference in refractive index (|n １ -n ２ |) are shown in Tables VII and VIII. The evaluation results of each display device are shown in Tables VII and VIII.

[0500]

[0501]

[0502] From the examples and comparative examples, it can be seen that the flexible display device of the present invention can achieve both impact resistance and folding resistance.

[0503] From the comparison of display devices 9, 12, 19 and 20, the tensile modulus E of the first film １ It can be seen that, by setting the modulus of elasticity within the range of 5.0 to 8.0 GPa, it is possible to achieve both impact resistance and folding resistance.

[0504] A comparison of the display devices 9, 25, 26, 27 and 28 reveals that the impact resistance is improved when the metal oxide is alumina.

[0505] A comparison of display devices 9, 29 and 30 shows that the impact resistance is improved by including an acrylic resin in the second film.

[0506] A comparison of the display devices 12 and 13 reveals that the folding endurance is improved by the second film containing rubber particles.

[0507] The visibility of the display devices 9, 29, and 30 was also confirmed before the keystroke test, and it was found that the visibility of the display device 9 before the keystroke test was higher than the visibility of the display devices 29 and 30 before the keystroke test. １ -n ２ It can be seen that the visibility is improved when |) satisfies the above formula (2).

[0508] (5) Other Examples (5.1) Stretching Ratio of First Film Display device 31 (Example 23) was produced in the same manner as Display device 9 (Example 1), except that the stretching ratio in the transverse (TD) direction of the first film was 0%, i.e., the film was not stretched. In this case, too, the ratio of tensile moduli (E １ / E ２ ) satisfied the above formula (1), and the evaluation results of the display device 31 showed that it was suitable for practical use in terms of both impact resistance and folding resistance.

[0509] Display device 32 (Example 24) was produced in the same manner as Display device 9 (Example 1), except that the stretching ratio in the transverse (TD) direction of the first film was 30%. １ / E ２ ) satisfied the above formula (1), and the evaluation results of the display device 32 showed that it was suitable for practical use in terms of both impact resistance and folding resistance.

[0510] (5.2) Thickness of the First Film Display device 33 (Example 25) was produced in the same manner as display device 9 (Example 1), except that the conditions during casting were adjusted so that the thickness of the first film was 30 μm. In this case, too, the ratio of tensile moduli (E １ / E ２ ) satisfied the above formula (1), and the evaluation results of the display device 33 showed that it was suitable for practical use in terms of both impact resistance and folding resistance.

[0511] Display device 34 (Example 26) was produced in the same manner as Display device 9 (Example 1), except that the conditions during casting were adjusted so that the thickness of the first film was 80 μm. １ / E ２ ) satisfied the above formula (1), and the evaluation results of the display device 34 showed that it was suitable for practical use in terms of both impact resistance and folding resistance.

[0512] (5.3) Hard Coat Layer Display device 35 (Example 27) was produced in the same manner as Display device 9 (Example 1), except that a hard coat layer was provided on the viewing side of the first film. The hard coat layer was formed in the following manner.

[0513] The following components were diluted with a diluent (propylene glycol monomethyl ether / methyl acetate=50 / 50 (mass %)) to obtain a composition for forming a hard coat layer.

[0514] Urethane acrylate "UA-1100H" (manufactured by Shin-Nakamura Chemical Co., Ltd.) 100.000 parts by mass Photopolymerization initiator "Irgacure (registered trademark) 184" (manufactured by BASF Japan Ltd.) 5.000 parts by mass Polyether-modified silicone "BYK (registered trademark) 3450" (manufactured by BYK Japan Ltd.) 1.000 parts by mass

[0515] After forming the first film, the obtained composition was applied to one side of the first film using a bar coater, and the first film was dried in a drying oven at 50°C for 40 seconds with a dryer to volatilize the solvent. Then, the first film was irradiated with a 0.2 J / cm irradiance while purging with nitrogen to maintain an atmosphere with an oxygen concentration of 1.0% by volume or less. 2 To achieve this, an ultraviolet lamp (illuminance of the irradiation part: 100 mW / cm 2 ) and cured by ultraviolet irradiation. A hard coat layer having a thickness of 3 μm was formed on the first film.

[0516] In this case too, the ratio of tensile moduli (E １ / E ２) satisfied the above formula (1), and the evaluation result of display device 35 was the same as that of display device 9. In particular, display device 35 had a lower front reflectance value in the impact resistance evaluation than display device 9, and it was found that impact resistance was further improved.

[0517] (5.4) Adhesive Layer Display device 36 (Example 28) was produced in the same manner as display device 9 (Example 1), except that adhesive layer 2 described below was provided instead of adhesive layer 1. Adhesive layer 2 was formed in the following manner.

[0518] The ultraviolet-curable acrylic pressure-sensitive adhesive composition (a-1) obtained in forming the adhesive layer 1 was applied to the surface of a release film so that the thickness after curing would be 30 μm, and a release film was then attached to the surface. Thereafter, ultraviolet irradiation was performed while adjusting the conditions of illuminance and integrated light dose to cure the composition, and the release film was peeled off to form the adhesive layer 2. The storage modulus of the adhesive layer 1 at 25° C. was 8.00 MPa, and the storage modulus of the adhesive layer 2 at 25° C. was 11.00 MPa.

[0519] In this case, the ratio of tensile moduli (E １ / E ２ ) satisfied the above formula (1), and the evaluation results of the display device 36 were the same as those of the display device 9.

[0520] In forming the second film, the first film was used as a support, and the second film was formed directly on the first film. In other words, the adhesive layer 1 was not provided between the first film and the second film. Except for this, the display device 37 (Example 29) was produced using the same procedure as that for the display device 9 (Example 1). In this case, too, the ratio of the tensile moduli (E １ / E ２ ) satisfied the above formula (1), and the evaluation results of the display device 37 showed that it was suitable for practical use in terms of both impact resistance and folding resistance.

[0521] In forming the second film, the first film was used as a support, and the second film was formed directly on the first film. The resin contained in the second film was the same as the resin used in forming the adhesive layer. That is, the adhesive layer 1 was not provided between the first film and the second film, and the adhesive layer 1 was not provided between the second film and the color filter. Apart from this, the display device 38 (Example 30) was fabricated using the same procedure as the display device 9 (Example 1). In this case, too, the ratio of the tensile moduli (E １ / E ２ ) satisfied the above formula (1), and the evaluation results of the display device 38 showed that it was suitable for practical use in terms of both impact resistance and folding resistance.

[0522] By using the present invention, a flexible display device that is both impact resistant and fold resistant can be obtained.

[0523] DESCRIPTION OF SYMBOLS 1 First film 2 Second film 3 Color filter 4 Light-emitting element 5 Adhesive layer 6 Adhesive layer 7 Hard coat layer 10 Flexible display device 41 Cathode 42 Light-emitting layer 43 Transparent electrode 44 Glass substrate 45 White light 46 RGB color filter 47 Blue light 48 Color filter (wavelength conversion film) 49 Laminated organic electroluminescence element 51 Black matrix 52 Transmission area 53 Irradiation area 60 Color filter 61 Blue light 62 Green light 63 Red light B110 Support B200 Manufacturing apparatus B210 Supply section B220 Coating section B230 Drying section B240 Cooling section B250 Winding section

Claims

1. A flexible display device having at least a cover member, a color filter, and a light-emitting element, wherein the cover member has at least a first film and a second film, the second film is disposed closer to the light-emitting element side than the first film, the first film contains acetyl cellulose and a filler of a metal oxide or a metal salt, the aspect ratio of the filler of the metal oxide or the metal salt is in the range of 110 to 2000, and the tensile elastic modulus of the first film is E １ [GPa], and the tensile elastic modulus of the second film is E ２ [GPa]. When the elastic modulus ratio (E １ / E ２ ) satisfies the following formula (1): Formula (1) 1.5 ≤ E １ / E ２ ≤ 15.

0. A flexible display device characterized by this.

2. The flexible display device according to claim 1, wherein the degree of substitution of acetyl groups in the acetyl cellulose is in the range of 2.3 to 3.

0.

3. Tensile modulus of elasticity E of the first film １ The flexible display device according to claim 1 or 2, characterized in that it is in the range of 5.0 to 8.0 GPa.

4. The flexible display device according to claim 1 or 2, wherein the metal oxide is alumina.

5. The flexible display device according to claim 1 or 2, wherein the content of the filler of the metal oxide or metal salt is in the range of 1 to 30% by mass based on the total mass of the first film.

6. The flexible display device according to claim 1 or 2, wherein the first film is a stretched film, and the stretching ratio in the width direction of the first film is respectively in the range of 5 to 30%.

7. The flexible display device according to claim 1 or 2, wherein the thickness of the first film is in the range of 30 to 80 μm.

8. Let the refractive index of the first film be n １ , and let the refractive index of the second film be n ２ . When the refractive index difference (|n １ - n ２ |) satisfies the following formula (2): Formula (2) 0.00 ≤ |n １ - n ２ | ≤ 0.

02. The flexible display device according to claim 1 or claim 2, characterized in that.

9. The flexible display device according to claim 1 or 2, wherein the second film contains an acrylic resin.

10. The flexible display device according to claim 1 or 2, wherein the second film contains rubber particles.

11. The flexible display device according to claim 10, wherein the content of the rubber particles is in the range of 20 to 90% by mass based on the total mass of the second film.

12. The flexible display device according to claim 1 or 2, wherein the cover member has a hard coat layer, and the hard coat layer is disposed on the viewing side with respect to the first film.

13. The flexible display device according to claim 1 or 2, wherein the light-emitting element is an organic electroluminescence element.

14. The flexible display device according to claim 13, wherein the color filter has an anti-reflection function for light incident from the outside.

15. A method for manufacturing a flexible display device for manufacturing the flexible display device according to claim 1, including a step of manufacturing the first film, the step of manufacturing the first film including a step of preparing a dope containing the acetyl cellulose and the filler of the metal oxide or metal salt, a step of casting the dope onto a support to form a cast film, a step of peeling the cast film from the support, and a step of drying the peeled cast film, characterized by the above.

16. The method for manufacturing a flexible display device according to claim 15, characterized in that the cast film is dried by heating.

17. A method for manufacturing a flexible display device for manufacturing the flexible display device according to claim 1, including a step of manufacturing the first film, the step of manufacturing the first film including a step of preparing a dope containing the acetyl cellulose and the filler of the metal oxide or metal salt, a step of applying the dope onto a support to form an applied film, a step of drying the applied film on the support, and a step of peeling the dried applied film from the support, characterized by the above.

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