Optical film, method for producing optical film, polarizing plate, and organic electroluminescent display device

Abstract

Provided is an optical film containing an alicyclic structure-containing polymer and an ultraviolet absorber, having a thickness of 5 μm or less and a light transmittance of 10% or less at a wavelength of 380 nm. The optical film further contains 0.01-10 wt.% of a residual solvent. Also provided is a method for producing an optical film comprising a step for forming a coating film by applying, on a substrate, a mixed solution containing the alicyclic structure-containing polymer, the ultraviolet absorber, a first solvent, and a second solvent. The first solvent is a good solvent for the alicyclic structure-containing polymer and a poor solvent for the ultraviolet absorber. The second solvent is a good solvent for the ultraviolet absorber.

Description

Optical Film, Method for Producing Optical Film, Polarizing Plate, and Organic Electroluminescence Display Device

[0001] The present invention relates to an optical film, a method for producing an optical film, a polarizing plate, and an organic electroluminescence display device.

[0002] As a display device such as an organic electroluminescence display device, there is known one provided with an optical film on the viewing side of a light-emitting element (that is, a position closer to the surface observed by an observer than the light-emitting element).

[0003] As an example, for adjusting the viewing angle, preventing an image outside the device from being reflected on the display surface, and other purposes, an optical component including a film-like polarizer layer is provided on the viewing side of the display device. The polarizer layer is usually a film mainly composed of a relatively soft material such as PVA (polyvinyl alcohol). Therefore, the polarizer layer is often used in a state protected by other optical films. Specifically, the polarizer layer can be used in the state of a polarizing plate having a structure in which protective films are provided on one or both sides thereof. In addition to the function of mechanically supporting the polarizer layer, the protective film can also have a function of suppressing deterioration of the polarizer layer and other components of the display device due to moisture. Since the protective film can usually be used within the display surface of the display device, high transparency to visible light is also required.

[0004] Another function that the protective film can have is a function of shielding ultraviolet rays. In many cases, the display element and the polarizer layer of the display device are easily deteriorated when irradiated with ultraviolet rays. Therefore, in order to protect these, a protective film having a low ultraviolet transmittance may be provided on the viewing side of the display device.

[0005] From the above-described circumstances, in a display device, a film containing an ultraviolet absorber may be used as an optical film having a function of protecting the polarizer layer, and materials therefor have been proposed (for example, Patent Documents 1 and 2). Such a film is generally a film composed of a mixture containing a polymer as a main component and an ultraviolet absorber having a function of shielding ultraviolet rays.

[0006] Japanese Patent Publication No. 2023-180147 Japanese Patent Publication No. 2023-007352

[0007] Generally, display devices are required to be thin, so the optical films that make up these display devices are also required to be thin.

[0008] When forming an optical film that possesses both UV shielding and polarizer layer protection functions, a large amount of UV absorber per unit area is required to achieve sufficient UV shielding. In this case, it is difficult to reduce the thickness, and insufficient mixing of the polymer and UV absorber can lead to high haze, resulting in insufficient transparency for use as an optical film. Therefore, it has been difficult to easily manufacture a film that is thin, possesses both sufficient UV shielding and polarizer layer protection functions, and has sufficient quality for use as an optical film.

[0009] Therefore, the object of the present invention is to provide an optical film that is thin, has sufficient ultraviolet shielding function and polarizer layer protection function, possesses sufficient quality to be used as an optical film, and can be easily manufactured.

[0010] A further object of the present invention is to provide a manufacturing method that allows for the easy production of an optical film that is thin, possesses both sufficient ultraviolet shielding and polarizer layer protection functions, and is of sufficient quality to be used as an optical film.

[0011] A further object of the present invention is to provide a polarizing plate that is thin in thickness and has sufficient ultraviolet shielding function and durability of its own, and an organic electroluminescent display device equipped therewith.

[0012] The inventors of the present invention conducted studies to solve the aforementioned problems. As a result, the inventors found that the aforementioned problems can be solved by employing an alicyclic structure-containing polymer as the polymer constituting the optical film and by specifying the composition of its components. The inventors further found that such an optical film can be easily manufactured by mixing the materials constituting the optical film using a specific solvent in the manufacturing method. The present invention was completed based on these findings. That is, the present invention includes the following.

[0013] (1) An optical film comprising an alicyclic structure-containing polymer and an ultraviolet absorber, wherein the film has a thickness of 5 μm or less, a light transmittance of 10% or less at a wavelength of 380 nm, and the optical film further contains 0.01% by weight or more and 10% by weight or less of residual solvent. (2) The optical film according to (1), wherein the proportion of the ultraviolet absorber in a total of 100 parts by weight of the alicyclic structure-containing polymer and the ultraviolet absorber is 10% by weight or more. (3) The optical film according to (1) or (2), wherein the ultraviolet absorber is a triazine compound. (4) The optical film according to (3), wherein the ultraviolet absorber is 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-1,3,5-triazine. (5) The optical film according to any one of (1) to (4), wherein the alicyclic structure-containing polymer does not contain polar groups. (6) The optical film according to any one of (1) to (5), wherein the alicyclic structure-containing polymer is amorphous. (7) The optical film according to any one of (1) to (6), wherein the light transmittance at a wavelength of 440 nm is 80% or more. (8) The optical film according to any one of (1) to (7), wherein the residual solvent comprises a first solvent, a second solvent, or both, the first solvent being a good solvent for the alicyclic structure-containing polymer and a poor solvent for the ultraviolet absorber, and the second solvent being a good solvent for the ultraviolet absorber. (9) The optical film according to (8), wherein the first solvent is a hydrocarbon solvent. (10) The optical film according to (8) or (9), wherein the second solvent is an ether solvent. (11) A method for manufacturing an optical film according to any one of (1) to (10), comprising: a first step of coating a mixed solution containing the alicyclic structure-containing polymer, the ultraviolet absorber, a first solvent and a second solvent onto a substrate to form a coating film; and a second step of drying the coating film to form a cured layer as the optical film, wherein the first solvent is a good solvent for the alicyclic structure-containing polymer and a poor solvent for the ultraviolet absorber, the second solvent is a good solvent for the ultraviolet absorber, and the cured layer contains the first solvent, the second solvent, or both as the residual solvent.(12) A method for producing an optical film according to (11), further comprising a third step of peeling the cured layer from the substrate. (13) A method for producing an optical film according to (11) or (12), wherein the first solvent is a hydrocarbon solvent. (14) A method for producing an optical film according to any one of (11) to (13), wherein the second solvent is an ether solvent. (15) A method for producing an optical film according to any one of (11) to (14), wherein the residual solvent contains the second solvent. (16) A polarizing plate comprising a polarizer layer and an optical film according to any one of (1) to (10) provided on one surface thereof. (17) An organic electroluminescent display device comprising the polarizing plate according to (16).

[0014] According to the present invention, an optical film is provided that is thin, has both sufficient ultraviolet shielding function and polarizer layer protection function, possesses sufficient quality to be used as an optical film, and can be easily manufactured.

[0015] The present invention further provides a manufacturing method that allows for the easy production of an optical film that is thin, possesses both sufficient ultraviolet shielding function and polarizer layer protection function, and has sufficient quality to be used as an optical film.

[0016] The present invention further provides a polarizing plate that is thin in thickness and has sufficient ultraviolet shielding function and durability, as well as an organic electroluminescent display device equipped therewith.

[0017] The present invention will be described in detail below with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples shown below, and may be implemented with modifications as appropriate without departing from the scope of the claims and equivalents of the present invention.

[0018] In the following explanation, a good solvent for a given material means a solvent that readily dissolves the material. A solvent that readily dissolves a material means a solvent in which, at 25°C, when 0.5 g of the material is dissolved in 100 g of the solvent, the insoluble content is less than 0.5% by weight.

[0019] In the following explanation, a poor solvent for a given material refers to a solvent that does not readily dissolve the material. A solvent that does not readily dissolve a material is defined as a solvent in which, at 25°C, when 0.5 g of the material is dissolved in 100 g of the solvent, the insoluble content is 0.5% by weight or more.

[0020] In the following explanation, the expression "(meth)acrylic" encompasses "acrylic," "methacrylic," and combinations thereof. For example, "(meth)acrylic acid" encompasses "acrylic acid," "methacrylic acid," and mixtures thereof.

[0021] In the following explanation, unless otherwise specified, "polarizing plate" includes not only rigid members but also flexible members such as resin films.

[0022] (Optical Film) The optical film of the present invention comprises an alicyclic structure-containing polymer and an ultraviolet absorber. The optical film of the present invention may be a film made of a specific material comprising an alicyclic structure-containing polymer and an ultraviolet absorber. In the following description, such a specific material may be referred to as "Resin A" for convenience to distinguish it from general resin materials containing polymers.

[0023] (Alicyclic Structure-Containing Polymers) Alicyclic structure-containing polymers are polymers in which the repeating units of the polymer contain an alicyclic structure. Alicyclic structure-containing polymers typically have low water vapor permeability and high mechanical strength. Therefore, when an optical film is formed with resin A containing an alicyclic structure-containing polymer, an optical film can be obtained that has low water vapor permeability and high mechanical strength, and thus possesses advantageous properties as a protective film.

[0024] A polymer containing an alicyclic structure may contain an alicyclic structure in the main chain, in the side chains, or in both the main chain and side chains. Among these, polymers containing an alicyclic structure in at least the main chain are preferred from the viewpoint of mechanical strength and heat resistance.

[0025] The alicyclic structure-containing polymer is preferably a polymer that does not contain polar groups. Since alicyclic structure-containing polymers that do not contain polar groups generally have low hydrophilicity, their water vapor transmission rate can be kept low. Therefore, by employing such a polymer, an optical film with advantageous properties as a protective film can be obtained.

[0026] In this application, the statement that a molecule of an alicyclic structure-containing polymer does not contain polar groups means that the proportion of monomer units containing polar groups in the alicyclic structure-containing polymer is 0.2 mol% or less. When a molecule of an alicyclic structure-containing polymer does not contain polar groups, the lower limit of the proportion of monomer units containing polar groups in the alicyclic structure-containing polymer may be 0.0 mol%.

[0027] In this context, polar groups refer to heteroatoms and groups of atoms containing heteroatoms. Examples of heteroatoms include oxygen, nitrogen, sulfur, silicon, and halogen atoms, and units containing these atoms can be monomeric units containing polar groups. Specific examples of polar groups include carboxyl groups, carbonyloxycarbonyl groups, epoxy groups, hydroxyl groups, oxy groups, ester groups, silanol groups, silyl groups, amino groups, amide groups, imide groups, nitrile groups, and sulfonic acid groups.

[0028] The alicyclic structure-containing polymer is preferably an amorphous polymer. Amorphous alicyclic structure-containing polymers have excellent mechanical properties, heat resistance, transparency, low moisture absorption, dimensional stability, and lightweight properties. By using such polymers, optical films with advantageous properties as protective films can be obtained. An amorphous polymer is a polymer whose melting point Tm cannot be observed by differential scanning calorimeter (DSC).

[0029] Examples of alicyclic structures found in polymers containing alicyclic structures include saturated alicyclic hydrocarbon (cycloalkane) structures and unsaturated alicyclic hydrocarbon (cycloalkene, cycloalkyne) structures. Of these, cycloalkane and cycloalkene structures are preferred from the viewpoint of mechanical strength and heat resistance, with cycloalkane structures being particularly preferred.

[0030] The number of carbon atoms constituting the alicyclic structure is preferably 4 or more, more preferably 5 or more, preferably 30 or less, more preferably 20 or less, and particularly preferably 15 or less per alicyclic structure. When the number of carbon atoms constituting the alicyclic structure is within this range, the mechanical strength, heat resistance, and moldability of resin A are highly balanced.

[0031] In polymers containing alicyclic structures, the proportion of repeating units containing alicyclic structures can be appropriately selected depending on the intended use. Preferably, the proportion of repeating units containing alicyclic structures in a polymer is 55% by weight or more, more preferably 70% by weight or more, and particularly preferably 90% by weight or more. When the proportion of repeating units containing alicyclic structures in a polymer is within this range, the transparency and heat resistance of resin A are good.

[0032] Examples of polymers containing alicyclic structures include norbornene polymers, monocyclic olefin polymers, cyclic conjugated diene polymers, vinyl alicyclic hydrocarbon polymers, and their hydrides. Among these, norbornene polymers and their hydrides exhibit good transparency and moldability.

[0033] Examples of norbornene polymers and their hydrides include ring-opening polymers of monomers having a norbornene structure and their hydrides; and addition polymers of monomers having a norbornene structure and their hydrides. Examples of ring-opening polymers of monomers having a norbornene structure include ring-opening homopolymers of one type of monomer having a norbornene structure, ring-opening copolymers of two or more types of monomers having a norbornene structure, and ring-opening copolymers of monomers having a norbornene structure and any monomer copolymerizable therewith. Furthermore, examples of addition polymers of monomers having a norbornene structure include addition homopolymers of one type of monomer having a norbornene structure, addition copolymers of two or more types of monomers having a norbornene structure, and addition copolymers of monomers having a norbornene structure and any monomer copolymerizable therewith. Examples of these polymers include those disclosed in Japanese Patent Application Publication No. 2002-321302, etc.

[0034] Specific examples of norbornene polymers and their hydrides include "Zeonor" manufactured by Nippon Zeon Corporation; "Arton" manufactured by JSR Corporation; and "TOPAS" manufactured by TOPAS ADVANCED POLYMERS. Among these, "Zeonor" manufactured by Nippon Zeon Corporation is particularly preferred as an example of an amorphous polymer without polar groups. These products may consist solely of polymers, or they may be resin products containing additives other than polymers. However, even when additives are included, in most cases the amount of additives is very small, and the product can be considered to be substantially entirely polymer.

[0035] The weight-average molecular weight of the alicyclic structure-containing polymer is preferably 10,000 or more, more preferably 15,000 or more, particularly preferably 20,000 or more, preferably 100,000 or less, more preferably 80,000 or less, and particularly preferably 50,000 or less. When the weight-average molecular weight is within this range, the mechanical strength and moldability of resin A are highly balanced. The weight-average molecular weight can be measured using gel permeation chromatography (GPC). Examples of solvents used in GPC include cyclohexane, toluene, and tetrahydrofuran. When using GPC, the weight-average molecular weight can be measured, for example, as the relative molecular weight in terms of polyisoprene or polystyrene.

[0036] (Ultraviolet Absorbers) In optical films, ultraviolet absorbers are materials that can absorb ultraviolet light incident on the film. The ultraviolet absorbers used in optical films are preferably materials with an absorption spectrum that has a high absorption rate for ultraviolet light and a low absorption rate for visible light. Specifically, materials with an absorption spectrum that has a high absorption rate at 380 nm, a representative wavelength of ultraviolet light, and a low absorption rate at 440 nm, a representative wavelength of visible light close to that of ultraviolet light, are preferred.

[0037] The molecular weight of the UV absorber compound is not particularly limited, but from the viewpoint of suppressing deposition on the optical film surface, it is preferable that the molecular weight be lower than a certain level. Specifically, the molecular weight of the UV absorber is preferably 800 or less, more preferably 750 or less. The lower limit of the molecular weight is not particularly limited, but can be 250 or more, or 650 or more.

[0038] Examples of ultraviolet absorbers include triazine compounds, benzophenone compounds, and benzotriazole compounds. Triazine compounds and benzotriazole compounds are preferred from the viewpoint of easily preparing resin A containing a high concentration of ultraviolet absorber in a homogeneous mixture. Furthermore, among these, triazine compounds are particularly preferred from the viewpoint of low environmental impact, having a desired high ultraviolet absorption rate and low visible light absorption rate, and having high heat resistance and low volatility, which allows for easy processing at high temperatures.

[0039] A preferred example of a triazine compound is 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-1,3,5-triazine. A commercially available product (product name "ADEKA Stab LA-F70", manufactured by ADEKA Corporation) can be used as this compound. The ultraviolet absorber may be used alone or in combination of two or more types.

[0040] The proportion of ultraviolet absorber in the optical film of the present invention can be adjusted as appropriate to obtain the desired ultraviolet shielding function. From the viewpoint of obtaining an optical film that exhibits good low ultraviolet transmittance even with a thin thickness of 5 μm or less, it is preferable that the optical film of the present invention contains a high concentration of ultraviolet absorber. Specifically, the proportion of ultraviolet absorber in the total of 100 parts by weight of the alicyclic structure-containing polymer and ultraviolet absorber is preferably 10% by weight or more, more preferably 15% by weight or more. The upper limit of the proportion of ultraviolet absorber is not particularly limited, but from the viewpoint of ease of manufacture, maintaining low water vapor transmittance, maintaining low haze, and maintaining high visible light absorption, it may be, for example, 40% by weight or less.

[0041] As the ultraviolet absorber, those having a sufficiently high ultraviolet absorption ability can be used. Specifically, when an optical film containing a certain ultraviolet absorber is manufactured and the transmittance at 380 nm is measured, the transmittance T (i.e., the ratio of the emitted light to the incident light at 380 nm), the film thickness d (unit: μm), the ratio c of the ultraviolet absorber in the film (i.e., the ratio of the weight of the ultraviolet absorber to the total weight of the film), and the specific coefficient ε (unit: μm ,

[0044] ) satisfy the relationship of the following formula (e1). -log １０ T = ε·c·d ··· formula (e1)

[0042] In this relationship, the ultraviolet absorber preferably has a value such that the transmittance at 380 nm is 10% (i.e., T = 0.1) or less when the thickness is 5 μm (i.e., d = 5) and the ultraviolet absorber concentration is 10% by weight (i.e., c = 0.1). That is, the ultraviolet absorber preferably has a coefficient ε of 2.0 or more. The transmittance at 380 nm at d = 5 and c = 0.1 is more preferably 7% or less (i.e., ε = 2.3 or more), and even more preferably 5% or less (i.e., ε = 2.6 or more).

[0043] (Residual solvent) The optical film of the present invention contains a specific proportion of residual solvent. The proportion of the residual solvent in the optical film is 0.01% by weight or more, preferably 0.1% by weight or more, more preferably 1% by weight or more, while it is 10% by weight or less, preferably 5% by weight or less, more preferably 3% by weight or less. Specifically, the optical film of the present invention can be a film made of resin A containing a residual solvent in such a proportion. According to what the present inventor has found, when a material containing a residual solvent in such a proportion is made into a film, even if the content ratio of the ultraviolet absorber is large, the alicyclic structure-containing polymer and the ultraviolet absorber can be well mixed, suppressing an increase in haze and the like, and it is possible to easily form a high-quality optical film.

[0044] The residual solvent may contain the first solvent, the second solvent, or both of them. It is preferable that the residual solvent contains the second solvent, or both the first solvent and the second solvent. Here, the first solvent is a good solvent for the polymer containing an alicyclic structure and a poor solvent for the ultraviolet absorber. The second solvent is a good solvent for the ultraviolet absorber. The second solvent may be a good solvent for the polymer containing an alicyclic structure, but in many cases, a good solvent for the ultraviolet absorber is a poor solvent for the polymer containing an alicyclic structure. Therefore, the second solvent can be a poor solvent for the polymer containing an alicyclic structure and a good solvent for the ultraviolet absorber. By the optical film containing these solvents as the residual solvent, a good distribution of the ultraviolet absorber can be achieved.

[0045] Both the first solvent and the second solvent can be compounds having physical properties that can be used as solvents when preparing a mixed solution containing a polymer containing an alicyclic structure and an ultraviolet absorber and coating the mixed solution onto a substrate during the production of the optical film. The first solvent and the second solvent are usually liquids at room temperature and can be compounds having a boiling point higher than room temperature. Specifically, the lower limit of the boiling point of the first solvent and the second solvent can preferably be 65°C or higher, more preferably 75°C or higher. The upper limit of the boiling point can be, for example, 150°C or lower.

[0046] The first solvent can be a hydrocarbon-based solvent. On the other hand, the second solvent can be an ether-based solvent. Specifically, as the hydrocarbon-based solvent, hydrocarbon compounds having a boiling point within the above preferable range can be adopted. Examples thereof include cyclic hydrocarbon compounds such as cyclohexane, and compounds having a structure in which a substituent that is a chain hydrocarbon group is provided on a cyclic hydrocarbon compound such as cyclohexane. Examples of the substituent preferably include an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms. Examples of such compounds include cyclohexane and ethylcyclohexane. Ethylcyclohexane is particularly preferable.

[0047] Specifically, as the ether solvent, a compound having an ether bond and a boiling point within the preferred range described above can be used. An example of such a compound is one having the structure of formula R-O-R' (where R- and R'- are the same or different groups, and are alicyclic hydrocarbon groups or linear hydrocarbon groups having 1 to 6 carbon atoms). Examples of R- include preferably alicyclic hydrocarbon groups having 1 to 6 carbon atoms, and more preferably alicyclic hydrocarbon groups having 1 to 5 carbon atoms. Examples of R'- include preferably linear hydrocarbon groups having 1 to 6 carbon atoms, and more preferably linear hydrocarbon groups having 1 to 3 carbon atoms. A particularly preferred example of such a compound is cyclopentyl methyl ether.

[0048] (Resin A: Optional components, properties) Resin A constituting the optical film of the present invention may consist only of an alicyclic structure-containing polymer, an ultraviolet absorber, and a residual solvent, but may also contain optional components. Examples of optional components include hygroscopic agents; dispersants; organometallic compounds; stabilizers such as antioxidants and light stabilizers; resin modifiers such as lubricants and plasticizers; colorants such as dyes and pigments; antistatic agents; and the like. Optional components may be used individually or in combination of two or more types.

[0049] (Shape and Properties of the Optical Film) The optical film of the present invention is a thin film whose thickness is within a specific range. Specifically, the thickness of the optical film of the present invention is 5 μm or less, preferably 4 μm or less, and more preferably 3 μm or less. Even as such a thin film, the optical film of the present invention can exhibit a sufficient ultraviolet shielding effect. The lower limit of the thickness can be, for example, 2 μm or more.

[0050] The optical film of the present invention is a film with low light transmittance at a wavelength of 380 nm. Specifically, the light transmittance of the optical film of the present invention at a wavelength of 380 nm is 10% or less. Ideally, the lower limit of the light transmittance at a wavelength of 380 nm is 0%.

[0051] The optical film of the present invention preferably has high light transmittance in the visible light region. In particular, it is preferable that it has high light transmittance at 440 nm, which is a representative wavelength in the visible light region close to the ultraviolet region. Due to its high 440 nm light transmittance, the optical film of the present invention can be usefully used as a component covering the display surface of a display device that displays images using visible light. The light transmittance at a wavelength of 440 nm is preferably 80% or more, more preferably 85% or more, and more preferably 90% or more. Ideally, the upper limit of the 440 nm light transmittance is 100%.

[0052] The optical film of the present invention may have a low haze value suitable for use as an optical film. The haze value may preferably be 5% or less, more preferably 3% or less, and even more preferably 1% or less. Ideally, the lower limit of the haze value may be 0%. The haze value is determined by the formula scattered light / total transmitted light × 100 (%), and can be determined using a haze meter NDH-7000 (manufactured by Nippon Denshoku Industries Co., Ltd.).

[0053] (Method for Manufacturing Optical Films) The optical film of the present invention can preferably be manufactured by a manufacturing method comprising the following first and second steps. Hereinafter, such a manufacturing method will be described as the method for manufacturing optical films of the present invention. The method for manufacturing optical films of the present invention may further include the following third step.

[0054] Step 1: A mixed solution containing an alicyclic structure polymer, an ultraviolet absorber, a first solvent, and a second solvent is applied to a substrate to form a coating film. Step 2: The coating film is dried to form a cured layer as an optical film. Step 3: The cured layer is peeled off the substrate.

[0055] (First step) The mixed solution used in the first step contains an alicyclic structure-containing polymer, an ultraviolet absorber, a first solvent, and a second solvent. The ratio of the alicyclic structure-containing polymer and the ultraviolet absorber in the mixed solvent may be the same as the ratios for the optical film described above.

[0056] The ratio of the first solvent to the second solvent can be adjusted as appropriate depending on the degree to which each solvent can dissolve other components, but a preferred ratio is in the range of 3:7 to 7:3 by weight.

[0057] The proportion of other components to the amount of the mixed solvent (i.e., the total amount of the first and second solvents) can be adjusted as appropriate to achieve good coating and drying. For example, the amount of alicyclic structure-containing polymer in the mixed solution can be adjusted to 5% to 30% by weight, and the amount of ultraviolet absorber in the mixed solution can be adjusted to achieve a desired ratio with respect to the alicyclic structure-containing polymer, thereby adjusting the concentration.

[0058] By setting the amount of alicyclic structure-containing polymer in the mixed solution to above the aforementioned lower limit, an optical film with good surface properties can be obtained, and the time required for the work process can be shortened, thereby improving work efficiency. In addition, the excessive presence of residual solvent in the optical film can be suppressed, improving the mechanical durability of the optical film.

[0059] On the other hand, by keeping the amount of alicyclic structure-containing polymer in the mixed solution below the aforementioned upper limit, good mixing of the alicyclic structure-containing polymer and the ultraviolet absorber can be achieved, forming a uniform mixed solution in which no solid suspended matter is visible, and thus enabling the production of high-quality optical films.

[0060] According to the present inventors, when an optical film is formed using such a mixed solution, even if the content of the ultraviolet absorber is high, the alicyclic structure-containing polymer and the ultraviolet absorber can be mixed well, suppressing the increase in haze and making it possible to easily form a high-quality optical film.

[0061] Specific examples of the first and second solvents are the same as the specific examples of the first and second solvents that constitute the residual solvent, as described above. As mentioned above, the first and second solvents are usually liquids at room temperature and can be compounds with boiling points higher than room temperature. By using solvents with boiling points somewhat higher than room temperature, roughening of the coating film and film surface in the first and second steps can be prevented.

[0062] The method for preparing the mixed solution is not particularly limited, and it can be prepared by mixing the components described above in any order. For example, the mixed solution can be prepared by mixing the first solvent and the second solvent to prepare a mixed solvent, and then sequentially dissolving the ultraviolet absorber and the alicyclic structure-containing polymer in it.

[0063] The mixed solution can be applied to the substrate by any coating method capable of forming a coating of the desired thickness. The amount of coating can also be adjusted as appropriate to obtain an optical film of the desired thickness.

[0064] The substrate used in the first step is not particularly limited, and a substrate suitable for film manufacturing can be appropriately selected. For example, polyethylene terephthalate film (e.g., Unitika Corporation, product name "Unipeel") can be used as the substrate for coating.

[0065] (Second step) The second step can be carried out by heating the multilayer material, including the substrate and the coating applied to its surface, using a suitable drying device such as an oven, and volatilizing a portion of the mixed solvent. This operation hardens the coating and yields an optical film as a cured layer. The heating temperature is the boiling point bp of the one with the higher boiling point of the first and second solvents. Ｈ Based on this, the temperature can be appropriately adjusted to produce an optical film with good surface properties. Specifically, the heating temperature is preferably (bp Ｈ -30°C or higher, more preferably (bp Ｈ -20°C or higher, preferably (bp Ｈ ) More preferably (bp Ｈ The temperature should be below -5°C. The heating time can be, for example, 10 seconds to 5 minutes.

[0066] (Third step) In the third step, the cured layer is peeled off the substrate. Furthermore, the peeled cured layer can be used as is, or further laminated to another substrate, to produce a product that can be used as an optical film. Including the third step increases the degree of freedom in selecting a substrate suitable for film formation in the first step.

[0067] (Polarizing plate) The polarizing plate of the present invention comprises a polarizer layer and the optical film of the present invention provided on one surface thereof.

[0068] Examples of polarizer layers include polyvinyl alcohol resin films containing vinyl alcohol polymers such as polyvinyl alcohol and partially formalized polyvinyl alcohol, which are subjected to appropriate treatments such as dyeing with a dichroic substance such as iodine, stretching, and crosslinking in an appropriate order and manner. It is preferable that the polarizer layer contains polyvinyl alcohol resin.

[0069] The optical film and the polarizer layer can be bonded by appropriate means. Bonding may be carried out via an adhesive if necessary. Examples of adhesives include acrylic adhesives, epoxy adhesives, urethane adhesives, polyester adhesives, polyvinyl alcohol adhesives, modified polyvinyl alcohol adhesives, polyolefin adhesives, modified polyolefin adhesives, polyvinyl alkyl ether adhesives, rubber adhesives, vinyl chloride-vinyl acetate adhesives, SEBS (styrene-ethylene-butylene-styrene copolymer) adhesives, ethylene-styrene copolymers and other ethylene-based adhesives, acrylic acid ester adhesives such as ethylene-(meth)acrylate copolymers and ethylene-(meth)acrylate copolymers. The term "adhesive" here also includes what are called pressure-sensitive adhesives or tacks.

[0070] The polarizing plate of the present invention may further comprise an additional protective layer provided on the surface of the polarizer layer opposite to the optical film. Preferably, the additional protective layer has a lower water vapor transmittance than the optical film of the present invention. That is, in a polarizing plate having an optical film on one surface of the polarizer layer and a protective layer on the other surface, if both the optical film and the protective layer have low water vapor transmittance, but the optical film side has a relatively higher water vapor transmittance, then the water vapor present in the polarizer layer will evaporate to the optical film side. The optical film is preferably provided on the viewing side of the polarizer layer in the display device in order to shield the polarizer layer from the incidence of ultraviolet rays. With such a configuration, the polarizer layer can be protected from ultraviolet rays by the optical film, and the intrusion of water vapor into the device can be effectively suppressed by the protective layer.

[0071] (Organic Electroluminescent Display Device) The organic electroluminescent display device of the present invention comprises the polarizing plate of the present invention. The polarizing plate is usually provided on the viewing side of the display element of the display device. Preferably, in the organic electroluminescent display device of the present invention, the polarizing plate of the present invention is provided with its optical film side facing the viewing side. With this configuration, the polarizing plate containing a thin optical film protects the display element in the display device from ultraviolet rays and also suppresses the intrusion of water vapor, making it possible to construct an organic electroluminescent display device that is thin and highly durable.

[0072] An example of a display element in a display device is an organic electroluminescent element comprising a transparent electrode layer, a light-emitting layer, and an electrode layer in that order. In this organic electroluminescent element, when a voltage is applied from the transparent electrode layer and the electrode layer, the light-emitting layer generates light, which can be transmitted through the transparent electrode layer and emitted. Examples of materials constituting the organic light-emitting layer include poly(p-phenylenevinylene), polyfluorene, and polyvinylcarbazole materials. The light-emitting layer may also have a laminate of multiple layers with different light-emitting colors, or a mixed layer in which a layer of one dye is doped with a different dye. Furthermore, the organic electroluminescent element may also include functional layers such as a hole injection layer, a hole transport layer, an electron injection layer, an electron transport layer, an equipotential surface forming layer, and a charge generation layer.

[0073] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the examples shown below, and can be modified and implemented as appropriate without departing from the scope of the claims and equivalents of the present invention.

[0074] In the following explanation, "%" and "parts" refer to weight unless otherwise specified. Furthermore, the operations described below were performed in ambient air at normal temperature and pressure (23°C, 1 atm) unless otherwise specified.

[0075] (Example 1 (1a-1f)) (1-1. Preparation of mixed solution) Ethylcyclohexane as the first solvent and cyclopentyl methyl ether as the second solvent were mixed in a 1:1 (weight ratio) to obtain a mixed solvent.

[0076] An ultraviolet absorber (ADEKA Corporation, product name "ADEKA Stab LA-F70") was added to a mixed solvent and dissolved to obtain an ultraviolet absorber solution. The amount of ultraviolet absorber added was adjusted so that the weight ratio of the alicyclic structure-containing polymer and the ultraviolet absorber to 100% by weight in the resulting optical film was one of the various values ​​shown in Table 1.

[0077] A polymer resin containing an alicyclic structure (manufactured by Zeon Corporation, product name "ZEONOR", glass transition temperature 138°C) was added to a UV absorber solution to a concentration of 11% by weight and dissolved to obtain a homogeneous mixed solution in which no solid suspended matter was visible.

[0078] (1-2. Formation of Optical Film) A mixed solution was applied to the surface of a coating substrate (PET film, manufactured by Unitika Corporation, product name "Unipeel") to form a coating film. A coating machine (manufactured by Tester Industries Co., Ltd., product name "PI-1210 Automatic Coating Machine") was used for coating. The amount of coating was adjusted so that the thickness of the resulting optical film would be 3 μm. Specifically, a preliminary film was manufactured, and the thickness of the obtained film was manually measured using a measuring device (manufactured by Filmetrix Co., Ltd., product name "F20-EXR Film Thickness Measurement System") to determine the relationship between the amount of coating and the film thickness. The amount of coating that would result in an optical film with a thickness of 3 μm was determined, and the coating was performed using that amount. After that, the coating film was dried for 120 seconds in an oven heated to 120°C (manufactured by Yamato Scientific Co., Ltd., product name "DNE400 Forced Air Constant Temperature Oven") to form a cured layer as an optical film. As a result, a multilayer material having a layer structure of (coated substrate) / (optical film) was obtained. When drying is performed under these drying conditions, both the first and second solvents remain in the optical film, and the proportion of residual solvent (total of the first and second solvents) in the optical film is considered to be between 0.01% and 10% by weight.

[0079] (1-3. Evaluation) An adhesive sheet (Nitto Denko Corporation, product name "LUCIACS CS9861US") was placed on the surface of a glass substrate (Corning Corporation, product name "Eagle XG"), and the optical film side of the multilayer obtained in (1-2) was then bonded onto it. After that, the coated substrate was peeled off. As a result, an evaluation multilayer with a layer structure of (glass substrate) / (adhesive sheet) / (optical film) was obtained.

[0080] The light transmittance of the evaluation multilayer material at 380 nm and 440 nm was measured using a spectrophotometer (manufactured by JASCO Corporation, product name "V-750 UV-Vis-Near-Infrared Spectrophotometer"). The light absorption of the glass substrate and adhesive sheet was negligibly low in this measurement, and their transmittances could be considered to be approximately 100%. Therefore, these measured values ​​were taken as the light transmittance of the optical film.

[0081] For some examples, the haze of the evaluation multilayer was measured using a haze meter NDH-7000 (manufactured by Nippon Denshoku Industries Co., Ltd.). The haze of the glass substrate and adhesive sheet was negligibly low in this measurement and could be considered to be approximately 0%, so this measured value was taken as the haze of the optical film.

[0082] The coating substrate was peeled off from the multilayer material obtained in (1-2) to obtain a single layer of optical film as a sample. The sample was cut into 40 mm x 200 mm pieces, weighed, and placed in a vial. The sample in the vial was heated at 150°C for 30 minutes to vaporize the solvent in the sample. The amount of vaporized solvent was measured using a gas chromatograph-mass spectrometer (Shimadzu GC-2010 Plus / Trubomatrix 40; column: Agilent Technologies DB-5ms). The specific amount of solvent was determined based on a pre-prepared calibration curve. From the determined amount of solvent, the content of residual solvent (total of the first and second solvents) in the optical film was calculated.

[0083] (Example 2 (2a-2c)) Except for the following changes, the same procedure as in Example 1 was performed to obtain and evaluate a multilayer material for evaluation that included an optical film. - The amount of UV absorber added in (1-1) was adjusted so that the weight ratio of the alicyclic structure-containing polymer and the UV absorber to 100% by weight in the resulting optical film was to the various values ​​shown in Table 2. - The coating thickness in (1-2) was changed to change the film thickness of the resulting optical film to 2 μm.

[0084] (Example 3 (3a-3e)) Except for the following changes, the same procedure as in Example 1 was performed to obtain and evaluate a multilayer material for evaluation that included an optical film. - The amount of UV absorber added in (1-1) was adjusted so that the weight ratio of the alicyclic structure-containing polymer and the UV absorber to 100% by weight in the resulting optical film was to the various values ​​shown in Table 3. - The coating thickness in (1-2) was changed to change the film thickness of the resulting optical film to 4 μm.

[0085] (Comparative Example 1) An attempt was made to produce an optical film by performing the same procedure as in Example 1, except that cyclopentyl methyl ether was used instead of ethylcyclohexane as the first solvent. However, solid suspended matter remained, and a uniform mixed solution could not be obtained, making it impossible to produce an optical film.

[0086] (Comparative Example 2) An attempt was made to produce an optical film by performing the same procedure as in Example 1, except that ethylcyclohexane was used instead of cyclopentyl methyl ether as the second solvent. However, solid suspended matter remained, and a uniform mixed solution could not be obtained, making it impossible to produce an optical film.

[0087] The results of the examples are shown in Tables 1 to 3.

[0088]

[0089]

[0090]

[0091] UVA concentration: The weight ratio (weight %) of the ultraviolet absorber relative to 100% by weight of the total of the alicyclic structure-containing polymer and the ultraviolet absorber. UVA parts by weight: Parts by weight of the ultraviolet absorber relative to 100 parts by weight of the alicyclic structure-containing polymer.

[0092] From the above results, it can be seen that the optical film of the present invention, manufactured using the first and second solvents and containing a predetermined amount of residual solvent, achieves a homogeneous mixture of polymer and ultraviolet absorber, and exhibits a good ultraviolet shielding function with a 380 nm transmittance of 10% while having a thin thickness of 5 μm or less (2 to 4 μm in the examples). In particular, in Examples 1a to 1e, it can be seen that by setting the concentration of the ultraviolet absorber within an appropriate range, the 440 nm transmittance can be further increased to a high value of 80% or more.

Claims

1. An optical film comprising an alicyclic structure-containing polymer and an ultraviolet absorber, wherein the film has a thickness of 5 μm or less, a light transmittance of 10% or less at a wavelength of 380 nm, and the optical film further contains 0.01% to 10% by weight of residual solvent.

2. The optical film according to claim 1, wherein the proportion of the ultraviolet absorber in a total of 100 parts by weight of the alicyclic structure-containing polymer and the ultraviolet absorber is 10% by weight or more.

3. The optical film according to claim 1, wherein the ultraviolet absorber is a triazine compound.

4. The optical film according to claim 3, wherein the ultraviolet absorber is 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-1,3,5-triazine.

5. The optical film according to claim 1, wherein the alicyclic structure-containing polymer does not contain polar groups.

6. The optical film according to claim 1, wherein the alicyclic structure-containing polymer is amorphous.

7. The optical film according to claim 1, wherein the light transmittance at a wavelength of 440 nm is 80% or more.

8. The optical film according to claim 1, wherein the residual solvent comprises a first solvent, a second solvent, or both thereof, the first solvent being a good solvent for the alicyclic structure-containing polymer and a poor solvent for the ultraviolet absorber, and the second solvent being a good solvent for the ultraviolet absorber.

9. The optical film according to claim 8, wherein the first solvent is a hydrocarbon solvent.

10. The optical film according to claim 8, wherein the second solvent is an ether-based solvent.

11. A method for manufacturing an optical film according to any one of claims 1 to 10, comprising: a first step of coating a mixed solution containing the alicyclic structure-containing polymer, the ultraviolet absorber, a first solvent, and a second solvent onto a substrate to form a coating film; and a second step of drying the coating film to form a cured layer as the optical film, wherein the first solvent is a good solvent for the alicyclic structure-containing polymer and a poor solvent for the ultraviolet absorber, the second solvent is a good solvent for the ultraviolet absorber, and the cured layer contains the first solvent, the second solvent, or both as the residual solvent.

12. The method for manufacturing an optical film according to claim 11, further comprising a third step of peeling the cured layer from the substrate.

13. The method for producing an optical film according to claim 11, wherein the first solvent is a hydrocarbon solvent.

14. The method for producing an optical film according to claim 11, wherein the second solvent is an ether-based solvent.

15. The method for producing an optical film according to claim 11, wherein the residual solvent includes the second solvent.

16. A polarizing plate comprising a polarizer layer and an optical film according to any one of claims 1 to 10 provided on one surface thereof.

17. An organic electroluminescent display device comprising the polarizing plate described in claim 16.

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