Method for manufacturing multilayer optical film

Abstract

Provided is a method for manufacturing a multilayer optical film in which at least a first optical film and a second optical film are stacked with an adhesive layer being interposed therebetween, the method including: a first coating step for coating a bonding surface of the first optical film with a first adhesive composition which contains at least an amino-based silane coupling agent; a second coating step for coating a bonding surface of the second optical film with a second adhesive composition which contains at least an epoxy-based silane coupling agent; a bonding step for bonding the first adhesive composition coated surface of the first optical film and the second adhesive composition coated surface of the second optical film to each other; and an adhesion step for having the first optical film and the second optical film adhered to each other by curing the first adhesive composition and the second adhesive composition bonded to each other in the bonding step.

Description

Method for manufacturing laminated optical film

[0001] The present invention relates to a method for producing a laminated optical film in which at least a first optical film and a second optical film are laminated via an adhesive layer. The laminated optical film can be used alone or in combination with a polarizing film or other film to form an image display device such as a liquid crystal display (LCD), an organic EL display, a CRT, or a PDP.

[0002] Generally, image display devices such as liquid crystal display devices and organic EL display devices are equipped with laminated optical films. Image display devices are expected to be used in a variety of environments, but when used in high-temperature and high-humidity environments, display unevenness due to dimensional changes can be an issue. Furthermore, while laminated optical films have become thinner in recent years, ensuring adhesion between optical films when bonding thin layers of optical films has been a challenge.

[0003] Incidentally, Patent Document 1 listed below describes an adhesive for use in bonding optical films, which has good adhesion and water resistance even when the film is thin, and which is made of a solution containing an amino-based silane coupling agent and an epoxy-based silane coupling agent in a molar ratio of 8:92 to 60:40.

[0004] JP 2015-59215 A

[0005] The technology described in Patent Document 1 does not mention anything about suppressing display unevenness in a laminated optical film including a retardation film, and does not incorporate any particular ingenuity into a method for manufacturing a laminated optical film.

[0006] The present invention was developed in consideration of the above-described circumstances, and aims to provide a method for manufacturing a laminated optical film in which display unevenness caused by the adhesive layer is reduced, the adhesive layer has excellent adhesion, and the pot life during the manufacturing process is excellent.

[0007] That is, the present invention relates to a method for producing a laminated optical film (1), in which at least a first optical film and a second optical film are laminated via an adhesive layer, the method comprising: a first coating step of coating a first adhesive composition containing at least an amino-based silane coupling agent on a bonding surface of the first optical film; a second coating step of coating a second adhesive composition containing at least an epoxy-based silane coupling agent on a bonding surface of the second optical film; a laminating step of bonding the first adhesive composition-coated surface of the first optical film and the second adhesive composition-coated surface of the second optical film together; and a bonding step of curing the first adhesive composition and the second adhesive composition bonded together in the laminating step, thereby bonding the first optical film and the second optical film together.

[0008] In the method (1) for producing a laminated optical film, a method (2) for producing a laminated optical film is preferred, in which at least one or both of the first adhesive composition and the second adhesive composition is an adhesive composition containing water.

[0009] In the method for producing a laminated optical film (2), a method for producing a laminated optical film (3) is preferred, in which, in the laminating step, the first adhesive composition-coated surface of the first optical film and the second adhesive composition-coated surface of the second optical film are laminated together in a state in which water remains in at least one or both of the first adhesive composition and the second adhesive composition.

[0010] In any of the above-mentioned methods (1) to (3) for producing a laminated optical film, a method (4) for producing a laminated optical film is preferred, in which both the first adhesive composition and the second adhesive composition contain water, and the concentration of the amino-based silane coupling agent in the first adhesive composition and the concentration of the epoxy-based silane coupling agent in the second adhesive composition are both 0.5 mass % or more.

[0011] In any one of the above-mentioned laminated optical film manufacturing methods (1) to (4), a laminated optical film manufacturing method (5) is preferred in which the first optical film is a retardation film.

[0012] In the method (5) for producing a laminated optical film, a method (6) for producing a laminated optical film is preferred, in which the thickness of the retardation film is 5 μm or less.

[0013] In any one of the above-mentioned laminated optical film manufacturing methods (1) to (6), a laminated optical film manufacturing method (7) is preferred, in which the second optical film is a retardation film.

[0014] In the method (7) for producing a laminated optical film, a method (8) for producing a laminated optical film is preferred, in which the thickness of the retardation film is 5 μm or less.

[0015] In any one of the above-mentioned methods (1) to (8) for producing a laminated optical film, the method (9) for producing a laminated optical film is preferred, in which the thickness of the adhesive layer is 1 to 200 nm.

[0016] In the method for producing a laminated optical film according to the present invention, the adhesive layer for laminating the first optical film and the second optical film is formed from a cured layer of a first adhesive composition containing an amino-based silane coupling agent and a second adhesive composition containing an epoxy-based silane coupling agent. The amino-based silane coupling agent has a strong penetrating power into the optical film, so it tends to penetrate between molecules on the surface of the optical film and increase the adhesion at the interface between the adhesive layer and the optical film. Meanwhile, the epoxy groups of the epoxy-based silane coupling agent are highly reactive with the amino groups of the amino-based silane coupling agent, and the reaction between the two forms a strong network structure (crosslinked structure) within the adhesive layer and at the interface with the optical film. As a result, the method for producing a laminated optical film according to the present invention can produce a laminated optical film with excellent adhesion of the adhesive layer interposed between the first optical film and the second optical film.

[0017] Furthermore, the method for producing a laminated optical film according to the present invention includes a first coating step of coating a first adhesive composition containing at least an amino-based silane coupling agent on the bonding surface of a first optical film, and a second coating step of coating a second adhesive composition containing at least an epoxy-based silane coupling agent on the bonding surface of a second optical film. By including two coating steps, the following effects (1) and (2) are achieved.

[0018] (1) As mentioned above, the epoxy group of an epoxy-based silane coupling agent and the amino group of an amino-based silane coupling agent have high reactivity. Due to this tendency, for example, in a method of forming an adhesive layer by coating one optical film with an adhesive containing an amino-based silane coupling agent and an epoxy-based silane coupling agent in a predetermined ratio, the pot life of the adhesive tends to be short, making production management difficult. However, in the method for producing a laminated optical film according to the present invention, the coating process is divided into two processes, and the amino-based silane coupling agent and the epoxy-based silane coupling agent come into contact (be bonded) at the final lamination process, and then they react, so that the pot life in the production process can be sufficiently ensured. As a result, production management is easy.

[0019] (2) In the laminating step following the first coating step and the second coating step, the first adhesive composition-coated surface of the first optical film is bonded to the second adhesive composition-coated surface of the second optical film while they are in contact with each other. In other words, the viscous adhesive compositions are bonded together while overlapping each other, which makes it difficult for air bubbles to become trapped in the uncured adhesive composition during lamination, and even if air bubbles are generated, they are easily released from the uncured adhesive composition. In particular, (i) when at least one or both of the first adhesive composition and the second adhesive composition are adhesive compositions containing water, (ii) when the first adhesive composition-coated surface of the first optical film and the second adhesive composition-coated surface of the second optical film are bonded together while water remains in at least one or both of the first adhesive composition and the second adhesive composition in the bonding step, or (iii) when both the first adhesive composition and the second adhesive composition contain water and the concentrations of the amino-based silane coupling agent in the first adhesive composition and the epoxy-based silane coupling agent in the second adhesive composition are both 0.5 mass % or more, the incorporation of air bubbles into the adhesive compositions before curing during bonding can be more effectively suppressed. As a result, the smoothness of the adhesive layer can be further improved, and the occurrence of display unevenness can be more effectively prevented when the laminated optical film is incorporated into an image display device.

[0020] The method for producing a laminated optical film according to the present invention is preferable because, when at least one or both of the first optical film and the second optical film are retardation films, particularly when the retardation films have a thickness of 5 μm or less, the occurrence of display unevenness can be more effectively prevented when the laminated optical film is incorporated into an image display device. The reason for this effect is that the retardation films constituting the laminated optical film are generally thin and have poor shape retention. For example, if unevenness occurs in the adhesive layer for laminating the retardation film due to curing shrinkage or the like, the smoothness of the retardation film is deteriorated due to this, and the laminate smoothness of the laminated optical film is expected to be deteriorated. However, in the present invention, in addition to being able to suppress the incorporation of air bubbles into the adhesive composition before curing during lamination, the adhesive layer interposed between the first optical film and the second optical film has excellent adhesion, so it is thought that the occurrence of display unevenness can be more effectively prevented when the laminated optical film is incorporated into an image display device.

[0021] The present invention relates to a method for producing a laminated optical film in which at least a first optical film and a second optical film are laminated via an adhesive layer, the adhesive layer being formed from a cured layer of a first adhesive composition containing an amino-based silane coupling agent and a second adhesive composition containing an epoxy-based silane coupling agent.

[0022] The amino-based silane coupling agent and the epoxy-based silane coupling agent are, for example, compounds represented by the following general formula (I).

[0023] In the above general formula (I), a compound containing an amino group as the substituent X is an amino-based silane coupling agent, and a compound containing an epoxy group as the substituent X is an epoxy-based silane coupling agent.

[0024] In the above general formula (I), R １ , R ２ and R ３ R each independently represents a hydrogen atom, an alkoxy group, or an alkyl group, and at least one of them is an alkoxy group.１ , R ２ and R ３ The silane coupling agent used in the adhesive layer of the present invention is R １ ~R ３ It is preferred that all of the groups are alkoxy groups. n is an integer of 1 to 10, preferably 1 to 5.

[0025] Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, an isobutoxy group, a tert-butoxy group, a pentyloxy group, and a hexyloxy group, and preferred are a methoxy group and an ethoxy group. １ , R ２ and R ３ In addition to an alkoxy group, R may be, for example, a group that becomes a hydroxyl group by hydrolysis. In this case, R １ , R ２ and R ３ At least one or all of these may be groups that become hydroxyl groups upon hydrolysis.

[0026] <Amino-based silane coupling agent> The amino-based silane coupling agent is an amino-group-containing organosilicon compound in which the substituent X in the above general formula (I) is represented by the following formula (II).

[0027] In the above formula (II), R ４ and R ５ R4 and R5 may be the same or different. ４ and R ５ When R is an alkyl group or an aminoalkyl group, the number of carbon atoms in the alkyl group is preferably 6 or less, and more preferably 4 or less. From the viewpoint of improving adhesion to the optical film and water resistance, R ４ and R ５ is preferably a hydrogen atom or an aminoalkyl group. ２The reason for this is unclear, but it is thought to be due to the high reactivity of the amino group at the end of the silane coupling agent with polar functional groups such as hydroxyl groups on the surface of the optical film and with the epoxy groups of the epoxy-based silane coupling agent.

[0028] Specific examples of amino-based silane coupling agents include N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldiethoxysilane, N-2-(aminoethyl)-3-aminopropyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyldiethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, 3-aminopropyldimethylmethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N,N'-bis(2-aminoethyl)-6-(3-trihydroxysilylpropyl)amino-1,3,5-triazine-2,4-diamine, and hydrochlorides thereof.

[0029] Commercially available amino silane coupling agents include KBM-602, KBM-603, KBM-903, KBE-603, KBE-903 (all manufactured by Shin-Etsu Chemical Co., Ltd.), Z-6011, Z-6020, Z-6026, Z-6032, Z-6094, Z-6610 (all manufactured by Dow Corning Toray Co., Ltd.), A-1100, A-1110, A-1120, A-2120, Y-9669 (all manufactured by Momentive Performance Materials, Inc.), and the like.

[0030] The amino-based silane coupling agent may be used alone or in combination of two or more. Among the above, the amino-based silane coupling agent is preferably a compound in which the substituent X in the general formula (I) is represented by formula (II) and R ４ or R ５ However, amino-based silane coupling agents having an aminoalkyl group having 1 to 3 carbon atoms are preferably used.

[0031] <Epoxy-based silane coupling agent> The epoxy-based silane coupling agent is an epoxy-group-containing organosilicon compound represented by the above general formula (I), in which the substituent X is represented by the following formula (III), (IV) or (V).

[0032]

[0033] Specific examples of epoxy-based silane coupling agents include 2-(3,4-epoxycyclohexyl)ethylmethyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltrimethoxysilane, and 3-glycidoxypropyltriethoxysilane.

[0034] Commercially available epoxy silane coupling agents include KBM-303, KBM-402, KBM-403, KBE-402, and KBE-403 (all manufactured by Shin-Etsu Chemical Co., Ltd.), SH6040, Z-6040, Z-6042, Z-6043, and Z-6044 (all manufactured by Dow Corning Toray Co., Ltd.), and A-186, A-187, and A-1871 (all manufactured by Momentive Performance Materials, Inc.).

[0035] The epoxy silane coupling agent may be used alone or in combination of two or more. Among the above, an epoxy silane coupling agent in which the substituent X in the general formula (I) is represented by formula (IV) is preferably used.

[0036] <First Adhesive Composition and Second Adhesive Composition> The first adhesive composition for forming the adhesive layer contains at least an amino-based silane coupling agent, and the second adhesive composition contains at least an epoxy-based silane coupling agent. In the first adhesive composition and the second adhesive composition, water is preferably used as a solvent for dispersing or dissolving the silane coupling agent. When at least one or both of the first adhesive composition and the second adhesive composition contain water, the incorporation of air bubbles into the adhesive composition before curing during lamination can be more effectively suppressed. As a result, the smoothness of the adhesive layer can be further improved, thereby more effectively preventing display unevenness when the laminated optical film is incorporated into an image display device. From the standpoint of further improving the smoothness of the adhesive layer and more effectively preventing display unevenness when the laminated optical film is incorporated into an image display device, the concentration of the amino-based silane coupling agent in the first adhesive composition and the concentration of the epoxy-based silane coupling agent in the second adhesive composition are both preferably 0.5% by mass or more, more preferably 1% by mass or more. However, if the concentration of the amino-based silane coupling agent in the first adhesive composition and the concentration of the epoxy-based silane coupling agent in the second adhesive composition are excessively high, there is a risk of display unevenness occurring when the laminated optical film is incorporated into an image display device. Therefore, the concentration of the amino-based silane coupling agent in the first adhesive composition and the concentration of the epoxy-based silane coupling agent in the second adhesive composition are both preferably 20 mass% or less, and more preferably 10 mass% or less.

[0037] The first adhesive composition and the second adhesive composition may contain various additives other than the amino silane coupling agent or epoxy silane coupling agent and water as optional components, provided that the objectives and effects of the present invention are not impaired. Examples of such additives include leveling agents, wettability improvers, surfactants, plasticizers, UV absorbers, inorganic fillers, pigments, and dyes. However, the content of the additives in the adhesive is preferably 20 parts by weight or less, more preferably 10 parts by weight or less, even more preferably 5 parts by weight or less, and particularly preferably 3 parts by weight or less, based on 100 parts by weight of the amino silane coupling agent or epoxy silane coupling agent.

[0038] <Adhesive Layer> The adhesive layer provided in the laminated optical film according to the present invention can ensure sufficient adhesion to the first optical film and the second optical film even if it is thin. Therefore, from the viewpoint of thinning the laminated optical film, the thickness of the adhesive layer is preferably 1 nm or more and 200 nm or less, more preferably 2 nm or more and 80 nm or less, and even more preferably 3 nm or more and 60 nm or less.

[0039] <First Optical Film and Second Optical Film> At least one of the first optical film and the second optical film constituting the laminated optical film is preferably a retardation film. However, in the present invention, a laminated optical film in which two retardation films are laminated via an adhesive layer is preferred, as excellent laminate smoothness is required, particularly from the viewpoint of suppressing display unevenness. Examples of retardation films include retardation films having a front retardation of 40 nm or more and / or a thickness retardation of 80 nm or more. The front retardation is typically controlled to a range of 40 to 200 nm, and the thickness retardation is typically controlled to a range of 80 to 300 nm. Retardation films may include birefringent films obtained by uniaxially or biaxially stretching a polymer material, as well as oriented films of liquid crystal polymers and films in which an oriented layer of liquid crystal polymer is supported by a film. The thickness of the retardation film may be approximately 1 to 150 μm, but from the viewpoint of thinning, it is preferable to use retardation films having a thickness of 5 μm or less.

[0040] The retardation film may be a film satisfying the following formulas (1) to (3): 0.70<Re

[450] / Re

[550] <0.97 (1) 1.5×10 －３ < Δn < 6 × 10 －３ ... (2) 1.13<NZ<1.50 ... (3) (wherein Re

[450] and Re

[550] are in-plane retardation values ​​of the retardation film measured at 23°C with light of wavelengths of 450 nm and 550 nm, respectively; Δn is in-plane birefringence, which is nx-ny, where nx and ny are the refractive indices in the slow axis direction and the fast axis direction of the retardation film, respectively; and NZ is the ratio of nx-nz, which is the birefringence in the thickness direction, to nx-ny, which is the in-plane birefringence, where nz is the refractive index in the thickness direction of the retardation film).

[0041] In the laminated optical film according to the present invention, examples of optical films that can be used other than the retardation film include a polyvinyl alcohol film, a resin protective film, and a polarizing film that includes at least a polarizer and a resin protective film.

[0042] <Resin Protective Film> Materials constituting the resin protective film include thermoplastic resins with excellent transparency, mechanical strength, thermal stability, moisture barrier properties, and isotropy. Specific examples of such thermoplastic resins include cellulose resins such as triacetyl cellulose-based resin films, polyester resins, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth)acrylic resins, cyclic polyolefin resins (norbornene-based resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. The resin protective film may contain one or more suitable additives. Examples of additives include ultraviolet absorbers, antioxidants, lubricants, plasticizers, release agents, color inhibitors, flame retardants, nucleating agents, antistatic agents, pigments, and colorants. The content of the thermoplastic resin in the resin protective film is preferably 50 to 100% by mass, more preferably 50 to 99% by mass, even more preferably 60 to 98% by mass, and particularly preferably 70 to 97% by mass. If the content of the thermoplastic resin in the resin protective film is 50% by mass or less, the inherent properties of the thermoplastic resin, such as high transparency, may not be fully exhibited.

[0043] The material for forming the resin protective film is preferably one that is excellent in transparency, mechanical strength, thermal stability, moisture blocking property, isotropy, etc., and in particular, a moisture permeability of 150 g / m ２ / 24h or less is more preferable, and 140g / m ２ / 24h or less is particularly preferred, and 120g / m ２ / 24 hours or less is even more preferable.

[0044] A functional layer such as a hard coat layer, an anti-reflection layer, an anti-sticking layer, a diffusion layer, an anti-glare layer, etc. may be provided on the surface of the resin protective film to which the polarizer is not adhered. The functional layer such as the hard coat layer, the anti-reflection layer, the anti-sticking layer, the diffusion layer, or the anti-glare layer may be provided on the resin protective film itself, or may be provided separately as a layer separate from the resin protective film.

[0045] The thickness of the resin protective film can be determined as appropriate, but is generally about 1 to 500 μm, preferably 1 to 200 μm, and more preferably 1 to 80 μm, from the standpoints of strength, workability such as handleability, and thinness.

[0046] Polarizing Film Examples of polarizing films include polarizing films in which a resin protective film is laminated on at least one surface of a polarizer via a pressure-sensitive adhesive layer or a conventional adhesive layer such as a cured layer of an active energy ray-curable adhesive, or an adhesive layer formed using at least one or both of an amino-based silane coupling agent and an epoxy-based silane coupling agent. The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is not particularly limited, and can be appropriately selected from those based on, for example, acrylic polymers, silicone polymers, polyesters, polyurethanes, polyamides, polyethers, fluorine-based polymers, rubber-based polymers, and the like. In particular, pressure-sensitive adhesives that exhibit excellent optical transparency, moderate wettability, cohesion, and adhesive properties, and excellent weather resistance and heat resistance, such as acrylic pressure-sensitive adhesives, are preferred. The adhesive layer is formed from a cured layer of an adhesive composition containing at least a polymerizable compound, and is particularly preferably formed from a cured layer of an active energy ray-curable adhesive composition such as an electron beam-curable, ultraviolet-curable, or visible light-curable adhesive composition. Active energy ray-curable adhesive compositions can be classified into radical polymerization-curable adhesive compositions and cationically polymerizable adhesive compositions. The thickness of the polarizing film can be determined as appropriate, but from the viewpoint of thinning the laminated optical film, it is preferably 10 to 500 μm, more preferably 20 to 150 μm.

[0047] In the present invention, from the viewpoint of thinning, the thickness of the polarizer is preferably 10 μm or less, and more preferably 5 μm or less. Examples of such polarizers include those obtained by adsorbing iodine onto a hydrophilic polymer film such as a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film, or a partially saponified ethylene-vinyl acetate copolymer film, followed by uniaxial stretching.

[0048] A polarizer obtained by dyeing a polyvinyl alcohol-based film with iodine and uniaxially stretching it can be produced, for example, by immersing the polyvinyl alcohol in an iodine aqueous solution to dye it and then stretching it to 3 to 7 times its original length. If necessary, the polyvinyl alcohol-based film may contain boric acid, zinc sulfate, zinc chloride, or the like, or may be immersed in an aqueous solution of potassium iodide or the like. Furthermore, if necessary, the polyvinyl alcohol-based film may be immersed in water and washed before dyeing. Washing the polyvinyl alcohol-based film with water not only removes dirt and antiblocking agents from the polyvinyl alcohol-based film surface, but also swells the polyvinyl alcohol-based film, thereby preventing unevenness such as uneven dyeing. Stretching may be performed after dyeing with iodine, or the film may be stretched while dyeing, or the film may be dyed with iodine after stretching. Stretching may also be performed in an aqueous solution of boric acid, potassium iodide, or the like, or in a water bath.

[0049] Representative examples of the thin polarizer include the thin polarizers described in Japanese Patent No. 4751486, Japanese Patent No. 4751481, Japanese Patent No. 4815544, Japanese Patent No. 5048120, WO 2014 / 077599, and WO 2014 / 077636, and the like, as well as thin polarizers obtained by the manufacturing methods described therein.

[0050] Among the thin polarizers obtained by manufacturing methods including a stretching step and a dyeing step in a laminated state, those obtained by a manufacturing method including a stretching step in a boric acid aqueous solution as described in Japanese Patent Nos. 4751486, 4751481, and 4815544 are preferred because they can be stretched at a high magnification and have improved polarization performance. In particular, those obtained by a manufacturing method including a supplementary in-air stretching step before stretching in a boric acid aqueous solution as described in Japanese Patent Nos. 4751481 and 4815544 are preferred. These thin polarizers can be obtained by a manufacturing method including a stretching step and a dyeing step of a polyvinyl alcohol-based resin (hereinafter also referred to as PVA-based resin) layer and a stretching resin substrate in a laminated state. With this manufacturing method, even if the PVA-based resin layer is thin, it can be stretched without problems such as breakage due to stretching because it is supported by the stretching resin substrate.

[0051] Each step of the method for producing a laminated optical film according to the present invention will be described below.

[0052] <Coating Step> The method for producing a laminated optical film according to the present invention is characterized by having two coating steps: a first coating step of applying a first adhesive composition containing at least an amino-based silane coupling agent to the bonding surface of a first optical film, and a second coating step of applying a second adhesive composition containing at least an epoxy-based silane coupling agent to the bonding surface of a second optical film.

[0053] In the first coating step, a first adhesive composition containing at least an amino-based silane coupling agent is applied to the bonding surface of the first optical film. In the second coating step, a second adhesive composition containing at least an epoxy-based silane coupling agent is applied to the bonding surface of the second optical film. The first and second coating steps may be performed simultaneously, or one may be performed first. As described above, water is preferred as the solvent for dispersing or dissolving the silane coupling agent in the first adhesive composition and the second adhesive composition. However, if water remains in at least one or both of the first adhesive composition and the second adhesive composition in the subsequent bonding step, the first adhesive composition-coated surface of the first optical film and the second adhesive composition-coated surface of the second optical film can be bonded together to more effectively prevent air bubbles from being trapped in the adhesive composition before curing during bonding. As a result, the smoothness of the adhesive layer can be further improved, and display unevenness can be more effectively prevented when the laminated optical film is incorporated into an image display device. For this reason, it is preferable not to provide a drying step after the completion of the first coating step and the second coating step and before the laminating step. Even if a drying step is provided, in order to bond the first adhesive composition-coated surface of the first optical film to the second adhesive composition-coated surface of the second optical film in a state in which water remains in at least one or both of the first adhesive composition and the second adhesive composition in the subsequent laminating step, it is preferable to set the drying conditions in the drying step after the completion of the first coating step and the second coating step and before the laminating step as mild as possible, specifically, it is preferable to set the drying conditions to be in the range of a drying temperature of 40 to 70°C and a drying time of about 30 to 300 seconds.

[0054] When applying the first adhesive composition containing at least an amino-based silane coupling agent to the bonding surface of the first optical film, and when applying the second adhesive composition containing at least an epoxy-based silane coupling agent to the bonding surface of the second optical film, the coating method is appropriately selected depending on the viscosity of the adhesive composition and the desired thickness, and examples include a reverse coater, a gravure coater (direct, reverse, or offset), a bar reverse coater, a roll coater, a die coater, a bar coater, and a rod coater.

[0055] In particular, when the first optical film and the second optical film are retardation films, polarizing films, or the like, it is preferable to perform a surface modification treatment before the coating process. Examples of surface modification treatments include corona treatment, plasma treatment, and Itro treatment, with corona treatment being particularly preferable. Corona treatment generates reactive functional groups such as carbonyl groups and amino groups on the surface of the adherend, improving adhesion to the adhesive layer. Furthermore, the ashing effect removes foreign matter from the surface of the adherend and reduces surface irregularities, allowing the production of a laminated optical film with excellent appearance characteristics.

[0056] <Laminating Step> In the laminating step, the first adhesive composition coated surface of the first optical film and the second adhesive composition coated surface of the second optical film are laminated together using a roll laminator or the like.

[0057] In the bonding step, the first and second optical films are bonded to each other by curing the first and second adhesive compositions bonded together in the laminating step. In the bonding step, the films may be heated at 30 to 120°C for 1 to 60 minutes, for example, as needed.

[0058] When the laminated optical film according to the present invention is produced on a continuous line, the line speed depends on the curing time of the first adhesive composition and the second adhesive composition in the bonding step, but is preferably 1 to 500 m / min, more preferably 5 to 300 m / min, and even more preferably 10 to 100 m / min. If the line speed is too slow, productivity will be poor or the damage to the first optical film and the second optical film will be too great, making it impossible to produce a laminated optical film that can withstand durability tests and the like. If the line speed is too high, the first adhesive composition and the second adhesive composition will be insufficiently cured, and the desired adhesive properties may not be obtained.

[0059] The obtained laminated optical film may be provided with an adhesive layer for adhering to other members such as a liquid crystal cell, etc. The adhesive for forming the adhesive layer may be the same as that described above.

[0060] The exposed surface of the adhesive layer is covered with a temporary separator to prevent contamination until the adhesive layer is put into practical use. This prevents contact with the adhesive layer during normal handling. As the separator, apart from the thickness requirements described above, any suitable conventional separator can be used, such as a suitable thin sheet such as a plastic film, rubber sheet, paper, cloth, nonwoven fabric, net, foam sheet, metal foil, or a laminate thereof, optionally coated with a suitable release agent such as a silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide-based release agent.

[0061] The laminated optical film of the present invention can be preferably used to form various devices such as liquid crystal displays and organic EL displays. The formation of various image displays can be carried out in a conventional manner. In other words, various image displays are generally formed by appropriately assembling an image display cell, a polarizing film or optical film, and, if necessary, components such as an illumination system, and incorporating a driving circuit. However, in the present invention, there are no particular limitations except for the use of the polarizing film or optical film of the present invention, and conventional methods can be used. Any type of image display cell, such as a TN type, STN type, or π type, can also be used.

[0062] Appropriate image display devices can be formed, such as those in which a laminated optical film is disposed on one or both sides of an image display cell, or those in which a backlight or reflector is used in the illumination system. In such cases, the laminated optical film according to the present invention can be disposed on one or both sides of the image display cell. When laminated optical films are disposed on both sides, they may be the same or different. Furthermore, when forming an image display device, appropriate components such as a diffuser plate, anti-glare layer, anti-reflection film, protective plate, prism array, lens array sheet, light diffuser plate, backlight, etc. can be disposed in one or more layers at appropriate positions.

[0063] Examples of the present invention will be described below, but the embodiments of the present invention are not limited to these.

[0064] <First Optical Film and Second Optical Film> Retardation Film 1 described below was used as the first optical film, and Retardation Film 2 described below was used as the second optical film. Retardation Film 1 and Retardation Film 2 were produced by the following method using the photopolymerizable liquid crystal composition prepared below as a raw material.

[0065] <Photopolymerizable Liquid Crystal Composition> A photopolymerizable liquid crystal compound exhibiting a nematic liquid crystal phase (BASF's "Paliocolor LC242") was dissolved in cyclopentanone to prepare a solution with a solids concentration of 30% by weight. A surfactant (BYK-360 manufactured by BYK-Chemie) and a photopolymerization initiator (IGM Resins' "Omnirad 907") were added to this solution to prepare a photopolymerizable liquid crystal composition that would serve as a raw material for producing a retardation film. The amounts of the leveling agent and polymerization initiator added were 0.01 parts by weight and 3 parts by weight, respectively, relative to 100 parts by weight of the photopolymerizable liquid crystal compound.

[0066] <Retardation Film 1 (λ / 2 Retardation Film)> A biaxially stretched norbornene film (Zeon Corporation's "ZEONORFILM," thickness: 33 μm, front retardation: 135 nm) was used as a substrate. The liquid crystal composition was applied to the substrate using a bar coater so that the phase difference was λ / 2, and the film was heated at 100° C. for 3 minutes to align the liquid crystal. After cooling to room temperature, the film was irradiated with an accumulated light intensity of 400 mJ / cm under a nitrogen atmosphere. ２ The first liquid crystal alignment solidified layer was homogeneously aligned and had a thickness of 2 μm.

[0067] <Retardation Film 2 (λ / 4 Retardation Film)> A biaxially stretched norbornene film (Zeon Corporation's "ZEONORFILM", thickness: 33 μm, front retardation: 135 nm) was used as a substrate. The liquid crystal composition was applied to the substrate using a bar coater so that the phase difference was λ / 4, and the substrate was heated at 100°C for 3 minutes to align the liquid crystal. After cooling to room temperature, the substrate was photocured by irradiating it with ultraviolet light at an integrated light intensity of 400 mJ / cm2 under a nitrogen atmosphere, obtaining a laminate having a substrate / retardation film 2 (λ / 4 retardation film) configuration. The second liquid crystal alignment solidified layer was homogeneously oriented and had a thickness of 2 μm.

[0068] <Laminated Optical Film> Examples 1 to 5 A corona treatment was performed using a corona treatment machine at a treatment density of 50 W·min / m on the first optical film (retardation film 1) surface of a laminate having a substrate / first optical film (retardation film 1) configuration and on the second optical film (retardation film 2) surface of a laminate having a substrate / second optical film (retardation film 2) configuration. ２The corona treatment was carried out. Using an MCD coater (manufactured by Fuji Machine Co., Ltd.) (cell shape: honeycomb, gravure roll line count: 1000 / inch, rotation speed 130% / relative to line speed), a first adhesive composition having the composition shown in Table 1 was applied to the corona-treated surface of the first optical film (retardation film 1) to a coating thickness of 1.2 μm (first coating step). The numerical values ​​in Table 1 represent the blend amount (% by mass) when the total amount of the composition is taken as 100% by mass. The first adhesive composition was prepared by mixing water and an amine-based silane coupling agent according to the formulation shown in Table 1. The amine-based silane coupling agent used was N-2-(aminoethyl)-3-aminopropyltriethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name "KBM-603", molecular weight: 222.4). Furthermore, using an MCD coater (manufactured by Fuji Machinery Co., Ltd.) (cell shape: honeycomb, gravure roll line count: 1000 / inch, rotation speed 130% / relative to line speed), a second adhesive composition having the composition shown in Table 1 was applied to the corona-treated surface of the second optical film (retardation film 2) to a coating thickness of 1 μm (second coating step). The second adhesive composition was prepared by mixing water and an epoxy-based silane coupling agent according to the formulation shown in Table 1. 3-glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name "KBM-403", molecular weight: 236.3) was used as the epoxy-based silane coupling agent.

[0069] After the first and second coating steps described above, the first adhesive composition-coated surface of the first optical film and the second adhesive composition-coated surface of the second optical film were bonded together using a roller so that the slow axis of the λ / 4 retardation film (retardation film 2) was at a 60° angle with the slow axis of the λ / 2 retardation film (retardation film 1) (lamination step). The lamination line speed was 15 m / min. Note that no drying step was performed after the first and second coating steps, and the lamination step was performed within at least 10 seconds after the completion of the first and second coating steps.

[0070] After the lamination step, the first adhesive composition and the second adhesive composition bonded in the lamination step were cured by heating at 40°C for 16 hours, thereby bonding the first optical film and the second optical film (adhesion step). After the adhesion step, the substrates (biaxially stretched norbornene-based films) were peeled from the first optical film and the second optical film, respectively, to obtain laminated optical films. Evaluation methods for the obtained laminated optical films will be described later.

[0071] Comparative Example 1 A laminated optical film was produced in the same manner as in Examples 1 to 5, except that only the first coating step was carried out and the second coating step was not carried out.

[0072] Comparative Example 2 A laminated optical film was produced in the same manner as in Examples 1 to 5, except that only the second coating step was carried out and the first coating step was not carried out.

[0073] Comparative Example 3 A laminated optical film was produced in the same manner as in Examples 1 to 5, except that, instead of performing the first and second steps, an adhesive composition having the composition shown in Table 1 (an amine-based silane coupling agent and an epoxy-based silane coupling agent mixed in advance in water) was applied to only the corona-treated surface of the first optical film (retardation film 1) using an MCD coater (manufactured by Fuji Machine Co., Ltd.) (cell shape: honeycomb, gravure roll line count: 1,000 / inch, rotation speed 130% / relative to line speed) to a coating thickness of 1 μm. The numerical values ​​in Table 1 represent the blend amounts (% by mass) when the total amount of the composition is taken as 100% by mass.

[0074] [Pot life of adhesive composition] The pot life of the first adhesive composition and second adhesive composition used in Examples 1 to 5, the first adhesive composition used in Comparative Example 1, the second adhesive composition used in Comparative Example 2, and the adhesive composition used in Comparative Example 3 (an amine-based silane coupling agent and an epoxy-based silane coupling agent mixed in water in advance) was evaluated visually, and compositions that became cloudy within one month after preparation were marked with "X", and compositions that remained transparent even after one month were marked with "O".

[0075] [Adhesive Layer Thickness (nm) (TEM Measurement)] Cross-sectional TEM observation was performed by frozen ultrathin sectioning including heavy metal staining using a Hitachi HT7820. The accelerating voltage during the measurement was 100 kV.

[0076] [Adhesion] The obtained laminated optical film was cut into a size of 200 mm x 15 mm, and the laminated optical film was bonded to a glass plate. Then, a cutter knife was used to make an incision between the first optical film and the second optical film, and the first optical film and the second optical film were peeled in a 90-degree direction at a peeling speed of 5000 mm / min using an angle-free type adhesive / film peeling analyzer "VPA-2" (manufactured by Kyowa Interface Science Co., Ltd.), and the peel strength (N / 15 mm) was evaluated as "room temperature adhesion." In addition, the obtained laminated optical film was left in an environment of 20 ° C. and 98% humidity, and the peel strength (N / 15 mm) measured in the same manner was evaluated as "adhesion after humidification."

[0077] [Presence or absence of display unevenness due to adhesive layer] When the obtained laminated optical film was attached to a blackboard, it was evaluated based on whether color unevenness due to the adhesive layer was visually recognized. If it was not recognized, it was judged as "◯" that display unevenness did not occur, and if it was recognized, it was judged as "×" that display unevenness occurred.

[0078]

[0079] The results in Table 1 show that the laminated optical film of Comparative Example 1, in which only the first coating step was performed without the second coating step, i.e., the first optical film and the second optical film were bonded using only a first adhesive composition composed of an amino-based silane coupling agent and water, exhibited poor adhesion after humidification. The laminated optical film of Comparative Example 2, in which only the second coating step was performed without the first coating step, i.e., the second adhesive composition composed of an epoxy-based silane coupling agent and water was used, failed to bond the first optical film and the second optical film. Furthermore, the adhesive composition used in Comparative Example 3, in which the amine-based silane coupling agent and the epoxy-based silane coupling agent were mixed in water in advance, had a poor pot life, posing production management problems. On the other hand, in Examples 1 to 5, laminated optical films were produced that exhibited reduced display unevenness due to the adhesive layer and had excellent adhesive layer adhesion. Furthermore, in Examples 1 to 5, laminated optical films with excellent pot life during the manufacturing process were produced.

Claims

1. A method for producing a laminated optical film in which at least a first optical film and a second optical film are laminated via an adhesive layer, comprising: a first coating step of coating a first adhesive composition containing at least an amino-based silane coupling agent on a bonding surface of the first optical film; a second coating step of coating a second adhesive composition containing at least an epoxy-based silane coupling agent on a bonding surface of the second optical film; a laminating step of bonding the first adhesive composition-coated surface of the first optical film and the second adhesive composition-coated surface of the second optical film together; and a bonding step of curing the first adhesive composition and the second adhesive composition bonded together in the laminating step, thereby bonding the first optical film and the second optical film together.

2. The method for producing a laminated optical film according to claim 1, wherein at least one or both of the first adhesive composition and the second adhesive composition is an adhesive composition containing water.

3. The method for producing a laminated optical film according to claim 2, wherein in the laminating step, the first adhesive composition-coated surface of the first optical film and the second adhesive composition-coated surface of the second optical film are bonded together while water remains in at least one or both of the first adhesive composition and the second adhesive composition.

4. The method for producing a laminated optical film described in claim 1, wherein both the first adhesive composition and the second adhesive composition contain water, and the concentration of the amino-based silane coupling agent in the first adhesive composition and the concentration of the epoxy-based silane coupling agent in the second adhesive composition are both 0.5 mass% or more.

5. The method for producing a laminated optical film according to any one of claims 1 to 4, wherein the first optical film is a retardation film.

6. The laminated optical film according to claim 5, wherein the thickness of the retardation film is 5 μm or less.

7. The method for producing a laminated optical film according to any one of claims 1 to 6, wherein the second optical film is a retardation film.

8. The method for producing a laminated optical film according to claim 7, wherein the thickness of the retardation film is 5 μm or less.

9. The method for producing a laminated optical film according to any one of claims 1 to 8, wherein the thickness of the adhesive layer is 1 to 200 nm.

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