Method for manufacturing laminated optical film

Abstract

To provide a method for manufacturing a laminated optical film that has reduced display unevenness caused by an adhesive layer, is excellent in adhesive properties of the adhesive layer, and has excellent pot life in a manufacturing process.SOLUTION: A method for manufacturing a laminated optical film with at least a first optical film and a second optical film laminated via an adhesive layer, includes the steps of: a first application step of applying a first adhesive composition containing at least an amino-based silane coupling agent to a bonding surface of the first optical film; a second application step of applying a second adhesive composition containing at least an epoxy-based silane coupling agent to a bonding surface of the second optical film; a bonding 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 an adhesion step of adhering the first optical film and the second optical film by hardening the first adhesive composition and the second adhesive composition bonded in the bonding step.SELECTED DRAWING: None

Description

[Technical Field]

[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. [Background technology]

[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, there has been the issue of how difficult it is to ensure adhesion between optical films when bonding thin layers of optical films.

[0003] Incidentally, Patent Document 1 listed below describes an adhesive for bonding optical films that has good adhesion and water resistance even when the film is thin, and 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-59215 Summary of the Invention [Problem to be solved by the invention]

[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 the method for manufacturing the laminated optical film.

[0006] The present invention was developed in consideration of the above-mentioned 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. [Means for solving the problem]

[0007] That is, the present invention relates to a method (1) 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 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 above-mentioned 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 (2) for producing a laminated optical film, a method (3) for producing a laminated optical film 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 while 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, preferred is method (4) for producing a laminated optical film, 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 methods (1) to (6) for producing a laminated optical film, the method (7) for producing a laminated optical film 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. [Effects of the Invention]

[0016] In the method for producing a laminated optical film according to the present invention, the adhesive layer for laminating the first and second optical films is formed from a cured layer of a first adhesive composition containing an amino-silane coupling agent and a second adhesive composition containing an epoxy-silane coupling agent. The amino-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-silane coupling agent are highly reactive with the amino groups of the amino-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 and second optical films.

[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 are highly reactive with each other. Due to this tendency, for example, in a method of forming an adhesive layer by applying an adhesive containing an amino-based silane coupling agent and an epoxy-based silane coupling agent in a predetermined ratio to one optical film, 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 steps, and the amino-based silane coupling agent and the epoxy-based silane coupling agent come into contact (be bonded) in the final lamination process, and then react with each other. This ensures a sufficient pot life in the production process. As a result, production management becomes easier.

[0019] (2) In the laminating step following the first and second coating steps, 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 do occur, 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 contain 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 during the bonding process, 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 higher, 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, this will cause the smoothness of the retardation film to deteriorate, and the laminate smoothness of the laminated optical film is expected to deteriorate. However, in the present invention, it is possible to suppress the incorporation of air bubbles into the adhesive composition before curing during lamination, and 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. DETAILED DESCRIPTION OF THE INVENTION

[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). [ka]

[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 preferable that all of the following are alkoxy groups. n is an integer of 1 to 10, and 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). [ka]

[0027] In the above formula (II), R4 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, 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. When a silane coupling agent has an unsubstituted amino group (-NH2) at the end, adhesion tends to improve. The reason for this is not clear, 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 optical film surface and with the epoxy groups of epoxy-based silane coupling agents.

[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).

[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, an amino-based silane coupling agent having an aminoalkyl group having 1 to 3 carbon atoms is preferably used.

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

[0032] [ka]

[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).

[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. Water is preferred as the solvent for dispersing or dissolving the silane coupling agent in the first adhesive composition and the second adhesive composition. 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% by mass or less, and more preferably 10% by 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 of 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 and second optical films 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 the retardation film include a retardation film 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. Examples of the retardation film include birefringent films obtained by uniaxially or biaxially stretching a polymer material, 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 a retardation film having a thickness of 5 μm or less.

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

[0450] / Re

[0550] <0.97···(1) 1.5×10 -3 <Δn<6×10 -3 ···(2) 1.13 <NZ<1.50···(3) (wherein Re

[0450] and Re

[0550] 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 of the retardation film in the slow axis direction and the fast axis direction, 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) may be used.

[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> The resin protective film is made of a thermoplastic resin that exhibits 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 properties, 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, 120g / m 2 / 24h 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 conventional adhesive layer, such as a pressure-sensitive adhesive layer or 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 adhesive forming the pressure-sensitive adhesive layer is not particularly limited, but suitable adhesives based on, for example, acrylic polymers, silicone polymers, polyesters, polyurethanes, polyamides, polyethers, fluorine-based polymers, or rubber-based polymers can be selected and used. In particular, adhesives such as acrylic pressure-sensitive adhesives, which have excellent optical transparency, adequate wettability, cohesion, and adhesive properties, and excellent weather resistance and heat resistance, 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 reducing the thickness of the laminated optical film, it is preferably 10 to 500 μm, more preferably 20 to 150 μm.

[0047] <Polarizer> In the present invention, from the viewpoint of thinning, the thickness of the polarizer is preferably 10 μm or less, more preferably 5 μm or less. Examples of such polarizers include those obtained by uniaxially stretching 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, after iodine is adsorbed thereon.

[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 solution may contain boric acid, zinc sulfate, zinc chloride, or the like, or it 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 surface of the polyvinyl alcohol-based film, 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 be performed in an aqueous solution of boric acid, potassium iodide, or the like, or in a water bath.

[0049] Representative examples of thin polarizers include: Patent No. 4751486 specification, Patent No. 4751481 specification, Patent No. 4815544 specification, Patent No. 5048120 specification, International Publication No. 2014 / 077599, International Publication No. 2014 / 077636, or a thin polarizer obtained by the manufacturing method described therein.

[0050] Among the thin polarizers obtained by manufacturing methods including stretching and dyeing a laminate, those obtained by manufacturing methods including stretching 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 manufacturing methods 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 manufacturing methods including stretching a polyvinyl alcohol-based resin (hereinafter also referred to as PVA-based resin) layer and a stretching resin substrate in a laminate state, and dyeing the layer. 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 process> 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 coating a first adhesive composition containing at least an amino-based silane coupling agent onto 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 onto 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 and second adhesive compositions. However, if water remains in at least one or both of the first and second adhesive compositions 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 and second coating steps and before the laminating step. Even if a drying step is provided, the drying conditions in the drying step after the completion of the first and second coating steps and before the laminating step are preferably as gentle as possible, so that in the subsequent 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. Specifically, the drying conditions are preferably within 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 adherend surface, improving adhesion to the adhesive layer. Furthermore, the ashing effect removes foreign matter from the adherend surface and reduces surface irregularities, allowing the production of a laminated optical film with excellent appearance characteristics.

[0056] <Lamination process> 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] <Adhesion process> In the bonding step, the first and second adhesive compositions bonded in the laminating step are cured to bond the first and second optical films together. 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 not cure sufficiently, and the desired adhesiveness may not be achieved.

[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. [Example]

[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> The first optical film was a retardation film 1 described below, and the second optical film was a retardation film 2 described below. Retardation films 1 and 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 "Paliocolor LC242") was dissolved in cyclopentanone to prepare a solution with a solids concentration of 30 wt%. To this solution, a surfactant (BYK-Chemie "BYK-360") and a photopolymerization initiator (IGM Resins "Omnirad907") were added to prepare a photopolymerizable liquid crystal composition, which will be used as the raw material for producing retardation films. The amounts of the leveling agent and polymerization initiator added were 0.01 and 3 parts by weight, respectively, per 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 "Zeonor Film", thickness: 33 μm, front retardation: 135 nm) was used as a substrate. The liquid crystal composition was applied to the substrate with a bar coater so that the phase difference was λ / 2, and the liquid crystal was aligned by heating at 100°C for 3 minutes. After cooling to room temperature, the liquid crystal was aligned by irradiating the film with an integrated light dose of 400 mJ / cm under a nitrogen atmosphere. 2 The film was photocured by irradiating it with ultraviolet light to obtain a laminate having a structure of substrate / retardation film 1 (λ / 2 retardation film). 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)> Using a biaxially stretched norbornene film (Zeon Corporation's "ZEONORFILM," thickness: 33 μm, front retardation: 135 nm) as a substrate, the above liquid crystal composition was applied to the substrate using a bar coater so that the phase difference was λ / 4, and the liquid crystal was aligned by heating at 100°C for 3 minutes. After cooling to room temperature, the film was photocured by irradiating it with ultraviolet light at an integrated dose of 400 mJ / cm2 in a nitrogen atmosphere, obtaining a laminate having a substrate / phase difference film 2 (λ / 4 phase difference film) configuration. The second liquid crystal alignment solidified layer was homogeneously aligned and had a thickness of 2 μm.

[0068] <Laminated optical film> Examples 1 to 5 A corona treatment was performed 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 using a corona treatment machine at a treatment density of 50 W·min / m 2The corona treatment was carried out as follows. Using an MCD coater (manufactured by Fuji Machine Co., Ltd.) (cell shape: honeycomb, gravure roll line count: 1000 rolls / inch, rotation speed: 130% / relative to line speed), the 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 values ​​in Table 1 represent the blending amounts (% 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. N-2-(aminoethyl)-3-aminopropyltriethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name "KBM-603", molecular weight: 222.4) was used as the amine-based silane coupling agent. Furthermore, using an MCD coater (manufactured by Fuji Machinery Co., Ltd.) (cell shape: honeycomb, gravure roll line count: 1000 rolls / inch, rotation speed 130% / 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 line speed for lamination 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 first and second coating steps were completed.

[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 (bonding step). After the bonding 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 Laminated optical films were produced in the same manner as in Examples 1 to 5, except that instead of performing the first and second steps, an adhesive composition (an amine-based silane coupling agent and an epoxy-based silane coupling agent mixed in water in advance) having the composition shown in Table 1 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: 1000 rolls / 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 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 visually evaluated, and compositions that became cloudy within one month after preparation were marked with "X", and compositions that remained transparent even after more than one month were marked with "O".

[0075] [Adhesive layer thickness (nm) (TEM measurement)] Cross-sectional TEM observation was performed using a Hitachi HT7820 cryo-ultrathin sectioning method including heavy metal staining. The accelerating voltage during the measurement was set to 100 kV.

[0076] [Adhesion] The resulting laminated optical film was cut into a 200mm x 15mm piece and bonded to a glass plate. An incision was then made between the first and second optical films with a utility knife, and the first and second optical films were peeled at a 90-degree angle at a peel rate of 5000mm / min using a "VPA-2" angle-flexible adhesive and film peeling analyzer (Kyowa Interface Science Co., Ltd.). The peel strength (N / 15mm) was evaluated as "room temperature adhesion." The resulting laminated optical film was also left in an environment with a temperature of 20°C and humidity of 98%, and the peel strength (N / 15mm) measured in the same way was evaluated as "post-humidification adhesion."

[0077] [Whether or not display unevenness occurs due to the adhesive layer] When the obtained laminated optical film was attached to a blackboard, the color unevenness due to the adhesive layer was visually recognized and evaluated as to whether it was possible to visually recognize it. If it was not visible, it was judged as "◯" that no display unevenness occurred, and if it was visible, it was judged as "×" that display unevenness occurred.

[0078] [Table 1]

[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, showed 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 a problem in terms of production management. 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 onto a bonding surface of the first optical film; and a second coating step of coating a second adhesive composition containing at least an epoxy-based silane coupling agent onto a bonding surface of the second optical film. a lamination step of laminating a first adhesive composition-coated surface of the first optical film and a second adhesive composition-coated surface of the second optical film; and a bonding step of bonding the first optical film and the second optical film together by curing the first adhesive composition and the second adhesive composition that have been bonded together in the bonding step.

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

3. 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 in a state in which water remains in at least one or both of the first adhesive composition and the second adhesive composition.

4. 2. The method for producing a laminated optical film according to 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% by mass or more.

5. The method for producing a laminated optical film according to claim 1 , wherein the first optical film is a retardation film.

6. 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 claim 1 , wherein the second optical film is a retardation film.

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

9. 2. The method for producing a laminated optical film according to claim 1, wherein the adhesive layer has a thickness of 1 to 200 nm.

Images