JP7623482B2 - Optical film, method for producing optical film, optical member, and image display device - Google Patents

Description

The present invention relates to an optical film, a method for manufacturing an optical film, an optical component, and an image display device.

Liquid crystal display devices and organic EL display devices are used for various image displays such as monitors and televisions. Liquid crystal display devices use polarizing plates. Organic EL display devices use polarizing plates and quarter-wave plates to prevent reflection of external light. Polarizing plates usually include a polarizer and a polarizer protective film attached to at least one surface of the polarizer via an adhesive layer.

Conventionally, cellulose-based films have been widely used as polarizer protective films. In recent years, films made of acrylic, polyester, polycarbonate, cyclic polyolefin, etc. have also been used. Although these films have low moisture permeability and excellent durability compared to cellulose-based films, the adhesion between these films and PVA-based polarizers is inferior to that of cellulose-based films. For this reason, a method has been proposed in which an easy-adhesion layer is provided on the surface of these films to improve the adhesion between the film and the polarizer. For example, Patent Document 1 describes that by providing an easy-adhesion layer containing fine particles and a binder resin on the surface of an acrylic film, it is possible to not only improve the adhesion between the acrylic film and the polarizer but also suppress blocking.

Patent Document 2 describes that the easy-adhesion layer contains alkaline components such as ammonia and amines, that excessive alkaline components remaining in the easy-adhesion layer deteriorate the polarizer, but that the alkaline components can also act as a catalyst to promote the reaction of the binder resin (precursor), and that the alkaline components improve the dispersibility of inorganic fine particles present in the easy-adhesion layer. It also describes that the alkaline components can be volatilized and removed by heating the easy-adhesion composition after coating it on a film substrate, thereby reducing the amount of alkaline components remaining in the easy-adhesion layer.

JP 2010-55062 A JP 2020-16872 A

However, for example, the adhesion between the film and the easy-adhesion layer and the uniformity of the easy-adhesion layer have not been fully considered. Also, for example, in the technology described in Patent Document 2, it is relatively difficult to adjust the amount of remaining alkaline components.

In view of the above circumstances, the present inventors have conducted extensive research and have completed the inventions described below in [1] to [9].
[1] An optical film having a resin film and an easy-adhesion layer formed on a surface of the resin film, the easy-adhesion layer containing a binder resin, a polyamine, and fine particles, the polyamine being a polymer having a plurality of amino groups, the plurality of amino groups including at least one selected from the group consisting of a secondary amino group and a tertiary amino group, and the content of the polyamine in the easy-adhesion layer being 0.0090% by weight to 1.4100% by weight.
[2] The optical film according to [1], wherein the binder resin contains a urethane resin.
[3] The optical film according to [1] or [2], wherein the plurality of amino groups include a primary amino group, the secondary amino group, and the tertiary amino group.
[4] The optical film according to any one of claims [1] to [3], wherein the polyamine comprises a polyalkyleneimine.
[5] The optical film according to [4], wherein the polyalkyleneimine contains a primary amino group, the secondary amino group, and the tertiary amino group, and has a branched structure.
[6] The optical film according to any one of [1] to [5], wherein the resin film contains a (meth)acrylic polymer.
[7] An optical member comprising the optical film according to any one of [1] to [6].
[8] An image display device comprising the optical film according to any one of [1] to [6].
[9] A method for producing an optical film according to any one of [1] to [6], comprising the steps of: applying an easy-adhesion composition containing a binder resin, a polyamine, and fine particles onto a surface of a resin film to form a coating film of the easy-adhesion composition; and drying the coating film to form an easy-adhesion layer containing the binder resin, the polyamine, and the fine particles on the surface of the resin film; the polyamine is a polymer having a plurality of amino groups, and the plurality of amino groups include at least one selected from the group consisting of a secondary amino group and a tertiary amino group.

The optical film of the present invention has a resin film and an easy-adhesion layer, and has excellent adhesion between them. In addition, the optical film of the present invention has an alkaline component contained in the easy-adhesion layer which is a polymer that is not easily volatilized during the production of the optical film, so that the amount of the alkaline component contained in the easy-adhesion layer is easy to control.

Unless otherwise specified, the term "resin" in this specification is a broader concept than "polymer." A resin may be composed of, for example, one or more polymers, and may contain materials other than polymers as necessary, such as additives such as ultraviolet absorbers, antioxidants, fillers, compatibilizers, and stabilizers.

[Optical film]
The optical film according to this embodiment has a resin film and an easy-adhesion layer formed on the surface of the resin film.

[Resin film]
The resin film is not particularly limited, but may be a film made of a material such as a (meth)acrylic polymer, polyester, polycarbonate, or cyclic polyolefin. Among these, an acrylic resin film obtained by molding an acrylic resin containing a (meth)acrylic polymer is preferred. The content of the (meth)acrylic polymer in the acrylic resin is usually 30% by weight or more, preferably 50% by weight or more, more preferably 70% by weight or more, particularly preferably 90% by weight or more, and most preferably 95% by weight or more.

The (meth)acrylic polymer is a polymer having structural units ((meth)acrylic acid ester units) derived from (meth)acrylic acid ester monomers. The content of (meth)acrylic acid ester units in the (meth)acrylic polymer is usually 10% by weight or more, preferably 30% by weight or more, more preferably 50% by weight or more, and particularly preferably 70% by weight or more. The weight average molecular weight of the (meth)acrylic polymer is preferably 10,000 to 500,000, and more preferably 50,000 to 300,000.

The (meth)acrylic acid ester unit is, for example, a structural unit derived from each monomer of methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, chloromethyl (meth)acrylate, 2-chloroethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2,3,4,5,6-pentahydroxyhexyl (meth)acrylate, and 2,3,4,5-tetrahydroxypentyl (meth)acrylate. The (meth)acrylic polymer preferably has a structural unit derived from methyl (meth)acrylate, in which case the optical properties and thermal stability of the finally obtained optical film are improved. The (meth)acrylic polymer may have two or more types of (meth)acrylic acid ester units.

The (meth)acrylic polymer may have a structural unit other than the (meth)acrylic acid ester unit. Such a structural unit is, for example, a structural unit derived from each monomer of styrene, vinyl toluene, α-methylstyrene, α-hydroxymethylstyrene, α-hydroxyethylstyrene, acrylonitrile, methacrylonitrile, ethylene, propylene, 4-methyl-1-pentene, vinyl acetate, 2-hydroxymethyl-1-butene, methyl vinyl ketone, N-vinylpyrrolidone, and N-vinylcarbazole. The (meth)acrylic polymer may have two or more of these structural units. When the (meth)acrylic polymer has an N-vinylpyrrolidone unit or an N-vinylcarbazole unit, the degree of freedom in controlling the wavelength dispersion of birefringence in the optical film is improved. For example, in the visible light region, a retardation film is obtained that exhibits wavelength dispersion (so-called reverse wavelength dispersion) in which the birefringence becomes smaller (the absolute value of the retardation becomes smaller) as the wavelength of light becomes shorter. The retardation film is suitable as a positive retardation film.

The (meth)acrylic polymer may have a ring structure in the main chain. Such a (meth)acrylic polymer can be obtained, for example, by copolymerizing a (meth)acrylic acid ester monomer with a monomer having a ring structure, or by polymerizing a monomer group containing a (meth)acrylic acid ester monomer and then carrying out a cyclization reaction. When the (meth)acrylic polymer has a ring structure in the main chain, the total content of the (meth)acrylic acid ester unit and the ring structure may be 50% by weight or more.

In addition, when a ring structure is introduced into the main chain by a cyclization reaction after polymerization, it is preferable to form the (meth)acrylic polymer by copolymerization of a monomer group including a monomer having a hydroxyl group and/or a carboxylic acid group. Examples of the monomer having a hydroxyl group are 2-(hydroxymethyl)methyl acrylate, 2-(hydroxymethyl)ethyl acrylate, 2-(hydroxymethyl)isopropyl acrylate, 2-(hydroxymethyl)butyl acrylate, 2-(hydroxyethyl)methyl acrylate, methallyl alcohol, and allyl alcohol. Examples of the monomer having a carboxylic acid group are acrylic acid, methacrylic acid, crotonic acid, 2-(hydroxymethyl)acrylic acid, and 2-(hydroxyethyl)acrylic acid. Two or more of these monomers may be used. It is not necessary for all of the monomers to be converted into a ring structure during the cyclization reaction, and the (meth)acrylic polymer after the cyclization reaction may have structural units derived from these monomers.

It is preferable that the (meth)acrylic polymer has a ring structure in the main chain. In this way, the acrylic resin film has excellent heat resistance and hardness. In addition, when it is made into a stretched film, it exhibits a large phase difference, making it suitable for use as a phase difference film or a polarizer protective film that functions as a phase difference film.

The ring structure is, for example, at least one selected from an N-substituted maleimide structure, a maleic anhydride structure, a glutarimide structure, a glutaric anhydride structure, and a lactone ring structure. The N-substituted maleimide structure is, for example, a cyclohexylmaleimide structure, a methylmaleimide structure, a phenylmaleimide structure, and a benzylmaleimide structure. From the viewpoint of the heat resistance of the optical film, the ring structure is preferably a lactone ring structure, a cyclic imide structure (for example, an N-alkyl substituted maleimide structure, a glutarimide structure), or a cyclic anhydride structure (for example, a maleic anhydride structure and a glutaric anhydride structure). The optical film of this embodiment can be used as a retardation film. From the viewpoint of imparting a positive retardation to the optical film as a retardation film, the ring structure is preferably a lactone ring structure, a glutarimide structure, and a glutaric anhydride structure. From the viewpoint of improving the wavelength dispersion of birefringence in the retardation film, the ring structure is preferably a lactone ring structure.

The following general formula (1) shows the glutaric anhydride structure and the glutarimide structure.

In the general formula (1), ^R1 and ^R2 are each independently a hydrogen atom or a methyl group, and ^X1 is an oxygen atom or a nitrogen atom. When ^X1 is an oxygen atom, ^R3 does not exist, and when ^X1 is a nitrogen atom, ^R3 is a hydrogen atom, a linear alkyl group having 1 to 6 carbon atoms, a cyclopentyl group, a cyclohexyl group, a benzyl group, or a phenyl group.

When ^X1 is an oxygen atom, the ring structure represented by the general formula (1) is a glutaric anhydride structure. The glutaric anhydride structure can be formed, for example, by intramolecular dealcoholization cyclization condensation of a copolymer of a (meth)acrylic acid ester and (meth)acrylic acid. When ^X1 is a nitrogen atom, the ring structure represented by the general formula (1) is a glutarimide structure. The glutarimide structure can be formed, for example, by imidizing a (meth)acrylic acid ester polymer with an imidizing agent such as methylamine.

The maleic anhydride structure and N-substituted maleimide structure are shown in the following general formula (2).

In the general formula (2), ^R4 and ^R5 are each independently a hydrogen atom or a methyl group, and ^X2 is an oxygen atom or a nitrogen atom. When ^X2 is an oxygen atom, ^R6 does not exist, and when ^X2 is a nitrogen atom, ^R6 is a hydrogen atom, a linear alkyl group having 1 to 6 carbon atoms, a cyclopentyl group, a cyclohexyl group, a benzyl group, or a phenyl group.

When ^X2 is an oxygen atom, the ring structure represented by the general formula (2) is a maleic anhydride structure. The maleic anhydride structure can be formed, for example, by copolymerizing maleic anhydride with a (meth)acrylic acid ester. When ^X2 is a nitrogen atom, the ring structure represented by the general formula (2) is an N-substituted maleimide structure.

In the method for forming the ring structure exemplified in the explanation of general formulas (1) and (2), the polymers used to form each ring structure all have (meth)acrylic acid ester units as constituent units, and therefore the resulting resin is an acrylic resin.

The lactone ring structure is shown in general formula (3) below.

In the general formula (3), R ⁷ , R ⁸ and R ⁹ are each independently a hydrogen atom or an organic residue having a carbon number of 1 to 20. The organic residue may contain an oxygen atom.

The organic residue in general formula (3) is, for example, an alkyl group having 1 to 20 carbon atoms, such as a methyl group, an ethyl group, or a propyl group; an unsaturated aliphatic hydrocarbon group having 2 to 20 carbon atoms, such as an ethenyl group or a propenyl group; or an aromatic hydrocarbon group having 6 to 20 carbon atoms, such as a phenyl group or a naphthyl group. One or more hydrogen atoms in the alkyl group, the unsaturated aliphatic hydrocarbon group, or the aromatic hydrocarbon group may be substituted with at least one type of group selected from a hydroxyl group, a carboxyl group, an ether group, and an ester group.

Although the general formula (3) shows a 6-membered lactone ring structure, the lactone ring structure is not limited to this. For example, it may be a 4- to 8-membered ring. A 5- or 6-membered ring is preferred because of its excellent ring structure stability, and a 6-membered ring is more preferred.

When the (meth)acrylic polymer has a ring structure in the main chain, the content of the ring structure in the polymer is not particularly limited, but is usually 5 to 90% by weight, preferably 10 to 70% by weight, more preferably 10 to 60% by weight, and even more preferably 10 to 50% by weight. When the content of the ring structure is high (e.g., 10% by weight or more), the heat resistance, solvent resistance, and surface hardness of the film are particularly excellent. When the content of the ring structure is low (e.g., 70% by weight or less), the ease of stretching the acrylic resin film and the handleability during production are particularly excellent.

When the ring structure of the main chain is other than a lactone ring structure (e.g., an N-substituted maleimide structure, a maleic anhydride structure, a glutarimide structure, and a glutaric anhydride structure), the content of the ring structure is not particularly limited, but is, for example, 5 to 90% by mass, preferably 10 to 70% by mass, more preferably 10 to 60% by mass, and even more preferably 10 to 50% by mass.

When the ring structure of the main chain is a lactone ring structure, the content of the ring structure is not particularly limited, but is, for example, 5 to 90% by mass, preferably 10 to 80% by mass, more preferably 10 to 70% by mass, and even more preferably 10 to 60% by mass.

(Meth)acrylic polymers having a ring structure in the main chain can be formed by known methods. (Meth)acrylic polymers having a lactone ring structure in the main chain are, for example, polymers described in JP-A-2000-230016, JP-A-2001-151814, JP-A-2002-120326, JP-A-2002-254544, and JP-A-2005-146084, and can be formed by the methods described in those publications.

(Meth)acrylic polymers having a glutaric anhydride structure in the main chain are, for example, polymers described in JP-A-2006-283013, JP-A-2006-335902, and JP-A-2006-274118, and can be formed by the methods described in those publications.

(Meth)acrylic polymers having a glutarimide structure in the main chain are, for example, polymers described in JP-A-2006-309033, JP-A-2006-317560, JP-A-2006-328329, JP-A-2006-328334, JP-A-2006-337491, JP-A-2006-337492, JP-A-2006-337493, JP-A-2006-337569, and JP-A-2007-009182, and can be formed by the methods described in those publications.

In forming various polymers in acrylic resins, it is preferable to filter the monomer raw materials, auxiliary raw materials such as polymerization initiators and catalysts, and solvents used in polymerization as much as possible before use, from the viewpoint of reducing foreign matter in the polymer and because filtration can be performed at a low viscosity stage rather than filtering after polymerization. As a method of filtration, if it is a liquid, it can be directly filtered, and if it is a solid, it can be dissolved in the solvent used in polymerization and then passed through various filters such as membrane filters and hollow fiber membrane filters. They can be filtered separately or as a mixture and then filtered. In addition, the accuracy of filtration in this case is preferably 5.0 μm or less, more preferably 1.0 μm or less, and even more preferably 0.5 μm or less.

The acrylic resin may be composed of a combination of a (meth)acrylic polymer and another polymer depending on the desired physical properties and application. The other polymer is not particularly limited, and may be a thermoplastic polymer, a curable polymer, or a combination of these. The other polymer may be used alone or in combination of two or more kinds.

Specific examples of other polymers include other (meth)acrylic polymers having a different composition ratio or molecular weight from the (meth)acrylic polymer, or a different copolymer composition, olefin-based polymers (e.g., polyethylene, polypropylene, ethylene-propylene copolymer, poly(4-methyl-1-pentene)), halogen-based polymers (e.g., vinyl halide polymers such as polyvinyl chloride, polyvinylidene chloride, and polyvinyl chloride), styrene-based polymers [e.g., polystyrene, styrene-based copolymers (e.g., styrene-methyl methacrylate copolymer, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene block copolymer (ABS resin), acrylate-styrene-acrylonitrile copolymer (ASA resin), etc.)], polyester-based polymers (e.g., polyethylene terephthalate, polybutylene terephthalate, polyethylene Examples of the polymerizable compound include aromatic polyesters (e.g., aromatic polyesters such as phenyl naphthalate, etc.), polyamide-based polymers (e.g., aliphatic polyamide-based polymers such as polyamide 6, polyamide 66, and polyamide 610), polyacetal-based polymers, polycarbonate-based polymers, polyphenylene oxide-based polymers, polyphenylene sulfide-based polymers, polyether ether ketone-based polymers, polysulfone-based polymers, polyether sulfone-based polymers, copolymers having a polymer block having units derived from a diene and/or an olefin and a polymer block having units derived from an aromatic vinyl monomer [e.g., styrene-ethylene/butylene-styrene block copolymer (SEBS), styrene-butadiene/butylene-styrene block copolymer (SBS), etc.], cellulose-based polymers (cellulose derivatives), and thermoplastic elastomers (styrene-based elastomers, etc.).

When the acrylic resin contains other polymers in addition to the (meth)acrylic polymer, the form in which the (meth)acrylic polymer and the other polymers are present is not particularly limited, and may be a polymer blend, or the above-mentioned (meth)acrylic polymer and the other polymer may be chemically bonded. In this case, the (meth)acrylic polymer and the other polymer may form a block copolymer, a graft copolymer, etc.

When the acrylic resin contains other polymers in addition to the (meth)acrylic polymer, the content of the other polymers may be, for example, 90% by mass or less (e.g., 0.1 to 85% by mass), 80% by mass or less (e.g., 0.5 to 70% by mass), preferably about 60% by mass or less (e.g., 1 to 55% by mass), 50% by mass or less (e.g., 2 to 45% by mass), 30% by mass or less (e.g., 2 to 25% by mass), 20% by mass or less (e.g., 2 to 15% by mass), etc.

For example, when the acrylic resin contains a styrene-based polymer, the acrylic resin film made of this acrylic resin can be made into a stretched film, and the positive phase difference exhibited by the (meth)acrylic polymer having a ring structure in the main chain can be canceled by the negative phase difference exhibited by the styrene-based polymer. By adjusting the content of the styrene-based polymer in the acrylic resin film, it is possible to make it into a negative phase difference film or a polarizer protective film with a low phase difference. When the acrylic resin film contains a styrene-based polymer, the styrene-based polymer is preferably a styrene-acrylonitrile copolymer from the viewpoint of compatibility with the (meth)acrylic polymer. When the acrylic resin film contains an ABS resin or an ASA resin, by adjusting the content of the ABS resin or the ASA resin in the acrylic resin film, it is possible to make the acrylic resin film into a negative phase difference film or a film with a low phase difference while increasing the flexibility.

The acrylic resin may contain materials other than the polymer, such as additives. The additives include, for example, antioxidants such as hindered phenols, phosphorus, and sulfur; stabilizers such as light stabilizers, weather stabilizers, and heat stabilizers; reinforcing materials such as glass fibers and carbon fibers; ultraviolet absorbers such as phenyl salicylate, (2,2'-hydroxy-5-methylphenyl)benzotriazole, and 2-hydroxybenzophenone; near-infrared absorbers; flame retardants such as tris(dibromopropyl)phosphate, triallyl phosphate, and antimony oxide; antistatic agents composed of anionic, cationic, and nonionic surfactants; colorants such as inorganic pigments, organic pigments, and dyes; organic fillers; antiblocking agents; resin modifiers; organic fillers; plasticizers; lubricants; and retardation reducers.

The content of additives in the acrylic resin is preferably 0 to 5% by weight, more preferably 0 to 2% by weight, and even more preferably 0 to 0.5% by weight.

The Tg (glass transition temperature) of the acrylic resin is preferably 100°C or higher, more preferably 110°C or higher, even more preferably 115°C or higher, and particularly preferably 120°C or higher. There is no particular upper limit to the Tg of the acrylic resin, but from the viewpoint of stretchability when made into an acrylic resin film, it is preferably 170°C or lower.

The acrylic resin film is obtained by molding acrylic resin. The thickness of the acrylic resin film is not particularly limited, but is preferably 5 to 200 μm, and more preferably 10 to 100 μm. If the thickness is 5 μm or more, the strength is excellent. If the thickness is 200 μm or less, the transparency is excellent.

The surface wet tension of the acrylic resin film is preferably 40 mN/m or more, more preferably 50 mN/m or more, and even more preferably 55 mN/m or more. When the surface wet tension is 40 mN/m or more, the adhesion between the optical film of this embodiment and other members is further improved. In order to adjust the surface wet tension, any appropriate surface treatment may be applied to the surface of the acrylic resin film. Examples of surface treatments include corona discharge treatment, plasma treatment, ozone spraying, ultraviolet irradiation, flame treatment, and chemical treatment. Of these, corona discharge treatment and plasma treatment are preferred.

[Method of manufacturing (acrylic) resin film]
The acrylic resin film can be formed by a known film-forming method using an acrylic resin. Examples of the film-forming method include a solution casting method, a melt extrusion method, a calendar method, and a compression molding method. Among them, the solution casting method and the melt extrusion method are preferable.

The acrylic resin used for film formation can be formed by a known method. For example, the acrylic resin is formed by thoroughly mixing the (meth)acrylic polymer, other thermoplastic polymers, and additives, etc., which are blended according to the composition of the acrylic resin to be obtained, by an appropriate mixing method. The mixing method is, for example, extrusion kneading or mixing in a solution state. A commercially available acrylic resin may be used for film formation. Examples of commercially available acrylic resins are ACRYPET VH and ACRYPET VRL20A (both manufactured by Mitsubishi Rayon). Any suitable mixer, such as an omnimixer, a single-screw extruder, a twin-screw extruder, or a pressure kneader, can be used for extrusion kneading.

Apparatuses for carrying out the solution casting method include, for example, drum-type casting machines, band-type casting machines, and spin coaters. The solvent used in the solution casting method is not limited as long as it dissolves the acrylic resin. Examples of the solvent include aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as cyclohexane and decalin; esters such as ethyl acetate and butyl acetate; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; alcohols such as methanol, ethanol, isopropanol, butanol, isobutanol, methyl cellosolve, ethyl cellosolve, and butyl cellosolve; ethers such as tetrahydrofuran and dioxane; halogenated hydrocarbons such as dichloromethane, chloroform, and carbon tetrachloride; dimethylformamide; and dimethyl sulfoxide. Two or more of these solvents may be used in combination.

Examples of melt extrusion methods include the T-die method and the inflation method. The molding temperature during melt extrusion is preferably 150 to 350°C, more preferably 200 to 300°C. In the T-die method, for example, a strip-shaped acrylic resin film can be formed by attaching a T-die to the tip of a known extruder. The formed strip-shaped acrylic resin film may be wound up on a roll to form a film roll.

The obtained acrylic resin film may be stretched. The stretching direction may be the longitudinal direction (MD direction) of the acrylic resin film, the width direction (TD direction) perpendicular to the longitudinal direction, or a diagonal direction relative to the longitudinal direction. When stretching in two axial directions, it may be sequential stretching in which stretching in the MD direction (longitudinal stretching) and stretching in the TD direction (transverse stretching) are performed sequentially, or simultaneous stretching in which stretching in the MD direction and stretching in the TD direction are performed simultaneously. The temperature during stretching is preferably within the range of (Tg-30) to (Tg+100)°C, more preferably within the range of (Tg-20) to (Tg+80)°C, and even more preferably within the range of (Tg-5) to (Tg+20)°C, where Tg is the glass transition temperature of the acrylic resin film. The stretching ratio is not particularly limited, but may be, for example, about 1.1 to 25 times (for example, 1.3 to 10 times) in terms of the area ratio. The stretching speed (in one direction) is not particularly limited, but may be, for example, about 10 to 20,000%/min (for example, 100 to 10,000%/min). The stretched acrylic resin film is suitable as a retardation film. The stretching method is not particularly limited, and a known stretching machine can be used for stretching. The stretching machine will be described later.

When forming an acrylic resin film by melt extrusion, the process from mixing the materials to forming the acrylic resin to forming and stretching the acrylic resin film can be carried out continuously. When forming an acrylic resin film by the T-die method, it is also possible to simultaneously perform uniaxial stretching in the MD direction and winding the film by adjusting the temperature of the roll that winds up the formed film.

In addition, for example, after stretching, the acrylic resin film may be subjected to heat treatment (annealing) in order to stabilize the optical isotropy and mechanical properties of the acrylic resin film. The method and conditions of the heat treatment can be selected appropriately.

[Easy-adhesion layer]
The easy-adhesion layer includes a binder resin, a polyamine, and fine particles. The polyamine is a polymer having a plurality of amino groups. The plurality of amino groups includes at least one selected from the group consisting of secondary amino groups and tertiary amino groups. The content of the polyamine in the easy-adhesion layer is 0.0090% by weight to 1.4100% by weight. The polyamine promotes the dispersion of the fine particles in the easy-adhesion layer, and improves the adhesion between the resin film and the easy-adhesion layer, the blocking resistance of the optical film, and the uniformity of the easy-adhesion layer.

The physical properties required for optical films include phase difference, tear resistance, folding resistance, etc. In order to obtain a biaxially stretched optical film that meets the required physical properties, it is necessary to strictly control the stretching temperature. The stretching temperature is changed according to subtle differences in the physical properties of each resin lot, such as molecular weight and composition ratio. Here, in the production of optical films, the drying of the easy-adhesion layer is often performed simultaneously with the transverse stretching process. Therefore, changing the stretching temperature means changing the drying temperature of the easy-adhesion layer. When the alkali component contained in the easy-adhesion layer is a low-molecular-weight compound, changing the drying temperature of the easy-adhesion layer changes the amount of evaporation of the alkali component, and the content of the alkali component in the easy-adhesion layer also changes. In this case, there is a possibility that the desired effect based on the alkali component cannot be fully obtained. It is difficult to change the stretching temperature to keep the content of the alkali component within the desired range. In particular, when manufacturing an optical film using a resin with a high Tg, such as an acrylic resin having a ring structure, it is necessary to increase the stretching temperature. Highly volatile low-molecular-weight alkali components are easily released to the outside during the stretching process at high temperatures. In this case, the effect of promoting the dispersion of the fine particles by the alkaline component becomes insufficient.

On the other hand, polymer polyamines are less likely to volatilize and can remain reliably in the adhesion layer. The polyamine content in the adhesion layer is less likely to change even if the stretching temperature is changed. Therefore, polymer polyamines are suitable for keeping the alkaline component content in the adhesion layer within the desired range, and can reliably promote the dispersion of fine particles. As a result, further improvement in the blocking resistance of the optical film can be expected.

It is also speculated that the cationic nature of the polyamine acts on the ester portion of the acrylic resin. In other words, it is speculated that the interaction between the amino group of the polyamine and the ester portion of the acrylic resin improves the adhesion between the adhesive layer and the resin film.

In addition, when an acrylic resin having a ring structure in the main chain is used as the material for the resin film, the stretching temperature of the resin film (≒ drying temperature of the easy-adhesion layer) is set high. It is considered that the binder resin of the easy-adhesion layer easily penetrates into the surface of the resin film whose temperature is higher than the Tg. As a result, the adhesion between the easy-adhesion layer and the resin film can be further improved.

The binder resin may be any known resin having good adhesion, such as urethane resin, cellulose resin, polyol resin, polycarboxylic acid resin, polyester resin, or acrylic resin. At least one resin selected from these resins may be used as the binder resin.

The number average molecular weight of the binder resin is preferably 5,000 to 600,000, and more preferably 10,000 to 400,000.

The binder resin includes, for example, a urethane resin. The binder resin is preferably a urethane resin. In this way, the adhesion of the easy-adhesion layer to the acrylic resin film is improved, and the easy-adhesion of the optical film to other members is also improved.

The urethane resin is not particularly limited, and is typically a resin obtained by reacting a polyol with a polyisocyanate. The polyol may be any polyol having two or more hydroxyl groups in the molecule. Examples of the polyol include polyacrylic polyol, polyester polyol, and polyether polyol. Two or more types of polyols may be combined.

Polyacrylic polyols are typically copolymers of (meth)acrylic acid ester monomers and monomers having a hydroxyl group. Examples of (meth)acrylic acid ester monomers include methyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate. Examples of monomers having a hydroxyl group include (meth)acrylic acid hydroxyalkyl esters such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxypentyl (meth)acrylate; (meth)acrylic acid monoesters of polyhydric alcohols such as glycerin and trimethylolpropane; and N-methylol (meth)acrylamide.

The polyacrylic polyol may be a copolymer with further other monomers. The other monomers are not limited as long as they can be copolymerized with the above (meth)acrylic acid ester monomer and the monomer having a hydroxyl group. The other monomers are, for example, unsaturated monocarboxylic acids such as (meth)acrylic acid; unsaturated dicarboxylic acids such as maleic acid and their anhydrides and mono- or diesters; unsaturated nitriles such as (meth)acrylonitrile; unsaturated amides such as (meth)acrylamide and N-methylol (meth)acrylamide; vinyl esters such as vinyl acetate and vinyl propionate; vinyl ethers such as methyl vinyl ether; α-olefins such as ethylene and propylene; halogenated α,β-unsaturated aliphatic monomers such as vinyl chloride and vinylidene chloride; and α,β-unsaturated aromatic monomers such as styrene and α-methylstyrene.

Polyester polyols are typically obtained by reacting a polybasic acid component with a polyol component. Examples of the polybasic acid component include aromatic dicarboxylic acids such as orthophthalic acid, isophthalic acid, terephthalic acid, 1,4-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, biphenyldicarboxylic acid, and tetrahydrophthalic acid; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, dodecanedicarboxylic acid, octadecanedicarboxylic acid, tartaric acid, alkylsuccinic acid, linoleic acid, maleic acid, fumaric acid, mesaconic acid, citraconic acid, and itaconic acid; alicyclic dicarboxylic acids such as hexahydrophthalic acid, tetrahydrophthalic acid, 1,3-cyclohexanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid; and reactive derivatives thereof such as acid anhydrides, alkyl esters, and acid halides.

Examples of polyol components include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, 1-methyl-1,3-butylene glycol, 2-methyl-1,3-butylene glycol, 1-methyl-1,4-pentylene glycol, 2-methyl-1,4-pentylene glycol, 1,2-dimethyl-neopentyl glycol, 2,3-dimethyl-neopentyl glycol, 1-methyl-1 ,5-pentylene glycol, 2-methyl-1,5-pentylene glycol, 3-methyl-1,5-pentylene glycol, 1,2-dimethylbutylene glycol, 1,3-dimethylbutylene glycol, 2,3-dimethylbutylene glycol, 1,4-dimethylbutylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediol, bisphenol A, bisphenol F, hydrogenated bisphenol A, and hydrogenated bisphenol F.

Polyether polyols are typically obtained by adding alkylene oxides to polyhydric alcohols through ring-opening polymerization. Examples of polyhydric alcohols include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, glycerin, and trimethylolpropane. Examples of alkylene oxides include ethylene oxide, propylene oxide, butylene oxide, styrene oxide, and tetrahydrofuran.

Examples of polyisocyanates include aliphatic diisocyanates such as tetramethylene diisocyanate, dodecamethylene diisocyanate, 1,4-butane diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2-methylpentane-1,5-diisocyanate, and 3-methylpentane-1,5-diisocyanate; isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4'-cyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, and 1,3-bis(isocyanate methyl)cycloisocyanate. alicyclic diisocyanates such as hexane; aromatic diisocyanates such as tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyldimethylmethane diisocyanate, 4,4'-dibenzyl diisocyanate, 1,5-naphthylene diisocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, and 1,4-phenylene diisocyanate; and araliphatic diisocyanates such as dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, and α,α,α,α-tetramethylxylylene diisocyanate.

The urethane resin preferably has a carboxyl group. By having a carboxyl group, the performance (easy adhesion) of the easy-adhesion layer is improved. This effect is particularly remarkable in high temperature and high humidity environments. The urethane resin having a carboxyl group can be obtained, for example, by reacting a chain lengthening agent having a free carboxyl group in addition to a polyol and a polyisocyanate. The chain lengthening agent having a free carboxyl group is, for example, a dihydroxycarboxylic acid or a dihydroxysuccinic acid. The dihydroxycarboxylic acid is, for example, a dialkylolalkanoic acid such as a dimethylolalkanoic acid (for example, dimethylolacetic acid, dimethylolbutanoic acid, dimethylolpropionic acid, dimethylolbutyric acid, dimethylolpentanoic acid).

The acid value of the urethane resin is preferably 10 or more, more preferably 10 to 50, and particularly preferably 20 to 45. In these cases, the performance of the easy-adhesion layer (for example, adhesion to other functional films such as polarizers) is further improved.

In addition to the above-mentioned components, the urethane resin may be obtained by reacting with other polyols or other chain extenders. The other polyols are, for example, polyols having three or more hydroxyl groups, such as sorbitol, 1,2,3,6-hexanetetraol, 1,4-sorbitan, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerin, trimethylolethane, trimethylolpropane, and pentaerythritol. Other chain lengthening agents include, for example, glycols such as ethylene glycol, diethylene glycol, triethylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, 1,6-hexanediol, and propylene glycol; aliphatic diamines such as ethylenediamine, propylenediamine, hexamethylenediamine, 1,4-butanediamine, and aminoethylethanolamine; alicyclic diamines such as isophoronediamine and 4,4'-dicyclohexylmethanediamine; and aromatic diamines such as xylylenediamine and tolylenediamine.

The urethane resin can be formed by applying a known method. Such methods include, for example, a one-shot method in which each component is reacted at once, and a multi-stage method in which the components are reacted in stages. It is preferable to form a urethane resin having a carboxyl group by a multi-stage method, since the carboxyl group can be easily introduced. There is no particular limitation on the catalyst used to form the urethane resin.

The polyamine may contain a primary amino group, a secondary amino group, and a tertiary amino group. Such polyamines also have the effect of improving the adhesion between the resin film and the easy-adhesion layer.

The polyamine may contain a polyalkyleneimine. The polyalkyleneimine is suitable as an alkaline component of the easy-adhesion layer. The polyalkyleneimine may be linear or may have a branched structure.

As the polyamine, polyalkyleneimines are preferably used. Examples of polyalkyleneimines include polyalkyleneimines obtained by polymerizing one or more alkyleneimines having 2 to 6 carbon atoms, and derivatives obtained by adding unsaturated carboxylic acids or alkylene oxides to polyalkyleneimines. Examples of alkyleneimines having 2 to 6 carbon atoms include ethyleneimine, propyleneimine, 1,2-butyleneimine, 2,3-butyleneimine, and 1,1-dimethylethyleneimine. As the polyalkyleneimines, polyethyleneimine, polypropyleneimine, polyethyleneimine derivatives, and polypropyleneimine derivatives are preferred, and polyethyleneimine and polyethyleneimine derivatives are more preferred. Examples of the polyethyleneimine and polyethyleneimine derivatives include the commercially available Epomin series manufactured by Nippon Shokubai Co., Ltd., such as Epomin SP-003, Epomin SP-006, Epomin SP-012, Epomin SP-018, Epomin SP-103, Epomin SP-110, Epomin SP-200, Epomin SP-300, Epomin SP-1000, and Epomin SP-1020 (all of which are trade names).

The polyalkyleneimine contains a primary amino group, a secondary amino group, and a tertiary amino group, and may have a branched structure. A polyalkyleneimine having such a structure is suitable as an alkaline component of the easy-adhesion layer.

By adjusting the polyamine content in the adhesion layer to the above range, the adhesion between the resin film and the adhesion layer can be improved. The polyamine content in the adhesion layer may be 0.0098% by weight to 1.4098% by weight.

The presence and content of polyamine in the adhesion layer can be determined by known analytical methods such as NMR.

The fine particles may be either inorganic or organic. The inorganic fine particles are, for example, inorganic oxides such as silica, titania, alumina, and zirconia; calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, and calcium phosphate. The organic fine particles are, for example, fine particles of silicone resin, fluorine resin, and acrylic resin. Among them, silica fine particles are preferred. Silica fine particles improve blocking resistance. In addition, silica fine particles have excellent transparency, so that coloring and an increase in the haze ratio of the optical film are unlikely to occur.

The particle diameter (average particle diameter) of the fine particles is preferably 10 to 1000 nm. By using fine particles with such a particle diameter, appropriate unevenness can be formed on the surface of the easy-adhesion layer, and blocking between the acrylic resin film and the easy-adhesion layer, or between the easy-adhesion layers themselves, can be effectively reduced. The average particle diameter of the fine particles is smaller than the visible light wavelength from the viewpoint of suppressing light scattering by the particles, and the smaller the better, but from the viewpoint of blocking properties, the larger the better. For this reason, the upper limit of the average particle diameter is, for example, 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, more preferably 500 nm or less, more preferably 400 nm or less, and even more preferably 350 nm or less. The lower limit is preferably 20 nm or more, 40 nm or more, 60 nm or more, 80 nm or more, 100 nm or more, more preferably 120 nm or more, 140 nm or more, 160 nm or more, 180 nm or more, 200 nm or more, and even more preferably 220 nm or more, 240 nm or more, 260 nm or more, 280 nm or more, 300 nm or more, 320 nm or more, 340 nm or more. The particle size distribution of the fine particles is preferably 1.0 to 1.2.

The content of the fine particles in the easy-adhesion layer is not particularly limited, but the upper limit of the content is preferably less than 30 parts by weight, more preferably less than 20 parts by weight, and even more preferably less than 5 parts by weight, relative to 100 parts by weight of the binder resin (solid content: solid content including the crosslinking agent if a crosslinking agent is included). When the content of the fine particles is less than 30 parts by weight, the strength of the easy-adhesion layer is excellent. The lower limit of the content is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, and even more preferably 0.5 parts by weight or more. When the content of the fine particles is 0.1 parts by weight or more, the blocking resistance of the optical film is excellent. Note that, when the average particle diameter is small (for example, less than 100 nm), the content of the fine particles is preferably high in order to obtain the effect of improving the blocking resistance, and the lower limit of the content is preferably 0.5 parts by weight or more, 1.0 parts by weight or more, 5.0 parts by weight or more, or 10.0 parts by weight or more. Furthermore, when the average particle size is large (for example, 200 nm or more), the content of fine particles is preferably small from the viewpoint of suppressing light scattering, and the upper limit of the content is preferably less than 2.0 parts by weight, and more preferably less than 1.0 part by weight.

The thickness of the easy-adhesion layer is not limited and varies depending on the thickness of the film, but is preferably 100 nm to 10 μm, more preferably 100 nm to 5 μm, and even more preferably 200 nm to 1.5 μm. In this range, the easy-adhesion layer provides good adhesion to other members of the optical film. In addition, the easy-adhesion layer itself can be prevented from exhibiting phase difference.

The ratio r/d of the thickness d of the easy-adhesion layer to the average particle diameter r of the fine particles contained in the easy-adhesion layer is preferably 0.3 to 1.4, more preferably 0.4 to 1.1, and even more preferably 0.6 to 1.0. Within this range, the optical film of this embodiment can more reliably achieve both blocking resistance and transparency.

The method of forming the easy-adhesion layer on the surface of the optical film is not limited, and may be any known method. The easy-adhesion layer is preferably formed by applying an easy-adhesion composition containing a binder resin, a polyamine, and fine particles to the surface of the resin film to form a coating film of the easy-adhesion composition, and drying the coating film. The easy-adhesion composition is preferably a water-based composition. Compared with organic solvent-based compositions, water-based compositions have a smaller environmental impact when forming the easy-adhesion layer and are excellent in workability. The water-based composition is, for example, a dispersion of a binder resin. The dispersion is typically an emulsion of a binder resin. The emulsion of the binder resin becomes a resin layer by drying. The fine particles contained in the emulsion remain in the resin layer as they are.

When the adhesive composition is water-based, the fine particles are preferably formulated as a water dispersion such as colloidal silica. The colloidal silica may be a commercially available product as long as the average particle size and particle size distribution are within the above-mentioned ranges.

When the easy-adhesion composition is a water-based composition containing a urethane resin, it is preferable to use an organic solvent that is inactive to polyisocyanates and compatible with water when forming the urethane resin. Examples of the organic solvent include ester-based solvents such as ethyl acetate, butyl acetate, and ethyl cellosolve acetate; ketone-based solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; and ether-based solvents such as dioxane, tetrahydrofuran, and propylene glycol monomethyl ether.

When the easy-adhesion composition contains a urethane resin, the performance of the easy-adhesion layer is improved by further containing a crosslinking agent. The crosslinking agent is not particularly limited. When the urethane resin has a carboxyl group, the crosslinking agent is preferably a polymer having a group capable of reacting with the carboxyl group. The group capable of reacting with the carboxyl group is, for example, an organic amino group, an oxazoline group, an epoxy group, or a carbodiimide group, and an oxazoline group is preferable. A crosslinking agent having an oxazoline group has a long pot life at room temperature when mixed with a urethane resin, and the crosslinking reaction proceeds by heating, so that the workability is good. The polymer is, for example, a (meth)acrylic polymer or a styrene-acrylic polymer, and a (meth)acrylic polymer is preferable. When the crosslinking agent is a (meth)acrylic polymer, the performance of the easy-adhesion layer is further improved. In addition, the (meth)acrylic polymer is stably compatible with the water-based easy-adhesion composition and crosslinks the urethane resin well.

When the easy-adhesion composition contains a urethane resin, the content of the urethane resin is preferably 1.5 to 15 weight percent, and more preferably 2 to 10 weight percent. When the content is within these ranges, the easy-adhesion composition has high coatability when applied to the surface of an optical film, particularly an acrylic resin film. When this composition further contains a crosslinking agent, the content of the crosslinking agent is preferably 1 to 30 parts by weight, and more preferably 3 to 20 parts by weight, per 100 parts by weight of the urethane resin (solid content).

When the easy-adhesion composition contains a urethane resin, it is preferable to contain a neutralizing agent. In this case, the stability of the urethane resin in the easy-adhesion composition is improved. Examples of neutralizing agents include ammonia, N-methylmorpholine, triethylamine, dimethylethanolamine, methyldiethanolamine, triethanolamine, morpholine, tripropylamine, ethanolamine, triisopropanolamine, and 2-amino-2-methyl-1-propanol.

The adhesive composition may contain additives. Examples of additives include dispersion stabilizers, thixotropic agents, antioxidants, ultraviolet absorbers, defoamers, thickeners, dispersants, surfactants, catalysts, and antistatic agents.

[Optical film characteristics and applications]
The optical film of the present embodiment has excellent adhesion to other members and excellent blocking resistance. It also has excellent transparency and usually has a haze ratio of 1.5% or less. Depending on the configuration of the optical film of the present embodiment, the haze ratio is 1.0% or less, or even 0.5% or less.

The optical film of this embodiment is, for example, a polarizer protection film, a phase difference film, a viewing angle compensation film, a light diffusion film, a reflection film, an anti-reflection film, an anti-glare film, a brightness enhancement film, or a conductive film for a touch panel. The phase difference exhibited by the optical film of this embodiment can be controlled by the composition and stretching state of the film. The optical film of this embodiment can be an optically isotropic film, or a film having optical anisotropy (for example, exhibiting birefringence such as phase difference).

When the optical film of this embodiment is used as a retardation film, it is suitable for use in image display devices such as LCDs. The retardation film can be used, for example, for color compensation and viewing angle compensation of LCDs.

Because the retardation film has an easy-adhesion layer, it can be used in forms other than those normally used as a retardation film. Specifically, for example, it can be used by bonding it to a polarizer equipped in an LCD. In this case, the retardation film functions as a normal retardation film for color compensation or viewing angle compensation, as well as a polarizer protective film that protects the polarizer. This form is advantageous for making LCDs thinner and more functional, since it makes it possible to omit the polarizer protective film that does not have a retardation, which has been used separately from the retardation film in the past.

When an easy-adhesion layer is formed only on one surface of the optical film, various functional coating layers may be formed on the opposite surface as necessary. Examples of functional coating layers include antistatic layers, adhesive layers, adhesive layers, easy-adhesion layers, anti-glare layers, anti-fouling layers such as photocatalyst layers, anti-reflection layers, hard coat layers, ultraviolet shielding layers, heat ray shielding layers, electromagnetic wave shielding layers, and gas barrier layers.

[Optical components]
The optical film of the present embodiment is suitable for optical members such as polarizing plates, diffusion plates, light guides, and prism sheets.

A polarizing plate will be described as an example of an optical component of this embodiment. In an LCD, a pair of polarizing plates are arranged to sandwich a liquid crystal cell based on the image display principle. The polarizing plate has a structure in which, for example, the optical film of this embodiment (polarizer protective film) is laminated on at least one surface of a polarizer via an easy-adhesion layer.

Conventionally, triacetyl cellulose (TAC) film has been used as a polarizer protective film. However, TAC film does not have sufficient moist heat resistance, and when TAC film is used as a polarizer protective film, the properties of the polarizing plate may deteriorate in a high temperature or high humidity environment. In addition, TAC film has a phase difference in the thickness direction, and this phase difference adversely affects the viewing angle properties of image display devices such as LCDs, particularly large-screen image display devices. In contrast, using an acrylic resin film as a polarizer protective film is preferable because it can improve moist heat resistance and optical properties compared to TAC film.

A polarizing plate is typically manufactured by laminating an optical film and a polarizer via an adhesive layer. When the optical film has an easy-adhesion layer, the two are laminated so that the easy-adhesion layer is on the polarizer side. Specifically, for example, an adhesive composition that will become an adhesive layer after drying is applied to the surface of either the polarizer or the optical film, and then the two are laminated and dried. The adhesive composition can be applied by, for example, a roll method, a spray method, or a dipping method. When the adhesive composition contains a metal compound colloid, the adhesive composition is applied so that the thickness of the adhesive layer after drying is larger than the average particle diameter of the metal compound colloid particles. The drying temperature is typically 5 to 150°C, preferably 30 to 120°C. The drying time is typically 120 seconds or more, preferably 300 seconds or more.

The polarizer is not limited, and any suitable polarizer can be used depending on the required function of the polarizing plate. The polarizer is, for example, a film obtained by uniaxially stretching a hydrophilic polymer film such as a polyvinyl alcohol (PVA) film, a partially formalized PVA film, or a partially saponified film of an ethylene-vinyl acetate copolymer (EVA) after adsorbing a dichroic substance such as iodine or a dichroic dye; or a polyene-based oriented film using a dehydrated PVA or a dehydrochlorinated polyvinyl chloride. Among them, a film obtained by adsorbing a dichroic substance to a PVA film and uniaxially stretching is preferred as a polarizer. This polarizer exhibits a high polarized dichroic ratio. The thickness of the polarizer is not limited, and is generally about 1 to 80 μm. A polarizer obtained by adsorbing iodine to a PVA film and uniaxially stretching it can be produced, for example, by dyeing the PVA film by immersing it in an aqueous solution containing iodine, and uniaxially stretching it at a stretching ratio of 3 to 7 times. The aqueous solution used for dyeing may contain boric acid, zinc sulfate, zinc chloride, etc. as necessary. As the aqueous solution containing iodine, an aqueous solution of an iodide such as potassium iodide may be used. The PVA-based film may be immersed in water and washed before dyeing. Washing the PVA-based film with water can remove dirt and antiblocking agents present on the surface of the film. Furthermore, since the PVA-based film swells by washing with water, unevenness during dyeing is suppressed. Stretching may be performed before dyeing, after dyeing, or simultaneously with dyeing.

The adhesive composition that becomes the adhesive layer after drying is not limited. The adhesion method is not limited, and may be water glue or UV adhesion. The adhesive composition preferably contains a PVA-based resin. The PVA-based resin includes, for example, the following polymers: saponification products of polyvinyl acetate and its derivatives; saponification products of copolymers of vinyl acetate and other monomers; modified PVA obtained by acetalization, urethane-ification, etherification, grafting, or phosphorylation of PVA. The other monomers are, for example, unsaturated carboxylic acids and their esters, such as (anhydride) maleic acid, fumaric acid, crotonic acid, itaconic acid, and (meth)acrylic acid; α-olefins, such as ethylene and propylene; (meth)allylsulfonic acid (soda), sodium sulfonate (monoalkyl maleate), sodium disulfonate alkyl maleate, N-methylol acrylamide, alkali salts of acrylamido alkyl sulfonates, N-vinyl pyrrolidone, and N-vinyl pyrrolidone derivatives. The PVA-based resin preferably contains an acetoacetyl group-containing PVA. In this case, the adhesion between the polarizer and the optical film (particularly the acrylic resin film) is improved, and the durability of the polarizing plate is improved.

From the viewpoint of the adhesive properties of the adhesive composition, the average polymerization degree of the PVA-based resin is preferably about 100 to 5000, and more preferably 1000 to 4000. From the viewpoint of the adhesive properties of the adhesive composition, the average saponification degree of the PVA-based resin is preferably about 85 to 100 mol%, and more preferably 90 to 100 mol%.

Acetoacetyl group-containing PVA can be obtained, for example, by reacting PVA with diketene by any method. Specific examples include a method of adding diketene to a dispersion of PVA in a solvent such as acetic acid, a method of adding diketene to a solution of PVA in a solvent such as dimethylformamide or dioxane, and a method of directly contacting PVA with diketene gas or liquid diketene.

The degree of acetoacetyl group modification in acetoacetyl group-containing PVA is typically 0.1 mol% or more, preferably 0.1 to 40 mol%, more preferably 1 to 20%, and even more preferably 2 to 7 mol%. By appropriately adjusting the degree of modification, the effect of modification (e.g., improved water resistance) can be sufficiently obtained. The degree of acetoacetyl group modification of PVA can be measured by NMR.

The adhesive composition may contain a crosslinking agent. The crosslinking agent is not limited, but is a compound having at least two functional groups that show reactivity with the PVA-based resin. Examples of the crosslinking agent include alkylene diamines having an alkylene group and two amino groups, such as ethylene diamine, triethylene diamine, and hexamethylene diamine; isocyanates such as tolylene diisocyanate, hydrogenated tolylene diisocyanate, trimethylolpropane tolylene diisocyanate adduct, triphenylmethane triisocyanate, methylene bis (4-phenylmethane triisocyanate), isophorone diisocyanate, and ketoxime-blocked or phenol-blocked products thereof; ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether, and the like. Examples of crosslinking agents include epoxies such as ethyl ether, trimethylolpropane triglycidyl ether, diglycidyl aniline, and diglycidyl amine; monoaldehydes such as formaldehyde, acetaldehyde, propionaldehyde, and butylaldehyde; dialdehydes such as glyoxal, malondialdehyde, succindialdehyde, glutaric dialdehyde, maleic dialdehyde, and phthaldialdehyde; amino-formaldehyde resins such as methylol urea, methylol melamine, alkylated methylol urea, alkylated methylol melamine, acetoguanamine, and condensates of benzoguanamine and formaldehyde; and salts and oxides of monovalent to trivalent metals such as sodium, potassium, magnesium, calcium, aluminum, iron, and nickel. Among these, the crosslinking agent is preferably an amino-formaldehyde resin or a dialdehyde. The amino-formaldehyde resin preferably has a methylol group, and is preferably methylolmelamine.The dialdehyde is preferably glyoxal.

The amount of crosslinking agent in the adhesive composition can be set appropriately depending on the type of PVA-based resin. Typically, it is about 10 to 60 parts by weight, and 20 to 50 parts by weight is preferable, per 100 parts by weight of PVA-based resin. Good adhesion can be obtained within this range. By appropriately adjusting the amount of crosslinking agent, gelation of the adhesive composition can be suppressed. In this case, the usable time (pot life) of the adhesive composition is extended, making it easier to use industrially.

The adhesive composition may contain a metal compound colloid. The metal compound colloid may be a colloid in which particles of a metal compound are dispersed in a dispersion medium. The metal compound colloid may be a colloid that has permanent stability due to electrostatic stabilization caused by mutual repulsion of like charges of the particles. By including a metal compound colloid in the adhesive composition, the stability of the adhesive composition is improved, for example, even when a large amount of a crosslinking agent is included.

The average particle size of the colloidal particles in the metal compound colloid can be set within a range that does not adversely affect the optical properties (e.g., polarization properties) of the polarizing plate. The average particle size of the colloidal particles is preferably 1 to 100 nm, and more preferably 1 to 50 nm. Within these ranges, the colloidal particles can be uniformly dispersed in the adhesive layer. This ensures adhesion and suppresses the occurrence of knick defects. If knick defects occur, for example, light leakage will occur in an image display device incorporating the polarizing plate.

The metal compound is not limited, and examples thereof include oxides such as alumina, silica, zirconia, and titania; metal salts such as aluminum silicate, calcium carbonate, magnesium silicate, zinc carbonate, barium carbonate, and calcium phosphate; and minerals such as celite, talc, clay, and kaolin. A positively charged metal compound colloid is preferred. The metal compound that becomes a positively charged colloid is preferably alumina or titania, and particularly preferably alumina.

The metal compound colloid is typically a colloidal solution dispersed in a dispersion medium. The dispersion medium is, for example, water or alcohol. The solids concentration in the colloidal solution is typically about 1 to 50% by weight, and preferably 1 to 30% by weight. The colloidal solution may contain an acid such as nitric acid, hydrochloric acid, or acetic acid as a stabilizer.

The amount of metal compound colloid in the adhesive composition (converted into solids) is preferably 200 parts by weight or less per 100 parts by weight of the PVA-based resin, more preferably 10 to 200 parts by weight, even more preferably 20 to 175 parts by weight, and particularly preferably 30 to 150 parts by weight. Within these ranges, the adhesive composition has a more reliable adhesive property while further suppressing the occurrence of knick defects.

The adhesive composition may contain coupling agents such as silane coupling agents and titanium coupling agents; various tackifiers; ultraviolet absorbers; antioxidants; and stabilizers such as heat stabilizers and hydrolysis-resistant stabilizers.

The adhesive composition is preferably an aqueous solution (resin solution). The concentration of the resin in the aqueous solution is preferably 0.1 to 15% by weight, more preferably 0.5 to 10% by weight, from the viewpoint of the coatability and shelf stability of the composition. The viscosity of the aqueous solution is preferably 1 to 50 mPa·s. When the adhesive composition contains a metal compound colloid, even a low viscosity of 1 to 20 mPa·s effectively suppresses the occurrence of knick defects. The pH of the aqueous solution is preferably 2 to 6, more preferably 2.5 to 5, even more preferably 3 to 5, and particularly preferably 3.5 to 4.5. In general, the surface charge of the metal compound colloid is adjusted by adjusting the pH of the aqueous solution. The surface charge is preferably a positive charge. The positive charge further suppresses the occurrence of knick defects. The surface charge of the metal compound colloid can be confirmed, for example, by measuring the zeta potential with a zeta potential measuring device.

The adhesive composition, which is an aqueous solution (resin solution), can be formed by a known method. When the adhesive composition contains a crosslinking agent and a metal compound colloid, for example, a method can be used in which a PVA-based resin and a crosslinking agent are mixed together and the solution adjusted to an appropriate concentration is mixed with the metal compound colloid. After mixing the PVA-based resin and the metal compound colloid, the crosslinking agent may be mixed in, taking into consideration the time of use of the adhesive composition. The concentration of the aqueous solution can be adjusted after the aqueous solution is prepared.

The thickness of the adhesive layer formed from the adhesive composition can be set appropriately depending on the composition of the composition. The thickness is preferably 10 to 300 nm, more preferably 10 to 200 nm, and particularly preferably 20 to 150 nm. Within this range, the adhesive layer exhibits sufficient adhesive strength.

[Image display device]
The optical film of the present embodiment is suitable for image display devices such as electroluminescence (EL) display panels, plasma display panels (PDPs), field emission displays (FEDs), LCDs, etc. The configuration of an image display device including the optical film of the present embodiment is not particularly limited, and it is sufficient to include components such as a power source, a backlight unit, and an operation unit as necessary.

[Method of manufacturing optical film]
The method for producing an optical film includes a step of applying an easy-adhesion composition containing a binder resin, a polyamine, and fine particles to the surface of a resin film to form a coating film of the easy-adhesion composition (coating step), and a step of drying the formed coating film to form an easy-adhesion layer on the surface of the resin film (drying step). The method for producing a resin film is as described above.

In the coating process, a coating film of the easy-adhesion composition is formed on at least one surface of the resin film. Typically, the coating film is formed on one surface of the optical film. A known method can be used to apply the easy-adhesion composition in the coating process.

The methods include, for example, the bar coating method, roll coating method, gravure coating method, rod coating method, slot orifice coating method, curtain coating method, and fountain coating method. The thickness of the coating film formed in the coating process can be appropriately adjusted according to the thickness required when the coating film becomes an easily adhesive layer.

The surface of the resin film to which the easy-adhesion composition is applied is preferably subjected to a surface treatment. The surface treatment is as described above, but corona discharge treatment and plasma treatment are preferred. The conditions for the corona discharge treatment are not limited. The electron irradiation dose in the corona discharge treatment is preferably 50 to 150 W/ ^m2 /min, more preferably 70 to 100 W/ ^m2 /min.

A known method can be used for the drying process. The drying temperature is typically 50°C or higher, preferably 90°C or higher, and more preferably 110°C or higher. By setting the drying temperature within these ranges, for example, an optical film with excellent corrosion resistance (especially in high temperature and high humidity environments) can be obtained. The upper limit of the drying temperature is preferably 200°C or lower, and more preferably 180°C or lower.

The resin film may be stretched between the coating step and the drying step, simultaneously with the drying step, or after the drying step. A known method can be used to stretch the resin film after the easy-adhesion composition is applied, and uniaxial or biaxial stretching can be performed in the same manner as the stretching method for the resin film (before the easy-adhesion layer is applied) described above.

The resin film that forms the coating film of the easy-adhesion composition in the coating process may be an unstretched resin film or a stretched resin film. If the resin film before the coating process is an unstretched film and the optical film that is finally produced is a biaxially stretched film, it can be biaxially stretched after the coating process. If the resin film before the coating process is a uniaxially stretched film and the optical film that is finally produced is a biaxially stretched film, the direction of uniaxial stretching is the MD direction, and it can be stretched in the TD direction after the coating process.

A known stretching machine can be used to stretch the resin film. The longitudinal stretching machine is not particularly limited, but an oven stretching machine is preferred. The oven longitudinal stretching machine is generally composed of an oven and a conveying roll provided at the entrance side and the exit side of the oven. The resin film is stretched in the conveying direction by providing a peripheral speed difference between the conveying roll at the entrance side of the oven and the conveying roll at the exit side. The transverse stretching machine is not particularly limited, but a tenter stretching machine is preferred. The tenter stretching machine may be of the grip type or the pin type, but the grip type is preferred because the resin film is less likely to tear. The grip type tenter stretching machine is generally composed of a clip running device for transverse stretching and an oven. In the clip running device, the resin film is transported with the transverse end of the resin film being clamped by clips. At this time, the guide rail of the clip running device is opened and the distance between the two rows of clips on the left and right is widened, so that the resin film is transversely stretched. In the grip-type tenter stretching machine, simultaneous biaxial stretching is possible by providing the clip with an expansion/contraction function in the transport direction of the resin film. Alternatively, the machine may be an oblique stretching machine that tensilely stretches the resin film in the transport direction of the film at different speeds on the left and right sides of the stretching direction.

The stretching temperature is preferably close to the Tg of the resin that constitutes the resin film. Specifically, the range of Tg-30°C to Tg+100°C is preferable, and the range of Tg-20°C to Tg+80°C is more preferable. By appropriately adjusting the stretching temperature, a stable and sufficient stretch ratio can be achieved.

The stretching ratio defined by the area ratio is preferably 1.1 to 25 times, more preferably 1.3 to 10 times. By appropriately adjusting the stretching ratio, the properties (e.g., toughness) of the optical film can be improved. The stretching speed is preferably 10 to 20,000%/min, more preferably 100 to 10,000%/min for stretching in one direction. By appropriately adjusting the stretching speed, the time required for stretching can be shortened while preventing breakage of the optical film.

When the formation of the easy-adhesion layer and the stretching of the resin film are performed simultaneously, for example, after the coating process, the resin film on which the coating film of the easy-adhesion composition is formed may be stretched in a heated atmosphere. The heat applied to the resin film for stretching dries the coating film of the easy-adhesion composition formed on the surface of the resin film, forming an easy-adhesion layer. Note that the Tg of the resin film is usually 100°C or higher, so the stretching temperature described above is a temperature high enough to form an easy-adhesion layer from the coating film of the easy-adhesion composition.

When the resin film is formed by melt extrusion, the steps from the formation of the resin film to obtaining an optical film that is a stretched film can be performed continuously. In this case, it is preferable to continuously perform the step of applying an easy-adhesion composition to the surface of the resin film and the step of stretching the film coated with the easy-adhesion composition in a heated atmosphere. Such a step of applying the easy-adhesion composition that is performed continuously is called in-line coating. When an optical film that is a biaxially stretched film is produced by the manufacturing method of this embodiment, it is particularly preferable to continuously perform the step of stretching an unstretched film to obtain a uniaxially stretched film, the step of applying an easy-adhesion composition to the surface of the film, and the step of stretching the film coated with the easy-adhesion composition in a heated atmosphere. Furthermore, when performing surface treatment such as corona discharge treatment and plasma treatment on the film, it is preferable to continuously perform the step of stretching an unstretched film to obtain a uniaxially stretched film, the step of surface-treating the surface of the film, the step of applying an easy-adhesion composition to the surface of the surface-treated film, and the step of stretching the film coated with the easy-adhesion composition in a heated atmosphere.

The manufacturing method of this embodiment may include any step other than the steps described above. Such steps are, for example, a step of laminating an additional layer (e.g., a resin layer) on the formed optical film, or a step of subjecting the formed optical film to post-processing such as a coating process or a surface treatment.

The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples.

(1) Analysis method (1-1) Weight average molecular weight (Mw)
The weight average molecular weight was determined in terms of polystyrene using gel permeation chromatography (GPC) using the following apparatus and conditions:
- System: Tosoh GPC system HLC-8220
- Measurement column configuration Guard column: TSKguardcolumn SuperHZ-L, manufactured by Tosoh Corporation
Separation column: Tosoh Corporation, TSKgel SuperHZM-M, two columns connected in series - Reference column configuration Reference column: Tosoh Corporation, TSKgel SuperH-RC
-Developing solvent: Chloroform (Wako Pure Chemical Industries, Ltd., special grade)
Flow rate of developing solvent: 0.6 mL/min. Standard sample: TSK standard polystyrene (manufactured by Tosoh Corporation, PS-oligomer kit)
- Column temperature: 40°C

(1-2) Glass transition temperature (Tg)
The glass transition temperature was determined in accordance with the provisions of Japanese Industrial Standard JIS K7121. Specifically, a differential scanning calorimeter (Rigaku Thermo plus EVO DSC-8230) was used to evaluate the glass transition temperature by the starting point method from a DSC curve obtained by heating about 10 mg of a sample from room temperature to 200° C. (heating rate: 20° C./min) under a nitrogen gas atmosphere. α-alumina was used as a reference.

(1-3) Thickness of Optical Film The thickness of the optical film was measured using a Digimatic Micrometer (manufactured by Mitutoyo Corporation). The sample for measuring and evaluating the physical properties of the optical film, including the physical properties for which the evaluation methods will be shown later, was taken from the center of the film in the width direction.

(1-4) Average particle size and particle size distribution of fine particles Silica particles were added to methanol to a concentration of 1% by mass, and dispersed for 10 minutes using an ultrasonic disperser to prepare a measurement sample. This sample was measured using a laser diffraction/scattering particle size distribution measuring device (LA-920, manufactured by Horiba, Ltd.). The arithmetic mean value of the obtained volume-based particle size distribution was taken as the average particle size, and the arithmetic maximum value was taken as the maximum particle size.

(1-5) Total Light Transmittance and Haze The total light transmittance, haze (total haze), and internal haze of the prepared optical film were measured using a turbidity meter (manufactured by Nippon Denshoku Industries Co., Ltd., NDH5000) in accordance with the provisions of JIS K 7136. The internal haze was measured in a state where the film to be measured was immersed in tetralin in a quartz cell.

(1-6) Adhesion between resin film and easy-adhesion layer The adhesion between the prepared resin film and the easy-adhesion layer was evaluated by carrying out a grain test in accordance with JIS K5400 3.5 as follows. A 1 mm square grain-like cut was made with a sharp blade at three places on the easy-adhesion layer surface of the test sample. Cellophane tape (24 mm wide, JIS Z1522) was adhered to the cut with a wooden spatula. The cellophane tape was then peeled off to check for peeling of the easy-adhesion layer. If the easy-adhesion layer did not peel off, a new cellophane tape was again adhered to the cut with a wooden spatula, and the cellophane tape was peeled off to evaluate the adhesion. This evaluation was carried out at three places. The evaluation criteria are as follows.
⊚: The easy-adhesion layer did not peel off at three out of three locations even after five peel tests.
◯: The easy-adhesion layer did not peel off at one or two of the three locations even after five peel tests.
×: The easy-adhesion layer peeled off in 3 out of 3 places during 1 to 4 peel tests.

(1-7) Blocking Resistance of Optical Film The blocking resistance of the prepared optical film was evaluated as follows. The prepared optical film was wound on a roll to form a film roll, which was then left for 24 hours. After leaving it, the film roll was visually inspected, and the optical film was unwound from the film roll while visually inspecting the surface of the optical film over the entire longitudinal direction to evaluate the blocking resistance. The evaluation criteria were as follows:
◯: No deformation of the film roll and no wrinkles in the unwound optical film were observed.
×: Deformation of the film roll or wrinkles in the unwound optical film were observed.

(1-8) Uniformity of the easy-adhesion layer The easy-adhesion composition (coating liquid) prepared was also applied to a resin film and dried to obtain an easy-adhesion layer (coating film), and the uniformity of the easy-adhesion composition and the uniformity of the easy-adhesion layer were visually observed to evaluate. The evaluation criteria were as follows, and were shown as (evaluation of the easy-adhesion composition)/(evaluation of the easy-adhesion layer).
Regarding the evaluation of the easy-adhesion composition,
A: A uniform, easily adhesive composition was easily obtained.
B: When the adhesive composition was prepared, non-uniform substances such as gel fractions were observed, but a uniform adhesive composition was obtained by stirring for less than 6 hours.
C: A case in which non-uniform substances such as gel fractions were observed during preparation of the easily adhesive composition, but a uniform easily adhesive composition could not be obtained without filtration.

Regarding the evaluation of the easy-adhesion layer,
A: No coating unevenness, streaks, or thickness unevenness can be visually confirmed, and a uniform coating film is obtained.
B: At least one of uneven coating, streaks, and uneven thickness was visually observed, and a uniform coating film was not obtained.

(2) Manufacturing Example (Manufacturing Example 1)
A 1000L reaction kettle equipped with a stirrer, a temperature sensor, a cooling tube and a nitrogen inlet tube was charged with 40 parts by weight of methyl methacrylate (MMA), 10 parts by weight of 2-(hydroxymethyl)methyl acrylate (MHMA), 50 parts by weight of toluene as a polymerization solvent and 0.025 parts by weight of an antioxidant (Adeka STAB 2112, manufactured by ADEKA), and the temperature was raised to 105°C while nitrogen was passed through the reaction kettle. When refluxing with the temperature increase began, 0.05 parts by weight of t-amyl peroxy isononanoate (manufactured by Arkema Yoshitomi, trade name: Luperox 570) was added as a polymerization initiator, and 0.10 parts by weight of the t-amyl peroxy isononanoate was added dropwise over 3 hours, while solution polymerization was allowed to proceed under reflux at about 105 to 110°C, and aging was further carried out for 4 hours.

Next, 0.05 parts by weight of 2-ethylhexyl phosphate (Phoslex A-8, manufactured by Sakai Chemical Industry Co., Ltd.) was added to the resulting polymerization solution as a catalyst for the cyclization condensation reaction (cyclization catalyst), and the cyclization condensation reaction to form a lactone ring structure was allowed to proceed for 2 hours under reflux at approximately 90 to 110°C. Next, the resulting polymerization solution was heated to 240°C using an autoclave, and the cyclization condensation reaction was allowed to proceed further at that temperature.

Next, the obtained polymerization solution was introduced into a vent-type screw twin-screw extruder (φ=50.0 mm, L/D=30) with a barrel temperature of 240° C., a rotation speed of 100 rpm, a reduced pressure of 13.3 to 400 hPa (10 to 300 mmHg), one rear vent and four fore vents (referred to as the first, second, third, and fourth vents from the upstream side), a side feeder between the third and fourth vents, and a leaf disk-type polymer filter (filtration accuracy 5 μm, filtration area 1.5 m ² ) at the tip, at a processing rate of 45 kg/hour (resin amount equivalent), and devolatilization was performed. At that time, a mixed solution of antioxidant/cyclization catalyst deactivator separately prepared was charged from behind the first vent at a charging rate of 0.68 kg/hour, and ion-exchanged water was charged from behind the second and third vents at a charging rate of 0.22 kg/hour, respectively. The antioxidant/cyclization catalyst deactivator mixed solution was prepared by dissolving 50 parts by weight of an antioxidant (Irganox 1010, manufactured by Ciba Specialty Chemicals) and 35 parts by weight of zinc octylate (Nihon Kagaku Sangyo, Nikka Octyx Zinc 3.6% by weight) as a deactivator in 200 parts by weight of toluene. In addition, pellets of styrene-acrylonitrile copolymer (AS resin: styrene unit/acrylonitrile unit ratio of 73% by weight/27% by weight, weight average molecular weight of 220,000) were fed from the side feeder at a feeding rate of 15 kg/hour during devolatilization.

After devolatilization was complete, the resin in a molten state remaining in the extruder was discharged from the tip of the extruder while being filtered through a polymer filter, and pelletized using a pelletizer to obtain transparent pellets (1A) of acrylic resin containing, as the main component, a (meth)acrylic polymer having a lactone ring structure in the main chain (content of 75% by weight), and further containing a styrene-acrylonitrile copolymer at a content of 25% by weight. The Tg of the acrylic resin that constitutes the pellets (1A) was 122°C, and the weight average molecular weight was 151,000.

Next, the prepared pellets (1A) were melt-extruded at 280°C using a single-screw extruder (φ=20.0 mm, L/D=25) and a coat hanger type T-die (width 150 mm) to form an acrylic resin film with a thickness of 100 μm. During melt-extrusion, the resin film was discharged from the T-die onto a cooling roll maintained at 110°C.

Next, the prepared acrylic resin film was uniaxially stretched at its free end in the MD direction (machine direction, extrusion direction) at a stretch ratio of 2.0 and a stretching temperature of 140°C using a biaxial stretching machine (TYPE EX4, manufactured by Toyo Seiki Seisakusho) to obtain a stretched acrylic resin film (F1).

(Production Example 2)
In a 100L stainless steel polymerization tank equipped with a submerged tank and a stirrer, 42.5 parts by weight of MMA, 5 parts by weight of N-phenylmaleimide (PMI), 0.5 parts by weight of styrene (St), 50 parts by weight of toluene as a polymerization solvent, 0.2 parts by weight of acetic anhydride as an organic acid, and 0.06 parts by weight of n-dodecyl mercaptan as a chain transfer agent were charged, and nitrogen gas was bubbled for 10 minutes while stirring at a rotation speed of 100 rpm. Next, the temperature in the tank was raised while maintaining a nitrogen atmosphere, and when the temperature in the tank reached 100 ° C., 0.075 parts by weight of t-butylperoxyisopropyl carbonate was added, and at the same time, bubbling of nitrogen was started in the submerged tank. Next, a mixed solution of 2 parts by weight of styrene and 0.075 parts by weight of t-butylperoxyisopropyl carbonate was added to the tank at a constant rate over 5 hours, while the polymerization reaction was allowed to proceed under reflux at a polymerization temperature of 105 to 110° C. for 15 hours.

Next, 0.1 parts by weight and 0.02 parts by weight of 9,10-dihydro-9-oxa-10-phosphanenanthrene-10-oxide (HCA, manufactured by Sanko Co., Ltd.) as a phosphoric acid-based antioxidant and pentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] (AO-60, manufactured by Asahi Denka Co., Ltd.) as a phenol-based antioxidant were added to the obtained polymerization solution.

Next, the polymerization solution to which the antioxidant was added was introduced into a vent-type twin-screw extruder (Φ=29.75 mm, L/D=30) with a barrel temperature of 240°C, a rotation speed of 100 rpm, a vacuum degree of 13.3-400 hPa (10-300 mmHg), one rear vent, and four fore vents, at a processing rate of 2.0 kg/hour (resin amount conversion). Next, the resin in a molten state inside the extruder was discharged from the tip of the extruder and pelletized with a pelletizer to obtain transparent pellets (2A) of an acrylic resin consisting of a (meth)acrylic polymer having an N-substituted maleimide structure in the main chain. The Tg of the acrylic resin constituting the pellets (2A) was 138°C and the weight average molecular weight was 200,000.

Next, the prepared pellets (2A) were melt-extruded at 280°C using a single-screw extruder (φ=20.0 mm, L/D=25) and a coat hanger type T-die (width 150 mm) to form an acrylic resin film with a thickness of 100 μm. During melt-extrusion, the acrylic resin film was discharged from the T-die onto a cooling roll maintained at 110°C.

Next, the prepared acrylic resin film was uniaxially stretched at its free end in the MD direction (machine direction, extrusion direction) at a stretch ratio of 2.0 and a stretching temperature of 155°C using a biaxial stretching machine (TYPE EX4, manufactured by Toyo Seiki Seisakusho) to obtain a stretched acrylic resin film (F2).

(Production Example 3)
An acrylic resin (KAMAX T-240, manufactured by Rohm and Haas) (this resin is referred to as 3A) mainly composed of a (meth)acrylic polymer having a glutarimide structure in the main chain was melt-extruded at 280°C using a single-screw extruder (φ=20 mm, L/D=25) and a coat hanger type T-die (width 150 mm) to form an acrylic resin film having a thickness of 100 μm. During melt-extrusion, the resin film was discharged from the T-die onto a cooling roll maintained at 110°C.

Next, the prepared acrylic resin film was uniaxially stretched at its free end in the MD direction (machine direction, extrusion direction) at a stretch ratio of 2.0 and a stretching temperature of 140°C using a biaxial stretching machine (TYPE EX4, manufactured by Toyo Seiki Seisakusho) to obtain a stretched acrylic resin film (F3).

(Production Example 4)
A stretched acrylic resin film (F4) was obtained in the same manner as in Production Example 3, except that an acrylic resin mainly composed of a (meth)acrylic polymer having a glutaric anhydride structure in the main chain (Sumipex B-TR, manufactured by Sumitomo Chemical) was used instead of KAMAX T-240.

(Production Example 5)
A stretched acrylic resin film (F5) was obtained in the same manner as in Production Example 3, except that an acrylic resin (Delpet 980N, manufactured by Asahi Kasei Chemicals) mainly composed of a (meth)acrylic polymer having a maleic anhydride structure in the main chain was used instead of KAMAX T-240.

(Production Example 6)
A reaction mixture consisting of 70 parts by weight of deionized water, 0.5 parts by weight of sodium pyrophosphate, 0.2 parts by weight of potassium oleate, 0.005 parts by weight of ferrous sulfate, 0.2 parts by weight of dextrose, 0.1 parts by weight of p-menthane hydroperoxide, and 28 parts by weight of 1,3-butadiene was charged into a pressure-resistant reaction vessel equipped with a stirrer, and the reaction mixture was heated to 65° C. to allow the polymerization reaction to proceed. After 2 hours had elapsed from the start of polymerization, 0.2 parts by weight of p-hydroperoxide was further added to the mixture, and 72 parts by weight of 1,3-butadiene, 1.33 parts by weight of potassium oleate, and 75 parts by weight of deionized water were continuously dropped over 2 hours. The polymerization reaction was then continued, and a latex of a butadiene-based rubber polymer having an average particle size of 0.240 μm was obtained by polymerization for 21 hours from the start of polymerization.

Next, 120 parts by weight of deionized water, 50 parts by weight (solid content) of the butadiene-based rubber polymer latex prepared above, 1.5 parts by weight of potassium oleate, and 0.6 parts by weight of sodium formaldehyde sulfoxylate (SFS) were put into a polymerization vessel equipped with a cooler and a stirrer, and the inside of the vessel was fully replaced with nitrogen gas. Next, the temperature inside the vessel was raised to 70°C, and then a mixed monomer solution consisting of 36.5 parts by weight of styrene and 13.5 parts by weight of acrylonitrile, and a polymerization initiator solution consisting of 0.27 parts by weight of cumene hydroxyperoxide and 20 parts by weight of deionized water were continuously dropped into the vessel separately over a period of 2 hours to allow the polymerization reaction to proceed. After the dropping was completed, the temperature inside the vessel was raised to 80°C, and the polymerization reaction was continued for another 2 hours. Next, the temperature inside the vessel was lowered to 40°C, and the contents were passed through a 300-mesh wire net to obtain an emulsion polymerization liquid of elastic organic fine particles.

The resulting emulsion polymerization liquid of elastic organic microparticles was salted out and coagulated using calcium chloride, and the coagulated material was washed with water and dried to obtain powdered elastic organic microparticles (G1: average particle diameter 0.260 μm, refractive index of the soft polymer layer 1.516).

Next, an acrylic resin (Delpet 980N, Asahi Kasei Chemicals) mainly composed of a (meth)acrylic polymer having a maleic anhydride structure in the main chain and the elastic organic fine particles (G1) prepared above were kneaded using a twin-screw extruder so that the acrylic resin/elastic organic fine particles was 90/10 (weight ratio) to prepare pellets (3A). Next, the prepared pellets (3A) were melt-extruded at 280°C using a single-screw extruder (φ=20.0 mm, L/D=25) and a coat hanger type T-die (width 150 mm) to form an acrylic resin film with a thickness of 100 μm. During melt extrusion, the resin film was discharged from the T-die onto a cooling roll maintained at 110°C.

Next, the prepared acrylic resin film was uniaxially stretched at its free end in the MD direction (machine direction, extrusion direction) at a stretch ratio of 2.0 and a stretching temperature of 140°C using a biaxial stretching machine (TYPE EX4, manufactured by Toyo Seiki Seisakusho) to obtain a stretched acrylic resin film (F6).

(Production Example 7)
A reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen inlet tube was charged with 229.6 parts by weight of methyl methacrylate (MMA), 33 parts by weight of methyl 2-(hydroxymethyl)acrylate (MHMA), 0.138 parts by weight of an antioxidant (ADEKA CORPORATION's "ADEKA STAB (registered trademark) 2112"), 248.6 parts by weight of toluene as a non-polymerizable organic solvent, and 0.1925 parts by weight of n-dodecyl mercaptan, and the mixture was heated to 105° C. while nitrogen was passed through it. When refluxing began with the temperature increase, 0.2838 part by weight of t-amyl peroxy isononanoate ("Luperox (registered trademark) 570" manufactured by Arkema Yoshitomi Co., Ltd.) was added as a polymerization initiator, and 0.5646 part by weight of the t-amyl peroxy isononanoate and 12.375 parts by weight of styrene (St) were added dropwise over 2 hours to allow solution polymerization to proceed under reflux at about 105 to 110°C, and after completion of the dropwise addition, the mixture was further aged for 4 hours at the same temperature.

Next, 0.206 parts by weight of stearyl phosphate ("Phoslex A-18" manufactured by Sakai Chemical Industry Co., Ltd.) was added to the obtained polymerization solution as a catalyst for the cyclization condensation reaction (cyclization catalyst), and the cyclization condensation reaction to form a lactone ring structure was allowed to proceed for 2 hours under reflux at approximately 90 to 110°C. Next, the obtained polymerization solution was passed through a multi-tube heat exchanger heated to 240°C to complete the cyclization condensation reaction, and then introduced into a vent-type screw twin-screw extruder (L/D=52) having a barrel temperature of 250°C, one rear vent, four fore vents (referred to as the first, second, third, and fourth vents from the upstream side), and a side feeder between the third vent and the fourth vent, and having a leaf disk-type polymer filter (filtration accuracy: 5 μm) disposed at the tip thereof, at a processing speed of 31.2 parts/hour (converted into resin amount), and the degree of vacuum at each vent was set to 798 hPa for the rear vent, 266 hPa for the first vent, and 27 hPa for each of the second vent to the fourth vent, to perform devolatilization. At that time, ion-exchanged water was fed from behind the second and fourth vents at a feeding rate of 0.47 parts/hour, and a toluene solution of zinc octylate (Nikka Octix Zinc 18% manufactured by Nippon Chemical Industry Co., Ltd.), 50 parts by weight of Irganox 1010 (manufactured by Ciba Specialty Chemicals), and Adeka STAB AO-412S (manufactured by ADEKA) was injected so that the mass ratio of zinc octylate was 160 ppm, Irganox 1010 was 50 ppm, and Adeka STAB AO-412S was 50 ppm relative to the thermoplastic resin composition to be obtained.

After the devolatilization was completed, the resin composition in the molten state remaining in the extruder was discharged from the tip of the extruder while being filtered through the polymer filter, passed through a die, and then filtered through a filter with a pore size of 1 μm (product name: Micropore Filter 1EU, manufactured by Organo Corporation). The strands were cooled in a water tank filled with cooling water maintained at a temperature within the range of 30±10°C, and then introduced into a cutting machine (pelletizer) to obtain pellets made of a resin composition (7A) containing a lactone ring-based polymer having a lactone ring structure in the main chain. The weight average molecular weight of the obtained resin composition (7A) was 132,000, the number average molecular weight was 59,000, the glass transition temperature was 121°C, the thermal decomposition onset temperature was 335°C, and the refractive index was 1.501.

Next, the prepared pellets (7A) were formed into a film in the same manner as in Production Example 1 to obtain a stretched acrylic resin film (F7).

(Production Example 11)
0.09% by weight of an emulsion containing amorphous silica fine particles (manufactured by Nippon Shokubai, Sea Hoster KE-W30, average particle size (primary particle size) 0.28 μm, particle size distribution 1.1, solid content 20% by weight), 20% by weight of a urethane resin (manufactured by Daiichi Kogyo Seiyaku, Superflex 210, solid content 35% by weight), and 0.0007% by weight of a polyamine (manufactured by Nippon Shokubai, Epomin SP-006) were added in that order to the stirred pure water, mixed thoroughly, and passed through a 1 μm filter to obtain an easily adhesive composition (1B) which is an emulsion-like dispersion. The remainder after removing the urethane resin, silica fine particles, and polyamine from the easily adhesive composition is pure water.

(Production Examples 12 to 83)
Using the raw materials shown in Tables 1A, 1B, and 1C below, easily adhesive compositions (2B to 73B) that were emulsion-like dispersions were obtained in the same manner as in Production Example 11. The crosslinking agent was added after the urethane resin and before the addition of the polyamine.

SF210: Superflex 210, manufactured by Daiichi Kogyo Seiyaku, solid content 35% by weight
W-5030: Takelac W-5030, manufactured by Mitsui Chemicals Polyurethanes, solid content 30% by weight
CP-7020: Hydran CP-7020, manufactured by DIC, solid content 40% by weight
SF620: Superflex 620, manufactured by Daiichi Kogyo Seiyaku, solid content 30% by weight
AP-40N: Hydran AP-40N, manufactured by DIC, solid content 35% by weight
KE-W30: Seahoster KE-W30, manufactured by Nippon Shokubai, average particle size (primary particle size) 0.28 μm, particle size distribution 1.1, solid content 20% by weight
・KE-W10: Nippon Shokubai, Seahoster KE-W10, average particle size (primary particle size) 0.11 μm, particle size distribution 1.1, solid content 15% by weight
・SP-006: Epomin SP-006, manufactured by Nippon Shokubai
WS-700: Nippon Shokubai, Epocross WS-700, solids content 25% by weight

(3) Example (Example 1)
The adhesive composition (1B) prepared in Production Example 11 was applied to one surface of the acrylic resin film (F1) prepared in Production Example 1 so that the thickness of the coating film after drying was 270 nm, and then the whole was dried at 100 ° C. for 2 minutes. In this way, an optical film having an adhesive layer formed on one surface was obtained. The fine particles contained in the formed adhesive layer maintained the shape in the adhesive composition (1B).

(Examples 2 to 58, Comparative Examples 1 to 16)
As shown in Tables 2A to 2C below, the combination of the acrylic resin film and the easy-adhesion composition was changed, and an optical film having an easy-adhesion layer formed on one surface was obtained in the same manner as in Example 1.

The evaluation results of the optical films prepared in each example and comparative example are summarized in Tables 2A, 2B and 2C below.

(Example 59)
The adhesive composition (1B) prepared in Production Example 11 was applied to one surface of the acrylic resin film (F1) prepared in Production Example 1 using a coating tester so that the thickness of the coating film after drying was 600 nm, and then the whole was dried for 2 minutes at 100 ° C. Next, the film thus obtained was stretched in the TD direction (direction perpendicular to the MD direction in the film plane, width direction during extrusion molding) at a stretching ratio of 1.5 times and a stretching temperature of 140 ° C. using a biaxial stretching machine (manufactured by Toyo Seiki Seisakusho, TYPE EX4), and the free end was uniaxially stretched at a stretching ratio of 1.5 times and a stretching temperature of 140 ° C. to obtain an optical film composed of an acrylic resin film, which is a biaxially stretched film, in which an adhesive layer containing urethane resin and fine particles was formed on one surface.

(Comparative Example 17)
As shown in Table 3 below, the combination of the acrylic resin film and the easy-adhesion composition was changed, and an optical film having an easy-adhesion layer formed on one surface was obtained in the same manner as in Example 11.

The evaluation results of the optical films prepared in each example and comparative example are summarized in Table 3 below.

(Example 60)
The pellets (1A) of the acrylic resin prepared in Production Example 1 were melt-extruded at a processing speed of 200 kg/h (resin amount equivalent) and a temperature of 270° C. using a single-screw extruder (φ=90.0 mm, L/D=32) equipped with a polymer filter (filtration accuracy 5 μm) and a T-die at the tip to produce a strip-shaped acrylic resin film with a thickness of 220 μm. Next, the produced acrylic resin film was continuously fed to an oven vertical stretching machine following melt extrusion, and stretched (vertical stretching) in the vertical direction of the acrylic resin film (flow direction during melt extrusion, MD direction) at a stretching temperature of 142° C. and a stretching ratio of 1.5 times in the stretching machine.

Continuing, the easy-adhesion composition (11B) prepared in Production Example 21 was applied to one surface of the acrylic resin film after longitudinal stretching by gravure coating so that the thickness of the coating film after drying was 1050 nm (in-line coating), and then the acrylic resin film was directly fed to a tenter transverse stretching machine and stretched in its width direction (transverse stretching) at a stretching temperature of 132°C and a stretching ratio of 3.0 times. In this way, an optical film (thickness 58 μm) composed of an acrylic resin film, which is a biaxially stretched film, was obtained, in which an easy-adhesion layer (thickness 350 nm) containing urethane resin and fine particles was formed on one main surface.

(Examples 61 to 79, Comparative Examples 18 to 20)
As shown in Table 4 below, the combination of the resin pellets and the easy-adhesion composition was changed, and an optical film having an easy-adhesion layer formed on one surface was obtained in the same manner as in Example 57.

The evaluation results of the optical films prepared in each example and comparative example are summarized in Table 4 below.

(Example 80)
The pellets (1A) of the acrylic resin prepared in Production Example 1 were melt-extruded at a processing speed of 200 kg/h (resin amount equivalent) and a temperature of 270° C. using a single-screw extruder (φ=90.0 mm, L/D=32) equipped with a polymer filter (filtration accuracy 5 μm) and a T-die at the tip to produce a strip-shaped film with a thickness of 220 μm. Next, the film thus produced was continuously fed to an oven longitudinal stretching machine following the melt extrusion, and stretched (longitudinal stretching) in the longitudinal direction of the film (flow direction during melt extrusion, MD direction) at a stretching temperature of 142° C. and a stretching ratio of 1.5 times in the stretching machine.

After that, one of the main surfaces of the acrylic resin film after longitudinal stretching was subjected to a corona treatment, and the easy-adhesion composition (11B) prepared in Production Example 21 was applied to the treated surface by gravure coating so that the thickness of the coating film after drying was 1050 nm (in-line coating). Next, the acrylic resin film was directly fed to a tenter transverse stretching machine and stretched in its width direction (transverse stretching) at a stretching temperature of 132°C and a stretching ratio of 3.0 times. In this way, an optical film (thickness 58 μm) composed of an acrylic resin film, which is a biaxially stretched film, was obtained, in which an easy-adhesion layer (thickness 350 nm) containing urethane resin and fine particles was formed on one main surface.

(Examples 81 to 82, Comparative Example 21)
As shown in Table 5 below, the combination of the resin pellets and the easy-adhesion composition was changed, and an optical film having an easy-adhesion layer formed on one main surface was obtained in the same manner as in Example 13.

The evaluation results of the optical films prepared in each example and comparative example are summarized in Table 5 below.

As shown in Tables 2A to 5, the adhesion layer contains a binder resin, polyamine, and fine particles, and the content of polyamine in the adhesion layer is 0.0090% by weight to 1.4100% by weight, so that the adhesion between the resin film and the adhesion layer is excellent and a uniform adhesion layer can be formed. It is presumed that the use of a polymer polyamine further improves the adhesion between the resin film and the adhesion layer due to the interaction between the polyamine and the base film. Furthermore, it was found that blocking resistance is also ensured by setting the polyamine content to, for example, 0.0489% by mass or more. It is presumed that this is because the viscosity of the adhesion composition is increased by the sufficient addition of polyamine, and the retention power of the fine particles is increased. It is presumed that the viscosity of the matrix part of the adhesion layer is improved by adding polyamine, and the embedding of the fine particles in the coating liquid during drying is suppressed. Furthermore, it is presumed that the polyamine also has the effect of suppressing the falling off of the fine particles. In contrast, Comparative Examples 1 to 11, 13, 15, and 17 to 20, which used easy-adhesion compositions (14B to 23B, 39B, and 57B) with a polyamine content of less than 0.0090% by weight, were not satisfactory in adhesion. In addition, Comparative Examples 12, 14, and 16, which used easy-adhesion compositions (37B, 56B, and 73B) with a polyamine content of more than 1.4100% by weight, were not satisfactory in uniformity of the easy-adhesion composition or easy-adhesion layer. This is presumably because the viscosity of the easy-adhesion composition became too high due to the excessive addition of polyamine.

The optical film of the present invention is used in image display devices such as LCDs, and is suitable for use as various protective films such as polarizer protective films, retardation films, and polarizing films.

Claims (8)

An optical film having a resin film containing a (meth)acrylic polymer and an easy-adhesion layer formed on a surface of the resin film,
The easy-adhesion layer contains a binder resin, a polyamine, and fine particles,
The adhesive layer may contain a crosslinking agent,
The polyamine is a polymer having a plurality of amino groups,
the plurality of amino groups includes at least one selected from the group consisting of a secondary amino group and a tertiary amino group,
When the easy-adhesion layer contains the crosslinking agent, the content of the polyamine is 0.0090% by weight to 1.4100% by weight in the total weight of the binder resin, the polyamine, the fine particles, and the crosslinking agent in the easy-adhesion layer ;
When the easy-adhesion layer does not contain the crosslinking agent, the content of the polyamine in the easy-adhesion layer is 0.0090% by weight to 1.4100% by weight in the total weight of the binder resin, the polyamine, and the fine particles . The optical film according to claim 1, wherein the binder resin comprises a urethane resin. The optical film according to claim 1, wherein the plurality of amino groups include a primary amino group, the secondary amino group, and the tertiary amino group. The optical film according to claim 1, wherein the polyamine comprises a polyalkyleneimine. The optical film according to claim 4, wherein the polyalkyleneimine contains a primary amino group, the secondary amino group, and the tertiary amino group, and has a branched structure. An optical member comprising the optical film according to any one of claims 1 to 5. An image display device comprising the optical film according to any one of claims 1 to 5. A method for producing the optical film according to any one of claims 1 to 5, comprising the steps of:
A coating film of an adhesive composition containing a binder resin, a polyamine, and fine particles is formed on a surface of a resin film;
The coating film is dried to form an easy-adhesion layer containing the binder resin, the polyamine, and the fine particles on a surface of the resin film;
The polyamine is a polymer having a plurality of amino groups,
The method for producing an optical film, wherein the plurality of amino groups include at least one selected from the group consisting of a secondary amino group and a tertiary amino group.