JP2014186265A - Optical film, polarizing plate and image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel optical film that secures transparency and can show reverse wavelength dispersibility.SOLUTION: An optical film comprises a layer composed of a resin composition comprising a polymer (A) having a constitutional unit of formula (1) and a polymer (B) having a molecular structure of formula (2) in a main chain. In the formula (1), n is a natural number of 1-4, and Rand Rindependently represent a hydrogen atom or a methyl group.

Description

  The present invention relates to an optical film, a polarizing plate including the optical film, and an image display device.

  Optical members having birefringence utilizing birefringence caused by polymer orientation are widely used in the field of image display. For example, a phase difference film using a phase difference caused by birefringence is widely used for color tone compensation and viewing angle compensation of an image display device.

  When the resin composition constituting the retardation film contains a polymer exhibiting a large optical anisotropy, the retardation that can be exhibited by the retardation film can be increased. A polymer having a large optical anisotropy is, for example, a polymer having an aromatic ring, such as polystyrene or polycarbonate. In fact, polystyrene and polycarbonate have been widely used for optical members such as optical films, but these polymers are optically affected by the influence of the aromatic ring that exhibits high optical anisotropy. As the wavelength becomes shorter, birefringence increases (phase difference increases), and wavelength dispersibility (forward wavelength dispersibility) is exhibited. However, in order to obtain an image display device with excellent display characteristics, on the contrary, an optical member exhibiting wavelength dispersion having a smaller birefringence (a smaller phase difference) is desired as the wavelength of light becomes shorter. In this specification, the wavelength dispersibility in which birefringence is reduced as the wavelength of light is shortened at least in the visible light region, according to the commonly used name of those skilled in the art, and a general polymer as well as an optical formed by the polymer. Based on the reverse of the wavelength dispersibility exhibited by the member, it is referred to as “reverse wavelength dispersibility”.

  As optical members exhibiting reverse wavelength dispersion, Patent Document 1 (Japanese Patent Laid-Open No. 2001-337222) discloses a polymer having positive intrinsic birefringence (polynorbornene) and a polymer having negative intrinsic birefringence ( A retardation plate made of a resin composition containing a styrene polymer) is disclosed. Patent Document 2 (Japanese Patent Laid-Open No. 2010-26029) is composed of a resin composition containing a polymer having a vinylpyrrolidone unit as a structural unit and a polymer having a (meth) acrylate unit as a structural unit. An optical film is disclosed.

JP 2001-337222 JP 2010-26029 A

  The present invention is an optical film composed of a resin composition, which has high compatibility between the polymers contained in the resin composition, thereby ensuring optical transparency as an optical film and a reverse wavelength. An object is to provide a novel optical film capable of exhibiting dispersibility.

The optical film of the present invention comprises a polymer (A) having a structural unit represented by the following formula (1) and a polymer (B) having a molecular structure represented by the following formula (2) in the main chain. The layer comprised from the resin composition (C) to contain is included. However, in formula (1), n is a natural number of 1 to 4, R ¹ and R ² is a hydrogen atom or a methyl group independently of one another.

  The polarizing plate of the present invention includes the optical film of the present invention.

  The image display device of the present invention includes the optical film of the present invention.

  According to the present invention, an optical film composed of a resin composition having high compatibility between polymers contained in the resin composition, thereby ensuring optical transparency as an optical film. Thus, a novel optical film that can exhibit reverse wavelength dispersion can be obtained.

  The “resin composition” in the present specification is a broader concept than the “polymer”. The resin composition can contain one or more polymers, and optionally contains materials other than the polymer, for example, additives such as ultraviolet absorbers, antioxidants, fillers, and plasticizers. You may go out.

[Polymer (A)]
The polymer (A) has a structural unit (N-vinyl lactam unit) represented by the following formula (1). In the formula (1), n is a natural number of 1 to 4, and R ¹ and R ² are each independently a hydrogen atom or a methyl group.

  The polymer (A) having an N-vinyl lactam unit has high compatibility with the polymer (B). For this reason, by setting it as the resin composition (C) containing both, the optical film as which the optical transparency as an optical film was ensured can be obtained.

  Moreover, the optical film with a high freedom degree of control of an optical characteristic can be obtained with the resin composition (C) containing the polymer (A) which has a N-vinyl lactam unit, and a polymer (B). For example, it is possible to obtain an optical film exhibiting reverse wavelength dispersion with the resin composition. The N-vinyl lactam unit has a function of giving negative intrinsic birefringence to a polymer having the unit as a constituent unit. For this reason, the polymer (A) is typically a polymer having negative intrinsic birefringence. On the other hand, as described later, the polymer (B) is typically a polymer having positive intrinsic birefringence. When orientation is added to the resin composition (C) containing such polymers (A) and (B), the slow axes (or fast axes) of the respective polymers are orthogonal to each other. Birefringence cancels out. Here, since the degree to which birefringence cancels differs depending on the wavelength, birefringence, for example, reverse wavelength dispersion of phase difference occurs.

  The action of the N-vinyl lactam unit that strengthens the birefringence wavelength dispersion in the polymer (A) is weak, in other words, the birefringence wavelength dispersion of the polymer (A) itself having an N-vinyl lactam unit. It is typically close to flat and can be made almost flat depending on the composition of the polymer (A), and the wavelength dispersion of birefringence in the polymer (B) having a specific molecular structure in the main chain is very high. Combined with its strength, it contributes to the realization of an optical film having a high degree of freedom in controlling optical characteristics such as reverse wavelength dispersion. For example, in the combination of polymers exemplified in Patent Document 1 (Japanese Patent Application Laid-Open No. 2001-337222), since the birefringence wavelength dispersibility in both polymers is weak, unlike the optical film of the present invention, The degree of freedom in controlling the optical characteristics cannot be increased.

  The structural unit having an action of giving negative (or positive) intrinsic birefringence to the polymer means that when the homopolymer of the unit is formed, the intrinsic birefringence of the formed homopolymer is negative (or positive). Is a structural unit. Whether the intrinsic birefringence of the polymer itself is positive or negative is determined by the balance between the birefringence generated by the unit and the birefringence generated by the other structural units of the polymer.

  The positive or negative of the intrinsic birefringence of the polymer is the direction in which the molecular chains in the layer of the layer in which the molecular chains of the polymer are uniaxially oriented (for example, a film) in the layer perpendicular to the main surface of the layer. This can be determined based on a value “n1-n2” obtained by subtracting the refractive index n2 of the layer for the vibration component perpendicular to the orientation axis from the refractive index n1 of the layer for the vibration component parallel to the (orientation axis). The intrinsic birefringence value can be determined by calculation based on the molecular structure of each polymer.

  Whether the intrinsic birefringence of the resin composition is positive or negative is determined by the balance of birefringence generated by each polymer contained in the resin.

  N-vinyl lactam units include, for example, N-vinyl-2-pyrrolidone units, N-vinyl-ε-caprolactam units, N-vinyl-2-piperidone units, N-vinyl-4-methyl-2-pyrrolidone units, N -Vinyl-5-methyl-2-pyrrolidone unit, N-vinyl-ω-heptalactam unit. The polymer (A) may have two or more types of N-vinyl lactam units as constituent units.

  As long as the effect of the present invention is obtained, the polymer (A) can further have a structural unit other than the structural unit represented by the formula (1). The structural unit is, for example, 1) (meth) acrylic such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, cyclohexyl (meth) acrylate, hydroxyethyl (meth) acrylate, etc. Acid esters; 2) (meth) acrylamide and derivatives thereof (for example, N-monomethyl (meth) acrylamide, N-monoethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, etc.); 3) (meth) acrylic Basic unsaturated monomers such as dimethylaminoethyl acid, dimethylaminoethyl (meth) acrylamide, vinylpyridine, and vinylimidazole, and salts and quaternized products thereof; 4) vinylamides such as vinylformamide, vinylacetamide, and vinyloxazolidone; 5) (meth) acrylic Carboxyl group-containing unsaturated monomers such as acid, itaconic acid, maleic acid and fumaric acid and salts thereof; 6) unsaturated anhydrides such as maleic anhydride and itaconic anhydride; 7) vinyl acetate, vinyl propionate, etc. 8) Vinyl ethylene carbonate and derivatives thereof; 9) Aromatic vinyl compounds and derivatives thereof; 10) Ethyl (meth) acrylate-2-sulfonate and derivatives thereof; 11) Vinyl sulfonic acid and derivatives thereof; 12) vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether; 13) olefins such as ethylene, propylene, octene, 4-methyl-1-pentene, butadiene; It is. The polymer (A) can have one or more of these structural units.

  The aromatic vinyl compound is, for example, styrene, vinyl toluene, α-methyl styrene, α-hydroxymethyl styrene, α-hydroxyethyl styrene, or chlorostyrene.

  When the polymer (A) further has a styrene unit as a constituent unit in addition to the N-vinyl lactam unit, for example, when the polymer (A) is an N-vinylpyrrolidone-styrene copolymer, the styrene unit during the orientation of the polymer (A) Based on the high birefringence exhibited by, a retardation film showing a larger retardation can be obtained as an optical film. Further, since the styrene unit has a function of giving negative intrinsic birefringence to the polymer having the unit as a constituent unit, the polymer (A) is negatively intrinsic as a synergistic action with the N-vinyl lactam unit. It can be set as the polymer which has birefringence, and the realization of the optical film which shows reverse wavelength dispersion becomes more reliable by this. In addition, the styrene unit is a polymer having a very strong birefringence wavelength dispersibility because the action of strengthening the birefringence wavelength dispersibility in the polymer (A) is weak like the N-vinyl lactam unit. Combined with the combination with (B), it contributes to the realization of an optical film having a high degree of freedom in controlling optical characteristics such as reverse wavelength dispersion. Furthermore, since the styrene unit has low hygroscopicity, it is possible to obtain an effect that film formation is facilitated and reduction in retardation due to wet heat can be improved (durability can be improved).

  When the polymer (A) is a copolymer having N-vinyl lactam units and aromatic vinyl compound units (for example, styrene units) as constituent units, the content of N-vinyl lactam units in the polymer (A) Is, for example, 20 to 99% by weight, preferably 40 to 90% by weight, and more preferably 45 to 80% by weight. Within these ranges, it is more certain to ensure compatibility with the polymer (B) and to realize a degree of freedom in controlling high optical properties. Moreover, Tg of a polymer (A) can be made high to the value suitable for use as an optical film. At the same time, the content of the aromatic vinyl compound unit in the polymer (A) is, for example, more than 0 wt% and 80 wt% or less, preferably 1 to 80 wt%, more preferably 10 to 60 wt%, More preferred is ˜55% by weight. In these ranges, the compatibility with the polymer (A) can be ensured, and the degree of freedom in controlling high optical properties can be realized more reliably. Moreover, while being able to hold | maintain the value of Tg suitable for use as an optical film, the birefringence (for example, phase difference) which the obtained optical film shows can be enlarged with the aromatic ring which an aromatic vinyl compound has. For an optical film having a large birefringence, for example, a desired retardation can be obtained while thinning the film, and the optical film having such a thin film is suitable for use in, for example, an image display device that is becoming thinner. ing.

The content of each structural unit in the polymer (A) is a known method, for example, ¹ H nuclear magnetic resonance ⁽¹ H-NMR), can be determined by infrared spectroscopy (IR) or elemental analysis. For example, the ratio of the N-vinyl lactam unit in all the structural units of the polymer (A) (the content of the N-vinyl lactam unit in the polymer (A)) can be determined by elemental nitrogen analysis.

  The weight average molecular weight (Mw) of the polymer (A) is, for example, from 50,000 to 1,000,000, preferably from 100,000 to 500,000, and more preferably from 150,000 to 400,000. Within these ranges, the compatibility of the polymer (A) and the polymer (B) in the resin composition (C) is more reliably ensured. Moreover, too high weight average molecular weight makes it difficult to mold the resin composition (C) into a film.

  The glass transition temperature (Tg) of the polymer (A) is, for example, 110 ° C. or higher, preferably 120 ° C. or higher, more preferably 140 ° C. or higher.

The polymer (A) can be formed by a known method. For example, the polymer (A) can be formed by polymerizing a monomer group containing N-vinyl lactam represented by the following formula (3) and, if necessary, another monomer. In the formula (3), n is a natural number of 1 to 4, and R ¹ and R ² are each independently a hydrogen atom or a methyl group.

  Various polymerization methods such as suspension polymerization, emulsion polymerization, and solution polymerization can be applied to the polymerization of the monomer group. Solution polymerization may be performed according to a known method. Polymerization solvents used for solution polymerization are, for example, cyclic ethers such as tetrahydrofuran and dioxane; glycol ethers such as ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and propylene glycol dimethyl ether; ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether Esters of glycol monoethers such as acetate and 3-methoxybutyl acetate; alkyl esters such as ethyl acetate, butyl acetate and methyl propionate; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; benzene, toluene and xylene , Aromatic hydrocarbons such as ethylbenzene; Aliphatic hydrocarbons such as xane, cyclohexane, and octane; Amides such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone; Alcohols such as methanol, ethanol, isopropanol, n-butanol, and diethylene glycol; A polymerization solvent can be appropriately selected and used. Only one type of polymerization solvent may be used alone, or two or more types may be used in combination.

[Polymer (B)]
The polymer (B) has a molecular structure represented by the following formula (2) in the main chain.

The polymer (B) has, for example, a molecular structure represented by the following formula (4) or formula (5) in the main chain. Y in the formula (4) is a direct bond, oxygen, sulfur, SO ₂ , CO, C (CH ₃ ) ₂ , CH (CH ₃ ) or CH ₂ .

  Examples of the polymer (B) include polyethersulfone (PES) which is a polymer represented by the following formula (6), polysulfone which is a polymer represented by the following formula (7), and the following formula (8). It is at least one selected from polyphenylsulfone which is a polymer to be shown.

  The polymer (B) having the molecular structure represented by the formula (2) is highly compatible with the polymer (A) having an N-vinyl lactam unit as a constituent unit. For this reason, by setting it as the resin composition (C) containing both, the optical film as which the optical transparency as an optical film was ensured can be obtained.

  In addition, an optical film having a high degree of freedom in controlling optical properties can be obtained by the resin composition (C) containing the polymer (A) and the polymer (B). It is possible to obtain an optical film exhibiting wavelength dispersion. The molecular structure represented by the formula (2) has an action of giving positive intrinsic birefringence to a polymer having the molecular structure in the main chain. For this reason, the polymer (B) is typically a polymer having positive intrinsic birefringence. On the other hand, as described above, the polymer (A) typically has a negative intrinsic birefringence. When orientation is added to the resin composition (C) containing such polymers (A) and (B), the slow axes (or fast axes) of the respective polymers are orthogonal to each other. Birefringence cancels out. Here, since the degree to which birefringence cancels differs depending on the wavelength, birefringence, for example, reverse wavelength dispersion of phase difference occurs.

  The above-described molecular structure that enhances the birefringence wavelength dispersibility in the polymer (B) is very strong. In other words, the birefringence wavelength dispersibility in the polymer (B) can be greatly increased. The optical dispersion of the optical film has a high degree of freedom in controlling the optical characteristics, for example, the reverse wavelength dispersion, in combination with the combination with the polymer (A) that is typically close to flat and is almost flat depending on the composition. Contributes to realization.

  In addition, since the molecular structure has the effect of greatly increasing the birefringence wavelength dispersibility of the polymer (B), the reverse is true even when the content of the polymer (B) in the resin composition (C) is low. An optical film exhibiting wavelength dispersion can be realized.

The reduced viscosity (RV) of the polymer (B) is, for example, from 0.30 to 1.00, preferably from 0.35 to 0.50. Within these ranges, the compatibility of the polymer (A) and the polymer (B) in the resin composition (C) is more reliably ensured. Moreover, too high reduced viscosity makes it difficult to mold the resin composition (C) into a film. The reduced viscosity is obtained by dissolving the polymer (B) in N, N-dimethylformamide (DMF) so as to have a concentration of 1% (w / v), and measuring the dropping time of the solution with an Ostwald viscometer. And it can obtain | require by following Formula from a measurement result.
Reduced viscosity (RV) = Drip time of DMF solution of polymer (B) / Drip time of DMF only-1.00

  The glass transition temperature (Tg) of the polymer (B) is, for example, 170 ° C. or higher, preferably 200 ° C. or higher. Within these ranges, a high Tg when the resin composition (C) and the optical film are combined with the polymer (A) is more certain.

  The polymer (B) can be formed by a known method. A commercially available polymer (B) may be used. In particular, polyethersulfone, polysulfone, and polyphenylsulfone represented by the formulas (6) to (8) can be obtained from commercial products relatively easily. Commercially available polymers (B) include, for example, “Sumika Excel” manufactured by Sumitomo Chemical, “Radel A”, “Radel R”, “Udel” manufactured by Solvay Advanced Polymers, and “Ultra Zone” manufactured by BASF. S "," Ultra Zone E "," Ultra Zone P "series and the like.

[Resin composition]
The resin composition (C) includes a polymer (A) and a polymer (B). The content of the polymer (A) in the resin composition (C) is, for example, 50 to 99% by weight, preferably 70 to 95% by weight, and more preferably 75 to 90% by weight. The content rate of a polymer (B) is 1 to 50 weight%, for example, 5 to 30 weight% is preferable and 10 to 25 weight% is more preferable. Within these ranges, it is possible to ensure the compatibility between the polymer (A) and the polymer (B) and to realize an optical film having a high degree of freedom in controlling optical properties. More specifically, the realization of an optical film exhibiting reverse wavelength dispersion becomes more reliable. Moreover, it becomes the resin composition (C) which has high Tg suitable for use as an optical film.

The content of each polymer in the resin composition (C) can be determined by a known method such as ¹ H-NMR or IR.

  The resin composition (C) typically includes a polymer (A) having a positive intrinsic birefringence and a polymer (B) having a negative intrinsic birefringence. The sign of the intrinsic birefringence of the resin composition (C) itself depends on the balance between the content of the polymer (A) and the degree of intrinsic birefringence, and the content of the polymer (B) and the degree of intrinsic birefringence. The film is typically negative, and at this time, an optical film (negative retardation film) exhibiting a negative retardation, and further a negative retardation film exhibiting reverse wavelength dispersion can be obtained. In the negative retardation film, the thickness direction retardation Rth is negative.

  The resin composition (C) may contain two or more kinds of the polymer (A) and / or the polymer (B).

  The Tg of the resin composition (C) is, for example, 120 ° C. or higher, and is 140 ° C. or higher, further 150 ° C. or higher depending on the composition. The optical film composed of the resin composition (C) having such a high Tg is suitable for use in an image display device such as a liquid crystal display device (LCD) because it can be disposed close to a heat generating part such as a light source. ing.

  The resin composition (C) may contain a polymer other than the polymers (A) and (B), or other various materials, as long as the effect of the present invention is obtained. Such materials include, for example, fillers, antioxidants, heat stabilizers, light stabilizers, UV absorbers, flame retardants, lubricants, antistatic agents, inorganic or organic colorants, rust inhibitors, crosslinkers, It is an optional additive such as a foaming agent, a fluorescent agent, a surface smoothing agent, a surfactant, a surface gloss improving agent, and a mold release improving agent such as a fluororesin. These materials may be added during the processing of the polymers (A) and (B).

  The filler may be either an inorganic filler or an organic filler. Further, the filler may be a fibrous filler, a plate-like filler, or a form other than a fibrous or plate-like shape, for example, a granular filler. Examples of the fibrous inorganic filler are glass fiber; carbon fiber such as pan-based carbon fiber and pitch-based carbon fiber; ceramic fiber such as silica fiber, alumina fiber and silica-alumina fiber; and metal fiber such as stainless steel fiber. Whiskers such as potassium titanate whisker, barium titanate whisker, wollastonite whisker, aluminum borate whisker, silicon nitride whisker and silicon carbide whisker are also included in the fibrous inorganic filler. Examples of fibrous organic fillers are polyester fibers and aramid fibers. Examples of the plate-like inorganic filler are talc, mica, graphite, wollastonite, glass flake, barium sulfate, and calcium carbonate. The mica may be any of muscovite, phlogopite, fluorine phlogopite, and tetrasilicon mica. Examples of particulate fillers are glass beads, glass powder, hollow glass, kaolin, clay, vermiculite; calcium silicate, aluminum silicate, feldspar powder, acid clay, waxy clay, sericite, sillimanite, bentonite, slate powder, Silicates such as silanes; carbonates such as calcium carbonate, pepper, barium carbonate, magnesium carbonate, dolomite; sulfates such as barite powder, blankfix, precipitated calcium sulfate, calcined gypsum, barium sulfate; hydrated alumina, etc. Hydroxides: Alumina, antimony oxide, magnesia, titanium oxide, zinc white, silica, silica sand, quartz, white carbon, diatomaceous earth and other oxides; sulfides such as molybdenum disulfide; nitrides such as boron nitride; silicon carbide, etc. Carbides; metal powders; organic polymers such as fluororesins; bromination Organic low molecular weight crystal such as phenyl ether. Spherical fillers and powders having a small aspect ratio are also included in the granular filler. The content of these materials in the resin composition (C) is, for example, 10% by weight or less, preferably 5% by weight or less, and more preferably 1% by weight or less.

  The resin composition (C) can be formed by a known method. For example, the polymer (A) and the polymer (B) and the various materials described above may be mixed at a predetermined ratio as necessary, and kneaded while applying heat. Further, the polymers (A) and (B) may be dissolved in a solvent that dissolves both polymers. The solution in which the polymers (A) and (B) are dissolved may be circulated as it is, or may be circulated as a solid resin composition (C) by volatilizing the solvent.

[Optical film]
The optical film has a layer composed of the resin composition (C). The optical film may have an arbitrary layer other than the layer, for example, another optical film such as a polarizer, a polarizer protective film, a polarizing plate, and a retardation film, if necessary. When the optical film is a single layer, the optical film is composed of the resin composition (C).

  As long as it has the layer comprised from the resin composition (C), the kind of optical film is not limited. The optical film is typically a retardation film that exhibits a retardation due to the orientation of the contained polymer. Focusing on the orientation of the polymers (A) and (B), the optical film as the retardation film is a member formed by giving orientation to the resin composition (C) containing the polymers (A) and (B). is there. In order to give orientation to the resin composition (C), the resin composition (C) molded into a film may be stretched.

  An optical film shows a negative phase difference, for example. Moreover, as above-mentioned, an optical film can show reverse wavelength dispersion by the combination of a polymer (A) and a polymer (B). An optical film is a negative phase difference film which shows reverse wavelength dispersion, for example. When the optical film exhibits reverse wavelength dispersion, the film may exhibit reverse wavelength dispersion even though it is a single layer. For this reason, desired optical characteristics can be obtained while making the film thinner, and further reduction in size and weight of the image display device can be realized. In addition, such an optical film has high productivity because it is unnecessary to adjust the bonding angle of each layer as compared with an optical film that achieves reverse wavelength dispersion by stacking a plurality of layers.

  An optical film exhibiting reverse wavelength dispersion is a broadband optical member. For example, by using this optical film, an image display device having excellent display characteristics can be constructed. More specifically, by using an optical film exhibiting reverse wavelength dispersion for an image display device, the visibility and contrast characteristics of the device are improved. This improvement in characteristics brings about a reduction in bluishness in black display, for example.

  The optical film which is a retardation film is usually a uniaxially stretchable, biaxially stretchable or obliquely stretchable film.

  The in-plane retardation Re (550) for light having a wavelength of 550 nm indicated by the optical film as the retardation film is, for example, 20 nm or more, and the composition of the polymer (A), the type of the polymer (B), the resin composition ( Depending on the composition of C) and the stretched state of the optical film, it is 70 nm or more, 130 nm or more, and further 250 nm or more. The in-plane retardation Re (550) per film thickness of 100 μm is, for example, 20 nm or more, and the composition of the polymer (A), the type of the polymer (B), the composition of the resin composition (C), and the optical Depending on the stretched state of the film, it is 70 nm or more, 160 nm or more, and further 300 nm or more. The in-plane retardation is defined as nx as the refractive index in the slow axis direction in the retardation film plane, ny as the refractive index in the fast axis direction in the retardation film plane, and d (nm) as the thickness of the retardation film. , A value given by the formula (nx−ny) × d.

  The retardation Rth (550) in the thickness direction with respect to light having a wavelength of 550 nm exhibited by the optical film that is a negative retardation film is, for example, -10 nm or less, the composition of the polymer (A), and the type of the polymer (B) Depending on the composition of the resin composition (C) and the stretched state of the optical film, it is −30 nm or less, −60 nm or less, and further −120 nm or less. The thickness direction retardation Rth (550) per 100 μm of the film is, for example, −5 nm or less, the composition of the polymer (A), the type of the polymer (B), the composition of the resin composition (C). Depending on the stretched state of the optical film, it is -30 nm or more, -80 nm or less, and further -150 nm or less. The retardation Rth in the thickness direction is a value given by the expression {(nx + ny) / 2−nz} × d, where nz is the refractive index in the thickness direction of the retardation film.

  When the optical film exhibits reverse wavelength dispersion, the ratio Re (450) / Re () is defined as Re (450) for the in-plane retardation for light having a wavelength of 450 nm and Re (550) for the light having a wavelength of 550 nm. 550) is less than 1, for example less than 0.98, depending on the composition of polymer (A), the type of polymer (B), the composition of resin composition (C), and the stretched state of the optical film. 94 or less, 0.90 or less, and further 0.85 or less.

  The total light transmittance of the optical film is, for example, 85% or more, preferably 90% or more, and more preferably 91% or more. The total light transmittance is an index of optical transparency of the optical film. An optical film having a total light transmittance of less than 85% is not suitable for optical applications. The total light transmittance of the optical film can be determined in accordance with JIS K7361.

  The thickness of the optical film is, for example, 10 μm to 500 μm, preferably 20 μm to 300 μm, and more preferably 30 μm to 150 μm.

  The Tg of the optical film is, for example, 120 ° C. or higher. Depending on the composition of the polymer (A), the type of the polymer (B), and the composition of the resin composition (C), 140 ° C. or higher, and further 150 ° C. or higher. It becomes. Although the upper limit of Tg is not limited, it is preferably 200 ° C. or lower, more preferably 180 ° C. or lower in consideration of the productivity and handling properties of the optical film.

  The haze exhibited by the optical film is, for example, 5% or less with a thickness of 100 μm. Depending on the composition of the polymer (A), the type of the polymer (B), and the composition of the resin composition (C) 3% or less, and further 2% or less. In addition, the haze which a phase difference film shows is equal to the haze which the original film before extending | stretching shows.

  Various functional coating layers may be formed on the surface of the optical film as necessary. Functional coating layers include, for example, antistatic layers, adhesive layers, adhesive layers, easy adhesion layers, antiglare (non-glare) layers, antifouling layers such as photocatalyst layers, antireflection layers, hard coat layers, and UV shielding layers. A layer, a heat ray shielding layer, an electromagnetic wave shielding layer, and a gas barrier layer. The functional coating layer can be formed at any time.

  The optical film can be suitably used as various optical members. The optical member is, for example, an optical protective film, specifically, a polarizing film used for a protective film for substrates of various optical disks (VD, CD, DVD, MD, LD, etc.), and a polarizing plate included in an image display device such as an LCD. It is a child protective film and a retardation film. You may use for a viewing angle compensation film, a light-diffusion film, a reflection film, an antireflection film, an anti-glare film, a brightness enhancement film, a conductive film for touch panels, etc.

  For example, a polarizing plate can be formed using the optical film of the present invention which is a retardation film. More specifically, the optical film of the present invention which is a retardation film can be preferably used as a λ / 4 plate for an elliptically polarizing plate, for example. The elliptically polarizing plate provided with the optical film of the present invention is suitably used as an antireflection film in an image display device such as a liquid crystal display device or an organic electroluminescence display device.

  The formation method of an optical film is not specifically limited, What is necessary is just to follow a well-known method. For example, the resin composition (C) containing the polymers (A) and (B) can be molded into a film by a casting method, a melt molding method (for example, melt extrusion molding, press molding) or the like to obtain an optical film. it can. An optical film that is a retardation film can be obtained by using a formed film as an original film and stretching the original film in a predetermined direction (typically, uniaxial stretching, biaxial stretching, or oblique stretching).

  A specific method for stretching the original film is not particularly limited, and may be a known method. Uniaxial stretching is, for example, free end uniaxial stretching in which a change in the width direction of the film is free. Biaxial stretching is, for example, sequential biaxial stretching or simultaneous biaxial stretching. The stretching method, stretching temperature, and stretching ratio can be appropriately selected according to the optical properties and mechanical properties of the target optical film. Stretching is usually performed in a heated atmosphere. A known stretching machine can be used for stretching the original film in a heated atmosphere. Although a longitudinal stretch machine is not specifically limited, For example, it is an oven stretcher. The oven vertical stretching machine is generally composed of an oven and transport rolls provided on the inlet side and the outlet side of the oven, respectively. An original film is stretched in the transport direction by giving a peripheral speed difference between the transport roll on the entrance side of the oven and the transport roll on the exit side. The transverse stretching machine is not particularly limited and is, for example, a tenter stretching machine. The tenter stretching machine may be either a grip type or a pin type, but the grip type is preferable because the original film is difficult to tear. A grip-type tenter stretching machine is generally composed of a clip traveling device for transverse stretching and an oven. In the clip traveling device, the film is conveyed in a state where the lateral end of the original film is sandwiched between the clips. At this time, the guide rail of the clip traveling device is opened, and the original film is stretched laterally by widening the distance between the left and right two rows of clips. In the grip-type tenter stretching machine, simultaneous biaxial stretching is possible by providing a clip expansion / contraction function in the transport direction of the original film. Moreover, the diagonal stretcher | stretcher which stretches | stretches in the conveyance direction of the said film at a different speed on the right and left of the extending direction of the original film may be used.

  When an optical film has layers other than the layer comprised from a resin composition (C), the said layer can be added at arbitrary time points. When stretching the original film, the layer may be stretched together with the original film.

[Image display device]
The image display device of the present invention is not particularly limited as long as it includes the optical film of the present invention. The image display device of the present invention is an LCD, for example, and the image display unit of the LCD includes the optical film of the present invention together with members such as a liquid crystal cell and a backlight.

  Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the examples shown below.

  Initially, the evaluation method of the polymer, resin composition, and optical film (retardation film) produced in the present Example is shown.

[Weight average molecular weight]
The weight average molecular weight (Mw) of the polymer (A) was determined by gel permeation chromatography (GPC) measurement based on the following apparatus and conditions.
Measurement system: System controller: SCL-10A VP (manufactured by Shimadzu Corporation)
Autoinjector: SIL-10A XL (manufactured by Shimadzu Corporation)
Column oven: CTO-10A (manufactured by Shimadzu Corporation)
Pump: LC-10AT (manufactured by Shimadzu Corporation)
Differential refractive index detector (RI): Shodex RI-71 (manufactured by Showa Denko)
Eluent: 0.1% by weight LiBr-containing dimethylformamide (DMF) (manufactured by Wako Pure Chemical Industries)
Flow rate: 0.8mL / min
Temperature: 40 ° C
Injection amount: 100 μm
Sample concentration: 0.5% by weight
Standard sample: TSK standard polystyrene (PS-oligomer kit, manufactured by Tosoh Corporation)
Measurement column configuration: guard column (Showa Denko, Shodex KD-G), separation column (Showa Denko, Shodex KD-806M) 2 in series

[Glass transition temperature (Tg)]
The glass transition temperature (Tg) of the polymer, the resin composition and the film was measured in accordance with the provisions of JIS K7121. Specifically, using a differential scanning calorimeter (Rigaku Corporation, Thermo plus EVO DSC-8230), a sample of about 10 mg was heated from room temperature to 250 ° C. under a nitrogen gas atmosphere (heating rate 20 ° C./min). From the DSC curve obtained as described above, the starting point method was used. Α-alumina was used as a reference.

[Film thickness]
The film thickness of the original film and the retardation film obtained by stretching the original film was measured using a Digimatic Micrometer (Mitutoyo).

[Phase difference value]
In-plane retardation Re (550) of the retardation film for light having a wavelength of 550 nm, In-plane retardation Re (450) of the retardation film for light having a wavelength of 450 nm, and thickness direction of the retardation film for light having a wavelength of 550 nm The phase difference Rth (550) was measured using a phase difference film / optical material inspection device (Otsuka Electronics, RETS-100). The wavelength dispersibility of the optical film was calculated as a ratio Re (450) / Re (550) serving as an index.

(Production Example 1)
N-vinylpyrrolidone (NVP) 95 parts by weight and styrene (St) 5 parts by weight were charged into a reaction kettle equipped with a stirrer, temperature sensor, cooling pipe and nitrogen introduction pipe, and the temperature was raised to 90 ° C. while passing nitrogen through the reactor. Allowed to warm. Thereafter, 0.025 part by weight of t-amylperoxy-2-ethylhexanoate (manufactured by Arkema Yoshitomi, trade name: Luperox 575) was added as a polymerization initiator, and solution polymerization was allowed to proceed for 4 hours. Next, the polymer in the obtained polymerization solution is precipitated using hexane, and the precipitate is accommodated in a vacuum dryer to volatilize the volatile component, so that the polymer (AV-St copolymer) (A -1) was obtained. The obtained polymer (A-1) had Tg of 146 ° C. and Mw of 260,000. Moreover, the weight composition ratio of the polymer (A-1) calculated | required by the nitrogen elemental analysis was NVP / St = 51/49.

(Production Example 2)
The polymer (A-1) produced in Production Example 1 and a commercially available polyethersulfone (PES); (Sumitomo Chemical, Sumika Excel 4100G, Tg 228 ° C., reduced viscosity (RV) 0.36) were individually N -After dissolving in methylpyrrolidone (NMP), the respective solutions were mixed so that the weight ratio of polymer (A-1) / PES = 85/15 was obtained, and the resulting mixed solution was placed in a vacuum dryer. It accommodated and devolatilized NMP and obtained the resin composition (C-1) which contains a polymer (A-1) and PES by weight ratio 85/15.

Example 1
The resin composition (C-1) produced in Production Example 2 was press-molded at 240 ° C. with a press molding machine to obtain an original film (F1A) having a thickness of 140 μm, which is an unstretched film. Next, the obtained original film (F1A) was uniaxially stretched at a free end with a stretching temperature of 170 ° C. and a stretching ratio of 2.0 times using an autograph (manufactured by Shimadzu Corporation, AG-1kNX) to obtain a retardation film. An optical film (F1B: thickness of 101 μm) was obtained. The obtained film (F1B) had a Tg of 155 ° C., Re (550) of 78 μm, Rth (550) of −39 nm, and a ratio Re (450) / Re (550) of 0.95. That is, a negative retardation film showing reverse wavelength dispersion was obtained.

(Comparative Example 1)
The polymer (A-1) produced in Production Example 1 was press molded at 240 ° C. with a press molding machine to obtain an unstretched film 115 μm thick original film (FC1A). Next, the obtained original film (FC1A) was subjected to free end uniaxial stretching at a stretching temperature of 156 ° C. and a stretching ratio of 2.0 times using the autograph, and an optical film (FC1B: thickness) as a retardation film. 80 μm). The obtained film (FC1B) had a Tg of 146 ° C., Re (550) of 623 nm, Rth (550) of −313 nm, and a ratio Re (450) / Re (550) of 1.05.

(Comparative Example 2)
Commercially available polystyrene (manufactured by PS Japan, HF77) was press-molded at 220 ° C. with a press molding machine to obtain an unstretched film 100 μm-thick original film (FC2A). Next, the obtained original film (FC2A) was subjected to free end uniaxial stretching at a stretching temperature of 98 ° C. and a stretching ratio of 2.0 times using the autograph, and an optical film (FC2B: thickness) as a retardation film. 61 μm) was obtained. The obtained film (FC2B) had a Tg of 95 ° C., Re (550) of 488 nm, Rth (550) of −246 nm, and a ratio Re (450) / Re (550) of 1.06.

(Comparative Example 3)
The polyethersulfone (Sumitomo Chemical, Sumika Excel 4100G) used in Example 1 was press-molded at 300 ° C. with a press molding machine to obtain an unstretched film 100 μm-thick original film (FC3A). Next, the obtained original film (FC3A) was subjected to free end uniaxial stretching at a stretching temperature of 238 ° C. and a stretching ratio of 2.0 times using the autograph, and an optical film (FC3B: thickness) as a retardation film. 68 μm) was obtained. The obtained film (FC3B) had a Tg of 228 ° C., Re (550) of 1423 nm, Rth (550) of 714 nm, and a ratio Re (450) / Re (550) of 1.14.

(Comparative Example 4)
A resin composition containing polystyrene and PES was obtained in the same manner as in Production Example 2 except that the polymer (A-1) was changed to the polystyrene used in Comparative Example 2. The obtained resin composition was cloudy and was clearly not suitable for use as an optical film. When Tg of the resin composition was evaluated, two Tg of 95 ° C. corresponding to Tg of polystyrene and 228 ° C. corresponding to Tg of PES were observed.

  The evaluation results of the retardation values of Example 1 and Comparative Examples 1 to 4 are summarized in Table 1 below. Re (100 μ) and Rth (100 μ) in Table 1 are values obtained by converting Re (550) and Rth (550) of the obtained retardation film per film thickness of 100 μm, respectively.

  As shown in Table 1, in Example 1, the resin composition was optically transparent, and a negative retardation film showing reverse wavelength dispersion was obtained by the resin composition. On the other hand, in Comparative Examples 1 to 3, although a negative or positive retardation film was obtained, an optical film showing reverse wavelength dispersion was not obtained. The retardation film of Comparative Example 3 composed of PES showed very strong forward wavelength dispersion. In Comparative Example 4, the optical transparency sufficient to form an optical film could not be secured.

  The optical film of the present invention can be used in applications similar to conventional optical films, for example, image display devices such as liquid crystal display devices (LCD) and organic EL displays (OLED). By using the optical film of the present invention, the display characteristics of the image display device are improved.

Claims (10)

A polymer (A) having a structural unit represented by the following formula (1);
The optical film containing the layer comprised from the resin composition containing the polymer (B) which has the molecular structure shown by the following formula | equation (2) in a principal chain.

In the formula (1), n is a natural number of 1 to 4, and R ¹ and R ² are each independently a hydrogen atom or a methyl group.   The optical film of Claim 1 whose content rate of the said polymer (A) in the said resin composition is 50 to 99 weight% and whose content rate of the said polymer (B) is 1 to 50 weight%.   The optical film of Claim 1 or 2 whose glass transition temperature (Tg) of the said resin composition is 120 degreeC or more.   The optical film in any one of Claims 1-3 in which the said polymer (A) further has a styrene unit as a structural unit.   The optical film in any one of Claims 1-4 which shows a negative phase difference.   The optical film according to claim 5, wherein a thickness direction retardation with respect to light having a wavelength of 550 nm is −10 nm or less.   The optical film in any one of Claims 1-6 whose in-plane phase difference with respect to the light of wavelength 550nm is 20 nm or more.   The ratio Re (450) / Re (550) between the in-plane retardation Re (550) for light having a wavelength of 550 nm and the in-plane retardation Re (450) for light having a wavelength of 450 nm is less than 0.98. The optical film in any one of 1-7.   A polarizing plate provided with the optical film in any one of Claims 1-8.   An image display apparatus provided with the optical film in any one of Claims 1-8.