JP2016014794A - Optical film, polarizing plate including the same, and image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical film that is formed of a resin composition including a polymer having a maleimide compound unit as a constitutional unit, has high strength, and can be manufactured by fusion extrusion molding.SOLUTION: There is provided an optical film comprising a resin composition (C) including a polymer (A) having a maleimide compound unit, vinyl cyanide compound unit, and aromatic vinyl compound unit as constitutional units, and a polymer (B) having a vinyl cyanide compound unit and aromatic vinyl compound unit as constitutional units, where the weight average molecular weight of the resin composition (C) is 150,000 or more and 300,000 or less.

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 image display devices. One type of retardation film is a negative retardation film made of a resin composition exhibiting negative intrinsic birefringence. The negative retardation film exhibits negative Rth (thickness direction retardation), and is used for various applications utilizing this optical characteristic. Other optical films other than the retardation film can also be composed of a resin composition exhibiting negative intrinsic birefringence.

  Patent Document 1 discloses negative intrinsic birefringence obtained by uniaxially stretching a film made of a copolymer obtained by copolymerizing two or more monomers including a styrene monomer and an N-substituted maleimide monomer. A birefringent film is disclosed. In Patent Document 1, the copolymer may be a copolymer of a styrene monomer and an N-substituted maleimide monomer and an acrylonitrile monomer or a methacrylonitrile monomer. It is described.

JP-A-6-67021

  While the polymer has a structural unit (N-substituted maleimide unit) formed by polymerization of an N-substituted maleimide monomer, the heat resistance of the polymer and a molded body containing the polymer is improved. These strengths tend to decrease and become brittle. In particular, in a film molded body such as an optical film, the influence of the strength (the influence of brittleness) on the product quality, such as handling properties, durability, and optical characteristics, is large. An increase in the molecular weight of the polymer is expected to improve the strength, but simply increasing the molecular weight reduces the fluidity of the resin composition containing the polymer, for example, melt extrusion with excellent production efficiency. Production of a film by molding becomes difficult. In Patent Document 1, production of a film by melt extrusion molding is not considered at all. Patent Document 1 describes only a casting method (cast method) as a method for producing a film, in which a solution of a resin composition is applied to a substrate surface and dried.

  One of the objects of the present invention is to provide an optical film having a high strength and capable of being produced by melt extrusion molding while being composed of a resin composition containing a polymer having a maleimide compound unit as a structural unit.

  The optical film of the present invention has a polymer (A) having maleimide compound units, vinyl cyanide compound units and aromatic vinyl compound units as constituent units, and vinyl cyanide compound units and aromatic vinyl compound units as constituent units. A resin composition (C) containing the polymer (B), and the resin composition (C) has a weight average molecular weight of 150,000 to 300,000.

  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.

  The optical film of the present invention has high strength and can be produced by melt extrusion molding while being composed of a resin composition containing a polymer having maleimide compound units as constituent units.

  The “resin composition” in the present specification is a broader concept than the “polymer”. The resin composition may contain one type or two or more types of polymers, and if necessary, materials other than the polymer, for example, additives such as ultraviolet absorbers, antioxidants, fillers, and plasticizers. May be included.

  In the description of the optical film of the present invention, “%” means “% by mass” unless otherwise specified.

[Polymer (A)]
The polymer (A) has a maleimide compound unit, a vinyl cyanide compound unit, and an aromatic vinyl compound unit as constituent units. The polymer (A) is a thermoplastic polymer. The polymer (A) typically exhibits negative intrinsic birefringence.

  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. In addition, the positive / negative of the intrinsic birefringence of a resin composition is determined by the balance of the birefringence produced by each polymer contained in the resin composition.

  The structural unit possessed by the polymer (A) will be described.

(Maleimide compound unit)
A maleimide compound unit has the effect | action which improves the heat resistance of the optical film which consists of a polymer (A), the resin composition (C) containing the said polymer (A), and the said resin composition (C). An optical film having high heat resistance is suitable for use in an image display device such as a liquid crystal display device (LCD).

The maleimide compound unit is a structural unit represented by the following formula (1). The maleimide compound unit is formed by polymerization of a maleimide monomer (N-substituted maleimide monomer) represented by the following formula (2). In the formulas (1) and (2), R ¹ and R ² are each independently a hydrogen atom, an alkyl group having 1 to 12 carbon atoms or an aryl group having 6 to 14 carbon atoms, and X is a substituent. A chain alkyl group having 1 to 12 carbon atoms which may have a cycloalkyl group having 3 to 12 carbon atoms which may have a substituent, or 6 carbon atoms which may have a substituent. -14 aryl groups.

R ¹ and R ² are preferably each independently a hydrogen atom, a methyl group, a benzyl group or a phenyl group, more preferably a hydrogen atom. X is a cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group, cyclooctyl group, phenyl group, chlorophenyl group, methylphenyl group, naphthylphenyl group, hydroxyphenyl group, methoxyphenyl group, nitrophenyl group, A carboxylphenyl group and a tribromophenyl group are preferable, and a cyclohexyl group, a phenyl group, and a benzyl group are more preferable.

  The maleimide compound unit is, for example, N-phenylmaleimide, N-chlorophenylmaleimide, N-methylphenylmaleimide, N-naphthylmaleimide, N-hydroxyphenylmaleimide, N-methoxyphenylmaleimide, when X is an aryl group, It is a structural unit derived from each monomer of N-carboxyphenylmaleimide, N-nitrophenylmaleimide, N-tribromophenylmaleimide, and N-benzylmaleimide.

  The maleimide compound unit is a structural unit derived from each monomer of N-cyclohexylmaleimide, N-cyclopropylmaleimide, N-cyclobutylmaleimide, N-cyclopentylmaleimide, for example, when X is a cycloalkyl group. .

  The maleimide compound unit is, for example, N-methylmaleimide, N-ethylmaleimide, N-propylmaleimide, N-butylmaleimide, N-octylmaleimide, N-laurylmaleimide, isopropylmaleimide for the case where X is a chain alkyl group. , Sec-butylmaleimide, and tert-butylmaleimide.

  The maleimide compound unit is at least one kind selected from N-phenylmaleimide, N-benzylmaleimide, N-cyclohexylmaleimide, N-naphthylmaleimide and N-tribromophenylmaleimide from the viewpoints of price, availability and heat resistance. A structural unit derived from a monomer is preferred, and a structural unit derived from at least one monomer selected from N-phenylmaleimide, N-benzylmaleimide and N-cyclohexylmaleimide, that is, an N-phenylmaleimide unit, N- More preferred is at least one selected from benzylmaleimide units and N-cyclohexylmaleimide units.

  The ratio of maleimide compound units in all the structural units of polymer (A) (content ratio of maleimide compound units in polymer (A)) is, for example, 10 to 50%, preferably 15 to 45%, more preferably. 20 to 40%. Within these ranges, the resin composition (C) containing the polymer (A) and the resin composition can be used while ensuring compatibility with the polymer (B) that can achieve optical transparency that can be used as an optical film. A better balance between the thermal characteristics (heat resistance), strength, and moldability (fluidity under melt extrusion molding conditions) of the resin composition (C) can be secured.

(Vinyl cyanide compound unit)
A vinyl cyanide compound unit has the effect | action which improves compatibility with a polymer (B). Thereby, the optical transparency of the resin composition (C) that can be used as an optical film is realized. The vinyl cyanide compound unit is formed by polymerization of a vinyl cyanide monomer.

  A vinyl cyanide compound unit is a structural unit derived from each monomer of acrylonitrile and methacrylonitrile, for example.

The content rate of the vinyl cyanide compound unit in a polymer (A) is 1 to 30%, for example, Preferably it is 5 to 25%, More preferably, it is 10 to 20%. Within these ranges, the resin composition (C) containing the polymer (A) and the resin composition can be used while ensuring compatibility with the polymer (B) that can achieve optical transparency that can be used as an optical film. A better balance between the thermal characteristics (heat resistance), strength, and moldability (fluidity under melt extrusion molding conditions) of the resin composition (C) can be secured. Further, yellowing due to heat application during melt molding is suppressed, and a color suitable for an optical film is realized. The color of the optical film is expressed, for example, by a b ^* value in the La ^* b ^* color system.

(Aromatic vinyl compound unit)
The aromatic vinyl compound unit has a function of negatively increasing the intrinsic birefringence of the polymer (A). For this reason, the retardation development of an optical film made of the resin composition containing the polymer (A) is improved, and for example, an optical film showing a large retardation value can be realized. Effects such as improvement in the degree of freedom of optical design and the possibility of further thinning of the optical film can be obtained.

The aromatic vinyl compound unit is a structural unit represented by the following formula (3). The aromatic vinyl compound unit is formed by polymerization of an aromatic vinyl monomer represented by the following formula (4). In the formulas (3) and (4), R ³ is an aromatic group, R ⁴ is a hydrogen atom, and R ⁵ and R ⁶ are each independently a hydrogen atom or a methyl group. R ³ is, for example, an aryl group which may have a substituent, and may be a heteroaromatic group.

  The aromatic vinyl compound unit is a structural unit derived from, for example, each monomer of styrene, α-methylstyrene, methoxystyrene, vinyltoluene, and halogenated styrene. Among these, a styrene unit is preferable because an optical film exhibiting high optical transparency and a large retardation value can be formed.

  The aromatic vinyl compound unit may be a heteroaromatic vinyl compound unit, for example, a structural unit derived from each monomer of vinyl carbazole, vinyl pyridine, vinyl imidazole, and vinyl thiophene.

  The content of the aromatic vinyl compound unit in the polymer (A) is, for example, 40 to 89%, preferably 45 to 80%, more preferably 50 to 75%. Within these ranges, the resin composition (C) containing the polymer (A) and the resin composition can be used while ensuring compatibility with the polymer (B) that can achieve optical transparency that can be used as an optical film. A better balance between the thermal characteristics (heat resistance), strength, and moldability (fluidity under melt extrusion molding conditions) of the resin composition (C) can be secured. Moreover, phase difference expression property when it is set as the optical film of a resin composition (C) improves more.

The content X1 of the maleimide compound unit, the content X2 of the vinyl cyanide compound unit, and the content X3 of the aromatic vinyl compound unit in the polymer (A) are expressed in mass% and satisfy the following formula. preferable. In this case, the balance of the above-described thermal characteristics, strength, and moldability is further improved.
10 ≦ X1 ≦ 50
1 ≦ X2 ≦ 30
40 ≦ X3 ≦ 89

  The polymer (A) may have two or more types of maleimide compound units as structural units, may have two or more types of vinyl cyanide compound units as structural units, and may have two or more types of aromatics. A group vinyl compound unit may be included as a constituent unit.

  The polymer (A) is not a maleimide compound unit, a vinyl cyanide compound unit or an aromatic vinyl compound unit as long as the effect of the present invention can be obtained, and preferably the intrinsic birefringence of the polymer (A) is negative. You may have the structural unit. The content rate of the unit is, for example, less than 5%. The unit is, for example, a (meth) acrylic acid unit; a (meth) acrylic acid ester unit such as a (meth) methyl acrylate unit, a (meth) ethyl acrylate unit, or a (meth) butyl acrylate unit; a vinyl acetate unit; Vinyl ester units such as vinyl propionate units; maleic anhydride units.

The content of the structural unit in the polymer (A) can be determined by a known method such as ¹ H nuclear magnetic resonance ( ¹ H-NMR) or infrared spectroscopy (IR). The content rate of the structural unit in the polymer (B) and the content rate of each polymer in the resin composition (C) can also be determined by the same method.

  The weight average molecular weight Mw of the polymer (A) is, for example, from 100,000 to 300,000, preferably from 150,000 to 250,000, and more preferably from 150,000 to 200,000.

  The glass transition temperature (Tg) of the polymer (A) is, for example, 110 ° C. or higher. Depending on the composition of the polymer (A) (type and content of constituent units of the polymer), 120 ° C. or higher, and further 130 It can be over ℃. Such an optical film made of a resin composition containing a polymer having a high Tg is excellent in heat resistance, such as an LCD having a structure in which heat generating parts such as a light source, a power supply part, and a circuit board are integrated in a limited space. It is suitable for use in an image display device.

  The polymer (A) can be formed by a known method. For example, the polymer (A) can be formed by polymerizing a monomer group including the maleimide monomer, vinyl cyanide monomer and aromatic vinyl monomer described above.

  Various polymerization methods such as suspension polymerization, emulsion polymerization, and solution polymerization can be applied to the polymerization of the monomer group. Among these, solution polymerization is preferable because the remaining amount of the maleimide monomer in the obtained polymer (A) can be reduced.

  Solution polymerization may be performed according to a known method. As the polymerization solvent used for the solution polymerization, for example, a general polymerization solvent such as toluene, xylene, ethylbenzene, isopropylbenzene, methyl isobutyl ketone, butyl cellosolve, dimethylformaldehyde, 2-methylpyrrolidone, methyl ethyl ketone can be appropriately selected and used. .

[Polymer (B)]
The polymer (B) is a polymer different from the polymer (A) having a vinyl cyanide compound unit and an aromatic vinyl compound unit as constituent units. The polymer (B) is a thermoplastic polymer. The polymer (B) typically exhibits negative intrinsic birefringence.

  Examples of the vinyl cyanide compound unit and the aromatic vinyl compound unit that the polymer (B) has as a structural unit are the same as those described above in the description of the polymer (A). However, the polymer (A) and the polymer (B) do not need to have the same vinyl cyanide compound unit and aromatic vinyl compound unit. The vinyl cyanide compound unit and the aromatic vinyl compound unit possessed by the polymer (A) and the vinyl cyanide compound unit and the aromatic vinyl compound unit possessed by the polymer (B) are the same or different from each other. May be.

  The content rate of the vinyl cyanide compound unit in a polymer (B) is 10 to 40%, for example, Preferably it is 15 to 35%, More preferably, it is 20 to 30%. Within these ranges, the resin composition (C) containing the polymer (B) and the resin composition can be used while ensuring compatibility with the polymer (A) that can achieve optical transparency that can be used as an optical film. A better balance between the thermal characteristics (heat resistance), strength, and moldability (fluidity under melt extrusion molding conditions) of the resin composition (C) can be secured. Further, yellowing due to heat application during melt molding is suppressed, and a color suitable for an optical film is realized.

  The content of the aromatic vinyl compound unit in the polymer (B) is, for example, 60 to 90%, preferably 65 to 85%, and more preferably 70 to 80%. Within these ranges, the resin composition (C) containing the polymer (B) and the resin composition can be used while ensuring compatibility with the polymer (A) that can achieve optical transparency that can be used as an optical film. A better balance between the thermal characteristics (heat resistance), strength, and moldability (fluidity under melt extrusion molding conditions) of the resin composition (C) can be secured. Moreover, phase difference expression property when it is set as the optical film of a resin composition (C) improves more.

It is preferable that the content Y1 of the vinyl cyanide compound unit and the content Y2 of the aromatic vinyl compound unit in the polymer (B) are expressed in mass% and satisfy the following formula. In this case, the balance of the above-described thermal characteristics, strength, and moldability is further improved.
10 ≦ Y1 ≦ 40
60 ≦ Y2 ≦ 90

  The polymer (B) may have two or more types of vinyl cyanide compound units as structural units, and may have two or more types of aromatic vinyl compound units as structural units.

  As long as the effect of the present invention is obtained and the intrinsic birefringence of the polymer (B) is negative, the polymer (B) preferably contains constituent units other than the vinyl cyanide compound unit and the aromatic vinyl compound unit. You may have. The polymer (B) may have a smaller amount of maleimide compound units than the polymer (A). The content of maleimide compound units in the polymer (B) is preferably less than 10%, more preferably less than 5%, and even more preferably 0%. That is, more preferably, the polymer (B) does not have a maleimide compound unit as a constituent unit.

  The weight average molecular weight Mw of the polymer (B) is, for example, from 100,000 to 300,000, preferably from 150,000 to 250,000, more preferably from 200,000 to 250,000.

  The Tg of the polymer (B) is, for example, less than 130 ° C., and may be less than 120 ° C. or even less than 110 ° C. depending on the composition of the polymer (B). It is preferable that Tg of a polymer (B) is lower than Tg of a polymer (A).

  Specific examples of the polymer (B) include a styrene-acrylonitrile copolymer, a styrene-acrylonitrile- (meth) acrylic acid ester copolymer, and a rubbery polymer containing a vinyl cyanide monomer and an aromatic vinyl monomer. A copolymer obtained by graft polymerization. The rubbery polymer is, for example, a rubbery polymer having a structural unit derived from a (meth) acrylic acid ester monomer or a rubbery polymer having a structural unit derived from a conjugated diene monomer. When the polymer (B) is a copolymer obtained by graft polymerization of the above monomer to a rubbery polymer, the resin (C) containing the polymer (B) and the resin composition (C) are included. The strength of the optical film is further improved while maintaining the above good balance.

  The polymer (B) can be formed by a known method. For example, the polymer (B) can be formed by polymerizing a monomer group including the above-described vinyl cyanide monomer and aromatic vinyl monomer. Various polymerization methods such as suspension polymerization, emulsion polymerization, solution polymerization, and bulk polymerization can be applied to the polymerization of the monomer group. The polymerization method of the polymer (B) is preferably solution polymerization or bulk polymerization. A known method can be applied to the graft polymerization.

[Resin composition (C)]
The resin composition (C) includes a polymer (A) and a polymer (B). The resin composition (C) is a thermoplastic resin composition. The resin composition (C) typically exhibits negative intrinsic birefringence.

  The content rate of the polymer (A) in a resin composition (C) is 20 to 90%, for example, Preferably it is 35 to 80%, More preferably, it is 45 to 70%. The content rate of the polymer (B) in the resin composition (C) is, for example, 10 to 80%, preferably 20 to 65%, more preferably 30 to 55%. Within these ranges, the thermal characteristics (heat resistance) and strength of the resin composition (C) and the optical film comprising the resin composition (C), and the moldability of the resin composition (C) (under melt extrusion molding conditions) Better fluidity).

  The resin composition (C) may contain two or more kinds of polymers (A), and may contain two or more kinds of polymers (B).

  The weight average molecular weight Mw of the resin composition (C) is 150,000 or more and 300,000 or less. Within this range, the thermal properties (heat resistance) and strength of the resin composition (C) and the optical film comprising the resin composition (C), and the moldability of the resin composition (C) (under melt extrusion molding conditions) A good balance of fluidity can be secured. When the Mw of the resin composition (C) is less than 150,000, the strength of the optical film is lowered. When Mw of a resin composition (C) exceeds 300,000, the moldability of the said composition (C) will fall. The Mw of the resin composition (C) is preferably 180,000 or more.

  The melt flow rate (MFR: unit is [g / 10 min]) of the resin composition (C) is, for example, 3.0 or more, preferably 5.0 or more, more preferably 10 or more, still more preferably. 15 or more. The upper limit of MFR of the resin composition (C) is, for example, 200 or less, preferably 50 or less, more preferably 30 or less.

  The Tg of the resin composition (C) is, for example, 110 ° C. or higher. Depending on the composition of the resin composition (C) (the type and content of the polymer contained in the resin composition), it is 120 ° C. or higher, and further 130 It can be over ℃. In addition, Tg of a resin composition (C) and Tg of the film which consists of the said resin composition are the same normally.

  For the resin composition (C), the strength (impact strength) when the resin composition is an unstretched film having a thickness of 100 μm is, for example, 5 mJ or more in terms of the breaking energy determined by the method described later in the examples. Depending on the composition of the resin composition (C), it can be 10 mJ or more, further 15 mJ or more. Thus, according to the resin composition (C) which can implement | achieve high intensity | strength, the optical film which handling property and durability improved is implement | achieved.

  In the resin composition (C), the above MFR, Tg and strength can be achieved at the same time.

  The resin composition (C) preferably has an intrinsic birefringence of the resin composition (C) as long as the compatibility with the polymers (A) and (B) is ensured and the effects of the present invention are obtained. As long as it is negative, polymers other than the polymers (A) and (B) may be contained. The content of the polymer is, for example, less than 10%, preferably less than 5%. Examples of the polymer include olefin resins such as polyethylene, polypropylene, ethylene-propylene polymer, and poly (4-methyl-1-pentene); halogen-containing resins such as vinyl chloride and chlorinated vinyl resins; polyethylene terephthalate, poly Polyesters such as butylene terephthalate and polyethylene naphthalate; polyamides such as nylon 6, nylon 66, nylon 610; polyacetals; polycarbonates; polyphenylene oxides; polyphenylene sulfides; polyether ether ketones; polysulfones; Imide; a rubbery polymer.

  As long as the effect of this invention is acquired, the resin composition (C) may contain various additives other than a polymer. Additives include, for example, ultraviolet absorbers (UVA); stabilizers such as antioxidants, light stabilizers, weathering stabilizers, heat stabilizers; phase increase agents, phase difference reducers, phase difference stabilizers, etc. Phase difference adjusting agent; Reinforcing materials such as glass fiber and carbon fiber; Near infrared absorbing agent; Flame retardant such as tris (dibromopropyl) phosphate, triallyl phosphate, antimony oxide; anionic, cationic and nonionic surfactants Including antistatic agents; coloring agents such as inorganic pigments, organic pigments, dyes; organic fillers, inorganic fillers, resin modifiers, plasticizers, lubricants. The content of the additive in the resin composition (C) is preferably 5% or less, more preferably 2% or less, and still more preferably 1% or less.

  The formation method of a resin composition (C) is not specifically limited. For example, the resin composition (C) can be formed by melt-kneading the polymer (A) and the polymer (B). Polymers and additives other than the polymers (A) and (B) can be added to the resin composition (C) at an arbitrary time and method.

[Optical film]
The optical film (1st optical film) of this invention consists of a resin composition (C). The first optical film is typically a negative retardation film made of the resin composition (C) exhibiting negative intrinsic birefringence.

  The first optical film is typically a film (melt extruded film) obtained by melt extrusion molding of the resin composition (C). The method for forming the first optical film is not limited to melt extrusion molding, but for the resin composition (C), the thermal characteristics and strength of the optical film comprising the resin composition (C), and the moldability of the resin composition. Considering that a good balance can be secured, when the first optical film is a film obtained by melt-extruding the resin composition (C), the effect of the present invention becomes more remarkable.

  The method of melt extrusion molding is not particularly limited, and a known method can be applied.

  The first optical film has heat resistance based on the high Tg of the resin composition (C). The specific value of Tg is as described above in the description of the resin composition (C).

  The first optical film may be an unstretched film or a stretched film such as a uniaxially stretched film or a biaxially stretched film. By setting it as a stretched film, intensity | strength can be further improved rather than the state of an unstretched film. Moreover, the retardation film which shows the birefringence based on the orientation of the molecular chain of a polymer by extending | stretching is obtained by control of extending | stretching conditions like extending | stretching temperature and a draw ratio. At this time, the first optical film is a negative retardation film that typically has a negative retardation Rth in the thickness direction.

The retardation of the first optical film that is a negative retardation film is, for example, 20 nm or more as an in-plane retardation Re for light having a wavelength of 550 nm, and 100 nm or more depending on the composition of the resin composition (C) and stretching conditions. Furthermore, it is 200 nm or more. Further, the thickness direction retardation Rth with respect to light having a wavelength of 550 nm is, for example, −10 nm or less, or −50 nm or less, and further −100 nm or less depending on the composition of the resin composition (C) and stretching conditions. Note that the in-plane retardation Re and the thickness direction retardation Rth are obtained by the following equations, respectively.
In-plane retardation Re = | nx−ny | × d (nm)
Thickness direction retardation Rth = {(nx + ny) / 2−nz} × d (nm)

  Here, nx is the refractive index in the direction in which the refractive index in the film plane is maximum (the slow axis direction), and ny is the direction perpendicular to the slow axis direction in the film plane (fast axis direction). Nz is the refractive index in the thickness direction of the film. d is the thickness (nm) of the film.

The first optical film, which is a negative retardation film, exhibits an NZ coefficient of, for example, −10 to 0, preferably −5 to 0. The NZ coefficient is obtained by the following equation.
NZ coefficient = (Rth / Re) +0.5

  The first optical film may be a film showing optical isotropy. Optical isotropy refers to a state where the absolute values of Re and Rth are, for example, less than 10 nm, preferably 5 nm or less, more preferably 3 nm or less. When the first optical film is a film showing optical isotropy, the film is a biaxially stretched film because the optical isotropy is more reliably ensured and the strength of the film is further improved. Preferably there is.

  The first optical film, which is a stretched film, can be formed, for example, by stretching an unstretched film (original film) obtained by melt extrusion molding the resin composition (C) by a known method. Biaxial stretching may be either sequential biaxial stretching or simultaneous biaxial stretching.

  By comprising the resin composition (C), the first optical film has high strength (impact strength). More specifically, the fracture energy in the state of an unstretched film having a thickness of 100 μm determined by the method described later in the examples is, for example, 5 mJ or more, and depending on the composition of the resin composition (C), 10 mJ or more. Furthermore, it becomes 15 mJ or more. Moreover, in the state of a stretched film, the strength is further improved as compared with an unstretched film having the same thickness.

  Based on the compatibility of the polymer (A) and the polymer (B), the first optical film has high optical transparency. For example, the effect derived from the shape of the film surface can be expressed by an internal haze that can be ignored, and an optical film having a thickness of 1.0% or less and further 0.5% or less per 100 μm thickness can be obtained.

  The thickness of the first optical film is, for example, 10 to 300 μm, preferably 15 to 150 μm, and more preferably 20 to 100 μm.

With the first optical film, it is possible to realize a color suitable for use as an optical film. For example, it can be an optical film having an absolute value of b ^* value in the La ^* b ^* color system of 10.0 or less, 5.0 or less, 3.0 or less, or 1.0 or less.

  The optical film of the present invention may be a film having a laminated structure including a first optical film having two or more layers, or a first optical film and another film different from the first optical film. The film (2nd optical film) which has a laminated structure containing may be sufficient. As a specific example, the second optical film includes a first optical film made of the resin composition (C) exhibiting negative intrinsic birefringence and another optical film made of a resin composition exhibiting positive intrinsic birefringence. And may have a stacked structure. The laminated structure improves the degree of freedom in optical design of the optical film, such as realizing optical characteristics that could not be realized only with the first optical film.

  The retardation of the second optical film having the laminated structure is, for example, 70 to 400 nm or less, preferably 90 to 300 nm, more preferably 120 to 280 nm, as in-plane retardation Re for light having a wavelength of 550 nm. is there. The absolute value of the thickness direction retardation Rth with respect to light having a wavelength of 550 nm is, for example, 70 nm or less, preferably 60 nm or less, more preferably 50 nm or less, and further preferably 20 nm or less.

  The 2nd optical film which has the said laminated structure shows NZ coefficient of 0.1-0.9, for example, Preferably 0.3-0.8.

  The second optical film may be a stretched film or an unstretched film. When the second optical film is a retardation film, the slow optical axis direction of the first optical film composed of a resin composition exhibiting negative intrinsic birefringence and the resin composition exhibiting positive intrinsic birefringence described above. By matching with the slow axis direction of another film, the value of the in-plane retardation Re can be increased and the retardation Rth in the thickness direction can be decreased (for example, close to zero). Further, by making the slow axis directions of both films orthogonal, it is possible to obtain a retardation film having a small retardation Rth in the thickness direction and showing reverse wavelength dispersion. Here, “reverse wavelength dispersion” means an optical characteristic in which the magnitude of birefringence, for example, the value of phase difference, becomes smaller as the wavelength becomes shorter.

  The other film comprising the resin composition exhibiting positive intrinsic birefringence is not limited as long as it exhibits positive intrinsic birefringence. For example, polycarbonate, cycloolefin polymer, cellulose derivative, (meth) acrylate polymer Or a film (urethane film) made of a urethane resin composition containing a urethane resin. The (meth) acrylic acid ester polymer is, for example, a polymer having a ring structure in the main chain, and the ring structure includes, for example, a lactone ring structure, a glutarimide structure, a glutaric anhydride structure, an N-substituted maleimide structure, and an anhydrous structure. It is at least one selected from maleic acid structures.

  The urethane resin contained in the urethane resin composition constituting the urethane film (urethane layer) is not limited, and is typically a resin formed by a reaction between a polyol and a polyisocyanate. In this reaction, two or more polyols and / or polyisocyanates may be reacted. The urethane resin composition may contain two or more types of urethane resins.

  A polyol is a compound having two or more hydroxyl groups (hydroxy groups) in the molecule. The polyol is, for example, a polyacryl polyol, a polyester polyol, or a polyether polyol.

  The polyacryl polyol is, for example, a copolymer of a (meth) acrylic acid ester monomer and a monomer having a hydroxyl group. The (meth) acrylic acid ester monomer is, for example, methyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, or cyclohexyl (meth) acrylate. Examples of the monomer having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, (Meth) acrylic acid hydroxyalkyl esters such as (meth) acrylic acid 4-hydroxybutyl and (meth) acrylic acid 2-hydroxypentyl; (meth) acrylic acid monoesters of polyhydric alcohols such as glycerin and trimethylolpropane; N-methylol (meth) acrylamide. The polyacryl polyol may be a copolymer of a (meth) acrylic acid ester monomer and a monomer having a hydroxyl group and another monomer. Still other monomers include, for example, unsaturated monocarboxylic acids such as (meth) acrylic acid; unsaturated dicarboxylic acids such as maleic acid and anhydrides and mono- or diesters thereof; 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; α, β-unsaturated aromatic monomers such as styrene and α-methylstyrene.

  The polyester polyol is, for example, a polymer formed by a reaction between a polybasic acid component and a polyol component. Examples of the polybasic acid component include orthophthalic acid, isophthalic acid, terephthalic acid, 1,4-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, biphenyldicarboxylic acid, and tetrahydrophthalic acid. Aromatic dicarboxylic acids; 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, Aliphatic dicarboxylic acids such as linolenic acid, maleic acid, fumaric acid, mesaconic acid, citraconic acid, itaconic acid; hexahydrophthalic acid, tetrahydrophthalic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, etc. Alicyclic dicarbo Acid; or their anhydrides, alkyl esters, reactive derivatives such as acid halides; a. Examples of the polyol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, and 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 Coal, 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.

  The polyether polyol can be obtained, for example, by adding an alkylene oxide to a polyhydric alcohol by ring-opening polymerization. The polyhydric alcohol is, for example, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, glycerin, or trimethylolpropane. The alkylene oxide is, for example, ethylene oxide, propylene oxide, butylene oxide, styrene oxide, tetrahydrofuran.

  Examples of the polyisocyanate include tetramethylene diisocyanate, dodecamethylene diisocyanate, 1,4-butane diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, Aliphatic diisocyanates such as 2-methylpentane-1,5-diisocyanate and 3-methylpentane-1,5-diisocyanate; isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4′-cyclohexylmethane diisocyanate, 1,4-cyclohexane Alicyclic diisodies such as diisocyanate, methylcyclohexylene diisocyanate, 1,3-bis (isocyanatomethyl) cyclohexane Anate; 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, 1,4-phenylene diisocyanate and other aromatic diisocyanates; dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, α, α, α, α-tetramethylxylylene Aromatic aliphatic diisocyanates such as range isocyanate;

  The urethane resin may be a resin formed by a reaction with another polyol or chain extender together with a polyol and a polyisocyanate. Other polyols include, for example, sorbitol, 1,2,3,6-hexanetetraol, 1,4-sorbitan, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerin, trimethylolethane , A polyol having three or more hydroxyl groups such as trimethylolpropane and pentaerythritol. Chain extenders include, for example, dihydroxy carboxylic acids such as dialkyrol alkanoic acids (eg dimethylol acetic acid, dimethylol butanoic acid, dimethylol propionic acid, dimethylol butyric acid, dimethylol pentanoic acid); dihydroxy succinic acid; ethylene glycol, Glycols such as diethylene glycol, triethylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, 1,6-hexanediol, propylene glycol; ethylenediamine, Aliphatic diamines such as propylene diamine, hexamethylene diamine, 1,4-butane diamine, and aminoethyl ethanol amine; isophorone diamine, 4,4′-dicyclohexyl methane diamine, etc. Alicyclic diamines; a; xylylenediamine, aromatic diamines such as tolylenediamine.

  A known method can be applied to the formation of the urethane resin. For example, a one-shot method in which each component is reacted at once or a multistage method in which the components are reacted in stages can be employed. The use amount ratio of each component when forming the urethane resin can also be set as appropriate.

  The molecular weight of the urethane resin is not particularly limited. For example, the number average molecular weight is preferably 5,000 to 600,000, and more preferably 10,000 to 400,000.

  An aqueous dispersion of a urethane resin composition can be used for forming the urethane film in the second optical film. Specifically, a urethane film can be formed by applying an aqueous dispersion of a urethane resin composition as a coating liquid to the main surface of the first optical film and drying the formed coating film.

  The aqueous dispersion is typically an emulsion of urethane resin particles. As the aqueous solvent as the dispersion medium, water or a mixed solvent of water and a hydrophilic organic solvent can be used, and the use of water is particularly preferable. Examples of hydrophilic organic solvents include alcohols such as methanol, ethanol, isopropyl alcohol, ethylene glycol, and propylene glycol; esters such as ethyl acetate, butyl acetate, and γ-butyrolactone; ketones such as acetone; ethers such as tetrahydrofuran and dioxane Aprotic polar solvents such as N-methylpyrrolidone; The content of the hydrophilic organic solvent in the mixed solvent is preferably 50% or less, more preferably 30% or less, and still more preferably 10% or less. The mixed solvent may contain two or more kinds of the organic solvents.

  The aqueous dispersion may contain a neutralizing agent. In this case, the stability of the urethane resin in the dispersion medium is improved. Examples of the neutralizing agent include ammonia, N-methylmorpholine, triethylamine, dimethylethanolamine, methyldiethanolamine, triethanolamine, morpholine, tripropylamine, ethanolamine, triisopropanolamine, 2-amino-2-methyl-1- Propanol.

  The aqueous dispersion may contain fine particles, and in this case, the blocking resistance of the formed film is improved. The fine particles are not particularly limited. For example, inorganic oxides such as silica, titania, alumina, zirconia, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, calcium phosphate Inorganic fine particles made of, for example; organic fine particles made of silicone resin, fluorine resin, acrylic resin, or the like. Of these, silica fine particles are preferable, and colloidal silica is more preferable.

  Aqueous dispersions include other materials such as dispersion stabilizers, thixotropic agents, antioxidants, UV absorbers, antifoaming agents, thickeners, dispersants, surfactants, catalysts, antistatic agents, etc. Various additives may be included.

  The content rate of the urethane resin in an aqueous dispersion is not specifically limited, Preferably it is 2.5 to 50%, More preferably, it is 5 to 40%, More preferably, it is 10 to 30%.

  The solid content of the aqueous dispersion can be appropriately set in consideration of, for example, workability during coating, and is preferably 5 to 50%, more preferably 10 to 40%, and still more preferably 20 to 30%.

  A commercially available thing can be used for an aqueous dispersion. Commercially available aqueous dispersions include, for example, Mitsui Chemicals Polyurethane, Takelac (registered trademark) series (WS-4000, etc.); ADEKA, Adekabon Titer (registered trademark) series (HUX-550, HUX-541, HUX-522). Etc.); manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Superflex (registered trademark) series (170, etc.).

  The urethane resin in the urethane film may be crosslinked with a crosslinking agent. By crosslinking, for example, a change with time of the retardation exhibited by the second optical film is suppressed, and the initial retardation can be increased.

  The crosslinking agent is preferably a water-soluble type. Examples of the cross-linking agent include alkylene diamines having two alkylene groups and two amino groups such as ethylene diamine, triethylene amine and hexamethylene diamine; tolylene diisocyanate, hydrogenated tolylene diisocyanate, trimethylene propane tolylene diisocyanate adduct, Isocyanates such as phenylmethane triisocyanate, methylenebis (4-phenylmethane) triisocyanate, isophorone diisocyanate and their ketoxime block or phenol block; ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin di or triglycidyl Ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl Epoxys such as ether, diglycidyl aniline, diglycidyl amine; monoaldehydes such as formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde; glyoxal, malondialdehyde, succindialdehyde, glutardialdehyde, maleindialdehyde, phthaldialdehyde And dialdehydes such as: methylol urea, methylol melamine, alkylated methylol urea, alkylated methylolated melamine, acetoguanamine, benzoguanamine and condensates of formaldehyde, etc .; oxazolines; carbodiimides. When the urethane resin has a carboxyl group, a polymer having a group capable of reacting with the carboxyl group (for example, (meth) acrylic polymer, styrene / acrylic polymer, etc.) can be used as the crosslinking agent. Examples of the group capable of reacting with a carboxyl group include an organic amino group, an oxazoline group, an epoxy group, and a carbodiimide group, and an oxazoline group is preferable. Two or more crosslinking agents can be used.

  A commercially available crosslinking agent can be used. Commercially available cross-linking agents include, for example, Nippon Shokubai's Epocross (registered trademark) series (WS-700, etc.) as oxazolines, and Nisshinbo Chemical, Carbodilite (registered trademark) as carbodiimides.

  The amount of the crosslinking agent used is preferably from 1 part by weight to 50 parts by weight, and more preferably from 5 parts by weight to 40 parts by weight, based on 100 parts by weight of the urethane resin, in terms of solid content. If the amount of the crosslinking agent used is excessively small, the effect of suppressing the change in retardation over time or the effect of increasing the initial retardation cannot be obtained sufficiently. On the other hand, if the amount of the crosslinking agent used is excessively large, crosslinking may be insufficient.

  The urethane resin composition may contain a resin other than the urethane resin. When the urethane resin composition contains a resin other than the urethane resin, the content of the urethane resin in the urethane resin composition is preferably 50 to 100%, more preferably 65 to 95% in terms of solid content. More preferably, it is 70 to 90%.

  The thickness of the urethane film in the second optical film is preferably 3 μm to 100 μm, more preferably 5 μm to 80 μm, and still more preferably 10 μm to 50 μm.

  The retardation of the urethane film in the second optical film is, for example, 650 nm or more in terms of the in-plane retardation Re per 100 μm thickness with respect to light having a wavelength of 550 nm.

  The method for forming the second optical film is not limited. For example, the second optical film may be formed by laminating the individually formed first optical film and the above-mentioned another film by a known method, or the above-mentioned another optical film may be formed on the main surface of the first optical film. After forming a coating film by applying a solution of the resin composition constituting the film (for example, the above-mentioned aqueous dispersion), the formed coating film is dried to form the above-mentioned another film, thus having the laminated structure A second optical film may be formed. In the latter case, the first optical film can be said to be a base material layer of the second optical film.

  As described above, the second optical film may be a stretched film or an unstretched film. Even if the second optical film that is a stretched film is, for example, the first optical film that is a stretched film and the other film that is a stretched film are laminated, as a more specific example, the slow axis of these films It may be formed by laminating the directions (or perpendicularly), or after laminating the first optical film which is an unstretched or stretched film and the other film, the whole is stretched in a predetermined direction. May be formed. Moreover, after forming the dry coating film of the resin composition which comprises said another film in the main surface of the 1st optical film which is an unstretched or stretched film, the whole may be extended | stretched and formed in a predetermined direction. Good.

  The use of the optical film of the present invention is not limited. Based on the optical properties of the film, it can be used for various applications. The uses include, for example, protective films for substrates of various optical disks (VD, CD, DVD, MD, LD, etc.), polarizer protective films used for polarizing plates provided in image display devices such as LCDs, retardation films, viewing angles A compensation film, a light diffusion film, a reflection film, an antireflection film, an antiglare film, a brightness enhancement film, and a conductive film for a touch panel.

[Polarizer]
The structure of the polarizing plate of the present invention is not particularly limited as long as it includes the optical film of the present invention (the first optical film and / or the second optical film). The polarizing plate of the present invention has, for example, a structure in which a polarizer protective film is bonded to one side or both sides of a polarizer. At this time, at least one polarizer protective film may be the optical film of the present invention, the polarizing plate has a layer other than the polarizer and the polarizer protective film, and the layer is the optical film of the present invention. It may be.

  The polarizer is not particularly limited. For example, a polarizer obtained by dyeing and stretching a polyvinyl alcohol film; a polyene polarizer such as dehydrated polyvinyl alcohol or dehydrochlorinated polyvinyl chloride; a multilayer laminate or a cholesteric liquid crystal Reflective polarizer used: a known polarizer such as a polarizer made of a thin film crystal film. Among these, a polarizer obtained by dyeing and stretching polyvinyl alcohol is preferable.

  A typical example of the structure of the polarizing plate of the present invention is that the polarizer is protected on one or both sides of a polarizer obtained by uniaxially stretching after dying a polyvinyl alcohol with a dichroic substance such as iodine or a dichroic dye. It is the structure which joined the optical film of this invention as a film.

[Image display device]
The structure of the image display device of the present invention is not particularly limited as long as it includes the optical film of the present invention (first optical film and / or second optical film). In the image display device of the present invention, for example, the image display unit of the device includes the optical film of the present invention together with members such as a liquid crystal cell, a polarizing plate, and a backlight. The image display apparatus of the present invention includes the optical film of the present invention as an optical compensation film such as a retardation film, for example. As the polarizer protective film for the polarizing plate, the optical film of the present invention may be provided.

  The specific image display device is not particularly limited. For example, a reflective type, a transmissive type, a transflective type LCD; various driving methods such as a TN type, an STN type, an OCB type, a HAN type, a VA type, and an IPS type. LCD; electroluminescence (EL) display; plasma display (PD); field emission display (FED).

  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.

  First, evaluation methods for the polymer, the resin composition, and the optical film (retardation film) used (or produced) in this example will be described.

[Weight average molecular weight]
The weight average molecular weight (Mw) of the polymer was determined by gel permeation chromatography (GPC) measurement based on the following apparatus and conditions.
Measuring system: Tosoh GPC system HLC-8220
Developing solvent: Chloroform (Wako Pure Chemical Industries, special grade)
Solvent flow rate: 0.6 mL / min Standard sample: TSK standard polystyrene (manufactured by Tosoh, PS-oligomer kit)
Measurement side column configuration: guard column (manufactured by Tosoh, TSK guardcolumn SuperHZ-L), separation column (manufactured by Tosoh, TSK Gel Super HZM-M) in series connection Reference side column configuration: reference column (manufactured by Tosoh, TSK gel SuperH- RC)

[Glass-transition temperature]
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, Thermo plus EVO DSC-8230), a sample of about 10 mg was heated from room temperature to 200 ° C. (heating rate 20 ° C./min) in a nitrogen gas atmosphere. From the DSC curve obtained in this way, it was determined by the starting point method. Α-alumina was used as a reference.

[Film thickness]
The film thickness was measured using a Digimatic Micrometer (Mitutoyo).

[Phase difference and NZ coefficient]
The retardation and NZ coefficient of the optical film were determined as follows.

  First, using a refractometer (manufactured by Atago, multi-wavelength Abbe refractometer DR-M2), the average refractive index of the optical film with respect to light having a wavelength of 550 nm was measured at 23 ° C. in accordance with the provisions of JIS K7142. .

Next, the in-plane retardation Re, the thickness direction retardation Rth, and the NZ coefficient of the optical film with respect to light having a wavelength of 550 nm were determined using a polarization / phase difference analysis system (AxoScan, manufactured by AxoMetrics). Specifically, the average refractive index of the optical film obtained by a refractometer and the thickness of the optical film are input to the above system, and from the three-dimensional refractive indexes nx, ny and nz of the optical film obtained by the system, The Re, Rth, and NZ coefficients were obtained by the following formula. Rth was measured under the condition where the film was tilted by 40 ° with the slow axis of the film as the tilt axis.
In-plane retardation Re = | nx−ny | × d (nm)
Thickness direction retardation Rth = {(nx + ny) / 2−nz} × d (nm)
NZ coefficient = (Rth / Re) +0.5

  nx is the refractive index in the direction (slow axis direction) in which the refractive index is maximum in the film plane, and ny is the refractive index in the direction (fast axis direction) perpendicular to the slow axis direction in the film plane. Nz is the refractive index in the thickness direction of the film. d is the thickness (nm) of the film.

[Intrinsic birefringence]
The positive and negative intrinsic birefringence of the polymer and the resin composition is determined by performing the above retardation measurement on the uniaxially stretched film formed from the polymer or the resin composition as the measurement object, and the slow axis direction found by this measurement is Judgment was made based on whether the stretched film was parallel (including substantially parallel) or perpendicular (including substantially vertical). When the slow axis direction is parallel to the stretching direction of the film, the intrinsic birefringence of the polymer or resin composition constituting the film is positive, and when it is perpendicular, the intrinsic birefringence is negative.

[Polymer composition]
The composition of the polymer was determined as follows.

First, a predetermined amount of the polymer was precisely weighed and then dissolved in chloroform to obtain a 3% solution. Next, this solution was subjected to infrared spectroscopic analysis (so-called infrared absorption method) under the condition of a cell thickness of 0.05 mm. From the absorption intensity of the obtained infrared absorption spectrum (IR spectrum), a polymer was obtained. The amounts of cyan group, carbonyl group and benzene ring contained in were determined, and the composition of the polymer was determined from the amounts. The cyan group is derived from a vinyl cyanide compound unit and has an infrared absorption peak at a wave number of 2237 cm ⁻¹ . The carbonyl group is derived from a maleimide compound unit, and has an infrared absorption peak at a wave number of 1712 cm ⁻¹ . The benzene ring is derived from an aromatic vinyl compound unit, and has an infrared absorption peak at a wave number of 760 cm ⁻¹ .

[Impact strength]
The strength (impact strength) of the optical film was evaluated by the breaking energy per 100 μm thickness of the film produced by hot pressing the resin composition or polymer pellets. The breaking energy was obtained as follows. First, a steel ball with a mass of 5.4 g is free from a height of 4 cm perpendicular to the main surface of the film (thickness: 100 ± 10 μm), which is a measurement object whose ends are fixed horizontally with a jig. The film was dropped, and the presence or absence of film destruction (assuming that the film was destroyed when irreversible deformation was observed on the film) was visually confirmed. When the film was not broken, the height was increased by 2 cm and the free fall of the iron ball was repeated, and the value 2 cm lower than the dropped height when the film was broken was defined as the non-destructive height of the film. The fracture energy of the film was determined by the following formula from the average value of the non-destructive height (average non-destructive height) obtained by carrying out this test three times and the mass of the iron ball.
Fracture energy (J) = mass of iron ball (kg) × gravity acceleration 9.8 m / s ² × average non-destructive height (m) × (100 μm / film thickness (μm))

[Internal haze]
The internal haze of the optical film was determined by a turbidimeter (Nippon Denshoku Industries Co., Ltd., NDH5000) in a state in which the film as the measurement object was immersed in decalin accommodated in a quartz cell.

[Melt flow rate]
The melt flow rate (MFR) of the polymer and the resin composition was determined at a test temperature of 240 ° C. and a load of 10 kg in accordance with JIS K7210.

[B ^* value]
B ^* values of the optical film (La ^* b ^* values of the b ^* color system) is in compliance with the provisions of JIS Z8729, colorimetric color sakei (Nippon Denshoku Kogyo, ZE6000) was determined by.

(Production Example 1)
90 parts by mass of a commercially available urethane resin dispersion (manufactured by ADEKA, Adekabon titer (registered trademark) HUX550; solid content 28%) and a crosslinking agent (manufactured by Nippon Shokubai, Epocross (registered trademark) WS-700; solid content 25%) 10 mass parts was mixed and the urethane resin composition (E-1) was obtained. The intrinsic birefringence of the urethane resin composition (E-1) was positive.

(Example 1)
Polymer (A-1) having N-phenylmaleimide (PMI) units, acrylonitrile (AN) units, and styrene (St) units as constituent units; (PMI / AN / St = 40/10/50 mass% with respect to composition) , A polymer having a weight average molecular weight of 181,000) and an AN unit and a St unit as a constituent unit (B-1); (composition AN / St = 27/73% by mass, weight average molecular weight 22.0 The pellets are 15 mm in diameter while feeding each pellet using a feeder so that the mass ratio of polymer (A-1) / polymer (B-1) = 40/60. The mixture was kneaded at 260 ° C. using a twin screw extruder to obtain pellets of the resin composition (C-1). The resin composition (C-1) had a Tg of 121 ° C., a weight average molecular weight of 187,000, and an MFR of 16.4 g / 10 minutes. Moreover, the fracture energy of the resin composition (C-1) was 15 mJ.

  Next, the pellet of the obtained resin composition (C-1) was melt-extruded at 265 ° C. from a coat hanger type T die having a width of 150 mm using a single screw extruder having a screw of 20 mmφ, A 120 μm film (D-1) was obtained. The film (D-1) exhibited negative intrinsic birefringence, and the internal haze per 100 μm thickness was 0.2%.

  Next, the obtained film (D-1) was uniaxially stretched at a stretching temperature of 124 ° C. (that is, Tg + 3 ° C.) and a stretching ratio of 1.4 times to obtain a stretched film (FD-1) having a thickness of 104 μm. Obtained. Uniaxial stretching of the film was performed as follows. First, both short sides of the film cut into a size of 20 mm × 60 mm are gripped by a pair of clips (upper clip and lower clip) with a distance between chucks of 40 mm, and then placed in an oven (Azuwan, DOV-450A) The film was suspended in the oven by hooking the upper clip onto the jig. Then, a weight of 78 g was attached to the lower clip to apply a constant load to the film, and then the film was heated for 30 minutes while maintaining the temperature in the oven at 124 ° C., which is the stretching temperature. Thereafter, the heating of the film in the oven was stopped, the film was allowed to cool slowly in the oven as it was, and the temperature in the oven dropped to Tg-30 ° C. (of the resin composition (C-1)). The film was taken out from the oven to obtain a stretched film (FD-1).

  The in-plane retardation Re of the stretched film (FD-1) with respect to light having a wavelength of 550 nm was 102 nm, the thickness direction retardation Rth was −55 nm, and the NZ coefficient was −0.04.

(Example 2)
A polymer (A-2) having PMI units, AN units and St units as constituent units; (PMI / AN / St = 32/14/54% by mass with respect to the composition, weight average molecular weight 16.69,000) pellets; Polymer (B-1) having AN units and St units as constituent units; (AN / St = 27/73% by mass with respect to composition, weight average molecular weight 22 million) pellets were prepared. Kneading at 260 ° C. using a twin screw extruder with a cylinder diameter of 15 mm while feeding using a feeder so that the mass ratio of combined (A-2) / polymer (B-1) = 50/50, A pellet of the resin composition (C-2) was obtained. The resin composition (C-2) had a Tg of 122 ° C., a weight average molecular weight of 190000, and an MFR of 19.4 g / 10 minutes. Moreover, the fracture energy of the resin composition (C-2) was 24 mJ.

Next, the pellet of the obtained resin composition (C-2) was melt-extruded at 265 ° C. from a coat hanger type T die having a width of 150 mm using a single screw extruder having a 20 mmφ screw, A 120 μm film (D-2) was obtained. The film (D-2) exhibited negative intrinsic birefringence, the internal haze per 100 μm thickness was 0.2%, and the b ^* value was 0.7.

  Next, the obtained film (D-2) was uniaxially stretched at a stretching temperature of 127 ° C. (ie, Tg + 5 ° C.) and a stretching ratio of 2.0 times to obtain a stretched film (FD-2) having a thickness of 80 μm. Obtained. Uniaxial stretching of the film was performed by an autograph (manufactured by Shimadzu Corporation, AGS-100D).

The in-plane retardation Re of the stretched film (FD-2) with respect to light having a wavelength of 550 nm was 850 nm, the thickness direction retardation Rth was −450 nm, the NZ coefficient was −0.03, and the b ^* value was 0.5. .

(Example 3)
Except that the thickness was 140 μm, melt extrusion molding was performed in the same manner as in Example 2 to obtain an unstretched film (D-3) made of the resin composition (C-2).

  Next, the obtained film (D-3) was subjected to free end uniaxial stretching in the MD direction (flow direction during melt extrusion molding) at a stretching temperature of 129 ° C. and a stretching ratio of 2.0 times (first stretching; longitudinal stretching). ). Uniaxial stretching of the film was performed with a biaxial stretching machine (X6-S, manufactured by Toyo Seiki Co., Ltd.). The thickness of the film after longitudinal stretching was 87 μm, and the in-plane retardation Re for light having a wavelength of 550 nm was 921 nm.

  Next, on one main surface of the film after longitudinal stretching, using a bar coater so that the thickness of the coating film after drying the urethane resin composition (E-1) produced in Production Example 1 is 24 μm. After coating, the entire film was heated at 100 ° C. for 3 minutes to dry the coating film of the urethane resin composition (E-1). Then, the dried film was uniaxially stretched at the fixed end in the TD direction (width direction at the time of melt extrusion molding) at a stretching temperature of 134 ° C. and a stretching ratio of 1.8 times by the above biaxial stretching machine (second stretching; transverse stretching). ). Thus, a film made of the urethane resin composition (E-1) showing positive intrinsic birefringence is formed on one surface of the optical film made of the resin composition (C-2) showing negative intrinsic birefringence. A stretched film (FD-3) having a laminated structure was obtained. The total thickness of the stretched film (FD-3) was 61 μm, of which the thickness of the urethane film was 13 μm. The in-plane retardation Re of the stretched film (FD-3) with respect to light having a wavelength of 550 nm was 154 nm, the thickness direction retardation Rth was 49 nm, and the NZ coefficient was 0.82.

(Comparative Example 1)
An attempt was made to melt-extrude the polymer (A-1) pellets used in Example 1 at 265 ° C. from a coat hanger type T die having a width of 150 mm using a single screw extruder having a 20 mmφ screw. The polymer was poor in fluidity and could not be melt extruded. The polymer (A-1) had a Tg of 167 ° C., an MFR of 1.8 g / 10 min, and a fracture energy of less than 2 mJ.

(Comparative Example 2)
Polymer (A-3) having PMI units, AN units, and St units as constituent units; (PMI / AN / St = 27/19/54 mass% for composition, weight average molecular weight 374,000) Attempts were made to melt-extrusion at 265 ° C from a coat hanger type T die with a width of 150 mm using a single-screw extruder having a 20 mmφ screw, but the polymer was poor in fluidity and could not be melt extruded. It was. The polymer (A-3) had a Tg of 147 ° C., an MFR of 0.5 g / 10 min, and a fracture energy of 20 mJ.

(Comparative Example 3)
Polymer (G-1) having PMI units and St units as constituent units; (PMI / St = 17/83 mass% with respect to composition, weight average molecular weight 133,000) pellets, and AN units and St units Polymer (B-1) as unit: pellets (AN / St = 27/73% by mass, weight average molecular weight 222,000 for composition) were prepared, and each pellet was polymer (G-1) / The polymer (B-1) was kneaded at 260 ° C. using a twin screw extruder having a cylinder diameter of 15 mm while feeding using a feeder so that the mass ratio was 50/50, and a resin composition was obtained. The obtained resin composition was cloudy and could not be used for an optical film. The polymer (G-1) had a Tg of 123 ° C., an MFR of 214.7 g / 10 min, and a fracture energy of 3 mJ.

  The results of these Examples and Comparative Examples are summarized in Tables 1 and 2 below.

  As shown in Table 1, in Examples 1 and 2, strength (impact strength) expressed by fracture energy while being composed of a resin composition containing a polymer (A) having an N-phenylmaleimide unit as a structural unit. And an optical film that can be manufactured satisfactorily by melt extrusion. On the other hand, the resin composition of Comparative Example 1 had low fluidity, and a film could not be formed by melt extrusion. In addition, although it was possible to shape | mold the resin composition of the comparative example 1 to a film by methods other than melt extrusion molding, the intensity | strength was low and it became a brittle film. In the resin composition of Comparative Example 2, the strength as a film could be improved due to an increase in the molecular weight of the polymer (A), but the fluidity was further deteriorated compared to Comparative Example 1, and the film by melt extrusion molding was used. Could not be molded. The resin composition of Comparative Example 3 was cloudy and was clearly unsuitable for use in an optical film.

  As shown in Table 2, the optical films of Examples 1 and 2 were negative retardation films. Further, by laminating with a film made of a resin composition exhibiting positive intrinsic birefringence (Example 3), it was possible to achieve an NZ coefficient that could not be realized with a single layer.

  The optical film of the present invention is used in the same manner as conventional optical films, such as a polarizer protective film for protecting a polarizer in a polarizing plate, or a retardation film in an image display device such as an LCD and an organic EL display. It can be used for optical compensation.

Claims (10)

A polymer (A) having a maleimide compound unit, a vinyl cyanide compound unit and an aromatic vinyl compound unit as constituent units;
A polymer (B) having a vinyl cyanide compound unit and an aromatic vinyl compound unit as constituent units, and a resin composition (C) comprising:
The optical film whose weight average molecular weights of the said resin composition (C) are 150,000 or more and 300,000 or less. The maleimide compound unit content X1, the vinyl cyanide compound unit content X2, and the aromatic vinyl compound unit content X3 in the polymer (A) are expressed in mass% and satisfy the following formula: 1. The optical film as described in 1.
10 ≦ X1 ≦ 50
1 ≦ X2 ≦ 30
40 ≦ X3 ≦ 89 The optical film according to claim 1 or 2, wherein the content Y1 of the vinyl cyanide compound unit and the content Y2 of the aromatic vinyl compound unit in the polymer (B) are expressed by mass% and satisfy the following formula. .
10 ≦ Y1 ≦ 40
60 ≦ Y2 ≦ 90   The optical film according to any one of claims 1 to 3, wherein the resin composition (C) has a melt flow rate (MFR) of 3.0 [g / 10 min] or more.   The optical film according to claim 1, wherein the resin composition (C) has a glass transition temperature (Tg) of 110 ° C. or higher.   The optical film according to any one of claims 1 to 5, obtained by melt extrusion molding.   The optical film according to claim 1, wherein the resin composition (C) exhibits negative intrinsic birefringence. The optical film according to claim 7;
An optical film having a laminated structure comprising: another optical film made of a resin composition exhibiting positive intrinsic birefringence.   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.