JP2012173530A - Retardation film, method for manufacturing the same, and image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a retardation film showing reverse wavelength dispersion, the film having little fluctuation in the wavelength dispersion even when stretching conditions of a raw film are changed during manufacturing.SOLUTION: The retardation film comprises a resin composition (C) containing a resin (A) having positive intrinsic birefringence and showing normal wavelength dispersion and a polymer (B) as a wavelength dispersion controlling material, having negative intrinsic birefringence, showing normal wavelength dispersion and a greater change in the wavelength dispersion in a visible light region than that of the resin (A), and having a Tg, which is different by less than 20°C from the Tg of the resin (A). A mixing ratio of the resin (A) to the polymer (B) in the resin composition (C) is in a range represented by resin (A): polymer (B)=(95 to 70 parts by weight):(5 to 30 parts by weight). At least one selected from a polymer included in the resin (A) and the polymer (B) includes a (meth)acrylate unit as a structural unit, and the content percentage of (meth)acrylate units in the resin composition (C) is 60 wt.% or more.

Description

  The present invention relates to a retardation film exhibiting wavelength dispersion (reverse wavelength dispersion) in which birefringence is reduced as the wavelength is shortened in the visible light region, a manufacturing method thereof, and an image display device including the retardation film.

  Optical members using birefringence generated by polymer orientation are widely used in the field of image display. One such optical member is a retardation film incorporated in an image display device for the purpose of color tone compensation, viewing angle compensation, and the like. For example, in a reflective liquid crystal display device (LCD), a retardation plate (λ / 4 plate) having an optical path length difference (retardation) based on a phase difference caused by birefringence is ¼ of the wavelength is used. . In an organic EL display (OELD), an antireflection plate combining a polarizing plate and a λ / 4 plate may be used for the purpose of preventing reflection of external light. These optical members exhibiting birefringence are expected to be further expanded in future.

  Conventionally, cellulose derivatives represented by triacetyl cellulose (TAC), polycarbonate, and polycycloolefin have been mainly used for optical members, but these general polymers are birefringent as the wavelength of light becomes shorter. The wavelength dispersibility is increased (the phase difference is increased). In contrast to this, in order to obtain an image display device having excellent display characteristics, a retardation film exhibiting wavelength dispersibility that decreases birefringence (a phase difference decreases) as the wavelength of light decreases is desired. In this specification, the wavelength dispersion in which the phase difference decreases as the wavelength of light in the visible light region becomes shorter, according to the commonly used name of those skilled in the art, and also a general polymer and a phase difference formed by the polymer. It is called “reverse wavelength dispersion” based on the fact that it is opposite to the wavelength dispersion exhibited by the film. On the other hand, wavelength dispersion in which the phase difference increases as the wavelength of light becomes shorter in the visible light region is called “forward wavelength dispersion”.

  Patent Document 1 (Japanese Patent Application Laid-Open No. 2009-162850) discloses that a polymer having a positive intrinsic birefringence and a ring structure in the main chain, a negative intrinsic birefringence and having a heteroaromatic group, α, A resin composition containing a polymer having a β-unsaturated monomer unit as a constituent unit is disclosed. Patent Document 1 describes that a retardation film exhibiting reverse wavelength dispersibility can be obtained by the resin composition.

  Patent Document 2 (International Publication No. 00/26705 pamphlet) includes (1) a blend polymer composed of a polymer having a positive refractive index anisotropy and a polymer having a negative refractive index anisotropy. (2) R (450) / R (550) of a polymer having positive refractive index anisotropy is R (450) / R (450) / of a polymer having negative refractive index anisotropy A polymer oriented film that is smaller than R (550) and has (3) positive refractive index anisotropy is disclosed. Patent Document 2 discloses a blend polymer obtained by combining polyphenylene oxide (PPO) as a polymer having positive refractive index anisotropy and polystyrene (PS) as a polymer having negative refractive index anisotropy, It is described that it is preferable from the viewpoint of transparency. Note that R (450) and R (550) in Patent Document 2 are in-plane retardations of the polymer alignment film at wavelengths of 450 nm and 550 nm, respectively.

  Non-Patent Document 1 (Japanese Journal of Applied Physics, vol. 42 (2003), pp. 5665-5669) describes the wavelength dispersibility of the oriented film of the PS / PPO blend polymer disclosed in Patent Document 2. Stretching temperature dependence is disclosed. In Non-Patent Document 1, when the stretching temperature when making an oriented film is changed in the range of Tg + 5 ° C. to Tg + 15 ° C. on the basis of the glass transition temperature (Tg) of the blend polymer, the above-mentioned R (450 ) / R (550) varies from about 0.95 to about 0.81 (FIGS. 1 and 2).

JP 2009-162850 A International Publication No. 00/26705 Pamphlet

Japanese Journal of Applied Physics, vol. 42 (2003), pp.5665-5669

  The retardation film is usually formed by forming a resin (resin composition) containing one or more polymers into a film and then stretching the resulting film (raw film). When the resin composition contains two or more polymers, the wavelength dispersion of the obtained retardation film is likely to vary depending on the stretching conditions of the raw film. On the other hand, in the production of a retardation film, especially in the mass production site of the retardation film, the stretching conditions are often changed for the purpose of changing or adjusting the retardation or strength of the retardation film. At that time, it is desirable that the wavelength dispersion does not change.

  The present invention is a retardation film exhibiting reverse wavelength dispersion, and even when the stretching conditions of the original film, specifically, the stretching temperature and / or the stretching ratio are changed during the production thereof, the wavelength dispersion An object of the present invention is to provide a retardation film with little variation in properties and a method for producing such a retardation film.

  The retardation film of the present invention has a positive intrinsic birefringence, a resin (A) exhibiting wavelength dispersion (forward wavelength dispersion) in which in-plane retardation increases as the wavelength becomes shorter in the visible light region, and wavelength As a dispersion control material, it has negative intrinsic birefringence, and shows wavelength dispersion (forward wavelength dispersion) in which the in-plane phase difference increases as the wavelength becomes shorter in the visible light region, and the wavelength dispersion in the visible light region. A resin composition comprising a polymer (B) having a greater change than the resin (A) and having a difference between the glass transition temperature (Tg) of the resin (A) and its own Tg of less than 20 ° C. C). The mixing ratio of the resin (A) and the polymer (B) in the resin composition (C) is resin (A): polymer (B) = 95 to 70 parts by weight: 5 to 30 parts by weight. . At least one polymer selected from one or two or more polymers contained in the resin (A) and the polymer (B) has a (meth) acrylic acid ester unit as a structural unit. In the resin composition (C), the proportion of (meth) acrylic acid ester units in all polymer constituent units is 60% by weight or more. The retardation film of the present invention exhibits wavelength dispersion (reverse wavelength dispersion) in which the in-plane retardation becomes smaller as the wavelength becomes shorter in the visible light region.

  The method for producing a retardation film of the present invention is a method for producing a retardation film that exhibits wavelength dispersion (reverse wavelength dispersion) in which in-plane retardation is reduced as the wavelength is shortened in the visible light region, and is a positive intrinsic property. Resin (A) that has birefringence and has a wavelength dispersion (forward wavelength dispersion) that increases in-plane retardation as the wavelength becomes shorter in the visible light region, and negative intrinsic birefringence as a wavelength dispersion control material And shows a wavelength dispersion (forward wavelength dispersion) in which the in-plane retardation increases as the wavelength becomes shorter in the visible light region, and the change in the wavelength dispersion in the visible light region is larger than that of the resin (A). A polymer (B) in which the difference between the glass transition temperature (Tg) of the resin (A) and its own Tg is less than 20 ° C. is referred to as resin (A): polymer (B) = 95 to 70 wt. Parts: mixed at a mixing ratio of 5 to 30 parts by weight, and the resin ( ) And the polymer (B) are formed, and the formed resin composition (C) is formed into a film (raw film), and then the obtained film is stretched. And forming the retardation film. Here, at least 1 polymer chosen from the 1 type (s) or 2 or more types of polymer contained in the said resin (A), and the said polymer (B) has a (meth) acrylic acid ester unit as a structural unit. In the resin composition (C), the proportion of the (meth) acrylic acid ester units in all polymer constituent units is 60% by weight or more.

  Unless otherwise specified, “resin” in this specification is a broader concept than “polymer”. The resin may be composed of, for example, one or more polymers, and if necessary, particles other than the polymer, for example, a particle containing an ultraviolet absorber, an antioxidant, a filler, and rubber particles. , Additives such as compatibilizers and stabilizers may be included.

  The intrinsic birefringence of the polymer is determined by the orientation of the molecular chain in the layer of light that is perpendicularly incident on the principal surface of the layer in a layer (for example, a film) in which the molecular chain of the polymer is uniaxially oriented. This can be determined based on a value “n1-n2” obtained by subtracting the refractive index n2 of light in the direction perpendicular to the alignment axis from the refractive index n1 of light in the direction parallel to the direction (alignment axis). The intrinsic birefringence value can be determined by calculation based on the molecular structure of each polymer.

  The positive or negative of the intrinsic birefringence of the resin (resin composition) is perpendicular to the main surface of the layer in the layer (for example, film) in which the molecular chains of the polymer contained in the resin (resin composition) are uniaxially oriented. Of the obtained light, a value obtained by subtracting the refractive index n4 of light in the direction perpendicular to the orientation axis from the refractive index n3 of light in the direction parallel to the direction in which the molecular chains are oriented (orientation axis) in the layer “n3− n4 ". The intrinsic birefringence of the resin (resin composition) is determined by the balance of birefringence generated by each polymer contained in the resin (resin composition).

  In this specification, the wavelength dispersibility indicated by the polymer (resin) is the wavelength dispersibility indicated by the oriented film of the polymer (resin). When the oriented film of a polymer (resin) exhibits forward wavelength dispersibility, the polymer (resin) is assumed to exhibit forward wavelength dispersibility.

  The wavelength dispersion exhibited by the resin (A), the polymer (B) and the retardation film of the present invention may be forward wavelength dispersion or reverse wavelength dispersion at least in the visible light region. It does not matter whether the wavelength dispersion in the region is forward wavelength dispersion or reverse wavelength dispersion.

  Whether the retardation film (alignment film) exhibits reverse wavelength dispersion or forward wavelength dispersion can be determined based on the in-plane retardation of the film. In the visible light region, the wavelength dispersibility in which the in-plane phase difference decreases as the light wavelength becomes shorter is the reverse wavelength dispersibility. Conversely, the wavelength dispersibility in which the in-plane phase difference increases as the light wavelength becomes shorter. It is wavelength dispersive. Specifically, the wavelength dispersibility of the retardation film (alignment film) having a later-described ratio Re (447) / Re (590) with respect to the in-plane retardation Re is less than 1, is reverse wavelength dispersibility, and Re ( 447) The wavelength dispersion exhibited by the retardation film (alignment film) having 1 / Re (590) of 1 or more is forward wavelength dispersion. As long as the ratio is satisfied, the direction of the in-plane phase difference change in a part of the wavelength range may be reversed. Such a change in in-plane retardation can occur when the wavelength dispersion of the resin or polymer has a partial maximum or minimum in the visible light region. The in-plane retardation of the retardation film is defined as nx as the refractive index in the visible light region of the slow axis in the plane of the film, ny as the refractive index in the visible light region of the fast axis, and d as the thickness of the film. , Re = (nx−ny) × d.

  The visible light region has a wavelength range of 440 nm to 760 nm.

  According to the present invention, specific intrinsic birefringence and wavelength dispersibility can be obtained as a wavelength dispersion control material for a resin (A) having positive intrinsic birefringence and exhibiting forward wavelength dispersion in the visible light region. A retardation film comprising a resin composition (C) having a specific mixing ratio of a polymer (B) having a difference between the Tg of the resin (A) as a base material and its own Tg of less than 20 ° C. In addition, in the resin composition (C), by changing the proportion of the (meth) acrylic acid ester units in all polymer constituent units to 60% by weight or more, the stretching conditions of the raw film are changed during production. In this case, a retardation film exhibiting reverse wavelength dispersion with little variation in wavelength dispersion can be realized. This variation in the wavelength dispersion is small because the difference between the Tg of the resin (A) and the Tg of the polymer (B) used as the wavelength dispersion control material is less than 20 ° C. This is because the degree of orientation between the resin (A) and the polymer (B) becomes the same when the retardation film is formed by stretching and orientation.

  In addition, in the combination of the polymer which has a positive intrinsic birefringence and the polymer which has a negative intrinsic birefringence currently disclosed by patent documents 1-2 and nonpatent literature 1, the difference of Tg between each polymer All exceed 20 ° C.

[Resin (A)]
The resin (A) is not limited as long as it has positive intrinsic birefringence and exhibits forward wavelength dispersion. The resin (A) is, for example, an acrylic resin or a cycloolefin resin. Acrylic resins and cycloolefin resins have high transparency and mechanical properties. The retardation film of the present invention and the retardation film obtained by the production method of the present invention include the resin (A) as a “base material”. The retardation film including such a resin (A) is a liquid crystal display. It is suitable as a retardation film for use in an image display device such as a device (LCD). Resin (A) is a thermoplastic resin.

  The acrylic resin is a resin containing a (meth) acrylic polymer in an amount of 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more, and further preferably 80% by weight or more. The cycloolefin resin is a resin containing a cycloolefin polymer of 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more, and further preferably 80% by weight or more.

  The glass transition temperature (Tg) of the resin (A) is, for example, 110 ° C. or higher. Depending on the type and content of the polymer contained in the resin (A), the Tg is 115 ° C. or higher, 120 ° C. or higher, and further 130 ° C. or higher. Such a retardation film containing a resin (A) having a high Tg has excellent heat resistance, and an image display device such as an LCD in which heating elements such as a light source, a power source and a circuit board are accommodated in a limited space. Suitable for use in. Moreover, since the processing temperature at the time of post-processing (for example, surface treatment such as coating) can be increased, the productivity of the retardation film is improved. The Tg of the resin and polymer can be determined according to JIS K7121.

  Even when the resin is composed of two or more kinds of polymers, the polymers are basically compatible with each other, and thus the measured Tg is basically one point. When Tg based on a polymer is measured at two or more points, a weighted average of each Tg may be obtained based on the content (% by weight) of each polymer in the resin, and this may be used as the Tg of the resin. If the additive is a low molecule, it does not affect the Tg of the resin. When the additive is a particle having a polymer component, for example, a rubber particle added to the retardation film for the purpose of improving mechanical properties, Tg derived from the particle may be measured. However, in this case, the Tg derived from these particles and the Tg derived from the polymer constituting the film can be easily distinguished, and the latter may be the resin Tg. These particles are not oriented by stretching when forming the retardation film. That is, it does not affect the wavelength dispersion and retardation of the retardation film.

  The resin (A) is preferably an acrylic resin having a Tg of 110 ° C. or higher.

  The resin (A) preferably contains a polymer having a ring structure in the main chain. Since the polymer having a ring structure in the main chain has a high Tg, the Tg of the resin (A) containing the polymer is high, and the heat resistance of the retardation film containing the resin (A) is improved. The polymer having a ring structure in the main chain is not particularly limited, and is, for example, a cycloolefin polymer.

  The cycloolefin polymer is a polymer having a cycloolefin unit of 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more of all structural units.

  The polymer having a ring structure in the main chain may be a (meth) acrylic polymer. In this case, a retardation film having improved properties such as mechanical strength, moldability, and surface strength is obtained.

  The (meth) acrylic polymer is a polymer having (meth) acrylic acid ester units in an amount of 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more based on all the structural units. The (meth) acrylic polymer may have a ring structure that is a derivative of the (meth) acrylic acid ester unit in the main chain, and in this case, the total of the (meth) acrylic acid ester unit and the ring structure is entirely composed. If it is 50 weight% or more of a unit, it will become a (meth) acrylic polymer.

  When the resin (A) contains a (meth) acrylic polymer having a ring structure in the main chain, particularly when the resin (A) is an acrylic resin containing 50% by weight or more of the (meth) acrylic polymer, the present invention The degree of freedom in controlling the reverse wavelength dispersion in the retardation film and the retardation film obtained by the production method of the present invention is improved. The change in wavelength dispersion (change in wavelength dispersion of retardation) in the visible light region indicated by the polymer (B) is larger than that of the resin (A). When the resin (A) contains a (meth) acrylic polymer having a ring structure in the main chain, since the change in wavelength dispersion in the visible light region indicated by the resin (A) is small, the resin (A ) And the polymer (B) have a large difference in change in wavelength dispersion. Thus, by combining the resin (A) and the polymer (B) having a large difference in wavelength dispersion, the degree of freedom in controlling the reverse wavelength dispersion in the retardation film is improved.

  The ring structure that the (meth) acrylic polymer may have in the main chain is, for example, a ring structure having an ester group, an imide group, or an acid anhydride group.

  A more specific example of the ring structure is at least one selected from a lactone ring structure, a glutarimide structure, a glutaric anhydride structure, an N-substituted maleimide structure, and a maleic anhydride structure. The (meth) acrylic polymer having such a ring structure in the main chain exhibits a large positive intrinsic birefringence depending on the orientation. For this reason, the combination with a polymer (B) improves the freedom degree of control of reverse wavelength dispersion in the retardation film of the present invention and the retardation film obtained by the production method of the present invention.

  The ring structure is preferably at least one selected from a lactone ring structure, a glutaric anhydride structure and a glutarimide structure, more preferably at least one selected from a lactone ring structure and a glutarimide structure, and even more preferably a lactone ring structure. A polymer having a lactone ring structure or a glutarimide structure, particularly a lactone ring structure, in the main chain has a further smaller change in wavelength dispersion in the visible light region. For this reason, the combination with a polymer (B) improves the freedom degree of control of reverse wavelength dispersion in the retardation film of the present invention and the retardation film obtained by the production method of the present invention.

  A specific lactone ring structure is not particularly limited. The lactone ring structure is, for example, a structure represented by the following formula (1).

In the formula (1), R ¹ , R ² and R ³ are each independently a hydrogen atom or an organic residue having 1 to 20 carbon atoms. The organic residue may contain an oxygen atom.

  The organic residue is, for example, an alkyl group having 1 to 20 carbon atoms such as a methyl group, an ethyl group, or a propyl group; an unsaturated aliphatic carbonization having 1 to 20 carbon atoms such as an ethenyl group or a propenyl group. A hydrogen group; an aromatic hydrocarbon group having 1 to 20 carbon atoms such as a phenyl group or a naphthyl group; one of hydrogen atoms in the alkyl group, the unsaturated aliphatic hydrocarbon group and the aromatic hydrocarbon group; One or more groups are substituted with at least one group selected from a hydroxyl group, a carboxyl group, an ether group and an ester group.

The lactone ring structure represented by the formula (1) is obtained by copolymerizing a monomer group including, for example, methyl methacrylate (MMA) and 2- (hydroxymethyl) methyl acrylate (MHMA), Adjacent MMA units and MHMA units in the coalescence can be formed by dealcoholization cyclocondensation. At this time, R ¹ is H, R ² and R ³ are CH ₃ .

  The following formula (2) shows a glutarimide structure and a glutaric anhydride structure.

In the formula (2), R ⁴ and R ⁵ are each independently a hydrogen atom or a methyl group, and X ¹ is an oxygen atom or a nitrogen atom. When X ¹ is an oxygen atom, R ⁶ does not exist, and when X ¹ is a nitrogen atom, R ⁶ is a hydrogen atom, a linear alkyl group having 1 to 6 carbon atoms, a cyclopentyl group, a cyclohexyl group, or a phenyl group. .

When X ¹ is a nitrogen atom, the ring structure represented by the formula (2) is a glutarimide structure. The glutarimide structure can be formed, for example, by imidizing a (meth) acrylic acid ester polymer with an imidizing agent such as methylamine.

When X ¹ is an oxygen atom, the ring structure represented by the formula (2) is a glutaric anhydride structure. The glutaric anhydride structure can be formed, for example, by subjecting a copolymer of (meth) acrylic acid ester and (meth) acrylic acid to dealcoholization cyclocondensation within the molecule.

  The following formula (3) shows an N-substituted maleimide structure and a maleic anhydride structure.

In the formula (3), R ⁷ and R ⁸ are each independently a hydrogen atom or a methyl group, and X ² is an oxygen atom or a nitrogen atom. When X ² is an oxygen atom, R ⁹ does not exist, and when X ² is a nitrogen atom, R ⁹ is a hydrogen atom, a linear alkyl group having 1 to 6 carbon atoms, a cyclopentyl group, a cyclohexyl group, or a phenyl group. .

When X ² is a nitrogen atom, the ring structure represented by Formula (3) is an N-substituted maleimide structure. The acrylic resin having an N-substituted maleimide structure in the main chain can be formed, for example, by copolymerizing an N-substituted maleimide and a (meth) acrylic ester.

When X ² is an oxygen atom, the ring structure represented by formula (3) is a maleic anhydride structure. The acrylic resin having a maleic anhydride structure in the main chain can be formed, for example, by copolymerizing maleic anhydride and (meth) acrylic acid ester.

  When the (meth) acrylic polymer has a ring structure in the main chain, the content of the ring structure in the polymer is not particularly limited, but is usually 5 to 90% by weight, and preferably 20 to 90% by weight. The content is more preferably 30 to 90% by weight, 35 to 90% by weight, 40 to 80% by weight, and 45 to 75% by weight. The content of the ring structure can be determined by the method described in JP-A-2001-151814.

  The polymer which resin (A) and resin (A) contain can be manufactured by a well-known method.

  As an example, a (meth) acrylic polymer having a lactone ring structure in the main chain is a lactone accompanied by dealcoholization by heating a polymer (a) having a hydroxyl group and an ester group in the molecular chain in the presence of an arbitrary catalyst. It can be obtained by proceeding the cyclization condensation reaction.

  The polymer (a) can be formed, for example, by polymerization of a monomer group including a monomer represented by the following formula (4).

In the formula (4), R ¹⁰ and R ¹¹ are each independently a hydrogen atom or a group exemplified as the organic residue in the formula (1).

  Specific examples of the monomer represented by the formula (4) include methyl 2- (hydroxymethyl) acrylate, ethyl 2- (hydroxymethyl) acrylate, isopropyl 2- (hydroxymethyl) acrylate, 2- ( Hydroxymethyl) normal butyl acrylate, 2- (hydroxymethyl) acrylate t-butyl. Of these, methyl 2- (hydroxymethyl) acrylate and ethyl 2- (hydroxymethyl) acrylate are preferable, and optical film 1 having high transparency and heat resistance can be obtained. Accordingly, 2- (hydroxymethyl) acrylic acid is obtained. Methyl (MHMA) is particularly preferred.

  In addition, the structural unit formed by the polymerization of these monomers has a function of giving positive intrinsic birefringence to the polymer having the unit by cyclization.

  The monomer group used for forming the polymer (a) may contain two or more monomers represented by the formula (4).

  The monomer group used for forming the polymer (a) may include a monomer other than the monomer represented by the formula (4). Such a monomer is not particularly limited as long as it is a monomer copolymerizable with the monomer represented by the formula (4). For example, (metha) other than the monomer represented by the formula (4) ) Acrylic acid ester.

  Examples of the (meth) acrylic acid ester include acrylic acid esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, cyclohexyl acrylate, and benzyl acrylate; methacrylic acid Methacrylic acid esters such as methyl, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate and benzyl methacrylate. Among these, methyl methacrylate (MMA) is preferable because a retardation film having high transparency and heat resistance can be obtained.

  The monomer group used for forming the polymer (a) may contain two or more of these (meth) acrylic acid esters.

  The monomer group used for forming the polymer (a) is one or two other monomers such as styrene, vinyl toluene, α-methyl styrene, acrylonitrile, methyl vinyl ketone, ethylene, propylene, and vinyl acetate. More than one species may be included.

  The (meth) acrylic polymer having a glutaric anhydride structure in the main chain is, for example, a polymer described in JP 2006-283013 A, JP 2006-335902 A, or JP 2006-274118 A. Yes, it can be formed by the method described in the publication.

  Examples of the (meth) acrylic polymer having a glutarimide structure in the main chain include, for example, JP-A-2006-309033, JP-A-2006-317560, JP-A-2006-328329, JP-A-2006-328334, JP-A-2006-337491, JP-A-2006-337492, JP-A-2006-337493, JP-A-2006-337569, JP-A-2007-009182 It can be formed by the method described in the publication.

  The resin (A) has positive intrinsic birefringence, exhibits forward wavelength dispersion, and may contain other thermoplastic polymers than the above-described polymers as long as the effects of the present invention are obtained. . Other thermoplastic polymers include, for example, polyethylene, polypropylene, ethylene-propylene copolymers, olefin polymers such as poly (4-methyl-1-pentene); polyvinyl chloride, polyvinylidene chloride, polychlorinated vinyl, etc. Styrene polymers such as polystyrene, styrene-methyl methacrylate copolymer, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene block copolymer; cellulose triacetate, cellulose acetate propionate, Cellulose polymers such as cellulose acetate butyrate; Polyesters such as polyethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate; Polyamides such as nylon 6, nylon 66 and nylon 610 Polyacetal; Polycarbonate; Polyphenylene oxide; Polyphenylene sulfide; Polyether ether ketone; Polysulfone; Polyether sulfone; Polyoxybenzylene; Polyamideimide; Coalescence;

  The content of the other thermoplastic polymer in the resin (A) is preferably 0 to 50% by weight, more preferably 0 to 40% by weight, further preferably 0 to 30% by weight, and particularly preferably 0 to 20% by weight. It is.

  The resin (A) has positive intrinsic birefringence, exhibits forward wavelength dispersion, and may contain a material other than a polymer, such as an additive, as long as the effects of the present invention are obtained. Additives include, for example, hindered phenol-based, phosphorus-based, sulfur-based antioxidants; light-resistant stabilizers, weather-resistant stabilizers, thermal stabilizers, and other stabilizers; reinforcing materials such as glass fibers and carbon fibers; UV absorbers such as tyrates, (2,2′-hydroxy-5-methylphenyl) benzotriazole, 2-hydroxybenzophenone; near infrared absorbers; difficulties such as tris (dibromopropyl) phosphate, triallyl phosphate, antimony oxide Antistatic agent composed of anionic, cationic and nonionic surfactants; Colorants such as inorganic pigments, organic pigments and dyes; Organic fillers, inorganic fillers; Antiblocking agents; Resin modifiers; Organic Fillers, inorganic fillers; plasticizers; lubricants; flame retardants.

  The content of the additive in the resin (A) is preferably 0 to 5% by weight, more preferably 0 to 2% by weight, and still more preferably 0 to 0.5% by weight.

[Polymer (B)]
The polymer (B) has a negative intrinsic birefringence, exhibits forward wavelength dispersion, a change in wavelength dispersion in the visible light region is larger than that of the resin (A), and the Tg of the resin (A) and its own As long as the difference with Tg is less than 20 degreeC, it is not limited. The polymer (B) is a thermoplastic polymer. Further, “the change in wavelength dispersion in the visible light region is larger than that of the resin (A)” means that the change in wavelength dispersion exhibited by the alignment film of the polymer (B) is indicated by the alignment film of the resin (A). It is larger than the change in wavelength dispersion. The change in wavelength dispersion is, for example, the ratio Re (447) between the in-plane retardation Re (447) of the alignment film with respect to light having a wavelength of 447 nm and the in-plane retardation Re (590) of the alignment film with respect to light having a wavelength of 590 nm. / Re (590).

  The polymer (B) has, for example, a (meth) acrylic acid ester unit as a structural unit. Such a polymer (B) is excellent in compatibility with a resin (A) containing a (meth) acrylic polymer, particularly a resin (A) which is an acrylic resin. When the compatibility between the polymer (B) and the resin (A) is excellent, the optical properties, particularly wavelength dispersibility, of the retardation film of the present invention and the retardation film obtained by the production method of the present invention are improved.

  The polymer (B) includes a (meth) acrylic acid ester unit and an α, β-unsaturated monomer unit having a heteroaromatic group (hereinafter simply referred to as “α, β-unsaturated monomer” as structural units. It is preferably a copolymer having a “unit”). At this time, the proportion of α, β-unsaturated monomer units in all the structural units of the polymer (B) (content of α, β-unsaturated monomer units in the polymer (B)) was 20 It is preferably more than 60% by weight and less than 60% by weight.

  The α, β-unsaturated monomer unit has an action of giving negative intrinsic birefringence to the polymer (B) and an action of improving the Tg of the polymer (B). The Tg of a polymer having only a (meth) acrylic acid ester unit as a structural unit and having no ring structure in the main chain is generally low. On the other hand, by using a copolymer having (meth) acrylic acid ester units and α, β-unsaturated monomer units as constituent units, the α, β-unsaturated monomer units act as a Tg improving component. And Tg of the polymer (B) is improved. Thereby, the difference of Tg of resin (A) and Tg of a polymer (B) can be more reliably made less than 20 degreeC. The copolymer is particularly preferable when the resin (A) includes a polymer having a ring structure in the main chain.

  The content of the α, β-unsaturated monomer unit in the polymer (B) having (meth) acrylic acid ester units and α, β-unsaturated monomer units as constituent units is 30% by weight or more. More preferred is 40% by weight or more. When the content is 20% by weight or less, the above-described action by the α, β-unsaturated monomer unit may be insufficient. If the content exceeds 60% by weight, it may be difficult to ensure compatibility with the resin (A), although it depends on the type of the resin (A).

  The α, β-unsaturated monomer unit is not particularly limited, and for example, the heteroaromatic group that the unit has is not particularly limited. The hetero atom in the heteroaromatic group is typically an oxygen atom, a sulfur atom or a nitrogen atom. Nitrogen atoms are preferred because the change in wavelength dispersion (change in wavelength dispersion of retardation) in the visible light region indicated by the polymer (B) becomes large. When the change in wavelength dispersion in the visible light region indicated by the polymer (B) is increased, the difference in change in wavelength dispersion between the resin (A) and the polymer (B) is relatively increased. Thus, by combining the resin (A) and the polymer (B) having a large difference in wavelength dispersion, the degree of freedom in controlling the reverse wavelength dispersion in the retardation film is improved.

  The heteroaromatic group is at least one selected from, for example, a carbazole group, a pyridine group, an imidazole group, and a thiophene group.

  The α, β-unsaturated monomer unit is, for example, at least one selected from an N-vinylcarbazole unit, a vinylpyridine unit, a vinylimidazole unit, and a vinylthiophene unit. The α, β-unsaturated monomer unit is preferably an N-vinylcarbazole unit because the change in wavelength dispersibility in the visible light region indicated by the polymer (B) is particularly large.

  The N-vinylcarbazole unit is shown in the following formula (5). In addition, a part of hydrogen atom on the ring shown in Formula (5) may be substituted by the group exemplified as the organic residue in Formula (1).

  The (meth) acrylic acid ester unit in the polymer (B) is, for example, a structural unit formed by polymerization of the exemplified (meth) acrylic acid ester monomer. The (meth) acrylate unit in the polymer (B) is a methyl (meth) acrylate unit from the viewpoint of compatibility with the resin (A) and copolymerization with the α, β-unsaturated monomer unit. (Meth) acrylic acid alkyl ester units such as (meth) ethyl acrylate units, (meth) propyl propyl units and (meth) butyl butyl units are preferred.

  When the polymer (B) is a copolymer having a (meth) acrylic acid ester unit and an α, β-unsaturated monomer unit as structural units, the polymer (B) is composed of acrylonitrile as the structural unit. It is preferable to further have a unit. Such a polymer (B) is excellent in compatibility with a resin (A) containing a (meth) acrylic polymer, particularly a resin (A) which is an acrylic resin. That is, when the resin (A) contains a (meth) acrylic polymer, in particular, when it is an acrylic resin, the polymer (B) has (meth) acrylic acid ester units, α, β-unsaturated as structural units. It preferably has a monomer unit and an acrylonitrile unit.

  When a polymer (B) has an acrylonitrile unit as a structural unit, 10 to 40 weight% is preferable and, as for the content rate of the acrylonitrile unit in a polymer (B), 20 to 35 weight% is more preferable.

  The polymer (B) has a Tg having a difference ΔTg from the Tg of the resin (A) of less than 20 ° C. ΔTg is preferably 15 ° C. or lower, more preferably 10 ° C. or lower, and further preferably 5 ° C. or lower. The magnitude relationship between the Tg of the resin (A) and the Tg of the polymer (B) is not limited.

  The polymer (B) can be produced by a known method.

[Resin composition (C)]
The resin composition (C) contains the resin (A) and the polymer (B) at a mixing ratio of resin (A): polymer (B) = 95 to 70 parts by weight: 5 to 30 parts by weight. Since the effect of the present invention can be obtained more reliably, the mixing ratio is preferably resin (A): polymer (B) = 95 to 80 parts by weight: 5 to 20 parts by weight. Resin (A) contains a (meth) acrylic acid ester polymer (particularly, resin (A) is an acrylic resin), and polymer (B) has (meth) acrylic ester units as constituent units, α, In the case of a copolymer having a β-unsaturated monomer unit, particularly when the copolymer further has an acrylonitrile unit as a constituent unit, high wavelength dispersion due to the α, β-unsaturated monomer unit. Compatibility control property and compatibility with resin (A) by (meth) acrylic ester unit (when polymer (B) further has acrylonitrile unit as a constituent unit, further compatibility with resin (A) by acrylonitrile unit) ), The effect of the present invention can be sufficiently obtained while reducing the mixing ratio of the polymer (B) to the resin (A). In addition, this mixing ratio is a mixing ratio of resin (A) which is a base material and polymer (B) which is a wavelength dispersion control material, and is not affected by other components contained in the resin composition (C).

  In the resin composition (C), at least one polymer selected from one or more polymers and the polymer (B) contained in the resin (A) is a (meth) acrylic acid ester unit as a structural unit. Have That is, in the resin composition (C), the polymer (B) has a (meth) acrylic acid ester unit as a structural unit, and / or the resin (A) has a (meth) acrylic acid ester unit as a structural unit. A polymer having

  In the resin composition (C), the proportion of (meth) acrylic acid ester units in all polymer constituent units is 60% by weight or more. The proportion is preferably 70% by weight or more, and more preferably 80% by weight or more. In the case of including a polymer having a ring structure that is a derivative of a (meth) acrylic acid ester unit, such as a lactone ring structure, in the resin composition (C), the ratio of the ring structure in all polymer constituent units And the ratio of the (meth) acrylic acid ester unit is 60% by weight or more. When the ratio in the resin composition (C) is 60% by weight or more, in addition to the retardation and wavelength dispersibility, optical characteristics and mechanical characteristics suitable as a retardation film are realized. In addition, all the polymers contained in the resin composition (C) are each 60% by weight or more of (meth) acrylic acid ester unit content (or the above-mentioned ring structure content and (meth) acrylic acid ester unit content). The content of the (meth) acrylic acid ester unit as the whole polymer contained in the resin composition (C) (or the content of the ring structure and (meth) The total content of the acrylic acid ester units) may be 60% by weight or more. In other words, the resin composition (C) may contain a (meth) acrylic acid ester unit as a constituent unit and a polymer having no ring structure.

  The resin composition (C) may contain components other than the resin (A) and the polymer (B) as long as the effects of the present invention are obtained. The said component is a thermoplastic polymer except the polymer of both the polymer contained in resin (A) and a polymer (B), for example. The said thermoplastic polymer is "another thermoplastic polymer" illustrated in description of resin (A), for example. The component may be, for example, the additive exemplified in the description of the resin (A).

  The resin composition (C) can be produced by a known method. The resin composition (C) can be formed into a raw film by a known method such as extrusion melt molding.

[Phase difference film]
The retardation film of this invention consists of a resin composition (C). The retardation film of the present invention is typically a single layer film made of the resin composition (C). However, you may have a functional coating layer on the surface.

  The retardation film of the present invention exhibits reverse wavelength dispersion. The retardation film of the present invention is a positive retardation film based on a resin (A) having positive intrinsic birefringence.

  The in-plane retardation Re for light having a wavelength of 590 nm, which is shown by the retardation film of the present invention, is, for example, 20 nm or more. Depending on the type and content of the resin (A) and polymer (B) contained in the resin composition (C) and the stretched state of the retardation film, the thickness is 40 nm or more, and further 100 nm or more. The in-plane retardation Re is defined by the formula Re = (nx−ny) × d, where the refractive index of the slow axis in the plane of the retardation film is nx and the refractive index of the fast axis is ny.

  The retardation Rth in the thickness direction with respect to light having a wavelength of 590 nm, which is shown by the retardation film of the present invention, is, for example, 10 nm or more. Depending on the type and content of the resin (A) and polymer (B) contained in the resin composition (C) and the stretched state of the retardation film, the thickness is 20 nm or more, and further 50 nm or more. The retardation Rth in the thickness direction is expressed by a formula in which the refractive index of the slow axis in the plane of the retardation film is nx, the refractive index of the fast axis is ny, and the refractive index in the thickness direction of the retardation film is nz. Rth = [(nx + ny) / 2−nz] × d.

  The retardation film of the present invention may be an oriented film obtained by uniaxially stretching a raw film or an oriented film obtained by biaxially stretching. That is, the retardation film of the present invention may be uniaxially stretchable or biaxially stretchable. Biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching. In sequential biaxial stretching, the time for heating and stretching the raw film is longer than in the case of uniaxial stretching and simultaneous biaxial stretching, and fluctuations in wavelength dispersibility are likely to occur due to changes in stretching conditions (stretching temperature and stretching ratio). However, in the present invention, even in such a case, fluctuations in the wavelength dispersion of the retardation film due to changes in the stretching conditions of the original film are suppressed.

  The NZ coefficient of the retardation film of the present invention is, for example, 1.0 to 2.5. In this invention, also when obtaining a phase difference film by sequential biaxial stretching, the fluctuation | variation of the wavelength dispersion of the obtained phase difference film is suppressed. For this reason, the retardation film which shows the high value of 2.3 or more as a NZ coefficient is implement | achieved. A retardation film exhibiting a high NZ coefficient is suitable for use in a VA (vertical alignment) mode LCD. The NZ coefficient is expressed by the equation {NZ = the refractive index of the slow axis in the plane of the retardation film is nx, the refractive index of the fast axis is ny, and the refractive index in the thickness direction of the retardation film is nz. It is defined by (nx−nz) / (nx−ny)}. In the case of a uniaxially stretchable retardation film, the NZ coefficient is 1.0.

  The retardation film of the present invention has, for example, a rectangular shape or a belt shape. When it is a belt-like retardation film, the film may be wound around a roll (retardation film roll). The band-shaped retardation film is formed by stretching a band-shaped original film. The rectangular retardation film can also be formed by stretching a strip-shaped raw film to obtain a strip-shaped retardation film, and then cutting the strip-shaped retardation film into a predetermined size. The retardation film of the present invention has little variation in wavelength dispersion even when the stretching conditions of the raw film are changed. For this reason, the retardation film of the present invention is a belt-like retardation film or retardation film roll having two or more portions having the same or substantially the same wavelength dispersion but different retardation values and / or NZ coefficients. It is possible.

  The retardation film of the present invention exhibits reverse wavelength dispersion, but the degree of strength thereof is, for example, an in-plane retardation measured at a measurement wavelength of 447 nm with respect to an in-plane retardation Re (590) measured at a measurement wavelength of 590 nm. The ratio D (= Re (447) / Re (590)) of Re (447) is 0.75 ≦ D ≦ 0.99. At this time, it is preferable that the following (1) and / or (2) corresponding to the fact that the retardation film of the present invention has a small variation in wavelength dispersion due to a change in stretching conditions is satisfied.

(1) The resin composition (C) constituting the retardation film is a non-oriented film composed of the composition (C) at a temperature 5 ° C. higher than the Tg of the composition (C), and Re (590) is the value D ₅ of the ratio D shown in stretching such that the 20nm or more, at a temperature from 15 ℃ high Tg of the composition (C), when other than stretching temperature was stretched by the same stretching conditions and the stretching And the value D _{15 of the} ratio D shown in FIG. 2 has a composition that satisfies the expression 0 ≦ | D ₁₅ −D ₅ | <0.05. More preferably, the resin composition (C) has a composition satisfying the formula 0 ≦ | D ₁₅ −D ₅ | ≦ 0.03 between D ₅ and D ₁₅ .

(2) The resin composition (C) constituting the retardation film is a value of the ratio D shown when the non-oriented film made of the composition (C) is stretched so that the NZ coefficient is 1.0. Between D _1.0 and the value D _{1.4-3.0 of the} ratio D shown when stretching at the same stretching temperature as the stretching so that the NZ coefficient is 1.4 or more and 3.0 or less, the formula 0 ≦ | D _1.4-3.0 −D _1.0 | ≦ 0.04. The resin composition (C) preferably has a composition _{satisfying the} formula 0 ≦ | D _1.4-3.0 −D _1.0 | ≦ 0.02 between D _1.0 and D _1.4-3.0 .

Whether or not the above-mentioned (1) or (2) is satisfied in the film when there is a certain retardation film can be examined as follows. First, the retardation film is heated once to eliminate the orientation of the polymer contained in the film, thereby forming a non-oriented film. Next, the obtained non-oriented film is stretched under the stretching conditions of (1) or (2) above, and the values of D ₅ and D ₁₅ , or D _1.0 and D _1.4-3.0 are determined, and the above (1) or It is verified whether (2) is satisfied. The heating for obtaining the non-oriented film may be performed at a temperature not higher than the temperature at which the heated retardation film can maintain the shape and at a temperature higher by 50 ° C. than the Tg of the separately heated retardation film. Although the heating method is not particularly limited, for example, a melt press method can be applied. The heating time may be at least a time until the orientation of the polymer contained in the retardation film to be heated disappears. For example, when the in-plane retardation Re (590) of the film becomes 3 nm or less, it can be determined that the orientation of the polymer contained in the film is lost and the film becomes a non-oriented film.

  The retardation film of the present invention can be produced by forming a raw film from the resin composition (C) by a known method (for example, melt extrusion, casting) and stretching the raw film by a known stretching method. The formation of the original film from the resin composition (C) and the stretching of the original film may be performed continuously or separately.

  The retardation film of the present invention can be produced, for example, by the production method of the present invention.

  The retardation film of the present invention exhibits reverse wavelength dispersion. By using such a broadband retardation film, an image display device having excellent display characteristics can be constructed. The retardation film of the present invention may be used in combination with other optical members depending on applications. The application of the retardation film of the present invention is not particularly limited, and can be used for the same applications as conventional retardation films (for example, image display devices such as LCD and OLED).

[Method for producing retardation film]
In the production method of the present invention, the resin (A) and the polymer (B) described above in the description of the retardation film of the present invention are combined with resin (A): polymer (B) = 95 to 70 parts by weight: 5 to 5 parts. The step of forming the resin composition (C) described above containing the resin (A) and the polymer (B) by mixing at a mixing ratio of 30 parts by weight, and the formed resin composition (C) with the film ( And forming a retardation film by stretching the obtained film after forming the original film. As long as the effects of the present invention are obtained, the production method of the present invention may include other steps.

  The mixing ratio of the resin (A) and the polymer (B) is preferably resin (A): polymer (B) = 95 to 80 parts by weight: 5 to 20 parts by weight.

  The order of mixing when mixing the resin (A) and the polymer (B) is not particularly limited. For example, the polymer (B) may be mixed with the resin (A), or the resin (A) may be mixed with the polymer (B). When an apparatus such as a melt extruder is used, the resin (A) and the polymer (B) may be simultaneously introduced into the apparatus and mixed.

  When the resin (A) and the polymer (B) are mixed, as long as the effects of the present invention are obtained, materials other than the resin (A) and the polymer (B), for example, in the description of the resin (A) The exemplified “other thermoplastic polymer” or additives may be mixed together.

  The method for mixing the resin (A) and the polymer (B) to form the resin composition (C) is not particularly limited, and a known method may be followed.

  The method for forming the resin composition (C) into a film (raw film) is not particularly limited, and may be a known method (for example, a melt extrusion method or a casting method). According to the melt extrusion method, the formation of the resin composition (C) by mixing the resin (A) and the polymer (B) and the formation of the raw film by melt extrusion of the formed resin composition (C) are continuously performed. It can also be done automatically. Furthermore, it is also possible to continuously form the resin composition (C), the raw film, and the retardation film together with the formation of the retardation film by stretching the raw film. The raw film to be formed may have a strip shape.

  The method of stretching the formed original film to form the retardation film is not particularly limited, and may be a known method. Stretching is, for example, uniaxial stretching or biaxial stretching. The belt-shaped raw film may be stretched to form a belt-shaped retardation film. The uniaxial stretching is typically free end uniaxial stretching in which a change in the width direction of the raw film is free. The fixed end uniaxial stretching which fixed the change of the width direction of the original fabric film may be sufficient. Transverse uniaxial stretching in which the raw film is stretched only in the width direction may be used. The biaxial stretching is typically sequential biaxial stretching, but simultaneous biaxial stretching in which longitudinal and transverse stretching are simultaneously performed can also be suitably used. Further, the stretching may be stretching in the thickness direction of the original film, or the original film may be in an oblique direction (a direction inclined with respect to both the flow direction and the width direction of the original film). It may be stretched.

  During stretching, the stretching conditions such as stretching temperature and / or stretching ratio may be changed. In the production method of the present invention, the wavelength dispersibility of the retardation film before and after the change of the stretching conditions is changed except when changing to the stretching conditions where the retardation film cannot be obtained and when the degree of change of the stretching conditions is excessively large. There are few fluctuations. For this reason, the production method of the present invention produces a belt-like retardation film or retardation film roll having two or more parts having the same or substantially the same wavelength dispersion but different retardation values and / or NZ coefficients. it can.

  The stretching temperature is preferably in the vicinity of Tg of the raw film. Specifically, Tg-5 ° C to Tg + 30 ° C is preferable, Tg ° C to Tg + 20 ° C is more preferable, and Tg + 5 ° C to Tg + 15 ° C is more preferable.

  The draw ratio can be adjusted, for example, in the range of 1.1 to 5 times, preferably in the range of 1.3 to 3 times, depending on the retardation to be obtained as the retardation film.

  A known stretching apparatus can be used for stretching the raw film.

[Image display device]
The image display device of the present invention includes the retardation film of the present invention. As a result, the image display device is excellent in image display characteristics. The image display device of the present invention is, for example, an LCD or an OELD.

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

  Initially, the evaluation method of the polymer, the resin composition, and retardation film which were produced in the present Example is shown.

[Weight average molecular weight]
The weight average molecular weight of the polymer was determined in terms of polystyrene using gel permeation chromatography (GPC). The apparatus and measurement conditions used for the measurement are as follows.

System: Tosoh GPC system HLC-8220
Developing solvent: Chloroform (manufactured by Wako Pure Chemical Industries, special grade) Flow rate 0.6 mL / min Standard sample: TSK standard polystyrene (manufactured by Tosoh, PS-oligomer kit)
Measurement side column configuration Guard column: Tosoh, TSKguardcolumn SuperHZ-L
Separation column: Tosoh, TSKgel SuperHZM-M 2 in series Reference column configuration Reference column: TSKgel SuperH-RC
Column temperature: 40 ° C

[Glass transition temperature (Tg)]
Tg of the polymer, the resin composition, and the unstretched film was determined in accordance with the provisions of JIS K7121. Specifically, a differential scanning calorimeter (manufactured by Rigaku, DSC-8230) is used, and a sample of about 10 mg is heated from normal temperature to 200 ° C. (temperature increase rate: 20 ° C./min) in a nitrogen gas atmosphere. The DSC curve was evaluated by the starting point method. Α-alumina was used as a reference. In addition, since Tg does not change when producing an unstretched film (raw fabric film) from the resin composition and when producing a retardation film by stretching the raw fabric film, the Tg of the resin composition remains as it is. It becomes Tg of the original fabric film and retardation film which consist of a resin composition.

[Refractive index anisotropy]
In-plane retardation Re (447) for light with a wavelength of 447 nm, in-plane retardation Re (590) for light with a wavelength of 590 nm, and in-plane with respect to light with a wavelength of 750 nm shown by the retardation films prepared in each Example and Comparative Example The phase difference Re (750) was measured using a phase difference measuring device (manufactured by Oji Scientific Instruments, KOBRA-WR). Specifically, incident angle dependency (single N calculation) was selected as a measurement item, the tilt central axis was set as the slow axis, and the incident angle was set at 40 °, and the measurement was separately performed with an Abbe refractometer. The average refractive index of the retardation film and the film thickness d of the retardation film were input and measured. The film thickness d of the retardation film was separately measured using a Digimatic micrometer (manufactured by Mitutoyo).

  The ratio D (= Re (447) / Re (590)) and the ratio E (= Re (750) / Re (590)) of the retardation film were measured in this way as Re (447) and Re (590). And the value of Re (750). The ratio E, like the ratio D, serves as an index for determining the wavelength dispersibility and the degree of the retardation film.

  The NZ coefficient of the retardation film was measured using the retardation measuring apparatus. Specifically, it was calculated by the formula NZ = (nx−nz) / (nx−ny) from the values of nx, ny and nz obtained when Re (590) was measured by the phase difference measuring device.

(Production Example 1)
In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, a nitrogen introduction pipe and a dropping funnel, 25 parts by weight of N-vinylcarbazole (NVCZ), 10 parts by weight of acrylonitrile (AN), 15 parts of n-butyl acrylate (BA) Part by weight and 29.6 parts by weight of methyl ethyl ketone as a polymerization solvent were charged, and the temperature was raised to 85 ° C. while introducing nitrogen into the solvent. At the start of the reflux accompanying the temperature increase, 0.005 part by weight of t-amylperoxy-2-ethylhexanoate (manufactured by Arkema Yoshitomi, trade name: Luperox 575) was added as a polymerization initiator, and at the same time, methyl ethyl ketone. Addition of a mixture of 20 parts by weight and 0.01 parts by weight of the above t-amylperoxy-2-ethylhexanoate was started. Solution polymerization was allowed to proceed under reflux at about 80 to 85 ° C. while dropping the mixture over 6 hours.

  Next, the obtained polymerization solution was subjected to a barrel temperature of 240 ° C., a rotation speed of 100 rpm, a degree of vacuum of 13.3 to 400 hPa (10 to 300 mmHg), a rear vent number of 1 and a forevent number of 4 (first and Introduced into a vent type screw twin screw extruder (L / D = 52.5) at a processing rate of 10 parts by weight / hour (resin amount conversion) went.

  After completion of devolatilization, the polymer in the heat-melted state remaining in the extruder is discharged from the tip of the extruder, pelletized using a strand cutter, and NVCZ units, AN units, and BA units are used as constituent units. A pellet of polymer (B-1) was obtained. The weight average molecular weight of the polymer (B-1) was 291200.

  Next, the obtained polymer (B-1) pellets were melt press-molded at 240 ° C. and 30 MPa for 5 minutes using a manual heating press machine (manufactured by Imoto Seisakusho, IMC-180C type). An unstretched film having a thickness of 120 μm made of the union (B-1) was produced. The Tg of the film, that is, the Tg of the polymer (B-1) was 101.5 ° C. Next, after cutting out the produced unstretched film to the size of 50 mm x 80 mm, the cut-out film was uniaxially stretched free end using the autograph with a thermostat (Shimadzu Corporation AG-X). Specifically, the distance between chucks when setting the cut film on the autograph is set to 40 mm, the film attached to the chuck is preheated at Tg + 5 ° C. for 3 minutes, and then the draw ratio is 2 at the temperature. The film was stretched so as to be doubled to obtain a stretched film having a thickness of 90 μm. When the orientation angle of the obtained stretched film was evaluated using a phase difference measuring device (manufactured by Oji Scientific Instruments, KOBRA-WR), the orientation angle (φ) of the stretched film was 89.6 °, that is, The intrinsic birefringence of the polymer (B-1) was negative. In addition, the ratio D (= Re (447) / Re (590) of the stretched film was 1.14, and the ratio E (= Re (750) / Re (590) was 0.95. Showed forward wavelength dispersion.

(Production Example 2)
In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, a nitrogen introduction pipe and a dropping funnel, 13.5 parts by weight of NVCZ, 5.5 parts by weight of AN, 13.75 parts by weight of BA, and 19.2 parts by weight of methyl ethyl ketone as a polymerization solvent The temperature was raised to 85 ° C. while nitrogen was passed through. At the start of reflux accompanying the temperature increase, 0.003 part by weight of t-amylperoxy-2-ethylhexanoate (manufactured by Arkema Yoshitomi, trade name: Luperox 575) was added as a polymerization initiator, and at the same time, NVCz11 Dropping of a mixture of 0.5 parts by weight, 5.75 parts by weight of AN, 30.3 parts by weight of methyl ethyl ketone and 0.02 parts by weight of the above t-amylperoxy-2-ethylhexanoate was started. Solution polymerization was allowed to proceed under reflux at about 80 to 85 ° C. while dropping the mixture over 4 hours. This polymerization method is called a drop polymerization method, and fine Tg control based on control of the copolymer composition in the polymer to be produced is possible.

  Next, the obtained polymerization solution was devolatilized and pelletized in the same manner as in Production Example 1 to obtain polymer (B-2) pellets having NVCZ units, AN units, and BA units as structural units. The weight average molecular weight of the polymer (B-2) was 184000.

  Next, the produced polymer (B-2) pellets were melt press-molded and stretched in the same manner as in Production Example 1 to evaluate the Tg and the intrinsic birefringence, and the Tg of the polymer (B-2) was evaluated. Was 108.8 ° C. and the intrinsic birefringence was negative. Further, the ratio D (= Re (447) / Re (590) of the stretched film used for the evaluation was 1.14, and the ratio E (= Re (750) / Re (590) was 0.95. The stretched film exhibited forward wavelength dispersibility.

(Production Example 3)
In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, a nitrogen introduction pipe and a dropping funnel, 11.2 parts by weight of NVCZ, 4.8 parts by weight of AN, 9.6 parts by weight of ethyl acrylate (EA), and a polymerization solvent 36.9 parts by weight of methyl ethyl ketone was charged, and the temperature was raised to 82 ° C. while passing nitrogen through the mixture. When refluxing with increasing temperature began, 0.001 part by weight of t-amylperoxy-2-ethylhexanoanoate (manufactured by Arkema Yoshitomi, trade name: Luperox 575) was added as a polymerization initiator, and at the same time, NVCz9 Addition of a mixture of .6 parts by weight, AN 4.8 parts by weight, methyl ethyl ketone 21.6 parts by weight and t-amylperoxy-2-ethylhexanoate 0.03 parts by weight was started. While the mixture was dripped over 4 hours, solution polymerization was allowed to proceed under reflux at about 78 to 82 ° C.

  Next, the obtained polymerization solution was devolatilized and pelletized in the same manner as in Production Example 1 to obtain polymer (B-3) pellets having NVCZ units, AN units, and EA units as structural units. The weight average molecular weight of the polymer (B-3) was 79000.

  Next, the polymer (B-3) pellets were melt press-molded and stretched in the same manner as in Production Example 1 to evaluate the Tg and the intrinsic birefringence, and the Tg of the polymer (B-3) was evaluated. Was 128.6 ° C. and the intrinsic birefringence was negative. Moreover, ratio D (= Re (447) / Re (590) of the stretched film used for the said evaluation was 1.14, and ratio E (= Re (750) / Re (590) was 0.95. That is, the stretched film exhibited forward wavelength dispersion.

(Production Example 4)
In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, a nitrogen introduction pipe and a dropping funnel, 20.8 parts by weight of NVCZ, 9.6 parts by weight of AN, 9.6 parts by weight of EA, and 47.5 parts by weight of methyl ethyl ketone as a polymerization solvent The temperature was raised to 84 ° C. while passing nitrogen through it. At the start of reflux with temperature rise, 0.02 part by weight of t-amylperoxy-2-ethylhexanoate (manufactured by Arkema Yoshitomi, trade name: Luperox 575) was added as a polymerization initiator, and at the same time, methyl ethyl ketone. The dropwise addition of a mixture of 10.2 parts by weight and 0.04 parts by weight of the above t-amylperoxy-2-ethylhexanoate was started. Solution polymerization was allowed to proceed under reflux at about 80 to 84 ° C. while dropping the mixture over 4 hours.

  Next, the obtained polymerization solution was devolatilized and pelletized in the same manner as in Production Example 1 to obtain polymer (B-4) pellets having NVCZ units, AN units, and EA units as structural units. The weight average molecular weight of the polymer (B-4) was 56000.

  Next, the pellet of the produced polymer (B-4) was melt press-molded and stretched in the same manner as in Production Example 1 to evaluate the Tg and the positive / negative of the intrinsic birefringence. The Tg of the polymer (B-4) was evaluated. Was 129.4 ° C. and the intrinsic birefringence was negative. Moreover, ratio D (= Re (447) / Re (590) of the stretched film used for the said evaluation was 1.14, and ratio E (= Re (750) / Re (590) was 0.95. That is, the stretched film exhibited forward wavelength dispersion.

(Production Example 5)
In a reaction kettle equipped with a stirrer, a temperature sensor, a cooling pipe and a nitrogen introduction pipe, 10.9 parts by weight of methyl methacrylate (MMA), 19.1 parts by weight of methyl 2- (hydroxymethyl) acrylate (MHMA), methacryl 24.6 parts by weight of ethyl acid (EMA), 43 parts by weight of toluene as a polymerization solvent and 1.5 parts by weight of methanol, and 0.027 parts by weight of an antioxidant (Adeka Stub 2112, manufactured by ADEKA) were charged, and nitrogen was passed through this. The temperature was raised to 88 ° C. When the reflux accompanying the temperature increase started, 0.008 part by weight of t-amylperoxy-2-ethylhexanoate (manufactured by Arkema Yoshitomi, trade name: Luperox 575) was added as a polymerization initiator. Simultaneously with this addition, the addition of a solution prepared by dissolving 0.044 parts by weight of the above t-amylperoxy-2-ethylhexanoate in 0.8 parts by weight of toluene was started, and the solution was added dropwise over 8 hours. did. When 3 hours passed after the start of dropping of the solution, dropping of 21.1 parts by weight of toluene was started, and the toluene was dropped over 4 hours. During this time, solution polymerization was allowed to proceed under reflux at about 95 to 100 ° C., and after the dropwise addition, aging was further performed for 1 hour.

  Next, 0.16 parts by weight of stearyl phosphate (Phoslex A-18, manufactured by Sakai Chemical Industry Co., Ltd.) is added to the obtained polymerization solution as a catalyst for the cyclization condensation reaction (cyclization catalyst), and about 80 to 95 ° C. The cyclization condensation reaction for forming a lactone ring structure was allowed to proceed for 2 hours under reflux.

  Next, after completing the cyclization condensation reaction through the multi-tube heat exchanger heated to 240 ° C., the obtained polymerization solution was barrel temperature 240 ° C., rotation speed 100 rpm, degree of vacuum 13.3 to 400 hPa (10 to 300mmHg), vent type screw twin screw extruder (L / D = 52.5) with 1 rear vent and 4 fore vents (referred to as first, second, third and fourth vents from the upstream side) Was introduced at a treatment rate of 24 parts by weight / hour (resin amount conversion), and devolatilization was performed. At that time, 0.4 parts by weight of ion-exchanged water was added after the second vent at a charging rate of 1.1 parts by weight / hour with a separately prepared mixed solution of antioxidant / cyclization catalyst deactivator. After the first and third vents, the charging was performed at a charging speed of / hour. In the mixed solution of antioxidant / cyclization catalyst deactivator, 0.6 part by weight of Irganox 1010 (manufactured by Ciba Specialty Chemicals) and 0.6 part by weight of Adekastab AO-412S (manufactured by ADEKA) were used as antioxidants. In addition, a solution prepared by dissolving 4.2 parts by weight of zinc octylate (manufactured by Nippon Chemical Industry Co., Ltd., 3.6% of Nikka octix zinc) in 94.7 parts by weight of toluene was used as a deactivator.

  Next, the obtained polymerization solution was devolatilized and pelletized in the same manner as in Production Example 1 to obtain pellets of (meth) acrylic polymer (A-1) having a lactone ring structure in the main chain. The weight average molecular weight of the polymer (A-1) was 100,000.

  Next, the pellet of the produced polymer (A-1) was melt press-molded and stretched in the same manner as in Production Example 1 to evaluate the Tg and the intrinsic birefringence, and the Tg of the polymer (A-1) was evaluated. Was 126.2 ° C. and the orientation angle (φ) was −0.8 °, that is, the intrinsic birefringence was positive. Moreover, ratio D (= Re (447) / Re (590) of the stretched film used for the said evaluation was 1.03, and ratio E (= Re (750) / Re (590) was 0.99. That is, the stretched film exhibited forward wavelength dispersion, and the change in wavelength dispersion in the visible light region was smaller than the change in wavelength dispersion in the visible light region of the stretched films formed in Production Examples 1 to 4. .

  The compositions and Tg of the polymers prepared in Production Examples 1 to 4 are shown in Table 1 below.

Example 1
A mixture obtained by dry blending 9 parts by weight of the polymer (B-2) pellets produced in Production Example 2 and 91 parts by weight of the polymer (A-1) pellets produced in Production Example 5 was tested in a laboratory. The resin composition (C-1) was formed by melt-kneading (rotating speed 100 rpm, 5 minutes) at 250 ° C. using a plast mill (manufactured by Toyo Seiki, R-60H). The mixing ratio (weight ratio) of the polymer (A-1) and the polymer (B-2) in the formed resin composition (C-1) is polymer (A-1): polymer (B-2). = 91: 9.

  Next, the formed resin composition (C-1) was melt press-molded at 240 ° C. and 30 MPa for 5 minutes using a manual heating press (manufactured by Imoto Seisakusho, IMC-180C type), and the thickness was 140 μm. An unstretched film (raw film) was prepared. Tg of the produced raw film was 127.5 ° C., that is, Tg of the resin composition (C-1) was 127.5 ° C. Next, after the produced unstretched film was cut into a size of 50 mm × 80 mm, the cut film was stretched using an autograph with a thermostatic bath (manufactured by Shimadzu Corporation, AG-X), and a retardation of 100 μm in thickness. A film was formed. Specifically, the distance between chucks when setting the cut film on the autograph is set to 40 mm, the film attached to the chuck is preheated at Tg + 5 ° C. for 3 minutes, and then the draw ratio is 2 at the temperature. The free end was uniaxially stretched so as to be doubled.

When the refractive index anisotropy of the retardation film thus obtained was evaluated, Re (447) was 108.0 nm, Re (590) was 117.4 nm, and Re (750) was 120.9 nm. D ₅ 0.92, the ratio E ₅ is was 1.03. The ratio E ₅ is a non-oriented film comprising the composition (C), at a temperature 5 ° C. higher than the Tg of the composition (C), Re (590) is obtained by stretching so that the above 20nm This is the value of the ratio E indicated by the retardation film.

Next, a retardation film having a thickness of 100 nm was formed in the same manner as described above except that the preheating and the stretching temperature were set to Tg + 15 ° C. When the refractive index anisotropy of the retardation film was evaluated, Re (447) was 40.1 nm, Re (590) was 45.1 nm, Re (750) was 46.9 nm, and the ratio D ₁₅ was 0.00. 89, the ratio E ₁₅ was 1.04. That is, ΔD (= | D ₁₅ −D ₅ |) was 0.03, and ΔE (= | E ₁₅ −E ₅ |) was 0.01. The ratio E ₁₅ is a non-oriented film comprising the composition (C), at a temperature from 15 ℃ high Tg of the composition (C), except the stretching temperature is the same stretching conditions stretching and obtained the E ₅ ratio It is the value of the ratio E which the retardation film obtained by extending | stretching by.

(Example 2)
Instead of the polymer (B-2) pellet produced in Production Example 2, the polymer (B-3) pellet produced in Production Example 3 was used in the same manner as in Example 1, except that the polymer ( A resin composition (C-2) in which A-1) and the polymer (B-3) were mixed at a mixing ratio (weight ratio) of 91: 1 was produced. Tg of the resin composition (C-2) was 129.0 ° C.

  Next, it extended | stretched at Tg + 5 degreeC of the said composition (C-2) like Example 1 except having used the resin composition (C-2) instead of the resin composition (C-1). A retardation film and a retardation film stretched at Tg + 15 ° C. were formed.

When the refractive index anisotropy of the retardation film thus obtained was evaluated, Re (447) was 113.6 nm for the retardation film formed by stretching the resin composition (C-2) at Tg + 5 ° C. , Re (590) was 126.2 nm, Re (750) was 131.2 nm, the ratio D ₅ was 0.90, and the ratio E ₅ was 1.04. On the other hand, regarding the retardation film formed by stretching the resin composition (C-2) at Tg + 15 ° C., Re (447) is 41.7 nm, Re (590) is 46.3 nm, and Re (750) is 48.2 nm. The ratio D ₁₅ was 0.90 and the ratio E ₁₅ was 1.04. That is, ΔD (= | D ₁₅ −D ₅ |) was 0.00, and ΔE (= | E ₁₅ −E ₅ |) was 0.00.

(Example 3)
In the same manner as in Example 1 except that the polymer (B-4) pellet produced in Production Example 4 was used instead of the polymer (B-2) pellet produced in Production Example 2, a polymer ( A resin composition (C-3) in which A-1) and the polymer (B-4) were mixed at a mixing ratio (weight ratio) of 91: 1 was produced. Tg of the resin composition (C-3) was 129.0 ° C.

  Next, in the same manner as in Example 1 except that the resin composition (C-3) was used instead of the resin composition (C-1), the composition (C-3) was stretched at Tg + 5 ° C. A retardation film and a retardation film stretched at Tg + 15 ° C. were formed.

When the refractive index anisotropy of the retardation film thus obtained was evaluated, Re (447) of the retardation film formed by stretching the resin composition (C-3) at Tg + 5 ° C. was 112.3 nm. , Re (590) was 122.1 nm, Re (750) was 125.8 nm, the ratio D ₅ was 0.92, and the ratio E ₅ was 1.03. On the other hand, regarding the retardation film formed by stretching the resin composition (C-3) at Tg + 15 ° C., Re (447) is 42.3 nm, Re (590) is 46.0 nm, and Re (750) is 47.4 nm. The ratio D ₁₅ was 0.92 and the ratio E ₁₅ was 1.03. That is, ΔD (= | D ₁₅ −D ₅ |) was 0.00, and ΔE (= | E ₁₅ −E ₅ |) was 0.00.

(Comparative Example 1)
Instead of the polymer (B-2) pellet produced in Production Example 2, the polymer (B-1) pellet produced in Production Example 1 was used in the same manner as in Example 1, except that the polymer ( A resin composition (C-4) in which A-1) and the polymer (B-1) were mixed at a mixing ratio (weight ratio) of 91: 1 was produced. Tg of the resin composition (C-4) was 123.6 ° C.

  Next, it extended | stretched at Tg + 5 degreeC of the said composition (C-4) like Example 1 except having used the resin composition (C-4) instead of the resin composition (C-1). A retardation film and a retardation film stretched at Tg + 15 ° C. were formed.

When the refractive index anisotropy of the retardation film thus obtained was evaluated, Re (447) was 104.1 nm for the retardation film formed by stretching the resin composition (C-4) at Tg + 5 ° C. , Re (590) was 118.3 nm, Re (750) was 124.2 nm, the ratio D ₅ was 0.88, and the ratio E ₅ was 1.05. On the other hand, regarding the retardation film formed by stretching the resin composition (C-4) at Tg + 15 ° C., Re (447) is 19.8 nm, Re (590) is 25.4 nm, and Re (750) is 27.7 nm. The ratio D ₁₅ was 0.78, and the ratio E ₁₅ was 1.09. That is, ΔD (= | D ₁₅ −D ₅ |) was 0.10, and ΔE (= | E ₁₅ −E ₅ |) was 0.04.

  The results of Examples 1 to 3 and Comparative Example 1 are summarized in Table 2 below.

  As shown in Table 2, in all Examples and Comparative Examples, Re (447) / Re (590) was less than 1, that is, a retardation film showing reverse wavelength dispersion was formed. In Examples 1 to 3 using the polymer (B) having a Tg of less than 20 ° C. from the Tg of the polymer (A-1) which is the resin (A), ΔD is smaller than that of Comparative Example 1. became. That is, fluctuations due to changes in the stretching temperature were suppressed for the wavelength dispersibility exhibited by the produced retardation film. In particular, in Examples 2 and 3 using the polymer (B) having a Tg of 5 ° C. or less from the polymer (A-1), ΔD is zero, that is, wavelength dispersion due to a change in the stretching temperature. There was no change in sex. The ratio E (= Re (750) / Re (590)) and ΔE showed the same tendency.

Example 4
The resin composition (C-1) produced in Example 1 was melt press-molded at 240 ° C. and 30 MPa for 5 minutes using a manual heating press (manufactured by Imoto Seisakusho, IMC-180C type) to obtain a thickness. A 140 μm unstretched film (raw film) was produced. Next, after the produced unstretched film was cut into a size of 70 mm × 97 mm, the cut film was stretched using a corner stretch type biaxial stretching test apparatus (X6-S, manufactured by Toyo Seiki Co., Ltd.), and the thickness was 80 μm. A retardation film was formed. Specifically, the distance between chucks when the cut film is set in a stretching test apparatus is set to 80 mm, the film attached to the chuck is preheated at the Tg + 10 ° C. for 3 minutes, and then the stretching ratio is set at the temperature. The free end was uniaxially stretched to be 2.5 times. The direction of stretching was the long side direction which is the MD direction (flow direction) of the cut unstretched film. When the refractive index anisotropy of the retardation film thus obtained was evaluated, the NZ coefficient was 1.0, Re (447) was 84.5 nm, Re (590) was 91.0 nm, and Re (750) was It was 93.7 nm, the ratio D _1.0 was 0.93, and the ratio E _1.0 was 1.03. In addition, ratio _E1.0 is the value of the said ratio E which the retardation film obtained by extending | stretching the non-oriented film which consists of a composition (C) so that NZ coefficient may be set to 1.0.

Next, apart from this, an unstretched film having a thickness of 200 μm produced in the same manner as described above was cut into a size of 97 mm × 97 mm, and then the cut film was subjected to a corner stretch type biaxial stretching test apparatus (manufactured by Toyo Seiki, X6-S) was used to sequentially biaxially stretch the fixed end to form a retardation film having a thickness of 74 μm. Specifically, it is as follows. First, the distance between chucks when the cut film was set in the stretching test apparatus was set to 80 mm in both the MD direction and the TD direction, and the film attached to the chuck was preheated at Tg + 10 ° C. for 3 minutes. Next, the length in the TD direction was fixed and stretched in the MD direction at a stretching ratio of 1.2 times, and then the length in the MD direction was fixed and stretched in the TD direction at a stretching ratio of 2.5 times. When the refractive index anisotropy of the retardation film thus obtained was evaluated, the NZ coefficient was 1.6, Re (447) was 50.2 nm, Re (590) was 54.0 nm, and Re (750) was The ratio D _1.4-3.0 was 0.93, and the ratio E _1.4-3.0 was 1.03. That is, ΔD (= | D _1.4-3.0 −D _1.0 |) was 0.00, and ΔE (= | E _1.4-3.0 −E _1.0 |) was 0.00. The ratio E _1.4-3.0 is when the non-oriented film made of the composition (C) is stretched so that the NZ coefficient is 1.0 so that the NZ coefficient is 1.4 or more and 3.0 or less. It is the value of the said ratio E which the retardation film obtained by extending | stretching at the same extending | stretching temperature shows.

Next, separately from these, the 200 μm-thick unstretched film produced above was cut into a size of 97 mm × 97 mm, and the cut film was then subjected to a corner stretch type biaxial stretching test apparatus (X6-S, manufactured by Toyo Seiki Co., Ltd.). ) To form a retardation film having a thickness of 63 μm. Specifically, it is as follows. First, the distance between chucks when the cut film was set in the stretching test apparatus was set to 80 mm in both the MD direction and the TD direction, and the film attached to the chuck was preheated at Tg + 10 ° C. for 3 minutes. Next, after the length in the TD direction was fixed and the film was stretched in the MD direction at a stretching ratio of 1.6 times, the length in the MD direction was fixed and the film was stretched in the TD direction at a stretching ratio of 2.0 times. When the refractive index anisotropy of the retardation film thus obtained was evaluated, the NZ coefficient was 2.3, Re (447) was 27.3 nm, Re (590) was 29.0 nm, and Re (750) was It was 29.3 nm, the ratio D _1.4-3.0 was 0.94, and the ratio E _1.4-3.0 was 1.01. That is, ΔD (= | D _1.4-3.0 −D _1.0 |) was 0.01, and ΔE (= | E _1.4-3.0 −E _1.0 |) was 0.02.

(Example 5)
In the same manner as in Example 4, except that the resin composition (C-2) prepared in Example 2 was used instead of the resin composition (C-1) prepared in Example 1, three types of positions were used. A phase difference film was prepared. When the refractive index anisotropy of the retardation film thus obtained was evaluated, the NZ coefficient was 1.0 and Re (447) for the retardation film obtained by free-end uniaxial stretching at a stretching ratio of 2.5. is 79.4nm, Re (590) is 86.0nm, Re (750) is 88.6Nm, the ratio D _1.0 0.92, the ratio E _1.0 was 1.03. About the retardation film obtained by fixed-end sequential biaxial stretching at a stretching ratio of 1.2 times (MD direction) × 2.5 times (TD direction), the NZ coefficient is 1.5, Re (447) is 53.9 nm, Re (590) was 58.0 nm, Re (750) was 59.7 nm, the ratio D _1.4-3.0 was 0.93, and the ratio E _1.4-3.0 was 1.03. That is, ΔD (= | D _1.4-3.0 −D _1.0 |) was 0.01, and ΔE (= | E _1.4-3.0 −E _1.0 |) was 0.00. About retardation film obtained by fixed-end sequential biaxial stretching at a stretching ratio of 1.6 times (MD direction) × 2.0 times (TD direction), NZ coefficient is 2.5, Re (447) is 24.2 nm, Re (590) was 26.0 nm, Re (750) was 26.5 nm, the ratio D _1.4-3.0 was 0.93, and the ratio E _1.4-3.0 was 1.02. That is, ΔD (= | D _1.4-3.0 −D _1.0 |) was 0.01, and ΔE (= | E _1.4-3.0 −E _1.0 |) was 0.01.

(Example 6)
In the same manner as in Example 4, except that the resin composition (C-3) prepared in Example 3 was used instead of the resin composition (C-1) prepared in Example 1, three types of positions were used. A phase difference film was prepared. When the refractive index anisotropy of the retardation film thus obtained was evaluated, the NZ coefficient was 1.0 and Re (447) for the retardation film obtained by free-end uniaxial stretching at a stretching ratio of 2.5. Was 69.2 nm, Re (590) was 76.0 nm, Re (750) was 78.3 nm, the ratio D _1.0 was 0.91, and the ratio E _1.0 was 1.03. About the retardation film obtained by fixed-end sequential biaxial stretching at a stretching ratio of 1.2 times (MD direction) × 2.5 times (TD direction), the NZ coefficient is 1.4, Re (447) is 53.7 nm, Re (590) was 59.0 nm, Re (750) was 60.8 nm, the ratio D _1.4-3.0 was 0.91, and the ratio E _1.4-3.0 was 1.03. That is, ΔD (= | D _1.4-3.0 −D _1.0 |) was 0.00, and ΔE (= | E _1.4-3.0 −E _1.0 |) was 0.00. About the retardation film obtained by fixed-end sequential biaxial stretching at a stretching ratio of 1.6 times (MD direction) × 2.0 times (TD direction), the NZ coefficient is 2.4, Re (447) is 23.3 nm, Re (590) was 25.0 nm, Re (750) was 25.8 nm, the ratio D _1.4-3.0 was 0.93, and the ratio E _1.4-3.0 was 1.03. That is, ΔD (= | D _1.4-3.0 −D _1.0 |) was 0.02, and ΔE (= | E _1.4-3.0 −E _1.0 |) was 0.00.

(Comparative Example 2)
In the same manner as in Example 4, except that the resin composition (C-4) prepared in Comparative Example 1 was used instead of the resin composition (C-1) prepared in Example 1, three types of positions were used. A phase difference film was prepared. When the refractive index anisotropy of the retardation film thus obtained was evaluated, the NZ coefficient was 1.0 and Re (447) for the retardation film obtained by free-end uniaxial stretching at a stretching ratio of 2.5. Was 96.9 nm, Re (590) was 108.0 nm, Re (750) was 114.5 nm, the ratio D _1.0 was 0.90, and the ratio E _1.0 was 1.06. About the retardation film obtained by fixed-end sequential biaxial stretching at a stretching ratio of 1.2 times (MD direction) × 2.5 times (TD direction), the NZ coefficient is 1.4, Re (447) is 93.1 nm, Re (590) was 98.0 nm, Re (750) was 100.9 nm, the ratio D _1.4-3.0 was 0.95, and the ratio E _1.4-3.0 was 1.03. That is, ΔD (= | D _1.4-3.0 −D _1.0 |) was 0.05, and ΔE (= | E _1.4-3.0 −E _1.0 |) was 0.03. About the retardation film obtained by fixed-end sequential biaxial stretching at a stretching ratio of 1.6 times (MD direction) × 2.0 times (TD direction), the NZ coefficient is 2.4, Re (447) is 48.0 nm, Re (590) was 49.0 nm, Re (750) was 49.5 nm, the ratio D _1.4-3.0 was 0.98, and the ratio E _1.4-3.0 was 1.01. That is, ΔD (= | D _1.4-3.0 −D _1.0 |) was 0.08, and ΔE (= | E _1.4-3.0 −E _1.0 |) was 0.05.

  The results of ratio D in Examples 4 to 6 and Comparative Example 2 are summarized in Table 3 below, and the results of ratio E in Examples 4 to 6 and Comparative Example 2 are summarized in Table 4 below.

  As shown in Table 3, in all Examples and Comparative Examples, Re (447) / Re (590) was less than 1, that is, a retardation film showing reverse wavelength dispersion was formed. In Examples 4 to 6 using the polymer (B) having a Tg of less than 20 ° C., the difference from the Tg of the polymer (A-1) which is the resin (A) is smaller than that of Comparative Example 2. became. That is, the fluctuation | variation by the change of a draw ratio was suppressed about the wavelength dispersibility which the produced retardation film showed. Further, as shown in Table 4, the ratio E (= Re (750) / Re (590)) and ΔE also showed the same tendency.

  The retardation film of the present invention is suitable for use in image display devices such as LCD and OELD. The production method of the present invention is suitable for the production of such a retardation film, particularly for mass production.

Claims (11)

Resin (A) having positive intrinsic birefringence and exhibiting wavelength dispersion in which the in-plane retardation increases as the wavelength becomes shorter in the visible light region;
As a wavelength dispersion control material, it has a negative intrinsic birefringence, shows a wavelength dispersion in which the in-plane retardation increases as the wavelength becomes shorter in the visible light region, and the change in the wavelength dispersion property in the visible light region is the resin A resin composition (C) that is larger than (A) and comprises a polymer (B) having a difference between the glass transition temperature (Tg) of the resin (A) and its own Tg of less than 20 ° C .;
The mixing ratio of the resin (A) and the polymer (B) in the resin composition (C) is resin (A): polymer (B) = 95 to 70 parts by weight: 5 to 30 parts by weight. ,
At least one polymer selected from one or two or more polymers and the polymer (B) contained in the resin (A) has a (meth) acrylic acid ester unit as a structural unit,
In the resin composition (C), the proportion of (meth) acrylic acid ester units in all polymer constituent units is 60% by weight or more,
A retardation film exhibiting wavelength dispersion in which in-plane retardation is reduced as the wavelength is shortened in the visible light region. The polymer (B) is a copolymer having (meth) acrylic acid ester units and α, β-unsaturated monomer units having a heteroaromatic group as structural units,
2. The retardation film according to claim 1, wherein the proportion of the α, β-unsaturated monomer units in all the structural units of the polymer (B) is more than 20 wt% and 60 wt% or less.   The retardation film according to claim 2, wherein the α, β-unsaturated monomer unit is an N-vinylcarbazole unit.   The retardation film of Claim 2 or 3 in which the said polymer (B) further has an acrylonitrile unit as a structural unit.   The retardation film according to claim 1, wherein the mixing ratio is resin (A): polymer (B) = 95 to 80 parts by weight: 5 to 20 parts by weight.   The retardation film according to claim 1, wherein the resin (A) is an acrylic resin having a Tg of 110 ° C. or higher.   The retardation film according to claim 1, wherein the resin (A) includes a polymer having a ring structure in the main chain. The ratio D of the in-plane retardation Re (447) measured at the measurement wavelength 447 nm to the in-plane retardation Re (590) measured at the measurement wavelength 590 nm is 0.75 ≦ D ≦ 0.99.
In the resin composition (C), an unoriented film made of the resin composition (C) is subjected to a temperature 5 ° C. higher than the Tg of the resin composition (C), so that Re (590) is 20 nm or more. the value D ₅ of the ratio D shown in stretching, at a temperature from 15 ℃ high Tg of the resin composition (C), the ratio D than the stretching temperature is shown in case of stretching at the same stretching conditions and the stretching The retardation film according to claim 1, having a composition satisfying the formula 0 ≦ | D ₁₅ −D ₅ | <0.05 with respect to the value D ₁₅ . The ratio D of the in-plane retardation Re (447) measured at the measurement wavelength 447 nm to the in-plane retardation Re (590) measured at the measurement wavelength 590 nm is 0.75 ≦ D ≦ 0.99.
The resin composition (C) has a ratio D _{1.0 of the} ratio D shown when the non-oriented film made of the resin composition (C) is stretched so that the NZ coefficient is _1.0, and the NZ coefficient is Between the value D _{1.4-3.0 of the} ratio D shown when the _film is stretched at the same stretching temperature as that of the stretching so as to be 1.4 or more and 3.0 or less, the formula 0 ≦ | D _1.4-3.0 −D _1.0 The retardation film according to claim 1, which has a composition satisfying | ≦ 0.04.   An image display apparatus provided with the retardation film in any one of Claims 1-9. A method for producing a retardation film showing wavelength dispersibility in which in-plane retardation is reduced as the wavelength is shortened in the visible light region,
Resin (A) having positive intrinsic birefringence and exhibiting wavelength dispersion in which the in-plane retardation increases as the wavelength becomes shorter in the visible light region;
As a wavelength dispersion control material,
It has a negative intrinsic birefringence, shows a wavelength dispersion that increases the in-plane retardation as the wavelength becomes shorter in the visible light region, the change in the wavelength dispersion in the visible light region is larger than the resin (A), A polymer (B) having a difference between the glass transition temperature (Tg) of the resin (A) and its own Tg of less than 20 ° C.,
Resin (A): Polymer (B) = 95 to 70 parts by weight: A resin composition (C) containing the resin (A) and the polymer (B) by mixing at a mixing ratio of 5 to 30 parts by weight. )
After the formed resin composition (C) is formed into a film, the obtained film is stretched to form the retardation film,
At least one polymer selected from one or two or more polymers and the polymer (B) contained in the resin (A) has a (meth) acrylic acid ester unit as a structural unit,
In the said resin composition (C), the manufacturing method of retardation film whose ratio of the said (meth) acrylic acid ester unit to all the polymer structural units is 60 weight% or more.