JP2012063480A - Retardation film manufacturing method, and retardation film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a retardation film manufacturing method capable of obtaining retardation films with the same wavelength dispersibility and different phase difference from one type of raw roll film.SOLUTION: The method comprises the steps of: stretching a belt shaped resin film used as a raw roll film using a stretching device to obtain a retardation film; and stretching the raw roll film using the stretching device at a stretching temperature different from that of the former step without exchange of the raw roll film in the stretching device to obtain a retardation film having the different value of phase difference and the same wavelength dispersibility of phase difference compared with the former retardation film. The resin film used as the raw roll film is a laminated film having a resin layer A consisting of a resin (A) with positive intrinsic birefringence, and a resin layer B consisting of a resin (B) with negative intrinsic birefringence. A glass transition temperature difference ΔTg between the resin (A) and the resin (B) is less than 5°C.

Description

  The present invention relates to a method for producing a retardation film having a laminated structure, and a retardation film.

  A retardation film is incorporated in an image display device such as a liquid crystal display device (LCD) for the purpose of color tone compensation and viewing angle compensation. The retardation film is generally composed of a stretched resin film. A phase difference is obtained by birefringence caused by the orientation of the polymer contained in the resin film.

  There is a retardation film having a structure in which two or more stretched resin films are laminated. By using a retardation film having such a laminated structure, its optical characteristics, for example, wavelength dispersion of retardation are controlled. Patent Document 1 discloses a retardation film obtained by bonding and laminating two types of retardation films having different retardation values and different wavelength dispersion properties so that their optical axes are orthogonal to each other. Patent Document 2 discloses a retardation film in which a λ / 4 plate and a λ / 2 plate are bonded so that their optical axes intersect each other. Patent Documents 1 and 2 attempt to realize a retardation film that can function as a specific wave plate over the entire visible light range. However, the method of adhering and bonding two or more types of retardation films having different optical characteristics while paying attention to each other's optical axes is difficult to continuously produce and is inferior in productivity.

  In order to improve the display characteristics of an image display device, a retardation film that exhibits wavelength dispersion (reverse wavelength dispersion) in which the phase difference decreases as the wavelength of light becomes shorter at least in the visible light region is desired. In Patent Document 3, a raw film which is a laminated film in which a layer made of a resin having a positive intrinsic birefringence and a layer made of a resin having a negative intrinsic birefringence is laminated uniaxially in a specific direction, A method for obtaining a retardation film having a laminated structure composed of a stretched product is disclosed. By this method, a retardation film having a flat wavelength dispersion and a retardation film showing reverse wavelength dispersion can be realized. In addition, in the method of Patent Document 3, since both layers are laminated and then stretched, continuous production of the retardation film, for example, from the extrusion of the layer itself to the formation of the retardation film is performed consistently. Production is possible.

  In this specification, the wavelength dispersibility in which the phase difference decreases as the wavelength of light becomes shorter at least in the visible light region, and the wavelength dispersibility of the retardation exhibited by a general polymer and an optical film formed of the polymer. Is called “inverse wavelength dispersion” based on the opposite. Hereinafter, “wavelength dispersion” means “wavelength dispersion of retardation” exhibited by the retardation film.

JP-A-5-27118 Japanese Patent Laid-Open No. 10-68816 JP 2009-237534

  The retardation value required for the retardation film varies depending on the use of the film, and it is no exception even in a retardation film exhibiting reverse wavelength dispersion. In the conventional method of obtaining a retardation film exhibiting reverse wavelength dispersion by the method of Patent Document 3 and the same method as that document, in order to change the value of the retardation exhibited by the retardation film to be formed, The film configuration, for example, the composition of the resin constituting each layer and the thickness of each layer are individually selected. In other words, in order to obtain a retardation film having the same wavelength dispersion but different retardation values, it is necessary to replace the stretched original fabric with a different one by one. This is a factor that increases the manufacturing cost of the retardation film. In particular, when consistently performing from the extrusion of the raw material or the layer itself constituting the raw material to the formation of the retardation film, it is necessary to “wash” the inside of the extrusion molding machine with a new resin one by one, The increase in manufacturing cost is remarkable.

  The present invention can produce a retardation film exhibiting reverse wavelength dispersion, and does not require the exchange of the raw material to obtain a retardation film having the same wavelength dispersion but different retardation values, It aims at providing the manufacturing method of retardation film from which the retardation film of the same wavelength dispersion and phase difference is obtained from one original fabric.

  The production method of the present invention differs from the step of obtaining a retardation film by stretching a belt-shaped resin film, which is a raw fabric, using a stretching device, and without replacing the original fabric in the stretching device. Stretching the resin film at a stretching temperature using the stretching device to obtain a retardation film having a retardation value different from that of the retardation film but having the same wavelength dispersion of the retardation. The resin film is a laminated film having a resin layer A made of a resin (A) having positive intrinsic birefringence and a resin layer B made of a resin (B) having negative intrinsic birefringence, In this method, the glass transition temperature ΔTg between the resins (A) and (B) is less than 5 ° C.

  The retardation film of the present invention, which is one form of the retardation film manufactured by the manufacturing method of the present invention, is mainly composed of a (meth) acrylic polymer having a lactone ring structure in the main chain and a positive intrinsic birefringence. The main component is a stretched resin layer A1 made of a resin (A) having positive intrinsic birefringence and a (meth) acrylic polymer having an N-substituted maleimide structure in the main chain and having a negative intrinsic birefringence. It has a laminated structure including a stretched resin layer B1 made of a resin (B) having negative intrinsic birefringence and contained as a component. The difference ΔTg in glass transition temperature between the resins (A) and (B) is less than 5 ° C. The retardation film of the present invention exhibits wavelength dispersibility in which the retardation decreases as the wavelength decreases, at least in the visible light region.

  In the production method of the present invention, a laminated film having a resin layer A made of a resin (A) having positive intrinsic birefringence and a resin layer B made of a resin (B) having negative intrinsic birefringence, which is a raw fabric Is stretched to form a retardation film. When the polymers contained in the resin layers A and B are oriented by stretching, birefringence due to the orientation of the polymers occurs in each of the resin layers A and B after stretching, and a phase difference is developed. Here, since the positive and negative of the intrinsic birefringence of the resins (A) and (B) are opposite to each other, the birefringence generated by the resin layers A and B cancel each other. And since the degree to which birefringence cancels changes with wavelengths, the wavelength dispersion of the obtained retardation film can be controlled. In the production method of the present invention, for example, a retardation film showing flat wavelength dispersion in the visible light region or a retardation film showing reverse wavelength dispersion can be obtained.

  In addition, in the manufacturing method of the present invention, the difference ΔTg in glass transition temperature between the resins (A) and (B) constituting the resin layers A and B of the original fabric is set to less than 5 ° C. When the resin layer is stretched, the degree of orientation of the polymer contained in the layer is greatly influenced by the magnitude relationship and temperature difference between the glass transition temperature (Tg) of the layer and the stretching temperature. Specifically, as the stretching temperature is lower than the Tg of the layer (if it is too low, the resin layer breaks, making stretching itself impossible), the degree of orientation of the polymer becomes stronger and the resulting complex Refraction increases. The magnitude of the effect also varies depending on how far the stretching temperature changes from the Tg. For example, even when the stretching temperature changes by the same amount, the change in the birefringence caused by the change in the stretching temperature is larger as the stretching temperature is farther from the Tg of the layer. That is, when ΔTg between the resins (A) and (B) is large, when the stretching temperature is changed, the degree of change in birefringence differs greatly for each of the resin layers A and B, and the retardation film. Changes the wavelength dispersion. In the production method of the present invention, by setting the ΔTg between the resins (A) and (B) to less than 5 ° C., there is a difference to the extent that the birefringence changes in the resin layers A and B when the stretching temperature changes. To suppress. Here, in the retardation film in which two or more stretched resin layers are laminated, the wavelength dispersion is determined by the cancellation of birefringence generated in each layer. On the other hand, the retardation value exhibited by the film depends purely on the magnitude of birefringence generated in each layer. Therefore, in the production method of the present invention, it is not necessary to replace the original fabric in order to obtain a retardation film having the same wavelength dispersion but different retardation values. On the other hand, using the same stretching apparatus, retardation films having the same wavelength dispersion and different retardation can be obtained.

It is a schematic diagram which shows an example of the manufacturing method of this invention. It is a schematic diagram which shows an example of the phase difference film formed by the method shown in FIG. It is a schematic diagram which shows another example of the manufacturing method of this invention.

  In the present specification, “resin” is a broader concept than “polymer”. The resin may be composed of, for example, one type or two or more types of polymers, and if necessary, materials other than the polymer, for example, additives such as ultraviolet absorbers, antioxidants, fillers, and compatibilizing agents. Further, it may contain a stabilizer and the like. However, when the resin is composed of two or more polymers, the polymers need to be compatible with each other for use as a retardation film.

  The glass transition temperature (Tg) of the resin can be determined according to JIS K7121. Even when the resin is composed of two or more kinds of polymers, the measured Tg is basically one point because the polymers are compatible with each other. 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. When 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 the original fabric, that is, do not affect the wavelength dispersion and retardation value of the retardation film.

  The positive / negative of the intrinsic birefringence of the resin is determined in the layer in which the molecular chain of the polymer contained in the resin is uniaxially oriented (for example, the uniaxially stretched film of the resin) A value “n1−n2” obtained by subtracting “layer refractive index n2” for the vibration component perpendicular to the orientation axis from “layer refractive index n1” for the vibration component parallel to the direction in which the molecular chains in the layer are oriented (orientation axis). It can be judged based on. The intrinsic birefringence value can be obtained by performing calculation based on the molecular structure of each polymer contained in the resin. The sign of the intrinsic birefringence of the resin is determined by the balance of birefringence generated by each polymer contained in the resin. The sign of the intrinsic birefringence of the resin made of one polymer is the same as the sign of the intrinsic birefringence of the polymer.

  The same wavelength dispersion of the phase difference means that the ratio of the in-plane phase difference Re (447) for light having a wavelength of 447 nm to the in-plane phase difference Re (590) for light having a wavelength of 590 nm [Re (447) / Re ( 590)], and the ratio [Re (750) / Re (590)] of the in-plane retardation Re (750) for light with a wavelength of 750 nm to the in-plane retardation Re (590) for light with a wavelength of 590 nm. The difference is 0.02 or less. Re (447), Re (590) and Re (750) are values obtained when the thickness of the retardation film is made uniform.

  The difference ΔTg in glass transition temperature between the resins (A) and (B) in the production method of the present invention is preferably less than 3 ° C., more preferably 2 ° C. or less. In this case, when the stretching temperature changes, the difference in the degree to which the birefringence changes in the resin layers A and B is further suppressed.

  The laminated film as a raw fabric has a resin layer A and a resin layer B. The number of resin layers A and B in the original fabric and the lamination pattern are not limited. When the original fabric has two or more resin layers A, even if all the resin layers A are made of the same resin (A), some of the resin layers A are different from other resin layers A (A) It may consist of. The same applies to the resin layer B and the resin (B). The laminated pattern is, for example, resin layer A / resin layer B, resin layer A / resin layer B / resin layer A, resin layer B / resin layer A / resin layer B.

  The raw fabric may have a layer other than the resin layers A and B as long as the effect of the present invention is obtained. The said layer is an adhesion layer which does not affect the optical characteristic of the phase difference film formed, for example. When the layer is a resin layer that develops birefringence by stretching, all of the glass transition temperature differences ΔTg between the resin layers constituting the original fabric are preferably less than 5 ° C, and preferably less than 3 ° C. More preferably, it is 2 ° C. or less. The original fabric typically consists of resin layers A and B.

  The original fabric is typically an unstretched laminated film, but at least one resin layer may be stretched in advance as long as the effects of the present invention are obtained.

  The production method of the present invention is different from Step A in which a belt-shaped resin film, which is a raw fabric, is stretched using a stretching device to obtain a retardation film A; The above-mentioned resin film, which is a raw fabric, is stretched at the stretching temperature using the same stretching apparatus as in step A, and the retardation film B has the same wavelength dispersibility as the retardation film A but has a different retardation value. And B for obtaining. The retardation films A and B have stretched bodies (stretched resin layers A and B) of the resin layers A and B. The value of the phase difference is, for example, an in-plane phase difference.

  FIG. 1 shows an example of the production method of the present invention. In the method shown in FIG. 1, a belt-shaped laminated resin film 1 that is an original fabric is sent from a roll 2 around which the original fabric 1 is wound to a stretching device 3, and the fed original fabric 1 is stretched by a stretching device 3. Thus, a strip-like retardation film 4 is formed. The original fabric 1 has a resin layer A made of a resin (A) having positive intrinsic birefringence and a resin layer B made of a resin (B) made of negative intrinsic birefringence, and the resins (A), ( The difference in glass transition temperature ΔTg between B) is less than 5 ° C. The retardation film 4 formed by stretching the original fabric 1 is wound into a roll 5. Here, the extending | stretching temperature in the extending | stretching apparatus 3 is changed, without exchanging the original fabric 1 sent out to the extending | stretching apparatus 3. FIG. The formation of the retardation film 4 before the change of the stretching temperature corresponds to the step A, and the retardation film 4 formed at that time corresponds to the retardation film A. On the other hand, the formation of the retardation film 4 after the change of the stretching temperature corresponds to the process B, and the retardation film 4 formed at that time corresponds to the retardation film B. However, the retardation film B may not be formed until the production system is stabilized after changing the stretching temperature.

  The stretching temperature may be changed while the original fabric 1 is being sent out to the stretching device 3, or may be performed in a state where the feeding of the original fabric 1 to the stretching device 3 is temporarily stopped. In any case, as shown in FIG. 2, part A (retardation film A) stretched before the change in stretching temperature and part B (retardation film B) stretched after the change in stretching temperature. A belt-like retardation film 4 having the following is obtained. Between the portions A and B of the retardation film 4, the wavelength dispersion is the same, and the retardation values are different from each other. The portion C corresponds to a portion stretched by the apparatus 3 until the stretching temperature of the raw fabric 1 in the stretching apparatus 3 changes and becomes stable at a new stretching temperature. By changing the stretching temperature in a state where the feeding of the raw fabric 1 to the stretching device 3 is temporarily stopped, the amount of the portion C to be formed can be reduced. Note that FIG. 2 is a schematic diagram to the last, and the boundaries between the portions A and C and the boundaries between the portions B and C in the actually formed retardation film 4 are not necessarily clear as shown in FIG. The right side of the retardation film 4 shown in FIG. 2 corresponds to the feed direction of the original 1 (winding direction of the retardation film 4).

  FIG. 3 shows another example of the production method of the present invention. In the manufacturing method shown in FIG. 3, the retardation film 4 is formed by stretching the raw fabric 1 with the stretching device 3, as in the manufacturing method shown in FIG. 1. Then, in the formed belt-like retardation film 4, the part A stretched before the change in the stretching temperature and the part B stretched after the change in the stretching temperature are separated from each other by the cutting / switching device 6. A belt-like retardation film 4a containing A (retardation film A) and a belt-like retardation film 4b containing phase B (retardation film B) are obtained. The phase difference films 4a and 4b are wound into rolls 5a and 5b, respectively. As described above, the production method of the present invention includes a portion A (retardation film A formed in step A) stretched before the change in stretching temperature in the retardation film formed by steps A and B, and stretching. A step of separating each of the stretched portions B after the temperature change (the retardation film B formed in the step B) from each other and individually obtaining each retardation film may be further included. The position where the phase difference film 4 is cut to separate the part A and the part B can be arbitrarily set.

  Stretching of the raw material in steps A and B may be performed according to a known method. Examples of the stretching method include uniaxial stretching and biaxial stretching.

  A person skilled in the art can construct the stretching apparatus 3 by adopting a known apparatus or applying a known apparatus. The same applies to the cutting / switching device 6.

  In the manufacturing method of this invention, you may adjust extending | stretching conditions other than extending | stretching temperature for the purpose of adjusting the value of retardation which the phase difference film to form forms. The stretching condition is, for example, a stretching ratio.

  In the example shown in FIGS. 1 and 3, the original fabric 1 is supplied from the roll 2 and stretched, but the method of supplying the original fabric for stretching is not limited. For example, the formation from the original fabric (for example, extrusion molding) to the stretching of the original fabric may be performed consistently and continuously.

  The formation method of the laminated film which is a raw fabric is not limited. The original fabric can be formed, for example, by coextrusion molding of the resins (A) and (B). In this case, the manufacturing cost of the retardation film is reduced. In addition, it is possible to continuously perform the process from the formation of the original fabric to the production of the retardation film. The original fabric is formed by separately forming a resin layer A made of resin (A) and a resin layer (B) made of resin (B), and laminating the formed resin layers A and B with each other. Also good.

  In the production method of the present invention, a retardation film showing flat wavelength dispersion and a retardation film showing reverse wavelength dispersion at least in the visible light region are obtained.

  In the production method of the present invention, a retardation film exhibiting a large in-plane retardation is obtained by controlling stretching conditions. For example, a retardation film having an in-plane retardation of 100 to 150 nm with respect to light having a wavelength of 590 nm is obtained. The retardation film is suitable for use as a λ / 4 plate.

  In the production method of the present invention, retardation films having the same wavelength dispersion are obtained from the same original fabric. The ratio [Re (447) / Re (590)] and the ratio [Re (750) / Re (590)], which are values reflecting the wavelength dispersion of the obtained retardation film, are 1 in the stretching temperature. When expressed in terms of how much changes due to a change in ° C (wavelength dispersion dependency on stretching temperature), in the production method of the present invention, the absolute value of the dependency is, for example, less than 0.003 / ° C. 0.0025 / ° C. or lower, 0.002 / ° C. or lower, and further 0.001 / ° C. or lower.

  In the manufacturing method of this invention, as long as the effect of this invention is acquired, you may have arbitrary processes other than process A and B. FIG. This step is, for example, a step of laminating a further layer (for example, a resin layer) on the formed retardation film or a step of performing post-processing such as coating treatment or surface treatment on the formed retardation film.

  Hereinafter, the resins (A) and (B) will be described.

  The resins (A) and (B) are not limited as long as they have positive intrinsic birefringence and negative intrinsic birefringence and can be used as retardation films.

  The Tg of at least one resin selected from the resins (A) and (B) is preferably 110 ° C. or higher, more preferably 120 ° C. or higher, and further preferably 130 ° C. or higher. It is preferable that Tg of both resin (A) and resin (B) is 110 degreeC or more, It is more preferable that it is 120 degreeC or more, It is further more preferable that it is 130 degreeC or more. In this case, a retardation film having excellent heat resistance can be obtained. In the case of a retardation film having excellent heat resistance, even when the retardation film is exposed to heat during use, such as when it is placed near a light source in an image display device, it suppresses the fluctuation of the retardation exhibited by the film over time. Is done. Moreover, since the processing temperature at the time of post-processing can be raised by improving heat resistance, the productivity of the retardation film is further increased.

  At least one selected from the resins (A) and (B) preferably contains a polymer having a ring structure in the main chain as a main component, and both resins preferably contain the polymer as a main component. In this case, the Tg of the resin containing the polymer as a main component increases. In addition, depending on the type of ring structure, the retardation exhibited by the retardation film increases. The main component means a component having the maximum content, and the content is usually 50% by weight or more, preferably 60% by weight or more, and more preferably 70% by weight or more.

[Resin (A)]
The resin (A) typically contains a polymer (C) having positive intrinsic birefringence as a main component. Resin (A) may consist of a polymer (C).

  The polymer (C) is at least one selected from, for example, a (meth) acrylic polymer, a cycloolefin polymer, and a cellulose derivative. The cycloolefin polymer and the cellulose derivative have a ring structure in the main chain.

  The (meth) acrylic polymer is a polymer having (meth) acrylic acid ester units in an amount of 50 mol% or more, preferably 60 mol% or more, more preferably 70 mol% or more based on all structural units. In the case of a polymer further including a ring structure which is a derivative of a (meth) acrylic acid ester unit, if the total of the (meth) acrylic acid ester unit and the ring structure is 50 mol% or more of all the structural units, (meth) acrylic It becomes a polymer.

  The cycloolefin polymer is a polymer having cycloolefin units in an amount of 50 mol% or more, preferably 60 mol% or more, more preferably 70 mol% or more of all the structural units.

  The cellulose derivative has a repeating unit such as a triacetyl cellulose (TAC) unit, a cellulose acetate propionate unit, a cellulose acetate butyrate unit, a cellulose acetate phthalate unit, etc. in an amount of 50 mol% or more, preferably 60 mol% or more of all the structural units. More preferably, it is a polymer having 70 mol% or more.

  The polymer (C) is preferably a (meth) acrylic polymer. The (meth) acrylic polymer has high transparency and excellent mechanical properties such as surface strength. For this reason, a retardation film suitable for use in an image display device can be obtained.

  The (meth) acrylic polymer preferably has a ring structure in the main chain.

  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. The ring structure preferably has an effect of imparting positive intrinsic birefringence to the (meth) acrylic polymer having the ring structure in the main chain.

  More specifically, the ring structure is a lactone ring structure, a glutarimide structure, or a glutaric anhydride structure. A (meth) acrylic polymer having such a ring structure in the main chain has a large positive intrinsic birefringence. For this reason, the freedom degree of control of wavelength dispersion further improves by setting it as the resin layer A which consists of resin (A) which contains the said polymer as a main component.

  The ring structure is preferably a lactone ring structure and / or a glutarimide structure, and more preferably a lactone ring structure. The (meth) acrylic polymer having such a ring structure, particularly a lactone ring structure in the main chain, has particularly small birefringence wavelength dispersibility caused by orientation. For this reason, depending on the combination with the resin (B) constituting the resin layer B, the degree of freedom in controlling the wavelength dispersion is further improved.

  The lactone ring structure is not particularly limited and 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 the hydrogen atoms in the alkyl group, the unsaturated aliphatic hydrocarbon group or the aromatic hydrocarbon group; The above is a group 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 is CH ₃ , and R ³ is CH ₃ .

  The glutarimide structure is a ring structure represented by the following formula (2). The glutarimide structure can be formed, for example, by polymerizing a monomer group containing (meth) acrylic acid ester and imidizing the obtained polymer with an imidizing agent such as methylamine.

In the formula (2), R ⁴ , R ⁵ and R ⁶ are each independently a hydrogen atom or a group exemplified as the organic residue in the formula (1).

  The glutaric anhydride structure is a ring structure represented by the following formula (3). The glutaric anhydride structure is obtained by, for example, copolymerizing a monomer group containing (meth) acrylic acid ester and (meth) acrylic acid, and then subjecting the obtained copolymer to dealcoholization cyclocondensation in the molecule. Can be formed.

In the formula (3), R ⁷ and R ⁸ are each independently a group exemplified as a hydrogen atom or an organic residue in the formula (1).

  In each method for forming a ring structure exemplified in the description of formulas (1) to (3), all polymers used for forming the ring structure are (meth) acrylic polymers, and all the ring structures formed are ( It is a derivative of a (meth) acrylic acid ester unit.

  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 (meth) acrylic polymer may have a structural unit other than the (meth) acrylic ester unit and the ring structure that is a derivative thereof.

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

  Resin (A) may contain 2 or more types of polymers (C). Moreover, as long as the effect of this invention is acquired, polymers other than a polymer (C) may be included.

  Resin (A) may contain additives, such as a ultraviolet absorber, antioxidant, and a filler, as needed.

[Resin (B)]
The resin (B) typically contains a polymer (D) having negative intrinsic birefringence as a main component. Resin (B) may consist of a polymer (D).

  A polymer (D) is not specifically limited, For example, it is a (meth) acrylic polymer.

  The (meth) acrylic polymer preferably has a ring structure in the main chain.

  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. The ring structure preferably has an effect of giving negative intrinsic birefringence to the (meth) acrylic polymer having the ring structure in the main chain.

  More specifically, the ring structure is an N-substituted maleimide structure. A (meth) acrylic polymer having an N-substituted maleimide structure in the main chain has a large negative intrinsic birefringence depending on the type of substituent of the structure. For this reason, the freedom degree of control of reverse wavelength dispersibility further improves by setting it as the resin layer B which consists of resin (B) which contains the said polymer as a main component.

  The N-substituted maleimide structure is a ring structure represented by the following formula (4).

In the formula (4), 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, and R ¹⁰ and R ¹¹ are each independently a hydrogen atom or It is a methyl group.

  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 (meth) acrylic polymer may have a structural unit other than the (meth) acrylic ester unit and the ring structure that is a derivative thereof.

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

  Resin (B) may contain 2 or more types of polymers (D). Moreover, as long as the effect of this invention is acquired, polymers other than a polymer (D) may be included.

  Resin (B) may contain additives, such as a ultraviolet absorber, antioxidant, and a filler, as needed.

  In the production method of the present invention, the resin (A) contains a (meth) acrylic polymer having a lactone ring structure in the main chain and a positive intrinsic birefringence as a main component, and the resin (B) contains N- It is preferable that the main chain contains a (meth) acrylic polymer having a substituted maleimide structure in the main chain and having a negative intrinsic birefringence.

  Among the retardation films obtained by the production method of the present invention, the retardation film of the present invention, which is one of the preferred forms, has a lactone ring structure in the main chain and has a positive (meth) acrylic intrinsic birefringence. A stretched resin layer A1 made of a resin (A) having a positive intrinsic birefringence containing a polymer as a main component, and a (meth) acryl having an N-substituted maleimide structure in the main chain and having a negative intrinsic birefringence It has a laminated structure of a stretched resin layer B1 made of a resin (B) having a negative intrinsic birefringence and containing a polymer as a main component. The difference ΔTg in glass transition temperature between the resins (A) and (B) is less than 5 ° C. The retardation film exhibits reverse wavelength dispersion.

  The difference ΔTg in glass transition temperature between the resins (A) and (B) in the retardation film of the present invention is preferably less than 3 ° C.

  Preferred forms of the retardation film of the present invention, such as a specific lactone ring structure and N-substituted maleimide structure, are as described above.

  The retardation film obtained by the production method of the present invention and the retardation film of the present invention are suitable for use in an image display device such as an LCD.

  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 produced in the present Example and retardation film is shown.

[Polymerization reaction rate, resin composition analysis]
The polymerization reaction rate in each production example was calculated from the amount of unreacted monomer remaining in the obtained polymerization solution. The amount of unreacted monomer was measured by gas chromatography (manufactured by Shimadzu Corporation, GC17A).

[Dealcoholization reaction rate (lactone cyclization rate)]
The content of the lactone ring structure in the (meth) acrylic polymer prepared in the production example was determined by the dynamic TG method as follows. First, a dynamic TG measurement is performed on a (meth) acrylic polymer having a lactone ring structure, and a weight reduction rate between 150 ° C. and 300 ° C. is measured. X). 150 ° C. is a temperature at which hydroxyl groups and ester groups remaining in the polymer start a cyclization condensation reaction, and 300 ° C. is a temperature at which thermal decomposition of the polymer begins. Separately, assuming that all the hydroxyl groups contained in the precursor have undergone a dealcoholization reaction to form a lactone ring, the weight loss rate due to the reaction (ie, the dealcoholization cyclocondensation reaction rate of the precursor is (Weight reduction rate assumed to be 100%) was calculated and used as the theoretical weight reduction rate (Y). Specifically, the theoretical weight reduction rate (Y) can be determined from the content of the structural unit having a hydroxyl group involved in the dealcoholization reaction in the precursor. In addition, the composition of the precursor was derived from the composition of the (meth) acrylic polymer to be measured. Next, the dealcoholization reaction rate of the (meth) acrylic polymer was determined by the formula [1- (actually measured weight reduction rate (X) / theoretical weight reduction rate (Y))] × 100 (%). In the (meth) acrylic polymer to be measured, it is considered that a lactone ring structure is formed for the determined dealcoholization reaction rate. Therefore, the content of the structural unit having a hydroxyl group involved in the dealcoholization reaction in the precursor is multiplied by the obtained dealcoholization reaction rate and converted to the weight of the lactone ring structure, thereby containing the lactone ring structure in the acrylic resin. Rate.

[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: Made by Tosoh Column: TSK-GEL SuperHZM-M 6.0 × 150 2 in series Guard column: TSK-GEL SuperHZ-L 4.6 × 35 1 Reference column: TSK-GEL SuperH-RC 6.0 × 150 2 in series Eluent: Chloroform Flow rate 0.6 mL / min Column temperature: 40 ° C

[Glass transition temperature (Tg)]
Tg of the polymer and the resin layer was determined by a midpoint method according to ASTM-D-3418. Specifically, using a differential scanning calorimeter (manufactured by Rigaku, DSC-8230), a sample of about 10 mg was heated from 30 ° C. to 250 ° C. in a nitrogen flow (50 mL / min) atmosphere (heating rate 10 ° C. / Min) and the DSC curve obtained. Α-alumina was used as a reference.

[Thickness of resin layer]
The thickness of the resin layer was measured using a Digimatic micrometer (manufactured by Mitutoyo Corporation).

[In-plane retardation and wavelength dispersion]
The in-plane retardation Re (in-plane retardation for light having a wavelength of 590 nm) of the produced retardation film was measured using a retardation film / optical material inspection apparatus RETS-100 (manufactured by Otsuka Electronics).

  The wavelength dispersion of the produced retardation film is different from the in-plane retardation [Re (590)] for light having a wavelength of 590 nm, the in-plane retardation [Re (447)] for light having a wavelength of 447 nm, and a wavelength of 750 nm. The in-plane retardation [Re (750)] with respect to light was separately determined and evaluated by the ratios [Re (447) / Re (590)] and [Re (750) / Re (590)].

(Production Example 1)
As a polymerization solvent, 7000 g of methyl methacrylate (MMA), 3000 g of methyl 2- (hydroxymethyl) acrylate (MHMA) and a polymerization solvent were added to a reaction vessel having an internal volume of 30 L equipped with a stirrer, a temperature sensor, a cooling pipe and a nitrogen introduction pipe. 12000 g of toluene was charged, and the temperature was raised to 105 ° C. while passing nitrogen through it. When refluxing with the temperature increase started, 6.0 g of t-amyl peroxyisononanoate (manufactured by Arkema Yoshitomi, trade name: Luperox 570) was added as a polymerization initiator, and the above t-amyl was added to 100 g of toluene. While a solution in which 12.0 g of peroxyisononanoate was dissolved was added dropwise over 2 hours, solution polymerization was allowed to proceed under reflux at about 105 to 110 ° C., followed by further aging for 4 hours. The polymerization reaction rate was 92.9%, and the content of MHMA units in the (meth) acrylic polymer formed by polymerization was 30.2% by weight.

  Next, 20 g of an octyl phosphate / dioctyl phosphate mixture (manufactured by Sakai Chemicals, Phoslex A-8) is added to the resulting polymerization solution as a catalyst for the cyclization condensation reaction (cyclization catalyst). The cyclization condensation reaction for forming a lactone ring structure was allowed to proceed for 2 hours under reflux at ° C. Next, 4000 g of methyl ethyl ketone was added to dilute the polymerization solution, and then the cyclization condensation reaction was further allowed to proceed for 1.5 hours under pressure (up to 2 MPa in terms of gauge pressure) in an autoclave at 240 ° C.

  Next, the obtained polymerization solution was introduced into a screwed twin screw extruder, and 26.5 g of zinc octylate (Nikka octix zinc 18%, manufactured by Nippon Chemical Industry Co., Ltd.), 4.4 g of antioxidant ( IRGANOX1010 (manufactured by Ciba Specialty Chemicals) 2.2 g + ADK STAB AO-412S (manufactured by Asahi Denka Kogyo Co., Ltd., 2.2 g) and 61.6 g of a mixed liquid of toluene were introduced into the extruder to further progress and volatilize the cyclization condensation reaction. The components were devolatilized. The introduction speed of the mixed liquid into the extruder was 20 g / h.

  Next, the polymer discharged from the tip of the extruder is cooled in a water bath, pelletized by a pelletizer, and transparent pellets made of a (meth) acrylic polymer (C-1) having a lactone ring structure in the main chain. Obtained. When dynamic TG was measured for the obtained pellets, the actual weight loss rate (X) was 0.21% by weight. Moreover, the weight average molecular weight of the polymer (C-1) was 11 million, and Tg was 140 degreeC.

(Production Example 2)
A reaction vessel having an internal volume of 1000 L equipped with a stirrer, a temperature sensor, a cooling pipe and a nitrogen introduction pipe was added to 30 parts by weight of methyl methacrylate (MMA) and 15 parts by weight of methyl 2- (hydroxymethyl) acrylate (MHMA). ) 5 parts by weight of n-butyl methacrylate (BMA), 50 parts by weight of toluene as a polymerization solvent, and 0.025 parts by weight of Adeka Stub 2112 (manufactured by ADEKA) as an antioxidant, The temperature was raised to ° C. When refluxing with the temperature increase started, 0.03 parts by weight of t-amylperoxyisonononanoate (manufactured by Arkema Yoshitomi, Luperox 570) was added as a polymerization initiator, and 0.7 parts by weight of toluene was added to 0.7 parts by weight of toluene. While the solution in which 0.06 part by weight of t-amylperoxyisononanoate was dissolved was dropped over 6 hours, solution polymerization was allowed to proceed under reflux at about 105 to 111 ° C., and the aging was further performed for 2 hours. . The polymerization reaction rate after aging was 96.2%, and the content of MHMA units in the intermediate obtained at this time was 30.2% by weight.

  Next, 0.1 part by weight of 2-ethylhexyl phosphate (manufactured by Sakai Chemical Industry, Phoslex A-8) is added to the resulting polymerization solution as a cyclization catalyst, and the mixture is refluxed at about 85 to 105 ° C. for 2 hours. The cyclization condensation reaction for forming a lactone ring structure was allowed to proceed. Subsequently, the polymerization solution was heated at 240 ° C. for 30 minutes by an autoclave to further advance the cyclization condensation reaction.

  Next, the temperature of the polymerization solution thus obtained was increased to 220 ° C. with a multi-tube heat exchanger, and then barrel temperature 250 ° C., rotation speed 170 rpm, reduced pressure 13.3 to 400 hPa (10 to 300 mmHg), To a vent type screw twin screw extruder (Φ = 42 mm, L / D = 42) having a rear vent number of 1 and a fore vent number of 4 (referred to as first, second, third, and fourth vents from the upstream side) Introduced at a treatment rate of 15 kg / hour in terms of resin amount, the cyclization condensation reaction was further advanced and devolatilized. At this time, after the first vent, a separately prepared antioxidant / deactivator mixed solution was injected at an injection rate of 0.46 kg / hour. In addition, after the second vent, a separately prepared ultraviolet absorber solution was injected at an injection rate of 0.52 kg / hour.

  The antioxidant / deactivator mixed solution contains 0.8 parts by weight of Irganox 1010 manufactured by Ciba Specialty Chemicals, 0.8 parts by weight of ADEKA Adeka Stub AO-412S, and 9.8 parts by weight of zinc octylate (Nippon Chemical Industry Co., Ltd.). Manufactured by Nikka Octyx Zinc (18%) was dissolved in 88.6 parts by weight of toluene.

  As the ultraviolet absorber solution, a solution in which 75 parts by weight of TINUVIN477 (active ingredient 80% by weight) manufactured by Ciba Specialty Chemicals was dissolved in 25 parts by weight of toluene was used.

  Next, the polymer discharged from the tip of the extruder is cooled in a water bath, pelletized by a pelletizer, and transparent pellets made of a (meth) acrylic polymer (C-2) having a lactone ring structure in the main chain. Obtained. The weight average molecular weight of the polymer (C-2) was 128,000 and Tg was 128 ° C.

(Production Example 3)
In a reactor equipped with a stirrer, a temperature sensor, a cooling pipe and a nitrogen introduction pipe, 9.9 parts by weight of N-phenylmaleimide (PMI) and 32.85 parts by weight of methyl methacrylate (MMA) as monomers, a polymerization solvent As a polymerization initiator, 55.0 parts by weight of toluene and 0.032 parts by weight of t-butylperoxyisopropyl carbonate (trade name: Kaya-Carbon BIC-75, manufactured by Kayaku Akzo) as a polymerization initiator were charged, and nitrogen was passed through to 105 ° C. The temperature was raised. When the reflux accompanying the temperature rise starts, 2.25 parts by weight of styrene (St) and 0.032 parts by weight of the polymerization initiator are added, and the solution polymerization proceeds under a reflux of about 105 to 110 ° C. Aging was performed for 2 hours.

  Next, the polymerization solution thus obtained was dried at 240 ° C. under reduced pressure for 1 hour to obtain a transparent polymer (D-1) composed of MMA units, St units and PMI units. The composition of the copolymer (D-1) is MMA: St: PMI = 71 wt%: 23 wt%: 6 wt%.

  The copolymer (D-1) had a Tg of 138 ° C. and a weight average molecular weight of 10,000,000.

(Production Example 4)
The polymer (C-1) pellets produced in Production Example 1 were extruded using a single screw extruder (cylinder diameter 20 mm, temperature 280 ° C.) and a coat hanger die (width 150 mm, temperature 290 ° C.). A resin film (F1) having a thickness of about 70 μm made of the resin (A-1) composed of the coalescence (C-1) was obtained. The Tg of the film (F1) was 140 ° C.

  In order to examine the positive / negative of the intrinsic birefringence of the produced film (F1), the following evaluation was performed. First, a film piece of 80 mm in the flow direction and 20 mm in the width direction was cut out from the produced film (F1). Next, the cut film piece was uniaxially stretched in the flow direction. For uniaxial stretching, an autograph (manufactured by Shimadzu Corporation) equipped with a heating chamber was used, and the stretching temperature was set to 140 ° C. which is Tg of the film (F1) to be evaluated, and the stretching ratio was doubled. In addition, when attaching the film piece to the autograph, since 20 mm of the both ends in the flow direction of the film piece was allowed to be attached to the chuck, the substantially stretched part of the film piece was 40 mm in width and width It was 20 mm in the direction. When the optical axis of the stretched film formed by this stretching was evaluated using a retardation film / optical material inspection apparatus RETS-100 (manufactured by Otsuka Electronics Co., Ltd.), the orientation angle was near 0 °, that is, the polymer (C -1) and the resin (A-1) composed of the polymer had positive intrinsic birefringence.

(Production Example 5)
The polymer (C-2) is constituted in the same manner as in Production Example 4 except that the polymer (C-2) pellet produced in Production Example 2 is used instead of the polymer (C-1) pellet. A resin film (F2) having a thickness of about 225 μm made of the resin (A-2) was obtained. The Tg of the film (F2) was 128 ° C. Further, the orientation angle of the film (F2) evaluated in the same manner as the film (F1) of Production Example 4 is around 0 °, that is, the polymer (C-2) and the resin (A- The intrinsic birefringence of 2) was positive. However, the extending | stretching temperature of the film piece cut out from the film (F2) was 128 degreeC which is Tg of the film (F2) which is evaluation object.

(Production Example 6)
The polymer (D-1) is constituted in the same manner as in Production Example 4 except that the polymer (D-1) pellet produced in Production Example 3 is used instead of the polymer (C-1) pellet. A resin film (F3) having a thickness of about 96 μm made of the prepared resin (B-1) was obtained. The Tg of the film (F3) was 138 ° C. Further, the orientation angle of the film (F3) evaluated in the same manner as the film (F1) of Production Example 4 is around 90 °, that is, the polymer (D-1) and the resin (B- The intrinsic birefringence of 1) was negative. However, the stretching temperature of the film piece cut out from the film (F3) was 138 ° C., which is the Tg of the film (F3) to be evaluated.

(Production Example 7)
Instead of the pellet of polymer (C-1), it was comprised with the said polymer similarly to manufacture example 4 except having used the pellet (JSR make, ARTON RH5200J) of the commercially available cycloolefin polymer. A resin film (F4) made of resin (A-3) and having a thickness of about 40 μm was obtained. The Tg of the film (F4) was 144 ° C. Further, the orientation angle of the film (F4) evaluated in the same manner as the film (F1) of Production Example 4 is around 0 °, that is, the cycloolefin polymer and the resin (A-3) constituted by the polymer. The intrinsic birefringence of was positive. However, the stretching temperature of the film piece cut out from the film (F4) was 144 ° C., which is the Tg of the film (F4) to be evaluated.

(Production Example 8)
Resin constituted by the polymer in the same manner as in Production Example 4 except that a commercially available polystyrene pellet (Toyostyrene, HI H650) was used instead of the polymer (C-1) pellet. A resin film (F5) made of (B-2) and having a thickness of about 150 μm was obtained. The Tg of the film (F5) was 100 ° C. Further, the orientation angle of the film (F5) evaluated in the same manner as the film (F1) of Production Example 4 is around 90 °, that is, the inherent compound of the resin (B-2) composed of the polystyrene and the polymer. Refraction was negative. However, the stretching temperature of the film piece cut out from the film (F5) was 100 ° C., which is the Tg of the film (F5) to be evaluated.

Example 1
The film (F1) produced in Production Example 4 and the film (F3) produced in Production Example 6 are laminated one by one so that the flow directions during film formation coincide with each other to produce a laminated film. did. ΔTg of the films (F1) and (F3) is 2 ° C.

  Next, a film piece of 80 mm in the flow direction and 20 mm in the width direction was cut out from the produced laminated film. Using the cut film piece as an original fabric, free end uniaxial stretching was performed under the stretching conditions shown in Table 1 below using an autograph (manufactured by Shimadzu Corporation) equipped with a heating chamber to obtain a retardation film. The stretching direction was the flow direction of each film. In addition, when attaching the film piece to the autograph, since 20 mm of the both ends in the flow direction of the film piece was allowed to be attached to the chuck, the substantially stretched part of the film piece was 40 mm in width and width It was 20 mm in the direction.

  The properties of the obtained retardation film are shown in Table 1 below together with the stretching conditions.

  As shown in Table 1, the maximum change in the wavelength dispersibility accompanying the change in the stretching temperature is 0.01, and the retardation film is the reverse wavelength dispersive and has the same wavelength dispersibility at any stretching temperature. was gotten. The stretching temperature dependence of wavelength dispersion was 0.001 / ° C. for [Re (477) / Re (590)] and −0.001 / ° C. for [Re (750) / Re (590)]. On the other hand, the in-plane retardation exhibited by the retardation film changed with changes in the stretching temperature.

(Comparative Example 1)
The film (F4) produced in Production Example 7 and the film (F3) produced in Production Example 6 are laminated so that the flow directions during film formation coincide with each other, and three layers of F3 / F4 / F3 are formed. A laminated film having a laminated structure was produced. ΔTg of films (F3) and (F4) is 6 ° C.

  Next, the produced laminated film was subjected to free end uniaxial stretching under the stretching conditions shown in Table 2 in the same manner as in Example 1 to obtain a retardation film.

  The properties of the obtained retardation film are shown in Table 2 below together with the stretching conditions.

  As shown in Table 2, a retardation film exhibiting reverse wavelength dispersion at any stretching temperature was obtained, but wavelength dispersion due to changes in stretching temperature, particularly [Re (477) / Re (590)], Has changed significantly. The stretching temperature dependence of wavelength dispersion was 0.006 / ° C. and −0.003 / ° C.

(Comparative Example 2)
The film (F2) produced in Production Example 5 and the film (F3) produced in Production Example 6 are laminated so that the flow directions during film formation coincide with each other, and three layers of F2 / F3 / F2 are formed. A laminated film having a laminated structure was produced. ΔTg of the films (F2) and (F3) is 10 ° C.

  Next, the produced laminated film was subjected to free end uniaxial stretching under the stretching conditions shown in Table 3 below in the same manner as in Example 1 to obtain a retardation film.

  The properties of the obtained retardation film are shown in Table 3 below together with the stretching conditions.

  As shown in Table 3, a retardation film exhibiting reverse wavelength dispersibility was obtained at any stretching temperature, but wavelength dispersion due to changes in the stretching temperature, particularly [Re (477) / Re (590)], Has changed significantly. The stretching temperature dependence of wavelength dispersion was 0.013 / ° C. and −0.006 / ° C. In addition, since the original fabric broke at a stretching temperature of 135 ° C., a retardation film could not be formed.

(Comparative Example 3)
The film (F4) produced in Production Example 7 and the film (F5) produced in Production Example 8 are laminated so that the flow directions during film formation coincide with each other, and three layers of F5 / F4 / F5 are formed. A laminated film having a laminated structure was produced. ΔTg of films (F4) and (F5) is 44 ° C.

  Next, the produced laminated film was subjected to free end uniaxial stretching under the stretching conditions shown in Table 4 in the same manner as in Example 1 to obtain a retardation film.

  The properties of the obtained retardation film are shown in Table 4 below together with the stretching conditions.

  As shown in Table 4, a retardation film exhibiting reverse wavelength dispersibility was obtained at any stretching temperature, but the wavelength dispersibility changed significantly due to the change in stretching temperature. The stretching temperature dependence of wavelength dispersion was 0.020 / ° C. and −0.010 / ° C. At a stretching temperature of 142 ° C., a retardation film could not be formed due to melting of the original fabric.

  By the production method of the present invention, a retardation film having the same wavelength dispersion and a different retardation can be produced from the same original fabric. Such a manufacturing method reduces the manufacturing cost of the retardation film, improves the adaptability to small-quantity production of other varieties, and enables flexible response to the demand from the retardation film user. That is, the production method of the present invention is very useful for industrial production of a retardation film.

  The retardation film obtained by the production method of the present invention is suitable for use in an image display device such as an LCD.

1 Original fabric (resin film)
2 (raw fabric) roll 3 stretching device 4, 4a, 4b retardation film 5, 5a, 5b (retardation film) roll 6 cutting / switching device

Claims (7)

A step of obtaining a retardation film by stretching a belt-shaped resin film that is a raw fabric using a stretching device;
Without changing the original fabric in the stretching apparatus, the resin film is stretched using the stretching apparatus at a stretching temperature different from that in the step, and the retardation value is different from that of the retardation film. A phase difference film having the same wavelength dispersion is obtained, and
The resin film is a laminated film having a resin layer A made of a resin (A) having positive intrinsic birefringence and a resin layer B made of a resin (B) having negative intrinsic birefringence,
The method for producing a retardation film, wherein a difference ΔTg in glass transition temperature between the resins (A) and (B) is less than 5 ° C.   2. The method for producing a retardation film according to claim 1, wherein the glass transition temperature difference ΔTg is less than 3 ° C. 3.   The manufacturing method of the retardation film of Claim 1 which obtains the said retardation film which shows the wavelength dispersion property from which a phase difference becomes small, so that a wavelength becomes short at least in visible light region.   The method for producing a retardation film according to claim 1, wherein a glass transition temperature of at least one resin selected from the resins (A) and (B) is 130 ° C. or higher.   The method for producing a retardation film according to claim 1, wherein at least one selected from the resins (A) and (B) contains a polymer having a ring structure in the main chain as a main component. The resin (A) contains a (meth) acrylic polymer having a lactone ring structure in the main chain and a positive intrinsic birefringence as a main component,
The method for producing a retardation film according to claim 1, wherein the resin (B) includes a (meth) acrylic polymer having an N-substituted maleimide structure in the main chain and having a negative intrinsic birefringence as a main component. . A stretched resin layer A1 made of a resin (A) having a positive intrinsic birefringence, having a lactone ring structure in the main chain and containing a (meth) acrylic polymer having a positive intrinsic birefringence as a main component;
A stretched resin layer B1 made of a resin (B) having a negative intrinsic birefringence, having an N-substituted maleimide structure in the main chain and containing a (meth) acrylic polymer having a negative intrinsic birefringence as a main component; Having a laminated structure of
The glass transition temperature difference ΔTg between the resins (A) and (B) is less than 5 ° C.,
A retardation film exhibiting wavelength dispersibility in which the retardation decreases as the wavelength decreases, at least in the visible light region.

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