JP2014170068A - Retardation film, polarizing plate, and image display apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a retardation film produced by stretching a resin composition which has high thermal decomposition resistance characteristics of the resin composition, and ensures compatibility with polymers contained therein.SOLUTION: A retardation film is produced by stretching a resin composition (C) containing 75 mass% or more and 90 mass% or less of a copolymer (A) including an N-substituted maleimide unit and a styrene-based unit as structural units, and 10 mass% or more and 25 mass% or less of polyphenylene ether (B). A ratio of the N-substituted maleimide unit to the total structural units of the copolymer (A) is 10 mass% or more and less than 35 mass%. The N-substituted maleimide unit is, for instance, at least one selected from an N-cyclohexylmaleimide unit, an N-phenylmaleimide and an N-benzylmaleimide.

Description

  The present invention relates to a retardation film obtained by stretching a resin composition, a polarizing plate and an image display device including the retardation film.

  A stretched film obtained by stretching a film made of a resin composition (resin film) is widely used in various fields including the field of image display. One type is a retardation film that utilizes birefringence based on orientation of a polymer by stretching. Retardation films are widely used for color tone compensation and viewing angle compensation in liquid crystal display devices (LCDs). One type of retardation film is an optical path length difference (retardation) based on a phase difference caused by birefringence. There are four λ / 4 plates. A circularly polarizing plate is obtained by a combination of a λ / 4 plate and a polarizer. The circularly polarizing plate is used, for example, for preventing reflection of external light and displaying a stereoscopic image.

  Conventionally, polymers having high optical transparency such as polycarbonate and cycloolefin have been used for retardation films. These general polymers exhibit wavelength dispersion (forward wavelength dispersion) in which birefringence increases (a phase difference increases) as the wavelength of light becomes shorter. 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, based on the fact that wavelength dispersion, in which birefringence decreases as the wavelength of light becomes shorter at least in the visible light region, is opposite to the wavelength dispersion exhibited by a general polymer, Called “sex”.

  Patent Document 1 discloses a resin composition having a specific composition, which includes polyphenylene ether and a copolymer including a repeating unit derived from styrene and a repeating unit derived from maleic anhydride, and has reverse wavelength dispersion. A resin composition capable of forming a retardation film exhibiting properties is disclosed.

International Publication No.2012 / 091009

  The retardation film is produced through molding of the resin composition into a film, but it is important that the resin composition is not thermally decomposed as much as possible by heat applied at that time. Thermal decomposition of the resin composition can result in foaming during film formation. Since bubbles generated by foaming remain and become an optical defect of the retardation film, if foaming occurs during film forming, a portion that cannot be used in the obtained retardation film is generated. In order to suppress foaming during film forming, a retardation film made of a resin composition having higher thermal decomposition characteristics is desired, but the resin composition disclosed in Patent Document 1 does not have sufficient thermal decomposition characteristics. Moreover, in order to maintain the optical transparency as a retardation film as well as the thermal decomposition characteristics, it is important to ensure the compatibility between the polymers contained in the resin composition.

  One of the objects of the present invention is a retardation film formed by stretching a resin composition, and the retardation of the resin composition is high and the compatibility between contained polymers is ensured while having high thermal decomposition resistance. In providing film.

  The retardation film of the present invention comprises 75% by mass to 90% by mass of a copolymer (A) containing N-substituted maleimide units and styrene units as constituent units, and 10% by mass to 25% of polyphenylene ether (B). It is obtained by stretching a resin composition (C) containing: Here, the ratio of the N-substituted maleimide unit in all the structural units of the copolymer (A) is 10% by mass or more and less than 35% by mass.

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

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

  According to the present invention, there is obtained a retardation film obtained by stretching a resin composition, wherein the resin composition has high heat decomposition characteristics and compatibility between contained polymers is ensured. It is done.

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

[Copolymer (A)]
The copolymer (A) contains an N-substituted maleimide unit and a styrenic unit as constituent units. The ratio of the N-substituted maleimide unit in all the structural units of the copolymer (A) (the content of the N-substituted maleimide unit in the copolymer (A)) is 10% by mass or more and less than 35% by mass. By combining such a copolymer (A) with the polyphenylene ether (B) at a specific ratio, the heat decomposition characteristics are high and the compatibility between the included polymers is ensured. A retardation film comprising the resin composition (C) compatible at a high level is obtained. The resin composition having a high heat decomposition property is, for example, a resin composition having a high heat decomposition temperature. When the thermal decomposition property of the resin composition is high, foaming when the composition is formed into a film is suppressed, and there are fewer bubbles remaining in the obtained film and the retardation film obtained by stretching the film. Residual air bubbles are optical defects in the retardation film. Therefore, a retardation film having few optical defects can be obtained due to the high thermal decomposition property of the resin composition. On the other hand, when the compatibility between the polymers contained in the resin composition is ensured, the optical transparency of the film obtained by molding the composition and the retardation film obtained by stretching the film is ensured. Is done. For example, the haze value of the film is an index for optical transparency.

  Resin containing copolymer (A) and polyphenylene ether (B) combined at a specific ratio for the above compatibility when the content of N-substituted maleimide units in copolymer (A) is less than 10% by mass The thermal balance of the composition (C) is lost, and high thermal decomposition characteristics cannot be obtained as the resin composition (C). On the other hand, when the content of the N-substituted maleimide unit in the copolymer (A) is 35% by mass or more, the copolymer (A) and the polyphenylene ether (B) combined at a specific ratio for the above-mentioned compatibility are obtained. The compatibility between the polymers (A) and (B) in the resin composition (C) to be contained is lowered, and the optical transparency of the retardation film is lost.

  When obtaining a retardation film exhibiting reverse wavelength dispersion, since the intrinsic birefringence of polyphenylene ether (B), which is one polymer contained in the resin composition (C), is positive, it is the other polymer. The intrinsic birefringence of the copolymer (A) is negative. This is because reverse wavelength dispersion is caused by a phenomenon in which the birefringences of polymers having different intrinsic birefringence signs (positive and negative) cancel each other against incident light. Whether the intrinsic birefringence of the copolymer is positive or negative is determined by the balance of birefringence generated by the structural unit contained in the copolymer. The styrenic unit has a function of making the intrinsic birefringence of the copolymer (A) negative. The N-substituted maleimide unit has a positive or negative effect on the intrinsic birefringence of the copolymer (A) depending on the type of substituent of the nitrogen atom. If the content of the N-substituted maleimide unit in the copolymer (A) is in the range of 10% by mass or more and less than 35% by mass, the N-substituted maleimide unit is assumed to have positive intrinsic birefringence of the copolymer (A). Even in the case of having an action (for example, in the case of an N-cyclohexylmaleimide unit), the formation of the copolymer (A) having negative intrinsic birefringence, and hence the formation of the retardation film exhibiting the reverse wavelength dispersion is ensured. It becomes.

  The positive or negative of the intrinsic birefringence of a polymer is determined by the molecular chain in the layer out of light incident perpendicularly to the principal surface of the layer in a layer (for example, a sheet or film) in which the molecular chain of the polymer is uniaxially oriented. Judgment based on “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 orientation direction (orientation axis) it can. A specific intrinsic birefringence value can be obtained by calculation based on the molecular structure.

  Whether the intrinsic birefringence of the resin composition is positive or negative is determined by the balance of birefringence generated by each polymer contained in the resin. The positive and negative intrinsic birefringence of the resin composition comprising one polymer is the same as the positive and negative intrinsic birefringence of the polymer.

  A structural unit having an action of imparting positive (negative) intrinsic birefringence to a polymer is a structural unit whose intrinsic birefringence exhibited by the homopolymer is positive (negative) when a homopolymer of the structural unit is formed. Say.

  The N-substituted maleimide unit has an action of improving the glass transition temperature (Tg) of the copolymer (A) and the resin composition (C). Tg of the copolymer (A) and the resin composition (C) containing the copolymer (A) tends to be lower as the content of the styrenic unit is larger, but the N in the copolymer (A) tends to be lower. -Realizing Tg of copolymer (A) and resin composition (C) suitable for use as a retardation film if the content of substituted maleimide units is in the range of 10% by mass or more and less than 35% by mass. Can do.

  The Tg of the copolymer (A) is, for example, 110 ° C. or higher, and is 120 ° C. or higher, further 130 ° C. or higher depending on the composition. Such a retardation film made of a resin composition having a high Tg has high heat resistance during use, and image display such as a liquid crystal display (LCD) in which a heat generating member such as a power source and a light emitter is accommodated in a narrow space. Suitable for use in devices.

  The content of the N-substituted maleimide unit in the copolymer (A) is preferably 10% by mass or more and 25% by mass or less. Within these ranges, the balance between the thermal decomposition characteristics and the compatibility of the resin composition (C) is particularly good, and the formation of a retardation film exhibiting reverse wavelength dispersion and / or high Tg is further ensured.

The N-substituted maleimide unit is a structural unit represented by the following formula (1). R ¹ in Formula (1) is a linear alkyl group having 1 to 6 carbon atoms, a cyclopentyl group, a cyclohexyl group, or a phenyl group. The N-substituted maleimide unit is preferably at least one selected from N-cyclohexylmaleimide units, N-phenylmaleimide units, and N-benzylmaleimide units.

  The ratio of the styrene unit in the total structural unit of the copolymer (A) (the content of the styrene unit in the copolymer (A)) is more than 65% by mass and 90% by mass or less. As for the content rate of the styrene-type unit in a copolymer (A), 75 to 90 mass% is preferable. Within these ranges, the balance between the thermal decomposition characteristics and the compatibility of the resin composition (C) is particularly good, and the formation of a retardation film exhibiting reverse wavelength dispersion and / or high Tg is further ensured.

  The styrene-based unit is a unit derived from a styrene-based monomer such as styrene, α-methylstyrene, methoxystyrene, vinyltoluene, or halogenated styrene. Of these, a styrene unit is preferred because a retardation film having high optical transparency and a large retardation can be obtained.

  The copolymer (A) may have a structural unit other than the N-substituted maleimide unit and the styrenic unit. Examples of the structural unit include methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, and 2-ethylhexyl methacrylate, acrylic acid esters such as methyl acrylate and butyl acrylate, acrylonitrile, and methacrylonitrile. It is a structural unit derived from each monomer of vinyl cyanide. The content rate of the said unit in a copolymer (A) is 20 mass% or less, for example, and 10 mass% or less is preferable.

The content of each structural unit in the copolymer (A) can be determined by a known method such as ¹ H nuclear magnetic resonance ( ¹ H-NMR) or infrared spectroscopy (IR).

  The weight average molecular weight (Mw) of the copolymer (A) is, for example, from 10,000 to 1,000,000, preferably from 50,000 to 500,000, and more preferably from 80,000 to 300,000. Within these ranges, the balance between the thermal decomposition characteristics and the compatibility of the resin composition (C) is particularly good. Moreover, too high weight average molecular weight makes it difficult to mold the resin composition (C) into a film.

  The copolymer (A) can be produced by a known method. For example, the copolymer (A) can be produced by polymerizing a monomer group including an N-substituted maleimide monomer and a styrene monomer. Various polymerization methods such as suspension polymerization, emulsion polymerization, and solution polymerization can be applied to the polymerization of the monomer group. Especially, since the residual amount of the N-substituted maleimide monomer in the obtained copolymer (A) can be reduced, solution polymerization is preferable.

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

[Polyphenylene ether (B)]
The polyphenylene ether (B) has a unit having a phenylene ether skeleton (phenylene ether unit) as a structural unit. The benzene ring of the phenylene ether skeleton may or may not have a substituent. When it has a substituent, the phenylene ether unit is, for example, a unit represented by the following formula (2).

In the formula (2), R ² and R ³ are independently of each other a halogen atom, an alkyl group (for example, an alkyl group having 7 or less carbon atoms), a phenyl group, a haloalkyl group, an aminoalkyl group, a hydrocarbonoxy group, a halo It is a hydrocarbon oxy group (provided that at least two carbon atoms are present between a halogen atom and an oxygen atom). R ⁴ and R ⁵ are each independently a hydrogen atom, a halogen atom, an alkyl group (for example, an alkyl group having 7 or less carbon atoms), a phenyl group, a haloalkyl group, a hydrocarbonoxy group, a halohydrocarbonoxy group (provided that A group in which at least two carbon atoms are present between a halogen atom and an oxygen atom). R ² and R ³ are preferably an alkyl group or a phenyl group, and particularly preferably an alkyl group having 1 to 4 carbon atoms. R ⁴ and R ⁵ are preferably hydrogen atoms. These preferable groups are the same in the combination of R ² , R ³ , R ⁴ and R ⁵ .

  The polyphenylene ether (B) may have one or more phenylene ether units as a constituent unit. The polyphenylene ether (B) having only one phenylene ether unit as a structural unit, that is, a homopolymer is, for example, poly (2,6-dimethyl-1,4-phenylene ether). The polyphenylene ether (B) having two or more phenylene ether units as a structural unit, that is, a copolymer (copolymer) is, for example, poly (2,6-dimethyl-1,4-phenylene ether / 2,3, 6-trimethyl-1,4-phenylene ether).

  The polyphenylene ether (B) may have a unit other than the phenylene ether unit as a constituent unit. The content rate of structural units other than the phenylene ether unit in the polyphenylene ether (B) is, for example, less than 50% by mass, preferably 30% by mass or less, and more preferably 20% by mass or less.

  From the viewpoint of compatibility with the copolymer (A), the weight average molecular weight (Mw) of the polyphenylene ether (B) is, for example, 5000 or more, preferably 5500 or more, and more preferably 6000 or more. The upper limit of Mw of the polyphenylene ether (B) is not particularly limited, but is usually 100,000 or less, preferably 30,000 or less, and more preferably 20,000 or less. Mw of polyphenylene ether (B) can be determined by gel permeation chromatography (GPC) measurement (standard polystyrene conversion) using chloroform as a developing solvent.

  The glass transition temperature (Tg) of the polyphenylene ether (B) is, for example, 150 ° C. or higher, and preferably 200 ° C. or higher. Although the upper limit of the said Tg is not specifically limited, For example, it is 250 degreeC. When the Tg is within these ranges, a retardation film having excellent heat resistance during use can be obtained.

  The method for producing polyphenylene ether (B) is not particularly limited, and may be a known method, for example, the method described in JP-A-11-302529.

[Resin composition (C)]
The resin composition (C) includes a copolymer (A) and a polyphenylene ether (B). The content of the copolymer (A) in the resin composition (C) is 75% by mass or more and 90% by mass or less, and the content of the polyphenylene ether (B) is 10% by mass or more and 25% by mass or less. In this range, a retardation film obtained by stretching the resin composition (C), wherein the resin composition has high thermal decomposition characteristics and compatibility between the contained polymers is ensured. can get. That is, a retardation film having few optical defects and ensuring optical transparency can be obtained. In addition, a retardation film exhibiting reverse wavelength dispersion and / or high Tg can be obtained while maintaining a high balance of thermal decomposition characteristics and compatibility.

  The content of the copolymer (A) in the resin composition (C) is preferably 75% by mass or more and 85% by mass or less. The content of the polyphenylene ether (B) in the resin composition (C) is preferably 15% by mass or more and 25% by mass or less. In these ranges, the balance between thermal decomposition characteristics and compatibility is particularly high.

  The resin composition (C) may contain one or more copolymers (A). The resin composition (C) may contain one or more polyphenylene ethers (B).

  The resin composition (C) may contain a polymer other than the copolymer (A) and the polyphenylene ether (B). The polymer is, for example, a polymer or copolymer (copolymer (A) using one or more monomers such as vinyltoluene, α-methylstyrene, acrylonitrile, methyl vinyl ketone, ethylene, propylene, and vinyl acetate. ), And preferably a styrene-acrylonitrile copolymer. The content rate of the said polymer in a resin composition (C) is 20 mass% or less, for example, and 10 mass% or less is preferable.

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

  Resin composition (C) can contain arbitrary additives, such as materials other than a polymer, for example, a ultraviolet absorber, antioxidant, a filler.

  The thermal decomposition temperature of the resin composition (C) is, for example, 320 ° C. or higher as a value measured in accordance with the provisions of JIS K7120. Depending on its composition, it is 330 ° C. or higher, and further 350 ° C. or higher. Such a high thermal decomposition temperature is based on the fact that the resin composition (C) contains the copolymer (A) and the polyphenylene ether (B) at the predetermined content.

  The Tg of the resin composition (C) is, for example, 120 ° C. or higher, and is 130 ° C. or higher, further 140 ° C. or higher depending on the composition. A retardation film made of a resin composition having such a high Tg is suitable for use in an image display device such as an LCD.

  The intrinsic birefringence of the resin composition (C) is typically negative. That is, a negative retardation film exhibiting reverse wavelength dispersion can be obtained by the resin composition (C).

  The resin composition (C) can be produced by a known method. For example, the copolymer (A) and polyphenylene ether (B) and additives as necessary may be mixed at a predetermined ratio and kneaded while applying heat.

[Phase difference film]
The retardation film of the present invention is obtained by stretching the resin composition (C). More specifically, the resin composition (C) is formed into a film (original film) and then stretched. A retardation film obtained by simultaneously molding and stretching the resin composition (C) into a film may be used. Since the composition basically does not change by molding and stretching into a film, the retardation film is composed of the resin composition (C).

  The retardation film of the present invention is usually a uniaxially stretchable, biaxially stretchable, or obliquely stretchable film, and a polymer, typically a copolymer (A) and a resin contained in the resin composition (C). The birefringence based on orientation by stretching of the polyphenylene ether (B) is shown. The retardation film of the present invention formed by stretching the resin composition (C) has few optical defects and high optical transparency. The retardation film is a retardation film exhibiting reverse wavelength dispersion, for example, an in-plane retardation Re (450) for light having a wavelength of 450 nm and an in-plane retardation Re (550) for light having a wavelength of 550 nm. A retardation film satisfying the relationship of the formula Re (450) <Re (550) can be obtained. Since the intrinsic birefringence of the resin composition (C) is typically negative, the retardation film is typically a negative retardation film (thickness direction retardation Rth is negative). Phase difference film).

  The in-plane retardation Re is defined as nx as the refractive index of the slow axis in the film plane, ny as the refractive index of the fast axis in the film plane, nz as the refractive index in the thickness direction of the film, and d as the film thickness. Is a value given by the equation (nx−ny) × d. The thickness direction retardation Rth is a value given by the expression {(nx + ny) / 2−nz} × d.

  The in-plane retardation Re shown by the retardation film of the present invention is, for example, 10 nm or more as a value for light having a wavelength of 550 nm (per 100 μm film thickness). The composition of the resin composition (C) and the retardation film Depending on the stretched state, it is 40 nm or more, 80 nm or more, and further 100 nm or more. Although the upper limit of the said value is not specifically limited, For example, it is 1000 nm or less.

  The retardation Rth in the thickness direction of the retardation film of the present invention is a value for light having a wavelength of 550 nm, for example, in the range of −10 nm to −100 nm.

  The ratio Re (450) / Re (550) exhibited by the retardation film of the present invention is, for example, less than 1, and is 0.95 or less depending on the composition of the resin composition (C) and the stretched state of the retardation film. Furthermore, it becomes 0.90 or less.

  The in-plane retardation Re shown in the retardation film of the present invention, the thickness direction retardation Rth, and the magnitude relationship between the refractive indices nx, ny and nz depend on the optical characteristics required for the target retardation film. It can be controlled by the composition of the resin composition (C) and the stretched state of the retardation film (for example, stretching method, stretching temperature, stretching ratio, etc.).

  Although the thickness of the retardation film of this invention is not specifically limited, For example, they are 10 micrometers-500 micrometers, 20 micrometers-300 micrometers are preferable, and 30 micrometers-100 micrometers are especially preferable.

  The haze exhibited by the retardation film of the present invention is, for example, 5% or less with a thickness of 100 μm. Depending on the composition of the resin composition (C) and the stretched state of the retardation film, 3% or less, and Is 2% or less. In addition, the haze which a phase difference film shows is the same as the haze which the original film before extending | stretching shows.

  The retardation film of the present invention may be uniaxially stretchable, biaxially stretchable, or obliquely stretchable. It can be selected according to the desired optical characteristics such as phase difference.

  The retardation film of the present invention may have a laminated structure in which two or more layers having the same or different optical properties are laminated.

  The application of the retardation film of the present invention is not particularly limited, and can be used for the same application as a conventional retardation film (for example, an image display device such as an LCD).

  The retardation film of the present invention can be combined with other optical members (for example, a polarizer). For example, when the retardation film is a λ / 4 plate, a circularly polarizing plate can be formed by a combination with a polarizer. The circularly polarizing plate is used, for example, for preventing reflection of external light and displaying a stereoscopic image.

  The retardation film of the present invention can be formed by a known method. For example, the resin composition (C) is formed into a film, and the obtained resin film (original film) is uniaxially stretched, biaxially stretched, or obliquely stretched in a predetermined direction, thereby polymer molecules contained in the film. What is necessary is just to orient a chain | strand.

  The method for forming the resin composition (C) into a film is not particularly limited, and a known film forming method can be applied. For example, the resin composition (C) may be melt extrusion molded or press molded.

  The method for stretching the obtained original film is not particularly limited, and may be a known method. Uniaxial stretching is, for example, free end uniaxial stretching in which a change in the width direction of the film is free. Biaxial stretching is, for example, sequential biaxial stretching or simultaneous biaxial stretching. The stretching method, stretching temperature, and stretching ratio can be appropriately selected according to the optical properties and mechanical properties of the target retardation film.

[Polarizer]
The configuration of the polarizing plate of the present invention is not particularly limited as long as the retardation film of the present invention is provided. The polarizing plate of the present invention has, for example, a structure in which the retardation film of the present invention is bonded to one side or both sides of a polarizer. The polarizing plate of the present invention may have layers other than the retardation film and the polarizer of the present invention.

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

  The polarizing plate of the present invention is, for example, a circular polarizing plate.

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

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

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

[Weight average molecular weight]
The weight average molecular weight (Mw) of the polymer was determined by gel conversion using gel permeation chromatography (GPC). The apparatus and measurement conditions used for the measurement are as follows.
System: manufactured 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]
The glass transition temperature (Tg) of the polymer and the resin composition 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 room temperature to 250 ° 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.

[Pyrolysis temperature (dynamic TG)]
The thermal decomposition temperature of the resin composition was determined by using a differential thermogravimetric simultaneous measurement device (TG8120, manufactured by Rigaku Corporation), a heating rate of 10 ° C./min, a nitrogen flow as an inflow gas of 50 mL / min, a step-like isothermal control method ( It was measured under the condition of a weight reduction rate value of 0.005% / sec or less between 60 ° C. and 500 ° C.).

[Haze]
The haze (film thickness of about 100 μm) of the film (original film) obtained by molding the resin composition uses a quartz cell containing tetrahydronaphthalene as a reference, and is in accordance with the provisions of JIS K7136 with respect to the film in tetrahydronaphthalene. Based on this, the turbidity meter (Nippon Denshoku Industries Co., Ltd., NDH-5000) was used.

[Total light transmittance]
The total light transmittance of the film (original film) obtained by molding the resin composition conforms to the provisions of JIS K7361-1 for the film in tetrahydronaphthalene using a quartz cell containing tetrahydronaphthalene as a reference. The turbidimeter was used to obtain the value.

[In-plane retardation Re]
In-plane retardation Re of a retardation film produced by further stretching an original film obtained by molding a resin composition, more specifically, an in-plane retardation Re (450) for light having a wavelength of 450 nm and a wavelength of 550 nm The in-plane retardation Re (550) for light was determined by a retardation film / optical material inspection apparatus RETS-100 (manufactured by Otsuka Electronics).

[Wavelength dispersion]
The wavelength dispersion of the retardation film was determined by a retardation film / optical material inspection apparatus RETS-100 (manufactured by Otsuka Electronics Co., Ltd.) as a ratio Re (450) / Re (550) serving as an index.

[Intrinsic birefringence sign]
The positive or negative of the intrinsic birefringence of the resin composition constituting the retardation film was evaluated based on the orientation angle of the film obtained using a fully automatic birefringence meter (manufactured by Oji Scientific Instruments, KOBRA-WR). . When the measured orientation angle is around 0 °, the intrinsic birefringence of the resin composition constituting the retardation film is positive, and when the measured orientation angle is around 90 °, the resin composition constituting the retardation film The intrinsic birefringence of an object is negative.

(Production Example 1)
A reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, a nitrogen introduction pipe and a dropping funnel was charged with 92 parts by mass of styrene (St) and 0.05 parts by mass of an antioxidant (ADEKA, ADK STAB 2112). The temperature was raised to 110 ° C. through nitrogen gas. When the reflux accompanying the temperature increase started, 0.045 parts by mass of t-amyl peroxyisononanoate (Arkema Yoshitomi, trade name: Luperox 570) was added as a polymerization initiator. Addition of a mixture of 8 parts by mass of N-cyclohexylmaleimide (CHMI) and 28 parts by mass of toluene; addition of a mixture of 0.090 parts by mass of t-amylperoxyisononanoate and 7.5 parts by mass of toluene as dropping system 2; Each started. In the dropping system 1, 20% by mass of the resultant was dropped over 0.5 hours, and then the remaining 80% by mass was further dropped over 3 hours. The total amount of the dropping system 2 was dropped over 3.5 hours. In this way, solution polymerization was allowed to proceed under reflux of about 115 ° C to 125 ° C. After completion of the dropping of the dropping systems 1 and 2, aging was further performed for 1.5 hours.

  When the composition of the polymer contained in the obtained polymerization solution was evaluated by gas chromatography, the CHMI unit content in the polymer was 10% by mass, and the St unit content was 90% by mass.

  Next, the obtained polymerization solution was dried at 240 ° C. under reduced pressure for 1 hour to obtain a transparent copolymer (A-1) containing CHMI units and St units as structural units. The weight average molecular weight (Mw) of the copolymer (A-1) was 14,000, and the glass transition temperature (Tg) was 114 ° C.

(Production Example 2)
Solution polymerization and aging were carried out in the same manner as in Production Example 1 except that the amount of St monomer charged into the reaction vessel was 88 parts by mass and the amount of CHMI monomer contained in the dropping system 1 was 12 parts by mass.

  When the composition of the polymer contained in the obtained polymerization solution was evaluated by gas chromatography, the CHMI unit content in the polymer was 15% by mass, and the St unit content was 85% by mass.

  Next, the obtained polymerization solution was dried at 240 ° C. under reduced pressure for 1 hour to obtain a transparent copolymer (A-2) containing CHMI units and St units as structural units. Mw of the copolymer (A-2) was 130,000 and Tg was 121 ° C.

(Production Example 3)
Solution polymerization and aging were allowed to proceed in the same manner as in Production Example 1 except that the amount of St monomer charged into the reaction vessel was 80 parts by mass and the amount of CHMI monomer contained in the dropping system 1 was 20 parts by mass.

  When the composition of the polymer contained in the obtained polymerization solution was evaluated by gas chromatography, the CHMI unit content in the polymer was 25% by mass, and the St unit content was 75% by mass.

  Next, the obtained polymerization solution was dried at 240 ° C. under reduced pressure for 1 hour to obtain a transparent copolymer (A-3) containing CHMI units and St units as structural units. Mw of the copolymer (A-3) was 135,000, and Tg was 134 ° C.

(Production Example 4)
Solution polymerization and aging were allowed to proceed in the same manner as in Production Example 1 except that the amount of St monomer charged into the reaction vessel was 71 parts by mass and the amount of CHMI monomer contained in the dropping system 1 was 29 parts by mass.

  When the composition of the polymer contained in the obtained polymerization solution was evaluated by gas chromatography, the CHMI unit content in the polymer was 35% by mass, and the St unit content was 65% by mass.

  Next, the obtained polymerization solution was dried at 240 ° C. under reduced pressure for 1 hour to obtain a transparent copolymer (D-1) containing CHMI units and St units as structural units. The copolymer (D-1) had a Mw of 130,000 and a Tg of 148 ° C.

(Production Example 5)
In the same manner as in Production Example 1 except that the amount of St monomer charged into the reaction vessel was 88 parts by mass, and a dropping system 1 containing 12 parts by mass of N-phenylmaleimide (PMI) monomer instead of CHMI monomer was used. The aging was advanced.

  When the composition of the polymer contained in the obtained polymerization solution was evaluated by gas chromatography, the PMI unit content in the polymer was 15% by mass, and the St unit content was 85% by mass.

  Next, the obtained polymerization solution was dried at 240 ° C. under reduced pressure for 1 hour to obtain a transparent copolymer (A-4) containing PMI units and St units as structural units. Mw of the copolymer (A-4) was 130,000 and Tg was 122 ° C.

Example 1
80 g of copolymer (A-1) produced in Production Example 1 and 20 g of polyphenylene ether (PPE) (Asahi Kasei Co., Ltd., Zyron S201A, Mw 190000, Tg 214 ° C.) were kneaded with a twin screw extruder. Thus, a resin composition (C-1) was obtained. The obtained resin composition (C-1) had a Tg of 129 ° C. and a thermal decomposition temperature of 345 ° C.

  Next, the produced resin composition (C-1) was melt-extruded using a single screw extruder to obtain a film having a thickness of 100 μm (an original film which is an unstretched film). At that time, a polymer filter having a filtration accuracy of 5 μm was used. The obtained film had a haze of 0.2% and a total light transmittance of 98% (per 100 μm thickness).

  Next, using the Instron universal testing machine (manufactured by Instron), the produced film was uniaxially stretched at a stretching temperature of 135 ° C. and a stretching ratio of 2 times to obtain a retardation film which is a uniaxially stretched film. . The obtained retardation film has an in-plane retardation Re (550) for light having a wavelength of 550 nm (the same applies hereinafter for a thickness of 100 μm) of 105 nm, and a ratio Re (450) / Re (550) that is an index of wavelength dispersion is 0.93, and the retardation film exhibited reverse wavelength dispersion. The intrinsic birefringence of the resin composition (C-1) obtained from the produced retardation film was negative.

(Example 2)
90 g of copolymer (A-2) produced in Production Example 2 and 10 g of PPE used in Example 1 were kneaded with a twin-screw extruder to obtain a resin composition (C-2). The obtained resin composition (C-2) had a Tg of 124 ° C. and a thermal decomposition temperature of 363 ° C.

  Next, the produced resin composition (C-2) was melt-extruded in the same manner as in Example 1 to obtain an original film having a thickness of 100 μm. The obtained film had a haze of 0.1% and a total light transmittance of 98%.

  Next, using the Instron universal testing machine (manufactured by Instron), the produced film was uniaxially stretched at a stretching temperature of 132 ° C. and a stretching ratio of 2 times to obtain a retardation film as a uniaxially stretched film. . The obtained retardation film has an in-plane retardation Re (550) of 126 nm and a ratio Re (450) / Re (550) of 0.98 with respect to light having a wavelength of 550 nm, and the retardation film exhibits reverse wavelength dispersion. Indicated. The intrinsic birefringence of the resin composition (C-2) obtained from the produced retardation film was negative.

(Example 3)
80 g of copolymer (A-2) produced in Production Example 2 and 20 g of PPE used in Example 1 were kneaded with a twin-screw extruder to obtain a resin composition (C-3). The obtained resin composition (C-3) had a Tg of 135 ° C. and a thermal decomposition temperature of 365 ° C.

  Next, the produced resin composition (C-3) was melt-extruded in the same manner as in Example 1 to obtain an original film having a thickness of 100 μm. The obtained film had a haze of 0.1% and a total light transmittance of 98%.

  Next, using the Instron universal testing machine (manufactured by Instron), the produced film was uniaxially stretched at a stretching temperature of 141 ° C. and a stretching ratio of 2 times to obtain a retardation film which is a uniaxially stretched film. . The obtained retardation film has an in-plane retardation Re (550) of 72 nm and a ratio Re (450) / Re (550) of 0.92 with respect to light having a wavelength of 550 nm, and the retardation film exhibits reverse wavelength dispersion. Indicated. The intrinsic birefringence of the resin composition (C-3) obtained from the produced retardation film was negative.

Example 4
75 g of copolymer (A-2) produced in Production Example 2 and 25 g of PPE used in Example 1 were kneaded with a twin-screw extruder to obtain a resin composition (C-4). The obtained resin composition (C-4) had a Tg of 138 ° C. and a thermal decomposition temperature of 365 ° C.

  Next, the produced resin composition (C-4) was melt-extruded in the same manner as in Example 1 to obtain an original film having a thickness of 100 μm. The obtained film had a haze of 0.2% and a total light transmittance of 98%.

  Next, using the Instron universal testing machine (manufactured by Instron), the produced film was uniaxially stretched at a stretching temperature of 142 ° C. and a stretching ratio of 2 times to obtain a retardation film as a uniaxially stretched film. . The obtained retardation film has an in-plane retardation Re (550) of 10 nm and a ratio Re (450) / Re (550) of 0.65 with respect to light having a wavelength of 550 nm, and the retardation film exhibits reverse wavelength dispersion. Indicated. The intrinsic birefringence of the resin composition (C-4) obtained from the produced retardation film was negative.

(Example 5)
80 g of the copolymer (A-3) produced in Production Example 3 and 20 g of PPE used in Example 1 were kneaded with a twin screw extruder to obtain a resin composition (C-5). The obtained resin composition (C-5) had a Tg of 145 ° C. and a thermal decomposition temperature of 370 ° C.

  Next, the produced resin composition (C-5) was melt-extruded in the same manner as in Example 1 to obtain an original film having a thickness of 100 μm. The obtained film had a haze of 0.2% and a total light transmittance of 98%.

  Next, the produced film was uniaxially stretched at a free end with a stretching temperature of 153 ° C. and a stretching ratio of 2 times using an Instron universal testing machine (manufactured by Instron) to obtain a retardation film which is a uniaxially stretched film. . The obtained retardation film has an in-plane retardation Re (550) of 43 nm and a ratio Re (450) / Re (550) of 0.93 with respect to light having a wavelength of 550 nm, and the retardation film exhibits reverse wavelength dispersion. Indicated. The intrinsic birefringence of the resin composition (C-5) obtained from the produced retardation film was negative.

(Example 6)
80 g of copolymer (A-4) produced in Production Example 5 and 20 g of PPE used in Example 1 were kneaded with a twin-screw extruder to obtain a resin composition (C-6). The obtained resin composition (C-6) had a Tg of 136 ° C. and a thermal decomposition temperature of 367 ° C.

  Next, the produced resin composition (C-6) was melt-extruded in the same manner as in Example 1 to obtain an original film having a thickness of 100 μm. The obtained film had a haze of 0.1% and a total light transmittance of 98%.

  Next, using the Instron universal testing machine (manufactured by Instron), the produced film was uniaxially stretched at a stretching temperature of 142 ° C. and a stretching ratio of 2 times to obtain a retardation film as a uniaxially stretched film. . The obtained retardation film has an in-plane retardation Re (550) of 75 nm and a ratio Re (450) / Re (550) of 0.92 with respect to light having a wavelength of 550 nm, and the retardation film exhibits reverse wavelength dispersion. Indicated. The intrinsic birefringence of the resin composition (C-6) obtained from the produced retardation film was negative.

(Comparative Example 1)
50 g of copolymer (A-2) produced in Production Example 2 and 50 g of PPE used in Example 1 were kneaded with a twin-screw extruder to obtain a resin composition (E-1). The obtained resin composition (E-1) had a Tg of 162 ° C. and a thermal decomposition temperature of 365 ° C.

  Next, the produced resin composition (E-1) was melt-extruded in the same manner as in Example 1 to obtain an original film having a thickness of 100 μm. The obtained film had a haze of 0.3% and a total light transmittance of 98%.

  Next, using the Instron universal testing machine (manufactured by Instron), the produced film was uniaxially stretched at a stretching temperature of 168 ° C. and a stretching ratio of 2 times to obtain a retardation film which is a uniaxially stretched film. . The obtained retardation film has an in-plane retardation Re (550) of 720 nm and a ratio Re (450) / Re (550) of 1.17 with respect to light having a wavelength of 550 nm, and the retardation film exhibits forward wavelength dispersion. Indicated. The intrinsic birefringence of the resin composition (E-1) obtained from the produced retardation film was positive.

(Comparative Example 2)
80 g of copolymer (D-1) produced in Production Example 4 and 20 g of PPE used in Example 1 were kneaded with a twin-screw extruder to obtain a resin composition (E-2). The obtained resin composition (E-2) had a Tg of 155 ° C. and a thermal decomposition temperature of 376 ° C.

  Next, the produced resin composition (E-2) was melt-extruded in the same manner as in Example 1 to obtain an original film having a thickness of 100 μm. The obtained film had a haze of 20% and a total light transmittance of 57%. Since it was clear at this time that the original film was stretched to obtain an optically transparent retardation film, the retardation film was not produced by uniaxially stretching the original film.

(Comparative Example 3)
80 g of a commercially available maleic anhydride-styrene copolymer (manufactured by Sartomer, SMA EF60) having a maleic anhydride (MA) unit content of 15% by mass and a St unit content of 85% by mass; 20 g of PPE used in the above was kneaded with a twin screw extruder to obtain a resin composition (E-3). The obtained resin composition (E-3) had a Tg of 116 ° C. and a thermal decomposition temperature of 319 ° C.

  The results of Examples and Comparative Examples are summarized in Table 1 below.

  As shown in Table 1, in Comparative Example 1 in which the PPE content in the resin composition exceeded 25% by mass, a retardation film showing reverse wavelength dispersion could not be obtained. In Comparative Example 2 in which the content of N-substituted maleimide units in the N-substituted maleimide-styrene copolymer reached 35% by mass, optical transparency usable as a retardation film could not be obtained. In Comparative Example 3 using a maleic anhydride-styrene copolymer, the thermal decomposition temperature was greatly reduced.

  The retardation film of this invention can be used for the same use as the conventional retardation film. For example, a retardation film showing a retardation of λ / 4 may be used, and a circularly polarizing plate may be obtained in combination with a polarizer.

Claims (6)

Resin containing 75% by mass or more and 90% by mass or less of copolymer (A) containing N-substituted maleimide units and styrene units as constituent units, and 10% by mass or more and 25% by mass or less of polyphenylene ether (B). The composition (C) is stretched,
The retardation film whose ratio of the N-substituted maleimide unit which occupies for all the structural units of the said copolymer (A) is 10 mass% or more and less than 35 mass%.   The in-plane retardation Re (450) for light having a wavelength of 450 nm and the in-plane retardation Re (550) for light having a wavelength of 550 nm satisfy the relationship of the formula Re (450) <Re (550). The retardation film described.   The retardation film according to claim 1, wherein the N-substituted maleimide unit is at least one selected from an N-cyclohexylmaleimide unit, an N-phenylmaleimide unit, and an N-benzylmaleimide unit.   The retardation film in any one of Claims 1-3 whose thermal decomposition temperature of the said resin composition (C) is 330 degreeC or more.   A polarizing plate comprising the retardation film according to claim 1.   An image display apparatus provided with the retardation film in any one of Claims 1-4.