JP5580643B2 - Thermoplastic resin composition having negative intrinsic birefringence, retardation film and image display device - Google Patents

Description

  The present invention relates to a thermoplastic resin composition having negative intrinsic birefringence, a retardation film using the resin composition, and an image display device including the retardation film.

  A stretched film obtained by stretching an original film made of a thermoplastic resin composition exhibits optical characteristics based on the orientation of the polymer contained in the composition. One type of such a stretched film is a retardation film utilizing birefringence generated by the orientation of a polymer. Retardation films are widely used in image display devices such as liquid crystal display devices (LCD).

  A stretched film comprising a resin composition containing an acrylic polymer having positive intrinsic birefringence and a styrene polymer having negative intrinsic birefringence and having an in-plane retardation Re in the vicinity of zero is known ( Patent Document 1). This stretched film is suitable for a polarizer protective film.

  In the resin composition of Patent Document 1, when the content of the styrenic polymer in the composition is increased, the intrinsic birefringence of the composition that is positive by the acrylic polymer changes negatively. A negative retardation film can be obtained by molding a resin composition having such a negative intrinsic birefringence to form an original film, and stretching the obtained original film to give orientation. The negative retardation film has an optical phase advance axis in the stretching direction, and can be used for various applications including optical compensation of an image display device. The original film is usually produced by melt extrusion molding of a resin composition.

JP 2006-171464 A

  However, when the content of the styrene polymer is increased in a resin composition including an acrylic polymer having a positive intrinsic birefringence and a styrene polymer having a negative intrinsic birefringence, At the time of producing the original film from the composition, it was obtained by evaporating the components contained in the composition from the resin composition after being discharged from the molding die or depositing deposits on the film molding roll. Optical defects may occur in the original film and the retardation film obtained by stretching and orienting the original film. The frequency with which optical defects occur in the original film increases as the content of the styrene polymer in the resin composition increases.

  The present invention relates to a thermoplastic resin composition having a negative intrinsic birefringence, comprising an acrylic polymer having a positive intrinsic birefringence and a styrenic polymer having a negative intrinsic birefringence. (For example, when forming a film from the composition by melt extrusion) Transpiration of components contained in the composition and accumulation of deposits on an apparatus used for extrusion (for example, a roll for film forming) is suppressed. An object of the present invention is to provide a finished resin composition.

  As a result of the study, the present inventors have found that by using a resin composition having a specific thermogravimetric change property, the above transpiration and deposit accumulation are suppressed during melt extrusion molding.

The thermoplastic resin composition of the present invention is a thermoplastic resin composition having a negative intrinsic birefringence, and is an acrylic polymer (A) having a positive intrinsic birefringence, and a styrenic resin having a negative intrinsic birefringence. A polymer (B). The acrylic polymer (A) is an acrylic polymer having a ring structure in the main chain. The styrenic polymer (B) is a polymer polymerized using a polymerization initiator. The resin composition having a weight of 15 mg was heated from 20 ° C. to 150 ° C. at a temperature increase rate of 20 ° C./min in a nitrogen atmosphere, and the resin composition weight W1 when held at 150 ° C. for 15 minutes, The ratio of the weight W2 of the resin composition when the resin composition held at 150 ° C. for 15 minutes is further heated to 280 ° C. at a heating rate of 20 ° C./min in a nitrogen atmosphere and held at 280 ° C. for 30 minutes. W2 / W1 is 0.995 or more.

  The retardation film of the present invention comprises a stretched oriented body of the thermoplastic resin composition of the present invention.

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

  The thermoplastic resin composition of the present invention has a thermogravimetric change characteristic indicated by a weight ratio W2 / W1 of 0.995 or more. Thereby, a thermoplastic resin composition having a negative intrinsic birefringence, including an acrylic polymer having a positive intrinsic birefringence and a styrenic polymer having a negative intrinsic birefringence, and at the time of melt extrusion molding, It becomes the resin composition in which the transpiration and deposits of deposits are suppressed.

  The weight W1 is a weight serving as a reference for evaluating the thermogravimetric change characteristics of a resin composition containing an acrylic polymer and a styrene polymer. The weight W1 of the composition was 15 mg in weight when the composition was heated from room temperature (20 ° C.) to 150 ° C. at a heating rate of 20 ° C./min in a nitrogen atmosphere and held at 150 ° C. for 15 minutes. It is weight. By this heating and holding, moisture and residual monomers contained in the resin composition are removed from the composition. In actual melt extrusion molding, components that are removed from the resin composition by heating to 150 ° C. and holding at 150 ° C., such as moisture and residual monomers, are extruded before the resin composition is discharged from the molding die. It is considered that it does not give an optical defect to the original film. Therefore, the weight W1 of the resin composition from which moisture and residual monomers have been removed by the heating and holding is a reference weight for evaluating the thermogravimetric change characteristics of the resin composition.

  The weight W2 is the resin composition whose weight W1 was measured (the resin composition held at 150 ° C. for 15 minutes), and further heated from 150 ° C. to 280 ° C. at a temperature increase rate of 20 ° C./min in a nitrogen atmosphere. And the weight of the composition when held at 280 ° C. for 30 minutes. This further heating and holding removes from the composition the components contained in the resin composition that cause optical defects to the original film by transpiration and adhesion. As the amount of the component to be removed increases, the weight W2 becomes smaller than the weight W1. In other words, the smaller the amount of the component contained in the resin composition, the closer the weight ratio W2 / W1 is to 1, and the effect of the present invention can be obtained when the ratio is 0.995 or more. This further holding condition is much harsher than the conditions in actual melt extrusion. As a result of the study, the present inventors have found this condition that the resin composition in which the above transpiration and deposit accumulation are suppressed during melt extrusion molding.

  The weight ratio W2 / W1 is a value with respect to a specific weight (15 mg) of the resin composition, and this is based on the shape and size of the composition while ensuring the measurement accuracy of the weight ratio. The purpose is to suppress as much as possible the fluctuation of the amount of components removed by holding. The weight of 15 mg is an amount by which it can be determined that the measurement accuracy of the weight ratio W2 / W1 can be sufficiently secured and that the components are removed from the resin composition uniformly by heating and holding. Considering this point, the weight of 15 mg does not need to be exactly 15.0 mg, and may be usually from 14.5 mg to 15.4 mg.

  The weights W1 and W2 can be measured by a general thermogravimetric measuring device such as a thermobalance (TG). The units of the weights W1 and W2 are not limited, but mg is reasonable because it is a value obtained by performing a predetermined treatment on 15 mg of the resin composition.

  The retardation film of the present invention is composed of a stretched and oriented body of the resin composition of the present invention, and has few optical defects even though it contains a styrene polymer. The retardation film of the present invention is a negative retardation film based on the fact that the intrinsic birefringence of the resin composition of the present invention is negative. The retardation film of the present invention is suitable for optical compensation of an image display device such as an LCD.

[Acrylic polymer (A)]
The acrylic polymer (A) is not limited as long as it has positive intrinsic birefringence.

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

  The acrylic polymer is a polymer having a (meth) acrylic acid ester unit and / or a (meth) acrylic acid unit as a constituent unit. The total of the proportions of (meth) acrylic acid ester units and (meth) acrylic acid units in all the structural units of the acrylic polymer is usually 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight. % Or more. In addition, when a ring structure that is a derivative of a (meth) acrylic acid ester unit, such as a lactone ring structure, is present in the main chain of the polymer, the (meth) acrylic acid ester unit and (meth) acrylic acid occupying all the structural units If the sum of the ratio of the unit and the content of the ring structure in the polymer is 50% by weight or more, an acrylic polymer is obtained.

  The (meth) acrylic acid ester unit is, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, t-butyl (meth) acrylate. N-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, chloromethyl (meth) acrylate, 2-chloroethyl (meth) acrylate, (Meth) acrylic acid 2-hydroxyethyl, (meth) acrylic acid 3-hydroxypropyl, (meth) acrylic acid 2,3,4,5,6-pentahydroxyhexyl, (meth) acrylic acid 2,3,4, Each (meth) acrylic such as 5-tetrahydroxypentyl, methyl 2- (hydroxymethyl) acrylate, methyl 2- (hydroxyethyl) acrylate It is a structural unit formed by polymerization of an acid ester. The acrylic polymer (A) may have two or more of these structural units as a (meth) acrylic acid ester unit. The acrylic polymer (A) preferably has methyl (meth) acrylate units. In this case, the optical properties and surface hardness of the retardation film are improved.

  The acrylic polymer (A) typically has a ring structure in the main chain.

  Since the acrylic polymer (A) having a ring structure in the main chain has a high glass transition temperature (Tg), the Tg of the resin composition of the present invention containing the acrylic polymer (A) is high. The retardation film of the present invention comprising the stretched alignment body of the resin composition having a high Tg as described above is excellent in heat resistance and suitable for use in an image display device, such as being able to be disposed in the vicinity of a heat generating part such as a light source. is there.

  In addition, depending on the type of ring structure, the compatibility between the acrylic polymer (A) having a ring structure in the main chain and the styrene polymer (B) is increased.

  The ring structure is at least one selected from, for example, a lactone ring structure, a glutaric anhydride structure, a glutarimide structure, a maleic anhydride structure, and an N-substituted maleimide structure.

  The ring structure is preferably at least one selected from a lactone ring structure and a glutarimide structure, and more preferably a lactone ring structure, because the retardation structure is excellent in stability as a ring structure and a retardation film excellent in optical properties is obtained.

  The lactone ring structure that the acrylic polymer (A) may have in the main chain is not particularly limited. For example, it may be a 4- to 8-membered ring, but it is excellent in stability as a ring structure. A membered ring or a 6-membered ring is preferable, and a 6-membered ring is more preferable. The lactone ring structure which is a 6-membered ring is a structure disclosed in, for example, Japanese Patent Application Laid-Open No. 2004-168882, but a precursor (having a lactone ring structure in the main chain by subjecting the precursor to a cyclization condensation reaction) A polymer having a high lactone ring content by a cyclocondensation reaction of the precursor, and a polymer having a methyl methacrylate unit as a constituent unit. The structure shown in the following formula (1) is preferable for the reason that it can be made.

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

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

The lactone ring structure can be formed by dealcoholization cyclocondensation of a precursor having a hydroxyl group and an ester group in the molecular chain. The lactone ring represented by the formula (1) is formed by, for example, forming a copolymer of methyl methacrylate (MMA) and 2- (hydroxymethyl) methyl acrylate (MHMA) and then adjoining MMA in the copolymer. It can be formed by dealcoholization cyclocondensation of units and MHMA units. At this time, R ¹ is H, R ² and R ³ are CH ₃ .

  When the acrylic polymer (A) has a lactone ring structure in the main chain, the content of the lactone ring structure in the acrylic polymer (A) is not particularly limited, but is usually 10 to 70% by weight, and 20 to 60% by weight. Is preferred. Moreover, the said content rate is further more preferable, so that it may become 25 to 55 weight% and 30 to 55 weight%.

  The content of the lactone ring structure in the acrylic polymer (A) can be determined by the dynamic TG method as follows. First, a dynamic TG measurement is performed on the acrylic polymer (A) having a lactone ring structure, a weight reduction rate between 150 ° C. and 300 ° C. is measured, and the obtained value is used as an actual weight reduction rate ( X). 150 ° C. is a temperature at which a hydroxyl group and an ester group remaining in the acrylic polymer (A) start a cyclization condensation reaction, and 300 ° C. is a temperature at which thermal decomposition of the acrylic polymer (A) starts. Separately, assuming that all the hydroxyl groups contained in the precursor polymer have undergone a dealcoholization reaction to form a lactone ring, the rate of weight loss due to the reaction (ie, dealcoholization of the precursor) The weight reduction rate (assuming that the condensation reaction rate was 100%) was calculated and used as the theoretical weight reduction rate (Y). 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. The composition of the precursor can be derived from the composition of the acrylic polymer (A). Next, the dealcoholization reaction rate of the acrylic polymer (A) is determined by the formula [1- (actually measured weight reduction rate (X) / theoretical weight reduction rate (Y))] × 100 (%). In the acrylic polymer (A), it is considered that a lactone ring structure is formed corresponding to the determined dealcoholization reaction rate. Therefore, the lactone in the acrylic polymer (A) is obtained by multiplying the content of the structural unit having a hydroxyl group involved in the dealcoholization reaction in the precursor by the obtained dealcoholization reaction rate and converting it to the weight of the lactone ring structure. The content of the ring structure can be determined.

  The acrylic polymer (A) may have a ring structure represented by the following formula (2) in the main chain.

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

When X ¹ is a nitrogen atom, the ring structure shown in Formula (2) is a glutarimide structure. The acrylic polymer (A) having a glutarimide structure in the main chain can be formed, for example, by imidizing a (meth) acrylic acid ester polymer with an imidizing agent such as methylamine.

When X ¹ is an oxygen atom, the ring structure shown in Formula (2) is a glutaric anhydride structure. The acrylic polymer (A) having a glutaric anhydride structure in the main chain can be formed, for example, by subjecting a copolymer of (meth) acrylic acid ester and (meth) acrylic acid to dealcoholization cyclocondensation in the molecule.

  The acrylic polymer (A) may have a ring structure represented by the following formula (3) in the main chain.

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

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

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

  When the acrylic polymer (A) has the ring structure represented by the formulas (2) and (3) in the main chain, the content of the ring structure represented by the formulas (2) and (3) in the acrylic polymer (A) is particularly Although not limited, it is 5 to 90 weight normally, 10 to 70 weight% is preferable, 10 to 60 weight% is more preferable, and 10 to 50 weight% is further more preferable.

  Tg of the acrylic polymer (A) having a ring structure in the main chain is usually 110 ° C. or higher. Depending on the type of ring structure and the content thereof, the Tg of the polymer is 115 ° C. or higher, 120 ° C. or higher, and further 130 ° C. or higher.

  The acrylic polymer (A) may have a structural unit other than the (meth) acrylic acid ester unit and the (meth) acrylic acid unit as long as it has positive intrinsic birefringence. The structural unit is, for example, styrene, vinyl toluene, α-methyl styrene, acrylonitrile, methyl vinyl ketone, ethylene, propylene, vinyl acetate, methallyl alcohol, allyl alcohol, 2-hydroxymethyl-1-butene, α-hydroxymethyl. It is a structural unit formed by polymerization of monomers such as styrene and α-hydroxyethylstyrene. When the acrylic polymer (A) has these structural units, the compatibility of the acrylic polymer (A) with the styrene polymer (B) is further increased. The acrylic polymer (A) may have two or more of these structural units.

  The weight average molecular weight of the acrylic polymer (A) is, for example, in the range of 1,000 to 300,000, preferably in the range of 5,000 to 250,000, more preferably in the range of 10,000 to 200,000, and still more preferably in the range of 50,000 to 200,000.

  The acrylic polymer (A) can be produced by a known method. The acrylic polymer (A) having a lactone ring structure in the main chain can be produced, for example, by the methods described in JP-A-2006-96960, JP-A-2006-171464, and JP-A-2007-63541. An acrylic polymer (A) having an N-substituted maleimide structure in the main chain, an acrylic polymer (A) having a glutaric anhydride structure in the main chain, and an acrylic polymer (A) having a glutarimide structure in the main chain are, for example, It can be produced by the methods described in JP 2007-31537 A, WO 2007/26659, and WO 2005/108438. The acrylic polymer (A) having a maleic anhydride structure in the main chain can be produced, for example, by the method described in JP-A-57-153008.

[Styrene polymer (B)]
The styrenic polymer (B) is not limited as long as it has negative intrinsic birefringence.

  The styrenic polymer is a polymer in which structural units formed by polymerization of styrenic monomers occupy 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more of all the structural units. . Styrene monomers are styrene and styrene derivatives having a substituent in the phenyl group or vinyl group in styrene, such as styrene, vinyl toluene, α-methyl styrene, α-hydroxymethyl styrene, α-hydroxyethyl styrene, Chlorostyrene.

  As long as the intrinsic birefringence is negative, the styrenic polymer may have a structural unit other than the structural unit formed by polymerization of the styrenic monomer. The structural unit is not limited as long as it is a structural unit formed by polymerization of a monomer having an unsaturated double bond and capable of copolymerization with a styrenic monomer. The structural unit is, for example, a structural unit formed by polymerization of the following monomers: (meth) acrylic acid ester such as methyl (meth) acrylate and ethyl (meth) acrylate; N-benzylmaleimide, N-substituted maleimides such as N-phenylmaleimide and N-cyclohexylmaleimide; maleic anhydride, itaconic anhydride, acrylonitrile, butadiene.

  Specific examples of the styrenic polymer include polystyrene, styrene-methyl (meth) acrylate copolymer, acrylonitrile-styrene copolymer, styrene-butadiene copolymer, and N-phenylmaleimide-methyl (meth) acrylate. -Styrene copolymer.

  The present inventors presume that the component that gives an optical defect to the original film by transpiration and adhesion is an oligomer component contained in the styrenic polymer. A large number of these oligomer components are produced in the styrene polymer by the radical generated from the Diels-Alder adduct of the styrene monomer generated by heat when the styrene polymer is synthesized by the bulk polymerization method. It is thought. Therefore, the styrenic polymer (B) is preferably a polymer synthesized by a polymerization method other than the bulk polymerization method, and particularly preferably a polymer synthesized by solution polymerization.

[Resin composition]
The resin composition of the present invention has negative intrinsic birefringence.

  The positive or negative of the intrinsic birefringence of the resin composition is determined by the layer out of the light incident perpendicularly to the principal surface of the layer in the layer (for example, film) in which the molecular chains of the polymer contained in the composition are uniaxially oriented. Judgment is based on a value “n3−n4” obtained by subtracting the refractive index n4 of the layer for the vibration component perpendicular to the orientation axis from the refractive index n3 of the layer for the vibration component parallel to the direction in which the molecular chain is oriented (orientation axis). it can. The sign of the intrinsic birefringence of the resin composition is determined by the balance of intrinsic birefringence of each polymer contained in the composition.

  The contents of the acrylic polymer (A) and the styrene polymer (B) in the resin composition of the present invention are not particularly limited as long as the intrinsic birefringence of the resin composition is negative. For example, acrylic polymer (A): styrene polymer (B) = 85: 15 to 50:50, 75:25 to 55:45 is preferable, and 70:30 to 60:40 is more preferable.

  As described above, the higher the content of the styrene polymer in the resin composition, the higher the frequency of occurrence of optical defects in the original film obtained by melt extrusion molding of the resin composition. For this reason, when the content rate of the styrene-type polymer (B) in the resin composition of this invention is 15 weight% or more, the effect of this invention becomes more remarkable.

  When an optical defect occurs in the original film due to the transpiration and adhesion at the time of forming the original film from the resin composition by melt extrusion molding, conventionally, an antioxidant is added to the resin composition or from the vent portion of the extruder. It has been considered effective to efficiently remove volatile components of a resin composition. However, according to the study by the present inventors, when the content of the styrene polymer (B) in the resin composition is 30% by weight or more, the effectiveness of these conventional countermeasures is significantly reduced. For this reason, when the content rate of the styrene-type polymer (B) in the resin composition of this invention is 30 weight% or more, the effect of this invention becomes further remarkable.

  The weight ratio W2 / W1 in the resin composition of the present invention is 0.995 or more, preferably 0.996 or more, and more preferably 0.997 or more.

  The resin composition of the present invention may consist of an acrylic polymer (A) and a styrenic polymer (B).

  The resin composition of the present invention may contain two or more acrylic polymers (A) and / or styrenic polymers (B).

  The resin composition of the present invention has a negative intrinsic birefringence as the resin composition, and a polymer other than the acrylic polymer (A) and the styrene polymer (B) as long as the effects of the present invention are obtained. Further, it may be included.

  The resin composition of the present invention may contain any material other than the acrylic polymer (A), the styrene polymer (B), and other polymers as long as the effects of the present invention are obtained. The material includes, for example, an antioxidant; a stabilizer such as a light stabilizer, a weather stabilizer and a heat stabilizer; a reinforcing material such as a glass fiber and a carbon fiber; a near infrared absorber; a tris (dibromopropyl) phosphate and a triallyl. Flame retardants such as phosphate and antimony oxide; Antistatic agents typified by anionic, cationic and nonionic surfactants; Colorants such as inorganic pigments, organic pigments and dyes; Organic fillers and inorganic fillers; Resin modification Agent; plasticizer; lubricant; flame retardant. The content rate of these materials in a resin composition is 0 to 5 weight%, for example, 0 to 2 weight% is preferable and 0 to 0.5 weight% is more preferable.

[Phase difference film]
The retardation film of the present invention comprises a stretched oriented body of the resin composition of the present invention. The retardation film of the present invention is a negative retardation film having an optical fast axis in the stretching direction.

  The method for obtaining the retardation film of the present invention from the resin composition of the present invention is not particularly limited. For example, an original film obtained by extrusion molding (melt extrusion molding) of the resin composition of the present invention may be stretched.

  The original film may be stretched based on a known stretching method such as uniaxial stretching (free end uniaxial stretching, fixed end uniaxial stretching, etc.) or biaxial stretching (sequential biaxial stretching, simultaneous biaxial stretching, etc.).

  The application of the retardation film of the present invention is not particularly limited, and can be used for applications similar to those of conventional retardation films, for example, image display devices such as liquid crystal display devices (LCD) and organic EL displays (OLED). .

  Specifically, since the retardation film of the present invention has few optical defects, it is suitable as an optical compensation member for LCD. For example, suitable for retardation films of various LCDs such as STN type LCD, TFT-TN type LCD, OCB type LCD, VA type LCD, IPS type LCD, optical compensation film, laminated film with polarizing plate, polarizing optical compensation film Can be used for The preferable optical properties of the retardation film of the present invention vary depending on the display mode of the liquid crystal used.

  The retardation film of this invention is suitable as a polarizer protective film used for the polarizing plate of LCD.

  The retardation film of the present invention may be used in combination with other optical members depending on applications.

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

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

  First, evaluation methods for the acrylic polymer (A), the styrene polymer (B), the resin composition, and the retardation film prepared in this example are shown.

[Tg of acrylic polymer (A), styrenic polymer (B) and resin composition]
The glass transition temperature (Tg) of the acrylic polymer (A), the styrenic polymer (B), and the resin composition was determined according to the provisions of JIS K7121. Specifically, it is obtained by using a differential scanning calorimeter (manufactured by Rigaku, DSC-8230) to raise a temperature of about 10 mg from room temperature to 200 ° C. (temperature increase rate 20 ° C./min) in a nitrogen gas atmosphere. The DSC curve was evaluated by the starting point method. Α-alumina was used as a reference.

[Weight average molecular weight of acrylic polymer (A) and styrenic polymer (B)]
The weight average molecular weights of the acrylic polymer (A) and the styrene polymer (B) were determined using gel permeation chromatography (GPC) according to the following measurement conditions:
Measurement system: Tosoh GPC system HLC-8220
Developing solvent: Chloroform (Wako Pure Chemical Industries, special grade)
Solvent flow rate: 0.6 mL / min Standard sample: TSK standard polystyrene (manufactured by Tosoh, PS-oligomer kit)
Measurement side column configuration: Guard column (Tosoh, TSK-GEL SuperHZ-L, 4.6X35, 1), Separation column (Tosoh, TSK-GEL Super HZM-M, 6.0X150, 2 in series)
Reference side column configuration: Reference column (Tosoh, TSK-GEL SuperH-RC, 6.0X150, 2 in series)
Column temperature: 40 ° C.

[Intrinsic birefringence of resin composition]
The intrinsic birefringence of the resin composition was determined as follows.

  Using the single-screw extruder (φ = 20 mm, L / D = 25) set at 280 ° C. and the coat hanger type T die (width 150 mm), the resin composition thus prepared is held at 110 ° C. from the T die. The film was extruded and discharged onto the cooled roll to produce an original film (unstretched film) having a thickness of 100 μm. Next, using the biaxial stretching machine (TYPE EX4, manufactured by Toyo Seiki Seisakusho Co., Ltd.), the produced original film is stretched at a temperature 7 ° C. higher than the Tg of the resin composition and in the MD direction (extrusion from T die, ejection direction) The film was uniaxially stretched at a free end at a stretching ratio of 2.0 to prepare a uniaxially stretchable retardation film having a thickness of 70 μm. Next, the orientation angle of the produced retardation film was determined by a fully automatic birefringence meter (manufactured by Oji Scientific Instruments, KOBRA-WR), and the positive / negative of the intrinsic birefringence of the resin composition was evaluated based on the value. When the measured orientation angle is near 0 ° with respect to the stretching direction, the intrinsic birefringence of the resin composition is positive, and when it is around 90 °, the intrinsic birefringence of the resin composition is negative.

  The positive and negative intrinsic birefringence of the acrylic polymer (A) and the styrenic polymer (B) can also be obtained by preparing an original film and a retardation film made of each polymer, and determining the orientation angle of the retardation film. Evaluation was performed in the same manner.

[Weight ratio of resin composition W2 / W1]
The weight ratio W2 / W1 of the resin composition was evaluated using a thermobalance (Rigaku, Thermo Plus 2 TG-8120 Dynamic TG). Specifically, the resin composition (weight 14.5 to 15.4 mg, columnar pellets having a height of 2 mm × diameter of 2.8 mm) is set on a thermobalance, under a nitrogen flow atmosphere at a flow rate of 200 mL / min. The weight ratio W2 / W1 was obtained by carrying out heating, temperature holding and weight measurement according to the following temperature raising program.

-Temperature raising program-
Step 1: Increase the temperature from room temperature (20 ° C.) to 150 ° C. at a temperature increase rate of 20 ° C./min.
Step 2: When reaching 150 ° C, hold at that temperature for 15 minutes,
Step 3: Measure the weight W1 (mg) of the resin composition at the time of holding at 150 ° C. for 15 minutes,
Step 4: After measuring the weight W1, the temperature is increased from 150 ° C. to 280 ° C. at a temperature increase rate of 20 ° C./min.
Step 5: When reaching 280 ° C., hold at that temperature for 30 minutes,
Step 6: Measure the weight W2 (mg) of the resin composition at the time of holding at 280 ° C. for 30 minutes,
Steps 1 to 6 were performed continuously.

[In-plane retardation Re of retardation film]
The in-plane retardation Re of the retardation film was evaluated using a fully automatic birefringence meter (manufactured by Oji Scientific Instruments, KOBRA-WR). The in-plane retardation Re is a value for light having a wavelength of 589 nm.

  The in-plane retardation Re of the retardation film is represented by the formula Re = (nx−ny) × d. Here, nx is the refractive index in the slow axis direction in the plane of the retardation film (direction showing the maximum refractive index in the film plane), ny is the fast axis direction in the plane of the retardation film (in the film plane) In the direction perpendicular to nx), d is the thickness (nm) of the retardation film.

[Retardation Rth in thickness direction of retardation film]
The retardation Rth in the thickness direction of the retardation film was evaluated using a fully automatic birefringence meter (manufactured by Oji Scientific Instruments, KOBRA-WR). Specifically, it was calculated based on a value measured by tilting the retardation film by 40 ° with the slow axis as the tilt axis. The thickness direction retardation Rth is a value for light having a wavelength of 589 nm.

  The retardation Rth in the thickness direction of the retardation film is represented by the formula Rth = {(nx + ny) / 2−nz} × d. Here, nx is the refractive index in the slow axis direction in the plane of the retardation film (direction showing the maximum refractive index in the film plane), ny is the fast axis direction in the plane of the retardation film (in the film plane) The refractive index in the direction perpendicular to nx), nz is the refractive index in the thickness direction of the retardation film, and d is the thickness (nm) of the retardation film.

(Production Example 1)
Into 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, 40 parts by weight of methyl methacrylate (MMA), 10 parts by weight of methyl 2- (hydroxymethyl) acrylate (MHMA) ), 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 were charged, and the temperature was raised to 105 ° C. while passing nitrogen through this. When refluxing with increasing temperature started, 0.05 parts by weight of t-amyl peroxyisononanoate (manufactured by Arkema Yoshitomi, Luperox 570) was added as a polymerization initiator, and 0.10 parts by weight of t-amyl was added. While peroxyisononanoate was added dropwise over 3 hours, solution polymerization was allowed to proceed under reflux at about 105 to 110 ° C., followed by further aging for 4 hours.

  Next, 0.05 parts by weight of 2-ethylhexyl phosphate (manufactured by Sakai Chemical Industry Co., Ltd., 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 110 ° C. Subsequently, the polymerization solution was heated in an autoclave at 240 ° C. for 30 minutes to further advance the cyclization condensation reaction.

Next, the obtained polymerization solution was subjected to a barrel temperature of 240 ° C., a rotation speed of 100 rpm, a degree of vacuum of 13.3 to 400 hPa (10 to 300 mmHg), a rear vent number of 1 and a forevent number of 4 (first and Vent type screw twin screw extruder (φ = 50) having a leaf disk type polymer filter (filtration accuracy 5 μm, filtration area 1.5 m ² ) arranged at the tip. Was introduced at a treatment rate of 45 kg / hour in terms of resin amount, and devolatilization was performed. At the time of devolatilization, a separately prepared mixed solution of antioxidant / cyclization catalyst deactivator was charged with 0.22 kg of ion-exchanged water from the back of the first vent at a charging rate of 0.68 kg / hour. The charging was performed from behind the second and third vents at a charging speed of / hour.

  In the mixed solution of the antioxidant / cyclization catalyst deactivator, 50 parts by weight of antioxidant (manufactured by Ciba Specialty Chemicals, Irganox 1010) and 35 parts by weight of zinc octylate (manufactured by Nippon Chemical Industry, Nikka octix zinc (3.6%) was dissolved in 200 parts by weight of toluene.

  After completion of devolatilization, the polymer in the molten state left in the extruder is discharged from the tip of the extruder while filtering through a polymer filter, pelletized by a pelletizer, and an acrylic having a lactone ring structure in the main chain Polymer (A-1) pellets were obtained. The acrylic polymer (A-1) had a Tg of 131 ° C., a weight average molecular weight of 131,000, and an intrinsic birefringence of positive.

(Production Example 2)
In 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, 36.5 parts by weight of styrene (St), 13.5 parts by weight of acrylonitrile (AN), and a polymerization solvent 50 parts by weight of toluene was charged, and the temperature was raised to 95 ° C. while passing nitrogen therein. When the reflux due to the temperature increase started, 0.05 parts by weight of t-amylperoxyisononanoate (manufactured by Arkema Yoshitomi, Luperox 570) was added as a polymerization initiator, and the mixture was refluxed at about 95 to 105 ° C. Solution polymerization was allowed to proceed.

  Next, the obtained polymerization solution was subjected to a barrel temperature of 240 ° C., a rotation speed of 100 rpm, a degree of vacuum of 13.3 to 400 hPa (10 to 300 mmHg), a rear vent number of 1 and a forevent number of 4 (first and Introduced into a vent type screw twin screw extruder (φ = 50.0 mm, L / D = 30) at a processing rate of 45 kg / hour in terms of resin amount Went. At the time of devolatilization, ion-exchanged water was added from behind the first, second, and third vents at a charging rate of 0.22 kg / hour.

  After completion of devolatilization, the polymer in the hot melt state remaining in the extruder is discharged from the tip of the extruder, pelletized by a pelletizer, and an acrylonitrile-styrene copolymer (B-) which is a styrene polymer (B). The pellet of 1) was obtained. The copolymer (B-1) had a Tg of 112 ° C., a weight average molecular weight of 161,000, and a negative intrinsic birefringence.

(Production Example 3)
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 charged with 6 parts by weight of N-phenylmaleimide (PMI), 36.5 parts by weight of MMA, and 7.5 parts by weight of MMA. St and 50 parts by weight of toluene as a polymerization solvent were charged, and the temperature was raised to 105 ° C. while nitrogen was passed through this. When the reflux accompanying the temperature increase started, 0.03 parts by weight of t-amyl peroxyisononanoate (manufactured by Arkema Yoshitomi, Luperox 570) was added as a polymerization initiator, and the mixture was refluxed at about 105 to 110 ° C. Solution polymerization was allowed to proceed.

  Next, the obtained polymerization solution was subjected to a barrel temperature of 240 ° C., a rotation speed of 100 rpm, a degree of vacuum of 13.3 to 400 hPa (10 to 300 mmHg), a rear vent number of 1 and a forevent number of 4 (first and Introduced into a vent type screw twin screw extruder (φ = 50.0 mm, L / D = 30) at a processing rate of 45 kg / hour in terms of resin amount Went. At the time of devolatilization, ion-exchanged water was added from behind the first, second, and third vents at a charging rate of 0.22 kg / hour.

  After completion of devolatilization, the polymer in the hot melt state remaining in the extruder is discharged from the tip of the extruder, pelletized by a pelletizer, and a styrenic polymer (B) PMI-MMA-St copolymer ( B-2) pellets were obtained. The copolymer (B-2) had a Tg of 142 ° C., a weight average molecular weight of 153,000, and a negative intrinsic birefringence.

Example 1
The acrylic polymer (A-1) pellet produced in Production Example 1 and the acrylonitrile-styrene copolymer (B-1) pellet produced in Production Example 2 were mixed with a single screw extruder (φ = 30 mm). It was used and kneaded at a weight ratio of (A-1) / (B-1) = 70/30 to prepare a thermoplastic resin composition (C-1). The resin composition (C-1) had a Tg of 122 ° C., an intrinsic birefringence of negative, and a weight ratio W2 / W1 of 0.9971.

Next, using the vented single screw extruder equipped with a polymer filter having a filtration accuracy of 5 μm and a filtration area of 0.75 m ² and a die, the produced resin composition (C-1) was continuously formed into a film (original film). And melt extruded. The cylinder of the single screw extruder was kept at 280 ° C. except that the resin composition supply part in the cylinder was kept at 180 ° C. The gear pump, polymer filter and die were kept at 282 ° C. The resin composition (C-1) was melt-kneaded in a single-screw extruder and then extrusion-molded. In the melt-kneading, volatile components were sucked from the pellet vent port at a suction pressure of 12 hPa and an exhaust speed of 200 L / kg · cm ^2. And using a barrier flight type screw. The melted resin composition (C-1) in a molten state was melt-extruded through a polymer filter and a die. At that time, a film (original film) was formed on a casting drum maintained at 90 ° C.

  When this extrusion molding was performed continuously for 20 hours, the surface of the casting drum and the state of the original film were visually confirmed. If there are deposits on the casting drum surface that cause optical defects in the original film (the deposits are based on organic matter), a cloudy or iridescent interference pattern can be seen on the surface. . However, no deposits that cause optical defects on the original film are observed on the surface of the casting drum, and the resulting original film also shows traces of deposited deposits (transfer marks). No optical defects were observed.

(Example 2)
The acrylic polymer (A-1) pellet produced in Production Example 1 and the acrylonitrile-styrene copolymer (B-1) pellet produced in Production Example 2 were mixed with a single screw extruder (φ = 30 mm). It was used and kneaded at a weight ratio of (A-1) / (B-1) = 60/40 to prepare a thermoplastic resin composition (C-2). The resin composition (C-2) had a Tg of 121 ° C., a negative intrinsic birefringence, and a weight ratio W2 / W1 of 0.9962.

  Next, similarly to Example 1, the produced resin composition (C-2) was continuously melt-extruded into a film (original film).

  When the extrusion was carried out continuously for 20 hours, the surface of the casting drum and the state of the original film were confirmed by visual observation. As a result, no optical defects were observed in the obtained original film, and the surface of the casting drum was also No deposits were observed that would cause optical defects in the original film.

Example 3
The acrylic polymer (A-1) pellets produced in Production Example 1 and the PMI-MMA-St copolymer (B-2) pellets produced in Production Example 3 were converted into a single screw extruder (φ = 30 mm). ) Was used and kneaded at a weight ratio of (A-1) / (B-2) = 70/30 to prepare a thermoplastic resin composition (C-3). The resin composition (C-3) had a Tg of 127 ° C., negative intrinsic birefringence, and a weight ratio W2 / W1 of 0.9984.

  Next, similarly to Example 1, the produced resin composition (C-3) was continuously melt-extruded into a film (original film).

  When the extrusion was carried out continuously for 20 hours, the surface of the casting drum and the state of the original film were confirmed by visual observation. As a result, no optical defects were observed in the obtained original film, and the surface of the casting drum was also No deposits were observed that would cause optical defects in the original film.

Example 4
The acrylic polymer (A-1) pellets produced in Production Example 1 and the PMI-MMA-St copolymer (B-2) pellets produced in Production Example 3 were converted into a single screw extruder (φ = 30 mm). ) Was used and kneaded at a weight ratio of (A-1) / (B-2) = 60/40 to prepare a thermoplastic resin composition (C-4). The resin composition (C-4) had a Tg of 127 ° C., an intrinsic birefringence of negative, and a weight ratio W2 / W1 of 0.9972.

  Next, similarly to Example 1, the produced resin composition (C-4) was continuously melt-extruded into a film (original film).

  When the extrusion was carried out continuously for 20 hours, the surface of the casting drum and the state of the original film were confirmed by visual observation. As a result, no optical defects were observed in the obtained original film, and the surface of the casting drum was also No deposits were observed that would cause optical defects in the original film.

(Comparative Example 1)
A single-screw extruder (φ = 30 mm) was used and kneaded at a weight ratio of (A-1) / Stylac AS783 = 70/30 to prepare a thermoplastic resin composition (D-1). The resin composition (D-1) had a Tg of 122 ° C., an intrinsic birefringence of negative, and a weight ratio W2 / W1 of 0.9925. Incidentally, the intrinsic birefringence of Stylac AS783 was negative.

  Next, similarly to Example 1, the produced resin composition (D-1) was continuously melt-extruded into a film (original film).

  When the extrusion molding was carried out for 5 hours, the surface of the casting drum and the state of the original film were confirmed by visual observation. As a result, deposits that caused optical defects on the original film were deposited on the surface of the casting drum. This was confirmed as a significant haze and interference pattern on the drum surface. At the same time, a large number of transfer traces of the deposit on the original film surface due to the deposit on the casting drum surface were confirmed. In addition, deposits were observed on the lip of the die.

(Comparative Example 2)
A single-screw extruder (φ = 30 mm) was used and kneaded at a weight ratio of (A-1) / Stylac AS767 = 60/40 to prepare a thermoplastic resin composition (D-2). The resin composition (D-2) had a Tg of 121 ° C., an intrinsic birefringence of negative, and a weight ratio W2 / W1 of 0.9910. Incidentally, the intrinsic birefringence of Stylac AS767 was negative.

  Next, as in Example 1, the produced resin composition (D-2) was continuously extruded into a film (original film).

  When the extrusion molding was carried out for 2 hours, the surface of the casting drum and the state of the original film were confirmed by visual observation. As a result, deposits that caused optical defects on the original film were deposited on the surface of the casting drum. This was confirmed as a significant haze and interference pattern on the drum surface. At the same time, a large number of transfer traces of the deposit on the original film surface due to the deposit on the casting drum surface were confirmed. In addition, deposits were observed on the lip of the die.

  The results of Examples and Comparative Examples are summarized in Table 1 below. The column of continuous film formation results in Table 1 is described according to the following criteria.

  ○: Even after 20 hours from the start of continuous melt extrusion of the resin composition, deposits that cause optical defects on the original film are not confirmed on the surface of the casting drum. At the same time, no transfer trace of the deposit due to the deposit on the surface of the casting drum was confirmed on the surface of the produced original film.

  X: Accumulation of deposits that cause optical defects on the original film was confirmed on the surface of the casting drum before 20 hours had passed since the start of continuous melt extrusion of the resin composition. In addition, a transfer trace of the deposit due to the deposit on the surface of the casting drum was confirmed on the surface of the produced original film. In this case, the elapsed time from the start of melt extrusion molding until these are confirmed is also shown in the column.

  As shown in Table 1, when the weight ratio W2 / W1 of the resin composition is 0.995, the continuous film formation results differ greatly, and when the weight ratio W2 / W1 is 0.995 or more, melt extrusion It was confirmed that the resin composition in which the evaporation of the components contained in the resin composition and the deposition of deposits on the film-forming roll were suppressed during molding was suppressed.

  The retardation film of the present invention can be widely used for image display devices such as a liquid crystal display device (LCD) and an organic EL display (OLED), similarly to the conventional retardation film.

Claims (5)

A thermoplastic resin composition having negative intrinsic birefringence,
An acrylic polymer (A) having a positive intrinsic birefringence, and a styrenic polymer (B) having a negative intrinsic birefringence,
The acrylic polymer (A) is an acrylic polymer having a ring structure in the main chain,
The styrenic polymer (B) is a polymer polymerized using a polymerization initiator,
The resin composition having a weight of 15 mg was heated from 20 ° C. to 150 ° C. at a temperature rising rate of 20 ° C./min in a nitrogen atmosphere, and held at 150 ° C. for 15 minutes, with respect to the weight W1 of the resin composition.
The resin composition held at 150 ° C. for 15 minutes is further heated to 280 ° C. at a heating rate of 20 ° C./min in a nitrogen atmosphere, and the weight W2 of the resin composition when held at 280 ° C. for 30 minutes. A thermoplastic resin composition having a ratio W2 / W1 of 0.995 or more.   The thermoplastic resin composition according to claim 1, wherein the content of the styrenic polymer (B) in the resin composition is 15% by weight or more.   The thermoplastic resin composition according to claim 1, wherein the content of the styrenic polymer (B) in the resin composition is 30% by weight or more. The retardation film which consists of an extending | stretching oriented body of the thermoplastic resin composition in any one of Claims 1-3 . An image display device comprising the retardation film according to claim 4 .