JP5124433B2 - Retardation film - Google Patents

Description

  The present invention relates to a retardation film.

  A stretched film obtained by stretching a film (original film) made of a thermoplastic resin exhibits various optical characteristics based on the orientation of polymer chains generated by stretching. One type of such a stretched film is a retardation film that utilizes birefringence caused by the orientation of polymer chains. Retardation films are widely used in image display devices such as liquid crystal display devices (LCDs). In recent years, thinning of image display devices has been strongly demanded, and in order to meet these demands. A thin retardation film showing a large retardation is desired.

  Acrylic resin represented by polymethyl methacrylate (PMMA) has high light transmittance and low photoelasticity, and has excellent optical properties, and also has a balance of mechanical strength, moldability and surface hardness. It is excellent and suitable as a thermoplastic resin used for a retardation film. However, the acrylic resin is difficult to produce a retardation film showing a large retardation because it is less likely to cause a retardation due to stretching than other thermoplastic resins generally used as a retardation film, such as a polycarbonate resin and a cycloolefin resin. .

  JP 2008-9378 A (Patent Document 1) discloses a retardation film mainly composed of an acrylic resin having a lactone ring structure in the main chain. Although depending on the type of the ring structure, the retardation exhibited by the retardation film is improved by including an acrylic resin having a ring structure in the main chain. Moreover, since the glass transition temperature of an acrylic resin improves with a ring structure, it becomes a phase difference film excellent in heat resistance. According to Patent Document 1, a retardation film showing a larger retardation can be obtained by increasing the content of the ring structure in the acrylic resin. However, since the acrylic resin becomes “hard” when the ring structure enters the main chain, and it becomes difficult to sufficiently stretch the original film, there is a limit to the improvement of the retardation only by introducing the ring structure. In addition, the hardened retardation film is easily damaged when folded or torn during handling, and the content of the ring structure cannot be increased unnecessarily.

  By the way, it is described in Patent Document 1 that a low molecular substance having the same sign as the birefringence sign indicated by the acrylic resin may be added to the retardation film for the purpose of further improving the retardation indicated by the retardation film. Examples of low-molecular substances include stilbene, biphenyl, diphenylacetylene, and liquid crystal substances ([0115], [0116]). Thus, the addition of the retardation increasing agent is expected to improve the retardation exhibited by the retardation film.

  JP-A-2006-241197 (Patent Document 2) describes a low-molecular compound containing two or more aromatic rings as such a retardation increasing agent, and examples of the low-molecular compound include biphenyl and dihydroxybiphenyl. And diphenyl sulfide, bisphenol, stilbene, diphenylacetylene, azobenzene and the like are exemplified ([0050]).

However, these low-molecular compounds have problems in compatibility with acrylic resins having a ring structure in the main chain, especially when forming an original film by melt molding, such as foaming, bleed-out, etc. The problem is likely to occur. In addition, when used as a retardation film after production, when heat is applied, such as when placed near the light source in an image display device, the low molecular weight compound bleeds out to improve the appearance or optically. Are likely to suffer.
JP 2008-9378 A JP 2006-241197 A

  The present invention is a retardation film comprising a resin composition containing an acrylic resin having a ring structure in the main chain, and can achieve a large retardation by an unprecedented composition, and on the appearance at the time of production and use or An object is to provide a retardation film in which the occurrence of optical defects is suppressed.

  The retardation film of the present invention is a retardation film comprising a resin composition containing an acrylic resin (A) having a ring structure in the main chain, and the resin composition increases the retardation exhibited by the retardation film. As a retardation increasing agent, the compound (B) having a 2,4,6-triphenyl-1,3,5-triazine skeleton is included, and the retardation Rth in the thickness direction with respect to light having a wavelength of 589 nm is 30 nm or more. .

  The retardation film of the present invention contains a compound (B) having a 2,4,6-triphenyl-1,3,5-triazine skeleton as a retardation increasing agent that increases the retardation exhibited by the retardation film. Thus, a large phase difference is exhibited, and appearance or optical defects are less likely to occur during manufacture and use.

[Acrylic resin (A)]
The resin (A) is not particularly limited as long as it is an acrylic resin having a ring structure in the main chain.

  The acrylic resin is a resin 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 resin is usually 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight. That's it. In addition, when the main chain has a ring structure that is a derivative of a (meth) acrylic acid ester unit such as a lactone ring structure, the proportion of the (meth) acrylic acid ester unit and the (meth) acrylic acid unit in all the structural units, The sum total with the content rate of a ring structure should just be 50 weight% or more.

  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. Resin (A) may have 2 or more types of these structural units as a (meth) acrylic acid ester unit. The resin (A) preferably has a methyl (meth) acrylate unit. In this case, the optical properties and surface hardness of the retardation film are improved.

  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. These ring structures increase the glass transition temperature of the resin (A) and improve the heat resistance of the retardation film. Moreover, depending on the specific structure such as the type of substituent, the retardation of the retardation film is increased. In particular, the lactone ring structure, the glutaric anhydride structure, and the glutarimide structure increase the intrinsic birefringence of the resin (A) positively and easily increase the retardation exhibited by the retardation film.

  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, since it is excellent in stability as a ring structure and also becomes a retardation film excellent in optical properties. .

  The lactone ring structure that the resin (A) may have in the main chain is not particularly limited, and may be, for example, a 4- to 8-membered ring. However, since it is excellent in stability as a ring structure, a 5-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 resin having a high lactone ring content by a cyclization condensation reaction of the precursor, and a polymer having a methyl methacrylate unit as a constituent unit can be used as a precursor. For the reasons such as, the structure represented by the following formula (2) is preferable.

In the formula (2), R ⁶ , R ⁷ and R ⁸ 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 (2) 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 ⁶ is H, and R ⁷ and R ⁸ are CH ₃ .

  Although the content rate of the lactone ring structure in resin (A) is not specifically limited, Usually, it is 10 to 70 weight%, and 20 to 60 weight% is preferable. 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 resin (A) can be determined by the dynamic TG method as follows. First, a dynamic TG measurement is performed on the resin (A) having a lactone ring structure, a weight reduction rate between 150 ° C. and 300 ° C. is measured, and the obtained value is an actually measured weight reduction rate (X). And 150 ° C. is a temperature at which the hydroxyl group and ester group remaining in the resin (A) start a cyclization condensation reaction, and 300 ° C. is a temperature at which thermal decomposition of the resin (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 resin (A). Next, the dealcoholization reaction rate of the resin (A) is determined by the formula [1- (actually measured weight reduction rate (X) / theoretical weight reduction rate (Y))] × 100 (%). In the resin (A), it is considered that a lactone ring structure is formed for the determined dealcoholization reaction rate. Therefore, the lactone ring structure in the resin (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 determined dealcoholization reaction rate and converting it to the weight of the lactone ring structure. The content of can be determined.

  As an example, the dealcoholization reaction rate of the resin (A) produced in Production Example 1 described later is obtained. The molecular weight of methanol produced by the dealcoholization reaction is 32, and the content of the MHMA unit, which is a constituent unit having a hydroxyl group involved in the dealcoholization reaction, in the precursor (copolymer of MHMA and MMA) is 20% by weight. Since the molecular weight of the MHMA unit in terms of monomer is 116, the theoretical weight reduction rate (Y) of the resin (A) is (32/116) × 30.2 = 5.52% by weight. Become. On the other hand, since the actual weight reduction rate (X) of the resin (A) was 0.18% by weight, the dealcoholization reaction rate was 96.7% (= (1−0.18 / 5.52) × 100 (%)).

  Next, the content rate of the lactone ring structure in the resin (A) is determined. Since the MHMA unit content in the precursor is 20% by weight, the MHMA unit monomer molecular weight is 116, the dealcoholization reaction rate is 96.7%, and the formula weight of the lactone ring structure is 170, the above resin The content of the lactone ring structure in (A) is 28.3% by weight (= 20 × 0.967 × 170/116).

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

In the formula (3), R ⁹ and R ¹⁰ 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 ¹¹ does not exist, and when X ¹ is a nitrogen atom, R ¹¹ 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 (3) is a glutarimide structure. The resin (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 (3) is a glutaric anhydride structure. The resin (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 within the molecule.

  The resin (A) may have a ring structure represented by the following formula (4) in the main chain.

In the formula (4), R ¹² and R ¹³ 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 ¹⁴ does not exist, and when X ² is a nitrogen atom, R ¹⁴ 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 (4) is an N-substituted maleimide structure. The resin (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 acid ester.

When X ² is an oxygen atom, the ring structure shown in Formula (4) is a maleic anhydride structure. The resin (A) having a maleic anhydride structure in the main chain can be formed, for example, by copolymerizing maleic anhydride and (meth) acrylic acid ester.

  The content of the ring structure represented by the formulas (3) and (4) in the resin (A) is not particularly limited, but is usually 5 to 90% by weight, preferably 10 to 70% by weight, more preferably 10 to 60% by weight. 10 to 50% by weight is more preferable.

  The glass transition temperature (Tg) of the resin (A) is usually 110 ° C. or higher because it has a ring structure in its main chain. Depending on the type of ring structure and the content thereof, the Tg of the resin (A) is 115 ° C. or higher, 120 ° C. or higher, and further 130 ° C. or higher.

  A high Tg of the resin (A) of 110 ° C. or higher, and in some cases 130 ° C. or higher is achieved by the resin (A) having a ring structure in the main chain. For example, Tg of polymethyl methacrylate (PMMA) which is a typical acrylic resin having no ring structure in the main chain is about 100 ° C. That is, since the resin (A) has a ring structure in the main chain, a retardation film with improved heat resistance is obtained. The retardation film having improved heat resistance as described above can be suitably used for an image display device because it can be easily placed near a heat generating part such as a light source.

  By the way, when Tg of a resin composition becomes high by including resin (A) which has ring structure in a principal chain, when making the said composition into a film by melt extrusion, it is necessary to make the molding temperature high. When the molding temperature becomes high, bleeding out of substances other than the resin contained in the composition, for example, a phase difference increasing agent tends to occur. However, in the retardation film of the present invention containing the compound (B) as a retardation increasing agent, bleeding out of the retardation increasing agent is suppressed even during the melt molding, so that the appearance or optical defects are reduced.

  The resin (A) may have a structural unit other than the (meth) acrylic acid ester unit and the (meth) acrylic acid unit. Such a structural unit includes, for example, styrene, vinyltoluene, α-methylstyrene, Formed by polymerization of monomers such as acrylonitrile, methyl vinyl ketone, ethylene, propylene, vinyl acetate, methallyl alcohol, allyl alcohol, 2-hydroxymethyl-1-butene, α-hydroxymethylstyrene, α-hydroxyethylstyrene Is a structural unit. Resin (A) may have 2 or more types of these structural units.

  The resin (A) may have a structural unit (UVA unit) having ultraviolet absorbing ability. In this case, the ultraviolet absorbing ability of the retardation film is improved. Depending on the structure of the UVA unit, the compatibility between the resin (A) and the compound (B) is improved.

  The monomer (C) that is the source of the UVA unit is not particularly limited, and is, for example, a benzotriazole derivative, a triazine derivative, or a benzophenone derivative into which a polymerizable group is introduced. The polymerizable group to be introduced can be appropriately selected according to the structural unit of the resin (A).

  Specific examples of the monomer (C) include 2- (2′-hydroxy-5′-methacryloyloxy) ethylphenyl-2H-benzotriazole (manufactured by Otsuka Chemical Co., Ltd., trade name RUVA-93), 2- (2′- Hydroxy-5'-methacryloyloxy) phenyl-2H-benzotriazole, 2- (2'-hydroxy-3'-t-butyl-5'-methacryloyloxy) phenyl-2H-benzotriazole.

  Specific examples of the monomer (C) other than the above are triazine derivatives represented by the following formulas (5), (6) and (7) or benzotriazole derivatives represented by the following formula (8). .

  When resin (A) contains a UVA unit, the content of the unit in resin (A) is preferably 20% by weight or less, and more preferably 15% by weight or less. When the content of the UVA unit in the resin (A) is excessively increased, the heat resistance of the retardation film is lowered.

  The weight average molecular weight of the resin (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.

  Resin (A) can be manufactured by a well-known method. The resin (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. For example, JP-A 2007-31537 discloses a resin (A) having an N-substituted maleimide structure in the main chain, a resin (A) having a glutaric anhydride structure in the main chain, and a resin (A) having a glutarimide structure in the main chain. It can be produced by the method described in Japanese Patent Publication No. WO 2007/26659 and WO 2005/108438. The resin (A) having a maleic anhydride structure in the main chain can be produced, for example, by the method described in JP-A-57-153008.

[Compound (B)]
The structure of the compound (B) is not particularly limited as long as it has a 2,4,6-triphenyl-1,3,5-triazine skeleton represented by the following formula (9). Compound (B) may be 2,4,6-triphenyl-1,3,5-triazine itself, or may be a compound in which the hydrogen atom of the phenyl group constituting the skeleton is substituted with a substituent. . Depending on the position of the substituent and the structure of the substituent, the compatibility with the resin (A) is higher, and the retardation film in which the occurrence of appearance and optical defects during production and use is further suppressed Become.

  In the compound (B), at least one hydrogen atom in the phenyl group constituting the 2,4,6-triphenyl-1,3,5-triazine skeleton is substituted with a hydroxyl group, in other words, 2,4, It is preferable that at least one of the phenyl groups constituting the 6-triphenyl-1,3,5-triazine skeleton is a hydroxyphenyl group. Such a compound (B) has particularly high compatibility with the resin (A).

  A specific example of the compound (B) in which at least one of the phenyl groups constituting the 2,4,6-triphenyl-1,3,5-triazine skeleton is a hydroxyphenyl group is represented by the following formula (10), ( Shown in 1). In addition, the compound shown to Formula (1) has higher compatibility with resin (A) than the compound shown to Formula (10).

R ¹⁵ in Formula (10) is a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, or an alkyl ester group.

R ¹ in Formula (1) is a hydrogen atom or a group represented by the formula “—OR ⁵ ”, and R ⁵ is a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, or an alkyl ester group. R < ² > -R < ⁴ > is a hydrogen atom or a C1-C18 alkyl group or alkylester group mutually independently. The alkyl ester group is preferably a group represented by the formula “—CH (—R ¹⁶ ) C (═O) OR ¹⁷ ”, wherein R ¹⁶ is a hydrogen atom or a methyl group, and R ¹⁷ is an alkyl group. The alkyl group in the present specification may be linear or branched.

  Although the molecular weight of a compound (B) is not specifically limited, 600 or more are preferable, 750 or more are more preferable, 900 or more are further more preferable. The resin composition containing an acrylic resin is usually formed into a film by melt extrusion, but the molecular weight of the compound (B) is 600 or more, more preferably 750 or more, and particularly preferably 900 or more. Bleed out of the compound (B) at the time of molding and use as a retardation film is further suppressed, and the retardation film has less appearance or optical defects due to bleed out. In other words, when the retardation film of the present invention is a retardation film obtained by stretching an original film obtained by melt-extruding the resin composition, the molecular weight of the compound (B) is preferably 600 or more, 750 or more is more preferable, and 900 or more is particularly preferable.

  When the retardation film of the present invention contains two or more compounds (B), it is preferable that the molecular weight of the compound (B) having the largest content in the retardation film is in the above range.

[Phase difference film]
The retardation film of this invention consists of a resin composition containing resin (A) and a compound (B). The method for obtaining the retardation film from the resin composition containing the resin (A) and the compound (B) is not particularly limited, and an original film obtained by molding the resin composition may be stretched.

  The original film can be produced by applying a known film forming technique such as melt extrusion or casting to a resin composition containing the resin (A) and the compound (B). 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 resin composition constituting the retardation film of the present invention will be described.

  Although the content rate of the compound (B) in a resin composition is not specifically limited, Usually, when the weight of the whole thermoplastic resin which the said composition contains is 100 weight part, it is 0.1-10 weight part, 0. 5 to 5 parts by weight is preferable, and 0.7 to 3 parts by weight is more preferable.

  The resin composition may contain a thermoplastic resin other than the resin (A). In this case, the ratio of the resin (A) in the entire thermoplastic resin included in the retardation film is usually 60% by weight or more, preferably 70% by weight or more, and more preferably 85% by weight or more.

  Thermoplastic resins other than the resin (A) include, for example, olefin polymers such as polyethylene, polypropylene, ethylene-propylene copolymer, poly (4-methyl-1-pentene); halogen-containing materials such as vinyl chloride and chlorinated vinyl resins. Polymer; Styrene polymer such as polystyrene, styrene-methyl methacrylate copolymer, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene block copolymer; Polyester such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate; Nylon 6 Polyamide such as nylon 66, nylon 610, polyacetal, polycarbonate, polyphenylene oxide, polyphenylene sulfide, polyether ether ketone, polysulfone, poly Terusaruhon; polyoxyethylene Penji alkylene; polyamideimide; polybutadiene rubber or ABS resin containing an acrylic rubber, rubber-like polymer such as ASA resin; and the like. The rubbery polymer preferably has on its surface a graft portion having a composition compatible with the resin (A). When the rubbery polymer is in the form of particles, the average particle diameter is the retardation. From the viewpoint of improving the transparency when formed into a film, it is preferably 300 nm or less, and more preferably 150 nm or less.

  Among the exemplified thermoplastic resins, the copolymer having a structural unit derived from a vinyl cyanide monomer and a structural unit derived from an aromatic vinyl monomer has excellent compatibility with the resin (A). Polymers are preferred. The copolymer is, for example, a styrene-acrylonitrile copolymer or a vinyl chloride resin.

  As long as the effect of this invention is acquired, the resin composition may contain materials other than resin (A) and a compound (B), for example, an additive. Additives include, for example, antioxidants; stabilizers such as light stabilizers, weather stabilizers and heat stabilizers; reinforcing materials such as glass fibers and carbon fibers; near infrared absorbers; tris (dibromopropyl) phosphate, 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 Agents; plasticizers; lubricants; flame retardants. The content rate of the additive 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.

  The retardation film of the present invention exhibits a large retardation based on the compound (B). Specifically, in the retardation film of the present invention, the thickness direction retardation Rth for light with a wavelength of 589 nm is 30 nm or more, and depending on the type of compound (B) and its content, 50 nm or more, 100 nm or more, Furthermore, it becomes 150 nm or more. In addition, since the retardation Rth in the thickness direction is positive, the retardation film of the present invention is a positive retardation film.

  In the retardation film of the present invention, the thickness direction retardation Rth (per 100 μm thickness of the film) with respect to light having a wavelength of 589 nm is, for example, 50 nm or more. Depending on the type of compound (B) and its content, 100 nm In addition, the thickness is 150 nm or more.

  In the retardation film of the present invention, the in-plane retardation Re for light with a wavelength of 589 nm is, for example, 30 nm or more, and depending on the type of compound (B) and the content thereof, 50 nm or more, 100 nm or more, and further 150 nm or more. Become.

  The retardation film of the present invention usually has a high glass transition temperature (Tg) of 110 ° C. or higher based on the resin (A) having a ring structure in the main chain. Depending on the type and content of the ring structure in the resin (A) and the content of the resin (A) in the retardation film, the Tg of the retardation film is 115 ° C. or higher, 120 ° C. or higher, and further 130 ° C. or higher.

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

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

  Specifically, the retardation film of the present invention 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 the present invention is suitable as a polarizer protective film used for a polarizing plate of LCD.

  The retardation film of the present invention is particularly effective when, for example, a positive retardation film having a large thickness direction retardation Rth is required in a VA LCD or the like.

  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 resin (A), the original film, and the retardation film prepared in this example are shown.

[Polymerization rate during polymerization and composition analysis of intermediates]
The polymerization reaction rate when the resin (A) is produced by polymerization, and the content of 2- (hydroxymethyl) methyl acrylate (MHMA) units in the intermediate before the cyclization condensation reaction are unreacted contained in the polymerization solution. The amount of the monomer was evaluated by measuring by gas chromatography (manufactured by Shimadzu Corporation, GC17A).

[Content of lactone ring structure in resin (A)]
The content of the lactone ring structure in the resin (A) was determined by the calculation method described above. The actually measured weight loss rate (X), which is a parameter used in the method, was determined by dynamic TG measurement as follows.

The prepared resin (A) pellets or the polymerization solution before the pellets are dissolved in tetrahydrofuran (THF) (or diluted with THF), and then the resin (A) is precipitated using excess hexane or methanol. I let you. Next, the precipitate is vacuum-dried (pressure 1.33 hPa, 80 ° C., 3 hours or longer) to remove volatile components, and the obtained white solid resin is subjected to dynamic TG measurement under the following measurement conditions. The measured weight loss rate (X) was determined.
Measuring device: Rigaku, Thermo Plus 2 TG-8120 Dynamic TG
Sample weight: 5-10mg
Temperature rising rate: 10 ° C./min Atmosphere: under nitrogen flow (200 ml / min) Measuring method: Step-like isothermal control method (between 60-500 ° C., weight loss rate value is 0.005%
// or less)

[Weight average molecular weight of resin (A)]
The weight average molecular weight of the resin (A) was determined according to the following measurement conditions using gel permeation chromatography (GPC).
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 guardcolumn SuperHZ-L), separation column (Tosoh, TSK Gel Super HZM-M), two in series Reference side column configuration: Reference column (Tosoh, TSK gel SuperH -RC)

[Glass transition temperature of the original film]
The glass transition temperature (Tg) of the original film was determined in accordance with JIS K7121 regulations. 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.

[Phase difference of retardation film]
The in-plane retardation Re and the thickness direction retardation Rth of the retardation film with respect to light having a wavelength of 589 nm were determined using a retardation measuring device (manufactured by Oji Scientific Instruments, KOBRA-WR). Specifically, the incident angle dependency (single N calculation) is selected as the measurement item, the average refractive index of the film measured with an Abbe refractometer, with the tilt axis as the slow axis and the incident angle as 40 °, The film thickness d was input and measured. The film thickness d of the retardation film was measured using a Digimatic micrometer (manufactured by Mitutoyo).

  The in-plane retardation Re and the thickness direction retardation Rth in the retardation film are represented by the formula Re = (nx−ny) × d and the formula Rth = [(nx + ny) / 2−nz] × d, respectively. 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.

[Change in turbidity of retardation film]
The amount of change in turbidity of the retardation film was evaluated as follows. First, a part (5 cm × 5 cm) of the obtained retardation film was cut out, and the turbidity of the cut out film was measured using a turbidimeter (manufactured by Nippon Denshoku Industries Co., Ltd., NDH-1001DP). Was the initial value. Next, after leaving the cut out film in a hot air dryer (manufactured by Tabai) kept at 100 ° C. for 200 hours, the turbidity of the film after being left was measured again to determine the amount of change from the initial value. As a factor that changes the turbidity of the retardation film, a bleedout of the retardation increasing agent due to heat can be considered.

(Production Example 1)
Into a reaction vessel having an internal volume of 30 L equipped with a stirrer, a temperature sensor, a cooling pipe and a nitrogen introduction pipe, 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) and 0.025 parts by weight of n-dodecyl mercaptan as an antioxidant, and 105 ° C. while introducing nitrogen into this. The temperature was raised to. 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 at 240 ° C. for 30 minutes by an autoclave to further advance the cyclization condensation reaction.

  Next, the polymerization solution thus obtained 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 fore vent number of 4 (first from the upstream side). (Referred to as 1, 2, 3 and 4 vents) vent type screw twin screw extruder (Φ = 29.75 mm, L / D = 30) at a processing rate of 2.0 kg / hour in terms of resin amount. Introduced and devolatilized. At the time of devolatilization, a separately prepared antioxidant / deactivator mixed solution is injected after the first vent at an injection rate of 0.02 kg / hr, and ion-exchanged water is added after the third vent. Injection was performed at an injection rate of 0.01 kg / hour.

  In the antioxidant / deactivator mixed solution, 2.3 parts by weight of Irganox 1010 manufactured by Ciba Specialty Chemicals, 2.3 parts by weight ADEKA ADEKA STAB AO-412S and 10 parts by weight zinc octylate (manufactured by Nippon Chemical Industry Co., Ltd., A solution of 3.6% of Nikka octix zinc) in 86 parts by weight of toluene was used.

  Through this series of operations, an acrylic resin (A) pellet (A-1) having a lactone ring structure in the main chain was obtained. The obtained pellet was transparent and the weight average molecular weight was 148,000.

(Production Example 2)
97 parts by weight of the pellet (A-1) produced in Production Example 1 and 3 parts by weight of 2,4,6-triphenyl-1,3,5-triazine (manufactured by Aldrich, molecular weight 309) as the compound (B) From a resin composition of an acrylic resin (A) having a lactone ring structure in the main chain and a compound (B) by dry blending and melt-kneading at a barrel temperature of 250 ° C. using a twin screw extruder having a 20 mmφ screw A transparent pellet (A-2) was obtained.

(Production Example 3)
To a reaction vessel container having an internal volume of 1000 L equipped with a stirrer, a temperature sensor, a cooling pipe and a nitrogen introduction pipe, 30 parts by weight of methyl methacrylate (MMA), 15 parts by weight of 2- (hydroxymethyl) methyl acrylate ( MHMA), 5 parts by weight of n-butyl methacrylate (BMA), 50 parts by weight of toluene as a polymerization solvent and 0.025 parts by weight of Adeka Stub 2112 (manufactured by ADEKA) as an antioxidant, The temperature was raised to 105 ° C. When refluxing with the temperature increase started, 0.03 parts by weight of t-amylperoxyisonononanoate (manufactured by Arkema Yoshitomi, Luperox 570) was added as a polymerization initiator, and 0.7 parts by weight of toluene was added to 0.7 parts by weight of toluene. While the solution in which 0.06 part by weight of t-amylperoxyisononanoate was dissolved was dropped over 6 hours, solution polymerization was allowed to proceed under reflux at about 105 to 111 ° C., and the aging was further performed for 2 hours. . The polymerization reaction rate after aging was 96.2%, and the content of MHMA units in the intermediate obtained at this time was 30.2% by weight.

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

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

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

  Through this series of operations, an acrylic resin (A) pellet (A-3) having a lactone ring structure in the main chain was obtained. The obtained pellet was transparent, and its weight average molecular weight was 128,000.

(Production Example 4)
In the case of further progress and devolatilization of the cyclization condensation reaction using the twin-screw extruder in Production Example 3, TINUVIN477 (manufactured by Ciba Specialty Chemicals, effective as the compound (B) after the second vent of the extruder Component 80% by weight) and acrylic having a lactone ring structure in the main chain in the same manner as in Production Example 3, except that a solution consisting of 75 parts by weight and 25 parts by weight of toluene was injected at an injection rate of 0.52 kg / hour. A transparent pellet (A-4) comprising a resin composition of the resin (A) and the compound (B) was obtained. The content rate of the compound (B) in a pellet (A-4) is 2 weight% calculated from the injection | pouring speed | rate.

  The components of TINUVIN477 are shown in the following formulas (11) to (13). In TINUVIN477, the compound represented by the formula (11) is a main component, and its molecular weight is 958. In addition, the main component in this specification is a component with the largest content rate, and the content rate of the said component is 50 weight% or more normally.

(Production Example 5)
98 parts by weight of the pellets (A-3) produced in Production Example 3 and 2 parts by weight of TINUVIN479 (manufactured by Ciba Specialty Chemicals) as a compound (B) are dry blended, and a twin screw extruder having a 20 mmφ screw is used. The mixture was melt-kneaded at a barrel temperature of 250 ° C. to obtain transparent pellets (A-5) composed of a resin composition of an acrylic resin (A) having a lactone ring structure in the main chain and the compound (B).

  The component of TINUVIN479 is shown in the following formula (14). The molecular weight of the component is 677.

(Production Example 6)
98 parts by weight of the pellet (A-3) produced in Production Example 3 and Adeka Stab LA as “low molecular compound containing two or more aromatic rings” described in JP-A-2006-241197 (Patent Document 2) -32 (made by ADEKA, containing benzotriazole ring as aromatic condensed ring, molecular weight 225) is dry blended and melt kneaded at a barrel temperature of 250 ° C. using a twin screw extruder having a 20 mmφ screw. Thus, a transparent pellet (A-6) was obtained.

Example 1
The pellet (A-2) produced in Production Example 2 was hot pressed to produce an unstretched film (original film) having a thickness of 160 μm. The obtained unstretched film had a Tg of 124 ° C.

  Next, after cutting the obtained unstretched film into a 97 mm × 97 mm square, the cut film was stretched using a corner stretch type biaxial stretching test apparatus (X6-S, manufactured by Toyo Seiki Seisakusho). Specifically, the distance between chucks when setting the film on the test apparatus is 80 mm, the film set on the chuck is preheated at 139 ° C., which is Tg + 15 ° C. of the film, for 3 minutes, and then stretched at 100% / min. Biaxial stretching was successively carried out at a speed such that the respective stretching ratios were doubled in the longitudinal and transverse directions.

  After the completion of stretching, 20 seconds after the chuck was stopped, the film was quickly taken out from the test apparatus and cooled to obtain a retardation film having a thickness of 40 μm. The retardation shown by the obtained retardation film is shown in Table 1 below.

(Comparative Example 1)
An unstretched film having a thickness of 160 μm was obtained in the same manner as in Example 1 except that the pellet (A-1) produced in Production Example 1 was used instead of the pellet (A-2). The obtained unstretched film had a Tg of 130 ° C.

  Next, the obtained unstretched film was sequentially biaxially stretched in the same manner as in Example 1 to obtain a retardation film having a thickness of 41 μm. The retardation shown by the obtained retardation film is shown in Table 1 below. The stretching temperature during sequential biaxial stretching was 145 ° C. (similar to Example 1, Tg + 15 ° C. of unstretched film).

(Example 2)
The pellet (A-4) produced in Production Example 4 was melt-extruded under the following conditions using a single screw extruder (cylinder diameter 20 mm) to produce an unstretched film having a thickness of 250 μm. The obtained unstretched film had a Tg of 127 ° C. In addition, the obtained unstretched film is roll shape, and makes the width direction of the roll in the said film TD direction, and makes the extending | stretching direction (direction orthogonal to TD direction in a film surface) MD direction.
Cylinder temperature: 260 ° C
Die: Coat hanger type, width 150mm, temperature 270 ° C
Casting: 2 rolls with gloss, 1st roll and 2nd roll are kept at 105 ° C

  After producing an unstretched film, the state of the casting roll surface was visually confirmed, but no deposits were confirmed.

  Next, the obtained unstretched film was successively biaxially stretched in the same manner as in Example 1 except that the stretching speed was 200% / min and the stretching ratio was 1.8 times in both the MD direction and the TD direction. A retardation film having a thickness of 67 μm was obtained. The retardation and turbidity change amount of the obtained retardation film are shown in Table 1 below. The stretching temperature during sequential biaxial stretching was 142 ° C. (similar to Example 1, Tg + 15 ° C. of unstretched film).

(Example 3)
An unstretched film having a thickness of 250 μm was obtained in the same manner as in Example 2 except that the pellet (A-5) produced in Production Example 5 was used instead of the pellet (A-4). The obtained unstretched film had a Tg of 130 ° C.

  After producing an unstretched film, the state of the casting roll surface was visually confirmed, but a slight amount of deposits was confirmed.

  Next, the obtained unstretched film was sequentially biaxially stretched in the same manner as in Example 2 to obtain a retardation film having a thickness of 68 μm. The retardation and turbidity change amount of the obtained retardation film are shown in Table 1 below. The stretching temperature during sequential biaxial stretching was 145 ° C. (similar to Example 1, Tg + 15 ° C. of unstretched film).

(Comparative Example 2)
An unstretched film having a thickness of 250 μm was obtained in the same manner as in Example 2 except that the pellet (A-3) produced in Production Example 3 was used instead of the pellet (A-4). Tg of the obtained unstretched film was 132 degreeC.

  After producing an unstretched film, the state of the casting roll surface was visually confirmed, but no deposits were confirmed.

  Next, the obtained unstretched film was sequentially biaxially stretched in the same manner as in Example 2 to obtain a retardation film having a thickness of 71 μm. The retardation and turbidity change amount of the obtained retardation film are shown in Table 1 below. The stretching temperature during sequential biaxial stretching was 147 ° C. (Tg + 15 ° C. of unstretched film as in Example 1).

(Comparative Example 3)
An unstretched film having a thickness of 250 μm was obtained in the same manner as in Example 2 except that the pellet (A-6) produced in Production Example 6 was used instead of the pellet (A-4). Before taking, the surface state was visually confirmed, and innumerable striped patterns thought to be caused by bleed-out of low molecular weight compounds were generated. Moreover, when the surface state of the casting roll was visually confirmed, a large number of deposits considered to be a bleed-out low molecular weight compound were confirmed on the surface of the roll.

  As shown in Table 1, by including the compound (B), the retardation of the produced retardation film was improved both in the in-plane retardation Re and in the thickness direction retardation Rth. In addition, the phase difference of the comparative example 2 which does not contain a compound (B) is larger than the comparative example 1 because the content rate of the lactone ring structure in the comparative example 2 is larger than the comparative example 1.

  Further, as shown in the turbidity change amounts of Examples 2 and 3, the compound (B) hardly bleeded out due to the heat applied after the film formation.

  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 (9)

A retardation film comprising a resin composition containing an acrylic resin (A) having a ring structure in the main chain,
The resin composition includes a compound (B) having a 2,4,6-triphenyl-1,3,5-triazine skeleton as a retardation increasing agent that increases the retardation exhibited by the retardation film,
A retardation film having a thickness direction retardation Rth of 30 nm or more with respect to light having a wavelength of 589 nm.   The retardation film according to claim 1, wherein a retardation Rth in the thickness direction (per thickness of 100 μm) with respect to light having a wavelength of 589 nm is 50 nm or more.   The retardation film according to claim 1, wherein an in-plane retardation Re for light having a wavelength of 589 nm is 30 nm or more.   The retardation film according to claim 1, wherein at least one of the phenyl groups constituting the skeleton is a hydroxyphenyl group. The retardation film according to claim 1, wherein the compound (B) has a structure represented by the following formula (1).

R ¹ in Formula (1) is a hydrogen atom or a group represented by the formula “—OR ⁵ ”, and R ⁵ is a C 1-18 alkyl group or alkyl ester group. R < ² > -R < ⁴ > in Formula (1) is a hydrogen atom or a C1-C18 alkyl group or alkylester group mutually independently.   The retardation film according to claim 1, wherein the molecular weight of the compound (B) is 600 or more.   The retardation film according to claim 1, wherein the molecular weight of the compound (B) is 900 or more.   The retardation film according to claim 1, which is obtained by stretching an original film obtained by melt-extruding the resin composition.   The retardation film according to claim 1, which has a glass transition temperature of 110 ° C. or higher.