JP2010164902A - Positive retardation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive retardation film essentially composed of an acrylic resin, the film achieving a large retardation value and suppressing an increase in haze. <P>SOLUTION: The positive retardation film is essentially composed of an acrylic resin (A), wherein the film contains a thermoplastic resin (B) having a positive intrinsic birefringence except for an acrylic resin, by 1 to 30 wt.% as a content proportion and exhibits a haze of not more than 5% measured conforming to JIS K7136, and a retardation Rth in a thickness direction (per 100 μm film thickness) of not less than 50 nm with respect to light at a wavelength of 589 nm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a positive retardation film which is a retardation film exhibiting positive birefringence.

  A stretched film obtained by stretching a raw 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 it depends on the kind of the ring structure, the retardation exhibited by the retardation film is improved by using 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 enters the main chain, the acrylic resin becomes “hard” and “brittle”, making it difficult to sufficiently stretch the original film. Therefore, there is a limit to improving the phase difference by introducing the cyclic structure into the acrylic resin. There is. Further, the retardation film that has become hard and brittle is easily damaged when folded or torn during handling, and the content of the ring structure cannot be increased unnecessarily. As described above, the method of controlling the structure of the acrylic resin itself has a limit in improving the phase difference, and it is desired to realize a large phase difference based on other methods.

  The lactone ring structure present in the main chain has a function of imparting positive intrinsic birefringence to the resin having the ring structure. For example, PMMA, which is a homopolymer of methyl methacrylate (MMA), exhibits weak negative intrinsic birefringence, but has a lactone ring structure in the main chain with a content of a certain level or more, so that the negative Intrinsic birefringence is canceled out, resulting in an acrylic resin exhibiting positive intrinsic birefringence. A retardation film (positive retardation film) exhibiting positive birefringence is usually obtained from an acrylic resin exhibiting positive intrinsic birefringence.

  Patent Document 1 describes that, for the purpose of further improving the retardation exhibited by the retardation film, a low molecular weight material having the same sign as the birefringence sign indicated by the acrylic resin may be added to the retardation film. Examples of low-molecular substances include stilbene, biphenyl, diphenylacetylene, and liquid crystal substances ([0115], [0116]). Thus, the realization of a large phase difference is expected by the addition of the phase difference increasing agent.

  JP-A-2006-241197 (Patent Document 2) describes a low molecular compound containing two or more aromatic rings as a phase difference increasing agent. Biphenyl, dihydroxybiphenyl, diphenyl sulfide are used as the low molecular compound. Bisphenol, stilbene, diphenylacetylene, azobenzene and the like are exemplified ([0050]).

  However, these low-molecular compounds have a problem in compatibility with acrylic resins, and problems such as foaming and bleed-out are likely to occur during molding at high temperatures, particularly when an original film is formed by melt molding. When foaming or bleed-out occurs, a low molecular compound adheres to a part of a molding apparatus such as a casting roll, and the part must be cleaned during the molding, resulting in a decrease in film productivity. In addition, depending on the degree, the obtained film has many appearance or optical defects, and cannot be used as a retardation film.

  Patent Document 1 describes that the retardation film may contain a polymer other than an acrylic resin. As such a polymer, “positive birefringence (positive retardation) is increased”. In view of the above, there is a description that a polymer exhibiting positive birefringence (positive phase difference) such as vinyl chloride, polycarbonate, and other polymers containing an aromatic ring in the main chain is preferable ([0112 ]).

  If the retardation exhibited by the retardation film can be improved by adding a resin instead of a low molecular compound, the occurrence of foaming and bleed-out as when the low molecular compound is added can be suppressed. However, different resins generally have low compatibility, and in fact, a combination of an acrylic resin and polycarbonate specifically exemplified in Patent Document 1 is used as a retardation film because of an increase in haze due to phase separation or the like. A possible transparent film is not obtained. In addition, vinyl chloride cannot be used as an optical film because it becomes black due to thermal decomposition during melt-kneading and melt-molding with an acrylic resin.

JP 2008-9378 A JP 2006-241197 A

  An object of the present invention is to provide a phase difference film which is a positive phase difference film mainly composed of an acrylic resin, which can realize a large phase difference and suppresses an increase in haze.

  The positive retardation film of the present invention is a positive retardation film mainly composed of an acrylic resin (A), and contains a thermoplastic resin (B) other than an acrylic resin having positive intrinsic birefringence. The haze measured in accordance with JIS K7136 is 5% or less, and the thickness direction retardation Rth (per 100 μm film thickness) is 50 nm or more.

  The positive or negative of intrinsic birefringence is the direction in which the molecular chains in the layer are aligned (orientated) in light that is perpendicularly incident on the principal surface of the layer in a layer (for example, sheet or film) in which the molecular chains of the resin are uniaxially aligned It can be determined by the sign of the value “npr−nvt” obtained by subtracting the refractive index nvt of the layer for the vibration component perpendicular to the orientation axis from the refractive index npr of the layer for the vibration component parallel to the axis).

  The positive retardation film of the present invention shows a large retardation of a thickness direction retardation Rth (per 100 μm film thickness) of 50 nm or more, and a haze measured in accordance with JIS K7136 is 5% or less, The increase in haze is suppressed.

[Acrylic resin (A)]
The positive retardation film of the present invention contains an acrylic resin (A) as a main component. The main component in the present specification is a component having the maximum content in the retardation film, and the content is usually 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more, and still more preferably. 85% by weight or more.

  A positive retardation film is a retardation film that exhibits positive birefringence. Positive birefringence is defined as nx ′> nz ′ by the three-dimensional refractive indices nx ′, ny ′ and nz ′. Here, nx ′ is the refractive index in the main stretching direction in the retardation film plane, ny ′ is the refractive index in the direction orthogonal to the main stretching direction in the retardation film plane, and nz ′ is the thickness in the retardation film. It is the refractive index in the vertical direction (normal direction to the film surface). The main stretching direction is the stretching direction in the case of a retardation film obtained by uniaxial stretching, and is the direction stretched so that the degree of orientation is higher in the case of a retardation film obtained by biaxial stretching. In terms of chemical structure, the main stretching direction corresponds to the orientation direction of the polymer main chain contained in the film. A film made of a resin having positive intrinsic birefringence usually exhibits nx ′> nz ′, that is, positive birefringence unless a special stretching method is adopted in which the refractive index increases in the film thickness direction. It becomes a retardation film. Specifically, nx ′> ny ′ ≧ nz ′ or nx′≈ny ′> nz ′.

  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 strength of the retardation film are improved.

  The resin (A) may have a ring structure (D) in the main chain. In this case, the glass transition temperature (Tg) of the resin (A) is increased, and the heat resistance of the retardation film containing the resin (A) as a main component is improved.

  The ring structure (D) 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 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 (1) is preferable.

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 .

  The content of the lactone ring structure in the resin (A) is not particularly limited, but is usually 10 to 70% by weight, preferably 15 to 60% by weight, more preferably 20 to 55% by weight, and further 25 to 50% by weight. preferable.

  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 weight loss rate due to the reaction (ie, the dealcoholization cyclization 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 2 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 (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 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 (2) 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 (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 represented by the formula (3) is 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 (3) 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 (2) and (3) 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.

  Among the ring structures exemplified above, when the lactone ring structure, glutaric anhydride structure, glutarimide structure and maleic anhydride structure are present in the main chain of the resin (A), the resin (A) has positive intrinsic birefringence. Has the effect of giving In particular, the lactone ring structure, glutaric anhydride structure and glutarimide structure have a large effect. For this reason, when the resin (A) has at least one ring structure selected from a lactone ring structure, a glutaric anhydride structure, a glutarimide structure, and a maleic anhydride structure in the main chain, the resin (A) is a main component. In addition to improving the heat resistance of the retardation film contained as, the retardation (positive retardation) is further improved.

  Among them, at least one selected from a lactone ring structure and a glutarimide structure is more preferable, and a lactone ring structure is more preferable because a retardation film having high stability as a ring structure and excellent optical characteristics can be obtained.

  When the resin (A) has a ring structure (D) in the main chain, its glass transition temperature (Tg) is usually 110 ° C. or higher. Depending on the type of ring structure (D) and its content, the Tg of the resin (A) is 115 ° C. or higher, 120 ° C. or higher, and further 130 ° C. or higher. Such a high heat-resistant retardation film obtained by containing the resin (A) having a high Tg 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, the retardation film which has an acrylic resin as a main component is normally manufactured by melt-molding the resin composition which contains the said acrylic resin as a main component into an original film, and extending | stretching the obtained original film. When the acrylic resin contains a ring structure in the main chain, it is necessary to increase the molding temperature of the resin composition in accordance with the improvement of the Tg. When the resin composition contains a low molecular compound as a retardation increasing agent, the compound tends to bleed out due to an increase in molding temperature. On the other hand, in the retardation film of the present invention, since the retardation is improved by adding the thermoplastic resin (B), there are few appearance or optical defects due to bleed out during production. That is, the effect of the present invention by adding the thermoplastic resin (B) is particularly remarkable when the resin (A) has a ring structure (D) in the main chain.

  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, By polymerization of each monomer such as acrylonitrile, methyl vinyl ketone, ethylene, propylene, vinyl acetate, methallyl alcohol, allyl alcohol, 2-hydroxymethyl-1-butene, α-hydroxymethylstyrene, α-hydroxyethylstyrene, etc. A structural unit to be formed. Resin (A) may have 2 or more types of these structural units.

  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 including the case where it has a ring structure (D) in a principal chain.

  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.

[Thermoplastic resin (B)]
The positive retardation film of the present invention contains a thermoplastic resin (B) other than an acrylic resin. The thermoplastic resin (B) needs to exhibit optical characteristics that increase the retardation of a positive retardation film containing the resin, and therefore has at least positive intrinsic birefringence. The absolute value of the intrinsic birefringence of the resin (B) is preferably not less than the absolute value of the intrinsic birefringence of the resin (A).

  Moreover, the haze measured based on JISK7136 (how to obtain the haze of a plastic-transparent material) in the positive retardation film of the present invention is 5% or less, and the thermoplastic resin (B) has a haze of 5 or less. % Compatible with the resin (A).

  The resin (B) is not particularly limited as long as it has positive intrinsic birefringence, has such compatibility, and is a thermoplastic resin other than an acrylic resin. Resin (B) has, for example, a ring structure (C) having an action of imparting positive intrinsic birefringence to the resin (B) and a structure that improves the compatibility of the resin (B) with the resin (A). And / or an oxyalkylene structure. It is preferable that resin (B) has a ring structure (C) and a hydroxyl group and / or oxyalkylene structure in the structural unit.

  The ring structure (C) is not particularly limited as long as it has a function of imparting positive intrinsic birefringence to the resin (B). For example, the ring structure (C) may be an aromatic ring structure such as a phenylene structure or a cycloolefin group. Alternatively, it may be a non-aromatic ring structure such as the lactone ring structure or glutarimide structure described above.

  The ring structure (C) preferably has aromaticity because it has a stronger effect of imparting positive intrinsic birefringence. The aromatic ring structure (C) is, for example, a phenylene structure, an oxyphenylene structure, or a naphthylene structure.

Good oxyalkylene structure even resin (B) have is a structure represented by the formula (-R ¹⁰ O-), R ¹⁰ is an alkylene group having 1 to 8 carbon atoms. The alkylene group may be linear or branched. The oxyalkylene structure is typically an oxymethylene structure, an oxyethylene structure, an oxypropylene structure, or an oxybutylene structure.

  The resin (B) preferably has a hydroxyl group as a structure that improves the compatibility with the resin (A). The resin (B) having a hydroxyl group has particularly high compatibility with the resin (A).

  The position of the hydroxyl group in the resin (B) is not particularly limited, but it is preferably bonded to an aliphatic hydrocarbon chain, more preferably bonded to an aliphatic hydrocarbon chain present in the main chain.

  In the resin (B), it is preferable that the aromatic ring structure (C) is present in the main chain of the resin (B), and the structure that improves the compatibility with the resin (A) is a hydroxyl group. With such a resin (B), the retardation exhibited by the retardation film is further improved, and the haze of the retardation film is further reduced due to the high compatibility with the resin (A). At this time, the ring structure (C) is more preferably a phenylene structure.

  The resin (B) is, for example, a phenoxy resin. Phenoxy resin is a kind of polyhydroxy ether formed from bisphenol and epichlorohydrin. The phenoxy resin has a hydroxyl group and an oxypropylene structure in its structural unit, and is very compatible with the resin (A). For this reason, when resin (B) is a phenoxy resin, the haze of retardation film becomes smaller. Moreover, since the phenoxy resin does not have a reactive epoxy ring at the end of the molecular chain, generation of gel during melt molding for obtaining the original film is suppressed. That is, by using a phenoxy resin as the resin (B), a retardation film can be obtained in which there are few appearance or optical defects due to gel generated during molding and the haze increase is suppressed.

  The phenoxy resin has a structural unit represented by the following formula (4), for example. A phenoxy resin having a structural unit represented by the formula (4) can be produced by a dehydrochlorination reaction between bisphenol A and epichlorohydrin.

  The weight average molecular weight of the resin (B) is preferably larger than 5000, more preferably 10,000 or more, and further preferably 20000 or more.

  Resin (B) can be manufactured by a well-known method. As a method for producing a phenoxy resin, a solution polymerization method is generally used.

[Phase difference film]
The positive retardation film of this invention contains an acrylic resin (A) and a thermoplastic resin (B), and the content rate of the resin (B) in the said retardation film is 1 to 30 weight%. When the content of the resin (B) in the retardation film exceeds 30% by weight, various properties suitable as a retardation film due to the resin (A) being an acrylic resin (for example, low photoelastic coefficient, high total Light transmittance, high weather resistance, high surface hardness, etc.) are difficult to obtain. 3-25 weight% is preferable and, as for the content rate of resin (B) in the positive phase difference film of this invention, 5-20 weight% is more preferable.

  The positive retardation film of the present invention can be produced by molding a resin composition containing the resin (A) and the resin (B) to form an original film, and stretching the obtained original film.

  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 resin (B). From the viewpoint of productivity, it is preferable to produce an original film by melt extrusion. Stretching of the original film is based on a known stretching method such as uniaxial stretching (typically free end uniaxial stretching, fixed end uniaxial stretching) or biaxial stretching (typically sequential biaxial stretching, simultaneous biaxial stretching). To do.

  The positive retardation film of the present invention has a haze measured in accordance with JIS K7136 of 5% or less, and has a thickness direction retardation Rth (per 100 μm film thickness) of 50 nm or more for light having a wavelength of 589 nm. As long as the retardation film is obtained, a thermoplastic resin other than the resins (A) and (B) may be included. Such a thermoplastic resin is, for example, an acrylonitrile-styrene copolymer (AS resin). However, since AS resin has negative intrinsic birefringence, in order to obtain a positive retardation film having a retardation Rth of 50 nm or more, it is necessary to prevent the content from becoming excessively large.

  The positive retardation film of the present invention has a haze measured in accordance with JIS K7136 of 5% or less, and has a thickness direction retardation Rth (per 100 μm film thickness) of 50 nm or more for light having a wavelength of 589 nm. As long as the retardation film is obtained, materials other than the resins (A) and (B), for example, additives may be included. 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 of the additive in the positive retardation film of the present invention is, for example, 0 to 5% by weight, preferably 0 to 2% by weight, and more preferably 0 to 0.5% by weight.

  The haze in the positive retardation film of the present invention is preferably 3% or less, more preferably 1% or less.

  The positive retardation film of the present invention exhibits a large positive retardation based on the resin (B). Specifically, in the positive retardation film of the present invention, the thickness direction retardation Rth (per 100 μm of film thickness) with respect to light having a wavelength of 589 nm is 50 nm or more. Depending on the type of resin (B) and the content thereof, Rth is 60 nm or more, and further 70 nm or more.

  In the positive retardation film of the present invention, the in-plane retardation Re (per 100 μm thickness of the film) with respect to light having a wavelength of 589 nm is, for example, 50 nm or more, and depending on the type of resin (B) and its content, 75 nm or more. , 100 nm or more, and further 125 nm or more.

  When the resin (A) has a ring structure (D) in the main chain, the positive retardation film of the present invention usually has a high glass transition temperature (Tg) of 110 ° C. or higher. Depending on the type and content of the ring structure (D) 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. It becomes.

  The total light transmittance in the positive retardation film of the present invention is preferably 85% or more, more preferably 90% or more, and further preferably 92% or more.

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

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

  Initially, the evaluation method of resin (A) produced in a present Example, the pellet containing resin (A) and resin (B), an original film (unstretched film), and retardation film is 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 resins (A) and (B)]
The weight average molecular weights of the resins (A) and (B) were 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.

[Haze of retardation film]
The haze of the retardation film was measured based on JIS K7136 using a turbidimeter (Nippon Denshoku Industries Co., Ltd., NDH-5000).

[Total light transmittance of retardation film]
The total light transmittance of the retardation film was measured based on JIS K7361-1 using the turbidimeter.

(Production Example 1)
90 parts by weight of commercially available polymethyl methacrylate (PMMA) pellets (Sumitomo Chemical, Sumipex EX) and 10 parts by weight of a commercially available phenoxy resin (InChem, PKHB, weight average molecular weight: 26000) as resin (B) are dried. The mixture was blended and melt kneaded at a barrel temperature of 240 ° C. using a twin screw extruder having a 20 mmφ screw to obtain transparent pellets (P-1) made of a resin composition of an acrylic resin and a phenoxy resin.

(Production Example 2)
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) methyl 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 (Phoslex A-8, manufactured by Sakai Chemical Industry Co., Ltd.) as a cyclization condensation reaction catalyst (cyclization catalyst) was added to the obtained polymerization solution, and about 90 to 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 of ADEKA Adekastab AO-412S and 10 parts by weight of zinc octylate (manufactured by Nippon Kagaku Kogyo, A solution of 3.6% of Nikka octix zinc) in 86 parts by weight of toluene was used.

  By this series of operations, a pellet (P-2) made of an acrylic resin (A) 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 3)
Dry blend of 95 parts by weight of the pellet (P-2) prepared in Production Example 2 and 5 parts by weight of a commercially available phenoxy resin (manufactured by InChem, PKHB, weight average molecular weight 26000) as a resin (B), and a 20 mmφ screw The pellet (P-3) which consists of a resin composition of an acrylic resin and a phenoxy resin was obtained by melt-kneading at a barrel temperature of 240 ° C. using a twin screw extruder.

(Production Example 4)
98 parts by weight of the pellet (P-2) produced in Production Example 2 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 (P-4) was obtained.

Example 1
The pellet (P-1) produced in Production Example 1 was melt-extruded using a single-screw extruder (cylinder diameter 20 mm) under the following conditions to produce an unstretched film (original film) having a thickness of 100 μm. The obtained unstretched film had a Tg of 103 ° 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: 240 ° C
Die: Coat hanger type, width 150mm, temperature 250 ℃
Casting: 2 rolls with gloss, 1st roll and 2nd roll are kept at 100 ° C

  The unstretched film is formed by solidifying the resin composition extruded from the T-die on the casting roll, but after producing the unstretched film, the state of the casting roll surface was confirmed visually. Was not confirmed.

  Next, after cutting the obtained unstretched film into a rectangle of 80 mm (MD direction) × 50 mm (TD direction), the cut film was stretched using an autograph (manufactured by Shimadzu Corporation, AG-X). Specifically, the distance between chucks when setting the film on the test apparatus is 40 mm, the film set on the chuck is preheated at 108 ° C., which is Tg + 5 ° C. of the film, for 5 minutes, and then stretched at 100% / min. The free end was uniaxially stretched in the MD direction at a speed so that the stretch ratio was 2.0 times.

  After the completion of stretching, 60 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 71 μm. Table 1 below shows the retardation and haze of the obtained retardation film.

(Comparative Example 1)
An unstretched film having a thickness of 100 μm was obtained in the same manner as in Example 1 except that the PMMA pellets (Sumitomo Chemical Co., Sumipex EX) used in Production Example 1 were used instead of the pellets (P-1). The obtained unstretched film had a Tg of 104 ° C.

  Next, the obtained unstretched film was subjected to free end uniaxial stretching in the same manner as in Example 1 except that the stretching temperature was 109 ° C. which was Tg + 5 ° C. of the film to obtain a retardation film having a thickness of 71 μm. It was. Table 1 below shows the retardation and haze of the obtained retardation film.

(Example 2)
The first and second pellets (P-3) produced in Production Example 3 were used instead of the pellet (P-1), the cylinder temperature of the single screw extruder was 260 ° C., the die temperature was 270 ° C., and the casting roll An unstretched film having a thickness of 100 μm was obtained in the same manner as in Example 1 except that the temperature of the second roll was set to 105 ° C. The obtained unstretched film had a Tg of 128 ° 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 subjected to free end uniaxial stretching in the same manner as in Example 1 except that the stretching temperature was 133 ° C., which is Tg + 5 ° C. of the film, and a retardation film having a thickness of 72 μm was obtained. It was. Table 1 below shows the retardation and haze of the obtained retardation film.

(Comparative Example 2)
An unstretched film having a thickness of 100 μm was obtained in the same manner as in Example 2 except that the pellet (P-2) produced in Production Example 2 was used instead of the pellet (P-3). The obtained unstretched film had a Tg of 130 ° C.

  Next, the obtained unstretched film was subjected to free end uniaxial stretching in the same manner as in Example 1 except that the stretching temperature was set to 135 ° C. which is Tg + 5 ° C. of the film to obtain a retardation film having a thickness of 72 μm. It was. Table 1 below shows the retardation and haze of the obtained retardation film.

  As shown in Table 1, by including a phenoxy resin as the resin (B), a positive retardation film in which the retardation of the produced retardation film was improved in both Re and Rth was obtained. In addition, the Re of Comparative Example 2 that does not contain the resin (B) is larger than that of Comparative Example 1, and the Rth that was negative in Comparative Example 1 became positive in Comparative Example 2 because of the acrylic resin of Comparative Example 2 This is because the main chain has a lactone ring structure.

(Comparative Example 3)
Dry blend of 95 parts by weight of the pellet (P-2) prepared in Production Example 2 and 5 parts by weight of a commercially available polycarbonate resin (manufactured by Teijin Chemicals, Panlite L-1225Y, weight average molecular weight 48000), and a 20 mmφ screw The pellet (P-4) which consists of a resin composition of an acrylic resin and a polycarbonate resin was obtained by melt-kneading at a barrel temperature of 260 ° C. using a twin screw extruder. The obtained pellet (P-4) was cloudy and the transparency was lost.

  Next, an unstretched film having a thickness of 100 μm was produced in the same manner as in Example 2 except that the produced pellet (P-4) was used in place of the pellet (P-3). Film was obtained and apparently could not be used as an optical film.

(Comparative Example 4)
90 parts by weight of the pellets (P-2) produced in Production Example 2 and 10 parts by weight of a commercially available vinyl chloride resin (Wako) are dry blended, and a barrel temperature of 240 using a twin screw extruder having a 20 mmφ screw. Attempts to obtain a pellet made of a resin composition of an acrylic resin and a vinyl chloride resin by melting and kneading at ℃, but the vinyl chloride resin decomposes during the melt kneading and is obviously not usable as a raw material for optical films. Became a black pellet.

(Comparative Example 5)
An unstretched film having a thickness of 100 μm was obtained in the same manner as in Example 2 except that the pellet (P-4) produced in Production Example 4 was used instead of the pellet (P-3). When the surface state was visually confirmed before winding, an infinite number of striped patterns thought to be caused by the bleed-out of the low-molecular compound 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.

  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 (8)

A positive retardation film mainly composed of an acrylic resin (A),
A thermoplastic resin (B) other than an acrylic resin having positive intrinsic birefringence is contained in an amount of 1 to 30% by weight,
The haze measured in accordance with JIS K7136 is 5% or less,
A positive retardation film having a thickness direction retardation Rth (per 100 μm film thickness) of 50 nm or more with respect to light having a wavelength of 589 nm. The thermoplastic resin (B) is
A ring structure (C) having an effect of imparting positive intrinsic birefringence to the resin (B);
The positive retardation film according to claim 1, which has a hydroxyl group and / or an oxyalkylene structure as a structure for improving the compatibility of the resin (B) with the acrylic resin (A).   The positive retardation film according to claim 2, wherein the ring structure (C) has aromaticity. The ring structure (C) is present in the main chain of the thermoplastic resin (B);
The positive retardation film according to claim 3, wherein the structure for improving the compatibility is a hydroxyl group.   The positive retardation film according to claim 4, wherein the ring structure (C) is a phenylene structure.   The positive retardation film according to claim 1, wherein the thermoplastic resin (B) is a phenoxy resin.   The positive retardation film according to claim 1, wherein the acrylic resin (A) has a ring structure (D) in the main chain.   The positive retardation film according to claim 1, wherein the glass transition temperature is 110 ° C. or higher.