JP2009286910A - Protective film for phase-difference film, and laminated phase-difference film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated phase-difference film high in cracking resistance in its handling and/or in undergoing a heat-shock test, etc., and to provide a protective film for phase-difference film, capable of obtaining such a laminated phase-difference film. <P>SOLUTION: The protective film for phase-difference film is made from (B) a thermoplastic resin composition having a breaking strength of 10-50 MPa, a breaking elongation of 300-1,500%, a planar impact fracture energy of 5×10<SP>-4</SP>J/μm or greater and dynamic storage modulus and dynamic loss modulus of 1×10<SP>5</SP>to 2×10<SP>8</SP>Pa each at -40°C and at a frequency of 1 Hz. This protective film is optically nearly isotropic. The laminated phase-difference film is such that these protective films are laminated respectively on both sides of a phase-difference film made from (A) a thermoplastic resin composition having a breaking strength of 20-80 MPa, a breaking elongation of 0.5-8% and a planar impact fracture energy of 9×10<SP>-5</SP>J/μm or less. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a laminated retardation film and a protective film for a retardation film. More specifically, the present invention relates to a laminated retardation film having good crack resistance during handling, a heat shock test, and the like, and a protective film for a retardation film capable of obtaining such a laminated retardation film.

  A retardation film plays an important role as a member for improving the display performance of a liquid crystal display (LCD). Various types of retardation films are known, such as a film in which liquid crystal is oriented, but since the production efficiency is particularly excellent, stretched films obtained by orienting resin films by stretching have been widely used.

  Examples of the resin used for the stretched film include various polymers including polycarbonate. However, some of these stretched film resins have the disadvantage that they are inferior in mechanical strength when formed into a film, and thus easily break when stretched, resulting in poor production efficiency. is doing.

  For example, as a resin for a stretched film, it has been proposed to use a material having a negative optical anisotropy along with a material having a positive optical anisotropy such as polycarbonate. As a material having negative optical anisotropy, a film using a resin made of a styrenic polymer, which is excellent in transparency and has a large effect on viewing angle compensation for an LCD such as an STN type, has attracted attention (Cited Document 1). ). However, since the styrenic polymer is inferior in mechanical strength when formed into a film, it has been pointed out that the styrene polymer easily breaks when stretched and inferior in production efficiency.

  In the present invention, the material having negative optical anisotropy means the refractive index in the stretching direction when the film of this material is uniaxially stretched, that is, the refractive index in the orientation direction of the polymer main chain in terms of chemical structure. Say the smallest material. The material having positive optical anisotropy refers to a material having the maximum refractive index in the orientation direction of the polymer main chain in terms of chemical structure.

JP-A-2-256603

  Certain types of retardation film resins, such as styrene polymers and polymethyl methacrylate polymers, are mechanically brittle, so they have poor crack resistance during handling and heat shock tests, and their use is limited. there were.

  Accordingly, an object of the present invention is to provide a laminated retardation film having good crack resistance during handling, a heat shock test, and the like, and a protective film for a retardation film that can be used to obtain such a laminated retardation film. Is to provide.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have arrived at the present invention described below.

[1] Tensile strength at break of 10 to 50 MPa, elongation at break of 300 to 1500%, surface impact fracture energy of 5 × 10 ⁻⁴ J / μm or more, and dynamic storage elastic modulus and dynamic loss elasticity at a frequency of 1 Hz at −40 ° C. A protective film for a retardation film, which is made of a thermoplastic resin composition (B) having a rate of 1 × 10 ^{5 to} 2 × 10 ⁸ Pa and is optically isotropic.

[2] A retardation film made of a thermoplastic resin composition (A) having a breaking strength of 20 to 80 MPa, a breaking elongation of 0.5 to 8%, and a surface impact breaking energy of 9 × 10 ⁻⁵ J / μm or less. A laminated retardation film in which the protective film for retardation film described in [1] above is laminated on both sides of the film.

  [3] Based on the total thickness of the laminated retardation film, the thickness ratio of the retardation film is 95 to 60%, and the thickness ratio of the protective film for retardation film is 5 to 40%. The laminated retardation film as described in the above item [2], which is characterized by the following.

  [4] The thermoplastic resin composition (A) is a polystyrene resin (A-1), a polymethyl methacrylate resin (A-2), or a combination thereof, and the thermoplastic resin composition (B ) Is an ethylene copolymer resin, The laminated retardation film according to [2] or [3] above.

  [5] A liquid crystal display device comprising the laminated retardation film according to any one of [2] to [4].

  According to the present invention, there are provided a laminated retardation film having good crack resistance during handling, a heat shock test, and the like, and a protective film for a retardation film that can be used to obtain such a laminated retardation film. The The laminated retardation film of the present invention can be widely applied to liquid crystal display devices and organic EL display devices as a retardation film.

<Various measured values>
With respect to the present invention and the examples shown herein, various measurements are obtained as follows.

(1) Breaking strength The breaking strength was determined by performing a tensile test on a sample film having a width of 10 mm at 23 ° C. under a condition according to JIS C2151-1990 at a test length of 100 mm and a pulling speed of 200 mm / min. It is a value obtained from the stress of time.

(2) Elongation at break The elongation at break was determined by performing a tensile test on a sample film having a width of 10 mm at 23 ° C. in a method in accordance with JIS C2151-1990 at a test length of 100 mm and a tensile speed of 200 mm / min. It is a value obtained from strain (elongation rate) at the time of fracture.

(3) Surface impact fracture energy (50% impact fracture energy)
For surface impact fracture energy, a pin (size φ4.0 mm) is set at the center of the sample with the periphery fixed, and weight (0.5 kg (for protective film) or 0.02 kg (for retardation film) from above is set. )) Is dropped, and the fracture energy per film thickness is calculated by the data processing method (staircase method) of JIS K7211-1.

(4) Dynamic storage elastic modulus and dynamic loss elastic modulus These are values measured at a measurement temperature of −40 ° C. and a frequency of 1 Hz in a tensile mode using RSA-II manufactured by Rheometrics.

(5) Interlaminar peel strength of laminated retardation film It is a value obtained by conducting a 180 degree peel test at a tensile speed of 100 mm / min according to JIS K6854-2.

(6) In-plane retardation (Re) and photoelastic coefficient The phase difference Re value (Δnd value) and photoelastic coefficient, which are products of birefringence Δn and thickness d, use ellipsometry as a phase difference measuring means. It is a value measured by a trade name “M150” manufactured by JASCO Corporation.

(7) Thickness of retardation film protective film and retardation film Samples were taken at intervals of 10 mm in the width direction (cut to 10 mm × 10 mm), and the laminated film was embedded in an epoxy resin, and then 0 using a microtome It is a value measured by slicing to .05 μm and observing the cross section with a transmission electron microscope.

(8) Thickness of laminated retardation film A value measured with an electronic micro manufactured by Anritsu Corporation.

(9) Total light transmittance and haze These are values measured by an integrating sphere transmittance measuring device in accordance with Japanese Industrial Standard JIS K 7105 “Testing Method for Optical Properties of Plastics”. In the examples, a turbidity measuring instrument (trade name “NDH2000”) manufactured by Nippon Denshoku Industries Co., Ltd. was used as an evaluation device.

(10) Glass transition temperature (Tg)
It is a value measured by a differential scanning calorimeter of trade name “DSC2920 Modulated DSC” manufactured by TA Instruments. The conditions were a sample weight of 10 mg and a heating rate of 20 ° C./min.

<Phase difference film>
The retardation film intended to be protected by the protective film for retardation film of the present invention and the retardation film constituting the laminated retardation film of the present invention have a breaking strength of 20 to 80 MPa and a breaking elongation of 0.5 to 8 %, And a surface impact fracture energy of 9 × 10 ⁻⁵ J / μm or less is made of the thermoplastic resin composition (A). As understood from the values of the above breaking strength, breaking elongation and surface impact breaking energy, the thermoplastic resin composition (A) has a relatively small mechanical strength.

  In the thermoplastic resin composition (A) for the retardation film, the breaking strength is 20 MPa or more, preferably 40 MPa or more. If the breaking strength is less than 20 MPa, the film may crack when stretched to obtain the laminated retardation film of the present invention. In the thermoplastic resin composition (A) for the retardation film, the breaking strength is 80 MPa or less. When the breaking strength exceeds 80 MPa, the retardation film obtained from the thermoplastic resin composition (A) may have sufficient mechanical strength by itself, and therefore, according to the retardation film protective film of the present invention. The effect may not be obtained effectively.

  In the thermoplastic resin composition (A) for the retardation film, the elongation at break is 0.5% or more, preferably 2% or more. When the elongation at break is less than 0.5%, the film may crack when stretched to obtain the laminated retardation film of the present invention. In the thermoplastic resin composition (A) for the retardation film, the elongation at break is 8% or less. When the elongation at break exceeds 8%, the retardation film obtained from the thermoplastic resin composition (A) may have sufficient mechanical strength by itself, and therefore the protection for retardation film of the present invention. The effect of the film may not be obtained effectively.

In the thermoplastic resin composition (A) for the retardation film, the surface impact fracture energy is 9 × 10 ⁻⁵ J / μm or less, particularly 6 × 10 ⁻⁵ J / μm or less, more particularly 4 × 10 ^−5. J / μm or less. When the surface impact fracture energy is large, the retardation film obtained from the thermoplastic resin composition (A) may have sufficient mechanical strength by itself, and therefore the retardation film protection of the present invention. The effect of the film may not be obtained effectively.

The photoelastic coefficient when the thermoplastic resin composition (A) is unstretched is preferably −10 × 10 ⁻¹² to + 10 × 10 ⁻¹² / Pa, more preferably −7 × 10 ⁻¹² to + 7 × 10 ^−12. / Pa, particularly preferably −5 × 10 ⁻¹² to + 5 × 10 ⁻¹² / Pa. When the photoelastic coefficient when not stretched is in this range, it can be suitably used for optical applications such as a polarizing plate protective film and a retardation film.

  The thermoplastic resin composition (A) may be any thermoplastic resin composition satisfying the above conditions. Examples of the thermoplastic resin composition (A) include polystyrene resin (A-1), polymethyl methacrylate resin ( Suitable examples include those containing A-2) or both.

<Phase difference film-polystyrene resin (A-1)>
The thermoplastic resin composition (A) may be a polystyrene resin (A-1). The polystyrene resin (A-1) is a resin containing a styrene monomer component as a constituent component of the polymer. For example, the content of the styrene monomer component is more than 50% by mass, more than 60% by mass. , More than 70% by mass, or more than 80% by mass resin.

  Here, the styrene monomer means a monomer having a styrene skeleton in the structure thereof, in addition to styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, And vinyl aromatic compound monomers such as ethyl styrene, nuclear alkyl-substituted styrene such as p-tert-butyl styrene, and α-alkyl-substituted styrene such as α-methyl styrene and α-methyl-p-methyl styrene. A typical one is styrene.

  Examples of the polystyrene resin (A-1) include those obtained by copolymerizing a styrene monomer component with another monomer component. Monomers copolymerizable with styrenic monomers include methyl methacrylate, cyclohexyl methacrylate, methylphenyl methacrylate, alkyl methacrylates such as isopropyl methacrylate, and methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl Unsaturated carboxylic acid alkyl ester monomers such as alkyl acrylates such as acrylates; Unsaturated carboxylic acid monomers such as methacrylic acid, acrylic acid, itaconic acid, maleic acid, fumaric acid, cinnamic acid; maleic anhydride, itacone Unsaturated dicarboxylic acid anhydride monomers that are anhydrides such as acid, ethylmaleic acid, methylitaconic acid, chloromaleic acid; unsaturated nitrile monomers such as acrylonitrile, methacrylonitrile, Conjugated dienes such as 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, and the like. . Two or more of these monomers can be copolymerized with a styrene monomer.

  Examples of the polystyrene resin (A-1) that can be suitably used in the present invention include styrene-acrylonitrile copolymers, styrene-methacrylic acid copolymers, and styrene-maleic anhydride copolymers, Is preferably a styrene-maleic anhydride copolymer. These are preferable because they have characteristics required for optical materials such as heat resistance and transparency.

  Moreover, when a styrene-acrylonitrile copolymer, a styrene-methacrylic acid copolymer, and a styrene-maleic anhydride copolymer are used in combination with a polymethyl methacrylate resin (A-2), polymethyl methacrylate is used. Since the compatibility with the resin (A-2) is high, the transparency is high, and it is also preferable because a molded product that does not cause phase separation during use and does not deteriorate in transparency can be obtained.

  The styrene-maleic anhydride copolymer preferably has a maleic anhydride content in the copolymer of 0.1 to 50% by mass, more preferably 0.1 to 40% by mass, and still more preferably a range. Is 0.1% by mass to 30% by mass. If the maleic anhydride content in the copolymer is 0.1% by mass or more, the heat resistance is excellent, and if it is in the range of 50% by mass or less, the transparency is excellent, which is preferable.

  Different types of polystyrene resin (A-1) such as composition and molecular weight can be used in combination. These can be obtained by known anion, block, suspension, emulsion or solution polymerization methods. In the styrene resin, the unsaturated double bond of the benzene ring of the conjugated diene or styrene monomer may be hydrogenated. The hydrogenation rate can be measured by a nuclear magnetic resonance apparatus (NMR). In the present invention, the polystyrene resin refers to a resin component containing more than 50% by weight of a styrene monomer.

<Phase difference film-polymethyl methacrylate resin (A-2)>
The thermoplastic resin composition (A) may be a polymethyl methacrylate resin (A-2). The polymethyl methacrylate resin (A-2) is a resin containing a methyl methacrylate monomer component as a constituent component of the polymer. For example, the content of the polymethyl methacrylate monomer component is 50. It is a resin of more than mass%, more than 60 mass%, more than 70% mass, or more than 80 mass%.

  The polymethyl methacrylate resin (A-2) may be, for example, a homopolymer of methyl methacrylate or a copolymer of methyl methacrylate and another monomer. Monomers that can be copolymerized with methyl methacrylate include other methallylic acid alkyl esters; acrylic acid alkyl esters; styrene and o-methyl styrene, p-methyl styrene, 2,4-dimethyl styrene, ethyl styrene, Aromatic vinyl compounds such as alkyl-substituted styrenes such as p-tert-butylstyrene and α-alkyl-substituted styrenes such as α-methylstyrene and α-methyl-p-methylstyrene; cyanides such as acrylonitrile and methacrylonitrile And vinylids; maleimides such as N-phenylmaleimide and N-cyclohexylmaleimide; unsaturated carboxylic acid anhydrides such as maleic anhydride; and unsaturated acids such as acrylic acid, methacrylic acid and maleic acid.

  Of these monomers copolymerizable with methyl methacrylate, acrylic acid alkyl esters are particularly preferred because of their excellent thermal decomposition resistance, and methacrylic resins obtained by copolymerizing alkyl acrylates are It is preferable in terms of high fluidity during molding. The amount of alkyl acrylates used when methyl acrylate is copolymerized with methyl methacrylate is preferably 0.1% by weight or more from the viewpoint of thermal decomposition resistance, and 15% from the viewpoint of heat resistance. % Or less is preferable. The amount of alkyl acrylates used in this case is more preferably 0.2 wt% or more and 14 wt% or less, and particularly preferably 1 wt% or more and 12 wt% or less. Among these alkyl acrylates, especially methyl acrylate and ethyl acrylate are most preferable because they have a remarkable improvement effect even when only a small amount is copolymerized with methyl methacrylate. The said monomer copolymerizable with methyl methacrylate can also be used 1 type or in combination of 2 or more types.

  The polymethyl methacrylate resin (A-2) preferably has a weight average molecular weight of 50,000 to 200,000. The weight average molecular weight is desirably 50,000 or more from the viewpoint of the strength of the molded product, and desirably 200,000 or less from the viewpoint of molding processability and fluidity. A more desirable weight average molecular weight range is 70,000 to 150,000. In the present invention, isotactic polymethacrylate and syndiotactic polymethacrylate can be used simultaneously.

  As a method for producing an acrylic resin, for example, generally used polymerization methods such as cast polymerization, bulk polymerization, suspension polymerization, solution polymerization, emulsion polymerization, and anionic polymerization can be used. It is preferable to avoid mixing of foreign substances as much as possible. From this viewpoint, bulk polymerization or solution polymerization without using a suspending agent or an emulsifier is desirable. When solution polymerization is performed, a solution prepared by dissolving a mixture of monomers in an aromatic hydrocarbon solvent such as toluene or ethylbenzene can be used. In the case of polymerization by bulk polymerization, the polymerization can be started by irradiation with free radicals generated by heating or ionizing radiation as is usually done.

  As the initiator used in the polymerization reaction, any initiator generally used in radical polymerization can be used. For example, azo compounds such as azobisisobutylnitrile, benzoyl peroxide, lauroyl peroxide, t-butylperoxy An organic peroxide such as -2-ethylhexanoate is used. In particular, when the polymerization is carried out at a high temperature of 90 ° C. or higher, solution polymerization is generally used. Therefore, the initiator used for the polymerization reaction has a 10-hour half-life temperature of 80 ° C. or higher and can be used as an organic solvent. Preferred are soluble peroxides, azobis initiators and the like.

  Specifically, the initiator used for the polymerization reaction is 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, cyclohexane peroxide, 2,5-dimethyl-2,5-di (Benzoylperoxy) hexane, 1,1-azobis (1-cyclohexanecarbonitrile), 2- (carbamoylazo) isobutyronitrile and the like can be mentioned. These initiators are used in the range of 0.005 to 5 wt%.

  As the molecular weight regulator used as necessary in the polymerization reaction, any one used in general radical polymerization is used, for example, mercaptan compounds such as butyl mercaptan, octyl mercaptan, dodecyl mercaptan, 2-ethylhexyl thioglycolate and the like. It is mentioned as preferable. These molecular weight regulators are added in a concentration range such that the degree of polymerization is controlled within the above range.

  As the method for producing the polymethyl methacrylate resin (A-2), the method described in JP-B-63-1964 can be used. As the polymethyl methacrylate resin (A-2), two or more types having different molecular weights, compositions and the like can be used at the same time.

<Combination of retardation film-polystyrene resin (A-1) and polymethyl methacrylate resin (A-2)>
The thermoplastic resin composition (A) may be a combination of a polystyrene resin (A-1) and a polymethyl methacrylate resin (A-2). In this case, in the thermoplastic resin composition (A) composed of the polystyrene resin (A-1) and the polymethyl methacrylate resin (A-2), based on the weight of the entire thermoplastic resin composition (A), From the viewpoint of heat resistance, the content ratio (parts by weight) of the polystyrene resin (A-1) is preferably 99 to 50%, more preferably 99 to 60%, and 99 to 70%. Particularly preferred.

<Retardation film-other components>
Further, the thermoplastic resin composition (A) does not impair the object of the present invention in addition to or in place of the polystyrene resin (A-1) and / or the polymethyl methacrylate resin (A-2). Other components can be included in the range. Other components that the thermoplastic resin composition (A) can contain include polyolefins such as polyethylene and polypropylene, polyamides, polyphenylene sulfide resins, polyether ether ketone resins, polyesters, polysulfones, polyphenylene oxides, polyimides, poly Examples thereof include at least one or more of thermoplastic resins such as ether imide and polyacetal, and thermosetting resins such as phenol resin, melamine resin, silicone resin, and epoxy resin.

  Furthermore, the thermoplastic resin composition (A) can contain any additive depending on various purposes within a range that does not significantly impair the effects of the present invention. The type of additive is not particularly limited as long as it is generally used for blending resins and rubber-like polymers. Additives include inorganic fillers such as silicon dioxide; pigments such as iron oxide; lubricants such as stearic acid, behenic acid, zinc stearate, calcium stearate, magnesium stearate, and ethylene bisstearamide; mold release agents; paraffin -Based process oil, naphthenic process oil, aromatic process oil, paraffin, organic polysiloxane, mineral oil and other softeners and plasticizers; hindered phenol-based antioxidants; phosphorus-based heat stabilizers and other antioxidants; Examples thereof include ultraviolet absorbers; hindered amine light stabilizers; flame retardants; antistatic agents; reinforcing agents such as organic fibers, glass fibers, carbon fibers, and metal whiskers; coloring agents; other additives;

<Protective film for retardation film (B)>
The protective film for retardation film of the present invention has a breaking strength of 10-50 MPa, a breaking elongation of 300-1500%, a surface impact breaking energy of 5 × 10 ⁻⁴ J / μm or more, and a dynamic at a frequency of 1 Hz at −40 ° C. It is made of a thermoplastic resin composition (B) having a storage elastic modulus and a dynamic loss elastic modulus of 1 × 10 ⁵ to 2 × 10 ⁸ Pa, and is optically substantially isotropic. As understood from the values of the above breaking strength, breaking elongation, surface impact fracture energy, dynamic storage elastic modulus, and dynamic loss elastic modulus, the thermoplastic resin composition (B) has a relatively large mechanical strength. Has strength and elasticity.

  The thermoplastic resin composition (B) has a breaking strength of 10 MPa or more, preferably 20 MPa or more. If the breaking strength is less than 10 MPa, the film may be cracked during stretching in the laminated retardation film having the protective film for retardation film made of the thermoplastic resin composition (B). The retardation film protective film obtained from the resin composition (B) may not function sufficiently as a protective film for the retardation film.

  The thermoplastic resin composition (B) has a breaking elongation of 300% or more and preferably 500% or more. When the elongation at break is less than 300%, there is a risk that the film will crack in stretching in the laminated retardation film having the protective film for retardation film made of the thermoplastic resin composition (B). The protective film for retardation films obtained from a thermoplastic resin composition (B) may not fully function as a protective film for retardation films.

In the thermoplastic resin composition (B), the surface impact fracture energy is 5 × 10 ⁻⁴ J / μm or more, particularly 8 × 10 ⁻⁴ J / μm or more. When the surface impact fracture energy is small, the retardation film protective film obtained from the thermoplastic resin composition (B) may not function sufficiently as a protective film for the retardation film.

The dynamic storage elastic modulus and dynamic loss elastic modulus at a frequency of 1 Hz at −40 ° C. of the thermoplastic resin composition (B) are both 1 × 10 ⁵ to 2 × 10 ⁸ Pa, and 5 × 10 ^{5 to} 5 × 10 ⁷ Pa is preferable. When these values are less than 1 × 10 ⁵ Pa, sticking when the film is wound up may be increased. Since the protective film for retardation films made of the thermoplastic resin composition (B) is present on both sides of the laminated retardation film of the present invention, it is important to suppress sticking of the protective film for retardation films. . Moreover, when these values exceed 2 × 10 ⁸ Pa, in the laminated retardation film having a retardation film protective film made of the thermoplastic resin composition (B), there is a possibility that cracking may occur in the heat cycle test. is there.

The photoelastic coefficient when the thermoplastic resin composition (B) is not stretched is preferably −10 × 10 ⁻¹² to + 10 × 10 ⁻¹² / Pa, more preferably −7 × 10 ⁻¹² to + 7 × 10 ^−12. / Pa, particularly preferably −5 × 10 ⁻¹² to + 5 × 10 ⁻¹² / Pa. When the photoelastic coefficient at the time of unstretching is in this range, it can be suitably used for optical applications such as a polarizing plate protective film and a retardation film.

  The thermoplastic resin composition (B) may be any thermoplastic resin composition satisfying the above conditions. Examples thereof include an ethylene copolymer resin (B-1) and a polymer comprising styrene. Suitable examples include a copolymer having a block and a polymer block made of butadiene or a polymer block made of isoprene, or a hydride polymer (B-2) of the copolymer.

<Protective film for retardation film-ethylene copolymer resin (B-1)>
The thermoplastic resin composition (B) may be an ethylene copolymer resin (B-1). The ethylene-based copolymer resin (B-1) is a resin containing ethylene as a monomer component as a constituent component of the polymer. For example, the ethylene content as the monomer component exceeds 30% by mass, The resin is more than 40% by mass, more than 50% by mass, more than 60% by mass, more than 70% by mass, or more than 80% by mass.

  Examples of the ethylene copolymer resin (B-1) include those obtained by copolymerization of ethylene as a monomer component and another monomer component. Specifically, ethylene-based copolymer resin (B-1) includes ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-propyl acrylate copolymer, ethylene-butyl acrylate. Examples thereof include a copolymer, an ethylene-methyl methacrylate copolymer, an ethylene-ethyl methacrylate copolymer, an ethylene-propyl methacrylate copolymer, and an ethylene-butyl methacrylate copolymer.

  As ethylene-based copolymer resin (B-1), other copolymerizable monomers were copolymerized with ethylene and (meth) acrylic acid ester as ethylene- (meth) acrylic acid ester copolymer. A ternary or higher copolymer can also be used. Other copolymerizable monomers include, for example, α-olefins such as propylene and 1-butene, monomers having a carboxyl group such as maleic acid, maleic anhydride, fumaric acid and itaconic acid, styrene and acetic acid. Examples thereof include vinyl monomers such as vinyl.

  As the ethylene copolymer resin (B-1), the proportion of the (meth) acrylate structural unit of the ethylene- (meth) acrylate copolymer resin is preferably 5 to 50% by weight, More preferably, it is 30% by weight. There exists a possibility that the adhesive strength between each layer may fall that the ratio of a (meth) acrylic-ester structural unit is less than 5 weight%. If the proportion of the (meth) acrylic ester structural unit exceeds 50% by weight, the strength of the protective film for retardation film made of the ethylene-based copolymer resin (B-1) may be reduced and wrinkles may occur. .

<Protective film for retardation film-copolymer having a polymer block made of styrene and a polymer block made of butadiene or a polymer block made of isoprene, or a hydride polymer (B-2) of the polymer>
As a copolymer having a polymer block composed of styrene and a copolymer block composed of butadiene or a polymer block composed of isoprene, or a hydride polymer (B-2) of the copolymer, styrene and a conjugated diene ( Examples thereof include a block or random copolymer with butadiene, isoprene, etc., and a block or random copolymer with styrene and hydrogenated conjugated diene (butadiene, isoprene, etc.).

  The copolymer (B-2) is preferably 5 to 80% by weight, more preferably 10 to 70% by weight, and still more preferably 15 to 50% by weight of a polymer block, and preferably 95 to 20% by weight. %, Preferably 90 to 30% by weight, and more preferably 85 to 50% by weight of a polymer block composed of butadiene or isoprene or a hydride polymer block thereof.

  In this copolymer, when the content ratio of the polymer block made of styrene is less than 5% by weight, the adhesion between the retardation film protective film and the retardation film may be lowered. On the other hand, in this copolymer, when the content ratio of the polymer block composed of styrene exceeds 80% by weight, when the laminated film of the present invention is formed by coextrusion, the protective film for retardation film and the retardation The interface with the film may be disturbed, especially the film thickness of these films may become non-uniform, and the adhesive strength between these layers will decrease over time, causing wrinkles in the laminated retardation film of the present invention There is a risk.

  Here, the block structure of the styrene monomer and the butadiene or isoprene monomer is not particularly limited, and the copolymer obtained from these is, for example, a general formula: SD; SDS; D-S-D-S; block copolymer represented by S-D-S-D-S or the like (wherein S represents a polymer block composed of styrene, D represents butadiene or isoprene) And the double bonds of polymer block D may be partially or fully hydrogenated). A triblock copolymer represented by DSD is particularly preferred.

<Protective film for retardation film-other components>
A thermoplastic resin composition (B) can contain the additive etc. which were described by thermoplastic resin composition (A) description as needed in the range which does not impair the effect of invention.

<In-plane retardation>
The protective film for retardation film is optically substantially isotropic and satisfies, for example, the following formula:
| Re (B) | ≦ 20 nm, especially 10 nm, more particularly 5 nm
(Where
Re (B): In-plane retardation of protective film for retardation film measured with light having wavelength of 400 to 700 nm (in-plane of all protective films for retardation film when a plurality of protective films for retardation film are present) Sum of retardation)).

Also preferably, the retardation film satisfies the following formula:
| Re (A) | >> | Re (B) |
(Where
Re (A): In-plane retardation of retardation film measured with light having a wavelength of 400 to 700 nm (total of in-plane retardation of all retardation films when a plurality of retardation films are present).

Re (a value of the in-plane retardation) in the present invention, the slow axis direction of the refractive indices n _x of the _film, the refractive index n _y in orthogonal directions in-plane to the slow _axis, and the thickness direction of the refractive index n _z , when the average thickness _{T w} of the film _is a value defined by _{(n x -n y) × T} w.

  The fact that the protective film for retardation film is optically isotropic means that the laminated retardation film having the protective film for retardation film and the retardation film has optical characteristics mainly resulting from the retardation film. Thereby making it possible to easily achieve optical control of the laminated retardation film.

  In addition, when | Re (A) |> | Re (B) | and | Re (B) | is 20 nm or less, the optical characteristics of the optically adjusted retardation film are effectively used. In addition, the coefficient Nz described below can be made 0.4 or less efficiently.

_{Nz = (n x -n z)} / (n z -n y)
(Where
n _x : Refractive index in the slow axis direction n _y : Refractive index in the direction perpendicular to the slow axis in the plane n _z : Refractive index in the thickness direction)

  On the other hand, if | Re (A) | ≦ | Re (B) |, the optical compensation function of the retardation film may not be sufficiently exhibited. Further, the protective film for retardation film is not optically isotropic. For example, if | Re (B) | exceeds 20 nm, the optical compensation function of the retardation film may not be sufficiently exhibited.

<Thickness ratio>
Based on the total thickness of the laminated retardation film of the present invention, the thickness ratio of the retardation film made of the thermoplastic resin composition (A) is preferably 95 to 60%, and preferably 90 to 60%. More preferably it is. If the thickness ratio of the retardation film exceeds 95%, cracks may occur in the heat cycle test of the laminated retardation film of the present invention, and if the thickness ratio of the retardation film is 60% or less, There is a possibility that the retardation stability of the laminated retardation film is deteriorated.

  Based on the total thickness of the laminated retardation film of the present invention, the thickness ratio of the protective film for retardation film made of the thermoplastic resin composition (B) is preferably 5 to 40%, and 10 to 40%. More preferably. When the thickness ratio of the protective film for retardation films exceeds 40%, the retardation stability of the laminated retardation film of the present invention may be deteriorated. Moreover, there exists a possibility that a crack may arise in the heat cycle test of a laminated phase difference film as the thickness ratio of the protective film for phase difference films is 5% or less.

<Manufacturing method>
There is no restriction | limiting in particular in the manufacturing method of the protective film for retardation films of this invention, and a laminated phase difference film. For example, a film is separately formed from a thermoplastic resin composition (A) for a retardation film and a thermoplastic resin composition (B) for a protective film for a retardation film, and the resulting unstretched film A film can be laminated by dry lamination using an adhesive, and the unstretched laminated film thus obtained can be stretched to obtain a laminated retardation film. From the thermoplastic resin composition (A) for the retardation film and the thermoplastic resin composition (B) for the protective film for the retardation film, an unstretched laminated film is formed by coextrusion, and this is done. The unstretched laminated film obtained by stretching can be stretched to obtain a laminated retardation film.

  Among these methods, film formation by coextrusion can be preferably carried out because a laminated retardation film having a high delamination strength is obtained and a laminated retardation film can be produced economically. . As the coextrusion molding method, there are a flat die coextrusion molding method using a flat die and a coinflation molding method using a cylindrical die, and the flat die coextrusion molding method is preferable.

  The flat die coextrusion molding method is a method in which a resin is heated and melted by an extruder and then coextruded from a flat die to continuously obtain a film-shaped molded product. Examples of the flat die include a T die, a coat hanger die, and a fish tail die according to the structure of the resin distribution flow path. The extruder heats and kneads the resin and extrudes the melt in the form of a film from the die with a constant extrusion amount. Usually, it is preferable to remove a gel or a foreign substance by inserting a screen or a filter between the extruder and the die. The resin used is preferably dried before being introduced into the extruder, and the content of water and volatile solvents is reduced in order to prevent the generation of fish eyes and bubbles.

  The coextrusion temperature is preferably 10 to 100 ° C. higher than the glass transition temperature of the thermoplastic resins (A) and (B), and is 10 times higher than the glass transition temperature of the thermoplastic resins (A) and (B). More preferably, the temperature is higher by -50 ° C. If the melting temperature in the extruder is excessively low, the fluidity of the resin may be insufficient. Conversely, if the melting temperature is excessively high, the resin may be deteriorated.

<Film shape>
The unstretched laminated film is preferably long. The long shape means one having a length of at least about 5 times or more with respect to the width direction of the film or laminate, preferably 10 times or more, and specifically in a roll shape. It has a length that is wound and stored or transported.

<Delamination strength>
In the laminated retardation film of the present invention, the delamination strength between the retardation film and the retardation film protective film is preferably 8 N / 25 mm or more, and more preferably 10 N / 25 mm or more. If the delamination strength of the laminated retardation film is less than 8 N / 25 mm, peeling may occur during uniaxial stretching to obtain a laminated retardation film.

<Film thickness>
The thickness of the unstretched laminated film can be appropriately determined according to the purpose of use of the obtained laminated retardation film. The thickness of the unstretched laminated film is preferably 30 to 200 μm, more preferably 50 to 150 μm, from the viewpoint of obtaining a uniform stretched film by a stable stretching process.

<Stretching method>
The laminated retardation film of the present invention is obtained by uniaxially stretching an unstretched laminated film. If the unstretched laminated film has a high delamination strength and does not cause delamination even when uniaxially stretched, a retardation film having excellent film thickness uniformity can be obtained. There is no particular limitation on the method of uniaxially stretching an unstretched laminated film. For example, it can be uniaxially stretched in the longitudinal direction by utilizing the difference in peripheral speed between rolls, or uniaxially stretched in the lateral direction using a tenter. You can also Among these, uniaxial stretching in the longitudinal direction is preferable. Although there is no restriction | limiting in particular in the draw ratio of uniaxial stretching, it is preferable that it is 1.1-3 times, and it is more preferable that it is 1.2-2.2 times.

  The laminated retardation film of the present invention has an in-plane retardation (Re) variation of 10 nm or less, preferably 5 nm or less, more preferably 2 nm or less. By setting the variation of Re within the above range, it is possible to improve the display quality when used in various display devices.

  Here, the variation in Re is the difference between the maximum value and the minimum value of Re when in-plane retardation is measured in the width direction of the film.

<Application>
An ultraviolet curable resin, a liquid crystal polymer (including a liquid crystal monomer before curing), an antireflection agent, and the like can be applied to the laminated retardation film of the present invention to form a cured resin layer or a liquid crystal polymer layer. .

  The laminated retardation film of the present invention can be widely applied to liquid crystal display devices, organic EL display devices, plasma display devices, FED (field emission) display devices, SED (surface electric field) display devices, and the like. Examples of the liquid crystal display device include an in-plane switching (IPS) mode, a vertical alignment (VA) mode, a multi-domain vertical alignment (MVA) mode, a continuous spin wheel alignment (CPA) mode, a hybrid alignment nematic (HAN) mode, Examples include a twisted nematic (TN) mode, a super twisted nematic (STN) mode, and an optically compensated bend (OCB) mode. Among these, the viewing angle compensation effect is particularly large for an IPS mode liquid crystal display device.

  The present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples. Parts and% are based on weight unless otherwise specified.

  In Examples and Comparative Examples, breaking strength, breaking elongation, surface impact fracture energy, dynamic storage elastic modulus, dynamic loss elastic modulus, delamination strength of laminated retardation film, in-plane retardation (Re), The photoelastic coefficient, the thickness of the protective film for retardation film and the retardation film, the thickness of the laminated retardation film, the total light transmittance and haze, and the glass transition temperature (Tg) were measured as described above.

The heat shock test was evaluated as follows. That is, 10 samples were prepared by laminating a laminated retardation film on a flat soda glass substrate through an adhesive, and −40 ° C. (30 minutes) and 85 ° C. (30 minutes) were applied to this sample. A heat shock test with one cycle was conducted for 100 cycles, and the presence or absence of cracks in the retardation film was evaluated as follows.
○: No cracking ×: Cracking present (when there is even one crack)

  In Examples and Comparative Examples, the following polymers and resins were used as the thermoplastic resin composition (A) for the retardation film and the thermoplastic resin composition (B) for the protective film for the retardation film. Using.

(Thermoplastic resin composition for retardation film (A))
A-1-1: Polystyrene resin (manufactured by NOVA Chemical Co., Ltd., trade name “Daylark D332”)
A-2-1: Polymethyl methacrylate resin (Kuraray Co., Ltd., trade name “Parapet G”)

(Thermoplastic resin composition (B) for protective film for retardation film)
B-1-1: Ethylene-based copolymer resin (manufactured by Sumitomo Chemical Co., Ltd., trade name “Aklift WH206”)
B-1-2: Ethylene copolymer resin (trade name “Modic AP A543” manufactured by Mitsubishi Chemical Corporation)
B-2-1: A polymer block made of styrene and a polymer made of butadiene (manufactured by Asahi Kasei Chemicals, trade name “Tufprene 126”)

Example 1
On both sides of an unstretched retardation film made of polystyrene resin (A-1-1) [manufactured by Nova Chemical Co., Ltd., trade name “Daylark D332”, glass transition temperature 134 ° C.], an ethylene copolymer resin (B- 1-1) An unstretched laminated film having an unstretched protective film for a retardation film made of [trade name “Aklift WH206” manufactured by Sumitomo Chemical Co., Ltd.] was obtained by coextrusion molding. Here, this unstretched laminated film had the following constitution: protective film for unstretched retardation film (20 μm) −unstretched retardation film (160 μm) −protection for unstretched retardation film Film (20 μm).

  This unstretched laminated film was transversely stretched by a tenter at a stretching temperature of 140 ° C., a stretching speed of 5 m / min, and a draw ratio of 2 to obtain a laminated retardation film having a thickness of 100 μm. This laminated phase difference film was affixed on a flat soda glass substrate via an adhesive. The presence or absence of cracking of the laminated retardation film by the heat shock test was evaluated.

  The evaluation results of the laminated retardation film of Example 1 are shown in Table 1. As can be seen from Table 1, the laminated retardation film of Example 1 had good delamination strength, good retardation characteristics, and was good without any cracking of the retardation film in the heat shock test.

(Examples 2 to 7)
Example 1 except that the resins listed in Table 1 were used as the thermoplastic resin composition (A) for the retardation film and the thermoplastic resin composition (B) for the protective film for the retardation film. Similarly, an unstretched laminated film was prepared, and this unstretched laminated film was stretched to produce a laminated retardation film. All evaluation results are shown in Table 1.

  As apparent from Table 1, the laminated phase difference films of Examples 2 to 7 had good delamination strength, phase difference characteristics, and crack resistance in a heat shock test.

(Comparative Example 1)
Except not laminating the retardation film protective film of Example 1, an unstretched retardation film was prepared in the same manner as in Example 1, and the unstretched retardation film was stretched to obtain a retardation film. Created. All evaluation results are shown in Table 1. The retardation film of Comparative Example 1 was cracked in the heat shock test and could not be used as a retardation film.

(Comparative Example 2)
A laminated film was prepared in the same manner as in Example 1 except that the protective film for retardation film used in Example 1 was changed to low density polyethylene (trade name “Evolue SP2520” manufactured by Mitsui Chemicals, Inc.) A retardation film was prepared, and all evaluation results are shown in Table 1. The retardation film had a low delamination strength and a large in-plane retardation, and therefore could not be used as a retardation film. .

Claims (5)

Breaking strength 10-50 MPa, breaking elongation 300-1500%, surface impact fracture energy 5 × 10 ⁻⁴ J / μm or more, and dynamic storage elastic modulus and dynamic loss elastic modulus 1 × at a frequency of 1 Hz at −40 ° C. A protective film for a retardation film, which is made of a thermoplastic resin composition (B) of 10 ^{5 to} 2 × 10 ⁸ Pa and is optically isotropic. On both surfaces of a retardation film made of a thermoplastic resin composition (A) having a breaking strength of 20 to 80 MPa, a breaking elongation of 0.5 to 8%, and a surface impact breaking energy of 9 × 10 ⁻⁵ J / μm or less. A laminated retardation film, wherein the protective film for retardation film according to claim 1 is laminated.   The thickness ratio of the retardation film is 95 to 60% based on the total thickness of the laminated retardation film, and the thickness ratio of the protective film for retardation film is 5 to 40%. The laminated retardation film according to claim 2.   The thermoplastic resin composition (A) is a polystyrene resin (A-1), a polymethyl methacrylate resin (A-2), or a combination thereof, and the thermoplastic resin composition (B) is The laminated retardation film according to claim 2, wherein the laminated retardation film is an ethylene copolymer resin.   A liquid crystal display device comprising the laminated retardation film according to claim 2.