JP2011102868A - Optical compensation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical compensation film that has large retardation in a film surface and in a thickness direction, has inverse wavelength dispersion where its retardation increases with wavelength of light used for measurement, has no film warpage (curling) and film smoothness. <P>SOLUTION: The optical compensation film is formed by laminating at least two or more maleimide system resin layers on a cellulose system film base material and has inverse wavelength dispersion. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical compensation film, in particular, a film in which at least two maleimide resin layers are laminated on a cellulose-based film substrate, and relates to an optical compensation film for a liquid crystal display element having reverse wavelength dispersion of retardation. It is.

  Liquid crystal displays are widely used as the most important display devices in the multimedia society, from mobile phones to computer monitors, notebook computers, and televisions. Many optical films are used in liquid crystal displays to improve display characteristics.

  In particular, the optical compensation film plays a major role in improving the contrast when viewed from the front or obliquely, compensating for the color tone, and the like. As a conventional optical compensation film, a biaxially stretched film of polycarbonate, cyclic polyolefin, or cellulose resin is used. These films have problems such as the need for a biaxial stretching process and difficulty in obtaining uniformity of retardation in the stretching process. In particular, in a large-area film, it becomes even more difficult to control the retardation produced by biaxial stretching.

  As a method for solving the problem due to stretching, studies have been made on an optical compensation film that exhibits an uncompensated optical compensation function by coating.

  Harris and Chen of Akron University have proposed an optical compensation film made of rigid rod-like polyimide, polyester, polyamide, poly (amide-imide), and poly (ester-imide) (see, for example, Patent Documents 1 and 2). Since these materials have spontaneous molecular orientation, they are characterized by developing a phase difference without undergoing a stretching process by coating.

  Furthermore, an optical compensation film made of polyimide with improved polyimide coating properties (solubility in a solvent) (see, for example, Patent Document 3), and a polarizing plate in which a protective film of a polarizing plate is coated with a discotic liquid crystal compound (for example, Patent Document 4) and the like have been proposed.

  Moreover, the stretched film (for example, refer patent document 5) which consists of a phenylmaleimide-isobutene copolymer is proposed.

  Further, an optical compensation film formed by uniaxially stretching a coating film made of maleimide resin is disclosed (for example, see Patent Document 6).

  In recent years, in response to the improvement of the characteristics of liquid crystal displays, there is a strong demand for optical compensation films such as retardation films. For example, the broadband property of retardation is regarded as important.

  For example, in a normal retardation film using polycarbonate, cyclic olefin resin, or the like, when a retardation of a quarter wavelength is expressed by a single sheet, it is generally a quarter wavelength of 550 nm (green light). .5 nm, but on the short wavelength side, for example, the wavelength is 450 nm (blue light), which is larger than the quarter wavelength of 112.5 nm, and on the long wavelength side, for example, the wavelength is 650 nm (red light). The optical compensation of the liquid crystal display is not sufficient in order to show wavelength dependence that is smaller than the four wavelengths of 162.5 nm, that is, the phase difference on the long wavelength side is smaller than the phase difference on the short wavelength side. A pure black display cannot be made, and the color becomes bluish-purple, which deteriorates the display quality of the display. As a method for solving this problem, a method of laminating a normal quarter-wave retardation film and a half-wave retardation film has been proposed (see, for example, Non-Patent Document 1). According to the proposed method, the wavelength dependence of retardation is improved by laminating two retardation films under specific conditions. However, since two films are required, the film thickness is increased and the weight is increased. There is a problem to do.

  Therefore, an attempt has been made to improve the wavelength dependence of the retardation with a single retardation film, and a copolymer having a positive birefringence unit and a negative birefringence unit, or a polymer exhibiting positive birefringence and a negative birefringence unit. It has been proposed to use a blend of polymers exhibiting birefringence (see, for example, Patent Documents 7, 8, and 9).

  In addition, optical materials such as optical films and optical adhesives using optically anisotropic fine particles have been proposed (see, for example, Patent Document 10 and Non-Patent Document 2).

US Pat. No. 5,344,916 Japanese National Patent Publication No. 10-508048 Japanese Patent Laid-Open No. 2005-070745 Japanese Patent No. 2565644 JP 2004-269842 A JP 2009-156908 A JP 2000-137116 A JP 2001-337222 A JP 2001-235622 A JP 2005-156864 A

H. Yoshimi, S .; Yano, Y. et al. Fujimura, SID '02 Digest p862 (2002) Polymer Science Society Proceedings 2003 Vol. 52, no. 4, 748 pages

  However, since the polymer used in the methods proposed in Patent Documents 1 to 3 is an aromatic polymer, the wavelength dependence of the retardation is large, and when used as an optical compensation film of a liquid crystal display element, image quality such as color shift is obtained. It had the subject of a fall.

  In addition, the method using the discotic liquid crystal compound proposed in Patent Document 4 not only has problems such as requiring uniform alignment of the liquid crystal compound, complicating the coating process, and large alignment unevenness. Since the liquid crystal compound is mainly composed of an aromatic compound, it also has a quality problem that the wavelength dependency of retardation is large.

  The stretched film obtained in Patent Document 5 does not develop a phase difference only by coating (nx = ny = nz).

  Patent Document 6 describes a coating film obtained by uniaxially stretching a coated film, such as phase difference characteristics, wavelength dependence, and film smoothness when a film coated with two or more layers is uniaxially stretched. The improvement effect is not described.

  The stretched film obtained in Patent Document 7 is a retardation film in which the birefringence Δn at a wavelength of 400 to 700 nm is larger as the wavelength is longer by polymer-orienting the cellulose acetate resin with an acetylation degree of 2.5 to 2.8, For controlling the wavelength dispersion, it is necessary to control the degree of acetylation, and there is no description of wavelength dispersion control using a cellulose resin regardless of the degree of acetylation.

  The stretched film obtained in Patent Document 8 is a retardation film in which the retardation is increased toward the longer wavelength side by providing a film made of a polymer blend having positive and negative intrinsic birefringence, and obtained in Patent Document 9. The stretched film uses a graft copolymer, and the phase difference is obtained by imparting orientation using a norbornene chain showing positive uniaxiality, a styrene chain showing negative uniaxiality, and a styrene copolymer chain as its components. It is a retardation film that becomes larger as it goes longer, and it is a combination of positive and negative birefringence. It is a polymer blend or copolymer, and describes a coated film obtained by uniaxially stretching a coated film. About improvement effect such as retardation characteristics, wavelength dependence and film smoothness when uniaxially stretching a film coated with two or more layers It has not been described.

  Patent Document 10 and Non-Patent Document 1 control birefringence by orienting a film that is a composite of optically anisotropic particles and a polymer. When a film coated with two or more layers is uniaxially stretched It does not describe improvement effects such as retardation characteristics, wavelength dependency and film smoothness.

  Therefore, the present invention aims to provide an optical compensation film having excellent optical characteristics, and more specifically, at least two specific maleimide resin layers having excellent transparency on a cellulose-based film substrate. A film in which more than one layer is laminated, and has an in-plane retardation amount (hereinafter referred to as Re) and an out-of-plane retardation amount (hereinafter referred to as Rth), and the retardation amount increases with the wavelength of light used for measurement. An object of the present invention is to provide an optical compensation film having no film curl (warping) exhibiting dispersibility and excellent film smoothness.

  As a result of intensive studies in view of the above problems, the present inventors have found that an optical film having a reverse wavelength dispersibility is a film in which at least two maleimide-based resin layers are laminated on a cellulose-based film substrate. As a result, the present invention was completed.

  That is, the present invention is a film in which at least two maleimide resin layers are laminated on a cellulose film substrate, and the retardation amount increases with wavelength, that is, measured with light having a measurement wavelength of 450 nm inclined by 40 degrees. The wavelength dependency (R450 / R550) of the phase difference amount indicated by the ratio of the phase difference amount (R450) and the phase difference amount (R550) measured with light having a measurement wavelength of 550 nm is smaller than 1.0, and the measurement wavelength is 630 nm. The wavelength dependence (R630 / R550) of the phase difference indicated by the ratio of the phase difference (R630) measured with light and the phase difference (R550) measured with light having a measurement wavelength of 550 nm is greater than 1.0. The present invention relates to an optical compensation film which exhibits such wavelength dispersion behavior and is a smooth film without curling.

  Hereinafter, the present invention will be described in detail.

  Examples of the cellulose-based film substrate used in the optical compensation film of the present invention include films made of a cellulose meter resin mainly composed of triacetyl cellulose resin, cellulose acetate butyrate resin, cellulose acetate acetate propionate resin, and the like. It is preferable to use a triacetyl cellulose-based resin as a film substrate because it is excellent in transparency, strength, and adhesiveness, and is suitable for controlling the wavelength dependency of the retardation amount. Here, the cellulose film may be a blend of a birefringence improver for controlling birefringence in addition to an additive such as a plasticizer and an ultraviolet stabilizer, and further a cellulose film that is stretched and oriented. It may be. As the plasticizer, UV stabilizer and birefringence improver used here, known ones can be used, and they may be stretched by a known method as a uniaxial or biaxial stretching method as a means for stretching the cellulose film.

  Examples of the maleimide resin used for the maleimide resin film of the optical compensation film of the present invention include N-substituted maleimide polymer resin and N-substituted maleimide-maleic anhydride copolymer resin. Examples of the constituting N-substituted maleimide residue unit include an N-substituted maleimide residue unit represented by the following general formula (1).

(Here, R ₁ is a linear alkyl group having 1 to 18 carbon atoms, a branched alkyl group having 1 to 18 carbon atoms, a cyclic alkyl group having 1 to 18 carbon atoms, a halogen group, an ether group, an ester group, Indicates an amide group.)
R ₁ in the N-substituted maleimide residue unit represented by the general formula (1) is a linear alkyl group having 1 to 18 carbon atoms, a branched alkyl group having 1 to 18 carbon atoms, or cyclic having 1 to 18 carbon atoms. An alkyl group, a halogen group, an ether group, an ester group, an amide group. Examples of the linear alkyl group having 1 to 18 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, and an n- A hexyl group, an n-octyl group, an n-lauryl group and the like can be mentioned. Examples of the branched alkyl group having 1 to 18 carbon atoms include isopropyl group, isobutyl group, s-butyl group and t-butyl group. Examples of the cyclic alkyl group having 1 to 18 carbon atoms include a cyclohexyl group, and examples of the halogen group include chlorine, bromine, fluorine, iodine and the like, preferably an n-butyl group and an n-hexyl group. Group, n-octyl group, isobutyl group, s-butyl group and t-butyl group, particularly preferably n-butyl group, n-hexyl group and n-octyl group.

  Specific examples of the N-substituted maleimide residue unit represented by the general formula (1) include, for example, N-methylmaleimide residue unit, N-ethylmaleimide residue unit, Nn-propylmaleimide residue unit, N -N-butylmaleimide residue unit, N-hexylmaleimide residue unit, Nn-octylmaleimide residue unit, Nn-laurylmaleimide residue unit, N-isopropylmaleimide residue unit, N-isobutylmaleimide residue Group units, Ns-butylmaleimide residue units, Nt-butylmaleimide residue units, N-cyclohexylmaleimide residue units, N-chloroethylmaleimide residue units, N-methoxyethylmaleimide residue units, etc. An optical compensation film that includes one or two or more types, particularly that easily develops a phase difference, and is excellent in solubility in a solvent and mechanical strength. Therefore, Nn-butylmaleimide residue unit, Nn-hexylmaleimide residue unit, Nn-octylmaleimide residue unit, N-isobutylmaleimide residue unit, Ns-butylmaleimide residue unit Units and Nt-butylmaleimide residue units are preferable, and Nn-butylmaleimide residue units, Nn-hexylmaleimide residue units, and Nn-octylmaleimide residue units are particularly preferable.

  Specific N-substituted maleimide-maleic anhydride copolymer resins include, for example, N-methylmaleimide-maleic anhydride copolymer resin, N-ethylmaleimide-maleic anhydride copolymer resin, N-chloroethylmaleimide -Maleic anhydride copolymer resin, N-methoxyethylmaleimide-maleic anhydride copolymer resin, Nn-propylmaleimide-maleic anhydride copolymer resin, N-isopropylmaleimide-maleic anhydride copolymer resin Nn-butylmaleimide-maleic anhydride copolymer resin, N-isobutylmaleimide-maleic anhydride copolymer resin, Ns-butylmaleimide-maleic anhydride copolymer resin, Nt-butylmaleimide -Maleic anhydride copolymer resin, Nn-hexylmaleimide-maleic anhydride copolymer resin N- cyclohexyl maleimide - maleic anhydride copolymer resin, N-n-octyl maleimide - maleic anhydride copolymer resin, N-n-lauryl maleimide - can be mentioned maleic anhydride copolymer resin.

  Among them, the Nn-butylmaleimide polymer resin, the Nn-hexylmaleimide polymer resin, and the Nn-butylmaleimide polymer resin, which are particularly excellent in film forming properties during film formation, become an optical compensation film excellent in optical compensation function and heat resistance, Nn-octylmaleimide polymer resin and Nn-octylmaleimide-maleic anhydride copolymer resin are preferred.

  In addition, the maleimide resin constituting the maleimide resin film in the optical compensation film of the present invention has a residue unit other than the N-substituted maleimide residue unit and the maleic anhydride residue unit unless departing from the object of the present invention. The residue unit may be, for example, a styrene residue unit such as a styrene residue unit or an α-methylstyrene residue unit; an acrylic acid residue unit; a methyl acrylate residue unit; Acrylic ester residue units such as ethyl acrylate residue units and butyl acrylate residue units; methacrylic acid residue units; methyl methacrylate residue units, ethyl methacrylate residue units, butyl methacrylate residue units, etc. Methacrylic acid ester residue units; vinyl ester residue units such as vinyl acetate residue units and vinyl propionate residue units; acrylo It can be exemplified one or two or more such methacrylonitrile residue unit; tolyl residue unit.

Moreover, as this maleimide-type resin, the number average molecular weight (Mn) of standard polystyrene conversion obtained from the elution curve measured by gel permeation chromatography (henceforth GPC) is 1 * 10 < ³ > or more. In particular, it is preferably 2 × 10 ⁴ or more and 2 × 10 ⁵ or less because it is an optical compensation film having excellent mechanical properties and excellent moldability during film formation.

  The maleimide resin constituting the maleimide resin film in the optical compensation film of the present invention may be produced by any method as long as the maleimide resin can be obtained. For example, N-substituted maleimides and anhydrous maleic acid may be used. It can be produced by radical polymerization or radical copolymerization using an acid, and optionally a monomer copolymerizable with N-substituted maleimides. Examples of N-substituted maleimides include N-methylmaleimide, N-ethylmaleimide, N-chloroethylmaleimide, N-methoxyethylmaleimide, Nn-propylmaleimide, N-isopropylmaleimide, Nn- 1 such as butylmaleimide, N-isobutylmaleimide, Ns-butylmaleimide, Nt-butylmaleimide, Nn-hexylmaleimide, N-cyclohexylmaleimide, Nn-octylmaleimide, Nn-laurylmaleimide Examples of the copolymerizable monomer include styrenes such as styrene and α-methylstyrene; acrylic acid; acrylic esters such as methyl acrylate, ethyl acrylate, and butyl acrylate. Methacrylic acid; methyl methacrylate, methacrylate Methacrylic acid esters such as butyl methacrylate, vinyl acetate, vinyl propionate, vinyl pivalate, vinyl laurate, vinyl stearate, etc .; acrylonitrile; one or more of methacrylonitrile, etc. Can be mentioned.

  Further, as the radical polymerization method, it can be carried out by a known polymerization method, and for example, any of a bulk polymerization method, a solution polymerization method, a suspension polymerization method, a precipitation polymerization method, an emulsion polymerization method and the like can be adopted. .

  Examples of the polymerization initiator used in the radical polymerization method include benzoyl peroxide, lauryl peroxide, octanoyl peroxide, acetyl peroxide, di-t-butyl peroxide, t-butylcumyl peroxide, and dicumyl peroxide. , Organic peroxides such as t-butylperoxyacetate and t-butylperoxybenzoate; 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (2-butyronitrile), 2 , 2′-azobisisobutyronitrile, dimethyl-2,2′-azobisisobutyrate, 1,1′-azobis (cyclohexane-1-carbonitrile) and the like.

  And there is no restriction | limiting in particular as a solvent which can be used in a solution polymerization method, a suspension polymerization method, a precipitation polymerization method, and an emulsion polymerization method, For example, aromatic solvents, such as benzene, toluene, xylene; Methanol, ethanol, propyl alcohol, butyl alcohol Alcohol solvents such as cyclohexane, dioxane, tetrahydrofuran (THF), acetone, methyl ethyl ketone, dimethylformamide, isopropyl acetate, water, N-methylpyrrolidone, and the like, and mixed solvents thereof.

  Moreover, the polymerization temperature at the time of performing radical polymerization can be suitably set according to the decomposition temperature of a polymerization initiator, and generally it is preferable to carry out in the range of 40-150 degreeC.

  The optical compensation film of the present invention is an optical compensation film comprising a film obtained by laminating at least two or more maleimide resin layers on a cellulosic film substrate. As a preferable production method, for example, maleimide is formed on a cellulosic film substrate. A method of manufacturing by coating a maleimide resin solution consisting of a resin and a solvent and drying to obtain a maleimide resin film on a cellulose film substrate, followed by uniaxial stretching in the glass transition temperature range of the cellulose film Is mentioned.

  Here, the solvent to be used is not particularly limited as long as the maleimide resin can be dissolved. For example, aromatic solvents such as toluene, xylene, chlorobenzene and nitrobenzene; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone. Solvents; ether solvents such as dimethyl ether, diethyl ether, methyl-t-butyl ether, tetrahydrofuran, dioxane; acetate solvents such as methyl acetate, ethyl acetate, acetic acid-n-propyl, isopropyl acetate, butyl acetate; hexane, cyclohexane, Hydrocarbon solvents such as octane and decane; Alcohol solvents such as methanol, ethanol, propanol, and butanol; Chlorine solvents such as carbon tetrachloride, chloroform, methylene chloride, dichloroethane, and trichloroethane ; Dimethylformamide, amide solvents such as dimethylacetamide; N- methylpyrrolidone and the like, which may be used in combination of two or more.

  Moreover, as a method of removing a solvent, methods, such as natural drying and heat drying, can be used, for example.

  Examples of the method for applying the maleimide resin include a method in which a solution in which a maleimide resin is previously dissolved in a solvent is applied on a cellulose film and then the solvent is removed by heating or the like. As a coating method at that time, for example, a doctor blade method, a bar coater method, a gravure coater method, a slot die coater method, a lip coater method, a comma coater method or the like is used. In industry, the gravure coater method is generally used for thin film coating, and the comma coater method is generally used for thick film coating. In order to apply at least two layers or more, a method in which coating is first performed on a cellulosic film substrate using any one of the above coating methods, and the coating is repeated after drying, or It is also possible to form two layers by simultaneously coating on both sides and drying. When two or more layers are repeatedly applied, it may be applied on both sides of the substrate, or may be applied on the already coated surface.

  The solvent used in the coating is not particularly limited as long as the maleimide resin can be dissolved. For example, aromatic solvents such as toluene, xylene, chlorobenzene, nitrobenzene; acetone, methyl ethyl ketone, methyl isobutyl ketone Ketone solvents such as cyclohexanone; ether solvents such as dimethyl ether, diethyl ether, methyl-t-butyl ether, tetrahydrofuran, and dioxane; acetate esters such as methyl acetate, ethyl acetate, acetic acid-n-propyl, isopropyl acetate, and butyl acetate Solvents; hydrocarbon solvents such as hexane, cyclohexane, octane, decane; alcohol solvents such as methanol, ethanol, propanol, butanol; carbon tetrachloride, chloroform, methylene chloride, dichloroethane, trichloroethane Chlorinated solvents; dimethylformamide, amide solvents such as dimethylacetamide; N- methylpyrrolidone and the like, which may be used in combination of two or more. In the coating of a solution comprising a maleimide resin and a solvent, an optical compensation film having higher transparency and excellent thickness accuracy and surface smoothness can be obtained more easily. It is preferable to set it as 2000 cps, and it is preferable to set it as 1-1000 cps especially.

  When coating this solution, an optical compensation film having excellent surface smoothness can be obtained. Therefore, the thickness of each layer of the coating film made of maleimide resin is the thickness after drying of each coating layer. It is preferable that it is 1-10 micrometers, Especially preferably, it is 2-10 micrometers.

  Examples of the method for drying a coating film made of a maleimide resin solution include a batch oven, an explosion-proof blast dryer, and a continuous drying furnace in continuous film formation.

  As a method for uniaxial stretching, a known stretching method can be used. As a known stretching method, for example, a continuous stretching apparatus such as a tenter stretching machine, a stretching machine for stretching a small sheet-like test piece, or the like can be used.

  In the uniaxial stretching process, the uniaxial stretching process temperature is determined by dynamic viscoelasticity measurement, differential scanning calorimeter, etc., the glass transition temperature range of the cellulose-based film substrate, that is, the material elasticity when the cellulose-based film is in the glass state. The glass transition temperature range where the material state transitions from the modulus to the elastic modulus of the rubber state on the high temperature side is preferably stretched, and the glass transition temperature of the cellulosic film is not less than 130 ° C. and less than 200 ° C. It is preferable to use those having a temperature of 130 ° C. or higher and lower than 180 ° C. The draw ratio is preferably 1.05 times or more and less than 3 times, and more preferably 1.05 times or more and less than 2 times.

  Examples of maleimide resins that can be used in the production method include N-substituted maleimide polymer resins, N-substituted maleimide-maleic anhydride copolymer resins, and the like, and N-substituted maleimides constituting the maleimide resins. Examples of the residue unit include an N-substituted maleimide residue unit represented by the general formula (1).

  The optical compensation film of the present invention is a film obtained by laminating at least two maleimide resin layers on a cellulose-based film substrate, and has an inverse wavelength dispersion, and is a drawing axis direction of the optical compensation film. Is the x-axis, the direction perpendicular to it is the y-axis, the out-of-plane direction is the z-axis, the refractive index in the x-axis direction is nx, the refractive index in the y-axis direction is ny, the refractive index in the z-axis direction is nz, uniaxial It is an optical compensation film characterized in that the three-dimensional refractive index relationship when the extending direction is the x axis is preferably nx> ny> nz, and there is no film curl (warp) and the film is smooth, In particular, it has an excellent optical compensation function when used as an optical compensation film.

  The in-plane retardation amount (Re) and the out-of-plane retardation amount (Rth) of the optical compensation film of the present invention are determined by the thickness of the film in which the cellulose-based film base material and the maleimide-based resin layer are laminated, and the uniaxial stretching operation of the film. It can be easily controlled.

Since the optical compensation film of the present invention is an optical compensation film that can be expected to be applied as a retardation film, an in-plane retardation amount (Re) represented by the following formula (2) when measured with light having a measurement wavelength of 550 nm. Is preferably in the range of 10 to 150 nm, more preferably 30 to 150 nm.
Re = | (nx−ny) | × d (2)
(Here, d represents the film thickness (nm) of the optical compensation film.)
Further, the out-of-plane retardation (Rth) represented by the following formula (3) is preferably in the range of 30 to 2000 nm, more preferably 30 to 1000 nm, and particularly preferably 30 to 500 nm.
Rth = ((nx + ny) / 2−nz) × d (3)
(Here, d represents the film thickness (nm) of the optical compensation film.)
The thickness of each layer of the maleimide-based resin layer is preferably 10 μm or less, and particularly preferably 2 to 10 μm because it becomes an optical compensation film that can be expected to be adapted as a retardation film.

  Since the optical compensation film of the present invention has good image quality characteristics when used in a liquid crystal display element, the optical transmittance of the optical compensation film measured according to JIS K 7361-1 (1997 edition) is high. It is preferably 85% or more, and particularly preferably 90% or more. Further, the haze (haze) of the optical compensation film measured in accordance with JIS K 7136 (2000 version) is preferably 2% or less, and particularly preferably 1% or less.

  The optical compensation film of the present invention preferably has high heat resistance from the stability of quality when used in a liquid crystal display element, and the glass transition temperature of the maleimide resin constituting the maleimide resin film is 100 ° C. or higher. Some are preferable, more preferably 120 ° C. or higher, and particularly preferably 135 ° C. or higher.

  The optical compensation film of the present invention can be used by being laminated with a polarizing plate.

  Further, the optical compensation film of the present invention may contain an antioxidant in order to improve the thermal stability. Examples of the antioxidant include hindered phenol antioxidants, phosphorus antioxidants, and other antioxidants. These antioxidants may be used alone or in combination. And since an antioxidant effect | action improves synergistically, it is preferable to use together and use a hindered phenolic antioxidant and phosphorus antioxidant, for example, 100 weight part of hindered phenolic antioxidants in that case It is particularly preferable to use a phosphorous antioxidant mixed in an amount of 100 to 500 parts by weight. Further, the addition amount of the antioxidant is preferably 0.01 to 10 parts by weight, particularly 0.5 to 1 with respect to 100 parts by weight of the maleimide resin constituting the maleimide resin film in the optical compensation film of the present invention. A range of parts by weight is preferred.

  Furthermore, as an ultraviolet absorber, for example, an ultraviolet absorber such as benzotriazole, benzophenone, triazine, or benzoate may be blended as necessary.

  The optical compensation film of the present invention is blended with other polymers, polymer electrolytes, conductive complexes, inorganic fillers, pigments, dyes, antistatic agents, antiblocking agents, plasticizers, lubricants, etc. within the scope of the invention. It may be what was done.

  The optical compensation film of the present invention is a film in which at least two maleimide resin layers are laminated on a cellulose-based film substrate and is an optical compensation film having reverse wavelength dispersion, and its optical compensation function can be easily controlled. Therefore, it is useful as an optical compensation film effective for improving the contrast and viewing angle characteristics of liquid crystal display elements, particularly VA-mode liquid crystal televisions.

  EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

-Measurement of number average molecular weight of maleimide resin-
Using gel permeation chromatography (GPC) (manufactured by Tosoh Corporation, trade name HLC-802A), dimethylformamide was used as a solvent to obtain a standard polystyrene equivalent value.

~ Measurement of glass transition temperature ~
A differential scanning calorimeter (manufactured by Seiko Denshi Kogyo Co., Ltd., trade name DSC2000) was used and the temperature was 10 ° C / min. It measured at the temperature increase rate of.

~ Measurement of light transmittance ~
As an evaluation of transparency, light transmittance was measured in accordance with JIS K 7361-1 (1997 edition).

~ Measurement of haze ~
As an evaluation of transparency, haze was measured according to JIS K 7136 (2000 version).

~ Measurement of refractive index ~
It measured using the Abbe refractometer (product made from Atago) based on JISK7142 (1981 edition).

~ Calculation of 3D refractive index ~
Using a sample tilt type automatic birefringence meter (trade name KOBRA-WR, manufactured by Oji Scientific Instruments Co., Ltd.), changing the elevation angle and measuring the in-plane retardation (Re) and the three-dimensional refractive index with light having a measurement wavelength of 550 nm It was measured. Further, the out-of-plane retardation (Rth) was calculated from the three-dimensional refractive index.

Synthesis Example 1 (Example of production of Nn-butylmaleimide polymer resin)
A glass sealed tube was charged with 32.4 g of Nn-butylmaleimide and 0.054 g of dimethyl-2,2′-azobisisobutyrate as a polymerization initiator, and after substitution with nitrogen, a polymerization temperature of 60 ° C. and a polymerization time of 5 The radical polymerization reaction was performed under time conditions. After the reaction, chloroform was added to form a polymer solution, and the polymer was precipitated by mixing with excess methanol. The obtained polymer was filtered, washed sufficiently with methanol and dried at 80 ° C. to obtain 20 g of Nn-butylmaleimide polymer resin. The number average molecular weight of the obtained Nn-butylmaleimide polymer resin was 120,000. The glass transition temperature (hereinafter referred to as Tg) was 185 ° C.

Synthesis Example 2 (Production Example of Nn-Hexylmaleimide Polymer Resin)
In a glass sealed tube, 40 g of Nn-hexylmaleimide and 0.05 g of dimethyl-2,2′-azobisisobutyrate as a polymerization initiator are charged, and after nitrogen substitution, a polymerization temperature of 60 ° C. and a polymerization time of 5 hours. The radical polymerization reaction was performed under the following conditions. After the reaction, chloroform was added to form a polymer solution, and the polymer was precipitated by mixing with excess methanol. The obtained polymer was filtered, sufficiently washed with methanol, and dried at 80 ° C. to obtain 32 g of Nn-hexylmaleimide polymer resin. The number average molecular weight of the obtained Nn-hexylmaleimide polymer resin was 160,000. Moreover, Tg was 148 degreeC.

Synthesis Example 3 (Production Example of Nn-Octylmaleimide Polymer Resin)
In a glass sealed tube, 28 g of Nn-octylmaleimide and 0.032 g of dimethyl-2,2′-azobisisobutyrate as a polymerization initiator were charged, and after nitrogen substitution, a polymerization temperature of 60 ° C. and a polymerization time of 5 hours The radical polymerization reaction was performed under the following conditions. After the reaction, chloroform was added to form a polymer solution, and the polymer was precipitated by mixing with excess methanol. The obtained polymer was filtered, washed sufficiently with methanol, and dried at 80 ° C. to obtain 15 g of Nn-octylmaleimide polymer resin. The number average molecular weight of the obtained Nn-octylmaleimide polymer resin was 270,000. Moreover, Tg was 138 degreeC.

Synthesis Example 4 (Production Example 1 of Nn-octylmaleimide-maleic anhydride copolymer resin)
In a glass sealed tube, 26 g of Nn-octylmaleimide, 2.4 g of maleic anhydride, 0.036 g of dimethyl-2,2′-azobisisobutyrate as a polymerization initiator were charged, and after substitution with nitrogen, the polymerization temperature A radical polymerization reaction was carried out under conditions of 60 ° C. and a polymerization time of 5 hours. After the reaction, chloroform was added to form a polymer solution, and the polymer was precipitated by mixing with excess methanol. The obtained polymer was filtered, sufficiently washed with methanol, and dried at 80 ° C. to obtain 19 g of Nn-octylmaleimide-maleic anhydride copolymer resin. The obtained Nn-octylmaleimide-maleic anhydride copolymer resin contained 20% by weight of maleic anhydride residue, and the number average molecular weight was 120,000. Moreover, Tg was 150 degreeC.

Example 1
The Nn-butylmaleimide polymer resin obtained in Synthesis Example 1 was dissolved in a mixed solvent composed of 50% by weight of toluene and 50 parts by weight of methyl ethyl ketone to prepare a 13% by weight of resin solid content solution, and a film coater Is applied to both sides of a 60 μm thick triacetylcellulose resin film substrate (product of Fuji Film, product name Fujitac TD60UL, thickness 60 μm, glass transition temperature range 150 to 180 ° C.) and dried at room temperature for 24 hours As a result, two coating films (maleimide-based resin layers) each having a width of 270 mm and a thickness of 7 μm were formed. Using the biaxial stretching apparatus manufactured by Imoto Seisakusho, the film on which this coating film was formed was heated at a temperature of 150 ° C. and a stretching speed of 10 mm / min. The film was stretched 1.2 times with a free width uniaxial. The physical properties of the obtained film are shown below.

  The obtained film was smooth without any film curl (warping), had a light transmittance of 91% and a haze of 0.7%, and the three-dimensional refractive index relationship of the film was nx = 1.51513, ny = 1. 51395, nz = 1.51262, nx> ny> nz, in-plane retardation amount Re = + 80 nm, out-of-plane retardation amount Rth = + 130 nm, both in-plane retardation amount and out-of-plane retardation amount The optical compensation function is developed with the wavelength as a retardation film, and the wavelength dependency of the retardation amount is R450 / R550 = 0.81 and R630 / R550 = 1.08, and the retardation amount increases with the wavelength. .

Example 2
Except for setting the draw ratio in Example 1 to 1.05 times, after forming a coating film by the same method as in Example 1, the film on which this coating film was formed was converted to a biaxial stretching apparatus manufactured by Imoto Seisakusho. Using a temperature of 155 ° C. and a stretching speed of 10 mm / min. Uniaxially stretching with a free width. The physical properties of the obtained film are shown below.

  The obtained film is smooth without film curl (warping), has a light transmittance of 91% and a haze of 0.4%, and the relationship of the three-dimensional refractive index of the film is nx = 1.51480, ny = 1. 51415, nz = 1.51275, nx> ny> nz, in-plane retardation amount Re = + 47 nm, out-of-plane retardation amount Rth = + 125 nm, both in-plane retardation amount and out-of-plane retardation amount The optical compensation function is developed with the wavelength as a retardation film, and the wavelength dependency of the retardation amount is R450 / R550 = 0.84 and R630 / R550 = 1.07, and the retardation amount increases with the wavelength. .

Example 3
The same method as in Example 1 except that two coating films each having a width of 270 mm and a thickness of 7 μm were formed on both surfaces of a triacetyl cellulose resin film substrate (product of Fuji Film, product name Fujitac TD80UL, thickness 80 μm). After forming the coating film by using a biaxial stretching apparatus manufactured by Imoto Seisakusho, the film having the coating film formed thereon was heated at a temperature of 155 ° C. and a stretching speed of 10 mm / min. The film was stretched 1.2 times with a free width uniaxial. The physical properties of the obtained film are shown below.

  The obtained film was smooth without film curl (warp), had a light transmittance of 92% and a haze of 0.5%, and the relationship of the three-dimensional refractive index of the film was nx = 1.51465, ny = 1. 51416, nz = 1.51289, nx> ny> nz, in-plane retardation amount Re = + 42 nm, out-of-plane retardation amount Rth = + 130 nm, both in-plane retardation amount and out-of-plane retardation amount It has optical compensation function such that it is expressed with the wavelength as a retardation film, and the wavelength dependency of the retardation amount is R450 / R550 = 0.83 and R630 / R550 = 1.06, and the retardation amount increases with the wavelength. .

Example 4
After forming the coating film in Example 1, the film was stretched 1.2 times in a free-width uniaxial manner by the same method as in Example 1 except that the stretching temperature was 160 ° C. The physical properties of the obtained film are shown below.

  The obtained film was smooth without film curl (warping), had a thickness of 83 μm, a light transmittance of 92.0%, and a haze of 0.4%. The relationship of the three-dimensional refractive index of the film was nx = 1. 51411, ny = 1.51485, nz = 1.51274 and nx> ny> nz, in-plane retardation amount Re = + 50 nm, out-of-plane retardation amount Rth = + 118 nm, in-plane retardation amount and out-of-plane As a retardation film having both retardation amounts, it appears with the wavelength, and the wavelength dependency of the retardation amount is R450 / R550 = 0.84 and R630 / R550 = 1.08, and the retardation amount increases with the wavelength. It has a function of optical compensation.

Example 5
After forming the coating film in Example 1, the same method as in Example 1 except that the film on which the coating film was formed was set to 170 ° C. using a biaxial stretching apparatus manufactured by Imoto Seisakusho. Thus, the film was stretched 1.2 times with a free width uniaxial. The physical properties of the obtained film are shown below.

  The obtained film was smooth without film curl (warping), had a thickness of 83 μm, a light transmittance of 92.0%, and a haze of 0.4%. The relationship of the three-dimensional refractive index of the film was nx = 1. 51486, ny = 1.51401, nz = 1.51283 and nx> ny> nz, in-plane retardation amount Re = + 58 nm, out-of-plane retardation amount Rth = + 108 nm, in-plane retardation amount and out-of-plane As a retardation film having both retardation amounts, it appears with the wavelength, and the wavelength dependency of the retardation amounts is R450 / R550 = 0.89 and R630 / R550 = 1.13, and the retardation amount increases with the wavelength. It has a function of optical compensation.

Example 6
Using the Nn-hexylmaleimide polymer resin obtained in Synthesis Example 2 and chloroform as a solvent, both sides of a triacetyl cellulose resin film substrate (product name: Fujitac TD60UL, thickness 60 μm, manufactured by Fuji Film) Except that two coating films (maleimide resin films) each having a width of 270 mm and a thickness of 4 μm were formed, a coating film was formed by the same method as in Example 1, and then the film on which this coating film was formed was manufactured by Imoto Seisakusho. Using a biaxial stretching apparatus manufactured by the company, a temperature of 150 ° C. and a stretching speed of 10 mm / min. The film was stretched 1.2 times with a free width uniaxial. The physical properties of the obtained film are shown below.

  The obtained film was smooth without film curl (warp), had a light transmittance of 92% and a haze of 0.5%, and the relationship of the three-dimensional refractive index of the film was nx = 1.51962, ny = 1. 51910, nz = 1.51768, nx> ny> nz, in-plane retardation amount Re = + 32 nm, out-of-plane retardation amount Rth = + 104 nm, both in-plane retardation amount and out-of-plane retardation amount The optical compensation function is manifested with the wavelength as a retardation film, and the wavelength dependency of the retardation amount is R450 / R550 = 0.82 and R630 / R550 = 1.02, and the retardation amount increases with the wavelength. .

Example 7
Using Nn-octylmaleimide polymer resin obtained in Synthesis Example 3 as a solvent and chloroform, the width of each side of a triacetyl cellulose resin film substrate (product of Fuji Film, product name Fujitac TD60UL, thickness 60 μm) is provided. A coating film was formed by the same method as in Example 1 except that two layers of a coating film (maleimide-based resin film) having a thickness of 270 mm and a thickness of 6.5 μm were formed. Using a biaxial stretching apparatus manufactured by the company, the temperature was 155 ° C. and the stretching speed was 10 mm / min. The film was stretched 1.2 times with a free width uniaxial. The physical properties of the obtained film are shown below.

  The obtained film was smooth without film curl (warping), had a light transmittance of 90% and a haze of 0.4%, and the relationship of the three-dimensional refractive index of the film was nx = 1.51042, ny = 1. 5099, nz = 1.50848, nx> ny> nz, in-plane retardation amount Re = + 35 nm, out-of-plane retardation amount Rth = + 112 nm, both in-plane retardation amount and out-of-plane retardation amount It has optical compensation function that appears as a retardation film with a wavelength, and the wavelength dependency of the retardation amount is R450 / R550 = 0.87 and R630 / R550 = 1.09, and the retardation amount increases with the wavelength. .

Comparative Example 1
In Example 1, a coating film (maleimide-based resin layer) made of a solution of Nn-butylmaleimide polymer resin was not formed, but only a triacetyl cellulose resin film substrate was used. Using a biaxial stretching apparatus manufactured by Imoto Seisakusho, the film was heated at a temperature of 145 ° C. and a stretching speed of 10 mm / min. The film was stretched 1.2 times with a free width uniaxial. The physical properties of the obtained film are shown below.

  The obtained film was smooth without film curl (warping), had a light transmittance of 92% and a haze of 0.4%, and the relationship of the three-dimensional refractive index of the film was nx = 1.48006, ny = 1. 48006, nz = 1.47988 and nx = ny> nz, the in-plane retardation amount Re = 0 nm, the out-of-plane retardation amount Rth = + 10 nm, and the wavelength dependence of the retardation amount is R450 / R550 = 1. 02 and R630 / R550 = 1.02, and since the maleimide resin layer was not used, the amount of phase difference becomes almost constant without depending on the wavelength.

Comparative Example 2
In the same manner as in Example 1, except that the stretching temperature was 185 ° C., and a coating film (maleimide-based resin layer) made of a solution of Nn-butylmaleimide polymer resin was formed on one side with a thickness of 12 μm. Stretching was performed.

  The obtained film was smooth without film curl (warping), had a light transmittance of 91% and a haze of 0.7%, and the relationship of the three-dimensional refractive index of the film was nx = 1.51493, ny = 1. 51394, nz = 1.51284 and nx> ny> nz, in-plane retardation amount Re = + 65 nm, out-of-plane retardation amount Rth = + 105 nm, and using a single layer maleimide resin film, the retardation amount The wavelength dependency is R450 / R550 = 1.15 and R630 / R550 = 0.90, and the amount of phase difference decreases with wavelength.

Comparative Example 3
In Example 1, a coating film was formed in the same manner except that a cyclic polyolefin film (manufactured by ZEON, product name: ZEONOR film ZF14, thickness: 100 μm) was used as a base material, and a stretching process was performed.

  The obtained film is smooth without any film curl (warp), has a light transmittance of 91% and a haze of 0.5%, and the relationship of the three-dimensional refractive index of the film is nx = 1.49354, ny = 1. 49323, nz = 1.49223, nx> ny> nz, in-plane retardation amount Re = + 32 nm, out-of-plane retardation amount Rth = + 120 nm, and the wavelength dependence of the retardation amount is R450 / R550 = 1. 05 and R630 / R550 = 0.96, and since the cellulosic film was not used as the substrate, the retardation amount gradually decreased with increasing wavelength.

Comparative Example 4
In Example 1, one layer of the coating film was formed on one side, and then it was not uniaxially stretched. The obtained film has a light transmittance of 91% and a haze of 0.6%, and the relationship of the three-dimensional refractive index of the film is nx = 1.51446, ny = 1.51445, nz = 1.512128 and nx≈ny > Nz. Further, the in-plane retardation amount Re = 0 nm, the out-of-plane retardation amount Rth = + 110 nm, and the wavelength dependency of the retardation amount is R450 / R550 = 1.05 and R630 / R550 = 1.05. Since only the film was formed, an inward film curl was generated, and the amount of retardation became almost constant regardless of the wavelength.

Comparative Example 5
Stretching was performed in the same manner except that one layer of the coating film was formed on one side in Example 1. The obtained film had a light transmittance of 91% and a haze of 0.7%, and the relationship of the three-dimensional refractive index of the film was nx = 1.51463, ny = 1.51439, nz = 1.51268 and nx> ny > Nz, in-plane retardation amount Re = 15 nm, out-of-plane retardation amount Rth = + 112 nm, and the wavelength dependence of the retardation amount is R450 / R550 = 0.89 and R630 / R550 = 1.02. Since only one layer was formed, inward film curling occurred, and the amount of retardation gradually decreased with increasing wavelength.

  The above evaluation results are shown in Table 1.

Claims (10)

An optical compensation film having at least two maleimide resin layers laminated on a cellulose film substrate and having reverse wavelength dispersion. 2. The optical compensation film according to claim 1, wherein the optical compensation film is a uniaxially stretched film in a glass transition temperature range of a cellulose-based film substrate. The film stretching axis direction is the x-axis, the direction perpendicular to it is the y-axis, the out-of-plane direction is the z-axis, the refractive index in the x-axis direction is nx, the refractive index in the y-axis direction is ny, and the refraction in the z-axis direction. 3. The optical compensation film according to claim 1, wherein the three-dimensional refractive index relationship when the index is nz is nx> ny> nz. The optical compensation film according to any one of claims 1 to 3, wherein the optical compensation film is a film in which at least one maleimide resin layer is laminated on both sides of the cellulose film substrate. The optical compensation film according to any one of claims 1 to 4, wherein the maleimide-based resin layer comprises an N-substituted maleimide residue unit represented by the following general formula (1).

(Here, R ₁ is a linear alkyl group having 1 to 18 carbon atoms, a branched alkyl group having 1 to 18 carbon atoms, a cyclic alkyl group having 1 to 18 carbon atoms, a halogen group, an ether group, an ester group, Indicates an amide group.) The cellulosic film base material is a film composed of a cellulose-based resin mainly composed of a triacetyl cellulose resin, a cellulose / acetate / butyrate resin, or a cellulose / acetate / propionate resin. Optical compensation film as described in When the in-plane retardation amount Re and the out-of-film retardation amount Rth are measured with light having a measurement wavelength of 550 nm, the in-plane retardation amount (Re) represented by the following formula (2) is 10 to 150 nm. The optical compensation film according to claim 1, wherein the optical compensation film is in a range and an out-of-plane retardation (Rth) represented by the following formula (3) is in a range of 30 to 2000 nm.
Re = | (nx−ny) | xd (2)
Rth = ((nx + ny) / 2−nz) × d (3)
(Here, d represents the film thickness (nm) of the optical compensation film.) The wavelength dependence of the retardation is indicated by the ratio of the retardation (R450) measured with light having a measurement wavelength of 450 nm and the retardation (R550) measured with light having a measurement wavelength of 550 nm when the optical film is tilted by 40 degrees. (R450 / R550) is less than 1.0, and is represented by the ratio of the phase difference amount (R630) measured with light having a measurement wavelength of 630 nm and the phase difference amount (R550) measured with light having a measurement wavelength of 550 nm (R630 / R550). The optical compensation film according to claim 1, which exhibits reverse wavelength dispersion exceeding 1.0. The optical compensation film according to any one of claims 1 to 8, wherein a stretching ratio for uniaxial stretching is 1.05 times or more and less than 3 times. An optical compensation film for a liquid crystal display element, comprising the optical compensation film according to claim 1.