JP6213135B2 - Trans-stilbene-N-substituted maleimide copolymer and retardation film using the same - Google Patents

Description

  The present invention relates to a novel trans-stilbene-N-substituted maleimide copolymer and a retardation film using the same, and more specifically, a retardation film having a high out-of-plane retardation even in a thin film, in particular, The present invention relates to a novel trans-stilbene-N-substituted maleimide copolymer suitable for an optical compensation film for liquid crystal display elements and a retardation film using the same.

  A liquid crystal display is widely used as a most important display device in a multimedia society, such as a mobile phone, a computer monitor, a notebook computer, and a television. Many optical films are used in liquid crystal displays to improve display characteristics. In particular, retardation films play a large role in improving contrast and compensating for color tone when viewed from the front or obliquely. As the conventional retardation film, polycarbonate or cyclic polyolefin is used, and these polymers are polymers having positive birefringence. Here, the sign of birefringence is defined as shown below.

  The optical anisotropy of the polymer film molecularly oriented by stretching or the like can be represented by a refractive index ellipsoid shown in FIG. Here, the refractive index in the fast axis direction in the film plane when the film is stretched is represented by nx, the refractive index in the film in-plane direction orthogonal thereto is represented by ny, and the refractive index in the thickness direction of the film is represented by nz. The fast axis indicates an axial direction having a low refractive index in the film plane.

  Negative birefringence means that the stretching direction is the fast axis direction, and positive birefringence means that the direction perpendicular to the stretching direction is the fast axis direction.

  That is, in the uniaxial stretching of the polymer having negative birefringence, the refractive index in the stretching axis direction is small (fast axis: stretching direction), and in the uniaxial stretching of the polymer having positive birefringence, the axial direction perpendicular to the stretching axis. Has a small refractive index (fast axis: direction perpendicular to the stretching direction).

  Many polymers have positive birefringence. As a polymer having negative birefringence, there are acrylic resin and polystyrene. However, acrylic resin has a small retardation, and the properties as a retardation film are not sufficient. Since polystyrene has a large photoelastic coefficient in the low-temperature region, it has a problem of stability of phase difference such as phase difference being changed by a slight stress, and a practical problem of low heat resistance, and is not used at present. .

  A stretched polymer film exhibiting negative birefringence has a high refractive index in the thickness direction of the film, resulting in an unprecedented retardation film. Useful as a retardation film for compensating viewing angle characteristics of displays (VA-LCD), in-plane oriented liquid crystal displays (IPS-LCD), reflective liquid crystal displays (reflective LCDs), and viewing angle compensation films for deflecting plates Therefore, the market demand is strong for retardation films having negative birefringence.

  A method for producing a film has been proposed in which a polymer having positive birefringence is used to increase the refractive index in the thickness direction of the film. One is a treatment method (for example, Patent Documents 1 to 3) in which a heat-shrinkable film is bonded to one side or both sides of a polymer film, the laminate is subjected to a heat stretching treatment, and a shrinkage force is applied in the film thickness direction of the polymer film. Reference). In addition, a method of uniaxial stretching in a plane while applying an electric field to a polymer film has been proposed (see, for example, Patent Document 4).

  In addition, a retardation film composed of fine particles having negative optical anisotropy and a transparent polymer has been proposed (for example, see Patent Document 5).

  However, the methods proposed in Patent Documents 1 to 4 have a problem that productivity is inferior because the manufacturing process becomes very complicated. In addition, the control of the uniformity of the phase difference and the like is significantly more difficult than the control by the conventional stretching.

  When polycarbonate is used as the base film, the photoelastic coefficient at room temperature is large and the phase difference is changed by a slight stress, so that there is a problem in the stability of the phase difference. Furthermore, there is a problem that the wavelength dependence of the phase difference is large.

  The retardation film obtained in Patent Document 5 is a retardation film that exhibits negative birefringence by adding fine particles having negative optical anisotropy. From the viewpoint of simplification of production method and economical efficiency, fine particles are obtained. There is a need for retardation films that do not require the addition of.

  Moreover, the fumaric-acid diester type resin and the film which consists of it are proposed (for example, refer patent documents 6-10).

Japanese Patent No. 2818983 JP 05-297223 A JP 05-323120 A Japanese Patent Laid-Open No. 06-88909 JP 2005-156862 A JP 2008-112141 A JP 2012-032784 A WO2012 / 005120 JP 2008-129465 A JP 2006-193616 A

  Although the fumaric acid diester resin proposed in Patent Documents 6 to 10 and a film comprising the same have a certain amount of out-of-plane retardation, at present, a film having a higher out-of-plane retardation even in a thin film Is required.

  An object of the present invention is to provide a novel trans-stilbene-N-substituted maleimide copolymer suitable for a retardation film having a high out-of-plane retardation even in a thin film using a specific resin and excellent in optical properties. It is in.

  As a result of intensive studies to solve the above problems, the present inventors have found that a specific trans-stilbene-N-substituted maleimide copolymer can solve the above problems, and have completed the present invention.

  That is, the present invention includes a trans-stilbene-N-substituted maleimide copolymer comprising a trans-stilbene residue unit and an N-substituted maleimide residue unit having a substituent having 1 to 8 carbon atoms, and The present invention relates to a retardation film using.

  Hereinafter, the trans-stilbene-N-substituted maleimide copolymer suitable for the retardation film of the present invention will be described in detail.

  The trans-stilbene-N-substituted maleimide copolymer of the present invention is a trans-stilbene-N-substituted maleimide comprising a trans-stilbene residue unit and an N-substituted maleimide residue unit having a substituent having 1 to 8 carbon atoms. It is a copolymer.

  Here, the substituents having 1 to 8 carbon atoms in the N-substituted maleimide residue unit having a substituent having 1 to 8 carbon atoms are independent, for example, a methyl group, an ethyl group, an n-propyl group, Alkyl groups such as isopropyl group, n-butyl group, isobutyl group, t-butyl group, n-pentyl group and n-hexyl group; cycloalkyl groups such as cyclopropyl group, cyclobutyl group and cyclohexyl group; phenyl group; methylphenyl Group, aryl groups such as dimethylphenyl group and ethylphenyl group. These may be substituted with halogen groups such as fluorine and chlorine; ether groups; ester groups; amino groups and the like. Examples of the N-substituted maleimide residue unit having a substituent having 1 to 8 carbon atoms include N-methylmaleimide residue, N-ethylmaleimide residue, Nn-propylmaleimide residue, and N-isopropylmaleimide residue. Group, Nn-butylmaleimide residue, N-isobutylmaleimide residue, Nt-butylmaleimide residue, Nn-hexylmaleimide residue, N-cyclobutylmaleimide residue, N-cyclohexylmaleimide residue N-phenylmaleimide residue, N-methylphenylmaleimide residue, N-ethylphenylmaleimide residue and the like. These may be contained alone or in combination of two or more.

  Specific trans-stilbene-N-substituted maleimide copolymers in the present invention include, for example, trans-stilbene-N-methylmaleimide copolymer, trans-stilbene-N-ethylmaleimide copolymer, trans-stilbene- Nn-propylmaleimide copolymer, trans-stilbene-N-isopropylmaleimide copolymer, trans-stilbene-Nn-butylmaleimide copolymer, trans-stilbene-N-isobutylmaleimide copolymer, trans- Stilbene-Nt-butylmaleimide copolymer, trans-stilbene-N-cyclobutylmaleimide copolymer, trans-stilbene-N-cyclohexylmaleimide copolymer, trans-stilbene-N-phenylmaleimide copolymer , Trans-stilbene-N-methylphenylmaleimide copolymer, trans-stilbene-N-ethylphenylmaleimide copolymer, and the like. Among them, a film excellent in retardation can be easily obtained particularly when a thin film is formed. Trans-stilbene-N-methylmaleimide copolymer, trans-stilbene-N-isopropylmaleimide copolymer, trans-stilbene-N-isobutylmaleimide copolymer, trans-stilbene-Nt-butylmaleimide A copolymer, a trans-stilbene-N-cyclohexylmaleimide copolymer, and a trans-stilbene-N-phenylmaleimide copolymer are preferable.

  The trans-stilbene-N-substituted maleimide copolymer may contain other monomer residue units as long as the scope of the present invention is not exceeded. For example, styrene residue units such as styrene residue units and α-methylstyrene residue units; (meth) acrylic acid residue units; (meth) methyl acrylate residue units, (meth) ethyl acrylate residue units (Meth) acrylic acid ester residue units such as butyl (meth) acrylate residue units; vinyl ester residue units such as vinyl acetate residue units and vinyl propionate residue units; acrylonitrile residue units; methacrylo Nitrile residue units; vinyl ether residue units such as methyl vinyl ether residue units, ethyl vinyl ether residue units, butyl vinyl ether residue units; ethylene residue units, pro Olefin residue units such as ren residue units; one or two selected from fumarate diester residue units such as di-n-butyl fumarate residue units and bis (2-ethylhexyl) fumarate residue units The above can be mentioned.

  Further, the trans-stilbene-N-substituted maleimide copolymer of the present invention has a polyfunctional group having two or more radical polymerizable functional groups in order to obtain a higher molecular weight trans-stilbene-N-substituted maleimide copolymer. It may contain a residue unit of a functional monomer, and examples of the radical polymerizable functional group include a vinyl group and a methacryl group. As the residue unit of the polyfunctional monomer, any residue unit of the polyfunctional monomer having two or more radical polymerizable functional groups may be used. A vinyl compound residue unit, a polyfunctional methacryl compound residue unit, etc. are mentioned, These may be contained 1 type or 2 or more types.

  Examples of polyfunctional vinyl compound residue units include divinylbenzene residue units, divinyltoluene residue units, divinylxylene residue units, trivinylbenzene residue units, divinylbiphenyl residue units, divinylnaphthalene residue units. Aromatic vinyl compound residue units such as divinylfluorene residue units, divinylcarbazole residue units, divinylpyridine residue units; divinyl adipate residue units, divinyl maleate residue units, divinyl phthalate residue units, isophthalate Polyvinyl ester compound residue units such as divinyl acid residue units and divinyl itaconate residue units; diallyl maleate residue units, diallyl phthalate residue units, diallyl isophthalate residue units, diallyl adipate residue units, etc. Polyallyl ester compound residue unit; divinyl ether Residue units, polyvinyl ether compound residue units such as diethylene glycol divinyl ether residue units, triethylene glycol divinyl ether residue units; diallyl ether residue units, diallyloxyethane residue units, triallyloxyethane residue units, tetra Polyallyl ether compound residue units such as allyloxyethane residue units, tetraallyloxypropane residue units, tetraallyloxybutane residue units, tetramethallyloxyethane residue units; 1,4-divinylperfluorobutane residue Group unit, polyvinyl fluorine compound residue unit such as 1,6-divinylperfluorohexane residue unit, 1,8-divinylperfluorooctane residue unit; 1,4-phenylenebismaleimide residue unit, 1,1 ′ -(Methylenedi-4,1-phenylene) bis Such as bismaleimides residues units such Reimido residue units and the like.

  Examples of the multifunctional methacrylic compound residue unit include a benzenetrimethacrylic acid ester residue unit, a 1,4-butanediol dimethacrylate residue unit, a 1,6-hexanediol dimethacrylate residue unit, 1 , 9-nonanediol dimethacrylate residue unit, ethylene glycol dimethacrylate residue unit, polyethylene glycol dimethacrylate residue unit, polypropylene glycol dimethacrylate residue unit, neopentyl glycol dimethacrylate residue unit, hydroxypivalate ester neopentyl Glycol dimethacrylate residue unit, caprolactone-modified hydroxypivalate ester neopentyl glycol dimethacrylate residue unit, glycerol trimethacrylate residue unit, trimethylolpropane Li methacrylate residue unit, ditrimethylolpropane tetramethacrylate residue unit, pentaerythritol trimethacrylate residue unit, such as pentaerythritol tetramethacrylate residue unit and the like.

  Since the composition of the trans-stilbene-N-substituted maleimide copolymer of the present invention is excellent in retardation characteristics and strength when used as a retardation film, the trans-stilbene residue unit is 30 to 70 mol%. N-substituted maleimide residue units having a substituent of 1 to 8 carbon atoms and 70 to 30 mol% of N-substituted maleimide residue units, preferably 40 to 60 mol% of trans-stilbene residue units and N-substituents of 1 to 8 carbon atoms. More preferably, the substituted maleimide residue unit is 60 to 40 mol%.

  In addition, when the trans-stilbene-N-substituted maleimide copolymer of the present invention includes a residue unit of a polyfunctional monomer having two or more radical polymerizable functional groups, trans-stilbene residue units 30 to 69 Residue unit of polyfunctional monomer having N-substituted maleimide residue unit having 5 to 5 mol%, substituent having 1 to 8 carbon atoms and 6 to 69.5 mol% and two or more radical polymerizable functional groups 0.01-0.5 mol% is preferable.

  Since the trans-stilbene-N-substituted maleimide copolymer of the present invention has excellent film forming properties and retardation characteristics when used as a retardation film, it was measured by gel permeation chromatography (GPC). The number average molecular weight in terms of standard polystyrene obtained from the elution curve is preferably 30,000 or more, and more preferably 50,000 to 500,000.

  The method for producing the trans-stilbene-N-substituted maleimide copolymer of the present invention may be any method as long as the trans-stilbene-N-substituted maleimide copolymer is obtained. For example, trans-stilbene and N- It can be produced by radical polymerization of a substituted maleimide.

  For the radical polymerization, any known polymerization method, for example, bulk polymerization method, solution polymerization method, suspension polymerization method, precipitation polymerization method or emulsion polymerization method can be employed.

  Examples of the polymerization initiator used for radical polymerization 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 Azo initiators such as 1,2′-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 solution polymerization method, suspension polymerization method, precipitation polymerization method, emulsion polymerization method, For example, aromatic solvents, such as benzene, toluene, xylene; Methanol, ethanol, propanol, butanol, etc. And cyclohexane, dioxane, tetrahydrofuran, acetone, methyl ethyl ketone, dimethylformamide, isopropyl acetate, water, 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 30-150 degreeC.

  When the trans-stilbene-N-substituted maleimide copolymer of the present invention is used as an optical film, it is preferably a retardation film because the thin film has a high out-of-plane retardation and excellent optical characteristics.

  In the retardation film using the trans-stilbene-N-substituted maleimide copolymer of the present invention, the refractive index in the fast axis direction in the film plane is nx, the refractive index in the film plane direction orthogonal to the film is ny, When the refractive index in the thickness direction is nz, each relationship is nx ≦ ny <nz, and satisfying nx ≦ ny <nz, STN-LCD, IPS- It is a retardation film excellent in viewing angle compensation performance such as LCD, reflective LCD, and transflective LCD. In general, the control of the three-dimensional refractive index of the film is performed by stretching the film, so the manufacturing process and quality control are complicated. However, the retardation film is unstretched and has a high refractive index in the film thickness direction. It has been found that it exhibits a unique behavior.

  There is no restriction | limiting in particular as a manufacturing method of retardation film using the trans-stilbene-N-substituted maleimide copolymer of this invention, For example, it can manufacture by methods, such as a solution cast method and a melt cast method.

  In the solution casting method, a solution in which a trans-stilbene-N-substituted maleimide copolymer is dissolved in a solvent (hereinafter referred to as a dope) is cast on a support substrate, and then the solvent is removed by heating or the like to form a film. How to get. In this case, as a method for casting the dope on the support substrate, for example, a T-die method, a doctor blade method, a bar coater method, a roll coater method, a lip coater method or the like is used. Particularly, industrially, a method of continuously extruding a dope from a die onto a belt-like or drum-like support substrate is common. Examples of the support substrate used include a glass substrate, a metal substrate such as stainless steel and ferrotype, and a film such as polyethylene terephthalate. In the solution casting method, when forming a film having high transparency and excellent thickness accuracy and surface smoothness, the solution viscosity of the dope is an extremely important factor, preferably 10 to 20000 cPs, More preferably, it is -10000 cPs.

  In this case, the coating thickness of the trans-stilbene-N-substituted maleimide copolymer is preferably 1 to 200 μm after drying, more preferably 5 to 100 μm, particularly preferably, since excellent surface smoothness and optical properties can be obtained. Is 10-50 μm.

  The melt casting method is a molding method in which a trans-stilbene-N-substituted maleimide copolymer is melted in an extruder, extruded into a film shape from a slit of a T die, and then cooled while being cooled with a roll or air. .

  The retardation film using the trans-stilbene-N-substituted maleimide copolymer of the present invention can be used after being peeled off from a glass substrate or other optical film as a base material. It can also be used as a laminate with the optical film.

  The retardation film using the trans-stilbene-N-substituted maleimide copolymer of the present invention can be laminated with a polarizing plate and used as a circular or elliptical polarizing plate, and includes polyvinyl alcohol / iodine and the like. It is also possible to form a polarizing plate by laminating with a polarizer. Furthermore, the retardation films can be laminated with each other or with another retardation film.

  It is preferable that the retardation film using the trans-stilbene-N-substituted maleimide copolymer of the present invention is blended with an antioxidant during film formation or in order to increase the thermal stability of the retardation film itself. Examples of the antioxidant include hindered phenolic antioxidants, phosphorus antioxidants, and other antioxidants, and these antioxidants may be used alone or in combination. And since an antioxidant action improves synergistically, it is preferable to use a hindered antioxidant and a phosphorus antioxidant in combination, and in that case, with respect to 100 parts by weight of the hindered antioxidant More preferably, the phosphorus-based antioxidant is used in a mixture of 100 to 500 parts by weight. Further, as the addition amount of the antioxidant, since a high antioxidant effect is obtained, 0.01 to 100 parts by weight of the trans-stilbene-N-substituted maleimide copolymer constituting the retardation film. 10 parts by weight is preferable, and 0.5 to 1 part by weight is more preferable.

  Further, as the ultraviolet absorber, for example, benzotriazole, benzophenone, triazine, benzoate and the like may be blended as necessary.

  The retardation film using the trans-stilbene-N-substituted maleimide copolymer of the present invention is within the range not exceeding the gist of the invention, other polymers, surfactants, polymer electrolytes, conductive complexes, inorganic fillers, A pigment, an antistatic agent, an antiblocking agent, a lubricant and the like may be blended.

  According to the present invention, a retardation film having excellent optical characteristics such as a large refractive index in the thickness direction and a large in-plane retardation, which is useful as a compensation film or antireflection film for contrast and viewing angle characteristics of a liquid crystal display. A trans-stilbene-N-substituted maleimide copolymer suitable for the above can be provided.

  The trans-stilbene-N-substituted maleimide copolymer of the present invention has a high out-of-plane retardation even in a thin film and is suitable for a retardation film having excellent optical properties such as a large refractive index in the thickness direction of the film. -A stilbene-N-substituted maleimide copolymer, particularly suitable for an optical compensation film for liquid crystal display elements.

Change in refractive index ellipsoid by stretching

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.

  In addition, the various physical properties shown by an Example were measured with the following method.

<Composition of trans-stilbene-N-substituted maleimide copolymer>
Using a nuclear magnetic resonance measuring apparatus (manufactured by JEOL, trade name JNM-GX270), it was determined by proton nuclear magnetic resonance spectroscopy ( ¹ H-NMR) spectrum analysis.

<Measurement of number average molecular weight>
Using a gel permeation chromatography (GPC) apparatus (manufactured by Tosoh Corporation, trade name C0-8011 (equipped with column GMH _HR- H)), tetrahydrofuran was measured as a solvent at 40 ° C., and the standard polystyrene equivalent value was obtained. Asked.

<Measurement of three-dimensional refractive index of film>
Measurement was performed using a fully automatic birefringence meter (trade name KOBRA-WR, manufactured by Oji Scientific Instruments).

Example 1
In a glass ampule with a capacity of 100 ml, trans-stilbene 36 g (0.2 mol), N-methylmaleimide 19.4 g (0.2 mol), 30 ml of toluene as a polymerization solvent and tert-butyl peroxypivalate 0 as a polymerization initiator .29 g (0.0016 mol) was added, and after nitrogen substitution and depressurization were repeated, the mixture was sealed under reduced pressure. The ampule was placed in a thermostatic bath at 50 ° C. and kept for 230 hours to carry out radical polymerization. After completion of the polymerization reaction, the polymer is taken out from the ampoule, dropped into 2 liters of methanol and precipitated, and then vacuum-dried at 80 ° C. for 10 hours to obtain a trans-stilbene-N-methylmaleimide copolymer. 5 g was obtained.

The number average molecular weight of the obtained trans-stilbene-N-methylmaleimide copolymer is 61000, and as a result of ¹ H-NMR measurement, the copolymer composition is trans-stilbene residue unit / N-methylmaleimide residue unit = It was confirmed to be 54.1 / 45.9 (mol%).

  The obtained trans-stilbene-N-methylmaleimide copolymer was dissolved in methyl isobutyl ketone, the solution was cast on a glass substrate by a coater, and dried at 140 ° C. for 10 minutes to produce a film on the glass substrate. did. When the three-dimensional refractive index of the obtained film was measured, nx = 1.4683, ny = 1.4683, nz = 1.4745, and nx = ny <nz.

Example 2
In a glass ampule having a capacity of 100 ml, trans-stilbene 36 g (0.2 mol), N-methylmaleimide 19.4 g (0.2 mol), divinylbenzene 0.038 g (2.9 ×) as a radical polymerizable polyfunctional monomer. 10 ^-4 mol (0.10 mol%)), 30 ml of toluene as a polymerization solvent and 0.29 g (0.0016 mol) of tert-butyl peroxypivalate as a polymerization initiator were added, and nitrogen substitution and depressurization were repeated. After that, it was sealed under reduced pressure. The ampule was placed in a thermostatic bath at 50 ° C. and kept for 230 hours to carry out radical polymerization. After completion of the polymerization reaction, the polymer is taken out from the ampoule, dropped into 2 liters of methanol and precipitated, and then vacuum-dried at 80 ° C. for 10 hours to obtain a trans-stilbene-N-methylmaleimide copolymer. 3 g was obtained.

The number average molecular weight of the obtained trans-stilbene-N-methylmaleimide copolymer is 106000, and the copolymer composition was determined to be trans-stilbene residue units / N-methylmaleimide residue units / by ¹ H-NMR measurement. It was confirmed that divinylbenzene residue unit = 54.0 / 45.9 / 0.1 (mol%).

  The obtained trans-stilbene-N-methylmaleimide copolymer was dissolved in methyl isobutyl ketone, the solution was cast on a glass substrate by a coater, and dried at 140 ° C. for 10 minutes to produce a film on the glass substrate. did. When the three-dimensional refractive index of the obtained film was measured, nx = 1.4683, ny = 1.4684, nz = 1.4749, and nx <ny <nz.

Example 3
In a glass ampule with a capacity of 100 ml, 45 g (0.25 mol) of trans-stilbene, 14.6 g (0.15 mol) of N-methylmaleimide, 30 ml of toluene as a polymerization solvent, and tert-butyl peroxypivalate 0 as a polymerization initiator .29 g (0.0016 mol) was added, and after nitrogen substitution and depressurization were repeated, the mixture was sealed under reduced pressure. The ampule was placed in a thermostatic bath at 50 ° C. and kept for 230 hours to carry out radical polymerization. 7. After completion of the polymerization reaction, the polymer is taken out from the ampoule, dropped into 2 liters of methanol and precipitated, and then vacuum-dried at 80 ° C. for 10 hours to obtain a trans-stilbene-N-methylmaleimide copolymer. 1 g was obtained.

The number average molecular weight of the obtained trans-stilbene-N-methylmaleimide copolymer is 69000, and as a result of ¹ H-NMR measurement, the copolymer composition is trans-stilbene residue units / N-methylmaleimide residue units = It was confirmed to be 51.1 / 48.9 (mol%).

  The obtained trans-stilbene-N-methylmaleimide copolymer was dissolved in methyl isobutyl ketone, the solution was cast on a glass substrate by a coater, and dried at 140 ° C. for 10 minutes to produce a film on the glass substrate. did. When the three-dimensional refractive index of the obtained film was measured, nx = 1.4676, ny = 1.4676, nz = 1.4784, and nx = ny <nz.

Example 4
In a glass ampule having a capacity of 100 ml, trans-stilbene 36 g (0.2 mol), N-phenylmaleimide 31.8 g (0.2 mol), 30 ml of toluene as a polymerization solvent and tert-butyl peroxypivalate 0 as a polymerization initiator .29 g (0.0016 mol) was added, and after nitrogen substitution and depressurization were repeated, the mixture was sealed under reduced pressure. The ampule was placed in a thermostatic bath at 50 ° C. and kept for 230 hours to carry out radical polymerization. After completion of the polymerization reaction, the polymer is taken out from the ampoule, dropped into 2 liters of methanol and precipitated, and then vacuum-dried at 80 ° C. for 10 hours to obtain a trans-stilbene-N-phenylmaleimide copolymer. 5 g was obtained.

The number-average molecular weight of the obtained trans-stilbene-N-phenylmaleimide copolymer is 65000, and the copolymer composition is determined to be trans-stilbene residue unit / N-phenylmaleimide residue unit by ¹ H-NMR measurement = It was confirmed to be 52.9 / 47.1 (mol%).

  The obtained trans-stilbene-N-phenylmaleimide copolymer is dissolved in methyl isobutyl ketone, the solution is cast on a glass substrate with a coater, and dried at 140 ° C. for 10 minutes to produce a film on the glass substrate. did. When the three-dimensional refractive index of the obtained film was measured, nx = 1.4670, ny = 1.4670, nz = 1.4786, and nx = ny <nz.

Comparative Example 1
Styrene 20.8 g (0.2 mol), N-methylmaleimide 19.4 g (0.2 mol), 100 ml of toluene as a polymerization solvent, and tert-butyl peroxypivalate 0 as a polymerization initiator .29 g (0.0016 mol) was added, and after nitrogen substitution and depressurization were repeated, the mixture was sealed under reduced pressure. The ampule was placed in a thermostatic bath at 50 ° C. and kept for 12 hours to carry out radical polymerization. After the completion of the polymerization reaction, the polymer was taken out from the ampoule, dropped into 2 liters of methanol and precipitated, and then vacuum dried at 80 ° C. for 10 hours to obtain 32.1 g of a styrene-N-methylmaleimide copolymer. Obtained.

The number average molecular weight of the obtained styrene-N-methylmaleimide copolymer is 158000, and the copolymer composition is styrene residue unit / N-methylmaleimide residue unit = 49.8 / by ¹ H-NMR measurement. It was confirmed to be 50.2 (mol%).

  The obtained styrene-N-methylmaleimide copolymer was dissolved in methyl isobutyl ketone, the solution was cast on a glass substrate with a coater, and dried at 110 ° C. for 10 minutes to produce a film on the glass substrate. When the three-dimensional refractive index of the obtained film was measured, nx = 1.4687, ny = 1.4687, and nz = 1.4687. nx = ny = nz.

Comparative Example 2
Glass ampoule with a capacity of 100 ml, 20.8 g (0.2 mol) of styrene, 31.8 g (0.2 mol) of N-phenylmaleimide, 30 ml of toluene as a polymerization solvent, and tert-butyl peroxypivalate 0 as a polymerization initiator .29 g (0.0016 mol) was added, and after nitrogen substitution and depressurization were repeated, the mixture was sealed under reduced pressure. The ampule was placed in a thermostatic bath at 50 ° C. and kept for 12 hours to carry out radical polymerization. After completion of the polymerization reaction, the polymer was taken out from the ampoule, dropped into 2 liters of methanol and precipitated, and then vacuum-dried at 80 ° C. for 10 hours, whereby 44.6 g of a styrene-N-phenylimide copolymer was obtained. Got.

The number average molecular weight of the obtained styrene-N-phenylmaleimide copolymer is 139000. According to ¹ H-NMR measurement, the copolymer composition is styrene residue unit / N-phenylmaleimide residue unit = 48.2 / It was confirmed to be 51.8 (mol%).

  The obtained styrene-N-phenylmaleimide copolymer was dissolved in methyl isobutyl ketone, the solution was cast on a glass substrate with a coater, and dried at 110 ° C. for 10 minutes to produce a film on the glass substrate. When the three-dimensional refractive index of the obtained film was measured, nx = 1.4623, ny = 1.4623, and nz = 1.4623. nx = ny = nz.

  The present invention provides a novel trans-stilbene-N-substituted maleimide copolymer, and the trans-stilbene-N-substituted maleimide copolymer is expected to be used as a film, particularly as a retardation film. Is.

Claims (4)

There the trans- stilbene residue unit and N- substituted maleimide residue unit having a substituent having 1 to 8 carbon atoms in the retardation film of the unstretched using including t Rans- stilbene -N- substituted maleimide copolymer The relationship when the refractive index in the fast axis direction in the film plane is nx, the refractive index in the film in-plane direction orthogonal thereto is ny, and the refractive index in the thickness direction of the film is nz is nx ≦ ny < A retardation film which is nz . trans- Stilbene -N- substituted maleimide copolymer trans- stilbene residue unit 30-70 mol% and has a substituent having 1 to 8 carbon atoms N- substituted maleimide residue unit 70-30 mole percent including t The retardation film according to claim 1, which is a rans-stilbene-N-substituted maleimide copolymer. The retardation film according to claim 1 or 2, wherein the number average molecular weight in terms of standard polystyrene of the trans-stilbene-N-substituted maleimide copolymer is 50,000 to 500,000. a trans-stilbene-N-substituted maleimide copolymer is a trans-stilbene-N-methylmaleimide copolymer, a trans-stilbene-Nt-butylmaleimide copolymer, a trans-stilbene-N-cyclohexylmaleimide copolymer, and The retardation film according to any one of claims 1 to 3, wherein the retardation film is any one selected from the group consisting of trans-stilbene-N-phenylmaleimide copolymers.

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