JP2014129472A - Fumaric acid diester-based resin and retardation film using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a material for a retardation film and a retardation film excellent in optical properties such as large refraction index in a thickness direction of the film, negative and large out-of-plane retardation, little wavelength dependence, and large out-of-plane retardation even in a thin film.SOLUTION: There are provided a fumaric acid diester-based resin and a retardation film comprising the same, whose monomer residue unit comprises: a fumaric acid di-tert-butyl residue unit of 30 to 69 mol%; a fumaric acid diethyl residue unit of 30 to 69 mol%; and one or more residue unit selected from a fumaric acid di-n-propyl residue unit, a fumaric acid di-n-butyl residue unit, a fumaric acid di-iso-butyl residue unit, and a fumaric acid di-1-methyl propyl residue unit of 1 to 20 mol% (where the total of the fumaric acid di-tert-butyl residue unit; the fumaric acid diethyl residue unit; and one or more residue unit selected from the fumaric acid di-n-propyl residue unit, the fumaric acid di-n-butyl residue unit, the fumaric acid di-iso-butyl residue unit, and the fumaric acid di-1-methyl propyl residue unit is 100 mol%).

Description

  The present invention relates to a fumaric acid diester resin suitable for a retardation film having a high out-of-plane retardation even in a thin film and excellent in optical characteristics such as wavelength dependency. In particular, the present invention relates to a fumaric acid diester resin suitable for an optical compensation film for a liquid crystal display element.

  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 for improving the display characteristics of the liquid crystal display. In particular, the retardation film plays a large role in improving contrast, color tone and compensation 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: the direction perpendicular to the stretching direction).

  Many polymers have positive birefringence. Examples of the polymer having negative birefringence include acrylic resin and polystyrene, but the acrylic resin has a small amount of retardation, and the characteristics as a retardation film are not sufficient. Polystyrene has a large photoelastic coefficient in the low-temperature region, so the phase difference changes due to slight stress, the problem of stability of the phase difference, the problem of optical properties such as the large wavelength dependence of the phase difference, and heat resistance However, it is not used at present.

  Here, the wavelength dependence of the phase difference means that the phase difference changes depending on the measurement wavelength. The phase difference measured at the wavelength of 450 nm (R450) and the phase difference measured at the wavelength of 550 nm (R550). The ratio can be expressed as R450 / R550. In general, a polymer having an aromatic structure has a strong tendency to increase R450 / R550, and the contrast and viewing angle characteristics in a low wavelength region are deteriorated.

  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. For example, super twisted nematic (STN-LCD) or vertical alignment liquid crystal display (VA) -LCD), in-plane alignment type liquid crystal display (IPS-LCD), reflection type liquid crystal display (reflection type LCD) and the like, useful as a retardation film for compensation of visual field characteristics of a display and a viewing angle compensation film of a polarizing plate, There is a strong market demand 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 method of applying a shrinkage force in the film thickness direction of the polymer film (see, for example, Patent Documents 1 to 3) by closely adhering a heat-shrinkable film to one or both sides of the polymer film and heating and stretching the laminate. ). 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. Further, when polycarbonate is used as the base film, there are problems that the photoelastic coefficient at room temperature is large, the phase difference is changed by a slight stress, and the wavelength dependency 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.

  A film made of a fumaric acid diester resin has been proposed (see, for example, Patent Document 6). Although the optical compensation film obtained in Patent Document 6 has a certain amount of out-of-plane retardation, a film having a higher retardation even in a thinner film is required.

Japanese Patent No. 2818983 JP-A-5-297223 JP-A-5-323120 JP-A-6-88909 JP 2005-156862 A JP 2008-112141 A

  An object of the present invention is to provide a material suitable for a retardation film, which has a high retardation even in a thin film using a specific resin and is excellent in optical properties such as wavelength dependency and heat resistance.

  As a result of intensive studies to solve the above problems, the present inventors have found that a specific fumaric acid diester resin can solve the above problems, and have completed the present invention.

  That is, in the present invention, monomer residue units are 30 to 69 mol% di-tert-butyl fumarate residue units, 30 to 69 mol% diethyl fumarate residue units, and di-n-propyl fumarate residue units. 1 to 20 mol% of one or more residue units selected from di-n-butyl fumarate residue units, diisobutyl fumarate residue units and di1-methylpropyl fumarate residue units (provided that di-tert-fumarate) -Butyl residue units, diethyl fumarate residue units, and di-n-propyl fumarate residue units, di-n-butyl fumarate residue units, diisobutyl fumarate residue units, and di-1-methylpropyl fumarate residues A fumaric acid diester resin characterized in that the total of one or more residue units selected from the units is 100 mol%, and a retardation film using the same It is.

  Hereinafter, the fumaric acid diester resin suitable for the retardation film of the present invention will be described in detail.

  In the fumaric acid diester resin of the present invention, the monomer residue unit is 30 to 69 mol% di-tert-butyl fumarate residue unit, 30 to 69 mol% diethyl fumarate residue unit, and di-n-fumarate. 1 to 20 mol% of one or more residue units selected from a propyl residue unit, a di-n-butyl fumarate residue unit, a diisobutyl fumarate residue unit and a di1-methylpropyl fumarate residue unit (provided that Di-tert-butyl fumarate residue unit, diethyl fumarate residue unit, di-n-propyl fumarate residue unit, di-n-butyl fumarate residue unit, diisobutyl fumarate residue unit and di-fumarate unit 1 -The sum of one or more residue units selected from methylpropyl residue units is 100 mol%).

  The composition of the fumaric acid diester resin of the present invention has a di-tert-butyl fumarate residue unit of 30 to 69 mol%, a diethyl fumarate residue unit of 30 to 69 mol%, and a di-n-propyl fumarate residue unit, 1 to 20 mol% of one or more residue units selected from di-n-butyl fumarate residue unit, diisobutyl fumarate residue unit and di1-methylpropyl fumarate residue unit (provided that di-tert-fumarate) Butyl residue units, diethyl fumarate residue units, and di-n-propyl fumarate residue units, di-n-butyl fumarate residue units, diisobutyl fumarate residue units, and di-1-methylpropyl fumarate residue units If the total of one or more residue units selected from the above is out of 100 mol%, the retardation characteristics and strength when the retardation film is obtained are inferior. Since the retardation characteristics and strength when the retardation film is obtained, the di-tert-butyl fumarate residue unit is 40 to 59 mol%, the diethyl fumarate residue unit is 40 to 59 mol%, and 1 to 10 mol of one or more residue units selected from di-n-propyl fumarate residue unit, di-n-butyl fumarate residue unit, diisobutyl fumarate residue unit and di1-methylpropyl fumarate residue unit % (Wherein di-tert-butyl fumarate residue unit, diethyl fumarate residue unit, and di-n-propyl fumarate residue unit, di-n-butyl fumarate residue unit, diisobutyl fumarate residue unit and The total of one or more residue units selected from di1-methylpropyl fumarate residue units is preferably 100 mol%).

  The fumaric acid diester resin of the present invention has a number average molecular weight in terms of standard polystyrene obtained from an elution curve measured by gel permeation chromatography (GPC). Since it is excellent, 50,000 to 500,000 are preferable, and 80,000 to 400,000 are more preferable.

  The fumarate diester resin of the present invention may be produced by any method as long as the fumarate diester resin is obtained. For example, radical polymerization of di-tert-butyl fumarate and diethyl fumarate is performed. Can be manufactured.

  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-tert-butyl peroxide, tert-butyl cumyl peroxide, and dicumyl peroxide. Organic peroxides such as tert-butylperoxyacetate, tert-butylperoxybenzoate, tert-butylperoxypivalate, tert-butylperoxy-2-ethylhexanoate; 2,2′-azobis (2 , 4-dimethylvaleronitrile), 2,2′-azobisisobutyronitrile, dimethyl-2,2′-azobisisobutyrate, 1,1′-azobis (cyclohexane-1-carbonitrile), etc. And system initiators.

  And 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 30-150 degreeC.

  When an optical film using the fumaric acid diester resin of the present invention is obtained, it has a high out-of-plane retardation even in a thin film and is excellent in wavelength-dependent optical properties. Is preferred. The retardation film is a retardation film that does not require addition of fine particles.

  The retardation film of the present invention has the following relationships when the refractive index in the fast axis direction in the film plane is nx, the refractive index in the film plane perpendicular to the film is ny, and the refractive index in the thickness direction of the film is nz. A retardation film characterized by satisfying nx ≦ ny <nz. By satisfying nx ≦ ny <nz, viewing angle compensation performance of STN-LCD, IPS-LCD, reflective LCD, transflective LCD, etc. It becomes an excellent retardation film. In general, since the control of the three-dimensional refractive index of the film is performed by stretching the film and the like, the manufacturing process and quality control are complicated. However, the retardation film of the present invention is unstretched and has a refractive index in the film thickness direction. Has been found to exhibit a specific behavior of high.

  In addition, since the retardation film of the present invention becomes a retardation film with more excellent optical properties, an out-of-plane retardation (Rth) measured at a wavelength of 550 nm represented by the following formula (a) is −50 to −2000 nm. It is preferable that it is -100--500 nm.

Rth = ((nx + ny) / 2−nz) × d (a)
(Here, d indicates the thickness of the film.)
Since the retardation film of the present invention has a high out-of-plane retardation even in a thin film, the absolute value of the relationship between the film thickness and the out-of-plane retardation is preferably 4.5 nm / film thickness (μm) or more, and 5 to 15 nm. / Film thickness (μm) is more preferable.

  The wavelength dependence of the phase difference can be expressed as a ratio R450 / R550 of the phase difference (R450) measured at a wavelength of 450 nm and the phase difference (R550) measured at a wavelength of 550 nm. In the retardation film of the present invention, the R450 / 550 is preferably 1.1 or less, more preferably 1.08 or less, and particularly preferably 1.05 or less.

  The retardation film of the present invention has good image quality characteristics when used in a liquid crystal display element, so that the light transmittance is preferably 85% or more, and more preferably 90% or more. The haze (cloudiness) of the retardation film is preferably 2% or less, more preferably 1% or less.

  There is no restriction | limiting in particular as a manufacturing method of the phase difference film of this invention, For example, methods, such as a solution cast method and a melt cast method, are mentioned.

  The solution casting method is a method of obtaining a film by casting a solution in which a fumaric acid diester resin is dissolved in a solvent (hereinafter referred to as a dope) on a support substrate and then removing the solvent by heating or the like. 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, the most common method is to continuously extrude a dope from a die onto a belt-like or drum-like support substrate. 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 10,000 cPs. In addition, the solvent used in that case is not particularly limited as long as the fumaric acid diester resin is dissolved. For example, aromatic hydrocarbons such as toluene and xylene; ketones such as acetone and methyl ethyl ketone; ethyl acetate and acetic acid Examples thereof include esters such as butyl; ethers such as tetrahydrofuran; halogenated hydrocarbons such as chloroform.

  In this case, the coating thickness of the fumaric acid diester resin is preferably 1 to 200 μm after drying, more preferably 5 to 100 μm, and particularly preferably 5 to 30 μm.

  The melt casting method is a molding method in which a fumaric acid diester resin is melted in an extruder, extruded into a film form from a slit of a T die, and then cooled and cooled with a roll or air.

  The retardation film of the present invention can be used by being peeled off from a glass substrate as a base material or another optical film, and can also be used as a laminate with a glass substrate as a base material or another optical film.

  The retardation film of the present invention can be laminated with a polarizing plate to be used as a circular or elliptical polarizing plate, and can be laminated with a polarizer containing polyvinyl alcohol / iodine or the like to form a polarizing plate. is there. Furthermore, the retardation films of the present invention can be laminated with each other or with other retardation films.

  In the retardation film of the present invention, an antioxidant is preferably blended in order to increase the thermal stability of the retardation film itself or during film formation. Examples of the antioxidant include hindered phenol antioxidants, phosphorus antioxidants, and other antioxidants, and these antioxidants may be used alone or in combination. And since an antioxidant effect | action improves synergistically, it is preferable to mix and use a phosphorus antioxidant by 100-500 weight part with respect to 100 weight part of hindered antioxidant. Moreover, as addition amount of antioxidant, 0.01-10 weight part is preferable with respect to 100 weight part of fumaric-acid diester type resin which comprises the phase difference film of this invention, 0.5-1 weight part is preferable. Further preferred.

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

  The retardation film of the present invention is blended with other polymers, surfactants, polymer electrolytes, conductive complexes, inorganic fillers, pigments, antistatic agents, antiblocking agents, lubricants and the like without departing from the spirit of the invention. May be.

  According to the present invention, the refractive index in the thickness direction of a film useful as a compensation film or antireflection film for contrast and viewing angle characteristics of a liquid crystal display is large, the out-of-plane retardation is negatively large, and the wavelength dependency is small. A fumaric acid diester resin suitable for a retardation film having excellent optical properties can be provided.

  The fumaric acid diester resin of the present invention has a high out-of-plane retardation even in a thin film, has a large refractive index in the thickness direction of the film, and is excellent in optical characteristics such as a low wavelength dependency. It is an acid diester resin and is particularly suitable as an optical compensation film material for liquid crystal display elements.

Change in refractive index ellipsoid by stretching

  EXAMPLES Hereinafter, although this invention is demonstrated based on an Example, this invention is not limited to these Examples. The evaluation / measurement method of the fumaric acid diester resin obtained in the examples is shown below. Unless otherwise noted, commercially available reagents were used.

<Isomerization rate of fumaric acid diester>
A gas chromatograph (trade name GC-14A, manufactured by Shimadzu Corporation) was used for quantitative analysis from a gas chromatograph.

<Composition of fumaric acid diester resin>
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.

<Number average molecular weight>
Using a gel permeation chromatography (GPC) apparatus (manufactured by Tosoh Corporation, trade name: HLC-8320GPC (equipped with column SuperHM-H)), tetrahydrofuran was used as a solvent at 40 ° C., and the standard polystyrene conversion value was obtained.

<Evaluation of transparency>
The total light transmittance and haze of the film were measured using a haze meter (trade name NDH5000, manufactured by Nippon Denshoku Industries Co., Ltd.).

<Measurement of refractive index>
Measurement was performed using an Abbe refractometer (manufactured by Atago) in accordance with JIS K 7142 (1981 version).

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

Synthesis Example 1 Synthesis of di-tert-butyl fumarate
A 300 mL autoclave equipped with a stirrer and a thermometer was charged with 60 mL of ethylene glycol dimethyl ether, 20 g of maleic acid, and 4 g of sulfuric acid, and then 51 g of 2-methylpropylene was injected into it and reacted at 40 ° C. for 2 hours with stirring.

  80 mL of ethylene glycol dimethyl ether solution of di-tert-butyl maleate and 0.3 g of piperidine obtained by neutralizing and washing the reaction solution obtained in the above reaction were equipped with a stirrer, a condenser and a thermometer. The mixture was charged into three 150 mL necks and reacted at 110 ° C. for 2 hours with stirring. As a result of GC analysis of the obtained reaction liquid, the isomerization rate to di-tert-butyl fumarate was 99%. After distilling off the solvent of the obtained reaction solution, sublimation was performed to obtain 22 g of 99% pure di-tert-butyl fumarate.

Example 1
In a glass ampule with a capacity of 75 mL, 32.8 g (0.14 mol) of di-tert-butyl fumarate obtained in Synthesis Example 1, 14.4 g (0.08 mol) of diethyl fumarate, 2.7 g of diisobutyl fumarate ( 0.01 mol), 6.7 g of cyclohexane, and 0.32 g (0.0015 mol) of tert-butylperoxy-2-ethylhexanoate as a polymerization initiator were added, and the pressure was reduced after repeating nitrogen substitution and depressurization. Sealed in the state. The ampoule was placed in a constant temperature bath at 60 ° C. and held for 6 hours to carry out radical polymerization. After completion of the polymerization reaction, the polymer was taken out from the ampoule and dissolved with 300 g of toluene. This polymer solution was dropped into 3 L of methanol and precipitated, and then vacuum-dried at 60 ° C. for 10 hours to obtain 33.0 g of a fumaric acid diester resin (yield: 58%).

  The number average molecular weight of the obtained fumaric acid diester resin was 143,000.

In addition, the ¹ H-NMR measurement confirmed that the resin composition was di-tert-butyl fumarate residue unit / diethyl fumarate residue unit / diisobutyl fumarate residue unit = 62/33/5.

Example 2
33.0 g (0.14 mol) of di-tert-butyl fumarate obtained in Synthesis Example 1 in a glass ampule with a capacity of 75 mL, 14.5 g (0.08 mol) of diethyl fumarate, di-n-propyl fumarate 2 .4 g (0.01 mol), cyclohexane 6.5 g and polymerization initiator tert-butylperoxy-2-ethylhexanoate 0.33 g (0.0015 mol) were added, and nitrogen substitution and depressurization were repeated. After that, it was sealed under reduced pressure. The ampoule was placed in a constant temperature bath at 60 ° C. and held for 6 hours to carry out radical polymerization. After completion of the polymerization reaction, the polymer was taken out from the ampoule and dissolved with 300 g of toluene. This polymer solution was dropped into 3 L of methanol and precipitated, and then vacuum-dried at 60 ° C. for 10 hours to obtain 33.5 g of a fumaric acid diester resin (yield: 59%).

  The number average molecular weight of the obtained fumaric acid diester resin was 140,000.

In addition, ¹ H-NMR measurement confirmed that the resin composition was di-tert-butyl fumarate residue unit / diethyl fumarate residue unit / di-n-propyl fumarate residue unit = 63/32/5. did.

Example 3
In a glass ampule with a capacity of 75 mL, 28.1 g (0.12 mol) of di-tert-butyl fumarate obtained in Synthesis Example 1, 19.1 g (0.11 mol) of diethyl fumarate, di-n-butyl fumarate 2 0.8 g (0.01 mol) and 0.17 g (0.0008 mol) of tert-butylperoxy-2-ethylhexanoate, which is a polymerization initiator, were added, and after nitrogen substitution and depressurization were repeated, Sealed. The ampoule was placed in a constant temperature bath at 60 ° C. and held for 6 hours to carry out radical polymerization. After completion of the polymerization reaction, the polymer was taken out from the ampoule and dissolved with 300 g of toluene. This polymer solution was dropped into 3 L of methanol and precipitated, and then vacuum-dried at 60 ° C. for 10 hours to obtain 5.0 g of a fumaric acid diester resin (yield: 10%).

  The number average molecular weight of the obtained fumaric acid diester resin was 200,000.

Also, ¹ H-NMR measurement confirmed that the resin composition was di-tert-butyl fumarate residue unit / diethyl fumarate residue unit / di-n-butyl fumarate residue unit = 53/43/4. did.

Example 4
In a glass ampule with a capacity of 75 mL, 28.1 g (0.12 mol) of di-tert-butyl fumarate obtained in Synthesis Example 1, 19.1 g (0.11 mol) of diethyl fumarate, di-1-methylpropyl fumarate 2.8 g (0.01 mol) and 0.17 g (0.0008 mol) of tert-butylperoxy-2-ethylhexanoate which is a polymerization initiator were added, and after nitrogen substitution and depressurization were repeated, the pressure was reduced. Sealed with. The ampoule was placed in a constant temperature bath at 60 ° C. and held for 6 hours to carry out radical polymerization. After completion of the polymerization reaction, the polymer was taken out from the ampoule and dissolved with 300 g of toluene. This polymer solution was dropped into 3 L of methanol and precipitated, and then vacuum-dried at 60 ° C. for 10 hours to obtain 6.0 g of a fumaric acid diester resin (yield: 12%).

  The number average molecular weight of the obtained fumaric acid diester resin was 192,000.

In addition, by ¹ H-NMR measurement, the resin composition is di-tert-butyl fumarate residue unit / diethyl fumarate residue unit / di1-methylpropyl fumarate residue unit = 54/40/6. confirmed.

Example 5
The fumaric acid diester resin obtained in Example 1 was dissolved in methyl isobutyl ketone to form a 13% by weight resin solution, cast on a polyethylene terephthalate film by a spin coater, and dried at 130 ° C. for 10 minutes. A film using a fumaric acid diester resin having a thickness of 10.5 μm was obtained.

  The obtained film had a total light transmittance of 93%, a haze of 0.3% and a refractive index of 1.465. The three-dimensional refractive indexes were nx = 1.4634, ny = 1.4634, and nz = 1.46883, and the obtained film exhibited a large value of refractive index in the thickness direction of nx = ny <nz. The out-of-plane retardation Rth was as negative as −52 nm, and the phase difference ratio (R450 / R550) (wavelength dependence) was as small as 1.01. The out-of-plane retardation (Rth) / film thickness (μm) was −4.9 nm / μm.

  From these results, the obtained film has negative birefringence, a large refractive index in the thickness direction, a large negative out-of-plane retardation, a small wavelength dependence, and a high out-of-plane retardation even in a thin film. Therefore, it was suitable for a retardation film.

Example 6
The fumaric acid diester resin obtained in Example 2 was dissolved in methyl isobutyl ketone to form a 13% by weight resin solution, cast on a polyethylene terephthalate film by a spin coater, and dried at 130 ° C. for 10 minutes. A film using a fumaric acid diester resin having a thickness of 13.0 μm was obtained.

  The obtained film had a total light transmittance of 93%, a haze of 0.3% and a refractive index of 1.465. The three-dimensional refractive index was nx = 1.4634, ny = 1.4634, nz = 1.4682, and the obtained film showed a large value of the refractive index in the thickness direction of nx = ny <nz. Further, the out-of-plane retardation Rth was as negative as −62 nm, and the phase difference ratio (R450 / R550) (wavelength dependence) was as small as 1.01. The out-of-plane retardation (Rth) / film thickness (μm) was −4.8 nm / μm.

  From these results, the obtained film has negative birefringence, a large refractive index in the thickness direction, a large negative out-of-plane retardation, a small wavelength dependence, and a high out-of-plane retardation even in a thin film. Therefore, it was suitable for a retardation film.

Example 7
The fumaric acid diester resin obtained in Example 3 was dissolved in methyl isobutyl ketone to form a resin solution of 11% by weight, cast on a polyethylene terephthalate film by a spin coater, and dried at 130 ° C. for 10 minutes. A film using a fumaric acid diester resin having a thickness of 12.5 μm was obtained.

  The obtained film had a total light transmittance of 93%, a haze of 0.3%, and a refractive index of 1.470. The three-dimensional refractive index was nx = 1.4682, ny = 1.4682, and nz = 1.4737, and the obtained film exhibited a large value of the refractive index in the thickness direction of nx = ny <nz. Further, the out-of-plane phase difference Rth was as negative as −69 nm, and the phase difference ratio (R450 / R550) (wavelength dependence) was as small as 1.01. The out-of-plane retardation (Rth) / film thickness (μm) was −5.5 nm / μm.

  From these results, the obtained film has negative birefringence, a large refractive index in the thickness direction, a large negative out-of-plane retardation, a small wavelength dependence, and a high out-of-plane retardation even in a thin film. Therefore, it was suitable for a retardation film.

Example 8
The fumaric acid diester resin obtained in Example 4 was dissolved in methyl isobutyl ketone to form an 11 wt% resin solution, cast onto a polyethylene terephthalate film by a spin coater, and dried at 130 ° C. for 10 minutes. A film using a fumaric acid diester resin having a thickness of 12.0 μm was obtained.

  The obtained film had a total light transmittance of 93%, a haze of 0.3% and a refractive index of 1.473. The three-dimensional refractive index was nx = 1.4711, ny = 1.4711, nz = 1.4768, and the obtained film exhibited a large value of the refractive index in the thickness direction of nx = ny <nz. Further, the out-of-plane retardation Rth was as negative as −68 nm, and the phase difference ratio (R450 / R550) (wavelength dependence) was as small as 1.01. The out-of-plane retardation (Rth) / film thickness (μm) was −5.7 nm / μm.

  From these results, the obtained film has negative birefringence, a large refractive index in the thickness direction, a large negative out-of-plane retardation, a small wavelength dependence, and a high out-of-plane retardation even in a thin film. Therefore, it was suitable for a retardation film.

Comparative Example 1
In a glass ampule having a capacity of 75 mL, 39.5 g (0.17 mol) of di-tert-butyl fumarate obtained in Synthesis Example 1, 7.45 g (0.04 mol) of diethyl fumarate, 7.9 g of toluene, and polymerization initiation After adding 0.15 g (0.0007 mol) of tert-butylperoxy-2-ethylhexanoate as an agent, repeating nitrogen substitution and depressurization, the mixture was sealed under reduced pressure. The ampule was placed in a constant temperature bath at 70 ° C. and held for 6 hours to carry out radical polymerization. After completion of the polymerization reaction, the polymer was taken out from the ampoule and dissolved with 300 g of toluene. This polymer solution was dropped into 3 L of methanol and precipitated, and then vacuum-dried at 60 ° C. for 10 hours to obtain 19 g of a fumaric acid diester resin (yield: 40%).

  The number average molecular weight of the obtained fumaric acid diester resin was 49,000.

Further, ¹ H-NMR measurement confirmed that the resin composition was di-tert-butyl fumarate residue unit / diethyl fumarate residue unit = 76/24.

Comparative Example 2
20.1 g (0.09 mol) of di-tert-butyl fumarate obtained in Synthesis Example 1, 35.2 g (0.20 mol) of diethyl fumarate, 4.0 g of cyclohexane and polymerization initiation in a glass ampule with a capacity of 75 mL After adding 0.20 g (0.0009 mol) of tert-butylperoxy-2-ethylhexanoate as an agent, repeating nitrogen substitution and depressurization, the mixture was sealed under reduced pressure. The ampoule was placed in a constant temperature bath at 55 ° C. and held for 6 hours to carry out radical polymerization. After completion of the polymerization reaction, the polymer was taken out from the ampoule and dissolved with 300 g of toluene. This polymer solution was dropped into 3 L of methanol and precipitated, and then vacuum-dried at 60 ° C. for 10 hours to obtain 1.7 g of a fumaric acid diester resin (yield: 3%).

  The number average molecular weight of the obtained fumaric acid diester resin was 11,000.

Further, ¹ H-NMR measurement confirmed that the resin composition was di-tert-butyl fumarate residue unit / diethyl fumarate residue unit = 27/73.

Comparative Example 3
The fumaric acid diester resin obtained in Comparative Example 1 was dissolved in toluene to give a 15% by weight resin solution, which was cast on a cover glass with a spin coater and dried at 130 ° C. for 10 minutes. A film using an acid diester resin was obtained.

  The obtained film had a total light transmittance of 93%, a haze of 0.3%, and a refractive index of 1.461. The three-dimensional refractive index is nx = 1.4597, ny = 1.4597, nz = 1.4625, and the obtained film has a large value of refractive index in the thickness direction of nx = ny <nz. However, the out-of-plane retardation Rth was as small as −25 nm, and the out-of-plane retardation (Rth) / film thickness (μm) was as small as −2.8 nm / μm.

  From these results, the obtained film had negative birefringence and a large refractive index in the thickness direction, but the out-of-plane retardation was negatively small, and a high out-of-plane retardation was expected in the thin film. It was impossible.

Comparative Example 4
The fumaric acid diester resin obtained in Comparative Example 2 was dissolved in methyl isobutyl ketone to give a resin solution of 15% by weight, cast on a cover glass with a spin coater, and dried at 130 ° C. for 10 minutes to obtain a thickness of 12 μm. A film using a fumaric acid diester resin was obtained.

  The obtained film had a total light transmittance of 93%, a haze of 0.3% and a refractive index of 1.478. The three-dimensional refractive index is nx = 1.4769, ny = 1.4769, nz = 1.4802, and the obtained film has a large refractive index in the thickness direction of nx = ny <nz. However, the out-of-plane retardation Rth was as negative as −40 nm, and the out-of-plane retardation (Rth) / film thickness (μm) was −3.3 nm / μm.

  From these results, the obtained film had negative birefringence and a large refractive index in the thickness direction, but the out-of-plane retardation was negatively small, and a high out-of-plane retardation was expected in the thin film. It was impossible.

nx: Refractive index in the fast axis direction in the film plane.
ny: Refractive index in the film in-plane direction orthogonal to nx.
nz: The refractive index in the thickness direction of the film.

Claims (7)

The monomer residue unit is 30-69 mol% di-tert-butyl fumarate residue unit, 30-69 mol% diethyl fumarate residue unit, and di-n-propyl fumarate residue unit, di-n-fumarate 1 to 20 mol% of one or more residue units selected from butyl residue units, diisobutyl fumarate residue units and di1-methylpropyl fumarate residue units (provided that di-tert-butyl fumarate residue units) 1 selected from diethyl fumarate residue units, di-n-propyl fumarate residue units, di-n-butyl fumarate residue units, diisobutyl fumarate residue units and di1-methylpropyl fumarate residue units A fumaric acid diester resin containing a total of 100 mol% of the above residue units. The fumaric acid diester resin according to claim 1, wherein the number average molecular weight is 50,000 to 500,000. A retardation film using the fumaric acid diester resin according to claim 1. 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 to it is ny, and the refractive index in the thickness direction of the film is nz is nx ≦ ny <nz. The retardation film according to claim 3, wherein the retardation film is present. The retardation film according to claim 3 or 4, wherein an out-of-plane retardation (Rth) measured at a wavelength of 550 nm represented by the following formula (a) is -50 to -2000 nm.
Rth = ((nx−ny) / 2−nz) × d (a)
(Here, d indicates the thickness of the film.) 6. The retardation film according to claim 3, wherein the relationship between the film thickness and the out-of-plane retardation is 4.5 nm / film thickness (μm) or more in absolute value. The ratio (R450 / R550) of the phase difference (R450) measured at a wavelength of 450 nm to the phase difference (R550) measured at a wavelength of 550 nm is 1.1 or less, and any one of claims 3 to 6 The retardation film described in 1.

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