JP5958516B2 - Fumaric acid diester resin and retardation film using the same - Google Patents

Description

  The present invention relates to a fumaric acid diester resin, and more specifically, a film fumarate suitable for a retardation film having a high out-of-plane retardation even in a thin film and excellent optical characteristics such as low wavelength dependency. The present invention relates to an acid diester resin.

  Liquid crystal displays are widely used as the most important display devices in the multimedia society, including cellular phones, computer monitors, laptop computers, and televisions. Many optical films are used for improving display characteristics in liquid crystal displays, and in particular, retardation films play 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 constant temperature range, so the phase difference changes due to slight stress, the problem of stability of the phase difference, the problem of optical characteristics 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 by applying a heat-stretching treatment to the laminate by heat-stretching the film on one or both sides of the polymer film (see, for example, Patent Documents 1 to 3). It is. In addition, a method of uniaxial stretching in a plane while applying an electric field to a polymer film has been proposed (for example, see Patent Document 4).

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

  Moreover, the film which consists of a fumaric acid diester type resin is proposed (for example, refer 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

  The present invention has been made in view of the above problems, and the object thereof is a material suitable for a retardation film having a high retardation even in a thin film and having excellent optical characteristics such as low wavelength dependency. Is to provide.

  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, the present invention is a fumaric acid diester resin for a film containing a diisopropyl fumarate residue unit and a di-tert-butyl fumarate residue unit, and a retardation film using the same.

  Hereinafter, the present invention will be described in detail.

  The fumaric acid diester resin for film of the present invention comprises a diisopropyl fumarate residue unit and a di-tert-butyl fumarate residue unit.

  The composition of the diisopropyl fumarate residue unit and the di-tert-butyl fumarate residue unit contained in the fumaric acid diester resin for a film of the present invention is not particularly limited. Since the phase difference characteristics are excellent, it is preferable that the diisopropyl fumarate residue unit is 50 to 99 mol% and the di-tert-butyl fumarate residue unit is 1 to 50 mol%. A fumaric acid diester resin composed of 60 to 95 mol% of diisopropyl fumarate residue units and 5 to 40 mol% of di-tert-butyl fumarate residue units is more preferable because the phase difference characteristics are more excellent.

  As long as the fumaric acid diester resin for film of the present invention does not exceed the scope of the present invention, it may contain other monomer residue units. Styrene residue units such as styrene residue units and α-methylstyrene residue units; (meth) acrylic acid residue units; (meth) acrylic acid methyl residue units, (meth) ethyl acrylate residue units, ( (Meth) acrylic acid ester residue units such as butyl acrylate residue units; vinyl ester residue units such as vinyl acetate residue units and vinyl propionate residue units; (meth) acrylonitrile residue units; methyl Vinyl ether residue units such as vinyl ether residue units, ethyl vinyl ether residue units and butyl vinyl ether residue units; N-methylmaleimide residue units, N-cyclohexylmale N-substituted maleimide residue units such as amide residue units and N-phenylmaleimide residue units; Olefin residue units such as ethylene residue units and propylene residue units; Dicyclohexyl residue units of fumarate; Bis fumarate Examples of the fumaric acid diester residue unit other than the fumaric acid diester residue unit such as a (2-ethylhexyl) residue unit can be exemplified, and these residue units may be one kind or two or more kinds. Also good.

  The fumaric acid diester resin for film of the present invention preferably has a standard polystyrene equivalent number average molecular weight of 50,000 to 500,000 obtained from an elution curve measured by gel permeation chromatography (GPC). 80,000 to 300,000 are more preferable because the solution viscosity when dissolved, the film forming property when used as a retardation film, and the retardation characteristics and strength are excellent.

  Examples of the method for producing the fumaric acid diester resin for film of the present invention include radical polymerization of diisopropyl fumarate and di-tert-butyl fumarate.

  For the radical polymerization, 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 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-butyl peroxyacetate, tert-butyl peroxybenzoate, tert-butyl peroxypivalate; 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′- Examples thereof include azo initiators such as azobisisobutyronitrile, dimethyl-2,2′-azobisisobutyrate, 1,1′-azobis (cyclohexane-1-carbonitrile), and the like.

  The polymerization temperature at the time of performing radical polymerization can be appropriately set according to the decomposition temperature of the polymerization initiator, and is generally preferably performed in the range of 30 to 150 ° C.

  When the fumaric acid diester resin for film of the present invention is used as an optical film, it has a high out-of-plane retardation even in a thin film and is excellent in optical characteristics such as small wavelength dependence. It is preferable. The retardation film is a retardation film that does not require addition of fine particles.

  In the retardation film 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 orthogonal thereto is ny, and the refractive index in the thickness direction of the film is nz. Is preferably nx ≦ ny <nz. By satisfying nx ≦ ny <nz, a retardation film excellent in viewing angle compensation performance for STN-LCD, IPS-LCD, reflective LCD, transflective LCD and the like is obtained. 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)
(In the formula, d represents the thickness of the film.)
The retardation film of the present invention has a high out-of-plane retardation even in the thin film, the absolute value of the out-of-plane retardation (Rth) / film thickness (μm) 5 ~15nm / μm virtuous 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, 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.

  The retardation film of the present invention preferably contains an antioxidant during film formation or in order to increase the thermal stability of the retardation film itself. 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 especially preferable to mix and use 100-500 weight part of phosphorus antioxidant with respect to 100 weight part of hindered phenolic 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.

  The retardation film of the present invention may contain an ultraviolet absorber in order to improve light resistance. Examples of the ultraviolet absorber include benzotriazole, benzophenone, triazine, benzoate and the like.

  The retardation film of the present invention can be added within the scope of the invention without adding other polymers, surfactants, polymer electrolytes, conductive complexes, inorganic fillers, pigments, antistatic agents, antiblocking agents, lubricants, etc. An agent may be contained.

  Examples of the method for producing the retardation film of the present invention include methods such as a solution casting method and a melt casting method.

  The solution cast method is a method of obtaining a film by casting a solution in which a fumaric acid diester resin for a film 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 addition to the fumaric acid diester resin for film, the dope may be obtained by dissolving an antioxidant, an ultraviolet absorber, and other additives in a solvent as necessary. 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 film fumaric acid diester resin is preferably 1 to 200 μm after drying, more preferably 5 to 100 μm, and particularly preferably 10 to 50 μm.

  The melt casting method is a molding method in which a fumaric acid diester resin for film is melted in an extruder and 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. It is. Furthermore, the retardation films of the present invention can be laminated with each other or with other retardation films.

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

  The film fumaric acid diester resin 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 and small wavelength dependency. Further, it is a fumaric acid diester resin, and is particularly suitable as an optical compensation film material for liquid crystal display elements.

It is a figure which shows the change of the refractive index ellipsoid by extending | 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 for film obtained by the Example is shown below. Unless otherwise noted, commercially available reagents were used.

<Measurement of composition of fumaric acid diesters>
It calculated | required from the proton nuclear magnetic resonance spectroscopy (1H-NMR) spectrum analysis using the nuclear magnetic resonance measuring apparatus (The JEOL make, brand name JNM-GX270).

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

<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 clothes refractometer (manufactured by Oji Scientific Instruments, trade name KOBRA-WR).

Synthesis example 1
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.

  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.

  Thereafter, the same synthesis as described above was performed 7 times to obtain 154 g of di-tert-butyl fumarate having a purity of 99%.

Example 1
In a glass ampule with a capacity of 75 mL, 61 g (0.305 mol) of diisopropyl fumarate, 3 g (0.013 mol) of di-tert-butyl fumarate obtained in Synthesis Example 1 and tert-butyl peroxypi which is a polymerization initiator are used. 0.2 g (0.001 mol) of barate was added, and after nitrogen substitution and depressurization were repeated, sealing was performed under reduced pressure. The ampoule was placed in a 45 ° C. thermostat and held for 48 hours to carry out radical polymerization. After completion of the polymerization reaction, the polymer was taken out from the ampule and dissolved in 400 g of tetrahydrofuran. This polymer solution was dropped into 3 L of methanol and precipitated, and then vacuum dried at 80 ° C. for 10 hours to obtain 53 g of a fumaric acid diester resin (yield: 82%).

  The number average molecular weight of the obtained fumaric acid diester resin was 173,000. Moreover, it was confirmed by 1H-NMR measurement that the resin composition was diisopropyl fumarate residue unit / di-tert-butyl fumarate residue unit = 96/4.

Example 2
In a glass ampule with a capacity of 75 mL, 33 g (0.165 mol) of diisopropyl fumarate, 31 g (0.136 mol) of di-tert-butyl fumarate obtained in Synthesis Example 1, and tert-butyl peroxypi which is a polymerization initiator are used. 0.5 g (0.003 mol) of valerate was added, and after nitrogen substitution and depressurization were repeated, it was sealed under reduced pressure. The ampule was placed in a constant temperature bath at 48 ° C. and kept for 24 hours to carry out radical polymerization. After completion of the polymerization reaction, the polymer was taken out from the ampule and dissolved in 400 g of tetrahydrofuran. This polymer solution was dropped into 3 L of methanol and precipitated, and then vacuum-dried at 80 ° C. for 10 hours to obtain 56 g of a fumaric acid diester resin (yield: 88%).

  The number average molecular weight of the obtained fumaric acid diester resin was 173,000. In addition, 1H-NMR measurement confirmed that the resin composition was diisopropyl fumarate residue units / di-tert-butyl fumarate residue units = 54/46.

Synthesis example 2
In a glass ampule with a capacity of 75 mL, 43 g (0.215 mol) of diisopropyl fumarate, 21 g (0.092 mol) of di-tert-butyl fumarate obtained in Synthesis Example 1, and tert-butyl peroxypi which is a polymerization initiator 0.4 g (0.002 mol) of valerate was added, and after nitrogen substitution and depressurization were repeated, it was sealed under reduced pressure. The ampule was placed in a constant temperature bath at 55 ° C. and kept for 24 hours to carry out radical polymerization. After completion of the polymerization reaction, the polymer was taken out from the ampule and dissolved in 400 g of tetrahydrofuran. This polymer solution was dropped into 3 L of methanol and precipitated, and then vacuum-dried at 80 ° C. for 10 hours to obtain 55 g of a fumaric acid diester resin (yield: 86%).

  The number average molecular weight of the obtained fumaric acid diester resin was 52,000. Moreover, it was confirmed by 1H-NMR measurement that the resin composition was diisopropyl fumarate residue unit / di-tert-butyl fumarate residue unit = 71/29.

Synthesis example 3
In a glass ampule with a capacity of 75 mL, 30 g (0.150 mol) of diisopropyl fumarate, 34 g (0.150 mol) of di-tert-butyl fumarate obtained in Synthesis Example 1, and tert-butyl peroxypi which is a polymerization initiator 0.1 g of barate (0.0006 mol) was added, and after nitrogen substitution and depressurization were repeated, it was sealed under reduced pressure. The ampoule was placed in a constant temperature bath at 35 ° C. and held for 120 hours for radical polymerization. After completion of the polymerization reaction, the polymer was taken out from the ampule and dissolved in 400 g of tetrahydrofuran. This polymer solution was dropped into 3 L of methanol and precipitated, followed by vacuum drying at 80 ° C. for 10 hours to obtain 42 g of a fumaric acid diester resin (yield: 65%).

  The number average molecular weight of the obtained fumaric acid diester resin was 455,000. In addition, 1H-NMR measurement confirmed that the resin composition was diisopropyl fumarate residue unit / di-tert-butyl fumarate residue unit = 50/50.

Example 3
The fumaric acid diester resin obtained in Example 1 was dissolved in methyl isobutyl ketone to form a 15% by weight resin solution, cast on a polyethylene terephthalate film with a coater, and dried at 100 ° C. for 10 minutes to obtain a thickness. A retardation film of 14 μm fumaric acid diester resin was obtained.

  The obtained retardation film had a total light transmittance of 93%, a haze of 0.3%, and a refractive index of 1.469. The three-dimensional refractive index was nx = 1.4672, ny = 1.4672, nz = 1.4726, and nx = ny <nz, indicating a large value of the refractive index in the thickness direction of the film. Further, the out-of-plane phase difference (Rth) was as negative as −76 nm, and the phase difference ratio (R450 / R550) (wavelength dependence) was as small as 1.01. The absolute value of out-of-plane retardation (Rth) / film thickness (μm) was 5.4 nm / μm.

  From these results, the obtained retardation film has negative birefringence, a large refractive index in the thickness direction, a large out-of-plane retardation, a small wavelength dependency, and a high surface even in a thin film. It had an external phase difference.

Example 4
The fumaric acid diester resin obtained in Example 2 was dissolved in p-xylene to give a 10% by weight resin solution, cast on a polyethylene terephthalate film with a coater, and dried at 130 ° C. for 10 minutes to obtain a thickness. A retardation film of 16 μm fumaric acid diester resin was obtained.

  The obtained retardation film had a total light transmittance of 93%, a haze of 0.3%, and a refractive index of 1.455. The three-dimensional refractive indexes were nx = 1.4533, ny = 1.4533, and nz = 1.4583, and nx = ny <nz, indicating a large value of the refractive index in the thickness direction of the film. The out-of-plane phase difference (Rth) was as negative as −80 nm, and the phase difference ratio (R450 / R550) (wavelength dependence) was as small as 1.01. The absolute value of out-of-plane retardation (Rth) / film thickness (μm) was 5.0 nm / μm.

  From these results, the obtained retardation film has negative birefringence, a large refractive index in the thickness direction, a large out-of-plane retardation, a small wavelength dependency, and a high surface even in a thin film. It had an external phase difference.

Comparative Example 1
The fumaric acid diester resin obtained in Synthesis Example 2 was dissolved in methyl isobutyl ketone to form a 20% by weight resin solution, cast on a polyethylene terephthalate film by a coater, and dried at 120 ° C. for 10 minutes to obtain a thickness. A retardation film of 20 μm fumaric acid diester resin was obtained.

  The obtained retardation film had a total light transmittance of 93%, a haze of 0.3%, and a refractive index of 1.460. The three-dimensional refractive index was nx = 1.4585, ny = 1.4585, and nz = 1.4631, and nx = ny <nz, indicating a large value of the refractive index in the thickness direction of the film. Further, the out-of-plane phase difference (Rth) was as negative as -92, and the phase difference ratio (R450 / R550) (wavelength dependence) was as small as 1.01. The absolute value of out-of-plane retardation (Rth) / film thickness (μm) was 4.6 nm / μm.

  From these results, the obtained retardation film has negative birefringence, a large refractive index in the thickness direction, a large out-of-plane retardation, a small wavelength dependency, and a high surface even in a thin film. It had an external phase difference.

Comparative Example 2
The fumaric acid diester resin obtained in Synthesis Example 3 was dissolved in methyl isobutyl ketone to form an 8% by weight resin solution, cast on a polyethylene terephthalate film with a coater, and dried at 100 ° C. for 10 minutes to obtain a thickness. A retardation film of 13 μm fumaric acid diester resin was obtained.

  The obtained retardation film had a total light transmittance of 93%, a haze of 0.3%, and a refractive index of 1.453. The three-dimensional refractive index was nx = 1.4515, ny = 1.4515, and nz = 1.4560, and nx = ny <nz, indicating a large value of the refractive index in the thickness direction of the film. Further, the out-of-plane phase difference (Rth) was as negative as −59, and the phase difference ratio (R450 / R550) (wavelength dependence) was as small as 1.01. The absolute value of out-of-plane retardation (Rth) / film thickness (μm) was 4.5 nm / μm.

  From these results, the obtained retardation film has negative birefringence, a large refractive index in the thickness direction, a large out-of-plane retardation, a small wavelength dependency, and a high surface even in a thin film. It had an external phase difference.

Synthesis example 4
Into a 75 mL glass ampule, 64 g (0.32 mol) of diisopropyl fumarate and 0.52 g (0.003 mol) of tert-butyl peroxypivalate as a polymerization initiator were added, and after nitrogen substitution and depressurization were repeated. Sealed under reduced pressure. The ampule was placed in a thermostatic bath at 50 ° C. and kept for 24 hours to carry out radical polymerization. After completion of the polymerization reaction, the polymer was taken out from the ampule and dissolved in 400 g of tetrahydrofuran. This polymer solution was dropped into 3 L of methanol and precipitated, and then vacuum-dried at 80 ° C. for 10 hours to obtain 57 g of a fumaric acid diester resin (yield: 89%).

  The number average molecular weight of the obtained fumaric acid diester resin was 115,000. Moreover, it was confirmed by 1H-NMR measurement that the resin composition was diisopropyl fumarate residue unit / di-tert-butyl fumarate residue unit = 100/0.

Synthesis example 5
A glass ampule with a capacity of 75 mL was charged with 60 g (0.263 mol) of di-tert-butyl fumarate and 0.4 g (0.002 mol) of 2,2′-azobiscyclohexanecarbonitrile as a polymerization initiator, and replaced with nitrogen. After repeating the depressurization, it was sealed in a reduced pressure state. The ampoule was placed in a constant temperature bath at 80 ° C. and kept for 24 hours to carry out radical polymerization. After completion of the polymerization reaction, the polymer was taken out from the ampule and dissolved in 400 g of tetrahydrofuran. This polymer solution was dropped into 3 L of methanol and precipitated, and then vacuum dried at 80 ° C. for 10 hours to obtain 48 g of a fumaric acid diester resin (yield: 80%).

  The number average molecular weight of the obtained fumaric acid diester resin was 48,000. Moreover, it was confirmed by 1H-NMR measurement that the resin composition was diisopropyl fumarate residue unit / di-tert-butyl fumarate residue unit = 0/100.

Comparative Example 3
The fumaric acid diester resin obtained in Synthesis Example 4 was dissolved in methyl isobutyl ketone to form a 20% by weight resin solution, cast on a polyethylene terephthalate film with a coater, and dried at 100 ° C. for 10 minutes to obtain a thickness. A retardation film of 13 μm fumaric acid diester resin was obtained.

  The obtained retardation 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 = 1.46889, ny = 1.4689, nz = 1.4723, and nx = ny <nz and the refractive index in the thickness direction of the film was large, but the out-of-plane retardation (Rth) was as negative as −44 nm, and the absolute value of out-of-plane retardation (Rth) / film thickness (μm) was also as small as 3.4 nm / μm.

Comparative Example 4
The fumaric acid diester resin obtained in Synthesis Example 5 was dissolved in tetrahydrofuran to give a 20% by weight resin solution, cast on a polyethylene terephthalate film with a coater, and dried at 120 ° C. for 10 minutes to obtain a thickness of 14 μm. A phase difference film of a fumaric acid diester resin was obtained.

  The obtained retardation film had a total light transmittance of 93%, a haze of 0.3%, and a refractive index of 1.437. The three-dimensional refractive index was nx = 1.4364, ny = 1.4364, nz = 1.4381, and nx = ny <nz and the refractive index in the thickness direction of the film was large, but the out-of-plane retardation (Rth) was as negative as −24 nm, and the absolute value of out-of-plane retardation (Rth) / film thickness (μm) was also as small as 1.7 nm / μm.

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: refractive index in the film thickness direction

Claims (7)

A fumaric acid diester resin for a film comprising a diisopropyl fumarate residue unit and a di-tert-butyl fumarate residue unit and having a number average molecular weight in terms of standard polystyrene of 173,000 to 300,000. 2. The fumaric acid diester resin for a film according to claim 1, wherein the diisopropyl fumarate residue unit is 50 to 99 mol% and the di-tert-butyl fumarate residue unit is 1 to 50 mol%. . A retardation film comprising the fumaric acid diester resin for film 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)
(In the formula, d represents the thickness of the film.) The retardation film according to any one of claims 3 to 5, wherein an absolute value of out-of-plane retardation (Rth) / film thickness (µm) is 4.5 nm / µm or more. 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 as described in the item.

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