KR102209659B1 - λ/4 retardation film, circularly polarizing plate and organic EL display device - Google Patents

Abstract

It is an object of the present invention to provide a λ/4 retardation film comprising a cellulose ether derivative and a lignin derivative, and to provide a λ/4 retardation film in which there are few defect sites caused by foaming during solution film formation, and coloration is suppressed. The λ/4 retardation film of the present invention contains a cellulose ether derivative having an aromatic-containing group, a lignin derivative, and an acid or a salt thereof.

Description

λ/4 retardation film, circularly polarizing plate and organic EL display device

The present invention relates to a λ/4 retardation film, a circularly polarizing plate, and an organic EL display device.

In the organic EL display device, the light source itself can be independently driven on/off for each pixel, and power consumption is reduced compared to a liquid crystal display device in which the backlight is always lit during image display. In addition, in order to control the transmission and non-transmission of light per pixel during image display, compared to a liquid crystal display device in which a liquid crystal cell and polarizing plates provided on both sides thereof are essential, in an organic EL display device, the light source itself is turned on/off. Since an image can be formed, a configuration similar to that of a liquid crystal display device is unnecessary, and it is possible to obtain a very high front contrast, and it is expected to provide a display device having very excellent viewing angle characteristics. In particular, by using an organic EL element that emits light in each of the colors B, G, and R, a color filter, which was essential in a liquid crystal display device, becomes unnecessary, so it is expected that higher contrast can be obtained in an organic EL display device. .

In an organic EL display device, in order to efficiently extract light from the light-emitting layer to the visible side, a metal material having high light reflectivity is used as the electrode layer constituting the cathode, or a metal plate is provided as a separate reflective member, thereby having a mirror surface. A method of providing a reflective member on a surface opposite to the light extraction surface is generally adopted.

In such an organic EL display device, as described above, unlike a liquid crystal display device, a polarizing plate arranged by cross Nicol is not provided. For this reason, external light is reflected by the reflective member for light extraction to cause projection, and the contrast tends to be greatly reduced under an environment with high illuminance.

In contrast, for example, Patent Document 1 discloses a method of using a circularly polarized light element to prevent reflection of mirror surface external light. The circularly polarizing element described in Patent Literature 1 is formed by laminating an absorption type linear polarizing plate and a λ/4 retardation film so that their respective optical axes cross 45° or 135°.

In such a conventional λ/4 retardation film, for monochromatic light, it is possible to adjust the phase difference of λ/4 or λ/2 of the ray wavelength, but for white light, which is a synthetic wave in which rays in the visible region are mixed, at each wavelength There is a problem in that distribution occurs in the polarization state of, and is converted into colored polarization. This means that even if the material constituting the λ/4 retardation film has a phase difference of λ/4 for the phase difference, for example, for a green monochromatic light of 550 nm, it is λ/4 for a blue wavelength of 450 nm or a red wavelength of 650 nm. It is due to the fact that there is no phase difference. In order to suppress such a phenomenon, it is desired that the λ/4 retardation film has a wavelength dispersion property in which the retardation also increases as the wavelength increases.

From this situation, various studies have been made on a broadband retardation plate capable of providing a retardation in which each wavelength is adjusted by a retardation of λ/4 or λ/2 to light in a wide wavelength range. For example, in Patent Document 2, a λ/4 wave plate having a phase difference of 1/4 wavelength of birefringence light and a λ/2 wave plate having a phase difference of 1/2 wavelength of birefringence are joined in a state where each optical axis crosses. One retardation plate is disclosed.

On the other hand, in order to manufacture the proposed retardation plate, a complicated process of adjusting the optical direction (optical axis or slow axis) of two polymer films is required, and it is necessary to bond a plurality of films with an adhesive layer. . Therefore, since this results in impairing the merit of the organic EL display device that it is possible to reduce the thickness, development of a broadband lambda /4 retardation film having a single layer structure that does not require lamination is required.

As a technique for obtaining a broadband λ/4 retardation film in a single layer configuration, for example, in Patent Document 3, a polymer film in which a monomer unit of a polymer having positive refractive index anisotropy and a monomer unit having negative birefringence are copolymerized. Using, a method of making a λ/4 retardation film by uniaxial stretching is disclosed. Since this uniaxially stretched polymer film has a wavelength dispersion property in which the retardation also increases as the wavelength increases, it becomes possible to manufacture a broadband λ/4 plate with one retardation film. However, while there is a problem in adhesion to a polarizer required as a polarizing plate protective film, there is a problem in that the total light transmittance is not sufficiently obtained.

In general, when the retardation fluctuation rate of the resin used for the retardation film is large, it is liable to be affected by subtle temperature fluctuations and air volume fluctuations in a stretching device. Here, the rate of change indicates how much the phase difference fluctuates when the stretching temperature is changed, and when the stretching temperature is changed greatly, the rate of change of the phase difference is large, and the value of the phase difference reacts sensitively to the stretching temperature.

In the case of a polycarbonate-based resin, this phase difference variation rate is large, and the phase difference is largely changed only by a slight variation in the stretching temperature, so that phase difference unevenness is liable to occur. In addition, since polycarbonate has a high photoelasticity, the retardation of the film changes greatly due to a slight stress, and the retardation of the film changes even with a slight stress generated during assembly or environmental changes, which affects the uniformity and stability of the screen. There was a problem.

In the case of a cellulose ester-based resin, reverse wavelength dispersion can be improved by increasing the degree of substitution, and the retardation variation rate is also small. Therefore, since the phase difference fluctuation due to the fluctuation of the stretching temperature is small, the fluctuation of the phase difference is small and nonuniformity is unlikely to occur. However, since it has the characteristic that the retardation development property decreases when the degree of substitution is increased, in order to obtain a broadband λ/4 retardation film in a single layer, it is necessary to lower the stretching temperature or increase the draw ratio, but break during stretching. There is a problem that this tends to occur. Further, even if the film thickness is increased, the retardation value in a preferable range can be obtained. However, when a circularly polarizing element of the organic EL display device is used for anti-reflection, the advantage of the organic EL display device that can be made thinner is impaired.

In the case of a cellulose ether-based resin, the retardation fluctuation rate is small, there is no nonuniformity and no decrease in the retardation expression property, and a required retardation can be obtained without thickening the film. For example, in Patent Document 4, a retardation film containing a cellulose ether derivative is disclosed. Among them, cellulose ether resin having an aromatic-containing group is suitable as a material for a λ/4 retardation film capable of expressing a retardation of λ/4 in a broadband because it has a wavelength dispersion property that increases the retardation as the wavelength increases. Do.

Japanese Patent Laid-Open No. Hei 8-321381 Japanese Patent Laid-Open No. Hei 10-68816 International Publication No. 2000/026705 Japanese Patent No. 4750982

A film containing such a cellulose ether resin (hereinafter, referred to as a cellulose ether derivative) may be prepared, for example, by a solution film forming method. Specifically, a film containing a cellulose ether derivative may be prepared through a process in which a dope obtained by dissolving the cellulose ether derivative in a solvent is pliable on a support, followed by drying and peeling. The cellulose ether derivative may form a mixture with a lignin derivative derived from the raw material, for example. However, in the process of manufacturing a film using such a cellulose ether derivative, there is a problem that foaming is likely to occur when drying a flexible dope on a support, and defect sites are likely to occur in the resulting λ/4 retardation film. In addition, there is also a problem that coloring is likely to occur in the resulting lambda /4 retardation film.

The present invention has been made in view of these circumstances, and is a λ/4 retardation film comprising a cellulose ether derivative and a lignin derivative, and a λ/4 retardation film having fewer defects due to foaming during solution film formation and suppressed coloring. It aims to provide.

[1] A λ/4 retardation film comprising a cellulose ether derivative having an aromatic-containing group, a lignin derivative, and an acid or a salt thereof.

[2] The alkoxy group contained in the cellulose ether derivative is an aliphatic alkoxy group, the aromatic-containing group is an aromatic acylate group, and the cellulose ether derivative satisfies the following formula (I), λ/4 described in [1] Retardation film.

Formula (I): 1.5≤X+Y≤3.0

1.0≤X≤2.5

0.1≤Y≤1.0

(In formula (I),

X is the degree of substitution of the aliphatic alkoxy group,

Y is the degree of substitution of the aromatic acylate group)

[3] The λ/4 retardation film according to [1] or [2], wherein the acid is an organic acid having an aromatic ring.

[4] The λ/4 retardation film according to any one of [1] to [3], wherein the content of the acid or salt thereof is 0.5 to 500 ppm by mass based on the total mass of the cellulose ether derivative.

[5] The λ/4 retardation film according to any one of [1] to [4], further comprising at least one additive selected from the group consisting of a phenolic compound, a phosphite compound, and a benzotriazole compound.

[6] A polarizer and the λ/4 retardation film according to any one of [1] to [5] are included, and the angle formed by the in-plane slow axis of the λ/4 phase difference film and the absorption axis of the polarizer is 40 to 50°, circularly polarizing plate.

[7] An organic EL display device comprising an organic EL element and the circularly polarizing plate according to [6].

The present invention is a lambda /4 retardation film containing a cellulose ether derivative and a lignin derivative, and it is possible to provide a broadband lambda /4 retardation film in which there are few defect sites due to foaming at the time of solution film formation and coloration is suppressed.

1 is a plan view showing an example of a configuration of an oblique stretching device.
2 is a plan view showing an example of a rail pattern of an elongated portion.
3 is a schematic diagram showing an example of a configuration of an organic EL display device.

As described above, in the process of producing a film containing an aromatic-containing group-containing cellulose ether derivative and a lignin derivative by a solution film forming method, the mechanism for generating bubbles is not clear, but it is estimated as follows.

That is, in the case of drying the film-like material on the support, drying starts from the surface, but at this time, if there is a part in the film-like material where the solvent is easily trapped, such as a part with a low density, the solvent is dried and vaporized later. When the surface is dry to some extent, the vaporized solvent loses its place to go and tends to form bubbles in the film-like material.

For example, cellulose ether derivatives using pulp as a raw material form a mixture with relatively many lignin derivatives. The lignin derivative is a so-called network-shaped molecule, and has a three-dimensional structure, and it is considered that a portion having a low density partially exists in the molecule of the three-dimensional structure. In particular, in the case of a cellulose ether derivative having an aromatic-containing group, since the aromatic moiety and the lignin derivative easily interact, the network-like three-dimensional structure tends to become more complex, and as a result, the content ratio of the partially low-density moiety increases. , It is thought that foaming is easily promoted.

In addition, the mechanism by which the film containing the cellulose ether derivative and the lignin derivative having an aromatic-containing group causes coloration or discoloration is not clear, but is estimated as follows.

That is, it is considered that the lignin derivative itself is colored, and that the lignin derivative is easily decomposed by light or heat, thereby causing discoloration or coloring. In particular, in the production process of the film, the lignin derivative triggers foaming, and the distribution of lignin is uneven around the foaming, and therefore, it is considered that coloration and discoloration are easily amplified because light and heat also act unevenly.

Therefore, in order to reduce defect sites caused by foaming of the resulting λ/4 retardation film and to suppress coloring or discoloration, it is desired to reduce the content of the lignin derivative contained in the cellulose ether derivative as much as possible. However, in order to highly reduce the content of the lignin derivative, it is expensive. Therefore, even when a cellulose ether derivative in which a small amount of the lignin derivative remains is used, it is desired to be able to suppress foaming, coloring and discoloration.

On the other hand, the present inventors found out that foaming in the manufacturing process of a film and coloring of a film can be suppressed by adding "acid or its salt" further. Although this mechanism is not obvious, it is estimated as follows. That is, the acid or its salt acts on the hydroxyl group of the lignin derivative to weaken the formation of hydrogen bonds constituting the three-dimensional structure, and thus the three-dimensional structure can be easily released. As a result, it is considered that the content ratio of the low-density portion in the three-dimensional structure in the lignin derivative can be reduced, foaming can be suppressed, and the resulting color non-uniformity can also be improved. The present invention has been made based on these findings.

1.λ/4 retardation film

The λ/4 retardation film contains a cellulose ether derivative, a lignin derivative, and an acid or a salt thereof.

<Cellulose ether derivative>

A cellulose ether derivative is a compound in which at least a part of a hydroxyl group of cellulose is substituted with an alkoxy group (-OR).

R in the alkoxy group (-OR) is an aliphatic hydrocarbon group or an aromatic group.

The number of carbon atoms in the aliphatic hydrocarbon group is preferably 1 to 20, more preferably 1 to 12, and still more preferably 1 to 6. The aliphatic hydrocarbon group may be any of linear, branched and cyclic groups. It is preferable that the aliphatic hydrocarbon group is an unsubstituted aliphatic hydrocarbon group. The aliphatic hydrocarbon group is preferably an alkyl group, and more preferably a straight-chain alkyl group. Among them, a methyl group or an ethyl group is particularly preferable.

The aromatic group is an aromatic hydrocarbon group or an aromatic heterocyclic group.

The number of carbon atoms in the aromatic hydrocarbon group is preferably 6 to 24, more preferably 6 to 12, and even more preferably 6 to 10. Examples of the aromatic hydrocarbon group include a phenyl group, a naphthyl group, an anthryl group, a biphenyl group, a terphenyl group, and the like, preferably a phenyl group, a naphthyl group, and a biphenyl group, and more preferably a phenyl group and a naphthyl group.

The aromatic heterocyclic group preferably contains at least one of an oxygen atom, a nitrogen atom or a sulfur atom, and examples thereof include furan, pyrrole, thiophene, imidazole, pyrazole, pyridine, pyrazine, pyridazine, triazole, triazole Azine, indole, indole, purine, thiazolin, thiadiazole, oxazoline, oxazole, oxadiazole, quinoline, isoquinoline, phthalazine, naphthyridine, quinoxaline, quinazoline, cinoline, pteridine , Acridine, phenanthroline, phenazine, tetrazole, benzimidazole, benzoxazole, benzthiazole, benzotriazole, tetrazaindene, and other aromatic heterocyclic groups. Among them, a pyridyl group, a thiophenyl group, a triazinyl group, and a quinolyl group are preferable.

Especially, it is preferable that an aromatic group is an aromatic hydrocarbon group.

The cellulose ether derivative may further have a substituent other than an alkoxy group (-OR). Examples of other substituents include an acylate group (-O-COR). R of the acylate group (-O-COR) is an aliphatic hydrocarbon group or an aromatic group. The aliphatic hydrocarbon group and the aromatic group have the same meaning as the aliphatic hydrocarbon group and the aromatic group represented by R of the alkoxy group (-OR).

It is more preferable that at least part of R of the alkoxy group (-OR) contained in the cellulose ether derivative, or at least part of R of the alkoxy group (-OR) and/or the acylate group (-O-COR) is an aromatic group. . That is, it is preferable that at least a part of the alkoxy group (-OR) and/or the acylate group (-O-COR) contained in the cellulose ether derivative is an aromatic-containing group. When at least a part of the alkoxy group (-OR) and/or the acylate group (-O-COR) contained in the cellulose ether derivative is an aromatic-containing group, the film can be given a wavelength dependence of the retardation. Thereby, a λ/4 retardation film that exhibits a λ/4 retardation in a wide wavelength range can be obtained. The aromatic-containing group is a group containing an aromatic group, and refers to an alkoxy group (-OR), an acylate group (-O-COR), and the like in which R is an aromatic group as described above.

Among them, from the viewpoint of ease of synthesis, the cellulose ether derivative contains an alkoxy group (-OR) and an acylate group (-O-COR), and R of the alkoxy group (-OR) is an aliphatic hydrocarbon group, It is more preferable that R of the acylate group (-O-COR) is an aromatic group.

It is preferable that the total degree of substitution of the cellulose ether derivative is 1.5 to 3.0. The total degree of substitution of the cellulose ether derivative refers to the sum of the alkoxy groups substituted with hydroxyl groups at the 2nd, 3rd and 6th positions in the glucose skeleton, and other substituents (acylate groups, etc.) in the whole cellulose ether derivative. It means the average value (average degree of substitution) of. When the total degree of substitution of the cellulose ether derivative is 1.5 or more, it is preferable to adjust the DSP to less than 1 while reducing the fluctuation of the phase difference to humidity fluctuations, and because it is easy to adjust Ro to a certain level or more.

Among these, the degree of substitution of the aromatic-containing group of the cellulose ether derivative is preferably 0.05 to 1.2, more preferably 0.1 to 1.0. When the degree of substitution of the aromatic-containing group is 0.05 or more, the variation of the phase difference to humidity fluctuation is reduced, and the DSP can be lowered while suppressing excessively low Ro. That is, wavelength dependence can be given to the retardation of the film. When the degree of substitution of the aromatic-containing group is 1.2 or less, it is possible to suppress excessively low DSP.

As described above, the cellulose ether derivative preferably contains an aliphatic alkoxy group (-OR, R: aliphatic hydrocarbon group) and an aromatic acylate group (-O-COR, R: aromatic group). In this case, the degree of substitution of the aliphatic alkoxy group (-OR) of the cellulose ether derivative is preferably 0.9 to 2.7, and more preferably 1.0 to 2.5. When the degree of substitution of the aliphatic alkoxy group is more than a certain degree, it is possible to suppress excessively low DSP. When the degree of substitution of the aliphatic alkoxy group is not more than a certain degree, it is possible to suppress a remarkable impairment of the retardation expression property by stretching. The degree of substitution of the aromatic acylate group of the cellulose ether derivative is preferably 0.05 to 1.2, and more preferably 0.1 to 1.0, as described above. That is, it is particularly preferable that the cellulose ether derivative satisfies the following formula (I).

Formula (I): 1.5≤X+Y≤3.0

1.0≤X≤2.5

0.1≤Y≤1.0

(In formula (I),

X is the degree of substitution of an aliphatic alkoxy group,

Y is the degree of substitution of an aromatic acylate group)

The degree of substitution of the aliphatic alkoxy group of the cellulose ether derivative is the average value (average degree of substitution) of the total aliphatic alkoxy groups substituted with the hydroxyl groups at the 2nd, 3rd and 6th positions in the glucose skeleton. it means. Similarly, the degree of substitution of an aromatic-containing group means the average value (average degree of substitution) in the whole cellulose ether derivative of the sum of the total aromatic-containing groups substituted with hydroxyl groups at the 2nd, 3rd, and 6th positions in the glucose skeleton. .

The degree of substitution of an alkoxy group or an aromatic-containing group of the cellulose ether derivative is ¹ H-NMR or ¹³ C-NMR using the method described in Cellulose Communication 6, 73-79 (1999) and Chrality 12 (9), 670-674. It can be measured by

The mass average molecular weight (Mw) of the cellulose ether derivative is preferably in the range of 7×10 ³ to 10000×10 ³ , and more preferably in the range of 15×10 ³ to 5000×10 ³ . When the mass average molecular weight of the cellulose ether derivative is more than a certain level, it is easy to increase the mechanical strength of the film, and if it is less than a certain level, the solubility in the solvent at the time of film formation is difficult to impair. The molecular weight distribution (MWD) is preferably 1.1 to 10, more preferably 1.5 to 8.0.

Measurement of the mass average molecular weight (Mw) and molecular weight distribution (MWD) can be performed using gel permeation chromatography (GPC). Specifically, N-methylpyrrolidone can be used as a solvent, a polystyrene gel is used, and a converted molecular weight calibration curve obtained in advance from a constitutional curve of a standard monodisperse polystyrene can be used.

The cellulose ether derivative can be prepared by referring to a known method, for example, a method described in pages 131 to 164 of "The Dictionary of Cellulose" (Asakura Bookstore, 2000). Specifically, cellulose in which nothing is substituted or cellulose ether in which some of the hydroxyl groups at the 2nd, 3rd and 6th positions are etherified (substituted with an alkoxy group (-OR)) are used as raw materials. For example, cellulose or cellulose ether as a raw material is dissolved in a suitable organic solvent, and acid chloride or acid anhydride is reacted in the presence of a base such as pyridine, and the remainder of the hydroxyl group is esterified to obtain a cellulose ether derivative. As the raw material of the cellulose ether used as a raw material, a known raw material can be used, and for example, cellulose made from pulp can be used.

<Lignin derivative>

As described above, the lignin derivative may be mainly derived from a raw material of a cellulose ether derivative, but may be contained artificially. The content of the lignin derivative may be 0.1 to 10.0 mass% based on the total mass of the cellulose ether derivative. From the viewpoint of facilitating generation of air bubbles in the film production process or coloration of the film, the content of the lignin derivative is preferably less than 5% by mass with respect to the total mass of the cellulose ether derivative.

The content of the lignin derivative in the λ/4 retardation film can be measured by the following method. That is, the film is finely ground as a sample, and the amount of the lignin derivative contained in the sample is measured according to the pulp material-lignin content test method of JAPANTAPPI paper pulp test method No.61:2000.

<acid or salt thereof>

The acid may be an inorganic acid or an organic acid.

Examples of inorganic acids include hydrochloric acid and sulfuric acid.

Examples of the organic acid include aliphatic carboxylic acids and aromatic carboxylic acids (organic acids having an aromatic ring). Examples of the aliphatic carboxylic acid include acetic acid and propionic acid. Examples of the aromatic carboxylic acid include benzoic acid, 3-thiophenecarboxylic acid, picolinic acid, nicotinic acid, 4-methoxybenzoic acid, trimethoxybenzoic acid, naphthoic acid, phthalic acid, and the like.

Examples of the metal forming the salt of the acid include alkali metals such as sodium and potassium; Alkaline earth metals such as calcium and magnesium are included, and sodium, potassium or magnesium is preferred.

Among them, an organic acid or a salt thereof is preferable, and an aromatic carboxylic acid or a salt thereof is more preferable. Aromatic carboxylic acid or its salt is highly compatible with the lignin derivative, and therefore acts highly on the hydroxyl group of the lignin derivative, making it easier to weaken the formation of hydrogen bonds constituting the three-dimensional structure, and to further loosen the three-dimensional structure. Because it can be done easily.

The average molecular weight of the acid or salt thereof may be, for example, 36 to 250. The acid or its average molecular weight can be measured as a relative molecular weight by mass spectrometry or the like.

The content of the acid or its salt is preferably 0.1 to 600 ppm by mass based on the total mass of the cellulose ether derivative. When the content of the acid or its salt is 0.1 mass ppm or more, foaming and coloring derived from the lignin derivative can be highly suppressed, and when it is 600 mass ppm or less, the breakage of the ester bond of the cellulose ether derivative can be highly suppressed. Thereby, the distribution of the molecular weight and the degree of substitution of the cellulose ether derivative widens, and a decrease in haze due to a decrease in compatibility can be highly suppressed. The content of the acid or its salt is more preferably 0.5 to 500 ppm by mass based on the total mass of the cellulose ether derivative.

The content of the acid or its salt can be measured by ion chromatography. Measurement conditions can be carried out as follows.

(Pretreatment)

The film is finely pulverized, 500 mg (M) of a sample is weighed into a container made of PP, and 10 ml of ultrapure water is added. After dispersing this for 30 minutes with an ultrasonic cleaner, it is filtered through an aqueous chromatography disk (0.45 µm), and the obtained liquid is used as a sample.

(Measure)

Apparatus: Ion Chromatograph DX-500 manufactured by DIONEX

Column: DIONEX IonPac ICE-AS1

Suppressor: AMMS-II

Eluent: 1.0mM-octanesulfonic acid

Regeneration liquid: 5.0mM-tetrabutylammonium hydroxide (send at 5psi of high purity nitrogen)

Flow rate: 1.0ml/min

Injection volume: 25μl

Conversion method: Content (ppm by mass) = measured value (mg/l)/1000×10/M(mg)×1000000

<Other ingredients>

The λ/4 retardation film may further contain other components within a range that does not impair the effects of the present invention. Examples of other components include additives such as an ultraviolet absorber, an antioxidant, and a light stabilizer, and a mat agent (fine particles).

(Ultraviolet absorber)

Examples of the ultraviolet absorber include benzotriazole-based compounds, benzophenone-based compounds, triazine-based compounds, and the like. Among them, a benzotriazole-based compound and a benzophenone-based compound are preferred, and a benzotriazole-based compound is more preferred from the viewpoint of relatively little coloring of the film.

(Benzotriazole-based compound)

The benzotriazole-based compound is a compound having a benzotriazole skeleton. Examples of the benzotriazole-based compound include 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3',5'-di-t-butylphenyl)benzotria Sol, 2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3',5'-di-t-butylphenyl)- 5-chlorobenzotriazole, 2-[2'-hydroxy-3'-(3",4",5",6"-tetrahydrophthalimidomethyl)-5'-methylphenyl]benzotriazole, 2, 2-methylenebis[4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol], 2-(2'-hydroxy-3'-t -Butyl-5'-methylphenyl)-5-chlorobenzotriazole, 2-(2H-benzotriazol-2-yl)-6-(straight and branched dodecyl)-4-methylphenol, octyl-3-[ 3-t-butyl-4-hydroxy-5-(chloro-2H-benzotriazol-2-yl)phenyl]propionate and 2-ethylhexyl-3-[3-t-butyl-4-hydroxy -5-(5-chloro-2H-benzotriazol-2-yl)phenyl]propionate, and the like. Examples of commercial products include TINUVIN (registered trademark) 111FDL, East 928, East 1130, East 123, East 123-DW, East 144, East 152, East 1577ED, East 1600, East 171, East 213, East 234, East 292, B292HP, B1212, B326, B328, B329, B360, B384-2, B400 (above, BASF Japan company make, brand name); Includes Adeka Staff LA-24, East LA-29, East LA-31, East LA-31RG, East LA-31G, East LA-32, East LA-36, East LA-36RG (above, manufactured by Adeka Corporation) do.

The content of the ultraviolet absorber is preferably 0.1 to 5.0% by mass, and more preferably 0.5 to 5.0% by mass, based on the total mass of the cellulose ether derivative. When the content of the ultraviolet absorber is 0.1% by mass or more, it is easy to highly suppress photolysis of the resin, and when it is 5% by mass or less, the optical properties of the obtained film are hardly impaired.

(Light stabilizer)

Examples of the light stabilizer include hindered amine compounds. Examples of commercially available products of hindered amine compounds include Adekastep LA-52, LA-57, LA-63P, LA-68, LA-72, LA-77Y, LA-77G, LA -81, East LA-82, East LA-87, East LA-402AF, East LA-502XP (above, Adeka Corporation) are included.

(Antioxidant)

Examples of antioxidants include phenolic compounds (including hindered phenolic compounds), phosphite compounds, and thioether compounds. Among them, a phenolic compound and a phosphite compound are preferable, and a phenolic compound is more preferable.

(Phenolic compound)

The phenolic compound is a compound having a phenolic skeleton or a hindered phenolic skeleton. Examples of phenolic compounds include 2,6-di-t-butyl-4-hydroxytoluene (BHT), pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl). )Propionate], octadodecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, tris(3,5-di-tert-butyl-4-hydroxybenzyl )Isocyanurate, 4,4'-butylidenebis-(3-methyl-6-t-butylphenol), triethylene glycol-bis[3-(3-t-butyl-4-hydroxy-5) -Methylphenyl)propionate], 3,9-bis[2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl]-2, 4,8,10-tetraoxaspiro[5,5]undecane, and the like. Examples of commercial items include IRGANOX1010, 1076, and 1726 (above, manufactured by BASF Japan); Adeka staff AO-20, copper AO-30, copper AO-40, copper AO-50, copper AO-60, copper AO-80, copper AO-330, etc. (above, manufactured by Adeka Corporation) are included. .

(Phosphite compound)

The phosphite-based compound is a compound having a P(OR) ₃ structure. R is an alkyl group, an alkylene group, an aryl group, an arylene group, etc., and three Rs may be the same or different, and two Rs may form a ring structure.

Examples of the phosphite-based compound include tris(2,4-di-tert-butylphenyl)phosphite, bis[2,4-bis(1,1-dimethylethyl)-6-methylphenyl]ethyl ester phosphorous acid, bis( 2,4-di-tert-butylphenyl) pentaerythritol diphosphite, bis(2,4-dicumylphenyl) pentaerythritol diphosphite, bis(2,6-di-tert-butyl-4-methylphenyl) penta Erythritol-di-phosphite, trisnonylphenylphosphite, tris(2,4-di-tert-butylphenyl)phosphite, tri(o-tolyl)phosphine, tri(p-tolyl)phosphine, cyclo Hexyldiphenylphosphine, ethyldiphenylphosphine, and the like are included. Examples of commercially available products include Adeka Staff (registered trademark) PEP-36, copper PEP-8, copper HP-10, copper 2112, copper 1178, copper 1500, copper C, 135A, 3010, and TPP (above, Decasa); SUMILIZER (registered trademark) GP (above, manufactured by Sumitomo Chemical Corporation); These include Irgafos (registered trademark) 38, East 168, and P-EPQ (above, all manufactured by BASF Japan).

The content of the antioxidant is preferably 0.02 to 5% by mass, more preferably 0.05 to 3% by mass with respect to the total mass of the cellulose ether derivative. When the content of the antioxidant is 0.02% by mass or more, it is easy to highly suppress decomposition of the resin, and when it is 5% by mass or less, the optical properties of the obtained film are hardly impaired.

Among these, the λ/4 retardation film preferably contains at least one selected from the group consisting of a benzotrisol compound as an ultraviolet absorber, a phenol compound and a phosphite compound as an antioxidant. When the λ/4 retardation film further contains these compounds, not only the ultraviolet absorbing function or the antioxidant function is obtained, but also generation of air bubbles and coloring of the film in the film manufacturing process can be further suppressed. The reason is not clear, but in benzotriazole-based compounds and phenol-based compounds, its aromatic ring and the aromatic ring of the cellulose ether derivative are likely to interact, and in the phosphite-based compound, the lone pair of phosphorus and the aromatic ring of the cellulose ether derivative interact. I think it's easy to do. As a result, it is thought that the interaction between molecules of the cellulose ether derivative is weakened, the distance between molecules is widened, and the moving speed of the solvent molecules between the molecules is increased. As a result, it is thought that the solvent remaining in the film-like substance decreases and foaming is more highly suppressed.

(Mat)

The mat agent (fine particles) has a function of enhancing the slipperiness of the λ/4 retardation film. Examples of fine particles include inorganic silicon dioxide (SiO ₂ ), titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, and calcium phosphate. Particulates are included.

Among them, in order to reduce the increase in haze of the obtained film, silicon dioxide is preferable. Examples of commercially available silicon dioxide particles include Aerosil R812, R972 (manufactured by Nippon Aerosil), NanoTek SiO ₂ (manufactured by CI Kasei), and the like.

The shape of the fine particles may be any of an irregular shape, a needle shape, a flat shape, and a spherical shape, and it is preferable to have a spherical shape from the viewpoint that transparency of the obtained film is hardly impaired.

The fine particles may be used alone or in combination of two or more. Further, by using particles having different particle diameters and shapes (eg, needle shape and spherical shape) together, transparency and slipperiness may be highly compatible.

The average primary particle diameter of the fine particles is preferably 5 to 50 nm. When the average primary particle diameter of the fine particles is 5 nm or more, since the surface of the film can be roughened, it is easy to impart slidability, and when it is 50 nm or less, it is easy to suppress an increase in haze. The average primary particle diameter of the fine particles is more preferably 5 to 30 nm.

The content of the fine particles can be, for example, 0.1 to 5 mass% with respect to the total mass of the cellulose ether derivative. When the content of the fine particles is 0.1% by mass or more, it is easy to sufficiently increase the slipperiness of the surface of the film, and when it is 5% by mass or less, it is easy to suppress an increase in the haze of the film. The content of the fine particles is more preferably 0.1 to 2.5% by mass, and still more preferably 0.3 to 2% by mass, based on the total mass of the cellulose ether derivative.

<Film properties>

(Phase difference Ro and Rt)

The in-plane retardation Ro of the λ/4 retardation film measured in an environment with a measurement wavelength of 550 nm and 23°C 55% RH preferably satisfies 30 nm≦Ro≦300 nm, more preferably satisfies 50 nm≦Ro≦250 nm And, it is more preferable to satisfy 120nm≤Ro≤150nm. The retardation Rt in the thickness direction of the λ/4 retardation film measured in an environment at a measurement wavelength of 550 nm and 23° C. 55% RH preferably satisfies 0 nm≦Rt≦200 nm, and more preferably satisfies 0 nm≦Rt≦150 nm Do. A λ/4 retardation film having such a retardation is suitable, for example, as a λ/4 retardation film of an organic EL display device.

Ro and Rt of the λ/4 retardation film are each defined by the following formula.

Equation (1): Ro=(nx-ny)×d

Equation (2): Rt=((nx+ny)/2-nz)×d

(In the formula,

nx is the refractive index in the direction x (in-plane slow axis direction) in which the refractive index becomes the largest in the in-plane direction of the film,

ny is a refractive index in a direction y orthogonal to the direction x (in-plane slow axis direction) in the in-plane direction of the film,

nz is the refractive index in the thickness direction of the film,

d is the film thickness (nm))

The in-plane slow axis of the λ/4 retardation film refers to the axis at which the refractive index becomes the largest in the film surface. The in-plane slow axis of the λ/4 retardation film can be confirmed by AxoScan manufactured by Axometrics.

The orientation angle (angle formed by the in-plane slow axis and the film width direction) of the λ/4 retardation film is preferably 40 to 50°, and more preferably 45°.

The measurement of Ro and Rt of the λ/4 retardation film can be performed by the following method.

1) The λ/4 retardation film is regulated for 24 hours in an environment of 23°C and 55%RH. The average refractive index of this optical film is measured with an Abbe refractometer, and the thickness d is measured using a commercially available micrometer.

2) The three-dimensional refractive indices nx, ny, and nz at a wavelength of 550 nm of the λ/4 retardation film after humidity control were measured in an environment of 23° C. 55% RH using AxoScan manufactured by Axometrics, and the refractive indexes nx, ny, nz Find the average value of The obtained values are applied to the above formulas (1) and (2), and Ro and Rt are calculated, respectively.

The retardation Ro and Rt of the λ/4 retardation film can be adjusted mainly in accordance with the degree of substitution of the cellulose ether derivative and the draw ratio. In order to increase the retardation Ro and Rt of the λ/4 retardation film, for example, it is preferable to increase the degree of substitution of the alkoxy group of the cellulose ether derivative, lower the degree of substitution of the aromatic-containing group, or increase the draw ratio. .

(DSP)

The DSP of the λ/4 retardation film is preferably less than 1, and more preferably more than 0.75 and 0.9 or less. This is because such a λ/4 retardation film can express a λ/4 retardation in a wide wavelength range.

The DSP measurement of the λ/4 retardation film can be performed by the following method.

1) In the same manner as the above-described measurement of the retardation Ro, the in-plane retardation value (Ro) at a wavelength of 450 nm and 550 nm of the λ/4 retardation film was measured using an Axoscan manufactured by Axometrics under an environment of a temperature of 23°C and a relative humidity of 55%. Measure each using.

2) The obtained in-plane retardation value Ro (450) at a wavelength of 450 nm and an in-plane retardation value Ro (550) at a wavelength of 550 nm are applied to the following equation (3) to calculate the wavelength dispersion value (DSP). .

Equation (3): DSP=Ro(450)/Ro(550)

The DSP of the λ/4 retardation film can be adjusted according to the degree of substitution of the aromatic-containing group of the cellulose ether derivative. In order to lower the DSP of the λ/4 retardation film, for example, it is preferable to increase the degree of substitution of the aromatic-containing group of the cellulose ether derivative.

(Haze)

It is preferable that the haze of the λ/4 retardation film is 0.01 to 2.0. When the haze of the λ/4 retardation film is 2.0 or less, the contrast of the display image of the organic EL display device can be increased. It is more preferable that the haze of the λ/4 phase difference film is 0.01 to 1.0. The haze of the λ/4 retardation film can be measured with a haze meter (model NDH 2000, manufactured by Nippon Denshoku Co., Ltd.).

The haze of the λ/4 retardation film can be adjusted according to the content of an acid or a salt thereof. In order to lower the haze of the λ/4 retardation film, for example, the content of an acid or a salt thereof is preferably set to a certain level or less.

(thickness)

The thickness of the λ/4 retardation film can be, for example, 5 to 100 µm, preferably 5 to 60 µm, and more preferably 10 to 50 µm.

2. Manufacturing method of λ/4 retardation film

The lambda /4 retardation film of the present invention is preferably produced by a solution film forming method (cast method) from the viewpoint that production efficiency is good and a film having high film thickness uniformity is easily obtained.

That is, in the λ/4 retardation film of the present invention, 1) a step of obtaining a dope containing the above-described cellulose ether derivative, a lignin derivative, an acid or a salt thereof, and a solvent (dope production step), 2) the dope It can be manufactured through a process of obtaining a film-like substance by flexible, drying and peeling on a support (a process of obtaining a film-like substance), and 3) a process of stretching the obtained film-like substance in an oblique direction (diagonal stretching process).

About the process of 1) (the dope manufacturing process)

The above-described cellulose ether derivative, lignin derivative, and acid or salt thereof are dissolved in a solvent to prepare a dope.

It is preferable that the solvent used for dope contains an organic solvent (good solvent) which can dissolve the above-mentioned cellulose ether derivative. Examples of such a good solvent include chlorine-based organic solvents such as methylene chloride (dichloromethane); Non-chlorine organic solvents, such as methyl acetate, ethyl acetate, acetone, and tetrahydrofuran, are contained. Among them, methylene chloride (dichloromethane) is preferable.

The solvent used for dope may further contain a poor solvent. Examples of poor solvents include linear or branched aliphatic alcohols having 1 to 4 carbon atoms. When the ratio of alcohol in the dope is increased, the film-like material is likely to be gelled, and peeling from the metal support is likely to become easy. Examples of linear or branched aliphatic alcohols having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol. Among these, ethanol is preferred from the viewpoint of stability of dope and its boiling point being relatively low, and good drying properties.

Since the acid or its salt is difficult to dissolve in the solvent constituting the main component of the dope solution, it is preferable not to dissolve directly in the solvent, but to dissolve after mixing it with a cellulose ether derivative. Mixing of a cellulose ether derivative and an acid or a salt thereof is performed by dissolving the cellulose ether derivative in a solvent, and then reprecipitation and purification with a solvent to which an acid or salt thereof is added when reprecipitating or purifying with a solvent containing water. I can. Thereby, a mixture in which a cellulose ether derivative and an acid or a salt thereof are uniformly mixed can be obtained, and the acid or a salt thereof can be dissolved in the solvent by dissolving the mixture in a solvent.

About the process of 2) (the process of obtaining a film-like material)

The obtained dope is flexible on a metal support. Casting of dope can be performed by discharging from the casting die. Subsequently, the solvent in the dope cast on the metal support is evaporated and dried, and then peeled from the metal support to obtain a film-like material.

It is preferable that the residual solvent amount (remaining solvent amount S ₀ at the time of peeling) of the dope when peeling from a metal support is 30 to 120 mass %. If the residual solvent amount S ₀ at the time of peeling is 120% by mass or less, the force required for peeling the dope is difficult to be excessively large, so that it is easy to suppress the breakage of the dope.

The amount of residual solvent in dope is defined by the following formula. It is the same also in the following.

Amount of residual solvent of dope (mass%) = (mass before heat treatment of dope-mass after heat treatment of dope)/mass after heat treatment of dope x 100

In addition, the heat treatment at the time of measuring the amount of residual solvent means a heat treatment at 120°C for 60 minutes.

About the process of 3) (gradient stretching process)

The obtained film-like object is stretched in a direction oblique to the width direction of the film-like object. Specifically, it stretches so that the orientation angle of the film obtained may become 40-50 degrees.

The draw ratio can be set to Tg-30 to Tg+80°C, for example, when the glass transition temperature of the cellulose ether derivative is Tg. The stretching temperature can be adjusted mainly at the heating temperature in the stretching zone Z2 (see Fig. 2). The draw ratio is different depending on the properties of the film required, but may be, for example, 1.01 to 3.0 times (10% to 300%). The draw ratio is defined as (size in the stretching direction of the film after stretching)/(size in the stretching direction of the film before stretching).

It is preferable that the residual solvent amount S ₁ in the film-like material at the start of stretching is 5 to 20% by mass. When the residual solvent amount S ₁ at the beginning of stretching is 5% by mass or more, the plasticizing effect due to the residual solvent tends to increase the stretchability. When the residual solvent amount S ₁ at the start of stretching is 20% by mass or less, generation of bubbles due to vaporization of the solvent in the film-like material can be highly suppressed. It is more preferable that the residual solvent amount S ₁ in the film-like material at the start of stretching is 8 to 15% by mass.

The stretching of the film-like object in the oblique direction can be performed by, for example, an oblique stretching device shown in FIG. 1. 1 is a plan view showing an example of a configuration of an oblique stretching device. In the figure, W represents a film-like material. As shown in FIG. 1, the oblique stretching device 10 includes a feeding part 11, a conveying direction changing part 12, and a guide roll 13 in order from the upstream side in the conveyance direction of a film-like object (raw film). ), an extension part 14, a guide roll 15, a conveyance direction change part 16, and a winding part 17. The stretching portion 14 will be described later.

The feeding part 11 feeds out the above-described elongated film-like object and supplies it to the stretching part 14. The feeder 11 may be configured separately from the film forming apparatus of a film-like object, or may be configured integrally.

The conveyance direction changing part 12 changes the conveyance direction of the film-like object unleashed from the feeding part 11 toward the entrance of the extending|stretching part 14. The conveyance direction change part 12 is comprised, for example, including a turn bar which changes a conveyance direction by folding while conveying a film, and a rotation table which rotates this turn bar in a plane parallel to a film.

At least one guide roll 13 is provided on the upstream side of the stretched portion 14 in order to stabilize the trajectory when the film-shaped object is traveling. At least one guide roll 15 is provided on the downstream side of the stretched part 14 in order to stabilize the trajectory at the time of running of the film-like object diagonally stretched by the stretched part 14.

The conveyance direction change part 16 changes the conveyance direction of the film-like article after extending|stretching conveyed from the extending|stretching part 14 to the direction toward the winding part 17.

The winding unit 17 winds up a film conveyed from the stretching unit 14 through the conveying direction changing unit 16, and is, for example, a winder device, an accumulator device, and a drive device.

2 is a plan view schematically showing an example of a rail pattern of the stretched portion 14. However, this is an example, and the configuration of the stretched portion 14 is not limited thereto.

In the stretching portion 14, a tenter (inclined stretching machine) capable of obliquely stretching is used to obliquely stretch the film-like object. The stretching portion 14 travels along a heating zone Z, a pair of rails Ri and Ro left and right, and rails Ri and Ro, and carries a plurality of gripping tools Ci and Co).

In FIG. 2, the feeding direction D1 of the film-like object is different from the winding direction D2 of the λ/4 retardation film after stretching, and forms a feeding angle θi between the winding direction D2. The feeding angle θi can be arbitrarily set to a desired angle in the range of more than 0° and less than 90°.

In this way, the feeding direction D1 and the winding direction D2 are different, and the moving distance of the gripping tool Co running the rail Ro is the movement of the gripping tool Ci running the rail Ri. It is longer than the distance. For this reason, the rail pattern of the tenter has a shape that is asymmetric left and right. In addition, it is possible to manually or automatically adjust the rail pattern according to the orientation angle θ to be given to the obliquely stretched film, the draw ratio, and the like.

The heating zone Z has a preheating zone Z1, a stretching zone Z2, and a heat fixing zone Z3. In the stretched portion 14, the film gripped by the gripping tools Ci and Co passes through the preheating zone Z1, the stretching zone Z2, and the heat setting zone Z3 in order. The preheating zone Z1 and the stretching zone Z2 are partitioned by partition walls, and the stretching zone Z2 and the heat fixing zone Z3 are partitioned by partition walls.

The preheating zone Z1 means that at the entrance of the heating zone Z, the holding tools (Ci and Co) holding both ends of the film-like object travel left and right (in the film width direction) while maintaining a constant interval. Refers to the section. The stretching zone Z2 refers to a section until the gap between the gripping tools Ci and Co that gripped both ends of the film-like material starts to widen and reaches a predetermined gap. The heat fixation zone (Z3) is a section in which the interval between the gripping tools (Ci and Co) becomes constant again behind the stretching zone (Z2), and the gripping tools (Ci and Co) at both ends are kept parallel to each other while running. It refers to the section to be played.

In the apparatus 10 for producing such an obliquely stretched film, both ends of the film-like object are gripped with a pair of gripping tools Ci and Co. Then, the film-like object is conveyed so that the moving distance of the gripping tool Co is longer than the moving distance of the gripping tool Ci, and extending in an oblique direction with respect to the width direction.

A pair of gripping tools (Ci and Co) face each other in a direction substantially perpendicular to the advancing direction of the film (feeding direction D1) at the entrance of the stretched portion 14 (position of P in the drawing). It runs on a pair of rails (Ri and Ro) that are asymmetric left and right, respectively.

At this time, since the rails (Ri and Ro) are left and right asymmetric, and the lengths are also different, the left and right gripping tools (Ci and Co) facing each other at the position P in FIG. 2 travel on the rails (Ri and Ro). Accordingly, the gripping tool Ci running on the rail Ri side (in-course side) becomes a positional relationship preceding the gripping tool Co running on the rail Ro side (out-course side). That is, of the gripping tools (Ci and Co) facing in a direction substantially perpendicular to the film feeding direction (D1) at the position P in the drawing, one of the gripping tools (Ci) is the position at the end of the stretching of the film (Q When) is reached first, the straight line connecting the gripping tools Ci and Co is inclined by an angle θL with respect to the direction substantially perpendicular to the winding direction D2 of the film. By the above operation, the film-like object is obliquely stretched at an angle of ?L with respect to the width direction. In addition, substantially vertical indicates that it is in the range of 90±1°.

After that, when reaching the exit portion at the end of stretching (position Q in the drawing), the held film is opened. The film opened from the holding tools Ci and Co is wound around the take-up core in the take-up section 17 described above. A pair of rails (Ri and Ro) each have an endless continuous track, and the gripping tools (Ci and Co) that open the gripping of the film at the outlet of the tenter are sequentially entranced by running the outer rail. It is returned to wealth.

3. Use of λ/4 retardation film

As described above, the λ/4 retardation film of the present invention can be preferably used for a circularly polarizing plate or an organic EL display device having the same.

<Circular polarizing plate>

The circularly polarizing plate of the present invention includes a polarizer and a λ/4 retardation film of the present invention.

The polarizer is an element that passes only light having a polarization surface in a predetermined direction, and a representative polarizer currently known is a polyvinyl alcohol-based polarizing film. Polyvinyl alcohol-based polarizing films include those obtained by dyeing a polyvinyl alcohol-based film with iodine and dyeing a dichroic dye.

The polyvinyl alcohol-based polarizing film may be a film (preferably a film further subjected to durability treatment with a boron compound) after uniaxially stretching a polyvinyl alcohol-based film and then dyed with iodine or a dichroic dye; The polyvinyl alcohol-based film may be dyed with iodine or a dichroic dye, and then uniaxially stretched (preferably, a film further subjected to durability treatment with a boron compound). The absorption axis of the polarizer is usually parallel to the maximum stretching direction.

The thickness of the polarizer is preferably 5 to 30 µm, and more preferably 5 to 20 µm from the purpose of thinning the polarizing plate.

The angle between the polarizer and the in-plane slow axis of the λ/4 retardation film of the present invention is preferably 40 to 50°, and more preferably 45°.

When the λ/4 retardation film of the present invention is disposed only on one side of the polarizer, a protective film may be disposed on the other side. Examples of the protective film include commercially available cellulose acylate films (e.g., Konica Minolta Tac KC8UX, KC4UX, KC5UX, KC8UY, KC4UY, KC12UR, KC8UCR-3, KC8UCR-4, KC8UCR-5, KC4FR-1, KC8UY -HA, KC8UX-RHA, KC8UE, KC4UE, KC4HR-1, KC4KR-1, KC4UA, KC6UA or higher, manufactured by Konica Minolta Opto Co., Ltd.), and the like.

The circularly polarizing plate can be obtained by bonding the polarizer and the λ/4 retardation film of the present invention through an adhesive. As the adhesive, a completely saponifiable polyvinyl alcohol aqueous solution (water paste) or an active energy ray-curable adhesive may be used, and preferably, a completely saponified polyvinyl alcohol aqueous solution (water paste) may be used.

Before bonding the λ/4 retardation film to one surface of the polarizer, it is preferable to further pretreat the λ/4 retardation film. That is, after pretreating the surface of the λ/4 retardation film, it is preferable to bond at least one surface of the polarizer to the polyvinyl alcohol-based adhesive. Examples of the pretreatment include saponification treatment, corona treatment, and plasma treatment.

Since the λ/4 retardation film of the present invention contains a cellulose ether derivative having an aromatic-containing group, it is thought that hydrogen atoms added to the aromatic ring are easily activated by corona treatment from the relationship between the electronegativity of the aromatic ring and the covalent state of electrons. . On the other hand, since the aromatic ring exhibits hydrophobicity, it is difficult to be affected by saponification. As described above, when the contact angle after the corona treatment and the contact angle after the saponification treatment of the λ/4 retardation film are compared, when the contact angle after the corona treatment is 10° or more, as a pretreatment, it is recommended to perform the corona treatment (not the saponification treatment). desirable.

The contact angle is based on JIS-R3257, in an atmosphere of a temperature of 23°C and a relative humidity of 55%, 3 μl of water is added dropwise, and the contact angle after 1 minute of dropping of this water droplet is measured using a contact angle meter DM300 (Kyowa Gaimen Chemical). Can be measured.

<Organic EL display device>

The organic EL display device 100 of the present invention includes an organic EL element 110 and a circularly polarizing plate 120.

3 is a schematic diagram showing an example of the configuration of the organic EL display device 100. As shown in FIG. 3, the organic EL display device 100 includes an organic EL element 110 and a circularly polarizing plate 120.

The organic EL element 110 is a metal electrode 112, a TFT 113, an organic light emitting layer 114, a transparent electrode (ITO, etc.) 115 in order on a transparent substrate 111 using glass or polyimide, etc. It has an insulating layer 116, a sealing layer 117, and a film 118 (can be omitted).

The metal electrode 112 functions as a cathode, and in order to facilitate electron injection and increase luminous efficiency, the cathode is made of a material having a small work function, for example, a metal such as Mg-Ag or Al-Li.

The organic light-emitting layer 114 is a laminate of various thin-film organic functional layers, for example, a laminate of a hole injection layer containing a triphenylamine derivative, and a light-emitting layer containing a fluorescent organic solid such as anthracene, or It may be a stacked body of an electron injection layer including such a light emitting layer and a perylene derivative, or a stacked body of various combinations such as a stacked body of a hole injection layer, a light emitting layer, and an electron injection layer thereof.

The transparent electrode 115 is a transparent electrode formed of a transparent conductor such as indium tin oxide (ITO), and functions as an anode. As described above, in the organic EL display device, at least one electrode is made transparent in order to extract light emission from the organic light-emitting layer.

The thickness of the organic EL element 110 is about 1 μm.

In such an organic EL display device, by applying a voltage to the transparent electrode 115 and the metal electrode 112, holes and electrons are injected into the organic light emitting layer 114, and energy generated by the recombination of the holes and electrons is fluorescence. It excites the substance and emits light by emitting light when the excited fluorescent substance returns to the ground state.

The circular polarizing plate 120 includes a polarizer 121, a λ/4 retardation film 122 of the present invention disposed on a surface of the polarizer 121 on the side of the organic EL element 110, and an organic EL of the polarizer 121 It has a protective film 123 disposed on the side opposite to the device 110. A cured layer 124 or an antireflection layer 125 may be further laminated on the protective film 123 as necessary. The cured layer 124 not only prevents scratches on the surface of the organic EL display device, but also has an effect of preventing warping due to a long circular polarizing plate.

The screen size of the organic EL display device 100 may be, for example, a large screen having a diagonal distance of 20 inches or more, that is, 50.8 cm or more.

In the organic EL display device 100 configured as described above, the organic light emitting layer 114 is formed of a very thin film having a layer thickness of about 10 nm. Therefore, the organic light-emitting layer 114 also transmits light almost completely like the transparent electrode 115. As a result, light incident from the surface of the circularly polarizing plate 120 at the time of non-emission, passing through the transparent electrode 115 and the organic light-emitting layer 114, and reflected by the metal electrode 112 Since it comes out to the front side, when visually recognized from the outside, the display surface of the organic EL display device 100 is observed like a mirror surface.

The circularly polarizing plate 120 including the λ/4 retardation film 122 polarizes light incident from the outside and reflected by the metal electrode 112, specifically, the λ/4 retardation film 122 and a polarizer By setting the angle formed by the polarization direction of 121 to 45°, the mirror surface of the metal electrode 112 is almost completely shielded, and the mirror surface of the metal electrode 112 is not visible from the outside.

That is, external light incident on the organic EL display device 100 transmits only a linearly polarized component by the polarizer, and this linearly polarized light becomes circularly polarized by the λ/4 retardation film 122. This circularly polarized light passes through the film 118, the sealing layer 117, the insulating layer 116, the transparent electrode 115, and the organic light-emitting layer 114, is reflected by the metal electrode 112, and is again reflected by the organic light-emitting layer ( 114), the transparent electrode 115, the insulating layer 116, the sealing layer 117, and the film 118 pass through, and become linearly polarized again in the λ/4 retardation film 122. And, since this linearly polarized light is orthogonal to the polarization direction of the polarizer 121, it cannot pass through the polarizer 121. As a result, the mirror surface of the metal electrode 112 can be completely shielded. Therefore, in the organic EL display device, projection of external light at the time of appreciation can be prevented, and black display properties can be improved.

Example

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto.

1. Film material

(1) Synthesis of cellulose ether derivative/lignin derivative mixture

<Synthesis of cellulose ether derivative/lignin derivative mixture 1>

In a container equipped with a stirring device, thermometer, cooling tube, and dropping funnel, 50 parts by mass of a cellulose ether derivative 1 (cellulose ether formed in a mixture with a lignin derivative) having an ethoxy group substitution degree of 2.35 obtained from the pulp raw material, and 1000 pyridine. Each part by mass was added and stirred at room temperature. 150 parts by mass of benzoyl chloride was slowly added dropwise thereto, and then stirred at 80°C for 7 hours. After the reaction, it stood to cool until it returned to room temperature, and when the reaction solution was added while stirring vigorously with 1500 parts by mass of methanol, a white solid precipitated.

The white solid was filtered off by suction filtration, washed with a large amount of methanol, dried at 60° C. overnight, and then vacuum dried at 90° C. for 6 hours.

50 parts by mass of a white solid after washing and drying, 600 parts by mass of acetone, and 500 parts by mass of methanol were added to a container equipped with a stirring device and a thermometer, respectively, and stirred at 70°C to dissolve. When the dissolved solution was charged with a mixed solvent of 7000 parts by mass of methanol and 4000 parts by mass of water while stirring vigorously, a white solid precipitated. The white solid was filtered and separated by suction filtration, and the obtained white solid was dried at 60°C for 12 hours and then vacuum dried at 90°C for 6 hours. The same operation was repeated once more to obtain a cellulose ether derivative/lignin derivative mixture 1 (a mixture containing a cellulose ether derivative 1 and a lignin derivative).

The degree of substitution of the substituent of the glucose skeleton of the cellulose ether derivative 1 contained in the obtained cellulose ether derivative/lignin derivative mixture 1 was measured by ¹ H-NMR and ¹³ C-NMR, and the average value thereof was obtained. The degree of substitution of the benzoate group was 0.65, the degree of substitution of the ethoxy group was 2.35, and the total degree of substitution was 3.00.

<Synthesis of cellulose ether derivative/lignin derivative mixture 2 to 11>

In the synthesis of cellulose ether derivative/lignin derivative mixture 1, cellulose ether derivative/lignin derivative mixtures 2 to 11 were carried out in the same manner, except that the reaction conditions were changed so that the degree of ethoxy substitution and the degree of benzoate substitution became the values shown in Table 1. (A mixture containing cellulose ether derivatives 2 to 11 and a lignin derivative) was obtained.

<Synthesis of cellulose ether derivative/lignin derivative mixture 12>

In a container equipped with a stirring device, a thermometer, a cooling tube and a dropping funnel, 50 parts by mass of cellulose ether (cellulose ether formed as a mixture with a lignin derivative) having an ethoxy group substitution degree of 2.35 obtained from the pulp raw material, and 1000 parts by mass of pyridine Each was added and stirred at room temperature. 160 parts by mass of thiophene-2-carbonyl chloride was slowly added dropwise thereto, followed by further stirring at 80°C for 8 hours. After the reaction, it stood to cool until it returned to room temperature, and when the reaction solution was added while stirring vigorously with 1500 parts by mass of methanol, a white solid precipitated.

The white solid was filtered off by suction filtration, washed with a large amount of methanol, dried at 60° C. overnight, and then vacuum dried at 90° C. for 6 hours.

50 parts by mass of a white solid after washing and drying, 600 parts by mass of acetone, and 500 parts by mass of methanol were added to a container equipped with a stirring device and a thermometer, respectively, and stirred at 70°C to dissolve. When the dissolved solution was charged with a mixed solvent of 7000 parts by mass of methanol and 4000 parts by mass of water while stirring vigorously, a white solid precipitated. The white solid was filtered and separated by suction filtration, and the obtained white solid was dried at 60°C for 12 hours and then vacuum dried at 90°C for 6 hours. The same operation was repeated once more to obtain a cellulose ether derivative/lignin derivative mixture 12 (a mixture containing a cellulose ether derivative 12 and a lignin derivative).

The degree of substitution of the substituent of the glucose skeleton of the cellulose ether derivative 12 contained in the obtained cellulose ether derivative/lignin derivative mixture 12 was measured by ¹ H-NMR and ¹³ C-NMR, and the average value thereof was calculated. The degree of substitution of the thiophene-2-carboxylate group was 0.65, the degree of substitution of the ethoxy group was 2.35, and the total degree of substitution was 3.00.

<Synthesis of cellulose ether derivative/lignin derivative mixture 13>

In a container equipped with a stirring device, a thermometer, a cooling tube and a dropping funnel, 50 parts by mass of cellulose ether (cellulose ether formed as a mixture with a lignin derivative) having an ethoxy group substitution degree of 2.35 obtained from the pulp raw material, and 1000 parts by mass of pyridine Each was added and stirred at room temperature. Here, 160 parts by mass of 2-naphthoyl chloride was slowly added dropwise, followed by further stirring at 80°C for 8 hours. After the reaction, it stood to cool until it returned to room temperature, and when the reaction solution was added while stirring vigorously with 1500 parts by mass of methanol, a white solid precipitated.

The white solid was filtered off by suction filtration, washed with a large amount of methanol, dried at 60° C. overnight, and then vacuum dried at 90° C. for 6 hours.

50 parts by mass of a white solid after washing and drying, 600 parts by mass of acetone, and 500 parts by mass of methanol were added to a container equipped with a stirring device and a thermometer, respectively, and stirred at 70°C to dissolve. When the dissolved solution was charged into a mixed solvent of 7000 parts by mass of methanol and 4000 parts by mass of water while stirring vigorously, a white solid precipitated. The white solid was filtered and separated by suction filtration, and the obtained white solid was dried at 60°C for 12 hours and then vacuum dried at 90°C for 6 hours. The same operation was repeated once more to obtain a cellulose ether derivative/lignin derivative mixture 13 (a mixture containing a cellulose ether derivative 13 and a lignin derivative).

The degree of substitution of the substituent of the glucose skeleton of the cellulose ether derivative 13 contained in the obtained cellulose ether derivative/lignin derivative mixture 13 was measured by ¹ H-NMR and ¹³ C-NMR, and the average value thereof was obtained. The degree of substitution of the 2-naphthoate group was 0.65, the degree of substitution of the ethoxy group was 2.35, and the total degree of substitution was 3.00.

<Synthesis of cellulose ether derivative/lignin derivative mixture 14>

In the synthesis of the cellulose ether derivative/lignin derivative mixture 1, the reaction solution was left to cool until it returns to room temperature, and then 3 parts by mass of lignin (dealkali) (manufactured by Tokyo Kasei Kogyo Co., Ltd.) was added. Thus, a cellulose ether derivative/lignin derivative mixture 14 (a mixture containing a cellulose ether derivative and a lignin derivative) was obtained.

(2) Preparation of a composition comprising a cellulose ether derivative/lignin derivative mixture and an acid or salt thereof

<Preparation of Compositions 1 and 16 to 27>

To a vessel equipped with a stirring device and a thermometer, 50 parts by mass of a cellulose ether derivative/lignin derivative mixture 1, 600 parts by mass of acetone, and 500 parts by mass of methanol were added, followed by stirring at 70°C to dissolve.

The solution was added to a mixed solvent in which 7000 parts by mass of methanol, 4000 parts by mass of water, and the acid shown in Table 1 were added to the amount shown in Table 1 with respect to the cellulose ether derivative, while vigorous stirring was added. Precipitated. The white solid was filtered and separated by suction filtration, and the obtained white solid was dried at 60°C for 12 hours and then vacuum dried at 90°C for 6 hours, and a composition containing the cellulose ether derivative/lignin derivative mixture 1 and the acid shown in Table 1 1 and 16 to 27 were obtained, respectively.

<Preparation of Composition 2>

In the preparation of the composition 1, the cellulose ether derivative/lignin derivative mixture 1 was changed to a cellulose ether derivative/lignin derivative mixture 0 including a cellulose ether derivative 0 having an ethoxy group substitution degree of 2.35 before reacting with benzoate. Except in the same manner, a composition 2 containing a cellulose ether derivative/lignin derivative mixture 0 and benzoic acid was obtained.

<Preparation of Compositions 3 to 12>

50 parts by mass of a cellulose ether derivative/lignin derivative mixture 2, 600 parts by mass of acetone, and 500 parts by mass of methanol were each added to a container equipped with a stirring device and a thermometer, followed by stirring at 70°C to dissolve.

When the solution was added with vigorous stirring to a mixed solvent in which 7000 parts by mass of methanol, 4000 parts by mass of water, and the acid shown in Table 1 were added to the amount shown in Table 1 with respect to the cellulose ether derivative, a white solid was precipitated. Became. The white solid was filtered and separated by suction filtration, and the obtained white solid was dried at 60° C. for 12 hours and then vacuum dried at 90° C. for 6 hours to obtain a composition 3 containing a cellulose ether derivative/lignin derivative mixture 2 and benzoic acid.

The same operation was performed for the cellulose ether derivative/lignin derivative mixtures 3 to 11, to obtain compositions 4 to 12 containing cellulose ether derivative/lignin derivative mixtures 3 to 11 and benzoic acid, respectively.

<Preparation of compositions 13 to 14>

To a vessel equipped with a stirring device and a thermometer, 50 parts by mass of a cellulose ether derivative/lignin derivative mixture 12, 600 parts by mass of acetone, and 500 parts by mass of methanol were each added, followed by stirring at 70°C to dissolve.

When the solution was added with vigorous stirring to a mixed solvent in which 7000 parts by mass of methanol, 4000 parts by mass of water, and the acid shown in Table 1 were added to the amount shown in Table 1 with respect to the cellulose ether derivative, a white solid was precipitated. Became. The white solid was filtered and fractionated by suction filtration, and the obtained white solid was dried at 60° C. for 12 hours and then vacuum dried at 90° C. for 6 hours, containing cellulose ether derivative/lignin derivative mixtures 13 to 14 and the acid shown in Table 1. Compositions 13 to 14 were obtained, respectively.

<Preparation of composition 15>

To a vessel equipped with a stirring device and a thermometer, 50 parts by mass of a cellulose ether derivative/lignin derivative mixture 13, 600 parts by mass of acetone, and 500 parts by mass of methanol were added, respectively, and stirred at 70°C to dissolve.

When the solution was added with vigorous stirring to a mixed solvent in which 7000 parts by mass of methanol, 4000 parts by mass of water, and the acid shown in Table 1 were added to the amount shown in Table 1 with respect to the cellulose ether derivative, a white solid was precipitated. Became. The white solid was filtered and separated by suction filtration, and the obtained white solid was dried at 60°C for 12 hours and then vacuum dried at 90°C for 6 hours to obtain a composition 15 containing a mixture of cellulose ether derivative 13/lignin derivative and naphthoic acid. .

<Preparation of composition 28>

To a vessel equipped with a stirring device and a thermometer, 50 parts by mass of a cellulose ether derivative/lignin derivative mixture 14, 600 parts by mass of acetone, and 500 parts by mass of methanol were added, respectively, and stirred at 70°C to dissolve.

When the solution was added with vigorous stirring to a mixed solvent in which 7000 parts by mass of methanol, 4000 parts by mass of water, and the acid shown in Table 1 were added to the amount shown in Table 1 with respect to the cellulose ether derivative, a white solid was precipitated. Became. The white solid was filtered and separated by suction filtration, and the obtained white solid was dried at 60° C. for 12 hours and then vacuum dried at 90° C. for 6 hours to obtain a composition 28 containing a cellulose ether derivative/lignin derivative mixture 14 and benzoic acid.

(3) additive

C-1: Adekastep AO-60 (made by ADEKA, phenolic antioxidant)

C-2: Adekastep PEP-36 (made by ADEKA, phosphite-based antioxidant)

C-3: SUMILIZER GP (manufactured by Sumitomo Chemical Co., Ltd., processing stabilizer)

C-4: IRGANOX 1010 (manufactured by BASF Japan, a hindered phenolic antioxidant)

C-5: Adekastep LA-31 (manufactured by ADEKA, Inc., 2,2'-methylenebis[6-(2-benzotriazolyl)-4-(1,1,3,3-tetramethylbutyl) Phenol], hindered amine light stabilizer)

C-6: TINUVIN 928 (made by BASF Japan Co., Ltd., a benzotriazole-based ultraviolet absorber)

2. Preparation of λ/4 retardation film

<Preparation of λ/4 retardation film 1>

(Preparation of fine particle additive solution)

Aerosil R812 (made by mat, manufactured by Nippon Aerosil Corporation): 4 parts by mass

Dichloromethane: 48 parts by mass

Ethanol: 48 parts by mass

After stirring and mixing each of the above-described constituent materials for 50 minutes with a dissolver, dispersion was performed with 10,000 ton Gaulin. This was filtered with Finemet NF manufactured by Nippon Seisen Co., Ltd. to prepare a fine particle addition liquid having a mat agent content of 4.0% by mass.

(Preparation of Dope 1)

Using the prepared composition 1, dope 1 of the following composition was prepared.

First, dichloromethane and ethanol were added to a pressure dissolution tank. Next, the composition 1 was added to the pressure dissolution tank while stirring so that the content of the cellulose ether derivative 1 was 100 parts by mass. Then, 15 minutes after the composition 1 was added, the prepared fine particle addition solution was added, heated to 80°C, and completely dissolved while stirring. The heating temperature was raised from room temperature to 5°C/min, dissolved for 30 minutes, and then cooled to 35°C at 3°C/min.

This was filtered with a filtration flow rate of 300 L/m ² ·h and a filtration pressure of 1.0×10 ⁶ Pa using Azumi Rossi No.244 (filtration accuracy 0.005 mm) manufactured by Azumi Rossi Co., Ltd. to prepare dope 1.

(Composition of Dope 1)

Cellulose ether derivative 1: 100.0 parts by mass

Lignin derivative: 0.1 parts by mass

Benzoic acid: 5 ppm by mass based on cellulose ether derivative 1

Dichloromethane: 1000.0 parts by mass

Ethanol: 150.0 parts by mass

Fine particle addition liquid: 2.5 parts by mass

(Unveiling)

The prepared dope 1 was fed from a pressure dissolution tank to a pressurized die by a gear pump, and cast (cast) onto an endless support (belt) made of stainless steel.

The solvent was evaporated until the amount of residual solvent in the flexible web became 40 mass%, and then the web was peeled from the endless support made of stainless steel with a peeling tension of 130 N/m.

While drying the peeled web, it extended|stretched at 100% of the elongation rate in the diagonal direction (the direction of 45 degrees with respect to the width direction) using the diagonal stretching apparatus as shown in FIG. At this time, the drying conditions from peeling to the tenter were adjusted so that the amount of residual solvent at the time of stretching might be 11 mass %. In addition, the temperature of the tenter stretching device was 160°C, and the stretching speed was 200%/min.

Next, drying was terminated while conveying the inside of the drying apparatus with a number of rollers. The drying temperature was 130°C, and the conveyance tension was 100 N/m. Both ends of the film obtained by drying were slit with a slit device having rotating teeth to prepare a λ/4 retardation film 1 having a width of 1000 mm and a film thickness of 50 µm.

<λ/4 Preparation of retardation films 2, 4 to 13 and 35>

Using Compositions 2 to 12 and 28, λ/4 retardation films 2, 4 to 13, and 35 were obtained in the same manner as in the λ/4 retardation film 1 except that the cellulose ether derivative was changed to the one shown in Table 1.

<Lambda / 4 Preparation of retardation films 14 to 22>

Using the compositions 13 to 21, λ/4 phase difference films 14 to 22 were obtained in the same manner as in the λ/4 phase difference film 1 except that at least one of the cellulose ether derivative and the acid was changed to the one shown in Table 1.

<λ/4 Preparation of retardation films 23 to 28>

Using the compositions 22 to 27, except having changed the content of the acid as shown in Table 1, in the same manner as in the λ/4 retardation film 1, λ/4 retardation films 23 to 28 were obtained.

<Preparation of λ/4 retardation films 29 to 34>

Using the composition 19, except having further added the additives of the types and amounts shown in Table 1, in the same manner as the λ/4 retardation film 1, λ/4 retardation films 29 to 34 were obtained.

<Preparation of λ/4 retardation films 3 and 36>

A cellulose ether derivative/lignin derivative mixture 1 or 14 was used, and λ/4 phase difference films 3 and 36 were obtained, respectively, in the same manner as the λ/4 retardation films 1 and 35 except that an acid was not added.

The number of bubbles, YI, haze, retardation Ro, and wavelength dispersion (DSP) of the obtained λ/4 retardation films 1 to 36 were evaluated by the following methods, respectively.

[bubble]

The λ/4 retardation film was placed on a black velvet cloth, and the presence or absence of air bubbles was confirmed by visual inspection under illumination of a fluorescent lamp. The λ/4 phase difference film was observed for 100 m in the long direction, and the number of bubbles was measured.

When the number of air bubbles is 20 or more, since the yield is lowered when a polarizing plate is produced using this film, it is judged that it is good if it is 30 or less, and even more if it is less than 20.

[YI]

(Early)

The yellow index (YI) of the λ/4 retardation film was measured by the method described in JIS K-7105-6.3. As a specific measurement method of the yellow index value, the three stimulus values X, Y, and Z of the color were measured using a spectrophotometer U-3200 manufactured by Hitachi High Technology Co., Ltd. and a saturation calculation program included. The obtained value was applied to the following formula to calculate a yellow index value.

Yellow Index (YI)=100(1.28X-1.06Z)/Y

If the yellow index (YI) is 1.5 or less, it is good, and if it is less than 1.2, it is judged to be more good (transparency is high, and it is particularly preferable as a λ/4 retardation film).

(After light resistance)

A λ/4 retardation film was cut to a size of 100 mm×100 mm. This film was irradiated with light for 300 hours at an intensity of 60 W/m ² in accordance with ISO4292-2 using an Atlas Weather Ometer Ci3000+ (manufactured by Atlas) as a xenon weather meter. About the film after irradiation, 25 points of 5x5 and YI were measured at 20 mm intervals, and the difference between the maximum value and the minimum value was made into the value after ΔYI light resistance.

When the value after the ?YI light resistance is greater than 0.85, color non-uniformity occurs in the film, and therefore, when this film is used for an organic EL display device, display non-uniformity is likely to occur. Therefore, the value after ΔYI light resistance was judged to be good if it was 0.85 or less, and even better if it was less than 0.8.

[Haze]

The haze of the λ/4 retardation film was measured using NDH-2000 (manufactured by Nippon Denshoku Kogyo Co., Ltd.) in accordance with JIS K-7136. As a light source, a 5V9W halogen sphere was used, and a silicon photocell (with a non-visibility filter) was used as the light receiving part. The measurement was performed in an environment at a temperature of 23°C and a relative humidity of 55%.

[In-plane phase difference value (Ro)]

The in-plane retardation value (Ro) at a wavelength of 550 nm of the λ/4 retardation film was measured in an environment of a temperature of 23°C and a relative humidity of 55%, using AxoScan manufactured by Axometrics.

Specifically, the three-dimensional refractive index at a wavelength of 550 nm of the λ/4 retardation film was measured in an environment at 23° C. 55% RH, and the average values of the refractive indices nx, ny, and nz were obtained. The obtained value was applied to the following equation to calculate the in-plane retardation value Ro.

Equation (1): Ro=(nx-ny)×d

In Formula (1), nx represents the refractive index in the direction x in which the refractive index becomes the largest in the in-plane direction of the film. ny represents the refractive index in the direction y orthogonal to the direction x in the in-plane direction of the film. nz represents the refractive index in the thickness direction z of the film. d represents the thickness (nm) of the film.

Ro was judged to be good if it was 30 to 300 nm, and even better if it was 120 to 150 nm.

[Wave variance value (DSP)]

The in-plane retardation value (Ro) at a wavelength of 450 nm and 550 nm of the λ/4 retardation film was measured in an environment at a temperature of 23°C and a relative humidity of 55% using Axoscan manufactured by Axometrics. The obtained in-plane retardation value Ro (450) at a wavelength of 450 nm and an in-plane retardation value Ro (550) at a wavelength of 550 nm were applied to the following equation to calculate a wavelength dispersion value (DSP).

Equation (3): DSP=Ro(450)/Ro(550)

DSP judged that if it was less than 1.0, it was good, and if it was more than 0.75 and 0.9 or less, it was more favorable.

In addition, about the λ/4 retardation films 1, 20, and 23 to 34, the thermal deterioration resistance was further evaluated.

[Heat resistance deterioration]

The λ/4 retardation film was maintained for 300 hours in an environment of 90°C. The in-plane retardation value Ro after 300 hours was measured, and the retention rate of the retardation was calculated.

Phase difference retention rate (%) = Ro (after 300 hours)/Ro (initial value) x 100

Table 1 shows the evaluation results of the λ/4 retardation films 1 to 36.

As shown in Table 1, it can be seen that both of the λ/4 retardation films 1 and 4 to 35 of the present invention have little generation of air bubbles in the film production process, and also little coloration of the film. In addition, since the λ/4 retardation films 1 and 4 to 35 of the present invention have a DSP of less than 1, it is suggested that a λ/4 phase difference can be expressed in a broadband.

In addition, by making the degree of substitution of the aromatic-containing group of the cellulose ether derivative within the range of 0.1 to 1.0 and the degree of substitution of the ethoxy group from 1 to 2.5, the in-plane retardation value Ro of the obtained film is appropriately increased, while appropriately increasing the DSP. It can be seen that it can be made low (contrast of λ/4 retardation films 4 to 13).

In addition, it can be seen that by using an acid containing an aromatic ring or a salt thereof, generation of air bubbles or coloration of the film can be further suppressed (compared to λ/4 retardation films 17 to 22).

In addition, the retardation retention rates of the λ/4 retardation films 1, 23, 24, 25, 26, 27, and 28 were 98%, 99%, 98%, 98%, 97%, 96%, and 80%, respectively. Similarly, the λ/4 retardation films 20, 29, 30, 31, 32, 33, and 34 were also evaluated. The retardation retention rates were 92%, 98%, 98%, 98%, 98%, 98%, respectively, It was 98%. As described above, it was found that the λ/4 retardation film of the present invention has a high retardation retention rate even after heat resistance.

In contrast, it can be seen that the comparative λ/4 retardation film 3 that does not contain an acid or a salt thereof has many generations of air bubbles in the film manufacturing process, and also many colors of the film. Further, it is suggested that the λ/4 retardation film 2 of the comparison using the cellulose ether derivative 2 having no aromatic-containing group has a DSP of 1, and that it is difficult to express a λ/4 phase difference in a broadband.

3. Fabrication and evaluation of polarizing plate

<Measurement of the contact angle of the λ/4 retardation film>

(Preparation of sample 1)

About each of the λ/4 retardation films 1 and 2 produced above, corona discharge treatment was performed to obtain Sample 1. Conditions for the corona discharge treatment were a discharge gap of 0.5 mm, an output of 14 kV, and a treatment speed of 50 m/min.

(Preparation of sample 2)

Each of the prepared λ/4 retardation films 1 and 2 was saponified for 90 seconds in 2N KOH heated to 50°C. Then, it washed with water and dried, and sample 2 was obtained.

The contact angles of the treated surfaces of the obtained samples 1 and 2 were respectively measured by the following method.

(Measurement of contact angle)

On the treated surface of the obtained sample, based on JIS-R3257, 3 μl of water was added dropwise in an atmosphere at a temperature of 23° C. and a relative humidity of 55%. Ku) was measured using. And the value of the contact angle of sample 1 and the contact angle of sample 2 was applied to the following formula, and the difference of the contact angle was calculated|required.

Contact angle difference =|Contact angle of sample 2 (contact angle after saponification)-Contact angle of sample 1 (contact angle after corona)|

The difference in the contact angle of the λ/4 retardation film 1 was 19°, and the difference in the contact angle of the λ/4 retardation film 2 was 6°. In other words, it was found that the difference in the contact angle of the λ/4 retardation film 1 was larger.

<Manufacture of polarizing plate 1>

(Manufacture of polarizer)

A 120 µm-thick polyvinyl alcohol film was uniaxially stretched (temperature 110° C., draw ratio 5 times). This was immersed for 60 seconds in an aqueous solution containing 0.075 g of iodine, 5 g of potassium iodide and 100 g of water. Then, it was immersed in an aqueous solution at 68°C containing 6 g of potassium iodide, 7.5 g of boric acid, and 100 g of water. This was washed with water and dried to obtain a polarizer.

(Manufacture of adhesive)

After dissolving 10 parts by weight of Kosenex Z200 (manufactured by Nippon Kosei Chemical Co., Ltd.) in 250 parts by weight of pure water, 1 part by weight of Safelink SPM-01 (manufactured by Nippon Kosei Chemical Co., Ltd.) was added to obtain an adhesive.

(Manufacture of polarizing plate 1)

Corona discharge treatment was performed on the surface of the produced λ/4 retardation film 1. Conditions for the corona discharge treatment were a discharge gap of 0.5 mm, an output of 14 kV, and a treatment speed of 50 m/min. Subsequently, the prepared adhesive was applied to the corona discharge treatment surface of the λ/4 retardation film 1 with a bar coater so that the thickness after drying was about 0.5 μm to form an adhesive layer. The prepared polarizer was bonded to the obtained adhesive layer. The bonding was performed so that the angle formed by the in-plane slow axis of the λ/4 retardation film 1 and the absorption axis of the polarizer was 45°.

Further, a protective film (Konica Minolta Tack KC2UA, thickness 25 µm, manufactured by Konica Minolta Co., Ltd.) was saponified in 2N KOH heated at 50°C for 90 seconds, and then washed with water. On the saponification-treated surface of the obtained protective film, the prepared adhesive solution was applied with a bar coater so that the film thickness after drying was about 0.5 µm to form an adhesive layer. And, this adhesive layer-equipped protective film was bonded to the polarizer to which the λ/4 retardation film 1 was bonded, so that the λ/4 retardation film 1/adhesive layer/polarizer/adhesive layer/protective film was laminated. Got it. This laminate was dried at 60°C for 10 minutes to prepare a polarizing plate 1.

<Manufacture of polarizing plate 2>

The polarizing plate 2 was produced in the same manner as the production of the polarizing plate 1 except that the λ/4 retardation film 1 was changed to the λ/4 retardation film 2.

The adhesion between the λ/4 retardation film and the polarizer was evaluated in terms of whether or not the λ/4 retardation films of the obtained polarizing plates 1 and 2 could be peeled from the polarizer by hand. As a result, it was found that the polarizing plate 1 could not peel the λ/4 retardation film 1 by hand, and the adhesiveness between the polarizer and the λ/4 retardation film 1 was high. On the other hand, as for the polarizing plate 2, it was possible to peel only the λ/4 retardation film 2 by hand, and it was found that the adhesion between the polarizer and the λ/4 retardation film 2 was insufficient.

This application claims priority based on Japanese Patent Application No. 2017-049115 for which it applied on March 14, 2017. All of the contents described in the application specification and drawings are incorporated in the specification of the present application.

According to the present invention, it is a λ/4 retardation film comprising a cellulose ether derivative and a lignin derivative, and it is possible to provide a broadband λ/4 retardation film in which there are few defect sites caused by foaming at the time of solution film formation and coloration is suppressed.

10: oblique stretching device
11: feeder
12: transfer direction change unit
13: guide roll
14: extension
15: guide roll
16: transfer direction change unit
17: winding
100: organic EL display device
110: organic EL element
111: transparent substrate
112: metal electrode
113: TFT
114: organic light emitting layer
115: transparent electrode (ITO, etc.)
116: insulating layer
117: sealing layer
118: film
120: circularly polarizing plate
121: polarizer
122: λ/4 retardation film
123: protective film
124: hardened layer
125: anti-reflection layer

Claims (7)

A λ/4 retardation film comprising a cellulose ether derivative having an aromatic-containing group, a lignin derivative, and an acid or a salt thereof. The method of claim 1, wherein the alkoxy group contained in the cellulose ether derivative is an aliphatic alkoxy group,
The aromatic-containing group is an aromatic acylate group, and
The cellulose ether derivative satisfies the following formula (I), λ/4 retardation film.
Formula (I): 1.5≤X+Y≤3.0
1.0≤X≤2.5
0.1≤Y≤1.0
(In formula (I),
X is the degree of substitution of the aliphatic alkoxy group,
Y is the degree of substitution of the aromatic acylate group) The λ/4 retardation film according to claim 1 or 2, wherein the acid is an organic acid having an aromatic ring. The λ/4 retardation film according to claim 1 or 2, wherein the content of the acid or salt thereof is 0.5 to 500 ppm by mass based on the total mass of the cellulose ether derivative. The λ/4 retardation film according to claim 1 or 2, further comprising at least one additive selected from the group consisting of a phenol compound, a phosphite compound, and a benzotriazole compound. Including a polarizer and the λ/4 retardation film according to claim 1 or 2,
A circular polarizing plate, wherein an angle formed by an in-plane slow axis of the λ/4 retardation film and an absorption axis of the polarizer is 40 to 50°. An organic EL display device comprising an organic EL element and the circularly polarizing plate according to claim 6.

Images