JP2016080994A - Retardation film, circularly polarizing plate, and organic electroluminescence image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin retardation film that features high retardation expressibility and superior wavelength dispersibility, a circularly polarizing plate having the same, and an organic electroluminescence image display device.SOLUTION: A retardation film of the present invention contains a cellulose derivative, where 2- or 3-position of a glucose skeleton constituting the cellulose derivative is substituted by a substituent group having an aromatic group represented by a general formula (1). The retardation film is controlled such that specific conditional expressions (1) through (6) are satisfied. [general formula (1)] *-L-R.SELECTED DRAWING: None

Description

  The present invention relates to a retardation film having a large retardation and excellent wavelength dispersion in a thin film, a circularly polarizing plate provided with the retardation film, and an organic electroluminescence image display device.

  In recent years, attention has been focused on organic electroluminescence image display devices (hereinafter also referred to as organic EL displays) having high contrast, fast response speed of moving image display, and excellent viewing angle characteristics.

  In an organic EL display, it is necessary to use a metal having a small work function such as aluminum or calcium for the cathode, and the cathode of the organic EL element is required to have a smoothness close to the atomic level, so that it is necessarily a mirror surface. . Therefore, there is a problem that the external light incident on the organic EL display is reflected by the cathode mirror surface, thereby reducing the contrast of the image. Therefore, a circularly polarizing plate is used in the organic EL display in order to prevent external light reflection by the cathode mirror surface.

  A circularly polarizing plate is usually composed of a polarizer, for example, a polyvinyl alcohol film that has been stretched and oriented with iodine, and a retardation film that has been stretched and has birefringence, called a λ / 4 retardation film. The A polarizer is an optical element that passes only light that vibrates in a specific direction (linearly polarized light). A λ / 4 retardation film has an axis with a high refractive index (slow axis) and an axis with a low refractive index in the in-plane direction. It is a film having a (fast axis) and a phase difference of light due to a difference in refractive index thereof being exactly ¼ wavelength. This λ / 4 retardation film is bonded to a polarizer so that the slow axis and the fast axis are at an angle of 45 ° with respect to the plane of vibration of linearly polarized light.

  Prevention of external light reflection of the organic EL display by the circularly polarizing plate is achieved by the light incident from the outside of the display being reflected by the mirror surface and then absorbed by the polarizer. This mechanism will be described with reference to FIGS.

  FIG. 1 is a conceptual diagram showing a vibrating surface of linearly polarized light after external light passes through the polarizer 1. In FIG. 1, the x-axis and y-axis are respectively arranged at an angle of 45 ° with respect to the vibration plane of the linearly polarized light, and the linearly polarized light is appropriately vector-decomposed into the x-axis and y-axis with respect to the traveling direction N of the light wave. Shows the change of the vibration surface. In linearly polarized light, it can be seen that the vibration planes of the x component 2 and the y component 3 of light travel in the same phase. The same phase means that when one wave has a peak, the other wave has a peak, and when one has a valley, the other has a valley, and the amplitudes of the x and y components coincide. .

FIG. 2 is a conceptual diagram showing the relationship between the stretching direction 4 of the retardation film R and the refractive index. As a result of stretching in the x-axis direction, the retardation film R has a slow axis on the x-axis, a fast axis on the y-axis, an in-plane x-axis direction refractive index n _x , and a y-axis direction refractive index. n _{y shows} the relationship of _n x> n _y. When passing through a λ / 4 retardation film in which the phase difference of light due to this refractive index difference is exactly ¼ wavelength, the polarization state of the light changes from linearly polarized light to circularly polarized light. FIGS. 3 and 4 show how the light waves change.

  FIG. 3 is a conceptual diagram of a vibration surface obtained by vector-decomposing a light wave before and after passing through a λ / 4 retardation film into an x component and a y component. FIG. 4 is a conceptual diagram showing the direction of the vibration plane in which the x component and the y component of the light wave after passing through the λ / 4 retardation film are vector-combined again. The x component and the y component (FIG. 3A) of the light wave that has traveled in the same phase before passing through the λ / 4 retardation film pass through the λ / 4 retardation film (the slow axis of the film is The x component is delayed by ¼ wavelength with respect to the y component (FIG. 3B). When the x-component and y-component light waves are vector-synthesized again, the synthesized vector 5 draws a spiral 6 with the light traveling direction as the axis, with the vibration direction viewed in terms of time and location (FIG. 4). Such a polarization state is called circular polarization.

  It is known that when this circularly polarized light is reflected by a mirror surface, the direction of rotation of the helix is reversed in the direction of travel. This is caused by reflection of the light wave at the fixed end at the mirror surface. Fixed-end reflection is a phenomenon in which positive and negative amplitudes are reversed and reflected when a wave is reflected. Hereinafter, a description will be given with reference to FIG.

  FIG. 5 is a conceptual diagram showing changes in light waves before and after specular reflection. FIG. 5A illustrates a light wave incident on the mirror surface when the xy plane is a mirror surface. FIG. 5B shows a state in which the light wave after the light incident in FIG. 5A is reflected by the mirror surface travels to the back side of the page. The light wave of the y component incident on the mirror surface in FIG. 5A (having a positive amplitude at the tip) is a reflected light wave in FIG. 5B, and the tip in the traveling direction of the light wave has a negative amplitude. It can be seen that the amplitudes have changed. Similarly, the amplitudes of the light waves of the x component are switched after being reflected by the mirror surface. Here, in FIGS. 5 (a) and 5 (b), looking at the vibration surface obtained by combining the x component and the y component of the light wave, the clockwise circularly polarized light in the traveling direction (FIG. 5 (a)). ) Shows that after reflecting on the mirror surface (xy plane), the spiral drawn by the vibration direction becomes counterclockwise circularly polarized light toward the traveling direction.

  FIG. 6 shows a conceptual diagram of the change of the vibration surface when the specularly reflected light wave passes through the λ / 4 retardation film again. When this circularly polarized light (FIG. 6 (a)) that has turned in the reverse direction passes through the λ / 4 retardation film again (the slow axis of the film is parallel to the x axis of FIG. 6), the x component of the light is Further, it is delayed by 1/4 wavelength. As a result, the phase of the x component and the y component of the light again becomes the same phase, and the light wave synthesized by the vector becomes linearly polarized light (FIG. 6B), but its vibration surface is incident on the incident light wave (FIG. 1). On the other hand, it is inclined 90 °. For this reason, the reflected light wave is absorbed by the polarizer 1 and cannot go out of the display.

  As described above, the circularly polarizing plate prevents the reflected light of the outside light from coming out again, thereby suppressing the decrease in the contrast of the display due to the outside light. At this time, what is important for achieving an excellent antireflection function for external light is the wavelength dispersion of the retardation value in the in-plane direction of the λ / 4 retardation film (hereinafter abbreviated as Ro). is there.

  Ro is defined as follows.

(Formula _{I) Ro = (n x -n} y) × d
Here, n _x, n _y, respectively, the maximum refractive index in the plane of the film (slow axis direction of the refractive index) and represents the refractive index in a direction perpendicular to the slow axis in the film plane. d represents the thickness (nm) of the film.

  Since this Ro changes with the wavelength of light, this characteristic is called wavelength dispersion. The λ / 4 retardation film is required to have wavelength dispersion that imparts a λ / 4 retardation to the wavelength λ of the entire visible light. For example, it is necessary to cause a phase difference of about 113 nm, which is a quarter wavelength, of light having a wavelength of 450 nm, and it is necessary to cause a phase difference of about 138 nm at 550 nm. In order to obtain an ideal λ / 4 retardation film as described above, the retardation generated by the film must increase as the wavelength of light increases.

  In a graph in which the horizontal axis indicates the wavelength of light and the vertical axis indicates the phase difference value (Ro) in the in-plane direction, when the line formed by the wavelength of the light and the Ro value decreases to the right, “forward wavelength dispersion” On the other hand, when the line rises to the right, it is called “reverse wavelength dispersion”. This is called forward wavelength dispersion because many general-purpose resin films such as a PET (polyethylene terephthalate) film have a downward slope. On the contrary, it is known that the cellulose ester film has reverse wavelength dispersion (for example, see Patent Document 1). Moreover, since the retardation of a film is proportional to the film thickness as in (Formula I), the larger the film thickness, the higher the retardation development. However, with the recent thinning of image display devices, there has been a demand for further thinning of the optical film used therefor. Therefore, there is a strong demand for a λ / 4 retardation film that retains a large retardation development property even in a thin film and has good reverse wavelength dispersion.

JP 2009-235374 A

  This invention is made | formed in view of the said problem and the situation, The solution subject is providing the retardation film which has a big retardation expression and the outstanding wavelength dispersion in a thin film. Moreover, it is providing the circularly-polarizing plate and organic electroluminescent image display apparatus which comprised it.

  As a result of studying the cause of the above-mentioned problems in order to solve the above-mentioned problems, the present inventors have found that both the 2-position and 3-position of the glucose skeleton constituting the cellulose derivative are substituted with a substituent having an aromatic group. And when the total substitution degree of the cellulose derivative is a specific value, it has been found that even a thin film exhibits a large retardation and excellent wavelength dispersion.

  That is, the said subject which concerns on this invention is solved by the following means.

  1. A retardation film containing a cellulose derivative, wherein the 2-position and 3-position of the glucose skeleton constituting the cellulose derivative are substituted with a substituent having an aromatic group represented by the following general formula (1) The retardation film is controlled so as to satisfy the following formulas (1) to (6).

(1): 1.50 ≦ DSa ≦ 2.40
(2): 110 nm ≦ Ro (450) ≦ 125 nm
(3): 135 nm ≦ Ro (550) ≦ 145 nm
(4): 0.80 ≦ Ro (450) / Ro (550) ≦ 0.90
(5): d ≦ 80 (μm)
(6): 0.06 ≦ DSb
(In the formula, DSa represents the total substitution degree of the cellulose derivative. Ro (450) and Ro (550) are in-plane directions measured at a light wavelength of 450 nm and 550 nm, respectively, in an environment of 23 ° C. and 55% RH. D represents the thickness (μm) of the retardation film, and DSb represents the sum of the substitution degrees of the substituents having aromatic groups substituted at the 2-position and 3-position. )
General formula (1)
* -LR ₁
(In the formula, R ₁ represents an aromatic group. L represents C (═O), C (═O) O or C (═O) NR _2. R ₂ represents a hydrogen atom, an alkyl group or an aromatic group. The two R ₁ groups at the 2-position and 3-position may be the same or different, and * represents the oxygen atom of the 2-position and 3-position hydroxy groups of the glucose skeleton, respectively.
2. The retardation film according to item 1, wherein the substituent having an aromatic group represented by the general formula (1) is a benzoyl group.

  3. The retardation film according to item 1 or 2, wherein a substituent other than the substituent having an aromatic group of the cellulose derivative is an aliphatic acyl group.

4). 4. The retardation film according to item 3, wherein the aliphatic acyl group is an acetyl group. The thickness of a retardation film is in the range of 40-60 micrometers, The retardation film as described in any one of 1st term | claim to 4th term | claim characterized by the above-mentioned.

  6). The retardation film according to any one of items 1 to 5, wherein the retardation film is stretched at an angle in a range of 40 to 50 ° with respect to a conveyance direction. the film.

  7). A circularly polarizing plate comprising the retardation film according to any one of items 1 to 6.

  8). An organic electroluminescence image display device comprising the circularly polarizing plate according to item 7.

  By the above means of the present invention, a retardation film having a large retardation development property and excellent wavelength dispersion can be provided with a thin film. Moreover, the circularly-polarizing plate and organic electroluminescent image display apparatus which comprise it can be provided.

  The expression mechanism or action mechanism of the effect of the present invention is not clear, but is presumed as follows. Arrangement of aromatic groups having high electron density at the short wave side of visible light and large absorbance at the long wave side at the 2nd and 3rd positions (side chains) of the cellulose derivative increases the reverse wavelength dispersion, and By defining the total substitution degree of the cellulose derivative within a specific range, it is considered that even a thin film can exhibit a large retardation and excellent wavelength dispersion.

Conceptual diagram of the vibration plane of linearly polarized light after external light passes through the polarizer Schematic diagram showing the relationship between the stretching direction of the retardation film and the refractive index Schematic diagram of a vibration plane obtained by vector decomposition of light waves before and after passing through a λ / 4 retardation film into x and y components Conceptual diagram showing the direction of the vibration surface obtained by vector synthesis of the x and y components of the light wave after passing through the λ / 4 retardation film again Conceptual diagram showing changes in light waves before and after specular reflection Conceptual diagram of change in vibration plane when specularly reflected light wave passes through λ / 4 retardation film again Conceptual diagram showing the conformation of acetylcellulose stretched in the x-axis direction Conceptual diagram showing the relationship between the absorbance of the benzoyl group and acetyl group relative to the light wavelength Conceptual diagram showing the wavelength dependence of the refractive index in the x-axis direction and the refractive index in the y-axis direction Schematic diagram explaining shrinkage ratio in oblique stretching of optical film Schematic which showed an example of the rail pattern of the diagonal stretcher applicable to the manufacturing method of (lambda) / 4 phase difference film of this invention Schematic which shows an example (example which extends | stretches diagonally after extending | stretching from a long film original fabric roll) which concerns on embodiment of this invention. Schematic which shows an example (example which extends continuously diagonally, without winding up a long film original fabric) concerning the manufacturing method which concerns on embodiment of this invention Schematic sectional view showing an example of the configuration of the organic electroluminescence image display device of the present invention

  The retardation film of the present invention is a retardation film containing a cellulose derivative, wherein the 2nd and 3rd positions of the glucose skeleton constituting the cellulose derivative are aromatic groups represented by the following general formula (1). It is substituted by the substituent which it has, and was controlled so that the following formula (1) to formula (6) may be satisfy | filled.

(1): 1.50 ≦ DSa ≦ 2.40
(2): 110 nm ≦ Ro (450) ≦ 125 nm
(3): 135 nm ≦ Ro (550) ≦ 145 nm
(4): 0.80 ≦ Ro (450) / Ro (550) ≦ 0.90
(5): d ≦ 80 (μm)
(6): 0.06 ≦ DSb
(In the formula, DSa represents the total substitution degree of the cellulose derivative. Ro (450) and Ro (550) are in-plane directions measured at a light wavelength of 450 nm and 550 nm, respectively, in an environment of 23 ° C. and 55% RH. D represents the thickness (μm) of the retardation film, and DSb represents the sum of the substitution degrees of the substituents having aromatic groups substituted at the 2-position and 3-position. )
General formula (1)
* -LR ₁
(In the formula, R ₁ represents an aromatic group. L represents C (═O), C (═O) O or C (═O) NR _2. R ₂ represents a hydrogen atom, an alkyl group or an aromatic group. The two R ₁ groups at the 2-position and 3-position may be the same or different, and * represents the oxygen atom of the 2-position and 3-position hydroxy groups of the glucose skeleton, respectively.
This feature is a technical feature common to the inventions according to claims 1 to 8.

  As an embodiment of the present invention, it is preferable that the substituent having the aromatic group represented by the general formula (1) is a benzoyl group from the viewpoint of the effect of the present invention and cost. Moreover, it is preferable that substituents other than the substituent which has the said aromatic group of the said cellulose derivative are aliphatic acyl groups from a saponification process suitably at the time of circularly-polarizing plate preparation.

  Moreover, it is preferable that the aliphatic acyl group is an acetyl group because it can be suitably saponified when producing a circularly polarizing plate from the viewpoint of cost. Furthermore, the thickness of the retardation film is preferably in the range of 40 to 60 μm because it is a thinner film.

  The retardation film is preferably stretched at an angle in the range of 40 to 50 ° with respect to the transport direction in order to obtain a λ / 4 retardation film.

  The retardation film of the present invention can be included in a circularly polarizing plate. The circularly polarizing plate of the present invention can be provided in an organic electroluminescence image display device.

  Hereinafter, the present invention, its components, and modes and modes for carrying out the present invention will be described in detail. In addition, in this application, "-" is used in the meaning which includes the numerical value described before and behind that as a lower limit and an upper limit.

(Reverse wavelength dispersion mechanism)
First, the expression mechanism of reverse wavelength dispersion in a cellulose derivative and the required chemical structure will be described below using a cellulose ester film as an example.

  Among the cellulose ester films having reverse wavelength dispersibility, aromatic groups such as benzoyl groups are used rather than those obtained by replacing aliphatic acyl groups such as acetyl groups and propionate groups with hydrogen atoms of cellulose hydroxy groups (a). Even if the substituted (b) has the same reverse wavelength dispersion, the slope of Ro with respect to the optical wavelength is (a) <(b).

  This phenomenon can be explained by the following principle of phase difference expression. A film containing a polymer as a main component can be oriented with a polymer chain by stretching. Of course, the degree of orientation varies depending on the molecular structure of the polymer, the draw ratio, the temperature at the time of drawing, etc., but in any case, if the polymer main chain is compared with the disordered state in the drawing direction, there is always ordering. Imparts an orientation phenomenon. Even in the cellulose ester film, the orientation phenomenon due to stretching actually develops.

  FIG. 7 is a conceptual diagram showing the conformation of acetylcellulose stretched in the x-axis direction. For example, when the left-right direction (x-axis direction) of the paper surface (xy axis) is the stretching direction, the β-glucose repeating structures forming the main chain are arranged in this direction as shown in FIG. The 2- and 3-position hydroxy groups or the ester group in which the hydroxy group is acylated are arranged in the vertical direction (y-axis direction) on the paper surface, and the 6-position hydroxymethyl group or the acylated acyloxymethyl group is also It is easy to understand qualitatively that they are arranged in the same direction (y-axis direction) (in fact, they are not completely oriented, but are generally ordered in that direction as a whole).

  Here, the expression mechanism of wavelength dispersion will be considered from the relationship between the light absorption wavelength (AWL), the absorbance (Abs), the density (ρ), and the refractive index (n) of the polymer and the phenomenon occurring at the molecular level.

  Light absorption is a phenomenon in which one of the two electrons in the highest occupied molecular orbital (HOMO) of the target molecule (polymer) is lifted to the lowest unoccupied molecular orbital (LUMO) by light energy (this is called This is called photoexcitation.) When the light has a long wavelength exceeding the absorption maximum wavelength of the polymer, the energy required for excitation becomes insufficient, so the probability of excitation from HOMO to LUMO decreases, and the absorbance. (Abs) becomes extremely small.

FIG. 8 is a conceptual diagram showing the relationship between the absorbance of the benzoyl group and the acetyl group with respect to the light wavelength. The absorbance (Abs _Ac ) 8 of the cellulose ester substituted with an acetyl group having no aromatic group has a maximum absorbance (= transition probability) in a wavelength band near about 200 nm (for convenience, Abs _Ac = 0.3). ), The absorbance (= transition probability) is nearly zero in the vicinity of 700 nm close to infrared. On the other hand, the absorbance (Abs _Bz ) 7 of the cellulose ester substituted with a benzoyl group becomes maximum at around 250 nm, and the maximum value of the absorption intensity in that wavelength band (for convenience, it is assumed that Abs _Bz = 1.0). Is greater than that of acetylcellulose (Abs _Ac ). Abs _Bz > Abs _Ac .

Further, the absorbance of acetylcellulose at 250 nm (Abs _Ac (250)) is further smaller than that at 200 nm from the viewpoint of the above-described excitation probability, and becomes Abs _Bz (250) >> Abs _Ac (250). In the graph with the axis as the wavelength and the y axis as the absorbance, the benzoylcellulose plot is more inclined to the right than the acetylcellulose plot.

  Next, consider the relationship between absorption wavelength and density. It is known that each atom has an intrinsic refractive index derived from that atom, but now it is not considered, and the difference in refractive index between acetyl cellulose and benzoyl cellulose formed by only three elements of carbon, oxygen, and hydrogen is not considered. Consider the expression mechanism in a simplified manner. The most obvious simplification is the density difference between cyclohexane and benzene. In this case, the density can be compared based on the degree of clogging of atoms packed in a fixed volume space. Compared to aliphatic cyclohexane, benzene, which has the same carbon number, degenerates and is conjugated with π electrons. However, as the interatomic distance becomes shorter, the degree of filling becomes higher. That is, it can be easily understood that the density of acetyl cellulose and benzoyl cellulose is relatively higher in the latter.

  This is noticed that the aforementioned absorption wavelength has the same tendency. In other words, by substituting the aromatic benzoyl group, benzoylcellulose has a relatively higher absorbance and higher density than acetylcellulose.

  Next, regarding the refractive index, the refractive index n is a physical property value defined by the formula n = C / V. Here, C is the speed of light in a vacuum, and V is the speed of light in an object. The phenomenon in which light is transmitted is a macro view of the fact that light is absorbed by an object and that light is radiated from the object to an adjacent object. Therefore, the more the object is clogged, the more the number of repetitions of absorption and emission increases, so the speed of light decreases. That is, if the density (ρ) increases, the light velocity V in the object decreases, and the ratio of the light velocity in the vacuum to the refractive index becomes the refractive index. Therefore, the refractive index (ρ) and the density (d) Is a proportional relationship. This explains the relationship that the higher the absorbance, the higher the density and the higher the refractive index.

  Next, consider the relationship between the stretching direction of the film and the absorbance. The cellulose ester film stretched as described above has a main chain oriented in the left-right direction (x-axis direction) of the paper surface (xy axis), and the ester (carbonyl) group is arranged in the vertical direction (y-axis direction) of the paper surface. Suppose that In other words, transition dipoles are arranged in the y-axis direction, and the polarization in the y-axis direction has a higher probability of exciting the carbonyl group than the polarization in the x-axis direction. As a result, the absorbance in the y-axis direction is higher, and the refractive index is higher from the above theory. Moreover, the relative refractive index difference between acetylcellulose and benzoylcellulose is further enhanced.

  On the other hand, since there is no transition dipole in the x-axis direction, it does not change whether it is acetyl cellulose or benzoyl cellulose.

FIG. 9 is a conceptual diagram showing the wavelength dependence of the refractive index in the x-axis direction and the refractive index in the y-axis direction. 9A shows the wavelength dependency of the refractive index 9 in the x-axis direction and the refractive index 10 in the y-axis direction when FIG. 9B shows benzoylcellulose. Figure 9 (c) and FIG. 9 (d) each of the difference between the x-axis and y-axis directions of the refractive index _(n x _-n y) represents the S.

As n _y benzoyl cellulose is larger than n _y acetylcellulose, and the wavelength increases, n _y benzoyl cellulose (large negative slope) and more reduction ratio is large. On the other hand since the n _x is the same for both in, Ro can be described as the slope of benzoyl cellulose is increased by (n x _{-n y)} are the × d (nm), plot of Ro and wavelength.

  An excellent λ / 4 retardation film is required to have a reverse wavelength dispersion property in which Ro increases as the wavelength of light increases. As described above, it is considered effective to introduce an aromatic substituent such as a benzoyl group into cellulose, but what is important here is the orientation of the aromatic substituent in the y-axis direction.

  As described above, it can be understood that both the 2-position, 3-position and 6-position substituents of the glucose skeleton of cellulose have directionality and anisotropy in the y-axis direction when the entire molecule is viewed after stretching. In detail, the hydroxy groups at the 2nd and 3rd positions are secondary, and the hydroxy group at the 6th position is primary and via a methylene group, and there is a difference in chemical structure. Since the substituent at the 6-position is via a methylene group, it is considered that the presence state tends to be more random. On the other hand, since the substituents at the 2nd and 3rd positions are secondary hydroxy groups, there is no degree of freedom in directionality compared to the 6th position, and it is considered that the orientational ordering is higher. In other words, when an aromatic substituent is introduced into the side chain, the anisotropy and orientation of the substituent on the y-axis are improved by positively introducing it into the 2nd and 3rd positions of the glucose skeleton of cellulose. It is thought that reverse wavelength dispersion can be expressed.

  Hereinafter, the structural formula will be described. The directionality and the degree of anisotropy of the substituents at the 2nd, 3rd and 6th positions after stretching are schematically shown using arrows. When the benzoyl group is substituted at the 6-position of the glucose skeleton of cellulose, the degree of freedom is higher than when the benzoyl group is substituted at the 2- and 3-positions. It is considered that not only the orientation indicated by the black arrow but also the orientation indicated by the white arrow is possible. That is, since the 6-position benzoyl group has directionality and anisotropy more randomly, the orientational order is lower, and the 2-position and 3-position benzoyl groups are more limited in directionality and anisotropy. It is considered that the alignment order is high.

  In other words, when an aromatic substituent is introduced into the side chain, the anisotropy and orientation of the substituent on the y-axis are improved by positively introducing it into the 2nd and 3rd positions of the glucose skeleton of cellulose. It is thought that reverse wavelength dispersion can be expressed.

Next, the chemical composition for expressing the retardation necessary for the λ / 4 retardation film in the thin film will be described. Cellulose, the introduction of substituents having a high electron density carbonyl group or an aromatic group, but is improved reverse wavelength dispersion as described above, since the refractive index in the stretching after the y direction n _y is increased plane direction of the retardation value _{Ro ((n x -n y)} × d) is reduced, the film thickness becomes thicker in order to express the phase difference required lambda / 4 phase difference film. In order to develop a large phase difference in a thin film, it is necessary to set an upper limit on the degree of substitution. The degree of substitution is the molar ratio of substituents when the glucose skeleton (unit structure) of cellulose is 1. When a substituent is introduced into all of the 2-position, 3-position and 6-position of the glucose skeleton of cellulose, the degree of substitution is 3.

  Here, taking the acetyl group and the benzoyl group as examples, the concept of the relationship between the retardation development property and the total substitution degree of the cellulose derivative (cellulose acetate benzoate) substituted with these groups will be described. In the following description, constants such as the degree of orientation of the substituents used are for convenience of description.

In order to appropriately use the cellulose derivative for the λ / 4 retardation film, the total substitution degree is important in the present invention. Taking cellulose acetate benzoate as an example, the acetyl group substituted on the cellulose skeleton as described above, and the benzoyl group have orientational ordering in the y-axis direction. y-axis direction of the refractive index is increased, as the plane direction of the retardation value _{Ro ((n x -n y)} × d), decreases. That is, if the number of substituents is increased in order to improve the wavelength dispersion, the retardation development is reduced correspondingly, and a thin λ / 4 retardation film cannot be produced.

  Here, for convenience, the difference in refractive index between the x-axis and y-axis and the degree of orientation of each functional group of cellulose acetate benzoate will be described with reference to the numerical values shown in Table 1. The degree of orientation used here takes a value of 0 to 1, and in the case of 0, the orientational ordering of the molecular chain is completely lost and no difference in refractive index occurs. On the other hand, in the case of 1, the molecular chain is completely oriented and the refractive index difference is maximized. Actually, all the molecular chains are not perfectly oriented, and take between 0 and 1. A negative refractive index difference indicates that there is a refractive index anisotropy in the y-axis direction. The unit structure of cellulose acetate benzoate will be discussed below by dividing it into a pyranose ring, an acetyl group, and a benzoyl group.

  In the λ / 4 retardation film, the necessary retardation for light having a wavelength of 550 nm is ¼, 137.5 nm. In order to express this phase difference with a film having a thickness of 80 μm, it is necessary to satisfy the relationship of (Formula II).

(Formula _{II) Ro = (n x -n} y) × d = Δn × d
In (Formula II), when Ro = 137.5 nm and d = 80 μm, Δn≈0.00172 is calculated from (Formula II). That is, in order to design a λ / 4 retardation film at 80 μm or less, a refractive index difference of 0.00172 or more is required between the slow axis direction and the fast axis direction.

  In order to design a film with a film thickness of 80 μm or less, the relationship between the refractive index difference of each substituent and the degree of substitution using the refractive index difference taking into account the refractive index and orientation degree of each functional group described in Table 1. (Equation III) inequality representing Since the degree of substitution is the ratio of the number of acetyl groups or benzoyl groups to the pyranose ring, the refractive index difference of the entire cellulose acetate benzoate is the degree of substitution (the pyranose ring is 1) in the refractive index difference Δn of each functional group. It is the sum of the values multiplied by. In Table 1, for the refractive index difference Δn caused by the functional group when the degree of orientation is 1, in the case of the 2- and 3-position benzoyl groups, the total value of the two benzoyl groups was used.

(Formula III) 0.00172 ≦ 0.0042−0.001 × DS ^Ac −0.0025 × DS ^{2 · 3 position Bz} −0.001 × DS ^{6th position Bz}
DS ^Ac , DS ^{2 / 3-position Bz} and DS ^{6-position Bz} represent the substitution degree of the acetyl group, the substitution degree of the benzoyl group substituted at the 2-position and the 3-position, and the substitution degree of the benzoyl group substituted at the 6-position, respectively. This inequality is an expression that defines the degree of substitution of each substituent when a film is designed at 80 μm or less.

Here, let us consider a case where a benzoyl group substituted at the 2-position and 3-position of cellulose is introduced with a substitution degree of 0.06. Substituting 0.06 into DS ^{2/3 position Bz} and transforming,
(DS ^Ac + DS ^{6th position Bz} ) ≦ 2.33
Is obtained. Therefore, when the benzoyl group is introduced at the 2-position and 3-position with a substitution degree of 0.06, the degree of substitution of other substituents (here, the acetyl group and the 6-position benzoyl group) can be designed with a film of 80 μm or less. It should be understood that the value must be 2.33 or less.

  That is, here, when the degree of substitution of other substituents is larger than 2.33, it means that a λ / 4 retardation film having a thickness of 80 μm or less cannot be produced. The total degree of substitution indicates that it must be 2.39 or less in order to produce a thin film of 80 μm or less.

Next, the film is designed with a benzoyl group substituted at the 2-position and 3-position at a substitution degree of 0.50 and 80 μm or less. Similarly, by substituting 0.50 for DS ^{2 / 3-position Bz} in (formula III) and transforming,
(DS ^Ac + DS ^{6th position Bz} ) ≦ 1.23
Is obtained. At this time, the total degree of substitution is 1.73. In other words, increasing the introduction amount of benzoyl groups at the 2nd and 3rd positions, which are highly oriented in the y-axis (fast axis direction), increases the refractive index in the y-axis direction. It can be seen that the total degree of substitution must be reduced to maintain.

Similarly, the necessary refractive index difference when the film is 60 μm is 137.5 = Δn × 60000 (nm) from the formula I Δn≈0.00229
When the benzoyl group substituted at the 2-position and 3-position of cellulose has a substitution degree of 0.06 and is similarly transformed using (Formula III),
(DS ^Ac + DS ^{6th position Bz} ) ≦ 1.76
Is obtained. In this case, the upper limit of the total substitution degree is 1.82. It can be seen that in order to make the film thinner, the total degree of substitution is lower than when it is 80 μm.

In addition, when the benzoyl group substituted at the 2-position and 3-position has a substitution degree of 0.25 and is similarly modified,
(DS ^Ac + DS ^{6th Bz} ) ≦ 1.29
It becomes. In this case, the upper limit of the total substitution degree is 1.54.

  From the viewpoint of wavelength dispersion, it is preferable to introduce a large number of benzoyl groups. However, as the concept was arranged using the above-mentioned model, the more aromatic groups were introduced at the 2nd and 3rd positions, the lower the position in the thin film. In order to maintain the phase difference, the total substitution degree must be lowered. However, in practice, the total degree of substitution is not infinitely reduced, and it is not preferable that the total degree of substitution is too low from the viewpoint of solvent solubility of the cellulose derivative. For example, when a film is formed by a solution fluent method, unless a cellulose derivative substituted to some extent is used, it cannot be dissolved in a solvent and the film cannot be formed.

  From the above viewpoint, in the present invention, as a result of intensive studies, by setting the total substitution degree to 1.50 or more, it is possible to maintain the solvent solubility and appropriately form a film. At that time, when designing a λ / 4 retardation film at 80 μm or less, the total substitution degree can be kept at 1.5 or more by setting the aromatic groups at the 2nd and 3rd positions to 0.50 or less. From the viewpoint of the production of Moreover, when designing a λ / 4 retardation film at 60 μm, the total substitution degree can be kept at 1.5 or more by setting it to 0.25 or less, which is preferable. Further, as a region where the wavelength dispersibility is clearly improved, the aromatic substituents at the 2nd and 3rd positions need to be 0.06 or more. At that time, the total degree of substitution needs to be 2.40 or less. When a substituent is further introduced, retardation developability deteriorates, and a thin film λ / 4 retardation film cannot be produced.

  In order to express the phase difference in this way, when introducing a substituent such as an aromatic group that is effective for improving the reverse wavelength dispersion, the degree of substitution must be limited from the viewpoint of phase difference development. I understand. Derivatives having a high degree of substitution exceeding 2.40 in cellulose and having a substituent introduced in the present invention will deteriorate the retardation, so that the degree of substitution should be specified appropriately. Thus, it is possible to provide a thin film retardation film having a large retardation.

<Phase difference film>
The retardation film of the present invention exhibits a large retardation even in a thin film by positively introducing aromatic groups at the 2nd and 3rd positions of cellulose and appropriately defining the total substitution degree based on the above technical idea. And excellent reverse wavelength dispersion. That is, the retardation film of the present invention is a retardation film containing a cellulose derivative, and the second and third positions of the glucose skeleton constituting the cellulose derivative are aromatic represented by the following general formula (1). It is substituted with a substituent having a group, and is controlled to satisfy the following formulas (1) to (6).

(1): 1.50 ≦ DSa ≦ 2.40
(2): 110 nm ≦ Ro (450) ≦ 125 nm
(3): 135 nm ≦ Ro (550) ≦ 145 nm
(4): 0.80 ≦ Ro (450) / Ro (550) ≦ 0.90
(5): d ≦ 80 (μm)
(6): 0.06 ≦ DSb
(In the formula, DSa represents the total substitution degree of the cellulose derivative. Ro (450) and Ro (550) are in-plane directions measured at a light wavelength of 450 nm and 550 nm, respectively, in an environment of 23 ° C. and 55% RH. D represents the thickness (μm) of the retardation film, and DSb represents the sum of the substitution degrees of the substituents having aromatic groups substituted at the 2-position and 3-position. )
General formula (1)
* -LR ₁
(In the formula, R ₁ represents an aromatic group. L represents C (═O), C (═O) O or C (═O) NR _2. R ₂ represents a hydrogen atom, an alkyl group or an aromatic group. The two R ₁ groups at the 2-position and 3-position may be the same or different, and * represents the oxygen atom of the 2-position and 3-position hydroxy groups of the glucose skeleton, respectively.
《Cellulose derivative》
Cellulose is a polymer that is insoluble in water or an organic solvent.For example, when a transparent film such as an optical film is formed by a solution pouring method, the substituent is generally adjusted to an appropriate degree of substitution. It is necessary to have solvent solubility. In the present invention, it is necessary from the viewpoint of solvent solubility in the solution pouring method that the total degree of substitution of the cellulose derivative is 1.50 or more.

  As described above, in order to maintain retardation development even in a thin film, it is necessary to suppress introduction of substituents into cellulose. From this viewpoint, the total substitution degree needs to be 2.40 or less.

  As described above, the circularly polarizing plate is composed of a polarizer and a retardation film, and the retardation film gives a quarter wavelength retardation to the wavelength of light, so that linearly polarized light becomes circularly polarized light. Considering light with wavelengths of 450 nm and 550 nm, it is necessary for the film to generate phase differences in the regions of 110 nm ≦ Ro (450) ≦ 125 nm and 135 nm ≦ Ro (550) ≦ 145 nm, respectively.

  Cellulose has a structure in which glucose, which is a unit structure, is repeatedly connected by 1,4-β bonds, and is named as the 1st to 6th positions in order from the carbon position adjacent to the ether oxygen of the glucose ring structure.

  Among them, the 1st and 4th positions are bonds that connect glucose to each other. By introducing various substituents at the remaining 2-position, 3-position and 6-position, various properties of the cellulose derivative can be extracted. In the present invention, it has been found that the orientational ordering of the substituents at the 2-position and the 3-position is excellent, and this knowledge is actively utilized.

  The 2nd and 3rd positions of the glucose skeleton constituting the cellulose derivative contained in the retardation film of the present invention are substituted with a substituent having an aromatic group. The substituent having this aromatic group is a group represented by the following general formula (1).

General formula (1)
* -LR ₁
(In the formula, R ₁ represents an aromatic group. L represents C (═O), C (═O) O or C (═O) NR _2. R ₂ represents a hydrogen atom, an alkyl group or an aromatic group. The two R ₁ groups at the 2-position and 3-position may be the same or different, and * represents the oxygen atom of the 2-position and 3-position hydroxy groups of the glucose skeleton, respectively.
Examples of the aromatic group represented by R ₁ include an aromatic hydrocarbon ring group and an aromatic heterocyclic group. Here, the aromatic ring is a chemical structure (cyclic structure) having at least one cyclic skeleton, and at least one of the cyclic skeletons satisfies the Hückel rule and has an electron that is delocalized in a cyclic manner. An aromatic group is a group obtained by removing one hydrogen atom from an aromatic ring.

  Examples of such an aromatic hydrocarbon ring include a benzene ring and a naphthalene ring which may have a substituent.

  Examples of the aromatic heterocycle include a furan ring, a pyrrole ring, a thiophene ring, a pyrazole ring, an imidazole ring, an oxazole ring, a thiazole ring, a triazole ring, a pyridine ring, and a quinoline ring which may have a substituent. .

  Examples of the substituent that may be substituted on these aromatic rings include, for example, a halogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, a cycloalkenyl group, an alkynyl group, an aromatic hydrocarbon ring group, and an aromatic heterocyclic group. , Cyano group, hydroxy group, nitro group, carboxy group, alkoxy group, aryloxy group, acyloxy group, amino group, acylamino group, alkyl and arylsulfonylamino group, mercapto group, alkylthio group, arylthio group, sulfamoyl group, sulfo group And each group such as an acyl group and a carbamoyl group.

L represents a C (= O), C ( = O) O or C (= O) NR _2. R ₂ represents a hydrogen atom, an alkyl group or an aromatic group. Among these, C (═O) and C (═O) O are preferable from the viewpoint of improving the reverse wavelength dispersion. This is because if the length of the linking group L is long, the degree of freedom in the directionality of the substituted aromatic group becomes high and the orientation of the aromatic group cannot be increased when substituted with glucose. It is preferable that * representing the oxygen atom of the hydroxyl group at the 2-position and 3-position of the glucose skeleton and the aromatic group are linked within 2 atoms.

As specific examples of preferred aromatic groups, when L is C (═O) or C (═O) O, R ₁ is phenyl group, p-tolyl group, naphthyl group, 2-furyl group, 2-thienyl. In combination with a group, 2-pyrimidyl group, 2-benzothiazolyl group or 2-pyridyl group, and when L is C (═O) NR ₂ , an N-phenylcarbamoyl group or the like is preferable.

  The degree of substitution of the substituent having an aromatic group needs to be 0.06 or more from the viewpoint of developing reverse wavelength dispersion. The degree of substitution of the substituent having an aromatic group substituted at the 2-position and the 3-position is preferably about the same from the viewpoint of ease of introduction and high degree of substitution. As described above, the substitution degree of the substituent having an aromatic group substituted at the 2-position and 3-position is preferably 0.50 or less for a film of 80 μm or less and 0.25 or less for a film of 60 μm or less. From the viewpoint of solvent solubility (as described above, increasing the number of aromatic groups at positions 2 and 3 tends to lower the total substitution degree and lower the solubility). A range of 25 is more preferred.

  The substituent other than the substituent having an aromatic group is preferably an aliphatic acyl group. Examples of the aliphatic acyl group include an acetyl group, a propionyl group, an isopropionyl group, and a butyryl group. Due to the presence of the acyl group, when the polarizer is saponified and bonded, it can be appropriately hydrolyzed and easily bonded.

  The aromatic group is preferably a benzoyl group because it can be synthesized relatively inexpensively from chlorides and acid anhydrides. For the same reason, an acetyl group is more preferable as the aliphatic acyl group.

[Method for producing cellulose derivative]
The detail of the manufacturing method of the cellulose derivative used by this invention is demonstrated.
The cellulose derivative of the present invention can be produced by referring to a known method, for example, a method described in “Encyclopedia of Cellulose” pages 131 to 164 (Asakura Shoten, 2000).

  For example, a typical synthesis method of cellulose acetate is a liquid phase acetylation method using acetic anhydride (acetyl group donor), acetic acid (solvent), and sulfuric acid (catalyst). Specifically, it is preferable to pre-treat a cellulose raw material such as wood pulp with an appropriate amount of acetic acid, and then add it to a precooled acetylated mixed solution to make an acetic ester to synthesize cellulose acetate. After completion of the acetylation reaction, a neutralizing agent (for example, sodium, potassium, calcium, magnesium, iron, etc.) is used for hydrolysis of excess acetic anhydride remaining in the system and neutralization of a part of the esterification catalyst. An aqueous solution of aluminum, zinc or ammonium carbonate, acetate or oxide) is added. The obtained cellulose acetate is aged by maintaining it at 50 to 90 ° C. in the presence of a small amount of an acetylation reaction catalyst (generally, remaining sulfuric acid) to obtain a cellulose acetate having a desired degree of acetyl substitution and degree of polymerization. Can be synthesized.

  In order to introduce an aromatic substituent or the like into cellulose, it can be produced by chemical synthesis from general-purpose substituted cellulose such as cellulose acetate. For example, an aromatic group can be introduced into a hydroxy group of cellulose acetate having a substitution degree of 2.40 using a reagent such as acid chloride. Reactants that are relatively sterically bulky, such as aromatic groups, react preferentially from the 6-position hydroxy group of cellulose. For example, when the 6-position hydroxy group in cellulose acetate is present at a substitution degree of 0.2, the 2-position and 3-position hydroxy groups do not react until almost all the 6-position hydroxy groups have reacted. Therefore, in order to introduce an aromatic group at the 2nd and 3rd positions, it can be introduced by further proceeding the reaction after almost all the 6th hydroxyl groups have reacted.

[Method for measuring degree of substitution of cellulose derivative]
In the present invention, the degree of substitution by each substituent of the glucose skeleton is determined by ¹ H-NMR or ¹³ using the method described in Cellulose Communication 6, 73-79 (1999) and Chality 12 (9), 670-674. It can be determined by C-NMR.

The average degree of acetyl substitution can be measured with reference to the method of Tezuka (Tezuka, Carbohydr. Res., 273, 83 (1995)). That is, the residual hydroxy group of the cellulose derivative substituted with an acetyl group is propionylated with propionic anhydride in pyridine, the obtained sample is dissolved in deuterated chloroform, and the ¹³ C-NMR spectrum is measured.

  The signal of the carbonyl carbon of the acetyl group appears in the region of 169 ppm to 171 ppm, the signals of the carbonyl carbon of the propionyl group appear in the same order in the region of 172 ppm to 174 ppm in the order of 2, 3, 6 from the high magnetic field. The distribution of acetyl groups in the original cellulose acetate can be determined from the abundance ratio of acetyl groups and propionyl groups at the corresponding positions. Other substituents can be measured and calculated in the same manner.

[Characteristics of retardation film]
The in-plane retardation value Ro of the retardation film of the present invention is represented by the above (Formula I) and is a value measured in an environment of 23 ° C. and 55% RH (relative humidity).

  If the in-plane retardation values Ro (450) and Ro (550) measured at the light wavelengths of 450 nm and 550 nm defined in the present invention are within the ranges of 110 to 125 nm and 135 to 145 nm, respectively, The retardation at the wavelength is approximately ¼ wavelength, and a circularly polarizing plate is produced using a retardation film having such characteristics. For example, by providing this circularly polarizing plate in an organic EL image display device, Excellent external light antireflection performance can be imparted and good contrast can be obtained.

  Further, in the retardation film of the present invention, Ro (450) / Ro (550) which is a ratio value of retardation value Ro (450) and Ro (550) in the film surface which is an indicator of wavelength dispersion. However, if it is within the range of 0.80 to 0.90, the retardation exhibits an appropriate reverse wavelength dispersion, and when a long circular polarizing plate is produced, An antireflection effect is obtained.

[Various additives for retardation film]
In addition to the cellulose derivative according to the present invention, the retardation film of the present invention can contain various additives for the purpose of controlling production suitability and durability of the film.

  The additive applicable to the present invention is not particularly limited, and for example, an ultraviolet absorber, a deterioration inhibitor, a matting agent, a plasticizer, and the like can be used as long as the object and effects of the present invention are not impaired. The typical additives applicable to the retardation film of the present invention are shown below.

(UV absorber)
The retardation film of the present invention can contain an ultraviolet absorber.

  Examples of ultraviolet absorbers include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like, but less benzotriazole compounds Compounds are preferred. In addition, ultraviolet absorbers described in JP-A-10-182621 and JP-A-8-337574 and polymer ultraviolet absorbers described in JP-A-6-148430 are also preferably used. As an ultraviolet absorber, from the viewpoint of preventing deterioration of a circularly polarizing plate and an organic EL image display device, it has an excellent ability to absorb ultraviolet rays having a wavelength of 370 nm or less, and from the viewpoint of display properties of the organic EL image display device, a wavelength of 400 nm or more. It is preferable to have a characteristic of less visible light absorption.

  Benzotriazole-based UV absorbers useful in the present invention include, for example, 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-t -Butylphenyl) benzotriazole, 2- (2'-hydroxy-3'-t-butyl-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-t-butyl Phenyl) -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- (linear and side chain 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- ( A mixture of 5-chloro-2H-benzotriazol-2-yl) phenyl] propionate can be mentioned, but is not limited thereto.

  Further, as a commercial product, “TINUVIN 109”, “TINUVIN 171”, “TINUVIN 326”, “TINUVIN 328” (above, trade name, manufactured by BASF Japan Ltd.) are preferable. Can be used.

  The addition amount of the ultraviolet absorber is preferably in the range of 0.1 to 5.0% by mass, more preferably in the range of 0.5 to 5.0% by mass with respect to the cellulose derivative.

(Degradation inhibitor)
The retardation film of the present invention may contain a deterioration inhibitor such as an antioxidant, a peroxide decomposer, a radical polymerization inhibitor, a metal deactivator, an acid scavenger, and amines. The deterioration inhibitor is described in, for example, JP-A-3-199201, JP-A-5-97073, JP-A-5-194789, JP-A-5-271471, and JP-A-6-107854. . The amount of the deterioration inhibitor added is the cellulose solution (dope) used for the production of the retardation film from the viewpoint of suppressing the bleed-out of the deterioration inhibitor to the film surface because the effect of the addition of the deterioration inhibitor is manifested. ) Is preferably within the range of 0.01 to 1% by mass, and more preferably within the range of 0.01 to 0.2% by mass. Examples of particularly preferred deterioration inhibitors include butylated hydroxytoluene (abbreviation: BHT) and tribenzylamine (abbreviation: TBA).

(Matting agent fine particles)
It is preferable to add fine particles as a matting agent to the retardation film of the present invention. Examples of the matting agent fine particles include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, and magnesium silicate. And calcium phosphate. Among these matting agent fine particles, those containing silicon are preferable in terms of low turbidity (haze), and silicon dioxide is particularly preferable. The fine particles of silicon dioxide preferably have a primary average particle size in the range of 1 to 20 nm and an apparent specific gravity of 70 g / liter or more. The primary average particle size is more preferably in the range of 5 to 16 nm from the viewpoint of reducing the haze of the retardation film. The apparent specific gravity is further preferably in the range of 90 to 200 g / liter, and particularly preferably in the range of 100 to 200 g / liter. A larger apparent specific gravity is preferable because a high-concentration dispersion can be produced, and haze and aggregates are improved.

  These fine particles usually form secondary particles having an average particle size in the range of 0.05 to 2.0 μm. These secondary particles exist as aggregates of primary particles in the retardation film, and form irregularities of 0.05 to 2.0 μm on the surface of the retardation film. The secondary average particle size is preferably in the range of 0.05 to 1.0 μm, more preferably in the range of 0.1 to 0.7 μm, and particularly preferably in the range of 0.1 to 0.4 μm. The primary particle size and the secondary particle size were determined by observing fine particles in the retardation film with a scanning electron microscope and determining the diameter of a circle circumscribing the particles as the particle size. Also, 200 particles are observed at different locations, and the average value is taken as the average particle size.

  As the silicon dioxide fine particles, for example, commercially available products such as Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600 (above, Nippon Aerosil Co., Ltd., trade name) may be used. it can. Zirconium oxide fine particles are commercially available, for example, as Aerosil R976 and R811 (above, trade name, manufactured by Nippon Aerosil Co., Ltd.) and can be used.

  Among these, Aerosil 200V and Aerosil R972V are fine particles of silicon dioxide having a primary average particle size of 20 nm or less and an apparent specific gravity of 70 g / liter or more, while maintaining the haze of the retardation film at a low coefficient of friction. This is particularly preferable because it has a great effect of lowering.

  The matting agent fine particles are preferably prepared by the following method and applied to the retardation film. That is, a matting agent fine particle dispersion in which a solvent and matting agent fine particles are stirred and mixed is prepared in advance, and this matting agent fine particle dispersion is added to various additive solutions prepared separately with a cellulose derivative concentration of less than 5% by mass. After stirring and dissolving, a method of further mixing with the main cellulose derivative dope solution is preferable.

  Since the surface of the matting agent fine particles is hydrophobized, when an additive having hydrophobicity is added, the additive is adsorbed on the surface of the matting agent fine particles, and the aggregate of the additive is formed using this as a core. Likely to happen. Therefore, by mixing a relatively hydrophilic additive with the matting agent fine particle dispersion in advance and then mixing a hydrophobic additive, aggregation of the additive on the surface of the matting agent can be suppressed. This is preferable because of low light leakage in black display when incorporated in a liquid crystal image display device.

  It is preferable to use an in-line mixer for mixing the matting agent fine particle dispersant and the additive solution and mixing the cellulose derivative dope liquid. Although the present invention is not limited to these methods, the concentration of silicon dioxide when the silicon dioxide fine particles are mixed and dispersed with a solvent or the like is preferably within the range of 5 to 30% by mass, and within the range of 10 to 25% by mass. More preferably, it is in the range of 15 to 20% by mass. A higher dispersion concentration is preferable because turbidity with respect to the same amount of addition is reduced, and generation of haze and aggregates can be suppressed. The addition amount of the matting agent in the final cellulose derivative dope solution is preferably in the range of 0.001 to 1.0% by mass, more preferably in the range of 0.005 to 0.5% by mass. A range of 01 to 0.1% by mass is particularly preferable.

[Method for producing retardation film]
The retardation film of the present invention is preferably produced by imparting a retardation by stretching an optical film containing a cellulose derivative. Although there is no restriction | limiting in particular as a method of manufacturing an optical film, The method of manufacturing by a solution casting method is preferable. In the solution casting method, an optical film is produced using a solution (dope) in which a cellulose derivative is dissolved in an organic solvent.

  The organic solvent used for the preparation of the dope includes ethers having 3 to 12 carbon atoms, ketones having 3 to 12 carbon atoms, esters having 3 to 12 carbon atoms, and 1 to 6 carbon atoms. It is preferable to use a solvent selected from halogenated hydrocarbons.

  Ethers, ketones and esters may have a cyclic structure. A compound having two or more functional groups of ethers, ketones and esters (that is, —O—, —CO— and —COO—) can also be used as the organic solvent. The organic solvent may have other functional groups such as alcoholic hydroxy groups. In the case of an organic solvent having two or more types of functional groups, the number of carbon atoms is preferably within the range of the above-mentioned preferable number of carbon atoms of the solvent having any functional group.

  Examples of ethers having 3 to 12 carbon atoms include diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, anisole, phenetole and the like.

  Examples of ketones having 3 to 12 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclohexanone, and methylcyclohexanone.

  Examples of esters having 3 to 12 carbon atoms include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate, pentyl acetate and the like.

  Examples of the organic solvent having two or more kinds of functional groups include 2-ethoxyethyl acetate, 2-methoxyethanol, 2-butoxyethanol and the like.

  The number of carbon atoms of the halogenated hydrocarbon is preferably 1 or 2, and most preferably 1. The halogen of the halogenated hydrocarbon is preferably chlorine. The proportion of halogen atoms in the halogenated hydrocarbon substituted with halogen is preferably in the range of 25 to 75 mol%, more preferably in the range of 30 to 70 mol%, and more preferably 35 to 65 mol%. More preferably, it is in the range of mol%, and particularly preferably in the range of 40 to 60 mol%. Methylene chloride is a representative halogenated hydrocarbon.

  For the preparation of the dope, it is preferable to use a mixed solvent of methylene chloride and alcohols, and the ratio of alcohols to methylene chloride is preferably in the range of 1 to 50% by mass, and in the range of 5 to 40% by mass. The range of 8 to 30% by mass is particularly preferable. As the alcohol, methanol, ethanol, and n-butanol are preferable, and two or more kinds of alcohols may be mixed and used.

  The dope can be prepared by a general method under a temperature of 0 ° C. or higher (room temperature or high temperature). The solution can be prepared using a dope preparation method and apparatus in a normal solution casting method. In the case of a general method, it is preferable to use a halogenated hydrocarbon (particularly methylene chloride) as the organic solvent.

  The concentration of the cellulose derivative in the dope is preferably in the range of 5 to 40% by mass, and more preferably in the range of 10 to 30% by mass. Various additives described above may be added to the organic solvent (main solvent).

  The dope can be prepared by stirring a cellulose derivative and an organic solvent at room temperature (0 to 40 ° C.). High concentration solutions may be stirred under pressure and heating conditions. Specifically, the cellulose derivative and the organic solvent are placed in a pressure vessel and sealed, and stirred while being heated to a temperature not lower than the boiling point of the solvent at normal temperature and in a range where the solvent does not boil.

  The heating temperature is usually 40 ° C or higher, preferably in the range of 60 to 200 ° C, more preferably in the range of 80 to 110 ° C.

  Each component may be roughly mixed in advance and then charged into the container. Moreover, you may put into a container sequentially. The container must be provided with a mechanism capable of stirring. An inert gas such as nitrogen gas can be injected to pressurize the container. Moreover, you may pressurize using the raise of the vapor pressure of the solvent by heating. Or after sealing a container, you may add each component under pressure.

  When heating, the method of heating from the outer peripheral part of a container is preferable. For example, a jacket type heating device can be used. Further, the entire container can be heated by providing a plate heater outside the container, or by installing a pipe on the outer periphery of the container and circulating the heated liquid in the pipe.

  It is preferable to provide a stirring blade inside the container and use this to stir. The stirring blade preferably has a length that reaches the vicinity of the wall of the container. A scraping blade is preferably provided at the end of the stirring blade in order to renew the liquid film on the vessel wall.

  Instruments such as a pressure gauge and a thermometer may be installed in the container. Each component is dissolved in a solvent in a container. The prepared dope is taken out of the container after cooling, or is taken out and then cooled using a heat exchanger or the like.

  A solution can also be prepared by a cooling dissolution method. In the cooling dissolution method, the cellulose derivative can be dissolved in an organic solvent that is difficult to dissolve by a normal dissolution method. In addition, even if it is a solvent which can melt | dissolve a cellulose derivative with a normal melt | dissolution method, there exists an effect by which a rapid and uniform solution is obtained by applying the cooling melt | dissolution method.

  In the cooling dissolution method, first, a cellulose derivative is gradually added to an organic solvent with stirring at room temperature. The amount of the cellulose derivative is preferably adjusted so as to be contained in the mixture in the range of 5 to 40% by mass. The amount of the cellulose derivative is more preferably in the range of 10 to 30% by mass. Furthermore, you may add the above-mentioned arbitrary additive in a mixture.

  Next, the mixture is cooled within a range of −100 to −10 ° C. (preferably −80 to −10 ° C., more preferably −50 to −20 ° C., particularly preferably −50 to −30 ° C.). The cooling can be performed, for example, in a dry ice / methanol bath (−75 ° C.) or a cooled diethylene glycol solution (−30 to −20 ° C.). By cooling, the mixture of the cellulose derivative and the organic solvent is solidified.

  The cooling rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more, and particularly preferably 12 ° C./min or more. The faster the cooling rate, the better. However, 10,000 ° C./second is the theoretical upper limit, 1000 ° C./second is the technical upper limit, and 100 ° C./second is the practical upper limit. The cooling rate is a value obtained by dividing the difference between the temperature at the start of cooling and the final cooling temperature by the time from the start of cooling to the final cooling temperature.

  Furthermore, when this is heated within the range of 0 to 200 ° C. (preferably 0 to 150 ° C., more preferably 0 to 120 ° C., and still more preferably 0 to 50 ° C.), the cellulose derivative is dissolved in the organic solvent. . The temperature may be increased by simply leaving it at room temperature or in a warm bath.

  The heating rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more, and even more preferably 12 ° C./min or more. The higher the heating rate, the better. However, 10,000 ° C./second is the theoretical upper limit, 1000 ° C./second is the technical upper limit, and 100 ° C./second is the practical upper limit. The heating rate is the value obtained by dividing the difference between the temperature at the start of heating and the final heating temperature by the time from the start of heating until the final heating temperature is reached. is there.

  A uniform solution is obtained as described above. If the dissolution is insufficient, the cooling and heating operations may be repeated. Whether or not the dissolution is sufficient can be determined by merely observing the appearance of the solution with the naked eye.

  In the cooling dissolution method, it is preferable to use an airtight container in order to avoid moisture mixing due to condensation during cooling. In the cooling and heating operation, when the pressure is applied during cooling and the pressure is reduced during heating, the dissolution time can be shortened. In order to perform pressurization and pressure reduction, it is preferable to use a pressure-resistant container.

  An optical film having a cellulose derivative is produced from the prepared cellulose derivative solution (dope) by a solution pouring method.

(Film formation by solution casting method)
The optical film according to the present invention is preferably manufactured by the solution casting method as described above. In the solution casting method, a step of preparing a dope by heating and dissolving a cellulose derivative and various additives satisfying the characteristics specified in the present invention in an organic solvent, and the prepared dope on a belt-shaped or drum-shaped metal support Includes a step of casting, a step of drying the cast dope as a web, a step of peeling from the metal support, a step of stretching or shrinking the peeled web, a step of further drying, a step of winding up the finished film, etc. .

  The dope is cast on a drum or band and the solvent is evaporated to form a film. It is preferable to adjust the concentration of the dope before casting so that the solid content is in the range of 18 to 35%. The surface of the drum or band is preferably finished in a mirror state. The dope is preferably cast on a drum or band having a surface temperature of 10 ° C. or less.

  Regarding the drying method in the solution pouring method, U.S. Pat. Nos. 2,336,310, 2,367,603, 2,429,078, 2,429,297, 2,429,978, 2,607,704, 2,273,069, and 2,739,070 Each specification, British Patent Nos. 640731 and 736892, and Japanese Examined Patent Publication Nos. 45-4554, 49-5614, Japanese Unexamined Patent Publication Nos. 60-176634, 60-203430 And JP-A-62-115035. Drying on the drum or band can be performed by blowing an inert gas such as air or nitrogen to the cast film.

  The prepared cellulose derivative solution (dope) can be cast into two or more layers to form a film. In this case, it is preferable to produce a cellulose derivative film by a solution pouring method. The dope is cast on a drum or band and the solvent is evaporated to form a film. It is preferable to adjust the concentration of the dope before casting so that the solid content is in the range of 5 to 40%. The surface of the drum or band is preferably finished in a mirror state.

(Stretching process)
As described above, the retardation film of the present invention has in-plane retardation values Ro (450) _and Ro (550) measured at light wavelengths of 450 nm and 550 nm in the ranges of 110 to 125 and 135 to 145 nm, respectively. The characteristics can be imparted by stretching the optical film formed as described above.

  Stretching methods applicable to the present invention include, for example, a method in which a circumferential speed difference is applied to a plurality of rollers, and a longitudinal stretching is performed using a circumferential speed difference between the plurality of rollers between the ends of the web. A method in which the distance between the clips and pins is fixed according to the direction of travel and stretched in the vertical direction, a method in which the paper is widened in the horizontal direction and stretched in the horizontal direction, or a method in which both the length and width are expanded simultaneously and stretched in both the vertical and horizontal directions. Can be used alone or in combination.

  That is, the film may be stretched in the transverse direction, longitudinally, or in both directions with respect to the film forming direction. Further, when stretching in both directions, simultaneous stretching or sequential stretching may be used. May be. In the case of the so-called tenter method, driving the clip portion by the linear drive method is preferable because smooth stretching can be performed and the risk of breakage and the like can be reduced.

  As the stretching process, the film is usually stretched in the width direction (TD direction) and contracted in the transport direction (MD direction), but when contracted, it is easy to match the main chain direction when transported in an oblique direction. In addition, the phase difference effect is even greater. The shrinkage rate can be determined by the transport angle.

FIG. 10 is a schematic diagram for explaining the shrinkage ratio in oblique stretching. In FIG. 10, when the optical film F is obliquely stretched in the direction of reference numeral 12, the optical film F is contracted to M ₂ by being obliquely bent. That is, when the gripping tool that grips the optical film F advances as it is without bending at the bending angle θ, it should advance by a length M ₁ ′ in a predetermined time. However, in reality, it bends at a bending angle θ and proceeds by M ₁ (where M ₁ = M ₁ ′). At this time, since the gripping tool advances by M ₂ in the film entering direction (direction orthogonal to the stretching direction (TD direction) A1), the optical film F has a length M ₃ (where M ₃ = M ₁ -M ₂₎ the fact that only shrinkage.

At this time, the shrinkage rate (%) is
Shrinkage rate (%) = (M ₁ −M ₂ ) / M ₁ × 100. If the bending angle is θ,
M ₂ = M ₁ × sin (π−θ), and the shrinkage rate is
Shrinkage rate (%) = (1-sin (π−θ)) × 100

  In FIG. 10, reference numeral 11 is the stretching direction (TD direction), reference numeral 13 is the transport direction (MD direction), and reference numeral 14 indicates the slow axis.

  Considering the productivity of the long circularly polarizing plate, the retardation film of the present invention is preferably stretched at an angle in the range of 40 to 50 ° with respect to the transport direction. More preferably, the angle is in the range of 43 to 47 °, and still more preferably 44 to 45 °. By setting it as such an angle, the roll-to-roll pasting with a polarizing film is attained.

<Stretching with an oblique stretching device>
Next, an oblique stretching method in which stretching is performed at an angle within a range of 40 to 50 ° with respect to the transport direction will be further described. In the method for producing a retardation film of the present invention, it is preferable to use an oblique stretching apparatus as a method for imparting an oblique orientation to an optical film to be stretched.

  As an oblique stretching apparatus applicable to the present invention, the orientation angle of the film can be freely set by changing the rail pattern in various ways, and the orientation axis of the film can be oriented with high accuracy evenly in the left-right direction across the film width direction. It is preferable that the film stretching apparatus be capable of controlling the film thickness and retardation with high accuracy.

  FIG. 11 is a schematic view showing an example of a rail pattern of an oblique stretching apparatus applicable to the production of the retardation film of the present invention. In addition, FIG. 11 shown here is an example, Comprising: The extending | stretching apparatus applicable in this invention is not limited to this.

  In general, in an oblique stretching apparatus, as shown in FIG. 11, a feeding direction D1 of a long film original is different from a winding direction D2 of a stretched film after stretching, and forms a feeding angle θi. doing. The feeding angle θi can be arbitrarily set to a desired angle in the range of more than 0 ° and less than 90 °. In the present specification, the term “long” refers to a film having a length of at least about 5 times the width of the film, preferably a film having a length of 10 times or more.

  The long film original is gripped at both ends by the left and right gripping tools (tenters) at the entrance of the oblique stretching apparatus (position A in the figure), and travels as the gripping tool travels. The left and right gripping tools are the left and right gripping tools Ci and Co at the entrance of the oblique stretching apparatus (position A in the figure) and facing the direction substantially perpendicular to the film traveling direction (feeding direction D1). The film travels on the asymmetric rails Ri and Ro, and the film gripped by the tenter is released at the position at the end of stretching (position B in the figure).

  At this time, as the left and right gripping tools facing each other at the entrance of the oblique stretching device (position A in the figure) travel on the left and right asymmetric rails Ri and Ro, the gripping tool Ci traveling on the Ri side becomes the Ro side. The positional relationship is advancing with respect to the gripping tool Co traveling.

  That is, at the entrance of the oblique stretching apparatus (the grip start position by the film gripping tool) A, the gripping tools Ci and Co that are opposed to the film feeding direction D1 are positioned at the end of the film stretching. In the state of B, the straight line connecting the grippers Ci and Co is inclined by an angle θL with respect to a direction substantially perpendicular to the film winding direction D2.

  According to the above method, the original film is stretched obliquely. Here, “substantially vertical” indicates that the angle is in a range of 90 ± 1 °.

  More specifically, in the method for producing the retardation film of the present invention, it is preferable to perform oblique stretching using the tenter capable of oblique stretching described above.

  This stretching apparatus is an apparatus that heats a film raw fabric to an arbitrary temperature at which stretching can be performed and obliquely stretches the film. This stretching apparatus includes a heating zone, a pair of rails on the left and right on which a gripping tool for transporting the film travels, and a number of gripping tools that travel on the rails. Both ends of the film sequentially supplied to the inlet of the stretching apparatus are gripped by a gripping tool, the film is guided into the heating zone, and the film is released from the gripping tool at the outlet of the stretching apparatus. The film released from the gripping tool is wound around the core. Each of the pair of rails has an endless continuous track, and the gripping tool which has released the grip of the film at the outlet portion of the stretching apparatus travels outside and is sequentially returned to the inlet portion.

  The rail pattern of the stretching device has an asymmetric shape on the left and right, and the rail pattern can be adjusted manually or automatically depending on the orientation angle, stretch ratio, etc. given to the long stretched film to be manufactured. It has become. In the oblique stretching apparatus used in the present invention, it is preferable that the position of each rail portion and the rail connecting portion can be freely set, and the rail pattern can be arbitrarily changed (the ○ portion in FIG. 2 indicates an example of the connecting portion). ).

  In the present invention, the gripping tool of the stretching apparatus travels at a constant speed with a constant interval from the front and rear gripping tools. Although the traveling speed of a holding | gripping tool can be selected suitably, it is 1-100 m / min normally. The difference in travel speed between the pair of left and right grippers is usually 1% or less, preferably 0.5% or less, more preferably 0.1% or less of the travel speed. This is because if there is a difference in the traveling speed between the left and right sides of the film at the exit of the stretching process, wrinkles and shifts occur at the exit of the stretching process, so the speed difference between the left and right gripping tools is required to be substantially the same speed. Because. In general stretching equipment, etc., there is a speed unevenness that occurs in the order of seconds or less depending on the period of the sprocket teeth driving the chain, the frequency of the drive motor, etc. This does not correspond to the speed difference described in the invention.

  In the stretching apparatus applicable to the present invention, a large bending rate is often required for the rail that regulates the locus of the gripping tool, particularly in a portion where the film is transported obliquely. For the purpose of avoiding interference between gripping tools due to sudden bending or local stress concentration, it is preferable that the trajectory of the gripping tool draws a curve at the bent portion.

  In the present invention, the long film original fabric is gripped in order by the right and left gripping tools at the entrance of the oblique stretching apparatus (position A in the drawing) and travels as the gripping tool travels. The left and right gripping tools facing the direction substantially perpendicular to the film traveling direction (feeding direction D1) at the entrance of the oblique stretching apparatus (position A in the figure) run on a rail that is asymmetrical to the preheating zone. Through a heating zone having a stretching zone and a heat setting zone.

  The preheating zone refers to a section that travels while maintaining a constant interval between the gripping tools that grip both ends at the entrance of the heating zone.

  The stretching zone refers to a section where the gap between the gripping tools gripping both ends starts to reach a predetermined distance. In the stretching zone, the oblique stretching as described above is performed, but the stretching may be performed in the longitudinal direction or the lateral direction before and after the oblique stretching as necessary. In the case of oblique stretching, there is contraction in the MD direction (fast axis direction) which is a direction perpendicular to the slow axis during bending.

  The heat setting zone refers to a section in which the gripping tools at both ends run in parallel with each other in a period in which the interval between the gripping tools after the stretching zone becomes constant again. You may pass through the area (cooling zone) by which the temperature in a zone is set to below the glass transition temperature Tg of the thermoplastic resin which comprises a film, after passing through a heat setting zone. At this time, in consideration of shrinkage of the film due to cooling, a rail pattern that narrows the gap between the opposing gripping tools in advance may be used.

  The temperature of each zone is the glass transition temperature Tg of the thermoplastic resin, the temperature of the preheating zone is in the range of Tg to Tg + 30 ° C., the temperature of the stretching zone is in the range of Tg to Tg + 30 ° C., and the temperature of the cooling zone is It is preferable to set within the range of Tg-30 ° C to Tg.

  In order to control thickness unevenness in the width direction, a temperature difference may be given in the width direction in the stretching zone. In order to give a temperature difference in the width direction in the stretching zone, a method of adjusting the opening degree of the nozzle for sending warm air into the temperature-controlled room so as to make a difference in the width direction, and controlling heating by arranging heaters in the width direction are known. Can be used.

  The length of the preheating zone, the stretching zone, the shrinking zone and the cooling zone can be appropriately selected. The length of the preheating zone is usually within a range of 100 to 150% with respect to the length of the stretching zone, and the length of the fixed zone. Is usually in the range of 50 to 100%.

  The draw ratio in the drawing step is the value of the ratio of the distance between the pair of grips opposed to each other at the stretching start position when the pair of grippers move to the stretching end position. The draw ratio R is preferably in the range of 1.3 to 3.0, more preferably in the range of 1.5 to 2.8, and preferably in the range of 1.3 to 3.0. More preferably, it exists in the range of 1.5-2.8. When the draw ratio is within this range, the thickness unevenness in the width direction can be reduced. In the stretching zone of the oblique stretching apparatus, it is possible to further improve the thickness unevenness in the width direction by making a difference in the stretching temperature in the width direction.

  As an oblique stretching method applicable in the present invention, in addition to the method shown in FIG. 11, the stretching methods shown in FIGS. 12 (a) to 12 (c) and FIGS. 13 (a) and 13 (b) are given. be able to.

  FIG. 12 is a schematic view showing an example of a production method applicable to the present invention (an example in which the film is drawn from a long film original fabric roller and then obliquely stretched), and the long film original material once wound up in a roll shape. The pattern which extends | stretches and diagonally stretches is shown. FIG. 13 is a schematic view showing an example of another manufacturing method applicable to the present invention (an example of continuous oblique stretching without winding a long film original), and winding the long film original. The pattern which performs a diagonal stretch process continuously, without showing is shown.

  12 and 13, reference numeral 15 denotes an oblique stretching apparatus, reference numeral 16 denotes a film feeding apparatus, reference numeral 17 denotes a transport direction changing apparatus, reference numeral 18 denotes a winding apparatus, and reference numeral 19 denotes a film forming apparatus. In each figure, the code | symbol which shows the same thing may be abbreviate | omitted.

  The film feeding device 16 is slidable and swivelable or slidable so that the film can be fed out at a predetermined angle with respect to the oblique stretching device inlet. It is preferable to be able to send (A)-(c) of FIG. 12 has shown the pattern which changed arrangement | positioning of the film feeding apparatus 16 and the conveyance direction change apparatus 17, respectively. FIGS. 13A and 13B show a pattern in which the film formed by the film forming apparatus 19 is directly fed to the stretching apparatus 15. By configuring the film feeding device 16 and the conveyance direction changing device 17 in such a configuration, it becomes possible to further narrow the width of the entire manufacturing apparatus, and to finely control the film feeding position and angle. Thus, it becomes possible to obtain a long stretched film with small variations in film thickness and optical value. In addition, by making the film feeding device 16 and the transport direction changing device 17 movable, it is possible to effectively prevent the left and right clips from being caught in the film.

  By arranging the winding device 18 so that the film can be pulled at a predetermined angle with respect to the outlet of the oblique stretching device, it is possible to finely control the film take-up position and angle, and variations in film thickness and optical value. It becomes possible to obtain a long stretched film having a small diameter. Therefore, it is possible to effectively prevent the film from being wrinkled and to improve the winding property of the film, so that the film can be wound up in a long length. In the present invention, the take-up tension T (N / m) of the stretched film is adjusted within a range of 100 N / m <T <300 N / m, preferably 150 N / m <T <250 N / m. .

(Melting method)
The optical film according to the present invention may be formed by a melt film forming method in addition to the solution casting method described above. The melt film forming method is a molding method in which a composition containing an additive such as a cellulose derivative and a plasticizer is heated and melted to a temperature exhibiting fluidity, and then cast as a melt containing a fluid thermoplastic resin. is there.

  The molding method for heating and melting can be classified into, for example, a melt extrusion molding method, a press molding method, an inflation method, an injection molding method, a blow molding method, and a stretch molding method. Among these molding methods, the melt extrusion molding method is preferable from the viewpoint of mechanical strength and surface accuracy.

  The plurality of raw materials used in the melt extrusion method are usually preferably kneaded and pelletized in advance. Pelletization can be performed by a known method. For example, dry cellulose derivatives, plasticizers, and other additives are fed to an extruder with a feeder, kneaded using a single or twin screw extruder, and then from a die. It can be obtained by extruding into a strand, cooling with water or air, and cutting.

  The additives may be mixed before being supplied to the extruder, or may be supplied by individual feeders. A small amount of additives such as matting agent fine particles and antioxidants are preferably mixed in advance in order to mix uniformly.

  The extruder used for pelletization preferably has a method of suppressing the shearing force and processing at the lowest possible temperature so that the resin can be pelletized so that the resin does not deteriorate (molecular weight reduction, coloring, gel formation, etc.). For example, in the case of a twin screw extruder, it is preferable to rotate in the same direction using a deep groove type screw. From the uniformity of kneading, the meshing type is preferable.

  A film is formed using the pellets obtained as described above. Of course, it is also possible to form the film as it is after it is not formed into pellets, and the raw material powder is put into the feeder as it is, supplied to the extruder, heated and melted.

  Using a single-screw or twin-screw type extruder, the melting temperature when extruding is within the range of 200 to 300 ° C., filtered through a leaf disk type filter or the like to remove foreign matter, and then from the T-die. The film is cast into a film, and the film is nipped with a cooling roller and an elastic touch roller, and solidified on the cooling roller.

  When introducing into the extruder from the supply hopper, it is preferable to carry out under vacuum or reduced pressure or in an inert gas atmosphere to prevent oxidative decomposition and the like.

  The extrusion flow rate is preferably performed stably by introducing a gear pump or the like. Further, a stainless fiber sintered filter is preferably used as a filter used for removing foreign substances. A stainless steel fiber sintered filter is a product in which stainless steel fiber bodies are intricately intertwined and compressed, and the contact points are sintered and integrated. The density is changed according to the thickness of the fiber and the amount of compression, and filtration is performed. The accuracy can be adjusted.

  Additives such as plasticizers and fine particles may be mixed with the resin in advance, or may be kneaded in the middle of the extruder. In order to add uniformly, it is preferable to use a mixing apparatus such as a static mixer.

  The film temperature on the touch roller side when the film is nipped between the cooling roller and the elastic touch roller is preferably in the range of Tg to Tg + 110 ° C. of the film. A known elastic touch roller can be used as the elastic touch roller having an elastic surface used for such a purpose. The elastic touch roller is also called a pinching rotary body, and a commercially available one can also be used.

  When peeling the film from the cooling roller, it is preferable to control the tension to prevent deformation of the film.

  The film obtained as described above can be subjected to stretching and shrinkage treatment by stretching operation after passing through the step of contacting the cooling roller. As a method of stretching and shrinking, a known roller stretching device or oblique stretching device as described above can be preferably used. The stretching temperature is usually preferably performed in the temperature range of Tg to Tg + 60 ° C. of the resin constituting the film.

  Before winding, the end may be slit and cut to the width to be the product, and knurling (embossing) may be applied to both ends to prevent sticking and scratching during winding. The knurling method can process a metal ring having an uneven pattern on its side surface by heating or pressing. In addition, since the film has deform | transformed and cannot use as a product normally, the holding | grip part of the clip of both ends of a film is cut out and reused.

  The retardation film of the present invention can be formed into a circularly polarizing plate by laminating so that the angle between the slow axis and the transmission axis or absorption axis of the polarizer described later is substantially 45 °. In the present invention, “substantially 45 °” means within a range of 40 to 50 °.

  The angle between the in-plane slow axis of the retardation film of the present invention and the transmission axis or absorption axis of the polarizer is preferably in the range of 41 to 49 °, and in the range of 42 to 48 °. It is more preferable that it is within the range of 43 to 47 °, and it is particularly preferable that it is within the range of 44 to 46 °.

[Circularly polarizing plate]
The circularly polarizing plate of the present invention is produced by cutting a long roll having a long protective film, a long polarizer and a long retardation film of the present invention in this order. Since the circularly polarizing plate of the present invention is produced using the retardation film of the present invention, it can be applied to an organic EL image display device, etc., which will be described later. An effect of shielding specular reflection can be exhibited. As a result, reflection during observation can be prevented and black expression can be improved.

  In addition, the circularly polarizing plate of the present invention preferably has an ultraviolet absorption function. It is preferable that the protective film on the viewing side has an ultraviolet absorbing function from the viewpoint that both the polarizer and the organic EL element can exhibit a protective effect against ultraviolet rays. Furthermore, when the retardation film on the light emitter side also has an ultraviolet absorbing function, when used in an organic EL image display device described later, deterioration of the organic EL element can be further suppressed.

  In addition, the circularly polarizing plate of the present invention has the retardation film (λ / 4) of the present invention adjusted so that the angle of the slow axis (that is, the orientation angle θ) is “substantially 45 °” with respect to the longitudinal direction. By using the retardation film, it is possible to form an adhesive layer and bond the polarizer and the retardation film together with a consistent production line. Specifically, after finishing the step of producing a polarizer by stretching a polarizing film, a step of laminating a polarizer and a retardation film can be incorporated during or after the subsequent drying step, Each can be continuously supplied, and can be connected in a production line that is consistent with the next process by winding in a roll state after bonding. In addition, when bonding a polarizer and retardation film, a protective film can also be simultaneously supplied in a roll state and can also be bonded continuously. From the viewpoint of performance and production efficiency, it is preferable to simultaneously bond a retardation film and a protective film to a polarizer. That is, after finishing the step of producing a polarizer by stretching the polarizing film, during the subsequent drying step or after the drying step, the protective film and the retardation film are respectively bonded to both sides with an adhesive, It is also possible to obtain a rolled circularly polarizing plate.

  In the circularly polarizing plate of the present invention, the polarizer is preferably sandwiched between the retardation film (λ / 4 retardation film) of the present invention and a protective film, and a cured layer is laminated on the viewing side of the protective film. Is preferred.

  The circularly polarizing plate can be provided in a liquid crystal image display device or an organic electroluminescence image display device, but as an example, by applying it to an organic electroluminescence image display device, the specular reflection of the metal electrode of the organic electroluminescence light emitter The effect which shields is expressed.

(Protective film)
In the circularly polarizing plate, the polarizer is preferably sandwiched between the retardation film of the present invention and a protective film. As such a protective film, other cellulose ester-containing films are suitably used. For example, a commercially available cellulose ester film (for example, Konica Minoltack KC8UX, KC5UX, KC4UX, KC8UCR3, KC4SR, KC4BR, KC4CR, KC4DR, KC4FR , KC4KR, KC8UY, KC6UY, KC4UY, KC4UE, KC8UE, KC8UY-HA, KC2UA, KC4UA, KC6UAKC, 2UAH, KC4UAH, KC6UAH, Z TD60UL, Fujitac TD40UL, Fujitac R02, Fujitac R06, Fujifilm Corporation) Used properly.

  Although the thickness in particular of a protective film is not restrict | limited, It can be set as about 10-200 micrometers, Preferably it is the range of 10-100 micrometers, More preferably, it is the range of 10-70 micrometers.

(Polarizer)
A polarizer is an element that passes only light having a plane of polarization in a certain direction. Examples thereof include a polyvinyl alcohol polarizing film. The polyvinyl alcohol polarizing film includes those obtained by dyeing iodine on a polyvinyl alcohol film and those obtained by dyeing a dichroic dye.

  The polarizer can be obtained by uniaxially stretching a polyvinyl alcohol film and then dyeing; or after dying a polyvinyl alcohol film and uniaxially stretching, and preferably by further performing a durability treatment with a boron compound. The film thickness of the polarizer is preferably in the range of 5 to 30 μm, and more preferably in the range of 5 to 15 μm.

  Examples of the polyvinyl alcohol film include ethylene unit content of 1 to 4 mol%, polymerization degree of 2000 to 4000, and saponification degree of 99.0 to 99 described in JP2003-248123A, JP2003-342322A, and the like. 99 mol% ethylene-modified polyvinyl alcohol is preferably used. Moreover, it is preferable to produce a polarizer by producing a polarizer by the method described in Japanese Patent Application Laid-Open No. 2011-1000016, Japanese Patent No. 4691205, and Japanese Patent No. 4804589, and then laminating it with the retardation film of the present invention. .

(adhesive)
The lamination of the retardation film and the polarizer of the present invention is not particularly limited, but can be performed using a completely saponified polyvinyl alcohol adhesive after saponifying the retardation film. It can also be bonded using an actinic ray curable adhesive or the like. However, since the elastic modulus of the obtained adhesive layer is high and the deformation of the polarizing plate is easily suppressed, the bonding using the photocurable adhesive is possible. It is preferable to be a combination.

  Preferred examples of the photocurable adhesive include (α) a cationic polymerizable compound, (β) a photo cationic polymerization initiator, and (γ) a wavelength longer than 380 nm, as disclosed in JP2011-08234A. And a photo-curable adhesive composition containing each component of a photosensitizer exhibiting maximum absorption in the light of (δ) and a naphthalene-based photosensitization aid. However, other photocurable adhesives may be used.

  Hereinafter, an example of the manufacturing method of the polarizing plate using a photocurable adhesive agent is demonstrated. The polarizing plate comprises (1) a pretreatment step for easily adhering the surface of the retardation film to which the polarizer is adhered, and (2) at least one of the adhesive surfaces of the polarizer and the retardation film, with the following photocurability. An adhesive application step of applying an adhesive, (3) a bonding step of bonding the polarizer and the retardation film through the obtained adhesive layer, and 4) a polarizer and a retardation through the adhesive layer It can manufacture by the manufacturing method including the hardening process which hardens an adhesive bond layer in the state bonded together. What is necessary is just to implement the pre-processing process of (1) as needed.

(Pretreatment process)
In the pretreatment step, an easy adhesion treatment is performed on the adhesion surface of the retardation film to the polarizer. When the retardation films are bonded to both surfaces of the polarizer, easy adhesion treatment is performed on the adhesive surfaces of the respective retardation films with the polarizer. Examples of the easy adhesion treatment include corona treatment and plasma treatment.

(Adhesive application process)
In the adhesive application step, the photocurable adhesive is applied to at least one of the adhesive surfaces of the polarizer and the retardation film. When the photocurable adhesive is directly applied to the surface of the polarizer or the retardation film, the application method is not particularly limited. For example, various coating methods such as a doctor blade, a wire bar, a die coater, a comma coater, and a gravure coater can be used. Moreover, after casting a photocurable adhesive between a polarizer and retardation film, the method of pressing with a roller etc. and spreading uniformly can also be utilized.

(Bonding process)
Thus, after apply | coating a photocurable adhesive agent, it uses for a bonding process. In this bonding step, for example, when a photocurable adhesive is applied to the surface of the polarizer in the previous application step, a retardation film is superimposed thereon. When a photocurable adhesive is applied to the surface of the retardation film in the previous application step, a polarizer is superimposed thereon. In addition, when a photocurable adhesive is cast between the polarizer and the retardation film, the polarizer and the retardation film are superposed in that state. When a retardation film is adhered to both surfaces of a polarizer, and both surfaces use a photocurable adhesive, a retardation film and a protective film are respectively attached to both surfaces of the polarizer via a photocurable adhesive. Superimposed. Usually, in this state, both sides (if the retardation film is superimposed on one side of the polarizer, the polarizer side and the retardation film side, and if the film is superimposed on both sides of the polarizer, The film is pressed with a roll or the like from the film side). As the material of the roll, metal, rubber or the like can be used. The rollers arranged on both sides may be made of the same material or different materials.

(Curing process)
In the curing step, the active energy ray is irradiated to the uncured photocurable adhesive to cure the adhesive layer containing the epoxy compound or the oxetane compound. Thereby, the polarizer and the retardation film which are overlapped with each other are bonded via the photocurable adhesive. When laminating a retardation film on one side of a polarizer, the active energy ray may be irradiated from either the polarizer side or the retardation film side. Moreover, when laminating a retardation film or a protective film on both sides of a polarizer, the active energy is applied from either film side in a state where the films are overlapped on both sides of the polarizer via a photocurable adhesive, respectively. It is advantageous to irradiate the line and cure the photocurable adhesive on both sides simultaneously.

  As the active energy ray, visible light, ultraviolet ray, X-ray, electron beam or the like can be used, and since it is easy to handle and has a sufficient curing speed, generally, an electron beam or ultraviolet ray is preferably used.

  Any appropriate condition can be adopted as the electron beam irradiation condition as long as the adhesive can be cured. For example, in the electron beam irradiation, the acceleration voltage is preferably in the range of 5 to 300 kV, more preferably in the range of 10 to 250 kV. If the acceleration voltage is less than 5 kV, the electron beam may not reach the adhesive and may be insufficiently cured. If the acceleration voltage exceeds 300 kV, the penetrating force through the sample is too strong and the electron beam rebounds. There is a risk of damaging the polarizer. The irradiation dose is in the range of 5 to 100 kGy, more preferably in the range of 10 to 75 kGy. When the irradiation dose is less than 5 kGy, the adhesive becomes insufficiently cured, and when it exceeds 100 kGy, the retardation film and the polarizer are damaged, resulting in a decrease in mechanical strength and yellowing to obtain predetermined optical characteristics. I can't.

Arbitrary appropriate conditions can be employ | adopted for the irradiation conditions of an ultraviolet-ray, if it is the conditions which can harden the said adhesive agent. The dose of ultraviolet rays is preferably in the range of 50~1500mJ / cm ² in accumulated light quantity, and even more preferably in the range of 100 to 500 mJ / cm ^2.

  In the polarizing plate obtained as described above, the thickness of the adhesive layer is not particularly limited, but is usually in the range of 0.01 to 10 μm, and preferably in the range of 0.5 to 5 μm.

<< Organic EL image display device >>
The organic EL image display device of the present invention is produced by including the above-described circularly polarizing plate of the present invention.

  More specifically, the organic EL image display device of the present invention includes a circularly polarizing plate using the retardation film of the present invention and an organic EL element. Therefore, in the organic EL image display device, reflection during observation is prevented, and black expression is improved. The screen size of the organic EL image display device is not particularly limited, and can be 20 inches or more.

  FIG. 14 is a schematic explanatory diagram of the configuration of the organic EL image display device of the present invention. The configuration of the organic EL image display device of the present invention is not limited to that shown in FIG.

  As shown in FIG. 14, a metal electrode 102, a TFT 103, an organic light emitting layer 104, a transparent electrode (ITO, etc.) 105, an insulating layer 106, a sealing layer 107, a film are sequentially formed on a transparent substrate 101 using glass, polyimide, or the like. On the organic EL element B having 108 (which can be omitted), the above-described long circular polarizing plate C in which the polarizer 110 is sandwiched between the retardation film 109 and the protective film 111 is provided, and the organic EL image display device A is provided. Configure.

  It is preferable that a hardened layer 112 is laminated on the protective film 111. The cured layer 112 not only prevents scratches on the surface of the organic EL image display device, but also has an effect of preventing warpage due to the long circularly polarizing plate. Further, an antireflection layer 113 may be provided on the cured layer. The thickness of the organic EL element itself is about 1 μm.

  In general, in an organic EL image display device, a metal electrode, an organic light emitting layer, and a transparent electrode are sequentially laminated on a transparent substrate to form a light emitting element (organic EL element). Here, the organic light emitting layer is a laminate of various organic thin films, for example, a laminate of a hole injection layer made of a triphenylamine derivative or the like and a light emitting layer made of a fluorescent organic solid such as anthracene, Also known are configurations having various combinations such as a laminate of such a light-emitting layer and an electron injection layer composed of a perylene derivative or the like, or a laminate of these hole injection layer, light-emitting layer, and electron injection layer. It has been.

  In organic EL image display devices, holes and electrons are injected into the organic light-emitting layer by applying a voltage to the transparent electrode and the metal electrode, and the energy generated by recombination of these holes and electrons excites the phosphor material. Then, light is emitted on the principle that the excited fluorescent material emits light when returning to the ground state. The mechanism of recombination in the middle is the same as that of a general diode, and as can be predicted from this, the current and the emission intensity show strong nonlinearity with rectification with respect to the applied voltage.

  In an organic EL image display device, in order to extract light emitted from the organic light emitting layer, at least one of the electrodes needs to be transparent, and is usually formed of a transparent conductor such as indium tin oxide (ITO). The electrode is preferably used as the anode. On the other hand, in order to facilitate electron injection and increase luminous efficiency, it is important to use a material having a small work function for the cathode, and usually metal electrodes such as Mg—Ag and Al—Li are used.

  The circularly polarizing plate having the retardation film described above can be applied to an organic EL image display device having a large screen having a screen size of 20 inches or more, that is, a diagonal distance of 50.8 cm or more.

  In the organic EL image display device having such a configuration, the organic light emitting layer is formed of a very thin film having a thickness of about 10 nm. Therefore, the organic light emitting layer transmits light almost completely like the transparent electrode. As a result, light that is incident from the surface of the transparent substrate at the time of non-light emission, passes through the transparent electrode and the organic light emitting layer, and is reflected by the metal electrode is again emitted to the surface side of the transparent substrate. The display surface of the organic EL image display device looks like a mirror surface.

  In an organic EL image display device including an organic EL element having a transparent electrode on the surface side of an organic light emitting layer that emits light by applying a voltage and a metal electrode on the back side of the organic light emitting layer, the surface side of the transparent electrode ( A polarizing plate can be provided on the viewing side), and a retardation plate can be provided between the transparent electrode and the polarizing plate.

  Since the λ / 4 retardation film and the polarizing plate have a function of polarizing light incident from the outside and reflected by the metal electrode, the polarizer has an effect of preventing the mirror surface of the metal electrode from being visually recognized by the polarization function. If the angle between the polarization directions of the film and the retardation film is adjusted to 45 ° or 135 °, the mirror surface of the metal electrode can be completely shielded.

  As described above, the external light incident on the organic EL image display device transmits only the linearly polarized light component by the polarizer, and this linearly polarized light is generally elliptically polarized by the retardation plate. In the case of a / 4 retardation film and the angle formed by the polarization direction of the polarizer and the retardation film is 45 ° or 135 °, it becomes circularly polarized light.

  This circularly polarized light is transmitted through the transparent substrate, the transparent electrode, and the organic thin film, is reflected by the metal electrode, is again transmitted through the organic thin film, the transparent electrode, and the transparent substrate, and becomes linearly polarized light again on the retardation film. And since this linearly polarized light is orthogonal to the polarization direction of a polarizing plate, it cannot permeate | transmit a polarizing plate. As a result, the mirror surface of the metal electrode can be completely shielded.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "mass part" or "mass%" is represented. Further, the degree of substitution and the number of substituents shown below all represent average values.

[Example 1]
<< Synthesis of cellulose derivatives >>
<Synthesis of Cellulose Derivative a-1>
100 g of cellulose acetate (acetyl substitution degree 2.40, weight average molecular weight 165000) was dissolved in 2 L of pyridine, 1.0 g of dimethylaminopyridine and 30 g of benzoyl chloride were added thereto, and the mixture was heated and stirred at 80 ° C. for 8 hours. The reaction solution was allowed to cool, methanol was added, and the mixture was stirred at 80 ° C. for 1 hr. Thereafter, the reaction solution was dropped into a methanol / water (= 1: 1) mixed solution, and the precipitated solid was separated by filtration and washed with methanol. The obtained solid was dried at 60 ° C. for 8 hours to obtain 98 g of an intermediate.

  Next, deacylation reaction was performed. The obtained intermediate was dissolved in 2 L of dichloromethane, and 50 g of potassium carbonate was added thereto, followed by stirring at room temperature for 8 hours. Thereafter, the reaction solution was added dropwise to water, and the solid was filtered off and washed with water and methanol. After drying at 60 ° C. for 8 hours, as shown in Table 4, 86 g of cellulose derivative a-1 having a total degree of substitution of 1.55, a benzoyl group substitution degree at the 2- and 3-positions of 0.06 was obtained.

In addition, the substitution degree by each substituent of the glucose skeleton is determined using ¹ H-NMR or ¹³ C— by using the methods described in Cellulose Communication 6, 73-79 (1999) and Chality 12 (9), 670-674. Determined by NMR.

<Synthesis of a-2 to a-18, b-1 to b-3, b-5>
Cellulose derivatives a-2 to a-18, b-1 to b-3 and b-5 are raw materials (cellulose esters), aromatic group reagents, reagent amounts and deacylation in the synthesis of cellulose derivative a-1. Was synthesized in the same manner as the cellulose derivative a-1 except that the conditions described in Table 2 were changed. The respective substituents and the degree of substitution are shown in Table 4.

<Synthesis of Cellulose Derivative a-19>
100 g of cellulose acetate (acetyl substitution degree 2.40, weight average molecular weight 165000) was dissolved in 2 L of pyridine, 23 g of phenyl isocyanate was added thereto, and the mixture was stirred at 80 ° C. for 5 hours. The reaction solution was allowed to cool, methanol was added, and the mixture was stirred at 80 ° C. for 1 hr. Thereafter, the reaction solution was dropped into a methanol / water (= 1: 1) mixed solution, and the precipitated solid was separated by filtration and washed with methanol. The obtained solid was dried at 60 ° C. for 8 hours to obtain 99 g of an intermediate.

  Next, deacylation reaction was performed. The obtained intermediate was dissolved in 2 L of dichloromethane, and 50 g of potassium carbonate was added thereto, followed by stirring at room temperature for 8 hours. Thereafter, the reaction solution was added dropwise to water, and the solid was filtered off and washed with water and methanol. It was dried at 60 ° C. for 8 hours to obtain 85 g of cellulose derivative a-19 having a total substitution degree of 1.55, substitution degree of N-phenylcarbamoyl group at the 2-position and 3-position of 0.06.

<Synthesis of Cellulose Derivatives a-20 to a-24, b-4>
Cellulose derivatives a-20 to a-24, b-4 were prepared in the same manner as in cellulose derivative a-19 except that the reagent amount of the aromatic group and the reaction time for deacylation were changed as shown in Table 3. Synthesized. The respective substituents and the degree of substitution are shown in Table 4.

  As the cellulose derivative h-1, cellulose acetate having an acetyl group substitution degree of 2.10 and a weight average molecular weight of 158000 was used.

<< Production of retardation film >>
[Preparation of retardation film 1]
(Preparation of fine particle dispersion)
Fine particles (Aerosil R812 manufactured by Nippon Aerosil Co., Ltd.) 11 parts by weight Ethanol 89 parts by weight The above was stirred and mixed with a dissolver for 50 minutes, and then dispersed using a Manton Gorin disperser to prepare a fine particle dispersion.

(Preparation of fine particle additive solution 1)
50 parts by mass of dimethyl chloride was placed in the dissolution tank, and 50 parts by mass of the fine particle dispersion prepared above was slowly added while sufficiently stirring the dimethyl chloride. Further, the particles were dispersed by an attritor so that the secondary particles had a predetermined particle size. This was filtered through Finemet NF manufactured by Nippon Seisen Co., Ltd. to prepare a fine particle additive solution 1.

(Preparation of dope)
First, the following dimethyl chloride and ethanol were added to the pressure dissolution tank. The synthesized cellulose derivative a-1 was charged into a pressure dissolution tank containing an organic solvent while stirring. This was completely dissolved with heating and stirring. Subsequently, after adding the fine particle addition liquid 1, Azumi filter paper No. 1 manufactured by Azumi Filter Paper Co., Ltd. was used. The dope was prepared by filtration using 244.

<Dope composition>
Dimethyl chloride 340 parts by mass Ethanol 64 parts by mass Cellulose derivative h-1 100 parts by mass Fine particle additive liquid 1 2 parts by mass (Film formation)
The prepared dope was cast on a stainless belt support, and then the film was peeled from the stainless belt support.

  The peeled raw film was uniaxially stretched only in the width direction (TD direction) using a tenter while heating, and the conveyance tension was adjusted so as not to shrink in the conveyance direction (MD direction).

  Next, drying was terminated while the drying zone was conveyed through many rollers, and a roll-shaped raw film was produced.

(Stretching process)
This raw film is stretched at a stretch ratio of 2.5 times in the oblique direction so that the slow axis of the film is 45 ° with respect to the transport direction, using the oblique stretching apparatus having the configuration shown in FIG. Thus, a roll-like retardation film 1 was produced. The stretching temperature was as low as possible as long as the film was not broken.

[Production of retardation films 2 to 30]
In the production of the retardation film 1, retardation films 2 to 30 were produced in the same manner except that the type of cellulose derivative was changed to the cellulose derivatives shown in Table 4, respectively.

<< Evaluation of retardation film >>
The following evaluation was performed about the produced retardation film.

[Measurement of phase difference Ro and wavelength dispersion]
About the produced retardation film, the phase difference Ro in the in-plane direction was measured according to the following method. The phase difference Ro in the in-plane direction is expressed by the following formula (i).

Formula (i) Ro (λ) = (n x (λ) -n y (λ)) × d
In the above formula (i), lambda represents an optical wavelength (nm) used in the _measurement, n x, _{n y} is measured under the environment of each _{23 ℃ · 55% RH, n} x is in the plane of the film represents the maximum refractive index (refractive index in a slow axis direction), n _y represents a refractive index in a direction perpendicular to the slow axis in the film plane, d represents the thickness of the film (nm).

  Specifically, by using an Axoscan manufactured by Axometrics and measuring the birefringence at wavelengths of 450 nm and 550 nm in an environment of 23 ° C. and 55% RH, Ro (450) and Ro (550), A value Ro (550) / Ro (450) of a ratio of Ro (450) and Ro (550) was obtained as wavelength dispersion.

  The results are shown in Table 4.

  From Table 4, it can be seen that the retardation film 1 in which the cellulose derivative is not substituted with an aromatic group does not have good wavelength dispersion. Further, the retardation film 30 is substituted with an aromatic group, but is not substituted at the 2nd and 3rd positions, and is substituted only at the 6th position, and the wavelength dispersion is not good. This is presumably because the orientation of the 6-position aromatic substituent is not sufficient. On the other hand, the retardation film of the present invention in which the aromatic group is substituted at the 2-position and 3-position is excellent in wavelength dispersion, and the ratio value of Ro (450) / Ro (550) is λ / 4 position. It turns out that it exists in the range of 0.80-0.90 preferable as a phase difference film.

  Although the retardation films 5, 12, 19 and 26 of the comparative examples are excellent in reverse wavelength dispersion, it is understood that the film thickness must be increased in order to increase the retardation value Ro. For example, in the retardation film 5, the total substitution degree is high and the retardation development is not sufficient. Since the phase difference of light having a wavelength of 550 nm is 136 nm with a film thickness of 84 μm, if this is set to a film thickness of 80 μm, the phase difference is proportional to the film thickness from the formula (i), so that it becomes 130 nm, and a λ / 4 retardation film As a result, a value within the range of the required retardation value of 135 to 145 nm cannot be obtained. It can be seen that in a region where the total degree of substitution exceeds 2.40, a film cannot be designed at 80 μm or less.

Example 2
<Production of circularly polarizing plate>
A 120 μm-thick polyvinyl alcohol film was uniaxially stretched (temperature: 110 ° C., stretch ratio: 5 times). This was immersed in an aqueous solution composed of 0.075 g of iodine, 5 g of potassium iodide and 100 g of water for 60 seconds, and then immersed in an aqueous solution of 68 ° C. composed of 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.

  Bonding was performed using an adhesive so that the slow axis of each retardation film produced in Example 1 and the absorption axis of the polarizer were 45 °, and a protective film (Konica Minolta) was attached to the back side of the polarizer. Tack KC4UY, thickness 40 μm, manufactured by Konica Minolta Co., Ltd.) were bonded together with water paste to produce circularly polarizing plates 1 to 30.

<< Production of organic EL cell >>
According to the method described in the example of JP 2010-20925 A using a 3 mm-thick 50 inch (127 cm) non-alkali glass, it was described in FIG. 8 of JP 2010-20925 A An organic EL cell having a configuration was produced.

<< Production of organic EL image display apparatus >>
After apply | coating an adhesive agent on the surface of the retardation film of each produced said circularly-polarizing plate, the organic EL image display apparatuses 1-30 were produced by bonding on the visual recognition side of an organic EL cell.

<< Evaluation of organic EL image display device >>
About each produced organic EL image display apparatus, as a result of evaluating basic display characteristics such as black color characteristics and reflectivity (visibility) according to a conventional method, organic EL using the retardation film of the present invention It was confirmed that the image display device can obtain good characteristics.

DESCRIPTION OF SYMBOLS 1 Polarizer 2 x component 3 y component 4 Stretching direction 5 Synthesized vector 6 Helix 7 Absorbance of cellulose ester substituted with benzoyl group 8 Absorbance of cellulose ester substituted with acetyl group 9 Refractive index in x-axis direction 10 y Refractive index in the axial direction 13 Conveying direction 14 Slow axis S Difference in refractive index between the x-axis direction and the y-axis direction D1 Feeding direction D2 Winding direction F Optical film R Phase difference film θi Bending angle (feeding angle)
Ci, Co Holding tool Ri, Ro Rail Wo Width of film before stretching W Width of film after stretching 16 Film feeding device 17 Transport direction changing device 18 Winding device 19 Film forming device A Organic EL image display device B Organic EL element C Circularly polarizing plate 101 Transparent substrate 102 Metal electrode 103 TFT
DESCRIPTION OF SYMBOLS 104 Organic light emitting layer 105 Transparent electrode 106 Insulating layer 107 Sealing layer 108 Film 109 (lambda) / 4 phase difference film 110 Polarizer 111 Protective film 112 Hardened layer 113 Antireflection layer

Claims (8)

A retardation film containing a cellulose derivative, wherein the 2-position and 3-position of the glucose skeleton constituting the cellulose derivative are substituted with a substituent having an aromatic group represented by the following general formula (1) The retardation film is controlled so as to satisfy the following formulas (1) to (6).
(1): 1.50 ≦ DSa ≦ 2.40
(2): 110 nm ≦ Ro (450) ≦ 125 nm
(3): 135 nm ≦ Ro (550) ≦ 145 nm
(4): 0.80 ≦ Ro (450) / Ro (550) ≦ 0.90
(5): d ≦ 80 (μm)
(6): 0.06 ≦ DSb
(In the formula, DSa represents the total substitution degree of the cellulose derivative. Ro (450) and Ro (550) are in-plane directions measured at a light wavelength of 450 nm and 550 nm, respectively, in an environment of 23 ° C. and 55% RH. D represents the thickness (μm) of the retardation film, and DSb represents the sum of the substitution degrees of the substituents having aromatic groups substituted at the 2-position and 3-position. )
General formula (1)
* -LR ₁
(In the formula, R ₁ represents an aromatic group. L represents C (═O), C (═O) O or C (═O) NR _2. R ₂ represents a hydrogen atom, an alkyl group or an aromatic group. The two R ₁ groups at the 2-position and 3-position may be the same or different, and * represents the oxygen atom of the 2-position and 3-position hydroxy groups of the glucose skeleton, respectively.   The retardation film according to claim 1, wherein the substituent having an aromatic group represented by the general formula (1) is a benzoyl group.   The retardation film according to claim 1, wherein a substituent other than the substituent having the aromatic group of the cellulose derivative is an aliphatic acyl group.   The retardation film according to claim 3, wherein the aliphatic acyl group is an acetyl group.   The thickness of a retardation film exists in the range of 40-60 micrometers, The retardation film as described in any one of Claim 1- Claim 4 characterized by the above-mentioned.   The retardation film according to any one of claims 1 to 5, wherein the retardation film is stretched at an angle within a range of 40 to 50 ° with respect to a conveyance direction. the film.   A circularly polarizing plate comprising the retardation film according to any one of claims 1 to 6.   An organic electroluminescence image display device comprising the circularly polarizing plate according to claim 7.

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