KR101684811B1 - Cellulose ester film having an improved barrier property at high temperature/humidity condition and method for preparing the same - Google Patents

Abstract

여기서, R은 치환기로서 총 8 개의 치환기 중 벤조산(Benzoic acid)로 7 개 내지 8 개로 치환되고, 치환되지 않은 R은 OH기로 남아 있다.The present invention relates to a retardation film for a VA (Vertical Alignment) having high reliability and a low molecular weight asymmetric ester system comprising an aromatic group represented by the following formula (1) capable of improving the high temperature and high humidity reliability of a cellulose ester phase difference film capable of producing a polarizing plate , A low molecular weight symmetrical ester compound containing an aromatic group represented by the general formula (2), and a plasticizer containing a saccharide compound represented by the general formula (3), and a process for producing the cellulose ester film.
[Chemical Formula 1]
T + [D] n
(2)
T + [D] n + T
Wherein T is a toluic acid residue or a benzene carboxylic acid residue, D is a propyleneglycol having 2 to 8 carbon atoms, neopentylglycol, diethyleneglycol, dipropylene glycol (Dipropyleneglycol), triethyleneglycol, an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms, and n is an integer of 1 or more .
(3)

Here, R is substituted with 7 to 8 benzoic acids among the total of 8 substituents as substituents, and the unsubstituted R remains as an OH group.

Description

[0001] The present invention relates to a cellulose ester film having excellent reliability at high temperature and high humidity, and a process for producing the cellulose ester film,

The present invention relates to a cellulose ester film excellent in reliability at high temperature and high humidity, and a method for producing the same. More particularly, the present invention relates to a cellulose ester film capable of improving reliability in a high temperature and high humidity of a retardation film for VA (Vertical Alignment) and a cellulose ester phase difference film capable of producing a polarizer, and a method for producing the same.

Recently, a liquid crystal display (LCD) has been used in various fields, so that it is desired to have high visibility when viewing an image. In particular, a polarizing plate or a retardation plate used in an LCD is required to have high flatness such as glass, . Also, in an LCD used in outdoor such as a car navigation system or a PDA, it is necessary to incorporate an ultraviolet absorber into a polarizing plate protective film in order to prevent deterioration of the polarizer.

In particular, a film used for the outermost surface due to the spread of a large-area television or a large-area monitor is required to have a high planarity and a high image quality, and defects such as spot defects become image defects, leading to deterioration of LCD quality. In addition, although cellulose triacetate (TAC) films are mainly used as protective films for polarizers currently used in LCDs, there is a problem that films used in LCDs tend to stick to each other due to their transparency and smoothness. Therefore, in order to improve the handling properties during film formation of these resin films and the surface treatment of these resin films, fine particles are added to the film to provide lubricity without impairing the transparency of the film, thereby improving handleability and stabilizing the winding property .

The cellulose ester film is usually produced by a solution casting film-forming method. Namely, a film is produced by softening a dope (thickened solution) of a cellulose ester from a flexible die on an endless support, releasing the self-supporting property of the dope, and peeling off the endless support. This film often contains additives such as fine particles, a plasticizer, and an ultraviolet absorber in addition to the cellulose ester. The fine particles are used for ease of lubrication and adhesion resistance of the film thus formed, and the ultraviolet absorber is used, for example, to prevent deterioration of the polarizing plate when used in a polarizing plate. These components are usually mixed together when preparing the dope.

However, the cellulose ester type polarizing plate produced by the conventional retardation film has a low resistance to high temperature and high humidity environments, and when exposed to a reliable environment at high temperature and high humidity, the barrier property of the retardation film is deteriorated and the polarizing plate and LCD There is a problem in that it is lowered.

DISCLOSURE Technical Problem Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a cellulose ester film capable of improving the reliability in high temperature and high humidity of a cellulose ester phase difference film capable of producing a VA retardation film and a polarizer, The purpose is to provide.

The cellulose ester film excellent in reliability at high temperature and high humidity according to the first embodiment of the present invention is a cellulose ester film having an acyl group total substitution degree of 2.10 to 2.70 and a film thickness of 20 to 60 占 퐉, An asymmetric ester compound having an aromatic group represented by the following formula (1), a symmetrical ester compound having an aromatic group represented by the following formula (2) And a saccharide compound represented by the general formula (3), and further, after allowing to stand for 500 hours in a high-temperature and high-humidity chamber at 60 ° C and 90% RH in a reliable environment, the amount of change in Moisture Vapor Permeability 50% or less, and the haze is 0.2 or less.

[Chemical Formula 1]

T + [D] n

(2)

T + [D] n + T

Wherein T represents a benzene carboxylic acid residue, D represents an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms, and n is an integer of 1 or more .

(3)

Here, R is substituted with 7 to 8 benzoic acids among the total of 8 substituents as substituents, and the unsubstituted R remains as the H group.

 [Equation 1]

Ro = (nx-ny) xd

Rth = {(nx + ny) / 2-nz} xd

Ny is the maximum refractive index in the vertical direction in the film plane and nz is the maximum refractive index in the thickness direction of the film and is 23 DEG C and 55% RH, respectively, where d is the film thickness (nm), nx is the maximum refractive index in the horizontal direction in the film plane, Under the environment of 550 nm.

&Quot; (2) "

? MVP = {MVP_reliability after -MVP_reliability transition} / (MVP_reliability x100 (%)) <50%

Here, Moisture Vapor Permeability (MVP) was allowed to stand for 24 hours under a 40 ° C and 90% RH environment of a high temperature and high humidity chamber using a humudity cup (model name: KP-M6680, application standard: KS A1013, KS M6886) Is the amount of water that passes (permeates) through the cellulose ester film. MVP value before and after MVP_reliability and after 60 hours and 90% RH of reliability after MVP_reliability for 500 hours, respectively, and MVP value measured according to the above-described moisture permeability evaluation conditions for the cellulose ester film.

The cellulose ester film according to the present invention has the effect of improving the reliability in high temperature and high humidity of the VA retardation film having high reliability and the cellulose ester phase difference film capable of producing the polarizing plate.

1 is a schematic view of an apparatus for producing a general cellulose ester film.
2 is an exploded perspective view of polarizer lamination.
3 is a perspective view of a conventional breathable cup.

The cellulose ester film excellent in reliability at high temperature and high humidity according to the first embodiment of the present invention is a cellulose ester film having an acyl group total substitution degree of 2.10 to 2.70 and a film thickness of 20 to 60 占 퐉, An asymmetric ester compound having an aromatic group represented by the following formula (1), a symmetrical ester compound having an aromatic group represented by the following formula (2) And a saccharide compound represented by the general formula (3), and further, after allowing to stand for 500 hours in a high-temperature and high-humidity chamber at 60 ° C and 90% RH in a reliable environment, the amount of change in Moisture Vapor Permeability Within 50%, and a haze of 0.2 or less.

[Chemical Formula 1]

T + [D] n

(2)

T + [D] n + T

Wherein T represents a benzene carboxylic acid residue, D represents an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms, and n is an integer of 1 or more .

(3)

Here, R is substituted with 7 to 8 benzoic acids among the total of 8 substituents as substituents, and the unsubstituted R remains as the H group.

[Equation 1]

Ro = (nx-ny) xd

Rth = {(nx + ny) / 2-nz} xd

Ny is the maximum refractive index in the vertical direction in the film plane and nz is the maximum refractive index in the thickness direction of the film and is 23 DEG C and 55% RH, respectively, where d is the film thickness (nm), nx is the maximum refractive index in the horizontal direction in the film plane, Under the environment of 550 nm.

&Quot; (2) &quot;

? MVP = {MVP_reliability after -MVP_reliability transition} / (MVP_reliability x100 (%)) <50%

Here, Moisture Vapor Permeability (MVP) is the amount of water that passes through (passes through) the cellulose ester film after being left in a high temperature and high humidity chamber at 40 ° C and 90% RH environment for 24 hours using a humidity cup. MVP value before and after MVP_reliability and after 60 hours and 90% RH of reliability after MVP_reliability for 500 hours, respectively, and MVP value measured according to the above-described moisture permeability evaluation conditions for the cellulose ester film.

The method for producing a cellulose ester film having excellent reliability at high temperature and high humidity according to the second embodiment of the present invention is characterized in that 10 to 30 parts by weight of a cellulose ester having an acyl group total substitution degree of 2.1 to 2.7, 2 to 8 parts by weight of a plasticizer containing an asymmetric ester compound, a symmetrical ester compound having an aromatic group represented by the formula (2) and a saccharide compound represented by the formula (3), and a mixture of methylene chloride and methanol at a ratio of 9: a mixed solvent mixture of 70 to 80 parts by weight, and a mixture of a metal oxide of silica (SiO ₂₎ 1 to 3 parts by weight to prepare a cellulose solution as a main dope solution;

Forming a flexible film by uniformly softening the cellulose solution on a support and drying under an environment of 150 to 200 캜;

 Peeling the flexible film from the support and stretching in the width direction; And

And drying the stretched flexible film under an environment of 100 to 150 캜 in a drying section to produce a film having a thickness of about 20 to 60 탆.

The cellulose esters can be used alone or in combination of cellulose esters synthesized from cellulose ester synthesized from linter pulp, wood pulp and kenaf pulp, and other raw materials.

According to the present invention, the cellulose ester film may contain a specific plasticizer, and the asymmetric ester-based compound represented by the formula (1), the symmetrical ester-based compound represented by the formula (2) Is particularly preferable for setting the barrier properties of the cellulose ester film before and after the reliability treatment in a high temperature and high humidity to a predetermined range.

The specific compounds of the symmetrical ester compounds including aromatic groups represented by formulas (4) to (8) and aromatic compounds containing aromatic group represented by formulas (9) to (13) according to the present invention are as follows, but the present invention is not limited thereto .

[Chemical Formula 4]

Mw = 194.2

[Chemical Formula 5]

Mw = 222.3

[Chemical Formula 6]

Mw = 224.3

(7)

Mw = 252.4

[Chemical Formula 8]

Mw = 268.3

[Chemical Formula 9]

Mw = 312.3

[Chemical formula 10]

Mw = 340.4

(11)

Mw = 342.4

[Chemical Formula 12]

Mw = 370.5

[Chemical Formula 13]

Mw = 386.5

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a film production apparatus which can be used for producing a cellulose ester film having an acetyl group, a propionyl group and a butyl group according to the present invention.

According to the second embodiment of the present invention, the main dope solution is extruded onto the surface of the belt 20 through the die 10 and applied in the form of a sheet. After evaporating the solvent present in the dope solution, And the stretching in the longitudinal direction MD and the transverse direction TD is performed in the tenter 40 (the first drying section), the residual solvent is evaporated in the second drying section 50, 60). &Lt; / RTI &gt;

The die 10 may be a conventional T-die 20 and the belt 20 is a high temperature band support that dries and forms a film by transferring the dope liquid, for example, a stainless steel conveyor belt is preferred Do. The thickness (for example, the final thickness after stretching and drying) of such a cellulose ester film can be appropriately adjusted as necessary, but according to the present invention, it is preferable that the thickness is in the range of 20 to 60 탆.

Hereinafter, the present invention will be described in more detail with reference to examples, but the following examples are for illustrative purposes only and the present invention is not limited thereto.

Example 1

(1) Preparation of cellulose solution (main doping solution)

17.95% by weight of a cellulose ester A having an acetyl group of 2.1, a butyryl group of 0.2 and a total substitution degree of an acyl group of 2.3 (see Tables 1 and 2), a plasticizer A (terminal asymmetric low molecular weight plasticizer 1), a plasticizer B low molecular weight plasticizer) and plasticizer C (saccharide plasticizer) (see tables 1 and 3) 2% by weight, as a solvent mixture of methylene chloride 72% by weight, methanol 8% by weight, and silica as the metal oxide (SiO ₂₎ 0.05% by weight And mixed to prepare a dilute cellulose solution as the main dope solution.

(2) Production of film of cellulose

100 parts by weight of the main dope liquid A and 5 parts by weight of the fine particle addition liquid were mixed sufficiently (main dope liquid A) with an inline mixer and then uniformly plied to a stainless steel band support having a width of 2000 mm . The solvent was evaporated on the stainless steel band support and peeled off from the stainless band support. Then, both ends of the web were held with a tenter and stretched so that the stretching magnification in the TD direction was 1.3 times in a temperature environment of 170 占 폚. After the stretching, the stretching was maintained for a few seconds, the tensile force in the width direction was relaxed, the stretching in the width direction was carried out, the stretching was continued for 35 minutes in the drying section set at 110 DEG C, A cellulose ester film (CF-1) (see Table 4) having a thickness of 40 占 퐉 and a knurling width of 10 mm and a height of 8 占 퐉 was prepared at the end.

(3) Measurement of physical properties of cellulose ester film

The cellulose ester film thus obtained was a retardation film having an in-plane retardation value Ro of 40 to 60 nm and a retardation value Rth in the thickness direction of 110 to 140 nm according to the following measurement.

Ro = (nx-ny) xd

Rth = ((nx + ny) / 2-nz) xd

Nx and ny represent refractive indices in the in-plane direction of the film, nz represent refractive indices in the thickness direction of the film, nx &gt; = ny, , And d represents the thickness (nm) of the film.

The retardation values Ro and Rth were measured at 550 nm under an environment of 23 ° C and 55% RH using an AxoScan (OPMF-1, Axometrics) optical measuring instrument. The cellulose ester film prepared above was subjected to reliability treatment for 500 hours at 60 ° C and 90% RH using a high temperature and high humidity chamber, and the moisture permeability of the cellulose ester film was measured using a moisture permeation cup (FIG. 3). The results are shown in Table 4.

The haze of the film was measured using a haze meter.

(4) Production of polarizer using PVA film

The polyvinyl alcohol film having a thickness of 120 占 퐉 was uniaxially stretched (temperature: 110 占 폚, stretching magnification: 5 times). This was immersed in an aqueous solution containing 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 at 68 DEG C containing 6 g of potassium iodide, 7.5 g of boric acid and 100 g of water. This was washed with water and dried to obtain a polarizer (PF-1).

Then, the polarizer, the cellulose ester film (polarizing plate protective film B: CF-1) and the TAC film (thickness 40um: TF-1) as the polarizing plate protective film A were laminated on the back side in accordance with the following steps 1 to 5, A polarizer (POL-1) was prepared by bonding a polarizer and a cellulose ester film as a polarizing plate protective film B according to the following steps.

Step 1: Immersed in a 2 mol / L sodium hydroxide solution at 60 占 폚 for 90 seconds, washed with water and then dried to obtain a polarizing film which was a saponified cellulose ester film on the side bonded to the polarizer.

Step 2: The polarizing membrane was immersed in a polyvinyl alcohol adhesive tank (tank) having a solid content of 2 mass% for 1 to 3 seconds.

Step 3: In step 2, excess glue adhered to the polarizing film was lightly wiped off, and placed on a cellulose ester film treated in step 1.

Step 4: The cellulose ester film laminated in Step 3, the polarizer, and the back side cellulose ester film were bonded at a pressure of 20 to 30 N / cm ² and a conveying speed of about 2 m / min.

Step 5: A sample obtained by bonding the polarizer prepared in Step 4 to the cellulose ester film and the back side cellulose ester film in a dryer at 80 占 폚 was dried for 2 minutes to prepare a polarizing plate (POL-1).

In the accompanying drawings, FIG. 2 illustrates a polarizing plate lamination with reference to an exploded perspective view, wherein reference numeral 100 denotes a transparent glass substrate of 0.5 mm, reference numeral 110 denotes a lower polarizer plate, and reference numeral 120 denotes an upper polarizer plate. Reference numerals 111 and 123 denote a polarizing plate protective film A (TAC film), 112 and 122 denote polarizers (PVA films), and reference numerals 113 and 121 denote a polarizing plate protective film B (cellulose ester phase difference film). In Fig. 2, the arrows indicated by a indicate the absorption axis of the polarizer, and the arrows indicated by b indicate the optical axis of the cellulose ester phase difference film.

(5) Reliability measurement and result of polarizer

The pressure-sensitive adhesive was coated on the surface of the polarizing plate protective film with respect to the prepared polarizing plate, and laminated so that the transmission axis of the polarizing plate was orthogonal to both surfaces of the glass substrate having a thickness of 0.5 mm (FIG. 2). The sample (SPL-1) prepared as shown in the following Table 6 was subjected to reliability at 60 ° C and 90% RH using a high temperature and high humidity chamber, and light leakage and optical staining were observed on the backlight. As shown in Table 6, when the cellulose ester film contains the plasticizer as proposed in the present invention and falls within the range of the degree of substitution of the cellulose ester film, the barrier properties of the cellulose ester film before and after the reliability treatment are superior to those of the comparative example, Light leakage and optical stain characteristics are excellent.

Examples 2 to 5

The main dope liquids (B to E) were prepared in the same manner as in Example 1, except that the cellulose ester and the plasticizer as shown in the following Tables 1 to 3 were used, and then the cellulose ester film (CF-40-2 to CF -40-5) was prepared and its physical properties were measured in the same manner as in Example 1 above. The results are shown in Table 4.

Example Dope Cellulose ester Plasticizer Example 1 A A * A + B + C ** Example 2 B B * A + B + C ** Example 3 C C * A + B + C ** Example 4 D D * A + B + C ** Example 5 E E * A + B + C ** Comparative Example 1 F A * D + C ** Comparative Example 2 G E * D + C ** Comparative Example 3 H A * E + C ** Comparative Example 4 I E * E + C **

* See Table 2, ** See Table 3

Cellulose ester Acetyl group Propionyl group Butyryl group Total degree of substitution A 2.1 0 0.2 2.3 B 2.1 0 0.5 2.6 C 1.7 0 0.5 2.2 D 1.7 0 0.8 2.5 E 1.8 0.5 0 2.3

Plasticizer Type Compound structure A
(Terminal asymmetric plasticizer 1)

B
(Cyclic symmetrical plasticizer 1)

C (sugar plasticizer)

D (terminal symmetric plasticizer 1)

E (terminal symmetric plasticizer 2)

Polarizers POL-2 to POL-5 were prepared in the same manner as in Example 1 using the PVA film in the same manner as in Table 5 below, and samples (SPL-2 to SPL-5 ) Were measured. The results are shown in Table 6 below.

Sample No. Polarizer and Glass Lamination Light and optical stains Remarks Upper polarizer Glass substrate Lower polarizer After reliability Results SPL-1 CF-40-1 Substrate (10) CF-40-1

Light and optical stains
Good Invention SPL-2 CF-40-2 In the substrate 11, CF-40-2

Light and optical stains
Good Invention SPL-3 CF-40-3 Substrate (12) CF-40-3

Light and optical stains
Good Invention SPL-4 CF-40-4 Substrate (13) CF-40-4

Light and optical stains
Good Invention SPL-5 CF-40-5 Substrate (14) CF-40-5

Light and optical stains
Good Invention SPL-6 CF-40-6 The substrate 15, CF-40-6

Light gauge intense. Comparative Example SPL-7 CF-40-7 Substrate (16) CF-40-7

Light gauge intense. Comparative Example SPL-8 CF-40-8 Substrate (17) CF-40-8

Luminous intense
Optical unevenness Comparative Example SPL-9 CF-40-9 Substrate (18) CF-40-9

Lights very severe Comparative Example

Comparative Examples 1 to 4

After preparing the main dope (F to I) in the same manner as in Example 1 except that the cellulose ester and the plasticizer as shown in Tables 1 to 3 were used, the cellulose ester film (CF-40-6 to CF -40-9) was prepared and its physical properties were measured in the same manner as in Example 1 above. The results are shown in Table 4 above.

Polarizers POL-6 to POL-9 were produced in the same manner as in Table 5 using a PVA film in the same manner as in Example 1, and the samples (SPL-6 to SPL-9 ) Were measured. The results are shown in Table 6 above.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention as defined in the appended claims. There will be.

10: Die
20: Belt
30: peeling roll
40: Tender (first drying section)
50: Second drying section
60: Winder
100: transparent glass substrate
110: lower polarizer plate
120: upper polarizer
111, 123: protective film A
112, 122: Polarizer
113,121: Protective film B

Claims (14)

An asymmetric ester compound having an aromatic group represented by the following general formula (1), a symmetrical ester group compound having an aromatic group represented by the general formula (2) A cellulose ester film excellent in reliability at high temperature and high humidity, which comprises a compound and a saccharide compound represented by Formula (3).
[Chemical Formula 1]
T + [D] n
(2)
T + [D] n + T
Wherein T represents a benzene carboxylic acid residue, D represents an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms, and n is 1 Lt; / RTI &gt;
(3)

Here, R is substituted with 7 to 8 benzoic acids among the total of 8 substituents as substituents, and the unsubstituted R remains as the H group. The film according to claim 1, wherein the film has an in-plane retardation Ro of 20 to 100 nm and a thickness direction retardation Rth of 100 to 300 nm, which is defined by the following formula (1): cellulose ester film.
[Equation 1]
Ro = (nx-ny) xd
Rth = {(nx + ny) / 2-nz} xd
Ny is the maximum refractive index in the vertical direction in the film plane and nz is the maximum refractive index in the thickness direction of the film and is 23 DEG C and 55% RH, respectively, where d is the film thickness (nm), nx is the maximum refractive index in the horizontal direction in the film plane, Under the environment of 550 nm. The cellulose ester film according to claim 1, wherein the film has a variation in water vapor permeability expressed by the following formula (2) within a range of 50% or less.
&Quot; (2) &quot;
? MVP = (MVP_reliability-MVP_reliability) / (MVP_reliability x100 (%)) <50%
Here, Moisture Vapor Permeability (MVP) is the amount of water that passes through (passes through) the cellulose ester film after being left in a high temperature and high humidity chamber at 40 ° C and 90% RH environment for 24 hours using a humidity cup. MVP value before and after MVP_reliability and after 60 hours and 90% RH of reliability after MVP_reliability for 500 hours, respectively, and MVP value measured according to the above-described moisture permeability evaluation conditions for the cellulose ester film. The cellulose ester film according to claim 1, wherein the film has a haze of 0.2 or less. A cellulose ester having a total degree of substitution of 2.1 to 2.7, an asymmetric ester compound having an aromatic group represented by the following formula (1), a symmetrical ester compound having an aromatic group represented by the formula (2) and a sugar compound represented by the formula preparing a cellulose solution as a main dope solution was mixed with silica (SiO ₂₎ as the mixed solvent, and a mixed metal oxide ratio of 1% by weight;: plasticizers, methylene chloride and methanol 9 comprising
Forming a flexible film by uniformly softening the cellulose solution on a support and drying under an environment of 150 to 200 캜;
Peeling the flexible film from the support and stretching in the width direction; And
And drying the stretched flexible film in an environment of 100 to 150 ° C. in a drying section. The method for producing a cellulose ester film according to claim 1,
[Chemical Formula 1]
T + [D] n
(2)
T + [D] n + T
Wherein T represents a benzene carboxylic acid residue, D represents an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms, and n is an integer of 1 or more .
(3)

Here, R is substituted with 7 to 8 benzoic acids among the total of 8 substituents as substituents, and the unsubstituted R remains as the H group. 6. The method for producing a cellulose ester film according to claim 5, wherein the film is manufactured to have a film thickness of 20 to 60 mu m. The film according to claim 5, wherein the in-plane retardation Ro of the film is in the range of 20 to 100 nm and the thickness direction retardation Rth is in the range of 100 to 300 nm, A method for producing a superior cellulose ester film.
[Equation 1]
Ro = (nx-ny) xd
Rth = {(nx + ny) / 2-nz} xd
Ny is the maximum refractive index in the vertical direction in the film plane and nz is the maximum refractive index in the thickness direction of the film and is 23 DEG C and 55% RH, respectively, where d is the film thickness (nm), nx is the maximum refractive index in the horizontal direction in the film plane, Under the environment of 550 nm. 6. The method for producing a cellulose ester film according to claim 5, wherein the film has a variation in water vapor permeability expressed by the following formula (2) within a range of 50% or less.
&Quot; (2) &quot;
? MVP = (MVP_reliability-MVP_reliability) / (MVP_reliability x100 (%)) <50%
Here, Moisture Vapor Permeability (MVP) is the amount of water that passes through (passes through) the cellulose ester film after being left in a high temperature and high humidity chamber at 40 ° C and 90% RH environment for 24 hours using a humidity cup. MVP value before and after MVP_reliability and after 60 hours and 90% RH of reliability after MVP_reliability for 500 hours, respectively, and MVP value measured according to the above-described moisture permeability evaluation conditions for the cellulose ester film. The plasticizer according to claim 5, wherein the plasticizer is selected from symmetrical ester compounds (4) to (8) containing aromatic groups and symmetrical ester compounds (9) Wherein the cellulose ester film has a thickness of 100 nm or less.
[Chemical Formula 4]

[Chemical Formula 5]

[Chemical Formula 6]

(7)

[Chemical Formula 8]

[Chemical Formula 9]

[Chemical formula 10]

(11)

[Chemical Formula 12]

[Chemical Formula 13]

[Claim 5] The method according to claim 5, wherein the cellulose ester comprises 10 to 30 parts by weight of an asymmetric ester compound having an aromatic group represented by the formula (1), a symmetrical ester compound having an aromatic group represented by the formula (2) a plasticizer comprising a saccharide compound represented from 2 to 8 parts by weight, 70 to 80 parts by weight of a mixed solvent of methylene chloride and methanol, and silica as the metal oxide (SiO ₂₎ is a high temperature, comprising a step of mixing 1 to 3 parts by weight A method for producing a cellulose ester film excellent in reliability in high humidity.
The cellulose ester film according to claim 1, wherein the benzene carboxylic acid residue is a toluene acid residue. The method according to claim 1, wherein the alkylene glycol residue is selected from the group consisting of propylene glycol, neopentyl glycol, diethyleneglycol, dipropyleneglycol, and triethyleneglycol residues. Which is excellent in reliability at high temperature and high humidity. The method for producing a cellulose ester film according to claim 5, wherein the benzene carboxylic acid residue is a toluene acid residue. 6. The method of claim 5, wherein the alkylene glycol residue is selected from the group consisting of propylene glycol, neopentyl glycol, diethyleneglycol, dipropyleneglycol, and triethyleneglycol residues. By weight based on the total weight of the cellulose ester film.

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