WO2020105810A1 - Cellulose ester phase difference film - Google Patents

Abstract

The present invention relates to a cellulose ester film having +C plate optical properties and, more specifically, first, to a phase difference film fabricated by a solvent casting method using a dope comprising a cellulose ester and a specific additive. Also, the present invention relates to a multilayered cellulose ester phase difference film and, more specifically, to a phase difference film which has enhanced phase difference uniformity, and has high compatibility with triacetyl cellulose (TAC), thus enabling the manufacture of a high-quality polarizing plate. The phase difference film according to the present invention exhibits the effects of inhibiting quality deterioration caused when used along with triacetyl cellulose (TAC) and enhancing diagonal visibility when applied to OLEDs and LCD panels.

Description

Cellulose ester phase difference film

This application claims the benefit of priority based on 2018.11.19 Korean Patent Application No. 2018-0142553 and 2018.11.19 Korean Patent Application No. 2018-0142554, and all contents disclosed in the literature of the Korean patent application are in this specification. It is included as part of.

The present invention relates to a cellulose ester phase difference film having + C plate optical properties, and more specifically, a phase difference film and phase difference uniformity produced by solvent casting a dope containing a cellulose ester and a specific additive are improved, and triacetyl cellulose It relates to a retardation film capable of producing an excellent quality polarizing plate with high compatibility with (TAC).

In recent years, the display has been developed with a liquid crystal display device and an OLED center. Accordingly, the protective film of the polarizing plate has been increasingly in demand for thinner and higher performance furnaces. Since a liquid crystal display device displays a display by polarization control by liquid crystal, a polarizing plate is necessary, and a stretched PVA film containing iodine is usually used as the polarizing plate. Since this polarizing plate is vulnerable, a polarizing plate protective film is used as a thing to protect it. In general, a triacetyl cellulose film is widely used for the polarizing plate protective film. Apart from these polarizing plate protective films, a retardation film is also used to control the retardation of polarization. The retardation film used in such a liquid crystal display device is used in combination with a polarizing plate to solve problems such as color compensation and wide viewing angle, and the retardation film used in OLED devices has an anti-reflection function.

As described above, the polarizing plate protective film is most preferably in the case of considering the manufacturing process of the polarizing plate using a film made of cellulose acetate in order to protect the polarizing plate made of PVA containing moisture and to protect the polarizing plate. On the other hand, as a retardation film, materials other than cellulose acetate have been used to express optical performance. That is, conventionally, as a material for the retardation film, there are, for example, polycarbonate, polysulfone, polyethersulfone, amorphous polyolefin, and the like. These polymer films have a characteristic that the longer the wavelength, the smaller the retardation, and it is difficult to impart ideal retardation characteristics to all wavelengths in the visible region.

When converting linearly polarized light into circularly polarized light with respect to the wavelength of the visible light region or conversely converting circularly polarized light into linearly polarized light, in order to obtain the above effect with a single retardation film, the retardation in the wavelength (λ) incident on the retardation film is λ It is desirable to be. Such a retardation film, for example, using a retardation film having a phase difference of λ and only one polarizing plate, can implement an anti-reflection function in an OLED image display device. However, it is known that as the viewing angle increases, there is significant light leakage along the diagonal (causing poor contrast ratio) and various combinations of optical films can be used to correct or "compensate" this light leakage. In addition, it must have a specific birefringence (or phase difference) depending on the type of liquid crystal used. In particular, in order to improve diagonal visibility in OLED liquid crystals, a retardation film showing + C behavior is applied.

The compensation and optical films are typically quantified in terms of the birefringence relative to the refractive index (n). There are three refractive indices of interest, designated nx, ny and nz, which correspond to the machine direction (MD), transverse direction (TD) and thickness direction, respectively. As the material becomes more anisotropic (e.g., by stretching of the material), the difference between any two refractive indices will increase. This difference is referred to as "birefringence." Since there are many combinations of material directions to choose from, there are different values of the corresponding birefringence. The most common are two birefringences, namely the plane birefringence (Δe) defined by Equation 1a below and the thickness birefringence (Δth) defined by Equation 1b below.

[Equation 1a]

Δe = nx-ny

[Equation 1b]

Δth = (nx + ny) / 2- nz

The plane birefringence (Δe) is a measure of the relative orientation in the plane between MD and TD, and is unitless. Conversely, Δth provides a measure of thickness direction orientation relative to the average planar orientation. Another term commonly used to characterize optical films is optical retardation (R). R is simply multiplied by the birefringence and thickness (d) of the target film, as in the following equations 2a and 2b.

[Equation 2a]

Re = Δed = (nx-ny) d

[Equation 2b]

Rth = Δthd = [(nx + ny) / 2 -nz] d

The phase difference is a direct measure of the relative phase shift between two orthogonal light waves and is typically reported in nanometers (nm). Note that the definition of Rth is defined differently according to some descriptors, especially for ± signs.

It is also known that the birefringence / phase difference behavior of a material varies. For example, most materials, when stretched, will exhibit a higher refractive index along the stretching direction and a lower refractive index perpendicular to the stretching direction. This is because the refractive index at the molecular level is typically higher along the axis of the polymer chain and lower perpendicular to the chain. Such materials are commonly referred to as "positive birefringence" and represent most standard polymers, including all commercial cellulose esters.

In addition to positive birefringence there are "negative birefringence" and "zero birefringence" materials. The negative birefringent polymer exhibits a higher refractive index perpendicular to the stretching direction (with respect to the parallel direction) and consequently has a negative intrinsic birefringence. Certain styrenes and acrylics are known to have negative birefringent behavior due to their relatively bulky side groups. On the other hand, the zero birefringence is a special case, and does not exhibit a birefringence during stretching, so it represents a material having a zero intrinsic birefringence. These materials are ideal for optical applications because they can be molded, stretched or otherwise stressed without exhibiting any optical retardation or distortion during processing. Such materials are also extremely rare. Importantly, the type of compensation film that can be produced is limited by the birefringence properties (ie, positive or negative) of the polymer.

In the above example, a film having a refractive index having a relational expression of Equation 3a below is referred to as a “+ A” plate.

[Equation 3a]

nx> ny = nz

In such films, the x direction of the film has a high refractive index, and the y and thickness directions have approximately the same (and lower than nx) size. Films of this type are also referred to as positive uniaxial crystal structures with optical axes along the x-direction. Such films are easily produced by, for example, uniaxially stretching a positive birefringent material using a film drafter.

On the other hand, the "-A" plate uniaxial film is defined by the following equation 3b:

[Equation 3b]

nx <ny = nz

In the above equation, the refractive index of the x-axis is lower than those of the other directions (they are approximately the same). The most common method of making the -A plate is to stretch the negative birefringent polymer, or alternatively coat the surface with a negative birefringent liquid crystal polymer so that the molecules are aligned in the desired direction.

Another class of uniaxial optical films are C plates, which can also be "+ C" or "-C". The difference between the C plate and the A plate is that, as in the following equations 4a and 4b, in the case of the C plate, a unique refractive index (or optical axis) exists in the thickness direction, not in the plane of the film.

[Equation 4a]

nz> ny = nx ("+ C" plate)

[Equation 4b]

nz <ny = nx ("-C" plate)

The C plate can be produced by biaxial stretching when the relative stretching in the x and y directions remains constant. Alternatively, the C plate can be made by compression molding. Compression or equibiaxial stretching of an initially isotropic positive intrinsic birefringent material will provide a -C plate because an effective orientation direction is present in the plane of the film. Conversely, the + C plate can be made by compressing or isoaxially stretching an initial isotropic film made of a negative intrinsic birefringent material. In the case of biaxial stretching, if the orientation level in the MD and TD directions remains the same, then the material is no longer a true C plate, only a biaxial film with only two optical axes.

A third, more common option for making C plates is to use the stress that is formed during solution casting of the film. Tensile stress is created in the plane of the film due to the strain imposed by the casting belt (which is also equiaxed in nature). This tends to orient the chains in the plane of the film, providing -C and + C films respectively for positive and negative intrinsic birefringent materials. It is clear that solvent cast cellulose esters generally only produce -C plates, since most of the cellulose ester films used in displays are solvent cast and all of them are essentially birefringent. These films can also be uniaxially stretched to produce + A plates (assuming the phase difference is very low during initial casting), but the ability to make + C or -A plates using cellulose esters is extremely limited.

For this reason, films based on retardation caused by negative birefringence, such as + C film, have a liquid crystal coating on the base film having a thickness of 1 to 3 micron, where the values of retardation Ro and Rth are retarded due to the difference in fine coating thickness. There was a problem that the uniformity was lowered. Commercial films that also exhibit + C plate behavior are made using a nematic liquid crystal coating and subsequently using a polymerization process. However, these coating processes and liquid crystal materials are very expensive and require additional processing steps to coat the film to achieve the desired properties. To date, there are no commercial films showing high + C behavior based on cellulose esters and additives.

Accordingly, there is a need in the art for films exhibiting + C plate behavior with improved diagonal visibility without the use of liquid crystal materials and without the need for additional coating steps.

The present invention has been devised to solve the problems of the prior art as described above, and is produced by solvent casting a dope containing one or more acetyls and a cellulose ester resin having an acetyl substitution degree of 0.5 to 2.9, and a specific additive. A cellulose ester phase difference film is prepared.

In addition, a first dope layer solvent-cast a first dope comprising a cellulose ester resin substituted with acetic acid and propionic acid or butyl acid and a phase difference controlling agent having a specific structure; And a second dope layer solvent-cast a second dope containing a cellulose ester resin.

Through this, it is intended to provide a cellulose ester multilayer retardation film that exhibits + C plate behavior, can be manufactured in a simple process without using expensive liquid crystal materials, and has excellent retardation uniformity.

According to an embodiment of the present invention, a cellulose ester resin containing at least one acetyl and having an acetyl substitution degree of 0.5 to 2.9; And a phase difference control agent having the structure of Chemical Formula 1; and a cellulose ester phase difference film having + C plate optical properties, which is produced by solvent casting.

[Formula 1]

(5-norbornene-2,3-dicarboxylate, 5-Norbornene-2,3-dicarboxylate)

(The above R1, R2 are each independently hydrogen, one or more of C1 ~ C20 alkyl, alcohol, acid, ester, aromatic hydrocarbons)

The content of the phase difference control agent is 0.1 to 35% by weight of 100% by weight of the retardation film, the structure is characterized in that one selected from the following formulas 2 to 5.

[Formula 2]

(Dimethyl 5-norbornene-2,3-dicarboxylate, Dimethyl 5-norbornene-2,3-dicarboxylate)

[Formula 3]

(Mono-methyl-5-norbornene-2,3-dicarboxylate, Mono-Methyl-5-norbornene-2,3-dicarboxylate)

[Formula 4]

(5-Norbornene-2,3-dicarboxylic acid, 5-Norbornene-2,3-dicarboxylic acid)

[Formula 5]

(Dimethyl-oxabicyclohept-5-ene-2,3-dicarboxylic acid, Dimethyl-oxabicyclohept-5-ene-2,3-dicarboxylic acid)

On the other hand, the thickness of the retardation film according to the present invention is 25 to 80 μm, the plane direction retardation value (Ro) is 0 to 30 nm, and the thickness retardation value (Rth) is −10 to −105 nm.

The retardation film is characterized in that more than one layer or two layers.

According to another embodiment of the present invention, 1 or 2 or more selected from R1 to R3 in Formula 6 is selected from the group consisting of acetic acid, propionic acid and butyric acid. A first cellulose ester resin substituted with a species; And a phase difference control agent; a first dope layer prepared by solvent casting a first dope comprising; And a second cellulose ester resin in which one or two or more selected from R1 to R3 in Formula 6 is substituted with a hydrocarbon having 5 to 15 carbon atoms; a second dope layer prepared by solvent casting a second dope comprising; Included, the thickness of the first dope layer provides a cellulose ester multilayer retardation film, characterized in that 10 to 90% of the total thickness of the entire film.

[Formula 6]

(R1 to R3 are each independently a hydrogen atom or a hydrocarbon having 1 to 15 carbon atoms, and n is 1 or more)

The content of the phase difference controlling agent is 0.01 to 10% by weight, preferably 0.03 to 9.94% by weight, based on the total weight of the first dope, 0.1% to 35% based on 100% by weight of the multi-layer retardation film, and the following Chemical Formula 1 It is characterized by the same structure.

[Formula 1]

(5-norbornene-2,3-dicarboxylate, 5-Norbornene-2,3-dicarboxylate)

(The above R1, R2 are each independently hydrogen, C1 ~ C20 alkyl, alcohol, acid, ester, aromatic hydrocarbons, one or more)

More specifically, the phase difference control agent is characterized in that it is one selected from the following formulas 2 to 5.

[Formula 2]

(Dimethyl 5-norbornene-2,3-dicarboxylate, Dimethyl 5-norbornene-2,3-dicarboxylate)

[Formula 3]

(Mono-methyl-5-norbornene-2,3-dicarboxylate, Mono-Methyl-5-norbornene-2,3-dicarboxylate)

[Formula 4]

(5-Norbornene-2,3-dicarboxylic acid, 5-Norbornene-2,3-dicarboxylic acid)

[Formula 5]

(Dimethyl-oxabicyclohept-5-ene-2,3-dicarboxylic acid, Dimethyl-oxabicyclohept-5-ene-2,3-dicarboxylic acid)

The total thickness of the cellulose ester multilayer retardation film according to the present invention is 20 to 80 μm, the plane direction retardation value (Ro) is 0 to 30 nm, and the thickness retardation value (Rth) is −5 to −105 nm. .

According to another preferred embodiment of the present invention, the cellulose ester multilayer retardation film is characterized by having a structure of three or more layers, and specifically, a second dope layer is provided on both sides of the first dope layer to provide a second dope layer, a first dope layer, and It is an object to provide a cellulose ester multilayer retardation film characterized in that the second dope layer has a three-layer structure sequentially stacked.

The present invention having the above configuration, it is possible to manufacture a single-layer or multi-layer retardation film that is economical because it does not use a liquid crystal material that is an expensive material that has been conventionally used in commercial films showing + C plate behavior.

Also, because the solvent casting process equipment requires a very expensive investment cost, it is difficult to change the equipment for each developed product and invest in it. Accordingly, the present invention is a single-layer or multi-layer retardation film production, the dope of the present invention is superior in compatibility when mixed with Tri Acetate Cellulose (TAC) (no rise in haze), when applying the dope of the present invention, solvent There is an advantage that two recipes can be operated in one process without additional casting equipment.

1 is a view showing the structure of a cellulose ester multilayer retardation film according to an embodiment of the present invention.

Hereinafter, the present invention will be described in more detail through the following examples, but the scope of the present invention is not limited thereto.

The retardation film according to an embodiment of the present invention includes at least one acetyl and a cellulose ester resin having an acetyl substitution degree of 0.5 to 2.9; And it provides a cellulose ester phase difference film having a + C plate optical properties, characterized in that produced by solvent casting a dope containing ;;

[Formula 1]

(5-norbornene-2,3-dicarboxylate, 5-Norbornene-2,3-dicarboxylate)

(The above R1, R2 are each independently hydrogen, one or more of C1 ~ C20 alkyl, alcohol, acid, ester, aromatic hydrocarbons)

Here, the thickness of the retardation film of the cellulose ester retardation film is 25 to 80 μm, the plane direction retardation value (Ro) is 0 to 30 nm, preferably 2.7 to 8.6 nm, and the thickness direction retardation value (Rth) is −10. To -105 nm, preferably -30 to -102 nm, more preferably -50 to -80 nm.

The retardation film according to the embodiment may have a multi-layer structure in which one or two or more layers are stacked.

Meanwhile, in the retardation film according to another embodiment of the present invention, one or two or more selected from R1 to R3 in the following Chemical Formula 6 is acetic acid, propionic acid, and butyric acid. A first cellulose ester resin substituted with one selected from the group consisting of; And a phase difference control agent; a first dope layer prepared by solvent casting a first dope comprising; And a second cellulose ester resin in which one or two or more selected from R1 to R3 in Formula 6 is substituted with a hydrocarbon having 5 to 15 carbon atoms; a second dope layer prepared by solvent casting a second dope comprising; Included, the thickness of the first dope layer provides a cellulose ester multilayer retardation film, characterized in that 10 to 90% of the total thickness of the entire film.

[Formula 6]

(R1 to R3 are each independently a hydrogen atom or a hydrocarbon having 1 to 15 carbon atoms, and n is 1 or more.

Here, the total thickness of the cellulose ester multilayer retardation film is 20 to 80 μm, preferably 40 to 80 μm, and the surface direction retardation value (Ro) is 0 to 30 nm, preferably 1.4 to 7.5 nm, and the thickness direction retardation The value Rth is -5 to -105 nm, preferably -7 to -102 nm.

In addition, the first dope layer is made of a first dope in which 18 to 28 wt% of the first cellulose ester resin is dissolved in a solvent, and the second dope layer is 10 to 20 wt% of the second cellulose ester resin in a solvent. It is preferably prepared as a dissolved second dope.

That is, in one embodiment of the present invention, it is possible to provide a monolayer cellulose ester phase difference film prepared by solvent casting a dope containing a cellulose ester resin and a phase difference control agent,

In another embodiment of the present invention, a first dope containing a first cellulose ester resin and a phase difference control agent and a second dope containing a second cellulose ester resin are prepared by solvent casting and laminating, respectively, to produce a multilayer cellulose ester phase difference film. It is characterized by providing.

First, the cellulose ester (resin) usable in the present invention is described.

The commonly used cellulose ester is preferably a lower fatty acid ester of cellulose. Lower fatty acids used in the production of lower fatty acid esters of cellulose refer to fatty acids having 6 or fewer carbon atoms. Examples of lower fatty acid esters are fatty acid esters of mixed cellulose such as cellulose acetate, cellulose propionate, cellulose butyrate and cellulose acetate propionate or cellulose acetate butyrate. Among the lower fatty acid esters of cellulose, cellulose triacetate (TAC) or cellulose acetate propionate (CAP) is particularly preferred.

The structure of the cellulose ester is generally represented by the following formula (6).

[Formula 6]

(R1 to R3 are each independently a hydrogen atom or a hydrocarbon having 1 to 15 carbon atoms, and n is 1 or more)

The cellulose ester resin used in the retardation film of the present invention contains at least one acetyl group, and it is preferable to use a cellulose ester having an acetyl substitution degree of 0.5 to 2.9. When the acetyl substitution degree is less than 0.5, a problem may occur in which the film is hazeed by an unsubstituted OH group, and when it exceeds 2.9, there is a problem in that solubility in a solvent is lowered and unsolvent is generated.

In addition, specifically, it is preferable to use a resin in which cellulose acetate is substituted for at least one of the three substituents (R1, R2 and R3) as the cellulose ester.

In other words, all three substituents of the cellulose ester have an acetyl group is called Tri Acetate Cellulose (TAC), and all three substituents have a propionyl group is called Cellulose Tripropionate (CTP). However, the present invention is characterized in that three substituents of the cellulose ester use cellulose acetate propionate (CAP) having at least one acetyl group and at least one propionyl group.

On the other hand, the first cellulose ester resin used in the cellulose ester multilayer retardation film according to another embodiment of the present invention is one or two or more of the three substituents of the cellulose ester is acetic acid (Acetic acid), propionic acid (Propionic acid) And it is preferable to use a resin substituted with one selected from the group consisting of butyric acid (butyric acid). As the second cellulose ester resin, it is preferable to use a resin in which one or two or more selected from R1 to R3 of Formula 6 is substituted with a hydrocarbon having 5 to 15 carbon atoms.

That is, the structures of acetic acid, propionic acid, and butyric acid that can be substituted for the cellulose ester resin are as follows.

The molecular weight range of the cellulose ester resin is not limited, but the weight average molecular weight is preferably in the range of 150,000 to 220,000. By setting the molecular weight to a certain level or more, it is possible to effectively prevent the strength of the film from being lowered. In addition, by making the molecular weight below a certain level, the viscosity of the cellulose ester solution (dope) is maintained below a certain level, making it easy to produce a retardation film by a solvent casting method. The degree of molecular weight distribution of the cellulose ester resin (weight average molecular weight Mw / number average molecular weight Mn) is in the range of 2.0 to 4.5, preferably 2.0 to 3.0. Molecular weight distribution affects the viscosity of the dope and the mechanical properties of the film to be produced. If the molecular weight distribution value is less than 2.0, the mechanical properties (especially modulus) are lowered. In the case of discharging to the die, a processability problem arises as the pressure increases.

In the present invention, a phase difference film is produced by performing solvent casting of a dope containing a cellulose ester resin and a phase difference control agent having a specific structure.

The phase difference control agent used in the present invention is characterized by having the structure of Formula 1 below.

[Formula 1]

(5-norbornene-2,3-dicarboxylate, 5-Norbornene-2,3-dicarboxylate)

(The above R1, R2 are each independently hydrogen, one or more of C1 ~ C20 alkyl, alcohol, acid, ester, aromatic hydrocarbons)

Specifically, the 5-Norbonene-2,3-dicarboxylate is preferably a structure of the formula 2 to 5 as follows.

[Formula 2]

(Dimethyl 5-norbornene-2,3-dicarboxylate, Dimethyl 5-norbornene-2,3-dicarboxylate)

[Formula 3]

(Mono-methyl-5-norbornene-2,3-dicarboxylate, Mono-Methyl-5-norbornene-2,3-dicarboxylate)

[Formula 4]

(5-Norbornene-2,3-dicarboxylic acid, 5-Norbornene-2,3-dicarboxylic acid)

[Formula 5]

(Dimethyl-oxabicyclohept-5-ene-2,3-dicarboxylic acid, Dimethyl-oxabicyclohept-5-ene-2,3-dicarboxylic acid)

In preparing the cellulose ester retardation film, which is an embodiment of the present invention, the content of the retardation control agent is 0.1 to 35% by weight, preferably 0.1 to 20% by weight, more preferably 0.1 to 10% in 100% by weight of the retardation film. Weight percent,

0.01 to 10% by weight of 100% by weight of the dope, preferably 0.03 to 9.94% by weight, more preferably 0.03 to 5.7% by weight.

When the content of the retardation control agent is less than 0.1% by weight of 100% by weight of the retardation film or less than 0.01% by weight of 100% by weight of dope, a high negative Rth value cannot be obtained, and thus there is a problem in improving the viewing angle, and the content in the film When the content exceeds 35% by weight, or the content in the dope exceeds 10% by weight, evaporation of the phase difference controlling agent in the production of the film deepens, causing serious problems in process contamination.

In addition, in manufacturing the cellulose ester multilayer retardation film, which is another embodiment of the present invention, the content of the retardation control agent is 0.1 to 35% by weight, preferably 0.1 to 20% by weight, more preferably 100% by weight of the multilayer retardation film. 0.1 to 10% by weight,

0.01 to 10% by weight of 100% by weight of the first dope, preferably 0.03 to 9.94% by weight, more preferably 0.03 to 5.7% by weight.

When the content of the retardation control agent is less than 0.1% by weight in 100% by weight of the multilayer retardation film or less than 0.01% by weight in 100% by weight of the first dope, a high negative Rth value cannot be obtained, and thus there is a problem in improving the viewing angle. When the content in the multi-layer retardation film exceeds 35% by weight or the content in the first dope exceeds 10% by weight, evaporation of the retardation control agent during film production increases, resulting in serious problems in process contamination.

Meanwhile, the cellulose ester retardation film or the cellulose ester multilayer retardation film according to the present invention may be prepared by solvent casting a dope (including first and second dope) containing the cellulose ester and a retardation control agent. Solvent casting method is prepared by dissolving in a stirrer dope (first and second dope) using additives such as cellulose ester, phase difference control agent and plasticizer, UV absorber, mat agent and mixed solvents such as methylene chloride and methanol, It can be used by filtration using a filtration device.

On the other hand, when preparing a retardation film by a solvent casting method, an organic solvent is preferably used as a solvent for preparing the dope. It is preferable to use halogenated hydrocarbons as the organic solvent, and halogenated hydrocarbons include chlorinated hydrocarbons, methylene chloride, and chloroform, and methylene chloride is most preferred.

Further, if necessary, an organic solvent other than halogenated hydrocarbons may be mixed and used. Organic solvents other than halogenated hydrocarbons include esters, ketones, ethers, alcohols and hydrocarbons. As the ester, methyl formate, ethyl formate, propyl formate, pentyl formate, methyl acylate, ethyl acylate, pentyl acetate, etc. can be used, and as the ketone, acetone, methyl ethyl ketone, diethyl ketone, di Isobutyl ketone, cyclopentanone, cyclohexanone, methylcyclohexanone, etc. can be used, and diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxane can be used as ether. Solan, tetrahydrofuran, anisole, phenitol, etc. can be used. As alcohol, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, t-butanol, 1-pentanol , 2-methyl-2-butanol, cyclohexanol, 2-fluoroethanol, 2,2,2-trifluoroethanol, 2,2,3,3-tetrafluoro-1-propanol, and the like.

More preferably, methylene chloride may be used as a main solvent, and alcohol may be used as a solvent. Specifically, methylene chloride and alcohol may be used by mixing in a weight ratio of 80:20 to 95: 5. Most suitably, it is preferable to use methyl chloride and methanol in a mixing ratio of 80:20 to 90:10.

In another embodiment of the present invention, the cellulose ester multilayer retardation film, one or two or more of the three substituents of the cellulose ester resin is composed of acetic acid, propionic acid or butyric acid It characterized in that a first dope in which 18 to 28% by weight of the first cellulose ester resin substituted with one selected from the group is dissolved in a solvent is used, preferably 25% by weight is dissolved.

In addition, it is characterized in that a second dope is used by dissolving 10 to 20% by weight of a second cellulose ester resin in which 5 to 15 carbon atoms of hydrocarbons are substituted in one or more of the three substituents of the cellulose ester, with respect to the solvent. Is preferably 15 to 18% by weight, more preferably 17% by weight.

When the first cellulose ester resin is dissolved in a solvent in an amount of less than 18% by weight or the second cellulose ester resin is dissolved in an amount of less than 10% by weight, the viscosity of each dope is low. It is difficult, and when the first cellulose ester resin is dissolved in a solvent in excess of 28% by weight, or when the second cellulose ester resin is dissolved in a solvent in excess of 20% by weight, solubility is lowered, thereby increasing the amount of undissolved products.

Various additives may be added to the production of the cellulose ester phase difference film and the cellulose ester multilayer phase difference film of the present invention, for example, UV blocking agents, plasticizers, deterioration inhibitors, fine particles, and optical property control agents.

Specifically, various additives according to the use in each preparation step in the dope containing cellulose ester used in the solvent casting method (including the first and second dope), for example, plasticizer, deterioration inhibitor, microparticles, release agent, ultraviolet light Additives such as stabilizers, UV blocking agents, UV absorbers, infrared absorbers, wavelength dispersion modifiers, and optical anisotropy modifiers can be added. Specific types of these additives can be used without limitation as long as they are commonly used in the field, and the content is preferably used in a range that does not degrade the physical properties of the film. The timing of adding the additive may be determined according to the type of additive. A process of adding an additive to the end of the dope (including the first and second dope) preparations may be performed.

On the other hand, the cellulose ester retardation film and the cellulose ester multilayer retardation film contain a plasticizer for improving mechanical strength, imparting good castability and water absorption, and reducing water permeability. The plasticizer may be used without limitation as long as it is commonly used, and examples thereof include carboxylic acid esters selected from phosphate esters and phthalic acid esters or citric acid esters, and terminal asymmetric aromatic compounds and terminal symmetric aliphatic compounds may also be used. Do. It is also preferable to use a polyhydric alcohol ester plasticizer, a polyester plasticizer, and a polyhydric carboxylic acid plasticizer.

The polyester plasticizer is preferably an aliphatic polyester plasticizer and an aromatic polyester plasticizer, and preferably has a weight average molecular weight of 500 to 1500. More preferably, the weight average molecular weight is 550 to 650.

When the plasticizer is contained, its content is preferably 2% to 15% by weight compared to the dope in consideration of dimensional stability and processability. If the content of the plasticizer is too small, the effect of reducing the moisture permeability of the film is small, and a smooth cut surface cannot be obtained when slit processing or punching processing is performed, and there is a tendency that the generation of cutting debris increases. That is, the effect of containing a plasticizer cannot be sufficiently exhibited. Moreover, when there are too many, the plasticizer tends to bleed out from a resin film, and the physical properties of the film tend to deteriorate.

As the UV blocking agent, a benzotriazole-based UV blocking agent or a triazine-based UV blocking agent having high transparency and having an excellent effect of preventing deterioration of a polarizing plate or a liquid crystal element is preferable, and a benzotriazole-based UV blocking agent having a more suitable spectral absorption spectrum is particularly preferable. Do.

The conventionally known benzotriazole-based UV blocking agent used particularly preferably in combination with the UV blocking agent according to the present invention may be bisized, for example, 6,6'-methylene bis (2- (2H-benzo [d ] [1,2,3] triazol-2-yl))-4- (2,4,4-trimethylpentan-2-yl) phenol, 6,6'- methylenebis (2- (2H-benzo [ d] [1,2,3] triazol-2-yl))-4- (2-hydroxyethyl) phenol and the like. In the present invention, the UV blocking agent is preferably added in an amount of 0.1% to 20% by mass compared to the dope, and preferably 0.5% to 10% by mass, and also preferably 1% to 5% by mass. . These may use 2 or more types together.

The solvent casting method used for manufacturing the cellulose ester retardation film and the cellulose ester multilayer retardation film of the present invention has an advantage of producing a film having excellent physical properties such as optical properties, compared to other manufacturing methods. In the solvent casting method, dope (including the first and second dope) is first prepared by mixing various additives such as cellulose ester resin, UV absorber, mat agent, retardation control agent, and plasticizer in a mixed solvent containing methyl chloride as a main solvent. .

Specifically, according to an embodiment of the present invention, a cellulose ester phase difference film is prepared by solvent casting a dope comprising a cellulose ester resin having an acetyl substitution degree of 0.5 to 2.9 and a phase difference control agent having the structure of Formula 1 as described above. can do.

Specifically, the dope dissolves 18 to 28% by weight of the cellulose ester resin in which acetic acid and propionic acid are substituted in one or more of the three substituents of the cellulose ester in a solvent, and preferably 25% by weight. The retardation control agent preferably contains 0.01 to 10% by weight in the dope, preferably 0.03 to 9.94% by weight.

When the cellulose ester resin is dissolved in less than 18% by weight, the viscosity is low, so it is difficult to properly form a film when discharging the dope from the T-Die.

 In addition, according to another embodiment of the present invention, as described above, the first dope containing the first cellulose ester resin is solvent cast to prepare a first dope layer, and the second dope containing the second cellulose ester resin is solvent. Cast to produce a two-layer cellulose ester multilayer retardation film.

Specifically, the first dope is 18 to 28% by weight of the first cellulose ester resin in which acetic acid, propionic acid or butyric acid is substituted in at least one of the three substituents of the cellulose ester in a solvent, preferably 25% by weight It is good to dissolve. In the second dope, the second cellulose ester resin having 5 to 15 carbon atoms in one or more of the three substituents of the cellulose ester is dissolved in a solvent by 10 to 20% by weight, preferably 15 to 18% by weight , More preferably 17% by weight.

In the present invention, the cellulose ester sheet in which the dope (including the first and second dope) is flexibly formed on a support from a flexible die or a T-die is peeled off from the support when the solvent volatilizes to obtain self-support, and is conveyed in a stretching process. The stretching process is generally performed in a temperature range of -50 ° C to Tg + 50 ° C, and the elongation is 100 to 150% in the width direction or the length direction. However, the higher the elongation, the more preferable the non-stretching because the retardation value due to the non-uniform stretching of the edges and the center is non-uniform.

The cellulose ester retardation film and the cellulose ester multilayer retardation film thus formed are dried inside a dryer of Tg or less, which can simultaneously obtain the heat setting effect of the dryer, thereby controlling the appearance of wrinkles and the like of the film, and dimensioning such as heat shrinkage and moist heat expansion rate. Stability can be increased.

In the above-described manufacturing method, the cellulose ester retardation film, which is an embodiment of the present invention, may be manufactured in a single-layer structure using dope, and is also preferably manufactured in a structure of two or more layers. It is preferable that at least one layer may be included by solvent casting the dope.

In addition, the cellulose ester multilayer retardation film, which is another embodiment of the present invention, is also preferably composed of three layers, as well as a multi-layer retardation film having a two-layer configuration using a first dope and a second dope. It is preferable if the first cellulose ester resin and the second cellulose ester resin include at least one layer in the multilayer retardation film, and the total film thickness is preferably 20 to 80 μm.

According to an embodiment of the present invention, according to FIG. 1, a three-layer cellulose ester multilayer retardation film is disclosed, and a first dope layer prepared by solvent casting a first dope as a core layer is located, Disclosed is a structure in which a second dope layer prepared by solvent casting a second dope as a skin layer on both surfaces of the first dope layer is located.

The cellulose ester retardation film according to an embodiment of the present invention preferably has a thickness of 25 μm to 80 μm. Particularly, when the thickness is less than 25 μm, physical properties are deteriorated, and when it is more than 80 μm, industrial applicability is poor.

In addition, the cellulose ester multilayer retardation film according to another embodiment of the present invention has a total thickness of 20㎛ to 80㎛. If the thickness is less than 20 μm, the physical properties are inferior, and if it is greater than 80 μm, industrial applicability is poor.

The cellulose ester retardation film and the cellulose ester multilayer retardation film have a retardation satisfying + C Plate characteristics, although the optimum retardation value varies depending on the liquid crystal, Ro is 0 to 30 nm, and Rth is -5 to -105 nm, preferably Is preferably in the range of -7 to -102 nm.

Specifically, in the case of a cellulose ester phase difference film, Rth is -10 to -105 nm, and in the case of a cellulose ester multilayer phase difference film, Rth is preferably -5 to -105 nm, more preferably -7 to -102 nm.

When the retardation film of the present invention satisfies the above conditions, the + C plate characteristic with improved diagonal visibility is exhibited. Particularly preferably, Ro is 0 to 10 nm, Rth is -50 to -80 nm, which is the most diagonal. It is known to have good visibility.

The Ro and Rth are represented by the following equations (1) and (2) as the phase direction retardation value and the thickness direction retardation value, respectively.

Equation (1) Ro = (Nx-Ny) × d

Equation (2) Rth = (Nx + Ny) / 2-Nz × d

+ C: Nz> Nx = Ny

 (However, d is the thickness (nm) of the film, Nx is the maximum refractive index in the plane of the film, Ny is the refractive index in the direction perpendicular to Nx in the film plane, and Nz is the refractive index of the film in the thickness direction)

The cellulose ester retardation film and the cellulose ester multilayer retardation film produced by the present invention are capable of producing a retardation film having the characteristics of + C plate according to the above formula.

For this reason, it is possible to lower the material compared to the + C film by the liquid crystal coating method having the + C plate characteristics of the prior art, and the solvent casting method has the advantage of higher process efficiency than the conventional liquid crystal coating method.

In addition, the cellulose ester retardation film and the cellulose ester multilayer retardation film of the present invention can be applied to polarizing plates and liquid crystal displays. The polarizing plate and the liquid crystal display device is characterized by comprising a retardation film. The polarizing plate is a protective film is attached to both sides of the polarizer, at least one of the protective film is characterized in that the retardation film of the present invention. The liquid crystal display device has a liquid crystal cell and two polarizing plates disposed on both sides of the liquid crystal cell, and is characterized in that the liquid crystal cell is in a vertical alignment mode.

The polarizing plate as described above may be manufactured according to a conventional method. For example, an aqueous solution of polyvinyl alcohol completely saponified on both sides of a polarizing film prepared by alkali saponifying the retardation film of the present invention, immersing the resulting film in a polyvinyl alcohol (PVA) film in an iodine solution, and stretching the film. Join using. Alkali saponification refers to a treatment in which a retardation film is immersed in a hot, strong alkaline solution to improve the wettability of the film to an aqueous adhesive and provide good adhesion to the film.

Hereinafter, the present invention will be described in more detail through the following examples, but the scope of the present invention is not limited thereto.

<Cellulose ester phase difference film>

Example 1

<Step 1> Cellulose ester resin

As the cellulose ester resin, CAP (Cellulose Acetate Propionate) resin in which R1 to R3 are acetic acid and propionic acid in the following Chemical Formula 6 was used.

[Formula 6]

(n is 1 or more)

<Step 2> Preparation of dope

Cellulose Acetate Propionate (CAP) prepared in Step 1, 22.7% by weight, 5.7% by weight of a phase difference controlling agent having the structure of Formula 2 below, and a mixed solvent of methylene chloride and methanol in a ratio of 80:20 (71.6 Dope).

[Formula 2]

(Dimethyl 5-norbornene-2,3-dicarboxylate, Dimethyl 5-norbornene-2,3-dicarboxylate)

<Step 3> Preparation of cellulose ester phase difference film

The dope prepared in step 2 was uniformly flexible to a stainless band support having a width of 800 mm using a belt casting device. The solvent was evaporated on the stainless band support and peeled from the stainless band support. Subsequently, it was conveyed for 3 minutes in the Tenter section set at 150 ° C, and dried at 100 ° C in the Dryer to prepare a cellulose ester phase difference film having a film thickness of 40 μm.

Example 2

A cellulose ester phase difference film was prepared by performing the same procedure as in Example 1, except that the film thickness was changed to 25 μm.

Example 3

A cellulose ester retardation film was prepared by performing the same procedure as in Example 1, except that the film thickness was changed to 60 μm.

Example 4

A cellulose ester retardation film was prepared by performing the same procedure as in Example 1, except that the film thickness was changed to 80 μm.

Example 5

A cellulose ester retardation film was prepared by performing the same procedure as in Example 1, except that the content of the dope retardation control agent was changed to 0.03% by weight.

Example 6

A cellulose ester retardation film was prepared by performing the same process as in Example 1, except that the content of the dope retardation control agent was changed to 2.84% by weight.

Example 7

A cellulose ester retardation film was prepared by performing the same procedure as in Example 1, except that the content of the dope retardation control agent was changed to 9.94% by weight.

Example 8

A cellulose ester phase difference film was prepared by performing the same process as in Example 1, except that a material having the structure of Formula 4 below was used as the phase difference control agent.

[Formula 4]

(5-Norbornene-2,3-dicarboxylic acid, 5-Norbornene-2,3-dicarboxylic acid)

Comparative Example 1

A cellulose ester phase difference film was prepared by performing the same procedure as in Example 1, except that no phase difference control agent was added.

1. Phase difference measurement

It is shown in Table 1 by measuring the phase difference value Ro in the in-plane direction and the phase difference value Rth in the thickness direction at a wavelength of 550 nm under an environment of 23 ° C. and 55% RH using Axoscan equipment.

division		Example 1	Example 2	Example 3	Example 4	Example 5	Example 6	Example 7	Example 8	Comparative Example 1
Thickness (㎛)		40	25	60	80	40	40	40	40	40
Additive content (wt%)	Dope Standard	5.7	5.7	5.7	5.7	0.03	2.84	9.94	5.7	0
	Film standard	20	20	20	20	0.1	10	35	20	0
Phase difference (nm)	Ro	4.3	2.7	6.5	8.6	2	2.4	4	8	5
	Rth	-50	-30	-75	-102	-10	-34	-71	-29	-8

According to Table 1, in the case of the cellulose ester retardation films produced by Examples 1 to 8 of the present invention, it can be seen that the negative Rth value is higher than that of Comparative Example 1, effectively showing the + C plate behavior. If the additive content and the film thickness are controlled by applying the additive, it can be confirmed that an optimum phase difference Rth value (-50 nm to -80 nm) can be implemented in the OLED without using a conventional liquid crystal coating.

<Cellulose ester multilayer retardation film>

Example 9

<Step 1> Cellulose ester resin

The first cellulose ester resin and the second cellulose ester resin are prepared.

First, as the first cellulose ester resin, R1 to R3 in the following Chemical Formula 6 are used as a resin substituted with acetic acid and propionic acid

Cellulose Triacetate (TAC) was used as the second cellulose ester resin.

 [Formula 6]

(R1 to R3 are each independently a hydrogen atom or a hydrocarbon having 1 to 15 carbon atoms, and n is 1 or more)

<Step 2> Preparation of first and second dope

The first dope was dissolved by dissolving 22.7% by weight of the first cellulose ester resin prepared in Step 1 and 5.7% by weight of a phase difference controlling agent having the structure of Formula 2 below in a mixed solvent of methylene chloride and methanol in a ratio of 80:20. It was prepared.

In addition, 17% by weight of the second cellulose ester resin prepared in step 1 was dissolved in a mixed solvent of methylene chloride and methanol mixed at a ratio of 90:10, 8% of a polyester plasticizer having a weight average molecular weight of 550 to 650, and EVONIC A second dope was prepared by dissolving 450 ppm of R972 (made by Mat) of the company.

 [Formula 2]

(Dimethyl 5-norbornene-2,3-dicarboxylate, Dimethyl 5-norbornene-2,3-dicarboxylate)

<Step 3> Preparation of cellulose ester multilayer retardation film

The first dope layer prepared in step 2 is prepared with a thickness of 36 µm, and a second dope prepared in step 2 is drawn on both sides of the first dope layer to a thickness of 2 µm, so that it is non-stretched and dried. Films were prepared through the process.

The first and second dope were uniformly flexible on a stainless band support having a width of 800 mm using a belt casting device. The solvent was evaporated on the stainless band support and peeled from the stainless band support. Subsequently, it was conveyed for 35 minutes in a drying section set at 110 ° C. and dried to prepare a three-layer retardation film of cellulose ester having a film thickness of 40 μm. At this time, the ratio of the thickness sum of the first dope layer and the second dope layer was 90:10.

Example 10

A first dope layer is prepared with a thickness of 18 µm for the first dope, and a second dope is drawn to each 1 µm thickness on both sides of the first dope layer to obtain a film having a final thickness of 20 µm through a non-stretching and drying process. A cellulose ester multilayer retardation film was prepared by performing the same procedure as in Example 9, except for preparing.

Example 11

A first dope layer was prepared with a thickness of 72 µm as a first dope, and a second dope was drawn at a thickness of 4 µm on both sides of the first dope layer to obtain a film having a final thickness of 80 µm through a non-stretching and drying process. A cellulose ester multilayer retardation film was prepared by performing the same procedure as in Example 9, except for preparing.

Example 12

A cellulose ester multilayer retardation film was prepared by performing the same process as in Example 9, except that the content of the retardation control agent in the first dope was changed to 0.03% by weight.

Example 13

A first dope layer was prepared with a thickness of 72 µm as a first dope, and a second dope was drawn at a thickness of 4 µm on both sides of the first dope layer to obtain a film having a final thickness of 80 µm through a non-stretching and drying process. A cellulose ester multilayer retardation film was prepared by performing the same procedure as in Example 12, except for preparing.

Example 14

A cellulose ester multilayer retardation film was prepared by performing the same process as in Example 9, except that the content of the retardation control agent in the first dope was changed to 2.84% by weight.

Example 15

A first dope layer was prepared with a thickness of 72 µm as a first dope, and a second dope was drawn at a thickness of 4 µm on both sides of the first dope layer to obtain a film having a final thickness of 80 µm through a non-stretching and drying process. A cellulose ester multilayer retardation film was prepared by performing the same procedure as in Example 14, except for preparing.

Example 16

A cellulose ester multilayer retardation film was prepared by performing the same process as in Example 9, except that the content of the retardation control agent in the first dope was changed to 9.94% by weight.

Example 17

A first dope layer was prepared with a thickness of 72 µm as a first dope, and a second dope was drawn at a thickness of 4 µm on both sides of the first dope layer to obtain a film having a final thickness of 80 µm through a non-stretching and drying process. A cellulose ester multilayer retardation film was prepared by performing the same procedure as in Example 16, except for preparing.

Comparative Example 2

In the first cellulose ester resin used in the first dope, the same process as in Example 9 was applied except that the cellulose resin in which R1 to R3 were all substituted with a naphthoyl group, and no phase difference control agent was added. By carrying out, a cellulose ester multilayer retardation film was prepared.

 (2-naphthoic acid)

1. Phase difference measurement

It is shown in Table 2 by measuring the phase difference value Ro in the in-plane direction and the phase difference value Rth in the thickness direction at a wavelength of 550 nm under an environment of 23 ° C. and 55% RH using Axoscan equipment.

2. Haze measurement

The first dope and the second dope of Examples and Comparative Examples were mixed at a ratio of 80:20, mixed for 15 hours, and then cast under a film at 22 ° C., 26% RH, and measured with a Haze meter.

Item		Example 9	Example 10	Example 11	Example 12	Example 13	Example 14	Example 15	Example 16	Example 17	Comparative Example 2
Content of phase difference control agent in the first dope (wt%)		5.7			0.03		2.84		9.94		0
Doping thickness (㎛)	1st dope layer (core layer)	36	18	72	36	72	36	72	36	72	36
	2nd dope layer (skin A, B layer)	4	2	8	4	8	4	8	4	8	4
Total film thickness (㎛)		40	20	80	40	80	40	80	40	80	40
Phase difference (nm)	Ro (deviation)	3.1 (± 0.2)	3.1 (± 0.1)	7.4 (± 0.4)	1.4 (± 0.1)	2.9 (± 0.2)	1.9 (± 0.1)	4.2 (± 0.3)	3.0 (± 0.1)	7.5 (± 0.1)	0.6 (± 0.4)
	Rth (deviation)	-43 (± 1.0)	-25 (± 1.0)	-86 (± 1.1)	-7 (± 0.4)	-14 (± 1.4)	-30 (± 0.7)	-58 (± 1.7)	-48 (± 1.1)	-102 (± 1.6)	-365 (± 10)
Haze (%)		0.3	0.3	0.3	0.2	0.2	0.2	0.2	0.4	0.4	84.0

According to Table 2, in the case of the cellulose ester multilayer retardation films produced by Examples 9 to 17 of the present invention, it can be seen that the phase difference uniformity is high as a whole because the deviation value of the retardation is small as compared with Comparative Example 2. In addition, when the first cellulose ester resin and the second cellulose ester resin in Comparative Example 2 are mixed, it causes a rapid rise in Haze, which makes it difficult to apply to the polarizing plate.

Claims (12)

1. A cellulose ester resin comprising at least one acetyl and having an acetyl substitution degree of 0.5 to 2.9; And

   Phase difference control agent having the structure of Formula 1; Cellulose ester phase difference film having a + C plate optical properties, characterized in that produced by solvent casting a dope containing.

   [Formula 1]

   

   (5-norbornene-2,3-dicarboxylate, 5-Norbornene-2,3-dicarboxylate)

   (The above R1, R2 are each independently hydrogen, one or more of C1 ~ C20 alkyl, alcohol, acid, ester, aromatic hydrocarbons)
2. According to claim 1,

   The content of the retardation control agent is a cellulose ester retardation film having + C plate optical properties comprising 0.1 to 35% by weight of 100% by weight of the retardation film.
3. According to claim 1,

   The phase difference control agent is a cellulose ester phase difference film having a + C plate optical properties, characterized in that one selected from the following formulas 2 to 5.

   [Formula 2]

   

   (Dimethyl 5-norbornene-2,3-dicarboxylate, Dimethyl 5-norbornene-2,3-dicarboxylate)

   [Formula 3]

   

   (Mono-methyl-5-norbornene-2,3-dicarboxylate, Mono-Methyl-5-norbornene-2,3-dicarboxylate)

   [Formula 4]

   

   (5-Norbornene-2,3-dicarboxylic acid, 5-Norbornene-2,3-dicarboxylic acid)

   [Formula 5]

   

   (Dimethyl-oxabicyclohept-5-ene-2,3-dicarboxylic acid, Dimethyl-oxabicyclohept-5-ene-2,3-dicarboxylic acid)
4. According to claim 1,

   The retardation film has a thickness of 25 to 80 μm, a plane direction retardation value (Ro) is 0 to 30 nm, and a thickness direction retardation value (Rth) is −10 to −105 nm, having a + C plate optical characteristic. Cellulose ester retardation film.
5. According to claim 1,

   The retardation film is a cellulose ester retardation film having a + C plate optical properties, characterized in that at least one layer or two layers.
6. First cellulose ester resin in which one or two or more selected from R1 to R3 in Formula 6 is substituted with one selected from the group consisting of acetic acid, propionic acid and butyric acid ; And a phase difference control agent; a first dope layer prepared by solvent casting a first dope comprising; And

   A second dope layer prepared by solvent casting a second dope comprising; a second cellulose ester resin substituted with a hydrocarbon having 5 to 15 carbon atoms selected from R1 to R3 in Formula 6 below; and,

   The thickness of the first dope layer is a cellulose ester multilayer retardation film, characterized in that 10 to 90% of the total thickness of the entire film.

   [Formula 6]

   

   (R1 to R3 are each independently a hydrogen atom or a hydrocarbon having 1 to 15 carbon atoms, and n is 1 or more)
7. The method of claim 6,

   The content of the phase difference controlling agent is 0.01 to 10% by weight based on the total weight of the first dope, and the cellulose ester multilayer phase difference film, characterized in that 0.1% to 35% based on 100% by weight of the multilayer retardation film.
8. The method of claim 6,

   The retardation control agent is a cellulose ester multilayer retardation film, characterized in that the structure of the formula (1).

   [Formula 1]

   

   (5-norbornene-2,3-dicarboxylate, 5-Norbornene-2,3-dicarboxylate)

   (The above R1, R2 are each independently hydrogen, C1 ~ C20 alkyl, alcohol, acid, ester, aromatic hydrocarbons, one or more)
9. The method of claim 8,

   The retardation control agent is a cellulose ester multilayer retardation film, characterized in that one selected from the following formulas 2 to 5.

   [Formula 2]

   

   (Dimethyl 5-norbornene-2,3-dicarboxylate, Dimethyl 5-norbornene-2,3-dicarboxylate)

   [Formula 3]

   

   (Mono-methyl-5-norbornene-2,3-dicarboxylate, Mono-Methyl-5-norbornene-2,3-dicarboxylate)

   [Formula 4]

   

   (5-Norbornene-2,3-dicarboxylic acid, 5-Norbornene-2,3-dicarboxylic acid)

   [Formula 5]

   

   (Dimethyl-oxabicyclohept-5-ene-2,3-dicarboxylic acid, Dimethyl-oxabicyclohept-5-ene-2,3-dicarboxylic acid)
10. The method of claim 6,

    The total thickness of the cellulose ester multilayer retardation film is 20 to 80 μm, the surface direction retardation value (Ro) is 0 to 30 nm, and the thickness direction retardation value (Rth) is -5 to -105 nm. Retardation film.
11. The method of claim 6,

    The cellulose ester multilayer retardation film is a cellulose ester multilayer retardation film, characterized in that the structure of three or more layers.
12. The method of claim 11,

    The cellulose ester multilayer retardation film

    Second dope layers are provided on both sides of the first dope layer

    Cellulose ester multilayer retardation film, characterized in that the second dope layer, the first dope layer and the second dope layer have a three-layer structure sequentially stacked.

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