KR101715402B1 - Additives for retardation compensating and Cellulose acetate film containing the same - Google Patents

Abstract

The present invention relates to an additive for compensating a retardation caused by an IPS liquid crystal cell and a cellulose acetate film containing the same, and more particularly, to an acrylic copolymer-type retardation compensation additive and a cellulose acetate film containing the same. Since the retardation-compensating additive of the present invention is simple in the production method and is made in the form of a copolymer, haze and leakage can be greatly suppressed during film formation, and it is easily deformed by an additive satisfying various physical properties depending on the choice of monomer IPS mode LCD polarizer protective film or the like.

Description

[0001] The present invention relates to a retardation-compensating additive and a cellulose acetate film containing the same,

The present invention relates to an additive for compensating a phase difference caused by an IPS liquid crystal cell and a cellulose acetate film containing the additive.

Liquid crystal display (LCD), which is a flat panel display device, is widely used in display portions of TVs, monitors, notebooks, navigation and mobile phones due to its low power consumption and high resolution. In the LCD, the polarizing plates are arranged one by one on the upper and lower plates of the liquid crystal layer, and the transmission axes of the upper and lower plates are arranged in a staggered relationship with each other. An electric field is applied to the liquid crystal to deform the liquid crystal array, Lt; / RTI >

The liquid crystal mode is classified according to the initial liquid crystal alignment, and the TN (Twisted Nematic) mode in which the liquid crystal is continuously twisted from the top plate to the bottom plate has excellent light efficiency and process efficiency and is produced by most LCD manufacturers. However, since the viewing angle is narrow, an IPS (In-Place-Switching) mode has been developed as an alternative to overcome this problem. That is, the initial liquid crystal molecules are arranged without twisting between the upper plate and the lower plate, and the liquid crystal molecules are rotated in parallel to the substrate by a horizontal electric field instead of a vertical electric field. In IPS mode, there is an advantage that the effective phase difference value is small according to viewing angle, and the viewing angle dependency of image quality is smaller than that of TN mode cell. However, since the retardation value still exists in the IPS mode, a narrow viewing angle problem is one of the problems to be solved. In general, the IPS liquid crystal cell exhibits the characteristic of + A (positive A plate), which is defined by the refractive index size of the x, y, and z axes, and the + A plate exhibits the characteristics of nx> ny = nz . That is, the IPS liquid crystal cell, which is a + A plate, has a large refractive index in the x-axis plane direction (in-plane).

On the other hand, a cellulose acetate film excellent in physical properties, transparency and optical isotropy is mainly used as a protective film of a polarizing plate. When an appropriate additive is added to such a cellulose acetate film, the retardation of the IPS liquid crystal cell can be compensated, and a wider viewing angle can be secured. That is, a cellulose acetate film showing a -A plate (nx = nz> ny) or a + C plate (nz> nx = ny) having a large refractive index out of plane by an additive is used as a protective film The phase difference due to the IPS liquid crystal cell can be effectively compensated.

Korean Patent No. 10-0980534 discloses a cellulose acetate film using a compound having a planar structure of two or more aromatic rings as an additive. In Korean Patent Laid-Open No. 10-2005-0030121, a retardation enhancer and a retarder We tried to compensate the phase difference by mixing. However, the additive used in the above technique has a low molecular weight, which causes haze phenomenon and bleed out during film formation.

Accordingly, the present inventors have made efforts to increase the refractive index in the thickness direction of the cellulose acetate film by using a polymer type additive in order to solve the above problems. As a result, it has been found that a cellulose acetate film having a high refractive index in the thickness direction can be prepared by using an acrylic copolymer having a specific structure having a simple and cost-effective production method as a phase difference additive. That is, an object of the present invention is to provide a novel additive capable of compensating for retardation caused by an IPS liquid crystal cell and a compensation film containing the same.

The present invention is characterized by a retardation compensation additive represented by the following formula (1).

[Chemical Formula 1]

Wherein R ₁ is a linear or branched alkyl group having 1 to 20 carbon atoms, R ₂ is a hydrogen atom or a linear or branched alkyl group having 1 to 5 carbon atoms, R ₃ is an oxygen atom, a sulfur atom, CH ₂ Or NH.

The present invention also features a cellulose acetate film containing the retardation compensation additive.

Since the retardation-compensating additive of the present invention is simple in the production method and is made in the form of a copolymer, haze and leakage can be greatly suppressed during film formation, and it is easily deformed by an additive satisfying various physical properties depending on the choice of monomer IPS mode LCD polarizer protective film or the like.

Hereinafter, the present invention will be described in detail.

The present invention relates to a retardation compensation additive represented by the following formula (1).

Wherein R ₁ is a linear or branched alkyl group having 1 to 20 carbon atoms, R ₂ is a hydrogen atom or a linear or branched alkyl group having 1 to 5 carbon atoms, R ₃ is an oxygen atom, a sulfur atom, CH ₂ Or NH.

The retardation compensation additive of the present invention has an advantage that the optical value can be easily changed according to the length of R ₁ . As the chain length of R ₁ or R ₂ increases, the degree of freedom of the chain increases and the tendency toward orientation in the plane becomes strong, which is disadvantageous for increasing the refractive index in the thickness direction z-axis direction. Therefore, it is preferable to use an acrylic copolymer produced by using a monomer having a carbon number within the above range. The retardation-compensating additive of the present invention is excellent in solubility in methylene chloride used as a solvent in the production of a cellulose acetate film by the solvent casting method and can greatly suppress the haze after film forming or leakage on the film surface, Excellent in durability.

형태의 아크릴 단량체 중 1종 이상과, 말레산 무수물, 말레이미드, 티오펜-2,5-디온 및 4-사이클로펜텐-1,3-디온 중에서 선택한 1종 이상을 유기용매 하에서 반응 개시제의 존재하에 중합반응시켜 얻을 수 있다. 상기 아크릴 단량체 중의 R₁ 및 R₂는 화학식 1에서 정의한 바와 같으며, 바람직하기로는 메틸메타아크릴레이트, 에틸메타아크릴레이트를 사용하는 것이 좋다. 이때, 위상차 보상 첨가제 중에서의 아크릴 단량체의 함량이 60 ~ 90 중량%로 조절하는 것이 바람직한데, 아크릴 단량체의 함량이 60 중량% 미만이면 중합도가 저하되는 문제가 있을 수 있고, 반대로 90 중량%를 초과하면 z축 방향 굴절률을 향상시키기 어렵다. 또한, 중합반응의 개시제로는 특별히 한정하지는 않으나, AIBN(2,2’-아조비스이소부티로니트릴)를 사용하는 것이 좋다.The retardation compensation additive

And at least one member selected from the group consisting of maleic anhydride, maleimide, thiophene-2,5-dione and 4-cyclopentene-1,3-dione in an organic solvent in the presence of a reaction initiator Polymerization reaction. R ₁ and R ₂ in the acrylic monomer are the same as defined in formula (1), preferably methyl methacrylate and ethyl methacrylate. At this time, it is preferable to adjust the content of the acrylic monomer in the retardation compensation additive to 60 to 90% by weight. If the content of the acrylic monomer is less than 60% by weight, the polymerization degree may be lowered. On the contrary, It is difficult to improve the refractive index in the z-axis direction. The initiator for the polymerization reaction is not particularly limited, but AIBN (2,2'-azobisisobutyronitrile) is preferably used.

The present invention also relates to a cellulose acetate film containing the retardation compensation additive.

Cellulose acetate is an ester of cellulose and acetic acid, and all or a part of the hydrogen atoms of the hydroxyl groups existing at the second, third, and sixth positions of the glucose unit constituting the cellulose are substituted with an acetyl group. In order to control the phase difference of the cellulose acetate film, the degree of acetylation of the cellulose acetate is important. In the present invention, the degree of acetylation is preferably 59.0 to 61.5. If the degree of acetalization is less than 59.0, there may be a problem in hygroscopicity and phase difference of cellulose acetate due to increase of -OH group in the molecule, and if it exceeds 61.5, there may be a problem in solubility. The content of the retardation compensation additive represented by the formula (1) in the film is preferably 0.01 to 30 parts by weight based on 100 parts by weight of the cellulose acetate. If the content of the upper body compensating additive is too small, it is difficult to expect an effect on the effect of the addition. If the content of the additive exceeds 30 parts by weight, the haze property of the film may be lowered due to the lower compatibility of the additive and cellulose acetate. The cellulose acetate film of the present invention may further contain known additives such as a plasticizer, an ultraviolet ray inhibitor, a fine particle, and a wavelength dispersion regulator as necessary.

Such a cellulose acetate film can be produced by a solvent casting method in which cellulose acetate, a phase difference compensation additive and other additives are dissolved in a solvent, the solution is cast on a support, and the solvent is evaporated to form a film. Examples of the solvent include methyl acetate, ethyl acetate, amyl acetate, ethyl formate, acetone, cyclohexanone, methyl acetoacetate, tetrahydrofuran, 1,3-dioxolane, 4-methyl- , 4-dioxane, 2,2,2-trifluoroethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, , 3,3,3-hexafluoro-2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3- At least one selected from the group consisting of fluoro-1-propanol, nitroethane, 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, methylene chloride and bromopropane , Preferably methyl acetate, acetone or methylene chloride is preferably used. In addition, when these solvents are used in combination with lower alcohols such as methanol, ethanol and butanol, the solubility of the cellulose acrylate in the solvent can be improved or the viscosity of the solution can be reduced.

The produced film has an excellent retardation value in the thickness direction without any additional stretching process. Specifically, it has a retardation value of 0 nm? Re? 5 nm and 0 nm? Rth? 10 nm at a wavelength of 550 nm. Re and Rth are plane retardation value thickness retardation values, respectively, and are defined by the following equations (1) and (2).

In the above equations (1) and (2), nx is the refractive index in the in-plane x-axis direction of the film, ny is the refractive index in the y-axis direction of the film, nz is the refractive index in the thickness direction of the film, .

As can be seen from Equation (2), as the refractive index in the z axis increases, Rth decreases. Therefore, as the Rth value approaches 0, the IPS mode compensation film is excellent in the retardation compensation effect, and a better viewing angle can be secured.

Since the retardation-compensating additive of the present invention is made in the form of a copolymer, haze and leakage can be greatly suppressed during film formation, and an additive that satisfies various physical properties depending on the selection of the monomer can be easily deformed. Such a retardation compensation additive can be added to a cellulose acetate film to produce a film having a high refractive index in the thickness direction, and thus can be effectively applied to an IPS-mode LCD polarizer protective film or the like.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by the following Examples.

[ Example ]

Example 1: Preparation of retardation-compensating additive

12 g (0.12 mol) of methyl methacrylate and 7.8 g (0.08 mol) of maleic anhydride were placed in a 1-neck flask, and 33 g of a mixed solution of tetrahydrofuran and methyl ethyl ketone . After the temperature was maintained at room temperature, all of the reactants were dissolved. Then, 3.2 g (0.02 mol) of AIBN (2,2'-azobisisobutyronitrile) as a reaction initiator was added and the temperature was raised to 60 ° C. After the reaction was allowed to proceed for 4 hours, the reaction solution was cooled to room temperature and methanol was added to precipitate the product. The precipitated polymer was washed with methanol while being filtered under reduced pressure, and then dried in a vacuum oven. The recovered polymer was in the form of a white powder with a yield of 67%.

Example 2: Preparation of phase difference compensation additive

Except that 13.7 g (0.12 mol) of ethyl methacrylate was used in place of methyl methacrylate to prepare a polymer-type retardation compensation additive. The yield of the recovered polymer was 65%.

Example 3: Preparation of an additive for retardation compensation

The procedure of Example 1 was repeated except that 17 g (0.12 mol) of butyl methacrylate was used instead of methyl methacrylate to prepare a polymer-type retardation compensation additive. The yield of the recovered polymer was 60%.

Example 4: Preparation of cellulose acetate film

10 parts by weight of the retardation-compensating additive (Poly (MMA-MA)) prepared in Example 1, 593.3 parts by weight of methylene chloride, and 65.9 parts by weight of methanol were added to 100 parts by weight of cellulose acetate having an acetylation degree of 60.6% (VM- Parts by weight were placed in a mixing tank and stirred to prepare a completely dissolved solution of cellulose acetate. Then, the prepared solution was cast on a support, and the solvent was evaporated to form a film. The drying temperature was 140 캜 and the drying time was 40 minutes. The thickness of the prepared film was 60 탆.

Example 5: Preparation of cellulose acetate film

(Poly (EMA-MA)) prepared in Example 2 was used as the retardation compensation additive.

Example 6: Preparation of cellulose acetate film

The same procedure as in Example 4 was carried out except that the retardation compensation additive prepared in Example 3 was used.

Comparative Example 1: Production of cellulose acetate film

A film was prepared in the same manner as in Example 4 except that the retardation compensation additive was not used.

Comparative Example 2: Preparation of cellulose acetate film

An oligomer type aliphatic polyester additive having a weight average molecular weight of 1,000 to 2,000 by condensation reaction of adipic acid and ethylene glycol was used as the retardation compensation additive.

Property measurement test

The retardation values of the films prepared in Examples 4 to 6 and Comparative Examples 1 and 2 were measured using an Axoscan apparatus, and the results are shown in Table 1 below. The reference wavelength was 550 nm.

division Re Rth Example 4 0 nm 4 nm Example 5 0 nm 7 nm Example 6 0 nm 10 nm Comparative Example 1 0 nm 50 nm Comparative Example 2 0 nm 35 nm

As can be seen from the above Table 1, in comparison with Comparative Example 1 in which a retardation compensation additive is not used and Comparative Example 2 in which a known aliphatic polyester additive is used, the retardation values in the thickness direction (Rth) in Examples 4 to 6 And a cellulose acetate film having a large refractive index in the thickness direction was produced. From the results of Examples 4 to 6, it can be seen that as the chain length of the acrylic monomer used in the production of the retardation compensation additive increases, the tendency toward orientation in the plane direction increases.

As a result, since the retardation-compensating additive of the present invention is made in the form of a copolymer, various physical properties can be satisfied according to the selection of monomers, so that it is possible to actively cope with the market demand and can be added to a cellulose acetate film, It can be confirmed that the film can be applied to an IPS-mode LCD polarizer protective film or the like.

Claims (5)

A retardation compensation additive represented by the following formula (1):
[Chemical Formula 1]

Wherein R ₁ is a linear or branched alkyl group having 1 to 20 carbon atoms, R ₂ is a hydrogen atom or a linear or branched alkyl group having 1 to 5 carbon atoms, R ₃ is an oxygen atom, a sulfur atom, CH ₂ Or NH, m and n are a copolymerization ratio of m + n = 1, m is 60 to 90% by weight, and n is 10 to 40% by weight.
A cellulose acetate film containing the retardation-compensating additive of claim 1. The cellulose acetate film according to claim 2, wherein the content of the retardation compensation additive is 0.01 to 30 parts by weight based on 100 parts by weight of the cellulose acetate.  3. The cellulose acetate film according to claim 2 or 3, wherein the film has a retardation value of 0 to 5 nm in the direction of the plane direction of 500 nm and a retardation value of 0 to 10 nm in the thickness direction. A polarizing plate containing the cellulose acetate film of claim 2.