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WO2015099368A1 - Polarizing plate and liquid crystal display device having the same - Google Patents

Polarizing plate and liquid crystal display device having the same Download PDF

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Publication number
WO2015099368A1
WO2015099368A1 PCT/KR2014/012614 KR2014012614W WO2015099368A1 WO 2015099368 A1 WO2015099368 A1 WO 2015099368A1 KR 2014012614 W KR2014012614 W KR 2014012614W WO 2015099368 A1 WO2015099368 A1 WO 2015099368A1
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WO
WIPO (PCT)
Prior art keywords
film
cellulose acylate
cte
thermal expansion
coefficient
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/KR2014/012614
Other languages
French (fr)
Inventor
Seok Won Kim
Ki Yup Kim
Yong Gyun Cho
Hye Jin Lee
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SK Innovation Co Ltd
Original Assignee
SK Innovation Co Ltd
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Filing date
Publication date
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Publication of WO2015099368A1 publication Critical patent/WO2015099368A1/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
    • B32B7/02—Physical, chemical or physicochemical properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/30—Layered products comprising a layer of synthetic resin comprising vinyl (co)polymers; comprising acrylic (co)polymers
    • B32B27/308—Layered products comprising a layer of synthetic resin comprising vinyl (co)polymers; comprising acrylic (co)polymers comprising acrylic (co)polymers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B23/00—Layered products comprising a layer of cellulosic plastic substances, i.e. substances obtained by chemical modification of cellulose, e.g. cellulose ethers, cellulose esters, viscose
    • B32B23/04—Layered products comprising a layer of cellulosic plastic substances, i.e. substances obtained by chemical modification of cellulose, e.g. cellulose ethers, cellulose esters, viscose comprising such cellulosic plastic substance as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B23/08—Layered products comprising a layer of cellulosic plastic substances, i.e. substances obtained by chemical modification of cellulose, e.g. cellulose ethers, cellulose esters, viscose comprising such cellulosic plastic substance as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B23/00—Layered products comprising a layer of cellulosic plastic substances, i.e. substances obtained by chemical modification of cellulose, e.g. cellulose ethers, cellulose esters, viscose
    • B32B23/20—Layered products comprising a layer of cellulosic plastic substances, i.e. substances obtained by chemical modification of cellulose, e.g. cellulose ethers, cellulose esters, viscose comprising esters
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/18—Layered products comprising a layer of synthetic resin characterised by the use of special additives
    • B32B27/22—Layered products comprising a layer of synthetic resin characterised by the use of special additives using plasticisers
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/30—Polarising elements
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/30—Polarising elements
    • G02B5/3025—Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state
    • G02B5/3033—Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state in the form of a thin sheet or foil, e.g. Polaroid
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/40—Properties of the layers or laminate having particular optical properties
    • B32B2307/42—Polarizing, birefringent, filtering
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2457/00—Electrical equipment
    • B32B2457/20—Displays, e.g. liquid crystal displays, plasma displays
    • B32B2457/202—LCD, i.e. liquid crystal displays

Definitions

  • the following disclosure relates to a polarizing plate including a cellulose acylate film and an acrylic film, and a liquid crystal display device having the same.
  • a polarizing plate generally has a structure in which a polarizer and a protective film are stacked using an aqueous adhesive layer made of a polyvinylalcohol based aqueous solution.
  • a polarizer a polyvinylalcohol film is generally used
  • a protective film a triacetyl cellulose film (hereinafter, referred to as “TAC film”) is used.
  • the existing in-plane phase difference Re and thickness direction phase difference Rth are significantly changed depending on high temperature and high humidity environments, and particularly, a change in a phase difference with respect to incident light in an inclined direction is large.
  • the polarizing plate having this stacking structure for a long period of time under high temperature and high humidity conditions, a degree of polarization may be deteriorated, the polarizer and the protective film may be separated from each other, or optical characteristics may be changed.
  • the polarizing plate including the TAC film having the above-mentioned characteristics as the protective film to a liquid crystal display device, viewing angle characteristics are changed depending on changes in ambient temperature and humidity environments, such that image quality may be deteriorated.
  • an acrylic resin As a material for compensating several disadvantages of the TAC film as described above, an acrylic resin has been known, but the acrylic resin does not have sufficient thermal resistance, and there are in-plane and thickness direction phase differences after stretching, such that the acrylic resin was not suitable for being used as the protective film.
  • the related art which is to use the acrylic resin instead of the TAC film, relates to a method of preparing an acrylic copolymer resin capable of being used as a protective film for a polarizer since after stretching, in-plane and thickness direction phase differences are rarely generated, a photoelastic coefficient is small, and thermal resistance is excellent.
  • the coefficient of thermal expansion means change in a length, an area, or a volume per unit temperature, and a coefficient of linear thermal expansion is defined as follows.
  • An embodiment of the present invention is directed to providing a polarizing plate capable of decreasing generation of curl by increasing a coefficient of thermal expansion of a cellulose acylate film to be similar to that of a film using an acrylic resin and using a specific additive to adjust a stretching rate.
  • Another embodiment of the present invention is directed to providing a method of manufacturing a film capable of adjusting a coefficient of thermal expansion of a cellulose acylate film to be similar to that of an acrylic film, and to providing an additive used in order to manufacture this film.
  • Another embodiment of the present invention is directed to providing a liquid crystal display device having the polarizing plate.
  • the present inventors tried to suppress generation of curls after manufacturing a polarizing plate by adjusting a coefficient of thermal expansion of a cellulose acylate film so as to be similar to a coefficient of thermal expansion of an acrylic resin film, and found that generation of curls was suppressed by adjusting an additive and a stretching condition in specific ranges in order to adjust the coefficient of thermal expansion of the cellulose acylate film, thereby completing the present invention.
  • a polarizing plate includes a cellulose acylate film, a polarizer, and an acrylic film that are sequentially stacked,
  • Equation 1 CTE ca is a coefficient of thermal expansion of the cellulose acylate film in a transverse direction (TD), and CTE ac is a coefficient of thermal expansion of the acrylic film).
  • CTE td is a coefficient of thermal expansion (ppm/K) in the transverse direction (TD)
  • CTE md is a coefficient of thermal expansion (ppm/K) in a machine direction (MD)).
  • a liquid crystal display device includes the polarizing plate as described above.
  • the polarizing plate manufactured by laminating the cellulose acylate film according to the present invention and the acrylic film may satisfy the following physical property: a height of a curl measured from a bottom is 30mm or less.
  • a polarizing plate includes a cellulose acylate film, a polarizer, and an acrylic film that are sequentially stacked,
  • Equation 1 CTE ca is a coefficient of thermal expansion of the cellulose acylate film in a transverse direction (TD), and CTE ac is a coefficient of thermal expansion of the acrylic film).
  • CTE td is a coefficient of thermal expansion (ppm/K) in the transverse direction (TD)
  • CTE md is a coefficient of thermal expansion (ppm/K) in a machine direction (MD)).
  • the cellulose acylate film and an acrylic film were laminated with each other and then used.
  • curls were generated after manufacturing the polarizing plate due to a difference in coefficient of thermal expansion between the acrylic film and the cellulose acylate film.
  • the present inventors found that in a range in which the coefficient of thermal expansion of the cellulose acylate film satisfies the following Equation 2, generation of curls may be prevented, thereby completing the present invention.
  • CTE td is the coefficient of thermal expansion (ppm/K) in the transverse direction (TD)
  • CTE md is the coefficient of thermal expansion (ppm/K) in the machine direction (MD)).
  • the coefficients of thermal expansion may satisfy the following Equation 3.
  • CTE td is the coefficient of thermal expansion (ppm/K) in the transverse direction (TD)
  • CTE md is the coefficient of thermal expansion (ppm/K) in the machine direction (MD)).
  • the coefficients of thermal expansion may satisfy the following Equation 4, more excellent physical properties may be exhibited.
  • Equation 4 CTE td is the coefficient of thermal expansion in the transverse direction (TD), and CTE md is the coefficient of thermal expansion in the machine direction (MD)).
  • the coefficients of thermal expansion may satisfy the following Equation 5, more excellent physical properties may be exhibited.
  • CTE td is the coefficient of thermal expansion in the transverse direction (TD)
  • CTE md is the coefficient of thermal expansion in the machine direction (MD)
  • the coefficient of thermal expansion in the transverse direction of the cellulose acylate film when the coefficient of thermal expansion in the transverse direction of the cellulose acylate film is in a range of 60 to 105 ppm/K, in the case of laminating the cellulose acylate film and the acrylic film with each other, curls may not be generated.
  • the coefficient of thermal expansion is in a range of preferably 60 to 95 ppm/K, more preferably 65 to 90 ppm/K, since the coefficient of thermal expansion of the cellulose acylate film is similar to that of the acrylic film, more excellent effect may be exhibited.
  • the cellulose acylate film according to the present invention may contain a cellulose acylate resin as a base resin and contain any one or two or more selected from compounds represented by the following Chemical Formulas 1 to 3, thereby making it possible to adjust the coefficient of thermal expansion in a desired range.
  • the cellulose acylate resin used in the present invention is ester of cellulose and acetic acid, all or some of the hydrogen atoms of hydroxyl group existing at 2-,3-, and 6-positions of a glucose unit constituting cellulose may be substituted with any one or two or more selected from acetyl groups, propionyl groups, and butyryl groups. More preferably, a cellulose acylate resin in which all or some of the hydrogen atoms of the hydroxyl groups existing at the 2-, 3-, and 6-positions of the glucose unit constituting cellulose are substituted with the acetyl group may be used. Specific examples thereof include diacetyl cellulose, triacetyl cellulose, and the like.
  • a degree of substitution of the cellulose acylate resin is not limited but may be preferably 2.0 to 3.0, and more preferably 2.5 to 2.9. The degree of substitution may be measured according to ASTM D-817-91.
  • a range of a molecular weight of the cellulose acylate resin is not limited, but a weight-average molecular weight thereof is preferably in a range of 200,000 to 350,000.
  • a molecular weight distribution Mw/Mn (Mw is a weight average of molecular weight, and Mn is a number average molecular weight) of the cellulose acylate resin is preferably 1.4 to 1.8, and more preferably, 1.5 to 1.7.
  • the compounds represented by Chemical Formulas 1 to 3 are used in order to adjust the coefficient of thermal expansion, and contents thereof are not limited.
  • the compounds represented by Chemical Formulas 1 to 3 may be contained so that a total content thereof is 0.1 to 20 parts by weight based on 100 parts by weight of the cellulose acylate resin, and a mixing weight ratio of the compound represented by Chemical Formula 1, the compound represented by Chemical Formula 2, and the compound represented by Chemical Formula 3 is 1 ⁇ 2: 1 ⁇ 1.5: 1.
  • the cellulose acylate film according to the present invention is prepared by a solvent cast method using a cellulose acylate dope solution.
  • a film is formed by casting a solution (dope) in which the cellulose acylate resin is dissolved in a solvent on a support and evaporating the solvent.
  • cellulose acylate particles may be preferably used as a raw material of the cellulose acylate dope solution.
  • the cellulose acylate particles have a shape close to sphere as possible, and it is preferable that the dope solution is prepared after drying the cellulose acylate particles so as to have a water content of 2 wt% or less, more preferably 1 wt% or less.
  • various kinds of additives according to the uses, for example, a plasticizer, an ultraviolet (UV) inhibitor, a deterioration inhibitor, fine particles, a peeling agent, an infrared (IR) absorber, an optically anisotropic controller, and the like may be added in respective preparing processes.
  • a plasticizer for example, an ultraviolet (UV) inhibitor, a deterioration inhibitor, fine particles, a peeling agent, an infrared (IR) absorber, an optically anisotropic controller, and the like
  • UV ultraviolet
  • IR infrared
  • optically anisotropic controller an optically anisotropic controller
  • the plasticizer is used in order to improve mechanical strength of the film, and in the case of using the plasticizer, a drying process time of the film may be decreased.
  • Any plasticizer may be used without limitation as long as it is generally used, and an example of the plasticizer may include phosphoric acid ester, carboxylic acid ester selected from phthalic acid ester or citric acid ester, and the like.
  • An example of phosphoric acid ester may include triphenyl phosphate (TPP), 4-biphenyldiphenylphosphate, tricresyl phosphate (TCP), and the like.
  • phthalic acid ester may include dimethyl phthalate (DMP), diethylphthalate (DEP), dibutylphthalate (DBP), dioctylphthalate (DOP), diphenylphthalate (DPP), diethylhexylphthalate (DEHP), and the like.
  • An example of the citric acid ester may include o-acetyltriethylcitrate (OACTE), o-acetyltributyl citrate (OACTB), and the like.
  • An example of another carboxylic acid ester may include butyl oleate, methyl acetyl lysine oleate, dibutyl sebacate, and various kinds of trimellitic acid ester.
  • the phthalic acid ester (DMP, DEP, DBP, DOP, DPP, and DEHP) plasticizer may be used.
  • a content of the plasticizer may be 2 to 20 parts by weight, more preferably, 5 to 15 parts by weight, based on 100 parts by weight of the cellulose acylate resin.
  • An example of the UV inhibitor may include a hydroxy benzophenone-based compound, a benzotriazole-based compound, a salicylic acid ester-based compound, a cyanoacrylate-based compound, and the like.
  • a content of the UV inhibitor may be 0.1 to 3 parts by weight, more preferably, 0.5 to 2 parts by weight, based on 100 parts by weight of the cellulose acylate resin.
  • deterioration inhibitor may include an antioxidant, a peroxide decomposer, a radical inhibitor, a metal deactivator, a deoxidizer, a light stabilizer (hindered amine, and the like), and the like.
  • a preferable example of the deterioration inhibitor may include butylated hydroxy toluene (BHT) and tribenzylamine (TBA).
  • BHT butylated hydroxy toluene
  • TAA tribenzylamine
  • a content of the deterioration inhibitor may be 0.01 to 5 parts by weight, more preferably, 0.1 to 1 part by weight, based on 100 parts by weight of the cellulose acylate resin.
  • the fine particles which are added in order to desirably inhibit curl of the film and favorably maintain a conveyance property, adhesion prevention in a roll shape, or scratch resistance, may be any one selected from an inorganic compound and an organic compound.
  • a preferable example of the inorganic compound may include a compound containing silicon, silicon dioxide, titanium oxide, zinc oxide, aluminum oxide, barium oxide, zirconium oxide, strontium oxide, antimony oxide, tin oxide, tin-antimony oxide, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, calcium phosphate, and the like.
  • the inorganic compound containing silicon, zirconium oxide, and the like may be used.
  • the fine particles have an average primary particle size of 80 nm or less, preferably, 5 to 80 nm, and more preferably, 5 to 60 nm, and most preferably, 8 to 50 nm. In the case in which the average primary particle size is more than 80 nm, surface smoothness of the film may be damaged.
  • a wavelength dispersion regulator may be further added as needed.
  • These additives may be used without limitation as long as they are generally used in the corresponding field.
  • an optional retardation additive may be further added in order to increase or decrease retardation as needed.
  • Any retardation additive may be used without limitation as long as it is generally used to adjust retardation in the corresponding field.
  • a cellulose acylate film to be applied to a VA mode liquid crystal display device may contain an additive increasing retardation and a cellulose acylate film to be applied to an IPS mode liquid crystal display device may contain an additive decreasing retardation.
  • the retardation additive has excellent compatibility with the compound represented by Chemical Formula 1 in a content range of 1 to 15 wt %, more preferably, 3 to 10 wt % in the film, such that a bleeding phenomenon may not occur and high quality images may be implemented.
  • the following cellulose acylate composition that is, a dope solution is prepared.
  • the cellulose acylate composition according to an exemplary embodiment of the present invention may contain the compounds represented by Chemical Formulas 1 to 3 so that a total content of the compounds is 0.1 to 20 parts by weight based on 100 parts by weight of the cellulose acylate resin.
  • a mixing weight ratio of the compound represented by Chemical Formula 1, the compound represented by Chemical Formula 2, and the compound represented by Chemical Formula 3 may be 1 ⁇ 2: 1 ⁇ 1.5: 1.
  • the cellulose acylate composition may further contain additives as needed.
  • a solid concentration of the dope solution may be 15 to 25 wt%, preferably 16 to 23 wt%.
  • the solid concentration of the dope is less than 15 wt%, fluidity is excessively high, such that it is difficult to form a film, and in the case in which the solid content is more than 25 wt%, it is difficult to completely dissolve a solid component.
  • a content of cellulose acylate resin may be 70 wt% or more, preferably 70 to 90 wt%, and more preferably 80 to 85 wt%, based on the entire solid content.
  • the cellulose acylate may be used by mixing two kinds or more of cellulose acylate of which degrees of substitution, degrees of polymerization or molecular weight distribution are different from each other.
  • a solvent for preparing the cellulose acylate composition is preferably an organic solvent.
  • organic solvent halogenated hydrocarbon is preferably used, and an example of the halogenated hydrocarbon includes chlorinated hydrocarbon, methylene chloride, and chloroform. Among them, methylene chloride is most preferable.
  • a solvent obtained by mixing organic solvents rather than halogenated hydrocarbon may be used as needed.
  • An example of the organic solvent rather than halogenated hydrocarbon may include ester, ketone, ether, alcohol, and hydrocarbon.
  • An example of the ester may include methyl formate, ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate, pentyl acetate, and the like
  • an example of the ketone may include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, methyl cyclohexanone, and the like
  • an example of the ether may include diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran
  • methylene chloride may be used as a main solvent, and alcohol may be used as a side-solvent.
  • methylene chloride and alcohol may be mixed at a weight ratio of 80:20 to 95:5 and then used.
  • the cellulose acylate composition may be prepared according to a room temperature, high temperature, or low temperature dissolution method.
  • a viscosity of the cellulose acylate composition is preferably 1 to 400 Pa ⁇ s at 40°C, more preferably, 10 to 200 Pa ⁇ s.
  • the cellulose acylate film may be manufactured by a general solvent cast method. More specifically, the prepared dope solution (cellulose acylate composition) is first stored in a storage tank, and foam contained in the dope solution is defoamed. The defoamed dope solution is transferred from a dope solution outlet through a pressurized quantitative gear pump capable of transferring a fixed quantity of liquid with high precision according to the number of rotation to a pressurized die, the dope solution is uniformly casted on an endlessly moved metal support from a mold (slit) of the pressurized die, and the casting film which is not completely dried is peeled from the metal support at a peeling point at which the metal support almost spins around.
  • a pressurized quantitative gear pump capable of transferring a fixed quantity of liquid with high precision according to the number of rotation to a pressurized die
  • the dope solution is uniformly casted on an endlessly moved metal support from a mold (slit) of the pressurized die, and the casting film which is not completely dried is
  • the film may be uniaxially and biaxially stretched in a machine direction and a transverse direction in a state in which a residual solvent amount is 10 to 40 wt %.
  • the film may be stretched in an off-line mode. The film may be stretched in the machine direction or the transverse direction or biaxially stretched in a simultaneous scheme or a sequential scheme.
  • a stretching rate is preferably 100 to 110 % in the machine direction (MD) and 103 to 105 % in the transverse direction (TD) (here, % indicates a length %).
  • the desired coefficient of thermal expansion may be achieved, a film having a higher coefficient of thermal expansion in the transverse direction (TD) as that in the machine direction (MD) may be manufactured, and generation of curl in a polarizing plate may be further suppressed.
  • a temperature is preferably in a range of 100°C below a glass transition temperature (Tg) of an optical film containing the compound of Chemical Formula 1 to 20 °C below the glass transition temperature (Tg).
  • a space temperature may be preferably - 50°C to 50°C, more preferably, - 30°C to 40°C, and most preferably, - 20°C to 30°C.
  • gas cooling the space general air, nitrogen, argon, or helium may be used.
  • a relative humidity is preferably 0 to 70%, more preferably 0 to 50%.
  • a temperature of the support (casting part) to which the cellulose acylate solution is applied may be preferably - 50°C to 130°C, more preferably, - 30°C to 25°C, and most preferably, - 20°C to 15°C.
  • cooled gas may be introduced into the casting part.
  • a cooling device may be disposed in the casting part to cool a space. In cooling the space, it is important to be cautious so that water is not attached to the casting part. In the case of cooling with a gas, it is preferable that the gas is prepared in a dried state.
  • a surface-treatment may be performed on the cellulose acylate film as needed.
  • the surface-treatment is generally performed in order to improve adhesion of the cellulose acylate film.
  • An example of the surface-treatment may include glow discharge treatment, ultraviolet irradiation treatment, corona treatment, flame treatment, saponification treatment, and the like.
  • a thickness of the cellulose acylate film is preferably 20 to 140 ⁇ m, more preferably, 20 to 80 ⁇ m.
  • a cellulose acylate film subjected to surface-treatment may be used, wherein the surface treatment may include hydrophilizing treatment, glow discharge treatment, corona discharge treatment, flame treatment, alkali saponification treatment, and the like.
  • the polarizer may be a polyvinyl alcohol film.
  • the polarizer may be stacked using an aqueous adhesive layer made of polyvinyl alcohol based aqueous solution.
  • the coefficient of thermal expansion of the acrylic film may be 70 to 75 ppm/K.
  • the coefficient of thermal expansion of the acrylic film is in range of a coefficient of thermal expansion of a general acrylic film, but is not limited thereto.
  • a height of the curl from a bottom may be 30 mm or less.
  • the polarizing plate may be applied as a polarizing plate.
  • the polarizing plate may use the cellulose acylate film and the acrylic film together with each other as protective films.
  • the liquid crystal display device since a liquid crystal cell in a liquid crystal display device is positioned between two sheets of polarizing plates, the liquid crystal display device has two sheets of polarizing plate protective films.
  • the cellulose acylate film according to the present invention may be positioned on any one of four sheets of polarizing plate protective films, but it is appropriate to use the cellulose acylate film as a protective film positioned between a polarizing plate and the liquid crystal cell of the liquid crystal display device.
  • the protective film positioned at an opposite side of the cellulose acylate film according to the present invention, that is, the acrylic film may form a transparent hard coating layer, an antiglare coating layer, an anti-reflection coating layer, and the like.
  • the liquid crystal display device having the polarizing plate is also included in the present invention.
  • one or two or more sheets of the polarizing plate according to the present invention may be stacked and used.
  • the polarizing plate according to the present invention may be used in a liquid crystal display device having various display modes, and a specific example of the display mode may include TN, IPS, FLC, AFLC, OCB, STN, ECB, VA, HAN, and the like. More specifically, the liquid crystal display device may be an IPS mode liquid crystal display device.
  • the liquid crystal display device may include a liquid crystal cell; and a polarizing plate disposed on at least one surface of the liquid crystal cell.
  • the polarizing plate may include a cellulose acylate film, a polarizer, and an acrylic film that are sequentially stacked, wherein the cellulose acylate film or acrylic film may be stacked adjacently to the liquid crystal cell.
  • the liquid crystal display device may be a liquid crystal display device in which the cellulose acylate film, the polarizer, the acrylic film, and the liquid crystal cell are sequentially stacked.
  • the liquid crystal display device may be a liquid crystal display device in which the cellulose acylate film, the polarizer, the acrylic film, the liquid crystal cell, the cellulose acylate film, the polarizer, and the acrylic film are sequentially stacked.
  • the liquid crystal display device may be a liquid crystal display device in which the acrylic film, the polarizer, the cellulose acylate film, and the liquid crystal cell are sequentially stacked.
  • the liquid crystal display device may be a liquid crystal display device in which the acrylic film, the polarizer, the cellulose acylate film, the liquid crystal cell, the acrylic film, the polarizer, and the cellulose acylate film are sequentially stacked.
  • a degree of substitution was measured according to ASTM D-817-91.
  • Films manufactured in the Examples and the Comparative Examples were cut at a size of 50 mm ⁇ 50 mm (length ⁇ width) to prepare samples, and thicknesses of the samples were measured using a thickness gauge (TESA- ⁇ HITE Height Gauge manufactured by Tesa technology). The thickness was measured at five points on the film sample including a central point thereof, respectively, and an average thereof was calculated.
  • a thickness gauge (TESA- ⁇ HITE Height Gauge manufactured by Tesa technology). The thickness was measured at five points on the film sample including a central point thereof, respectively, and an average thereof was calculated.
  • TMA thermo mechanical analysis
  • Measuring method Both ends of the prepared sample were fixed using a clamp and hung on a hook of TMA. A change in length was measured while raising a temperature, thereby calculating a CTE value corresponding to a gradient when the sample was fixed to the clamp, an effective length of the film was 10 mm, and the change in the length was measured at several ppm levels.
  • the sample was left at a constant temperature of 25°C for 10 minutes (purge gas: N 2 ) and then heated at a heating rate of 5°C/min in a temperature range of 25 to 120°C, and an average CTE value was calculated in a temperature range of 40 to 80°C.
  • the manufactured polarizing plate was spread on a flat bottom, whether or not curl was generated at an edge portion was confirmed by the naked eyes.
  • a height of the curl was measured as a height of a portion at which the curl was generated from the bottom using a ruler.
  • UV absorber 2-(2H-benzotriazol-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl)phenol was used.
  • UV absorber 2 parts by weight
  • Silicon dioxide (Average particle size: 16 nm)
  • the heated dope solution was transferred through a gear pump, filtered through a filter having an absolute filtration precision of 0.01mm, and then, filtered again through a cartridge filtration device having an absolute filtration precision of 5 ⁇ m.
  • the obtained dope solution through the filtering process was cast on a mirror surface stainless support through a casting die and peeled. An amount of remaining solvent at the time of peeling was adjusted so as to be 25 wt%. After being peeled, the film was stretched in a stretching machine at a stretching rate of 100% in a machine direction, connected to a tenter, and stretched again in a transverse direction of the film at a stretching rate of 103%. After the film came out of the tenter and each 150 mm of end portions at left and right sides of the film was removed.
  • the end-cut film was dried by a drier, both ends of the dried film were cut by 3 cm, and a knurling process with a height of 70 ⁇ m was performed at a portion of 10 mm from the end portions. Then, the film was wound in a roll shape. A dried thickness of the manufactured film was 60 ⁇ m. Physical properties of the manufactured cellulose acylate film were measured and shown in the following Table 1.
  • a polarizing plate having an entire thickness of 220 ⁇ m was manufactured by laminating the cellulose acylate film on one surface of a PVA polarizer film and an acrylic film (LG Chemical Ltd., CTE: 74.34 ppm/K) on the other surface thereof so as to be adhered to each other using an adhesive.
  • a film was manufactured using the same composition as that in Example 1 by the same method as in Example 1 except that the film was stretched at a stretching rate of 110% in a machine direction and then stretched in a transverse direction at a stretching rate of 105% at the time of manufacturing the film.
  • a dried thickness of the manufactured film was 60 ⁇ m.
  • Physical properties of the manufactured cellulose acylate film were measured and shown in the following Table 1.
  • a film was manufactured by the same method as in Example 1 except for using only 10 parts by weight of the compound represented by Chemical Formula 1 at the time of preparing a cellulose acylate film.
  • a dried thickness of the manufactured film was 60 ⁇ m.
  • Physical properties of the manufactured cellulose acylate film were measured and shown in the following Table 1.
  • a film was manufactured by the same method as in Example 1 except for using only 10 parts by weight of the compound represented by Chemical Formula 3 at the time of preparing a cellulose acylate film.
  • a dried thickness of the manufactured film was 60 ⁇ m.
  • Physical properties of the manufactured cellulose acylate film were measured and shown in the following Table 1.
  • a film was manufactured by the same method as in Example 1 except for using the following Composition instead of the composition in Example 1.
  • UV absorber 2 parts by weight
  • Silicon dioxide (average particle size: 16nm) 0.5 parts by weight
  • a dried thickness of the manufactured film was 60 ⁇ m.
  • Physical properties of the manufactured cellulose acylate film were measured and shown in the following Table 1.
  • a film was manufactured using the same composition as that in Example 1 by the same method in Example 1 except that the film was stretched at a stretching rate of 100.5% in a machine direction and then stretched in a transverse direction at a stretching rate of 105% at the time of manufacturing the film.
  • a dried thickness of the manufactured film was 60 ⁇ m.
  • Physical properties of the manufactured cellulose acylate film were measured and shown in the following Table 1.
  • a film was manufactured using the same composition as that in Example 1 by the same method in Example 1 except that the film was stretched at a stretching rate of 100% in a machine direction and then stretched in a transverse direction at a stretching rate of 120% at the time of manufacturing the film.
  • a dried thickness of the manufactured film was 60 ⁇ m.
  • Physical properties of the manufactured cellulose acylate film were measured and shown in the following Table 1.
  • a film was manufactured by the same method as in Example 1 except for using only 10 parts by weight of the compound represented by Chemical Formula 2 at the time of preparing a cellulose acylate film.
  • a dried thickness of the manufactured film was 60 ⁇ m.
  • Physical properties of the manufactured cellulose acylate film were measured and shown in the following Table 1.
  • TPP indicates triphenyl phosphate (Chemical Formula 1)
  • BDP indicates biphenyl diphenyl phosphate (Chemical Formula 2)
  • DOT indicates dioctyl terephthalate (Chemical Formula 3).
  • Comparative Examples 1 and 2 in spite of using the same additive as that in Examples 1 and 2, the coefficient of thermal expansion of the cellulose acylate film in the transverse direction was lower than that of the cellulose acylate film in the machine direction by changing the stretching rate. In the case of Comparative Example 1, it may be appreciated that even though a difference between the coefficients of thermal expansion of the cellulose acylate film in the transverse direction and the acrylic film was 0.1, the coefficient of thermal expansion in the transverse direction was lower than that in the machine direction, such that the curl having a high height was generated.

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Abstract

Provided is a cellulose acylate film for being used as an optical film, and more particularly, a cellulose acylate film used to manufacture a polarizing plate.

Description

POLARIZING PLATE AND LIQUID CRYSTAL DISPLAY DEVICE HAVING THE SAME
The following disclosure relates to a polarizing plate including a cellulose acylate film and an acrylic film, and a liquid crystal display device having the same.
A polarizing plate generally has a structure in which a polarizer and a protective film are stacked using an aqueous adhesive layer made of a polyvinylalcohol based aqueous solution. As the polarizer, a polyvinylalcohol film is generally used, and as the protective film, a triacetyl cellulose film (hereinafter, referred to as “TAC film”) is used.
In the TAC film, the existing in-plane phase difference Re and thickness direction phase difference Rth are significantly changed depending on high temperature and high humidity environments, and particularly, a change in a phase difference with respect to incident light in an inclined direction is large.
In the case of using the polarizing plate having this stacking structure for a long period of time under high temperature and high humidity conditions, a degree of polarization may be deteriorated, the polarizer and the protective film may be separated from each other, or optical characteristics may be changed.
Further, in the case of applying the polarizing plate including the TAC film having the above-mentioned characteristics as the protective film to a liquid crystal display device, viewing angle characteristics are changed depending on changes in ambient temperature and humidity environments, such that image quality may be deteriorated.
As a material for compensating several disadvantages of the TAC film as described above, an acrylic resin has been known, but the acrylic resin does not have sufficient thermal resistance, and there are in-plane and thickness direction phase differences after stretching, such that the acrylic resin was not suitable for being used as the protective film.
In order to solve this problem, a technology of lowering a coefficient of thermal expansion (CTE) of an acrylic resin to be similar to that of the TAC film by adjusting a molecular weight of an acrylic copolymer resin to induce formation of a glutaric acid anhydride structure has been disclosed in Korean Patent Laid-Open Publication No. 10-2012-0116840 (October 23, 2012).
The related art, which is to use the acrylic resin instead of the TAC film, relates to a method of preparing an acrylic copolymer resin capable of being used as a protective film for a polarizer since after stretching, in-plane and thickness direction phase differences are rarely generated, a photoelastic coefficient is small, and thermal resistance is excellent.
The coefficient of thermal expansion (CTE) means change in a length, an area, or a volume per unit temperature, and a coefficient of linear thermal expansion is defined as follows.
Figure PCTKR2014012614-appb-I000001
In general, it is known that the CTE is adjusted by stretching a film, but there is a limitation in increasing the CTE of the TAC film by stretching, and the development of an additive for increasing the CTE has been required.
[Related Art Document]
[Patent Document]
Korean Patent Laid-Open Publication No. 10-2012-0116840 (October 23, 2012)
An embodiment of the present invention is directed to providing a polarizing plate capable of decreasing generation of curl by increasing a coefficient of thermal expansion of a cellulose acylate film to be similar to that of a film using an acrylic resin and using a specific additive to adjust a stretching rate.
Another embodiment of the present invention is directed to providing a method of manufacturing a film capable of adjusting a coefficient of thermal expansion of a cellulose acylate film to be similar to that of an acrylic film, and to providing an additive used in order to manufacture this film.
Another embodiment of the present invention is directed to providing a liquid crystal display device having the polarizing plate.
The present inventors tried to suppress generation of curls after manufacturing a polarizing plate by adjusting a coefficient of thermal expansion of a cellulose acylate film so as to be similar to a coefficient of thermal expansion of an acrylic resin film, and found that generation of curls was suppressed by adjusting an additive and a stretching condition in specific ranges in order to adjust the coefficient of thermal expansion of the cellulose acylate film, thereby completing the present invention.
In one general aspect, a polarizing plate includes a cellulose acylate film, a polarizer, and an acrylic film that are sequentially stacked,
wherein a coefficient of thermal expansion of the cellulose acylate film and a coefficient of thermal expansion of the acrylic film satisfy the following Equations 1 and 2:
[Equation 1]
0 ppm/K ≤ |CTEca - CTEac| ≤ 30 ppm/K
(In Equation 1, CTEca is a coefficient of thermal expansion of the cellulose acylate film in a transverse direction (TD), and CTEac is a coefficient of thermal expansion of the acrylic film).
[Equation 2]
CTEtd > CTEmd
(In Equation 2, CTEtd is a coefficient of thermal expansion (ppm/K) in the transverse direction (TD), and CTEmd is a coefficient of thermal expansion (ppm/K) in a machine direction (MD)).
In another general aspect, a liquid crystal display device includes the polarizing plate as described above.
The polarizing plate manufactured by laminating the cellulose acylate film according to the present invention and the acrylic film may satisfy the following physical property: a height of a curl measured from a bottom is 30mm or less.
Hereinafter, an aspect of a polarizing plate according to the present invention will be described, but the present invention is not limited thereto.
In an aspect of the present invention, a polarizing plate includes a cellulose acylate film, a polarizer, and an acrylic film that are sequentially stacked,
wherein a coefficient of thermal expansion of the cellulose acylate film and a coefficient of thermal expansion of the acrylic film satisfy the following Equations 1 and 2:
[Equation 1]
0 ppm/K ≤ |CTEca - CTEac| ≤ 30 ppm/K
(In Equation 1, CTEca is a coefficient of thermal expansion of the cellulose acylate film in a transverse direction (TD), and CTEac is a coefficient of thermal expansion of the acrylic film).
[Equation 2]
CTEtd > CTEmd
(In Equation 2, CTEtd is a coefficient of thermal expansion (ppm/K) in the transverse direction (TD), and CTEmd is a coefficient of thermal expansion (ppm/K) in a machine direction (MD)).
At the time of manufacturing the polarizing plate, in the case of using a cellulose acylate film as a protective film, since a change in the phase difference was generated under high temperature and high humidity conditions, in order to solve this problem, the cellulose acylate film and an acrylic film were laminated with each other and then used. However, there was a problem that curls were generated after manufacturing the polarizing plate due to a difference in coefficient of thermal expansion between the acrylic film and the cellulose acylate film. Since a coefficient of thermal expansion of the acrylic film is about 70 to 75 ppm/K, and a coefficient of thermal expansion of an unstretched triacetyl cellulose film is about 50 to 65 ppm/K, the present inventors conducted studies to adjust the coefficient of thermal expansion of the cellulose acylate film to be similar to that of the acrylic film to prevent generation of curls.
As a result, it was judged that generation of curls may be suppressed in a range in which the coefficient of thermal expansion of the cellulose acylate film and the coefficient of thermal expansion of the acrylic film satisfy Equation 1. However, even though the coefficients of thermal expansion satisfy Equation 1, curls were generated in some cases.
Therefore, as a result obtained by performing experiments through changing the stretching and additive conditions, the present inventors found that in a range in which the coefficient of thermal expansion of the cellulose acylate film satisfies the following Equation 2, generation of curls may be prevented, thereby completing the present invention.
[Equation 2]
CTEtd > CTEmd
(In Equation 2, CTEtd is the coefficient of thermal expansion (ppm/K) in the transverse direction (TD), and CTEmd is the coefficient of thermal expansion (ppm/K) in the machine direction (MD)).
That is, in the present invention, it was confirmed that in a range in which the coefficients of thermal expansion of the cellulose acylate film and the acrylic film satisfy Equation 1, and at the same time, the coefficient of thermal expansion of the cellulose acylate film in the transverse direction is larger than the coefficient of thermal expansion thereof in the machine direction, generation of curls were suppressed.
More preferably, the coefficients of thermal expansion may satisfy the following Equation 3.
[Equation 3]
CTEtd - CTEmd > 3 ppm/K
(In Equation 3, CTEtd is the coefficient of thermal expansion (ppm/K) in the transverse direction (TD), and CTEmd is the coefficient of thermal expansion (ppm/K) in the machine direction (MD)).
More preferably, the coefficients of thermal expansion may satisfy the following Equation 4, more excellent physical properties may be exhibited.
[Equation 4]
CTEtd - CTEmd > 15 ppm/K
(In Equation 4, CTEtd is the coefficient of thermal expansion in the transverse direction (TD), and CTEmd is the coefficient of thermal expansion in the machine direction (MD)).
More preferably, the coefficients of thermal expansion may satisfy the following Equation 5, more excellent physical properties may be exhibited.
[Equation 5]
CTEtd - CTEmd > 35 ppm/K
(In Equation 5, CTEtd is the coefficient of thermal expansion in the transverse direction (TD), and CTEmd is the coefficient of thermal expansion in the machine direction (MD)).
In an aspect of the present invention, when the coefficient of thermal expansion in the transverse direction of the cellulose acylate film is in a range of 60 to 105 ppm/K, in the case of laminating the cellulose acylate film and the acrylic film with each other, curls may not be generated. When the coefficient of thermal expansion is in a range of preferably 60 to 95 ppm/K, more preferably 65 to 90 ppm/K, since the coefficient of thermal expansion of the cellulose acylate film is similar to that of the acrylic film, more excellent effect may be exhibited.
The cellulose acylate film according to the present invention may contain a cellulose acylate resin as a base resin and contain any one or two or more selected from compounds represented by the following Chemical Formulas 1 to 3, thereby making it possible to adjust the coefficient of thermal expansion in a desired range.
[Chemical Formula 1]
Figure PCTKR2014012614-appb-I000002
[Chemical Formula 2]
Figure PCTKR2014012614-appb-I000003
[Chemical Formula 3]
Figure PCTKR2014012614-appb-I000004
The cellulose acylate resin used in the present invention is ester of cellulose and acetic acid, all or some of the hydrogen atoms of hydroxyl group existing at 2-,3-, and 6-positions of a glucose unit constituting cellulose may be substituted with any one or two or more selected from acetyl groups, propionyl groups, and butyryl groups. More preferably, a cellulose acylate resin in which all or some of the hydrogen atoms of the hydroxyl groups existing at the 2-, 3-, and 6-positions of the glucose unit constituting cellulose are substituted with the acetyl group may be used. Specific examples thereof include diacetyl cellulose, triacetyl cellulose, and the like.
A degree of substitution of the cellulose acylate resin is not limited but may be preferably 2.0 to 3.0, and more preferably 2.5 to 2.9. The degree of substitution may be measured according to ASTM D-817-91. A range of a molecular weight of the cellulose acylate resin is not limited, but a weight-average molecular weight thereof is preferably in a range of 200,000 to 350,000. Further, a molecular weight distribution Mw/Mn (Mw is a weight average of molecular weight, and Mn is a number average molecular weight) of the cellulose acylate resin is preferably 1.4 to 1.8, and more preferably, 1.5 to 1.7.
The compounds represented by Chemical Formulas 1 to 3 are used in order to adjust the coefficient of thermal expansion, and contents thereof are not limited. As a specific example, the compounds represented by Chemical Formulas 1 to 3 may be contained so that a total content thereof is 0.1 to 20 parts by weight based on 100 parts by weight of the cellulose acylate resin, and a mixing weight ratio of the compound represented by Chemical Formula 1, the compound represented by Chemical Formula 2, and the compound represented by Chemical Formula 3 is 1~2: 1~1.5: 1.
It is preferable that the cellulose acylate film according to the present invention is prepared by a solvent cast method using a cellulose acylate dope solution. In the solvent cast method, a film is formed by casting a solution (dope) in which the cellulose acylate resin is dissolved in a solvent on a support and evaporating the solvent.
As a raw material of the cellulose acylate dope solution, cellulose acylate particles may be preferably used. In this case, it is preferable that 90 wt% of the cellulose acylate particles have an average particle size of 0.5 to 5 mm. In addition, it is preferable that at least 50 wt% of the cellulose acylate particles have an average particle size of 1 to 4 mm.
It is preferable that the cellulose acylate particles have a shape close to sphere as possible, and it is preferable that the dope solution is prepared after drying the cellulose acylate particles so as to have a water content of 2 wt% or less, more preferably 1 wt% or less.
In the cellulose acylate dope solution used in the solvent cast method, various kinds of additives according to the uses, for example, a plasticizer, an ultraviolet (UV) inhibitor, a deterioration inhibitor, fine particles, a peeling agent, an infrared (IR) absorber, an optically anisotropic controller, and the like may be added in respective preparing processes. Specific kinds of these additives are not particularly limited as long as they are generally used in the art, and contents thereof may be in a range in which the physical properties of the film are not deteriorated. The time to add the additive is determined depending on the kind of additive. A process of adding the additives may be performed at the end of the preparation of the dope solution.
The plasticizer is used in order to improve mechanical strength of the film, and in the case of using the plasticizer, a drying process time of the film may be decreased. Any plasticizer may be used without limitation as long as it is generally used, and an example of the plasticizer may include phosphoric acid ester, carboxylic acid ester selected from phthalic acid ester or citric acid ester, and the like. An example of phosphoric acid ester may include triphenyl phosphate (TPP), 4-biphenyldiphenylphosphate, tricresyl phosphate (TCP), and the like. An example of phthalic acid ester may include dimethyl phthalate (DMP), diethylphthalate (DEP), dibutylphthalate (DBP), dioctylphthalate (DOP), diphenylphthalate (DPP), diethylhexylphthalate (DEHP), and the like. An example of the citric acid ester may include o-acetyltriethylcitrate (OACTE), o-acetyltributyl citrate (OACTB), and the like. An example of another carboxylic acid ester may include butyl oleate, methyl acetyl lysine oleate, dibutyl sebacate, and various kinds of trimellitic acid ester. Preferably, the phthalic acid ester (DMP, DEP, DBP, DOP, DPP, and DEHP) plasticizer may be used. A content of the plasticizer may be 2 to 20 parts by weight, more preferably, 5 to 15 parts by weight, based on 100 parts by weight of the cellulose acylate resin.
An example of the UV inhibitor may include a hydroxy benzophenone-based compound, a benzotriazole-based compound, a salicylic acid ester-based compound, a cyanoacrylate-based compound, and the like. A content of the UV inhibitor may be 0.1 to 3 parts by weight, more preferably, 0.5 to 2 parts by weight, based on 100 parts by weight of the cellulose acylate resin.
An example of the deterioration inhibitor may include an antioxidant, a peroxide decomposer, a radical inhibitor, a metal deactivator, a deoxidizer, a light stabilizer (hindered amine, and the like), and the like. In particular, a preferable example of the deterioration inhibitor may include butylated hydroxy toluene (BHT) and tribenzylamine (TBA). A content of the deterioration inhibitor may be 0.01 to 5 parts by weight, more preferably, 0.1 to 1 part by weight, based on 100 parts by weight of the cellulose acylate resin.
The fine particles, which are added in order to desirably inhibit curl of the film and favorably maintain a conveyance property, adhesion prevention in a roll shape, or scratch resistance, may be any one selected from an inorganic compound and an organic compound. For example, a preferable example of the inorganic compound may include a compound containing silicon, silicon dioxide, titanium oxide, zinc oxide, aluminum oxide, barium oxide, zirconium oxide, strontium oxide, antimony oxide, tin oxide, tin-antimony oxide, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, calcium phosphate, and the like. More preferably, the inorganic compound containing silicon, zirconium oxide, and the like, may be used. The fine particles have an average primary particle size of 80 nm or less, preferably, 5 to 80 nm, and more preferably, 5 to 60 nm, and most preferably, 8 to 50 nm. In the case in which the average primary particle size is more than 80 nm, surface smoothness of the film may be damaged.
In addition, a wavelength dispersion regulator, and the like, may be further added as needed. These additives may be used without limitation as long as they are generally used in the corresponding field.
In addition, an optional retardation additive may be further added in order to increase or decrease retardation as needed. Any retardation additive may be used without limitation as long as it is generally used to adjust retardation in the corresponding field. In general, a cellulose acylate film to be applied to a VA mode liquid crystal display device may contain an additive increasing retardation and a cellulose acylate film to be applied to an IPS mode liquid crystal display device may contain an additive decreasing retardation. The retardation additive has excellent compatibility with the compound represented by Chemical Formula 1 in a content range of 1 to 15 wt %, more preferably, 3 to 10 wt % in the film, such that a bleeding phenomenon may not occur and high quality images may be implemented.
Next, a method of manufacturing the cellulose acylate film according to the present invention will be described. In order to manufacture the cellulose acylate film according to the present invention, the following cellulose acylate composition, that is, a dope solution is prepared.
The cellulose acylate composition according to an exemplary embodiment of the present invention may contain the compounds represented by Chemical Formulas 1 to 3 so that a total content of the compounds is 0.1 to 20 parts by weight based on 100 parts by weight of the cellulose acylate resin. In addition, a mixing weight ratio of the compound represented by Chemical Formula 1, the compound represented by Chemical Formula 2, and the compound represented by Chemical Formula 3 may be 1~2: 1~1.5: 1. In addition, the cellulose acylate composition may further contain additives as needed.
In the present invention, a solid concentration of the dope solution may be 15 to 25 wt%, preferably 16 to 23 wt%. In the case in which the solid concentration of the dope is less than 15 wt%, fluidity is excessively high, such that it is difficult to form a film, and in the case in which the solid content is more than 25 wt%, it is difficult to completely dissolve a solid component.
In an aspect of the present invention, a content of cellulose acylate resin may be 70 wt% or more, preferably 70 to 90 wt%, and more preferably 80 to 85 wt%, based on the entire solid content. In addition, the cellulose acylate may be used by mixing two kinds or more of cellulose acylate of which degrees of substitution, degrees of polymerization or molecular weight distribution are different from each other.
In the case of manufacturing the film by a solvent cast method, a solvent for preparing the cellulose acylate composition (dope solution) is preferably an organic solvent. As the organic solvent, halogenated hydrocarbon is preferably used, and an example of the halogenated hydrocarbon includes chlorinated hydrocarbon, methylene chloride, and chloroform. Among them, methylene chloride is most preferable.
In addition, a solvent obtained by mixing organic solvents rather than halogenated hydrocarbon may be used as needed. An example of the organic solvent rather than halogenated hydrocarbon may include ester, ketone, ether, alcohol, and hydrocarbon. An example of the ester may include methyl formate, ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate, pentyl acetate, and the like, an example of the ketone may include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, methyl cyclohexanone, and the like, an example of the ether may include diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, anisole, phenetol, and the like, and an example of the alcohol may include 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 side-solvent. Specifically, methylene chloride and alcohol may be mixed at a weight ratio of 80:20 to 95:5 and then used.
The cellulose acylate composition may be prepared according to a room temperature, high temperature, or low temperature dissolution method.
A viscosity of the cellulose acylate composition is preferably 1 to 400 Pa·s at 40℃, more preferably, 10 to 200 Pa·s.
The cellulose acylate film may be manufactured by a general solvent cast method. More specifically, the prepared dope solution (cellulose acylate composition) is first stored in a storage tank, and foam contained in the dope solution is defoamed. The defoamed dope solution is transferred from a dope solution outlet through a pressurized quantitative gear pump capable of transferring a fixed quantity of liquid with high precision according to the number of rotation to a pressurized die, the dope solution is uniformly casted on an endlessly moved metal support from a mold (slit) of the pressurized die, and the casting film which is not completely dried is peeled from the metal support at a peeling point at which the metal support almost spins around. After both ends of the manufactured web are inserted into a clip and conveyed to a tenter while maintaining a width thereof and dried, the dried material is conveyed to a roller of a drying apparatus, dried, and then wound by a winder so as to have a predetermined length. In addition, at the time of manufacturing the casting film, the film may be uniaxially and biaxially stretched in a machine direction and a transverse direction in a state in which a residual solvent amount is 10 to 40 wt %. Alternatively, after the casting film is manufactured, the film may be stretched in an off-line mode. The film may be stretched in the machine direction or the transverse direction or biaxially stretched in a simultaneous scheme or a sequential scheme. A stretching rate is preferably 100 to 110 % in the machine direction (MD) and 103 to 105 % in the transverse direction (TD) (here, % indicates a length %). In the above-mentioned stretching range, the desired coefficient of thermal expansion may be achieved, a film having a higher coefficient of thermal expansion in the transverse direction (TD) as that in the machine direction (MD) may be manufactured, and generation of curl in a polarizing plate may be further suppressed.
At the time of stretching, a temperature is preferably in a range of 100℃ below a glass transition temperature (Tg) of an optical film containing the compound of Chemical Formula 1 to 20 ℃ below the glass transition temperature (Tg). At the time of applying the solution, a space temperature may be preferably - 50℃ to 50℃, more preferably, - 30℃ to 40℃, and most preferably, - 20℃ to 30℃. As gas cooling the space, general air, nitrogen, argon, or helium may be used. A relative humidity is preferably 0 to 70%, more preferably 0 to 50%.
A temperature of the support (casting part) to which the cellulose acylate solution is applied may be preferably - 50℃ to 130℃, more preferably, - 30℃ to 25℃, and most preferably, - 20℃ to 15℃. In order to cool the casting part, cooled gas may be introduced into the casting part. A cooling device may be disposed in the casting part to cool a space. In cooling the space, it is important to be cautious so that water is not attached to the casting part. In the case of cooling with a gas, it is preferable that the gas is prepared in a dried state.
In addition, a surface-treatment may be performed on the cellulose acylate film as needed. The surface-treatment is generally performed in order to improve adhesion of the cellulose acylate film. An example of the surface-treatment may include glow discharge treatment, ultraviolet irradiation treatment, corona treatment, flame treatment, saponification treatment, and the like.
A thickness of the cellulose acylate film is preferably 20 to 140 μm, more preferably, 20 to 80 μm.
In the case of using the cellulose acylate film according to the present invention as a polarizing plate protective film, a cellulose acylate film subjected to surface-treatment may be used, wherein the surface treatment may include hydrophilizing treatment, glow discharge treatment, corona discharge treatment, flame treatment, alkali saponification treatment, and the like.
In the polarizing plate according to the present invention, the polarizer may be a polyvinyl alcohol film.
In addition, in the polarizing plate, the polarizer may be stacked using an aqueous adhesive layer made of polyvinyl alcohol based aqueous solution.
In the polarizing plate according to the present invention, the coefficient of thermal expansion of the acrylic film may be 70 to 75 ppm/K. The coefficient of thermal expansion of the acrylic film is in range of a coefficient of thermal expansion of a general acrylic film, but is not limited thereto.
In the polarizing plate according to the present invention, a height of the curl from a bottom may be 30 mm or less. Within the above-mentioned range, the polarizing plate may be applied as a polarizing plate.
In the present invention, the polarizing plate may use the cellulose acylate film and the acrylic film together with each other as protective films.
In general, since a liquid crystal cell in a liquid crystal display device is positioned between two sheets of polarizing plates, the liquid crystal display device has two sheets of polarizing plate protective films. The cellulose acylate film according to the present invention may be positioned on any one of four sheets of polarizing plate protective films, but it is appropriate to use the cellulose acylate film as a protective film positioned between a polarizing plate and the liquid crystal cell of the liquid crystal display device. The protective film positioned at an opposite side of the cellulose acylate film according to the present invention, that is, the acrylic film may form a transparent hard coating layer, an antiglare coating layer, an anti-reflection coating layer, and the like.
The liquid crystal display device having the polarizing plate is also included in the present invention. In this case, one or two or more sheets of the polarizing plate according to the present invention may be stacked and used.
The polarizing plate according to the present invention may be used in a liquid crystal display device having various display modes, and a specific example of the display mode may include TN, IPS, FLC, AFLC, OCB, STN, ECB, VA, HAN, and the like. More specifically, the liquid crystal display device may be an IPS mode liquid crystal display device.
In an aspect of the present invention, the liquid crystal display device may include a liquid crystal cell; and a polarizing plate disposed on at least one surface of the liquid crystal cell. In this case, the polarizing plate may include a cellulose acylate film, a polarizer, and an acrylic film that are sequentially stacked, wherein the cellulose acylate film or acrylic film may be stacked adjacently to the liquid crystal cell.
As a more specific example, the liquid crystal display device may be a liquid crystal display device in which the cellulose acylate film, the polarizer, the acrylic film, and the liquid crystal cell are sequentially stacked.
In another aspect, the liquid crystal display device may be a liquid crystal display device in which the cellulose acylate film, the polarizer, the acrylic film, the liquid crystal cell, the cellulose acylate film, the polarizer, and the acrylic film are sequentially stacked.
In another aspect, the liquid crystal display device may be a liquid crystal display device in which the acrylic film, the polarizer, the cellulose acylate film, and the liquid crystal cell are sequentially stacked.
In another aspect, the liquid crystal display device may be a liquid crystal display device in which the acrylic film, the polarizer, the cellulose acylate film, the liquid crystal cell, the acrylic film, the polarizer, and the cellulose acylate film are sequentially stacked.
Hereinafter, Examples will be provided in order to describe the present invention in more detail. However, the present invention is not limited to the following Examples.
Hereinafter, physical properties of films were measured by the following measuring methods.
1) Degree of Substitution
A degree of substitution was measured according to ASTM D-817-91.
2) Thickness of Film
Films manufactured in the Examples and the Comparative Examples were cut at a size of 50 mm × 50 mm (length × width) to prepare samples, and thicknesses of the samples were measured using a thickness gauge (TESA-μHITE Height Gauge manufactured by Tesa technology). The thickness was measured at five points on the film sample including a central point thereof, respectively, and an average thereof was calculated.
3) Coefficient of Thermal Expansion
After MD/TD samples of the manufactured films were prepared at a size of 4 × 16mm2, test was performed 7 times, and an average value thereof was used.
Apparatus: TMA (thermo mechanical analysis) (Mettler Toledo)
Measuring method: Both ends of the prepared sample were fixed using a clamp and hung on a hook of TMA. A change in length was measured while raising a temperature, thereby calculating a CTE value corresponding to a gradient when the sample was fixed to the clamp, an effective length of the film was 10 mm, and the change in the length was measured at several ppm levels.
Conditions: The sample was left at a constant temperature of 25℃ for 10 minutes (purge gas: N2) and then heated at a heating rate of 5℃/min in a temperature range of 25 to 120℃, and an average CTE value was calculated in a temperature range of 40 to 80℃.
4) Height of Curl
After manufacturing a polarizing plate, the manufactured polarizing plate was spread on a flat bottom, whether or not curl was generated at an edge portion was confirmed by the naked eyes. A height of the curl was measured as a height of a portion at which the curl was generated from the bottom using a ruler.
[Example 1]
1) Preparation of Cellulose acetate composition (dope solution )
The following composition was put into a stirrer and dissolved at a temperature of 30℃.
In the following composition, as the UV absorber, 2-(2H-benzotriazol-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl)phenol was used.
Cellulose triacetate powder (degree of substitution: 2.87) 100 parts by weight
Chemical Formula 1 4 parts by weight
Chemical Formula 2 3.5 parts by weight
Chemical Formula 3 3 parts by weight
Methylene chloride 440 parts by weight
Methanol 50 parts by weight
UV absorber 2 parts by weight
Silicon dioxide (Average particle size: 16 nm)
0.5 parts by weight
After the obtained dope solution was heated to 30℃, the heated dope solution was transferred through a gear pump, filtered through a filter having an absolute filtration precision of 0.01mm, and then, filtered again through a cartridge filtration device having an absolute filtration precision of 5㎛.
2) Manufacturing of Cellulose Acylate Film
The obtained dope solution through the filtering process was cast on a mirror surface stainless support through a casting die and peeled. An amount of remaining solvent at the time of peeling was adjusted so as to be 25 wt%. After being peeled, the film was stretched in a stretching machine at a stretching rate of 100% in a machine direction, connected to a tenter, and stretched again in a transverse direction of the film at a stretching rate of 103%. After the film came out of the tenter and each 150 mm of end portions at left and right sides of the film was removed. The end-cut film was dried by a drier, both ends of the dried film were cut by 3 cm, and a knurling process with a height of 70 μm was performed at a portion of 10 mm from the end portions. Then, the film was wound in a roll shape. A dried thickness of the manufactured film was 60 ㎛. Physical properties of the manufactured cellulose acylate film were measured and shown in the following Table 1.
3) Manufacturing of Polarizing Plate
A polarizing plate having an entire thickness of 220 ㎛ was manufactured by laminating the cellulose acylate film on one surface of a PVA polarizer film and an acrylic film (LG Chemical Ltd., CTE: 74.34 ppm/K) on the other surface thereof so as to be adhered to each other using an adhesive.
Whether or not curl was formed in the manufactured polarizing plate was observed, and a height of the curl was measured and shown in the following Table 1.
[Example 2]
A film was manufactured using the same composition as that in Example 1 by the same method as in Example 1 except that the film was stretched at a stretching rate of 110% in a machine direction and then stretched in a transverse direction at a stretching rate of 105% at the time of manufacturing the film.
A dried thickness of the manufactured film was 60 ㎛. Physical properties of the manufactured cellulose acylate film were measured and shown in the following Table 1.
In addition, after a polarizing plate was manufactured by the same method, whether or not curl was formed in the manufactured polarizing plate was observed, and a height of the curl was measured and shown in the following Table 1.
[Example 3]
A film was manufactured by the same method as in Example 1 except for using only 10 parts by weight of the compound represented by Chemical Formula 1 at the time of preparing a cellulose acylate film.
A dried thickness of the manufactured film was 60 ㎛. Physical properties of the manufactured cellulose acylate film were measured and shown in the following Table 1.
In addition, after a polarizing plate was manufactured by the same method, whether or not curl was formed in the manufactured polarizing plate was observed, and a height of the curl was measured and shown in the following Table 1.
[Example 4]
A film was manufactured by the same method as in Example 1 except for using only 10 parts by weight of the compound represented by Chemical Formula 3 at the time of preparing a cellulose acylate film.
A dried thickness of the manufactured film was 60 ㎛. Physical properties of the manufactured cellulose acylate film were measured and shown in the following Table 1.
In addition, after a polarizing plate was manufactured by the same method, whether or not curl was formed in the manufactured polarizing plate was observed, and a height of the curl was measured and shown in the following Table 1.
[Example 5]
A film was manufactured by the same method as in Example 1 except for using the following Composition instead of the composition in Example 1.
Cellulose triacetate powder (degree of substitution: 2.87) 100 parts by weight
Chemical Formula 1 7 parts by weight
Chemical Formula 2 3.5 parts by weight
Methylene chloride 440 parts by weight
Methanol 50 parts by weight
UV absorber 2 parts by weight
Silicon dioxide (average particle size: 16nm) 0.5 parts by weight
A dried thickness of the manufactured film was 60 ㎛. Physical properties of the manufactured cellulose acylate film were measured and shown in the following Table 1.
In addition, after a polarizing plate was manufactured by the same method, whether or not curl was formed in the manufactured polarizing plate was observed, and a height of the curl was measured and shown in the following Table 1.
[Comparative example 1]
A film was manufactured using the same composition as that in Example 1 by the same method in Example 1 except that the film was stretched at a stretching rate of 100.5% in a machine direction and then stretched in a transverse direction at a stretching rate of 105% at the time of manufacturing the film.
A dried thickness of the manufactured film was 60 ㎛. Physical properties of the manufactured cellulose acylate film were measured and shown in the following Table 1.
In addition, after a polarizing plate was manufactured by the same method, whether or not curl was formed in the manufactured polarizing plate was observed, and a height of the curl was measured and shown in the following Table 1.
[Comparative example 2]
A film was manufactured using the same composition as that in Example 1 by the same method in Example 1 except that the film was stretched at a stretching rate of 100% in a machine direction and then stretched in a transverse direction at a stretching rate of 120% at the time of manufacturing the film.
A dried thickness of the manufactured film was 60 ㎛. Physical properties of the manufactured cellulose acylate film were measured and shown in the following Table 1.
In addition, after a polarizing plate was manufactured by the same method, whether or not curl was formed in the manufactured polarizing plate was observed, and a height of the curl was measured and shown in the following Table 1.
[Comparative example 3]
A film was manufactured by the same method as in Example 1 except for using only 10 parts by weight of the compound represented by Chemical Formula 2 at the time of preparing a cellulose acylate film.
A dried thickness of the manufactured film was 60 ㎛. Physical properties of the manufactured cellulose acylate film were measured and shown in the following Table 1.
In addition, after a polarizing plate was manufactured by the same method, whether or not curl was formed in the manufactured polarizing plate was observed, and a height of the curl was measured and shown in the following Table 1.
[Table 1]
Figure PCTKR2014012614-appb-I000005
In Table 1, TPP indicates triphenyl phosphate (Chemical Formula 1), BDP indicates biphenyl diphenyl phosphate (Chemical Formula 2), and DOT indicates dioctyl terephthalate (Chemical Formula 3).
As shown in Table 1, it may be appreciated that in the case in which the coefficient of thermal expansion of the cellulose acylate film in the transverse direction was higher than that of the cellulose acylate film in the machine direction, the height of the curl was further decreased, and in the case in which a difference between the coefficients of thermal expansion of the cellulose acylate film in the transverse direction and the acrylic film was in a range of 0 to 30 ppm/K and at the same time, the coefficient of thermal expansion of the cellulose acylate film in the transverse direction was higher than that of the cellulose acylate film in the machine direction, generation of the curl was decreased.
Particularly, as shown in Examples 1 and 2, it was confirmed that in the case of using a mixture of TPP, BDP, and DOT, the CTE value in the transverse direction was further increased, and the height of the curl was further decreased.
In Comparative Examples 1 and 2, in spite of using the same additive as that in Examples 1 and 2, the coefficient of thermal expansion of the cellulose acylate film in the transverse direction was lower than that of the cellulose acylate film in the machine direction by changing the stretching rate. In the case of Comparative Example 1, it may be appreciated that even though a difference between the coefficients of thermal expansion of the cellulose acylate film in the transverse direction and the acrylic film was 0.1, the coefficient of thermal expansion in the transverse direction was lower than that in the machine direction, such that the curl having a high height was generated.

Claims (13)

  1. A polarizing plate comprising a cellulose acylate film, a polarizer, and an acrylic film which are sequentially stacked therein,
    wherein coefficients of thermal expansion of the cellulose acylate film and the acrylic film satisfy the following Equations 1 and 2:
    [Equation 1]
    0 ppm/K ≤ |CTEca - CTEac| ≤ 30 ppm/K
    (In Equation 1, CTEca is a coefficient of thermal expansion of the cellulose acylate film in a transverse direction (TD), and CTEac is a coefficient of thermal expansion of the acrylic film).
    [Equation 2]
    CTEtd > CTEmd
    (In Equation 2, CTEtd is a coefficient of thermal expansion (ppm/K) in the transverse direction (TD), and CTEmd is a coefficient of thermal expansion (ppm/K) in a machine direction (MD)).
  2. The polarizing plate of claim 1, wherein the coefficient of thermal expansion of the cellulose acylate film satisfies the following Equation 3:
    [Equation 3]
    CTEtd - CTEmd > 3 ppm/K
    (in Equation, CTEtd is the coefficient of thermal expansion (ppm/K) in the transverse direction (TD), and CTEmd is the coefficient of thermal expansion (ppm/K) in the machine direction (MD)).
  3. The polarizing plate of claim 1, wherein the coefficient of thermal expansion of the cellulose acylate film satisfies the following Equation 4:
    [Equation 4]
    CTEtd - CTEmd > 15 ppm/K
    (in Equation, CTEtd is the coefficient of thermal expansion (ppm/K) in the transverse direction (TD), and CTEmd is the coefficient of thermal expansion (ppm/K) in the machine direction (MD)).
  4. The polarizing plate of claim 1, wherein the coefficient of thermal expansion of the cellulose acylate film in the transverse direction (TD) is 60 to 105 ppm/K.
  5. The polarizing plate of claim 1, wherein the cellulose acylate film contains a cellulose acylate resin and any one or two or more selected from compounds represented by Chemical Formulas 1 to 3.
    [Chemical Formula 1]
    Figure PCTKR2014012614-appb-I000006
    [Chemical Formula 2]
    Figure PCTKR2014012614-appb-I000007
    [Chemical Formula 3]
    Figure PCTKR2014012614-appb-I000008
  6. The polarizing plate of claim 5, wherein the cellulose acylate film contains the compounds represented by Chemical Formulas 1 to 3 so that a total content of the compounds is 0.1 to 20 parts by weight based on 100 parts by weight of the cellulose acylate resin, and
    a mixing weight ratio of the compound represented by Chemical Formula 1, the compound represented by Chemical Formula 2, and the compound represented by Chemical Formula 3 is 1 ~ 2 : 1 ~ 1.5 : 1.
  7. The polarizing plate of claim 1, wherein the coefficient of thermal expansion of the acrylic film is 70 to 75 ppm/K.
  8. The polarizing plate of claim 1, wherein in the polarizing plate, a height of curl from a bottom is 30 mm or less.
  9. A liquid crystal display device comprising the polarizing plate of any one of claims 1 to 8.
  10. The liquid crystal display device of claim 9, wherein the cellulose acylate film, the polarizer, the acrylic film, and a liquid crystal cell are sequentially stacked in the liquid crystal display device.
  11. The liquid crystal display device of claim 9, wherein the cellulose acylate film, the polarizer, the acrylic film, a liquid crystal cell, the cellulose acylate film, the polarizer, and the acrylic film are sequentially stacked in the liquid crystal display device.
  12. The liquid crystal display device of claim 9, wherein the acrylic film, the polarizer, the cellulose acylate film, and a liquid crystal cell are sequentially stacked in the liquid crystal display device.
  13. The liquid crystal display device of claim 9, wherein the acrylic film, the polarizer, the cellulose acylate film, a liquid crystal cell, the acrylic film, the polarizer, and the cellulose acylate film are sequentially stacked in the liquid crystal display device.
PCT/KR2014/012614 2013-12-23 2014-12-22 Polarizing plate and liquid crystal display device having the same Ceased WO2015099368A1 (en)

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TWI801931B (en) * 2021-07-13 2023-05-11 住華科技股份有限公司 Optical film and display device formed therefrom
KR20240021318A (en) * 2022-08-09 2024-02-19 삼성에스디아이 주식회사 Polarizing plate and optical display apparatus comprising the same

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CN112088325B (en) * 2018-05-11 2022-09-20 住友化学株式会社 Polarizing plate and display device

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