JP5720683B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device having an LED backlight.

  In a polarizing plate used for a liquid crystal display device, a protective film is usually bonded to both surfaces of a polarizer having polarizing ability via an adhesive layer.

  Conventionally, it is known that when this polarizing plate is exposed to heat and humidity due to long-term use, the polarizing performance fluctuates, and further, the display performance of the liquid crystal display device decreases.

  One reason for this is thought to be that moisture in the environment permeates into the polarizing plate, thereby changing the size of the polarizer. Therefore, the use of a polymer film with low moisture permeability as the protective film is considered. It was thought that it contributed to the improvement of durability of a polarizing plate (patent document 1).

  On the other hand, liquid crystal display devices are used in various ways, and durability is required not only in high-temperature and high-humidity environments, but also in low-temperature and high-humidity environments. -It has been found that the durability of the polarizing plate in a high-humidity environment is improved, so that the durability in other environments may be impaired.

  For example, when a polarizing plate is used for a long time in a relatively low temperature and high humidity environment of about 20 ° C., red discoloration may occur. This is a polarization having a low moisture permeability polymer film on both sides of the polarizer. It became clear that it became more remarkable when using a board (patent document 2).

  However, this discoloration has not been a practically problematic level unless a low moisture-permeable polymer film is used on both sides, and so far, it has been dealt with by the existing polarizing plate protective film design.

  However, in the latest liquid crystal display device using an LED for the backlight and further increasing the aperture ratio, it has become very noticeable and has become a problem level.

  The difference in the light source spectrum between the conventional cold-cathode tube and the visible region (white) of the LED is presumed to be the root cause.

JP 2008-107499 A JP 2010-78967 A

  An object of the present invention is to provide a liquid crystal display device having an optical film group which does not cause reddish discoloration in a polarizing plate and does not deteriorate display image quality in a liquid crystal display device using an LED as a backlight.

  The above object of the present invention has been achieved by the following.

  1. A viewing side polarizing plate having a structure sandwiched between two polarizing plate protective films, a liquid crystal cell, a backlight side polarizing plate having a structure sandwiched between two polarizing plate protective films, and an LED backlight, In the liquid crystal display device in this order from the viewing side, the two polarizing plate protective films of the viewing side polarizing plate are both cellulose ester films, and the polarizing plate protective film on the liquid crystal cell side of the backlight side polarizing plate Is a cellulose ester film.

  2. 2. The liquid crystal display according to 1 above, wherein the polarizing plate protective film on the viewing side polarizing plate is a cellulose acetate film having an acetyl group substitution degree X of 2.10 ≦ X <2.50. apparatus.

  3. 3. The liquid crystal display device according to 1 or 2, wherein an aperture ratio of the liquid crystal display device is 65% or more.

  According to the configuration of the present invention, in a liquid crystal display device using an LED as a backlight, it is possible to obtain a liquid crystal display device that does not cause reddish discoloration in the polarizing plate and does not deteriorate display image quality.

It is the schematic of the liquid crystal display device of this invention.

<Liquid Crystal Display Device of the Present Invention>
The liquid crystal display device of the present invention is a viewing side polarizing plate having a structure sandwiched between two polarizing plate protective films, a liquid crystal cell, a backlight side polarizing plate having a structure sandwiched between two polarizing plate protective films, And the LED backlight in this order from the viewing side, the two polarizing plate protective films of the viewing side polarizing plate are both cellulose ester films, and the liquid crystal cell of the backlight side polarizing plate The polarizing plate protective film on the side is a cellulose ester film.

FIG. 1 is a schematic view of a basic liquid crystal display device of the present invention. In the liquid crystal display device of the present invention, the backlight is an LED, and in that case, a polarizing plate protective film T1 (viewing side polarizing plate protective film of the viewing side polarizing plate) and T2 (liquid crystal cell side polarizing plate protection of the viewing side polarizing plate). Film) and T3 (liquid crystal cell side polarizing plate protective film of the backlight side polarizing plate) are cellulose ester films. In particular, a cellulose acetate film having an acetyl group substitution degree X of T2 of 2.1 ≦ X <2.5 is preferable. And the effect of this invention is remarkable when the aperture ratio of a liquid crystal display device is 65% or more.
<Cellulose ester film>
As a main component of the cellulose ester film of T1 to T3 of the present invention, cellulose triacetate, cellulose diacetate, cellulose acetate butyrate, and cellulose acetate propionate are preferable, and among these, cellulose diacetate is preferably used.

  The cellulose ester film of T1 of the present invention is X, Y when the substitution degree of acetyl groups is X and the substitution degree of other acyl groups is Y, particularly from the viewpoint of optical isotropy required for a polarizing plate protective film. Is a film in which the cellulose ester in the range of the following formula is 50% by mass or more of the film constituents.

Formula 2.5 ≦ X + Y ≦ 3.0
In particular, a cellulose triacetate film is preferable. Another resin may be mixed as long as the function of the present invention is not impaired, and various additives may be added according to the purpose.

  As T1, the commercially available cellulose triacetate film currently used with the normal polarizing plate protective film can be used.

  The cellulose ester film of T2 and T3 of the present invention has high retardation development and can be made into a thin film even when it is a retardation film having a high retardation, stretching for expressing the retardation. From the viewpoint of keeping the magnification low, a film made of cellulose ester that satisfies the range of the following formula is used.

Formula 2.1 ≦ X + Y <2.5
The non-substituted part exists as a hydroxyl group.

  The cellulose ester film of T2 and T3 of the present invention is preferably a cellulose acetate film in which T2 is 2.1 ≦ X <2.5, and T2 and T3 are simultaneously 2.1 ≦ X <2.5. Most preferred is a cellulose diacetate film.

  The cellulose acetate films T2 and T3 of the present invention can appropriately adjust the retardation required for the required optical compensation effect, and from the viewpoint of taking advantage of high retardation development, retardation Ro in the in-plane direction. Is preferably 30 nm or more, more preferably in the range of 30 to 200 nm, and the retardation Rth in the thickness direction is preferably 70 nm or more, and more preferably in the range of 70 to 300 nm.

  A method for adjusting the phase difference is not particularly limited, but a method of adjusting by a stretching process is common. A detailed adjustment method will be described later.

  The cellulose acetate used for these polarizing plate protective films and retardation films of the present invention can be synthesized by a known method.

  The cellulose used as a raw material for cellulose acetate used in the retardation film and the polarizing plate protective film of the present invention is not particularly limited, and examples thereof include cotton linters, wood pulp (derived from coniferous trees, derived from hardwoods), kenaf and the like. . Moreover, the cellulose acetate obtained from them can be mixed and used in arbitrary ratios, respectively.

  The cellulose acetate of the present invention can be produced by a known method. Specifically, it can be synthesized with reference to the method described in JP-A-10-45804.

  Examples of commercially available products include Daicel Corporation L20, L30, L40, and L50, and Eastman Chemical's Ca398-3, Ca398-6, Ca398-10, Ca398-30, and Ca394-60S.

(Solution viscosity)
As the cellulose acetate used in the present invention, it is preferable to use a mixture of those having a weight average molecular weight / viscosity value of 1.2 to 2.4 and those of 4.4 to 5.5. Increasing the weight average molecular weight improves the film breakability and increases the solid content concentration by lowering the viscosity when a dope (a solution obtained by dissolving a resin in a solvent is hereinafter referred to as a dope). This improves film productivity. By combining the above effects, it was found that a film having high productivity and not breaking can be produced.

  As a dope preparation method, a method of preparing at a temperature of 0 ° C. or higher (ordinary temperature or high temperature) and a cooling preparation method of preparing at a low temperature are known. When preparing at a temperature of 0 ° C. or higher, it is preferable to use a halogenated hydrocarbon (particularly methylene chloride) as the organic solvent. Regarding these preparation methods and organic solvents, the Invention Society public technique (public technical number 2001-1745, issued on March 15, 2001, hereinafter abbreviated as public technique 2001-1745) And the preparation method is described in the items 22 to 25.

  The viscosity of the cellulose acetate solution of the present invention is preferably 15 to 140 Pa · s, and the dope temperature during dissolution and filtration is preferably 20 ° C. or higher and 30 ° C. or lower. More preferably, the viscosity of the low-viscosity cellulose acetate solution is 30 to 90 Pa · s.

  The viscosity of the cellulose acetate solution of the present invention can be measured at 25 ° C. using a B-type viscometer model VS-A1 (Shibaura System Co., Ltd.) according to the method described in JIS Z 8803.

(Molecular weight distribution)
Since the average molecular weight and molecular weight distribution of the cellulose ester which is the main component of the T1-T3 cellulose ester film of the present invention can be measured using high performance liquid chromatography, the number average molecular weight (Mn) and the weight average molecular weight ( Mw) and the ratio can be calculated.

The measurement conditions are as follows.
Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three Showa Denko Co., Ltd.)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (GL Science Co., Ltd.)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0 ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 100000 to 500 samples were used. The 13 samples are preferably used at approximately equal intervals.

  The molecular weight of the cellulose ester is preferably 100,000 to 200,000, more preferably 130,000 to 160,000 in terms of weight average molecular weight (Mw). The cellulose acetate used in the present invention preferably has a Mn / Mw ratio of 1.0 or more and less than 5.0, more preferably 2.5 or more and less than 4.0.

The degree of polymerization of cellulose acetate is preferably 200 to 800, more preferably 250 to 650, still more preferably 250 to 450, and particularly preferably 250 to 400 in terms of viscosity average degree of polymerization. The viscosity average degree of polymerization can be measured according to Uda et al.'S limiting viscosity method (Kazuo Uda, Hideo Saito, Journal of Textile Science, Vol. 18, No. 1, pages 105-120, 1962). A method for measuring the viscosity average degree of polymerization is also described in JP-A-9-95538.
<Additives>
The cellulose ester film of the present invention preferably contains a sugar ester compound represented by the general formula (1) as a physical property improving agent.

(Wherein R _{1 to} R ₈ represent a substituted or unsubstituted alkylcarbonyl group or a substituted or unsubstituted allylcarbonyl group, and R _{1 to} R ₈ may be the same or different. Good.)
The cellulose ester film of the present invention preferably contains an ester compound represented by the general formula (2) as a plasticizer.

General formula (2) B- (GA) n-GB
(Wherein B is a hydroxy group or carboxylic acid residue, G is an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms) , A represents an alkylene dicarboxylic acid residue having 4 to 12 carbon atoms or an aryl dicarboxylic acid residue having 6 to 12 carbon atoms, and n represents an integer of 1 or more.)
In the general formula (2), the alkylene glycol component having 2 to 12 carbon atoms includes ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,2-propanediol, 2-methyl 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2 , 2-diethyl-1,3-propanediol (3,3-dimethylolpentane), 2-n-butyl-2-ethyl-1,3-propanediol (3,3-dimethylolheptane), 3-methyl- 1,5-pentanediol 1,6-hexanediol, 2,2,4-trimethyl 1,3-pentanediol, 2-ethyl 1, -Hexanediol, 2-methyl 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-octadecanediol, etc., and these glycols are one kind or two kinds or more Used as a mixture.

  The specific compound of the ester compound represented by General formula (2) of this invention below is shown.

  The compound represented by General formula (1) or (2) can be used suitably in the range of 1-40 mass% of a cellulose-ester film.

<Other additives>
(Other plasticizers)
The cellulose acetate film of the present invention can contain a plasticizer other than the compounds represented by the general formulas (1) and (2) as necessary for obtaining the effects of the present invention.

  The plasticizer is not particularly limited, but is preferably a polycarboxylic acid ester plasticizer, a glycolate plasticizer, a phthalate ester plasticizer, a fatty acid ester plasticizer, a polyhydric alcohol ester plasticizer, or an ester plasticizer. Agent, acrylic plasticizer and the like.

  Of these, when two or more plasticizers are used, at least one plasticizer is preferably a polyhydric alcohol ester plasticizer.

  The polyhydric alcohol ester plasticizer is a plasticizer comprising an ester of a dihydric or higher aliphatic polyhydric alcohol and a monocarboxylic acid, and preferably has an aromatic ring or a cycloalkyl ring in the molecule. Preferably it is a 2-20 valent aliphatic polyhydric alcohol ester.

  The polyhydric alcohol preferably used in the present invention is represented by the following general formula (a).

Formula _{(a) R 11 - (OH} ) n
However, R ₁₁ represents an n-valent organic group, n represents a positive integer of 2 or more, and the OH group represents an alcoholic and / or phenolic hydroxyl group.

  Below, the specific compound of a polyhydric alcohol ester is illustrated.

  The glycolate plasticizer is not particularly limited, but alkylphthalylalkyl glycolates can be preferably used.

  Examples of alkyl phthalyl alkyl glycolates include methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, octyl phthalyl octyl glycolate, methyl phthalyl ethyl Glycolate, ethyl phthalyl methyl glycolate, ethyl phthalyl propyl glycolate, methyl phthalyl butyl glycolate, ethyl phthalyl butyl glycolate, butyl phthalyl methyl glycolate, butyl phthalyl ethyl glycolate, propyl phthalyl butyl glycol Butyl phthalyl propyl glycolate, methyl phthalyl octyl glycolate, ethyl phthalyl octyl glycolate, octyl phthalyl methyl glycolate, octyl phthalate Ethyl glycolate, and the like.

  Examples of the phthalate ester plasticizer include diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, dioctyl phthalate, dicyclohexyl phthalate, and dicyclohexyl terephthalate.

  Examples of the citrate plasticizer include acetyl trimethyl citrate, acetyl triethyl citrate, and acetyl tributyl citrate.

  Examples of fatty acid ester plasticizers include butyl oleate, methylacetyl ricinoleate, and dibutyl sebacate.

  Examples of the phosphate ester plasticizer include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate and the like.

  The polyvalent carboxylic acid ester compound is composed of an ester of divalent or higher, preferably divalent to 20 valent polyvalent carboxylic acid and alcohol. The aliphatic polyvalent carboxylic acid is preferably 2 to 20 valent, and in the case of an aromatic polyvalent carboxylic acid or an alicyclic polyvalent carboxylic acid, it is preferably 3 to 20 valent.

  The polyvalent carboxylic acid is represented by the following general formula (b).

Formula (b) R ₁₂ (COOH) _m1 (OH) _n1
In the formula, R ₁₂ represents an (m1 + n1) -valent organic group, m1 represents a positive integer of 2 or more, n1 represents an integer of 0 or more, a COOH group represents a carboxyl group, and an OH group represents an alcoholic or phenolic hydroxyl group.

  The molecular weight of the polyvalent carboxylic acid ester compound is not particularly limited, but is preferably in the range of 300 to 1000, and more preferably in the range of 350 to 750. The larger one is preferable in terms of improvement in retention, and the smaller one is preferable in terms of moisture permeability and compatibility with cellulose acetate.

  The alcohol used for the polyvalent carboxylic acid ester that can be used in the present invention may be one kind or a mixture of two or more kinds.

  Examples of particularly preferred polyvalent carboxylic acid ester compounds include, for example, triethyl citrate, tributyl citrate, acetyl triethyl citrate (ATEC), acetyl tributyl citrate (ATBC), benzoyl tributyl citrate, acetyl triphenyl citrate, Acetyl tribenzyl citrate, dibutyl tartrate, diacetyl dibutyl tartrate, tributyl trimellitic acid, tetrabutyl pyromellitic acid and the like can be mentioned.

  In the cellulose ester film of the present invention, the plasticizer can be appropriately used in the range of 1 to 40% by mass of the cellulose ester film.

(UV absorber)
The cellulose ester film of the present invention can also contain an ultraviolet absorber. The ultraviolet absorber is intended to improve durability by absorbing ultraviolet rays of 400 nm or less, and in particular, the transmittance at a wavelength of 370 nm is preferably 10% or less, more preferably 5% or less, and further Preferably it is 2% or less.

  The amount of the UV absorber used is not uniform depending on the type of UV absorber, the operating conditions, etc., but when the dry film thickness of the polarizing plate protective film is 30 to 200 μm, it is 0.5 with respect to the polarizing plate protective film. -10 mass% is preferable, and 0.6-4 mass% is still more preferable.

(Antioxidant)
Antioxidants are also referred to as deterioration inhibitors. When a liquid crystal image display device or the like is placed in a high humidity and high temperature state, the cellulose acetate film may be deteriorated.

  The antioxidant has a role of delaying or preventing the cellulose acetate film from being decomposed by, for example, the residual solvent amount of halogen in the cellulose acetate film or phosphoric acid of the phosphoric acid plasticizer. It is preferable to make it contain in a film.

  As such an antioxidant, a hindered phenol compound is preferably used. For example, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di- -T-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3 -(3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino)- 1,3,5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octa Sil-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide) 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-t-butyl-4-hydroxy Benzyl) -isocyanurate and the like.

  In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3 -(3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di- A phosphorus processing stabilizer such as t-butylphenyl) phosphite may be used in combination.

  The addition amount of these compounds is preferably 1 ppm to 1.0%, more preferably 10 to 1000 ppm in terms of mass ratio with respect to the cellulose derivative.

<Fine particles>
The cellulose ester film of the present invention has, for example, silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, kaolin, talc, calcined calcium silicate, hydrated calcium silicate, aluminum silicate in order to improve handleability. Further, it is preferable to contain inorganic fine particles such as magnesium silicate and calcium phosphate and a matting agent such as a crosslinked polymer. Of these, silicon dioxide is preferable because it can reduce the haze of the film.

The primary average particle diameter of the fine particles is preferably 20 nm or less, more preferably 5 to 16 nm, and particularly preferably 5 to 12 nm. The amount added can be appropriately determined.
<Method for producing cellulose ester film>
Next, the manufacturing method of the cellulose-ester film of this invention is demonstrated.

  The cellulose ester film of the present invention can be preferably used regardless of whether it is a film produced by a solution casting method or a film produced by a melt casting method.

  Production of the cellulose ester film of the present invention by the solution casting method is a step of preparing a dope by dissolving cellulose ester and additives in a solvent, a step of casting the dope on an endless metal support that moves infinitely It is performed by a step of drying the cast dope as a web, a step of peeling from the metal support, a step of stretching or maintaining the width, a step of further drying, and a step of winding up the finished film.

  The process for preparing the dope will be described. The concentration of cellulose ester in the dope is preferably higher because the drying load after casting on the metal support can be reduced. However, if the concentration of cellulose ester is too high, the load during filtration increases and the filtration accuracy is poor. Become. As a density | concentration which makes these compatible, 10-35 mass% is preferable, More preferably, it is 15-25 mass%.

  The solvent used in the dope may be used alone or in combination of two or more, but it is preferable to use a mixture of a good solvent and a poor solvent of cellulose ester in terms of production efficiency, and there are many good solvents. This is preferable from the viewpoint of the solubility of the cellulose ester.

  The preferable range of the mixing ratio of the good solvent and the poor solvent is 70 to 98% by mass for the good solvent and 2 to 30% by mass for the poor solvent. With a good solvent and a poor solvent, what dissolve | melts the cellulose ester to be used independently is defined as a good solvent, and what poorly swells or does not melt | dissolve is defined as a poor solvent.

  Therefore, a good solvent and a poor solvent change with the average acetylation degree (acetyl group substitution degree) of a cellulose ester.

  Although the good solvent used for this invention is not specifically limited, Organic halogen compounds, such as a methylene chloride, dioxolanes, acetone, methyl acetate, methyl acetoacetate, etc. are mentioned. Particularly preferred is methylene chloride or methyl acetate.

  Moreover, although the poor solvent used for this invention is not specifically limited, For example, methanol, ethanol, n-butanol, cyclohexane, cyclohexanone, etc. are used preferably. Moreover, it is preferable that 0.01-2 mass% of water contains in dope.

  Moreover, the solvent used for melt | dissolution of a cellulose ester collect | recovers the solvent removed from the film by drying at the film-forming process, and uses this again.

  The recovery solvent may contain trace amounts of additives added to the cellulose ester, such as plasticizers, UV absorbers, polymers, monomer components, etc., but even if these are included, they are preferably reused. Can be purified and reused if necessary.

  A general method can be used as a dissolution method of the cellulose ester when preparing the dope described above. When heating and pressurization are combined, it is possible to heat above the boiling point at normal pressure.

  It is preferable to stir and dissolve while heating at a temperature that is equal to or higher than the boiling point of the solvent at normal pressure and that the solvent does not boil under pressure, in order to prevent the generation of massive undissolved materials called gels and mamacos.

  A method in which a cellulose ester is mixed with a poor solvent and wetted or swollen, and then a good solvent is added and dissolved is also preferably used.

  The pressurization may be performed by a method of injecting an inert gas such as nitrogen gas or a method of increasing the vapor pressure of the solvent by heating. Heating is preferably performed from the outside. For example, a jacket type is preferable because temperature control is easy.

  The heating temperature with the addition of a solvent is preferably higher from the viewpoint of the solubility of the cellulose ester, but if the heating temperature is too high, the required pressure increases and the productivity deteriorates.

  A preferable heating temperature is 45 to 120 ° C, more preferably 60 to 110 ° C, and still more preferably 70 ° C to 105 ° C. The pressure is adjusted so that the solvent does not boil at the set temperature.

  Alternatively, a cooling dissolution method is also preferably used, whereby the cellulose ester can be dissolved in a solvent such as methyl acetate.

  Next, this cellulose ester solution is filtered using a suitable filter medium such as filter paper. As the filter medium, it is preferable that the absolute filtration accuracy is small in order to remove insoluble matters and the like, but there is a problem that the filter medium is likely to be clogged if the absolute filtration accuracy is too small.

  For this reason, a filter medium with an absolute filtration accuracy of 0.008 mm or less is preferable, a filter medium with 0.001 to 0.008 mm is more preferable, and a filter medium with 0.003 to 0.006 mm is still more preferable.

  There are no particular restrictions on the material of the filter medium, and ordinary filter media can be used. However, plastic filter media such as polypropylene and Teflon (registered trademark), and metal filter media such as stainless steel do not drop off fibers. preferable.

  It is preferable to remove and reduce impurities, particularly bright spot foreign matter, contained in the raw material cellulose ester by filtration.

Bright spot foreign matter means that when two polarizing plates are placed in a crossed Nicol state, an optical film or the like is placed between them, light is applied from one polarizing plate side, and observation is performed from the other polarizing plate side. It is a point (foreign matter) where light from the opposite side appears to leak, and the number of bright spots having a diameter of 0.01 mm or more is preferably 200 / cm ² or less.

More preferably, it is 100 pieces / cm < ² > or less, More preferably, it is 50 pieces / m < ² > or less, More preferably, it is 0-10 pieces / cm < ² > or less. Further, it is preferable that the number of bright spots of 0.01 mm or less is small.

  The dope can be filtered by a normal method, but the method of filtering while heating at a temperature not lower than the boiling point of the solvent at normal pressure and in a range where the solvent does not boil under pressure is the filtration pressure before and after filtration. The increase in the difference (referred to as differential pressure) is small and preferable.

  A preferred temperature is 45 to 120 ° C, more preferably 45 to 70 ° C, and still more preferably 45 to 55 ° C.

  A smaller filtration pressure is preferred. The filtration pressure is preferably 1.6 MPa or less, more preferably 1.2 MPa or less, and further preferably 1.0 MPa or less.

  Here, the dope casting will be described.

  The metal support in the casting (casting) step preferably has a mirror-finished surface. As the metal support, a stainless steel belt or a drum whose surface is plated with a casting is preferably used.

  The cast width can be 1 to 4 m. The surface temperature of the metal support in the casting step is −50 ° C. to a temperature lower than the boiling point of the solvent, and a higher temperature is preferable because the web can be dried faster. May deteriorate.

  A preferable support temperature is 0 to 55 ° C, and more preferably 25 to 50 ° C. Alternatively, it is also a preferable method that the web is gelled by cooling and peeled from the drum in a state containing a large amount of residual solvent.

  The method for controlling the temperature of the metal support is not particularly limited, and there are a method of blowing hot air or cold air, and a method of contacting hot water with the back side of the metal support. It is preferable to use warm water because heat transfer is performed efficiently, so that the time until the temperature of the metal support becomes constant is short. When warm air is used, wind at a temperature higher than the target temperature may be used.

  In order for the cellulose ester film to exhibit good flatness, the residual solvent amount when peeling the web from the metal support is preferably 10 to 150% by mass, more preferably 20 to 40% by mass or 60 to 130% by mass. Especially preferably, it is 20-30 mass% or 70-120 mass%.

  In the present invention, the amount of residual solvent is defined by the following formula.

Residual solvent amount (% by mass) = {(MN) / N} × 100
M is the mass of a sample collected during or after the production of the web or film, and N is the mass after heating M at 115 ° C. for 1 hour.

  Further, in the drying step of the cellulose ester film, the web is peeled off from the metal support, and further dried, and the residual solvent amount is preferably 1% by mass or less, more preferably 0.1% by mass or less, Especially preferably, it is 0-0.01 mass% or less.

  In the film drying step, generally, a roll drying method (a method in which webs are alternately passed through a plurality of rolls arranged above and below) and a method in which the web is dried while being conveyed by a tenter method are employed.

  In order to produce the cellulose ester film of the present invention, it is particularly preferable to perform stretching in the width direction (lateral direction) by a tenter method in which both ends of the web are held with clips or the like. Peeling is preferably performed at a peeling tension of 300 N / m or less.

  The means for drying the web is not particularly limited, and can be generally performed with hot air, infrared rays, a heating roll, microwave, or the like, but it is preferably performed with hot air in terms of simplicity.

  The drying temperature in the web drying step is preferably increased stepwise from 40 to 200 ° C.

  Although the film thickness of a cellulose-ester film is not specifically limited, 10-200 micrometers is used. In particular, the film thickness is particularly preferably 10 to 100 μm. More preferably, it is 20-60 micrometers.

  The cellulose ester film of the present invention has a width of 1 to 4 m. In particular, those having a width of 1.4 to 4 m are preferably used, and particularly preferably 1.6 to 3 m. If it exceeds 4 m, conveyance becomes difficult.

  In order to obtain the target retardation values Ro and Rt in the present invention, it is preferable that the cellulose ester film has the structure of the present invention, and the refractive index is controlled by controlling the transport tension and stretching.

  For example, the retardation value can be changed by lowering or increasing the tension in the longitudinal direction.

  Further, biaxial stretching or uniaxial stretching can be performed sequentially or simultaneously with respect to the longitudinal direction (film forming direction) of the film and the direction orthogonal to the longitudinal direction of the film, that is, the width direction.

  The draw ratios in the biaxial directions perpendicular to each other are preferably in the range of 0.8 to 1.5 times in the casting direction and 1.1 to 2.5 times in the width direction, respectively. It is preferable to carry out in the range of 0.8 to 1.0 times in the direction and 1.2 to 2.0 times in the width direction.

  The stretching temperature is preferably 120 ° C. to 200 ° C., more preferably 150 ° C. to 200 ° C., and more preferably 150 ° C. to 190 ° C. or less.

  The residual solvent in the film is preferably 20 to 0%, more preferably 15 to 0%.

  Specifically, it is preferable that the residual solvent is stretched by 11% at 155 ° C., or the residual solvent is stretched by 2% at 155 ° C. Alternatively, it is preferable that the residual solvent is stretched at 11% at 160 ° C, or the residual solvent is stretched at less than 1% at 160 ° C.

  There is no particular limitation on the method of stretching the web. For example, a method in which a difference in peripheral speed is applied to a plurality of rolls, and the roll peripheral speed difference is used to stretch in the longitudinal direction between the rolls. And a method of stretching in the vertical direction, a method of stretching in the horizontal direction and stretching in the horizontal direction, a method of stretching in the vertical and horizontal directions and stretching in both the vertical and horizontal directions, and the like. Of course, these methods may be used in combination.

  In the case of the so-called tenter method, driving the clip portion by the linear drive method is preferable because smooth stretching can be performed and the risk of breakage and the like can be reduced.

  These width maintenance or lateral stretching in the film forming step is preferably performed by a tenter, and may be a pin tenter or a clip tenter.

  The slow axis or the fast axis of the cellulose ester film of the present invention is present in the film plane, and θ1 is preferably −1 ° or more and + 1 ° or less, assuming that the angle formed with the film forming direction is θ1. More preferably, it is 5 ° or more and + 0.5 ° or less.

This θ1 can be defined as an orientation angle, and θ1 can be measured using an automatic birefringence meter KOBRA-21ADH (Oji Scientific Instruments). Each of θ1 satisfying the above relationship can contribute to obtaining high luminance in a display image, suppressing or preventing light leakage, and contributing to obtaining faithful color reproduction in a color liquid crystal display device.
<Physical properties of cellulose ester film>
The moisture permeability of the cellulose ester film of the present invention, 40 ° C., of preferably 300~1800g ^/ m 2 · 24h at 90% RH, further 400~1500g ^/ m 2 · 24h are preferred, 40~1300g ^/ m 2 · 24h Particularly preferred. The moisture permeability can be measured according to the method described in JIS Z 0208.

  The breaking elongation of the cellulose ester film of the present invention is preferably 10 to 80%, more preferably 20 to 50%.

  The visible light transmittance of the cellulose ester film of the present invention is preferably 90% or more, and more preferably 93% or more.

  The haze of the cellulose ester film of the present invention is preferably less than 1%, particularly preferably 0 to 0.1%.

Further, by applying a liquid crystal layer to the cellulose ester film of the present invention, retardation values over a wider range can be obtained.
<Polarizing plate>
The cellulose ester film of the present invention can be used for a polarizing plate and a liquid crystal display device using the polarizing plate.

  The polarizing plate of the present invention can be produced by a general method. The cellulose ester film of the present invention is preferably bonded to at least one surface of a polarizer produced by subjecting the polarizer side to alkali saponification treatment and immersion drawing in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution.

  As the polarizing plate protective film for T1 and T4 of the present invention, for example, a commercially available cellulose ester film (for example, Konica Minoltack KC8UX, KC5UX, KC8UCR3, KC8UCR4, KC8UCR5, KC8UY, KC4UY, KC4UE, KC8UE, KC8UY-X, -RHA, KC8UXW-RHA-C, KC8UXW-RHA-NC, KC4UXW-RHA-NC, manufactured by Konica Minolta Opto Co., Ltd.) are also preferably used.

  In addition to the antiglare layer or the clear hard coat layer, the polarizing plate used on the surface side of the display device preferably has an antireflection layer, an antistatic layer, an antifouling layer, and a backcoat layer.

  A polarizer, which is a main component of a polarizing plate, is an element that allows only light of a plane of polarization in a certain direction to pass. A typical polarizer currently known is a polyvinyl alcohol-based polarizing film, which is polyvinyl alcohol. There are one in which iodine is dyed on a system film and one in which dichroic dye is dyed.

  For the polarizer, a polyvinyl alcohol aqueous solution is formed into a film and dyed by uniaxial stretching or dyed or uniaxially stretched and then preferably subjected to a durability treatment with a boron compound. The film thickness of the polarizer is preferably 5 to 30 μm, particularly preferably 10 to 20 μm.

  Further, the ethylene unit content described in JP-A-2003-248123, JP-A-2003-342322, etc. is 1 to 4 mol%, the degree of polymerization is 2000 to 4000, and the degree of saponification is 99.0 to 99.99 mol%. Ethylene-modified polyvinyl alcohol is also preferably used.

  Among them, an ethylene-modified polyvinyl alcohol film having a hot water cutting temperature of 66 to 73 ° C. is preferably used.

  The difference in hot water cutting temperature between two points 5 cm away in the TD direction of the film is more preferably 1 ° C. or less in order to reduce color spots, and two points separated 1 cm in the TD direction of the film. In order to reduce color spots, it is more preferable that the difference in the hot water cutting temperature is 0.5 ° C. or less.

  A polarizer using this ethylene-modified polyvinyl alcohol film is excellent in polarization performance and durability, and has few color spots, and is particularly preferably used for a large-sized liquid crystal display device.

The polarizer obtained as described above is usually used as a polarizing plate with a protective film bonded to both sides or one side thereof. Examples of the adhesive used for pasting include a PVA-based adhesive and a urethane-based adhesive. Among them, a PVA-based adhesive is preferably used. The polarizing plate of the present invention preferably uses a polarizing plate protective film.
<Liquid crystal display device>
By using the cellulose ester film of the present invention for a liquid crystal display device using an LCD backlight, the liquid crystal display device of the present invention having excellent visibility can be obtained.

  A general LED backlight reproduces white by combining a blue LED and a phosphor. The LED called the pseudo-white type has two peaks around 480 nm (blue) and 570 nm (yellow), and the LED called the high color rendering white type has 530 nm (green) and 620 nm (red) in addition to blue. 3 peaks are observed. However, since the wavelength characteristics are different from those of the cold cathode tube, white reproduction is different.

  In the present invention, the effect is remarkable in the case of the vertical alignment ECB type liquid crystal display device described in JP-A-2009-301010. This is because the liquid crystal display device has a high aperture ratio of 65% or more, so that the red color change of the polarizing plate can be clearly seen.

Example 1
<Production of Cellulose Ester Film 101>
<Fine particle dispersion 1>
Fine particles (Aerosil R972V manufactured by Nippon Aerosil Co., Ltd.)
11 parts by mass Ethanol 89 parts by mass The above was stirred and mixed with a dissolver for 50 minutes, and then dispersed with Manton Gorin.

<Fine particle addition liquid 1>
The fine particle dispersion 1 was slowly added to the dissolution tank containing methylene chloride with sufficient stirring. Further, the particles were dispersed by an attritor so that the secondary particles had a predetermined particle size. This was filtered through Finemet NF manufactured by Nippon Seisen Co., Ltd. to prepare a fine particle additive solution 1.

Methylene chloride 99 parts by mass Fine particle dispersion 1 5 parts by mass A main dope solution having the following composition was prepared. First, methylene chloride and ethanol were added to the pressure dissolution tank. Cellulose acetate C was charged into a pressure dissolution tank containing a solvent while stirring. This is completely dissolved with heating and stirring. This was designated as Azumi Filter Paper No. The main dope solution was prepared by filtration using 244.

<Composition of main dope solution>
Methylene chloride 340 parts by mass Ethanol 64 parts by mass Cellulose discetate (acetyl group substitution degree 2.41) 100 parts by mass Ester compound 1-2 6.0 parts by mass Ester compound 2-16 6.0 parts by mass Fine particle additive liquid 1 1 part by mass The above was put into a closed container and dissolved while stirring to prepare a dope solution. Next, using an endless belt casting apparatus, the dope solution was uniformly cast on a stainless steel belt support at a temperature of 33 ° C. and a width of 1500 mm. The temperature of the stainless steel belt was controlled at 30 ° C.

  On the stainless steel belt support, the solvent was evaporated until the residual solvent amount in the cast (cast) film became 75%, and then peeled off from the stainless steel belt support with a peeling tension of 130 N / m.

  The peeled cellulose acetate film was stretched 36% in the width direction using a tenter while applying heat at 160 ° C. The residual solvent at the start of stretching was 15%.

Next, drying was terminated while the drying zone was conveyed by a number of rolls. The drying temperature was 130 ° C. and the transport tension was 100 N / m. As described above, a cellulose ester film 101 having a dry film thickness of 40 μm was obtained.
<Production of cellulose ester films 102 to 302>
Cellulose ester films 102 to 302 were produced in the same manner as the cellulose ester film 101 except that the dope composition was changed as shown in the table.
<Preparation of polarizing plate>
A polyvinyl alcohol film having a thickness of 75 μm was swollen with water at 35 ° C. and immersed in an aqueous solution consisting of 0.075 g of iodine, 5 g of potassium iodide, and 100 g of water, and then 3 g of potassium iodide and 7. It was immersed in a 45 ° C. aqueous solution consisting of 5 g and 100 g of water and uniaxially stretched (temperature 55 ° C., stretch ratio 5 times). This was washed with water and dried to obtain a polarizer.

  Subsequently, a polarizer, the cellulose acetate film, and Konica Minolta Tack KC4UY (Konica Minolta Opto Co., Ltd. cellulose triacetate film, acetyl group substitution degree of 2.90) are bonded to each other according to the following steps 1 to 5 for polarization. A plate was made.

  Step 1: Soaked in a 2 mol / L sodium hydroxide solution at 60 ° C. for 90 seconds, then washed with water and dried to obtain a cellulose acetate film saponified on the side to be bonded to the polarizer.

  Process 2: The said polarizer was immersed in the polyvinyl alcohol adhesive tank of 2 mass% of solid content for 1-2 seconds.

  Step 3: Excess adhesive adhered to the polarizer in Step 2 was lightly wiped off, and this was placed on the cellulose ester film treated in Step 1.

Step 4: Step 3 Cellulose ester film laminated with the polarizer and the pressure backside cellulose ester film 20-30 N / cm ^2, the conveyance speed was pasted at approximately 2m / min.

  Step 5: A sample obtained by bonding the polarizer, the cellulose ester film, and Konica Minoltack KC4UY prepared in Step 4 in a dryer at 80 ° C. is dried for 2 minutes, and a polarizing plate corresponding to the cellulose ester film is prepared. did.

  In Table 1, COP means ZEONOR film ZF14-060 manufactured by Nippon Zeon Co., Ltd., and bonding with a polarizer was subjected to corona discharge treatment.

<Production of liquid crystal display device>
The polarizing plates on both surfaces of the 40-inch display BRAVIA-KDL-40EX700 (opening ratio 53%) made in advance were peeled off, and the prepared polarizing plates were bonded to both surfaces of the glass surface of the liquid crystal cell.

  Further, the LED backlight unit of the above liquid crystal display is diverted to a liquid crystal display device using a liquid crystal cell (opening ratio: 67%) described in FIG. 18 of JP2009-301010A to produce a liquid crystal display device. A polarizing plate was bonded to the substrate.

  These liquid crystal display devices were evaluated as follows.

  The liquid crystal display device was conditioned at 23 ° C. and 55% RH for 24 hours, and then a white image was displayed. The front color was visually observed and the transmission spectrum was observed (CS2000 manufactured by Konica Minolta Sensing Co., Ltd.). As a result, the visual tint on the front of the bonded polarizing plate was the same. In addition, no difference was observed in the transmission spectrum.

The liquid crystal display device was placed at 23 ° C. and 95% RH for 48 hours. It was taken out and a white image was displayed, which was similarly observed in an atmosphere of 23 ° C. and 55% RH. The observation results are shown in Table 3.
<Red image evaluation level>
5 Visually white and 650 nm transmittance change with respect to 550 nm is less than 1% 4 Visually white 650 nm with respect to 550 nm is less than 1% to less than 3% 3 Visually slightly pinkish with a change of 650 nm with respect to 550 nm being 1 % To less than 3% 2 It is pinkish by visual observation, and the change at 650 nm with respect to 550 nm is 1% to less than 3%. 1 The redness can be clearly recognized visually, and the transmittance change at 650 nm with respect to 550 nm is 3% or more.

  In the transmission spectrum of the part where the reddishness is strong, the transmittance in the red region is increased, and the result turns red and supports the hypothesis.

1 viewing side polarizing plate T1 viewing side polarizing plate protective film of viewing side polarizing plate T2 liquid crystal cell side polarizing plate protective film of viewing side polarizing plate CE liquid crystal cell 2 backlight side polarizing plate T3 liquid crystal cell side polarizing of backlight side polarizing plate Plate protective film T4 Backlight side polarizing plate protective film of backlight side polarizing plate BL LED backlight 3, 4 Polarizer

Claims (2)

A viewing side polarizing plate having a structure sandwiched between two polarizing plate protective films, a liquid crystal cell, a backlight side polarizing plate having a structure sandwiched between two polarizing plate protective films, and an LED backlight on the viewing side In this order, in a liquid crystal display device having an aperture ratio of 65% or more,
The two polarizing plate protective films of the viewing side polarizing plate are both cellulose ester films, and the polarizing plate protective film on the liquid crystal cell side of the backlight side polarizing plate is a cellulose ester film,
Cellulose satisfying 2.5 ≦ X + Y ≦ 3.0, where the polarizing plate protective film on the side opposite to the liquid crystal cell of the viewing side polarizing plate has X as the acetyl group substitution degree and Y as the other acyl group substitution degree. An ester film, and
Cellulose polarizing plate protective film of the liquid crystal cell side of the front SL viewing side polarizing plate, when the degree of acetyl group substitution and X, which satisfies a 2.10 ≦ X <2.50, and does not include the acyl groups other than acetyl group Ru acetate film der, a liquid crystal display device.   The polarizing plate protective film on the liquid crystal cell side of the backlight side polarizing plate is a cellulose acetate film having an acetyl group substitution degree X of 2.10 ≦ X <2.50 and containing no acyl group other than the acetyl group. The liquid crystal display device according to claim 1.