KR101441839B1 - Polarizing plate protective film - Google Patents

Abstract

An object of the present invention is to provide a polarizing plate protective film with improved transparency.
And a degree of substitution of acetyl groups of 2.80 to 2.99, wherein the cellulose acetate satisfies the following conditions.
(1) 15 ppm? (Ca component + Mg component)? 55 ppm
(2) 0.5? (Ca component + Mg component) / Na component? 2.6

Description

POLARIZING PLATE PROTECTIVE FILM

The present invention relates to a polarizing plate protective film excellent in transparency.

A cellulose triacetate film has been used as a polarizing plate protective film because of its excellent transparency and excellent adhesion with a polarizer.

This cellulose triacetate film contains a variety of impurities in that the raw material is a natural product of cellulose, and thus adverse effects on a polarizing plate protective film of a metal and a solution thereof have been proposed.

A metal such as alkali metals, alkaline-earth metal with respect to the transparency of the film as the total amount of 5.5 × 10 ^{- 6} has been proposed that it is necessary or lower equivalent weight (Patent Document 1).

Further, from the viewpoint of foreign matter of spots, it is proposed that the Ca component is regulated to 60 ppm or less, the Mg component to 15 to 70 ppm, and the Fe component to 1 ppm or less (Patent Document 2).

Furthermore, in the case of processing a discotic liquid crystal layer on the surface or the like, it has been proposed to use a film using cellulose acetate having a Ca component content of 120 ppm or less (Patent Document 3).

Thus, in spite of the recognition that it is necessary to limit the total amount of alkali metals and alkaline earth metals, the incorporation of such metals is unavoidable in the current production process of cellulose triacetate, and effective countermeasures have been demanded.

Particularly, transparency has been greatly demanded with the enlargement of the screen size of the display device.

Japanese Patent Application Laid-Open No. 10-316701 Japanese Patent Application Laid-Open No. 2000-31376 Japanese Patent Application Laid-Open No. 2008-201902

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a polarizing plate protective film with improved transparency.

The above object of the present invention can be achieved by the following arrangement.

1. A polarizing plate protective film comprising cellulose acetate as a main component having an acetyl group substitution degree of 2.80 to 2.99, wherein the cellulose acetate satisfies the following conditions.

(1) 15 ppm? (Ca component + Mg component)? 55 ppm

(2) 0.5? (Ca component + Mg component) / Na component? 2.6

According to the present invention, a transparent polarizing plate protective film can be obtained.

Hereinafter, the present invention will be described in detail. In the present specification, "ppm" means "mass ppm".

[Polarizing plate protective film of the present invention]

The present invention is a polarizing plate protective film comprising cellulose acetate as a main component having an acetyl group substitution degree of 2.80 to 2.99, wherein the cellulose acetate satisfies the following conditions.

(1) 15 ppm? (Ca component + Mg component)? 55 ppm

(2) 0.5? (Ca component + Mg component) / Na component? 2.6

In the above formula, "Ca component", "Mg component", and "Na component" refer to the mass of the atomic conversion of Ca, Mg and Na contained in the cellulose acetate, respectively.

Up to now, it has been considered that the Ca component and the Mg component in the cellulose acetate should be smaller, but it has been deemed that the cellulose component is included in the cellulose acetate.

Generally, the Ca component and the Mg component exist as divalent metal ions in the cellulose acetate, and these divalent metal ions serve to mediate the unsubstituted hydroxyl groups of the cellulose acetate, increase the haze against the stretching treatment, It is believed that it acts to generate aggregates in the fluid.

In the present invention, since the monovalent Na ion is coordinated to the unsubstituted hydroxyl group and the bivalent Ca component and the Mg component inhibit the mediating role of the unsubstituted hydroxyl group of the cellulose acetate, it is possible to increase the haze at the time of stretching, And as a result, transparency of the film is secured.

This action is not clear due to strong hydrogen bonding between the hydroxyl groups at the sites where the unsubstituted hydroxyl group of the cellulose acetate is large, but is remarkably exhibited at the acetyl group substitution degree of 2.80 to 2.99 in which the unsubstituted hydroxyl group is low.

Thus, the present invention has found that the action of the Ca component and the Mg component is suppressed when the Ca component and the Mg component are present even if the Na component is present.

[Cellulose acetate having an acetyl group substitution degree of 2.80 to 2.90]

In the polarizing plate protective film of the present invention, the main component is a component that occupies 50% by mass or more of the entire polarizing plate protective film.

In the present invention, cellulose acetate having an acetyl group substitution degree of 2.80 to 2.90 is the main component.

The "acetyl group substitution degree" refers to the average number of acetyl groups per 1 glucose unit, and represents the ratio of any one of the hydroxyl groups of the second, third, and sixth hydroxyl groups of 1 glucose unit substituted with an acetyl group. That is, when the hydrogen atoms of the second, third, and sixth hydroxyl groups are all substituted with acetyl groups, the degree of substitution (maximum degree of substitution) becomes 3.0.

The degree of acyl substitution can be measured in accordance with ASTM D-817-91, and the degree of acetyl group substitution is 2.80 to 2.99.

The number average molecular weight (Mn) of the cellulose acetate is preferably in the range of 30000 to 300000 because the film has strong mechanical strength. Further, it is preferably used in the range of 50000 to 200000.

The value of the ratio Mw / Mn of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the cellulose acetate is preferably 2.0 to 5.0.

The number average molecular weight (Mn) and the weight average molecular weight (Mw) of cellulose acetate can be measured using gel permeation chromatography (GPC).

The measurement conditions are as follows.

Solvent: methylene chloride

Column: Shodex K806, K805, K803G (used by connecting three manufactured by Showa Denko K.K.)

Column temperature: 25 ° C

Sample concentration: 0.1 mass%

Detector: RI Model 504 (manufactured by GL Science)

Pump: L6000 (manufactured by Hitachi Seisakusho Co., Ltd.)

Flow rate: 1.0 ml / min

Calibration curve: Standard curve of polystyrene STK standard A calibration curve with 13 samples of polystyrene (manufactured by Tosoh Corporation) Mw = 1000000 to 500 was used. 13 The samples are used at almost equal intervals.

Examples of cellulose as a raw material of cellulose acetate include, but are not limited to, cotton linter, wood pulp (derived from softwood, hardwood), kenaf, and the like. The cellulose esters obtained therefrom may be mixed and used in an arbitrary ratio.

The cellulose acetate of the present invention can be produced by a known method. Specifically, it can be synthesized by referring to the methods described in JP-A-10-45804 and JP-A-2009-161701.

Commercially available products include LT-35, LT-55, and LT-105 of Daicel.

[Ca component and Mg component]

The Ca component and the Mg component contained in the cellulose acetate of the present invention are 15 ppm or more and 55 ppm or less, preferably 25 ppm or more and 40 ppm or less, with respect to the total mass of the cellulose acetate. In the process for producing cellulose acetate, the Ca salt and the Mg salt may be used, or the partial addition may be carried out by adjusting the amount thereof or by not adding the whole amount at once (partial neutralization in the aging step is repeated (continuous or intermittent , And the amount of the metal contained in the cellulose acetate is adjusted by repeating the washing, and the amount of the Ca component (hereinafter, referred to as " Ca component And the Mg component can be set in this range. Further, the Ca component and the Mg component contained in the cellulose acetate are preferably 10 ppm or more and 50 ppm or less, and more preferably 20 ppm or more and 35 ppm or less, with respect to the total mass of the polarizing plate protective film.

The Ca component contained in the cellulose acetate is preferably 5 ppm or more and 50 ppm or less, more preferably 10 ppm or more and 40 ppm or less, with respect to the total mass of the cellulose acetate.

The Mg component contained in the cellulose acetate is preferably 10 ppm or less, more preferably 5 ppm or less, with respect to the total mass of the cellulose acetate.

If the amount of metal contained in the cellulose acetate is larger than the above range, the transparency of the film deteriorates. If the amount of metal contained in the cellulose acetate is smaller than the above range, the humidity resistance of the film tends to be lowered.

The Ca component, Mg component and Na component of the present invention can be measured by the following atomic absorption method.

(1) A washed 50 mL magnetic crucible was immersed in a 2N nitric acid aqueous solution overnight.

(2) The magnetic crucible immersed in 2N nitric acid is cleaned with pure water, rinsed with ultrapure water, and dried in a drier.

(3) 2 g of the cellulose acetate sample is crystallized in the magnetic crucible.

(4) Carbonizing the sample in the magnetic crucible on the electric heater.

(5) The magnetic crucible is placed in an electric furnace, and the mixture is calcined at 500 ° C for about 1 hour and at 600 ° C for about 1.5 hours.

(6) When it is completely whitened, stop the electric furnace and cool it in the furnace as it is.

(7) Add 10 mL of a 0.5N aqueous hydrochloric acid solution to the magnetic crucible, and heat-dissolve in a sand bath.

(8) After cooling, the solution is transferred to a 50 ml volumetric flask using a cleaned funnel. The magnetic crucible is thoroughly washed with ultra-pure water and diluted to the line of the measuring flask (hydrochloric acid concentration: 0.1 N) .

(9) As a standard solution, a standard solution having a concentration of 1000 ppm is diluted with a 0.1 N hydrochloric acid aqueous solution, and is prepared at a concentration of 0.1 ppm, 0.75 ppm, and 1.5 ppm.

(10) Measure by frame atomic absorption.

The calibration curve was prepared by the following method. The standard solution for calibration curve was prepared by diluting a commercially available standard solution for atomic absorption spectrometry (manufactured by Wako Pure Chemical Industries, Ltd.) with a 0.1N hydrochloric acid aqueous solution at a concentration of 0.1, 0.75 and 1.5 ppm. The atomic absorption device was a product "AA-680" manufactured by Shimadzu Corporation.

[Na component]

In the cellulose acetate of the present invention, by setting the Na component to 0.5? (Ca component + Mg component) / Na component? 2.6, ion-equivalent action can be exhibited. The Na component can be measured by the atomic absorption method described above.

The Na component contained in the cellulose acetate is preferably 5 ppm or more and 60 ppm or less, more preferably 15 ppm or more and 55 ppm or less, with respect to the total mass of the cellulose acetate.

When the content of Na in the cellulose acetate is larger than the above range, transparency of the film deteriorates. When the content of Na in the cellulose acetate is smaller than the above range, the humidity resistance of the film tends to be lowered.

The adjustment of the Ca component, the Mg component and the Na component is carried out by adding an organic fatty acid salt such as an organic fatty acid Ca salt, an organic fatty acid Mg salt, an organic fatty acid Na salt, an inorganic Ca salt, an inorganic Mg salt, an inorganic Na salt Of inorganic salts.

As the organic fatty acid salt, an acetate salt, a citrate salt, a maleate salt and the like can be used. As an example of using an inorganic salt, there is a method of adding sulfate or salt.

In addition, a method of washing with water prepared by adjusting the respective ions (Ca, Mg, Na) to the washing water in the cellulose acetate production process is not limited to the addition of the direct salt. Generally, since water contains ground water and tap water, ion content differs depending on the region, so it is preferable to measure the amount of ion for each region.

[Polarizing plate protective film]

The polarizing plate protective film of the present invention preferably contains 70% by mass or more of cellulose acetate having an acetyl group substitution degree of 2.80 to 2.90, and may contain cellulose esters having different degrees of substitution.

Various additives may be contained as a physical property improving agent.

[additive]

The polarizing plate protective film of the present invention preferably contains at least one of a pyranose structure or a furanose structure in an amount of 1 to 12 and a sugar ester compound in which all or a part of OH groups in the structure is esterified Do.

The ratio of the esterification is preferably 40 to 70% or more of the OH groups present in the pyranose structure or the furanose structure.

Examples of sugar as a starting material for synthesizing the sugar ester compound include, for example, the following substances, but the present invention is not limited thereto.

The present invention also relates to a method for producing a compound of formula (I) or a salt thereof, wherein the compound is selected from the group consisting of glucose, galactose, mannose, fructose, xylose, arabinose, lactose, sucrose, Maltose, celotriose, maltotriose, raffinose or kestose.

Other examples include gentiobiose, gentiootriose, gentiotetraose, xylotriose, and galactosyl sucrose.

Among these compounds, a compound having both a pyranose structure and a furanose structure is particularly preferable.

Examples include sucrose, cestose, nistose, 1F-fructosylnitose, stachyose, and the like, more preferably sucrose.

The monocarboxylic acid used for esterifying all or a part of the OH groups in the pyranose structure or the furanose structure is not particularly limited and known aliphatic monocarboxylic acids, alicyclic monocarboxylic acids, Aromatic monocarboxylic acids and the like can be used. The carboxylic acid used may be a single kind or a mixture of two or more kinds.

Specific examples thereof include sucrose pentabenzoate and sucrose octabenzoate.

The polarizing plate protective film of the present invention preferably contains an ester compound represented by the general formula (1) as a plasticizer.

(Wherein B is a hydroxyl group or a carboxylic acid residue, G is an alkylene glycol residue having 2 to 12 carbon atoms or an aryl glycol residue having 6 to 12 carbon atoms or an oxyalkylene glycol residue having 4 to 12 carbon atoms, An alkylene dicarboxylic acid residue of 12 to 12 carbon atoms or an aryl dicarboxylic acid residue of 6 to 12 carbon atoms, and n represents an integer of 1 or more)

Examples of the alkylene glycol component having 2 to 12 carbon atoms in the general formula (1) include ethylene glycol, propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,2-propanediol, , 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2,2- Ethyl-1,3-propanediol (3,3-dimethylolheptane), 3-methyl-1,5-pentanediol 1,6-hexanediol, 2,2 , 4-trimethyl 1,3-pentanediol, 2-ethyl 1,3-hexanediol, 2-methyl 1,8-octanediol, 1,9-nonanediol, 1,10- Decanediol, and the like, and these glycols are used as one kind or a mixture of two or more kinds.

The compound represented by the formula (1) can be suitably used in the range of 1 to 30% by mass of the polarizing plate protective film.

<Other additives>

(Other plasticizer)

In order to obtain the effect of the present invention, the cellulose acetate film of the present invention may contain a plasticizer other than the compound represented by the general formula (1).

The plasticizer is not particularly limited, but is preferably selected from polyvalent carboxylic acid ester plasticizers, glycolate plasticizers, phthalate ester plasticizers, fatty acid ester plasticizers and polyhydric alcohol ester plasticizers, ester plasticizers, and acrylic plasticizers.

When two or more plasticizers are used, at least one of them is preferably a polyhydric alcohol ester plasticizer.

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

In the polarizing plate protective film of the present invention, the plasticizer can be suitably used in the range of 1 to 40% by mass of the polarizing plate protective film.

(Ultraviolet absorber)

The polarizing plate protective film of the present invention may contain an ultraviolet absorber. The ultraviolet absorber is intended to improve durability by absorbing ultraviolet rays of 400 nm or less. Particularly, the transmittance at a wavelength of 370 nm is preferably 10% or less, more preferably 5% or less, still more preferably 2 % Or less.

The amount of the ultraviolet absorber to be used is not the same depending on the kind of the ultraviolet absorber and the conditions of use, but when the dried thickness of the polarizer protective film is 30 to 200 탆, the amount is preferably 0.5 to 10% by mass, And more preferably 4% by mass.

(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, deterioration of the cellulose acetate film may occur.

The antioxidant has a role of retarding or preventing decomposition of the cellulose acetate film by, for example, halogen in the residual solvent amount in the cellulose acetate film or phosphoric acid in the phosphoric acid-based plasticizer, etc. Therefore, the antioxidant is preferably contained in the cellulose acetate film Do.

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

&Lt; Particles >

The polarizing plate protective film of the present invention may contain at least one member selected from the group consisting of silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, kaolin, talc, calcined calcium silicate, hydrated calcium silicate, It is preferable to contain a matting agent such as an inorganic fine particle such as calcium phosphate or a crosslinked polymer. Among them, silicon dioxide is preferable because the haze of the film can be reduced.

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 addition amount can be appropriately determined.

[Polarizer]

And a known polarizing plate protective film may be used on the other side. For example, commercially available cellulose ester films (for example, Konica Minolta Tact KC8UX, KC4UX, KC5UX, KC8UY, KC4UY, KC12UR, KC8UCR-3, KC8UCR-4, KC8UCR-5, KC8UE, KC4UE, KC4FR- KC4FR-4, KC4HR-1, KC8UY-HA, and KC8UX-RHA, all of which are manufactured by Konica Minolta Opto).

[Liquid crystal display device]

By incorporating the polarizing plate bonded with the scattering plate of the present invention in a liquid crystal display device, it is possible to manufacture a liquid crystal display device having excellent visibility, but it is particularly preferable for a liquid crystal display device for outdoor use such as a large liquid crystal display device and digital signage Is used. The polarizing plate of the present invention is bonded to the liquid crystal cell through the adhesive layer or the like.

The polarizing plate of the present invention can be applied to various types of driving methods such as reflective type, transmissive type, transflective type LCD or TN type, STN type, OCB type, HAN type, VA type (PVA type, MVA type) and IPS type It is preferably used in LCD. Particularly, in the display device of a VA type screen having a screen size of 30 or more, especially 30 to 54, there is no outline phenomenon at the periphery of the screen and its effect is maintained for a long time.

<Examples>

Hereinafter, the present invention will be described in detail by way of examples, but the present invention is not limited thereto.

(Production of polyester A)

In a nitrogen atmosphere, 4.85 g of dimethyl terephthalate, 4.4 g of 1,2-propylene glycol, 6.8 g of p-toluic acid and 10 mg of tetraisopropyl titanate were mixed and stirred at 140 DEG C for 2 hours, Followed by stirring for 16 hours. Then, the temperature was lowered to 170 DEG C, and 1,2-propylene glycol as an unreacted product was distilled off under reduced pressure to obtain polyester A.

Acid value: 0.1

Number average molecular weight: 490

Dispersion degree: 1.4

Content of components having a molecular weight of 300 to 1800: 90%

Hydroxyl (hydroxyl group): 0.1

Content of hydroxyl group (hydroxyl group): 0.04%

Polyester A has a monocarboxylic acid twice the molar amount of dicarboxylic acid, and thus the polyester is terminated with a toluic acid ester.

(Fine particle dispersion 1)

Fine particles (Aerosil R812, manufactured by Nitto Aero Chemical Co., Ltd.): 11 parts by mass

Ethanol: 89 parts by mass

The mixture was stirred for 50 minutes in a dissolver, and dispersed with martensol.

(Fine particle addition liquid 1)

The fine particle dispersion 1 was slowly added while sufficiently stirring in a dissolution tank containing methylene chloride. Further, the particles were dispersed in the attritor so that the particle diameter of the secondary particles became a predetermined value. This was filtered with Fine Mat NF manufactured by Nippon Seisen Co., Ltd. to prepare a fine particle addition liquid 1.

Methylene chloride: 99 parts by mass

Fine particle dispersion 1: 5 parts by mass

To prepare a main dope solution having the following composition. First, methylene chloride and ethanol were added to the pressure-melting tank. The cellulose ester was added to the pressurized dissolution tank containing the solvent while stirring. The solution was heated and completely dissolved while stirring, and this was dissolved in an aqueous solution of azulic acid (manufactured by Azumi Co., Ltd.). 244, to prepare a main dope solution.

(Preparation of cellulose triacetate)

With reference to paragraphs "0062" to "0078" of Japanese Patent Laid-Open Publication No. 2008-20192, except that wood pulp is used as the cellulose raw material and hard water made in China is used as pure water, cellulose triacetate (acetyl group substitution degree 2.84 , A Ca component of 24.1 ppm, a Mg component of 2.8 ppm, and an Na component of 32.0 ppm).

(Composition of the main doping solution)

Methylene chloride: 340 parts by mass

Ethanol: 64 parts by mass

Cellulose triacetate (acetyl group degree of substitution: 2.84, Ca component: 24.1 ppm, Mg component: 2.8 ppm, Na component: 32.0 ppm): 100 parts by mass

Sucrose benzoate (average degree of substitution: 5.5): 7.0 parts by mass

Polyester A: 2.5 parts by mass

TINUVIN 928 (BASF Japan Ltd.): 1.5 parts by mass

Fine particle addition liquid 1: 1 part by mass

Was added to a closed vessel and dissolved while stirring to prepare a dope solution.

Subsequently, the dope solution was softened on the stainless steel belt support at a temperature of 33 DEG C and a width of 1,500 mm using an endless belt softening apparatus. The temperature of the stainless steel belt was controlled at 30 占 폚.

On the stainless steel belt support, the solvent was evaporated until the amount of residual solvent in the cast (cast) film was 75%, and then peeled off from the stainless belt support with a peel tension of 110 N / m.

The peeled film was stretched by 20% in the transverse direction using a tenter while applying heat at 160 캜. The residual solvent at the start of the stretching was 15%.

Subsequently, the drying was terminated while conveying the drying zone to a plurality of rolls, and the end of the tenter clip was slit with a laser cutter to obtain a wound sample 1 thereafter. The drying temperature was 130 占 폚, and the conveying tension was 100 N / m.

Subsequently, the acetyl group substitution degree of cellulose triacetate and the Ca component, the Mg component and the Na component in cellulose triacetate were adjusted to prepare a sample as shown in Table 1 for each amount of the polarizing plate protective film.

More specifically, by adjusting the production conditions such as changing the pure water used in the production process to Japanese soft water or adjusting the amount of pure water, Ca salt, Mg salt, Na salt, or changing the number of cleaning, Respectively.

The transparency of these samples was evaluated by haze.

(Hayes)

Each of the samples thus prepared was stored for 24 hours under an atmosphere of 23 ° C and 55% RH. Thereafter, five film samples were subjected to measurement in accordance with JIS K-6714 in a haze meter (1001DP type, Nippon Denshoku Kogyo Co., ). &Lt; / RTI &gt;

From the results of Tables 1 and 2, transparency can be improved by the presence of Na having a composition of 0.5? (Ca component + Mg component) / Na component? 2.6 in the range of 15 ppm? (Ca component + Mg component)? 55 ppm .

Claims (1)

And a degree of substitution of acetyl groups of 2.80 to 2.99, wherein the cellulose acetate satisfies the following conditions.
(1) 15 ppm? (Ca component + Mg component)? 55 ppm
(2) 0.5? (Ca component + Mg component) / Na component? 2.6