JPWO2012077397A1 - Polarizing plate protective film - Google Patents

Abstract

An object of the present invention is to provide a polarizing plate protective film having improved transparency. A polarizing plate protective film comprising, as a main component, cellulose acetate 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

Description

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

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

  This cellulose triacetate film contains various impurities because the raw material is a natural product of cellulose, and for example, adverse effects on metal polarizing plate protective films and solutions for the same have been proposed.

With regard to the transparency of the film, it has been proposed that the total amount of metals such as alkali metal and alkaline earth metal is 5.5 × 10 ⁻⁶ equivalent or less (Patent Document 1).

  From the viewpoint of bright spot foreign matter, it has been proposed to regulate the Ca component 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 such as coating a discotic liquid crystal layer on the surface, it has been proposed to use a film using cellulose acetate having a Ca component content of 120 ppm or less as a base material (Patent Document 3). ).

  In this way, despite the recognition that it is necessary to limit the total amount of alkali metals and alkaline earth metals, the current production process of cellulose triacetate is inevitable and effective. Response was required.

  In particular, with regard to transparency, there has been a great demand for display devices with a larger screen.

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

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

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

  1. A polarizing plate protective film comprising, as a main component, cellulose acetate 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 best mode for carrying out the present invention will be described in detail. In this specification, “ppm” means “mass ppm”.

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

(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” mean the mass in terms of atoms of Ca, Mg, and Na contained in cellulose acetate, respectively.

  So far, it has been considered that the Ca component and Mg component in cellulose acetate should be small, but in reality, they cannot be reduced to zero and have been used to some extent.

  Usually, Ca component and Mg component exist as divalent metal ions in cellulose acetate, and these divalent metal ions bridge the unsubstituted hydroxyl group of cellulose acetate, resist stretching treatment and increase haze, It is supposed to act such as generating aggregates.

  In the present invention, a monovalent Na ion is coordinated to an unsubstituted hydroxyl group, hindering bridging of the unsubstituted hydroxyl group of cellulose acetate formed by a divalent Ca component and an Mg component, thereby increasing haze during stretching, doping It is considered that the generation of aggregates therein is suppressed, and as a result, the transparency of the film is ensured.

  Although this action is originally not strong and clear when the hydroxyl groups of cellulose acetate have a large number of unsubstituted hydroxyl groups, the effect is prominent when the degree of acetyl group substitution is 2.80 to 2.99 with a small number of unsubstituted hydroxyl groups. .

  As described above, the present invention has been found that even when the Ca component and the Mg component are present, the action of the Ca component and the Mg component is suppressed when the Na component coexists.

[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 means a component occupying 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.

  “Degree of acetyl group substitution” means the average number of acetyl groups per glucose unit, and one of the hydrogen atoms of the hydroxyl groups at the 2nd, 3rd and 6th positions of the 1 glucose unit is substituted with the acetyl group. Indicates the percentage. That is, when all of the hydrogen atoms of the hydroxyl groups at the 2-position, 3-position and 6-position are substituted with an acetyl group, the substitution degree (maximum substitution degree) is 3.0.

  The measuring method of acyl substitution degree can be implemented according to ASTM D-817-91, and acetyl group substitution degree is 2.80-2.99.

  The number average molecular weight (Mn) of cellulose acetate is preferred because the mechanical strength of the film from which a range of 30000-300000 is obtained is strong. Furthermore, the thing of 50000-200000 is used preferably.

  The value of the ratio Mw / Mn of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of 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 Showa Denko Co., Ltd.)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corporation) Mw = 100000 to 500 calibration curves with 13 samples were used. Thirteen samples are used at approximately equal intervals.

  The cellulose as a raw material for cellulose acetate is not particularly limited, and examples thereof include cotton linters, wood pulp (derived from conifers and hardwoods), kenaf and the like. Moreover, the cellulose ester 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 methods described in JP-A-10-45804 and JP-A-2009-161701.

  As a commercial item, Daicel Corporation LT-35, LT-55, LT-105, etc. are mentioned.

[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 cellulose acetate production process, Ca salt, Mg salt are used, or the amount thereof is adjusted, or partial addition is performed instead of adding all at once (partial neutralization is repeated in the aging step (continuous, Or neutralize by adding a base intermittently)), adjusting the amount of recovered and reclaimed products to be used, or selecting pure water with adjusted amounts of each ion, and repeating washing to contain the cellulose acetate The Ca content and the Mg component can be set within this range by adjusting the content of the metal. Further, the Ca component and the Mg component contained in the cellulose acetate are preferably 10 ppm or more and 50 ppm or less, 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 cellulose acetate is preferably 5 ppm to 50 ppm, more preferably 10 ppm to 40 ppm, based on the total mass of cellulose acetate.

  The Mg component contained in the cellulose acetate is preferably 10 ppm or less, more preferably 5 ppm or less, based on 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 is deteriorated, and if the amount of metal contained in the cellulose acetate is smaller than the above range, the moisture and heat resistance of the film tends to be inferior. A range is preferred.

The Ca component, Mg component, and Na component of the present invention can be measured by the following atomic absorption method.
(1) Immerse the washed 50 ml capacity magnetic crucible in 2N aqueous nitric acid solution overnight.
(2) A magnetic crucible soaked in 2N nitric acid is washed with pure water, rinsed with ultrapure water, and dried in a drier.
(3) Weigh accurately 2 g of cellulose acetate sample in a magnetic crucible.
(4) Carbonize the sample in the magnetic crucible on the electric heater.
(5) Place the magnetic crucible in an electric furnace and incinerate at 500 ° C. for about 1 hour and at 600 ° C. for about 1.5 hours.
(6) When the ash is completely white, stop the electric furnace and let it cool in the furnace.
(7) Put 10 ml of 0.5N hydrochloric acid aqueous solution in a magnetic crucible and dissolve by heating on a sand bath.
(8) The solution is allowed to cool and then transferred to a 50 ml volumetric flask using a washed funnel, and the magnetic crucible is washed with ultrapure water to make up the volume (hydrochloric acid concentration: 0.1 N).
(9) As a standard solution, a standard solution having a concentration of 1000 ppm is diluted with a 0.1N hydrochloric acid aqueous solution and prepared at concentrations of 0.1 ppm, 0.75 ppm, and 1.5 ppm.
(10) Measured by flame atomic absorption.

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

[Na component]
In the cellulose acetate of the present invention, an ion equivalent action can be exhibited by setting the Na component to 0.5 ≦ (Ca component + Mg component) / Na component ≦ 2.6. The Na component can be measured by the aforementioned atomic absorption method.

  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 amount of Na contained in cellulose acetate is larger than the above range, the transparency of the film is deteriorated, and when the amount of Na contained in cellulose acetate is smaller than the above range, the moisture and heat resistance of the film tends to be inferior. A range is preferred.

  Adjustment of the said Ca component, Mg component, and Na component is organic fatty acid Ca salt, organic fatty acid Mg salt, organic fatty acid salt, such as organic fatty acid Na salt, inorganic Ca salt, inorganic Mg salt, inorganic Na to cellulose acetate which removed the salt This can be achieved by including an inorganic salt such as a salt.

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

  Moreover, the method of wash | cleaning using the water which adjusted each ion (Ca, Mg, Na) for the washing water in a cellulose acetate manufacturing process instead of adding salt directly is mentioned. In general, since water uses ground water and tap water, the ion content varies depending on the region. Therefore, it is preferable to measure and use the ion amount 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 other cellulose esters having different substitution degrees.

  Moreover, various additives can be contained as a physical property improving agent.

[Additive]
The polarizing plate protective film of the present invention preferably contains a sugar ester compound having at least one pyranose structure or at least one furanose structure and having all or part of the OH groups of the structure esterified. .

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

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

  Glucose, galactose, mannose, fructose, xylose or arabinose, lactose, sucrose, nystose, 1F-fructosyl nystose, stachyose, maltitol, lactitol, lactulose, cellobiose, maltose, cellotriose, maltotriose, raffinose or kestose .

  In addition, gentiobiose, gentiotriose, gentiotetraose, xylotriose, galactosyl sucrose, and the like are also included.

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

  Examples include sucrose, kestose, nystose, 1F-fructosyl nystose, stachyose, and more preferably sucrose.

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

  Specific examples 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 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 (1), the alkylene glycol component having 2 to 12 carbon atoms includes ethylene glycol, 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-hexane Diol, 2,2,4-trimethyl 1,3-pentanediol, 2-ethyl 1,3-hexanediol, 2-methyl 1,8 Octanediol, 1,9-nonanediol, 1,10-decanediol, there are 1,12-octadecane diol, these glycols may be used alone or in combination.

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

<Other additives>
(Other plasticizers)
The cellulose acetate film of this invention can contain plasticizers other than the compound represented by General formula (1) as needed, when obtaining the effect of this 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.

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

(UV absorber)
The polarizing plate protective 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.

  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 polarizing plate protective 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, and silicic acid in order to improve handling properties. It is preferable to include a matting agent such as inorganic fine particles such as aluminum, magnesium silicate and calcium phosphate, and 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.

[Polarizer]
A known polarizing plate protective film can be used on the other surface. For example, a commercially available cellulose ester film (for example, Konica Minoltack KC8UX, KC4UX, KC5UX, KC8UY, KC4UY, KC12UR, KC8UCR-3, KC8UCR-4, KC8UCR-5, KC8UE, KC4R-4, KC4FR-3, KC4FR-3, KC4FR-3, KC4FR-3, KC4FR-3, KC4FR-3, -1, KC8UY-HA, KC8UX-RHA, manufactured by Konica Minolta Opto Co., Ltd.) and the like are preferably used.

[Liquid Crystal Display]
By incorporating the polarizing plate bonded with the scattering plate of the present invention into a liquid crystal display device, it is possible to produce various liquid crystal display devices with excellent visibility, but particularly outdoors such as large liquid crystal display devices and digital signage. It is preferably used for a liquid crystal display device for use. The polarizing plate of the present invention is bonded to a liquid crystal cell via the adhesive layer or the like.

  The polarizing plate of the present invention includes various types such as a reflective type, a transmissive type, a transflective type LCD, a TN type, an STN type, an OCB type, a HAN type, a VA type (PVA type, MVA type), and an IPS type (including an FFS type). It is preferably used in a drive type LCD. In particular, in a large-screen display device having a VA type screen of 30 type or more, particularly 30 type to 54 type, there is no white spot in the periphery of the screen and the effect is maintained for a long time.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

(Preparation 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 ° C. for 2 hours. Stirring was carried out at ° C for 16 hours. Next, the temperature was lowered to 170 ° C., and unreacted 1,2-propylene glycol was distilled off under reduced pressure to obtain polyester A.

Acid value: 0.1
Number average molecular weight: 490
Dispersity: 1.4
Component content of molecular weight 300-1800: 90%
Hydroxyl (hydroxyl) value: 0.1
Hydroxyl group (hydroxyl group) content: 0.04%
Polyester A has a terminal toluic acid ester because the monocarboxylic acid is used in an amount twice as much as that of the dicarboxylic acid.

(Fine particle dispersion 1)
Fine particles (Aerosil R812 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. The cellulose ester was added to the pressure dissolution tank containing the solvent while stirring. This was heated and stirred to dissolve completely, and this was dissolved in Azumi Filter Paper No. The main dope solution was prepared by filtration using 244.

(Manufacture of cellulose triacetate)
Cellulose triacetate (acetyl group substitution degree 2) with reference to paragraphs “0062” to “0078” of JP-A-2008-20192 except that wood pulp is used as the cellulose raw material and Chinese hard water is used as pure water. .84, Ca component 24.1 ppm, Mg component 2.8 ppm, Na component 32.0 ppm).

(Main dope composition)
Methylene chloride 340 parts by mass Ethanol 64 parts by mass Cellulose triacetate (acetyl group substitution degree 2.84 Ca component 24.1 ppm, Mg component 2.8 ppm, Na component 32.0 ppm) 100 parts by mass Sucrose benzoate (average substitution degree 5.5) 7.0 parts by mass Polyester A 2.5 parts by mass TINUVIN 928 (manufactured by BASF Japan Ltd.) 1.5 parts by mass Particulate additive solution 1 1 part by mass Prepared.

  Next, using an endless belt casting apparatus, the dope solution was 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 110 N / m.

  The peeled film was stretched 20% 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 completed while transporting the drying zone with a large number of rolls, and the ends sandwiched between tenter clips were slit with a laser cutter, and then a wound sample 1 was obtained. The drying temperature was 130 ° C. and the transport tension was 100 N / m.

  Next, samples having the respective amounts in the polarizing plate protective film as shown in Table 1 were prepared by adjusting the degree of acetyl group substitution of cellulose triacetate and the Ca component, Mg component, and Na component in cellulose triacetate.

  Specifically, adjust the manufacturing conditions such as changing the pure water used in the manufacturing process to Japanese soft water, adjusting the amount of pure water, Ca salt, Mg salt, Na salt used, changing the number of washings, etc. Thus, the amount of contained metal was adjusted.

  The transparency of these samples was evaluated with haze.

(Haze)
Each of the prepared samples was stored in an atmosphere of 23 ° C. and 55% RH for 24 hours, and thereafter, in the same atmosphere, five film samples were subjected to a haze meter (1001DP type, manufactured by Nippon Denshoku Industries Co., Ltd.) according to JIS K-6714. ).

  From the results of Tables 1 and 2, if 15 ppm ≦ (Ca component + Mg component) ≦ 55 ppm, the presence of 0.5 ≦ (Ca component + Mg component) / Na component ≦ 2.6 makes it transparent. It can be seen that the property can be improved.

Claims (1)

A polarizing plate protective film comprising, as a main component, cellulose acetate 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