JP5724820B2 - Cellulose ester film, retardation film, polarizing plate and liquid crystal display device - Google Patents

Description

  The present invention relates to a cellulose ester film, a retardation film, a polarizing plate, and a liquid crystal display device.

  Liquid crystal display devices are widely used in monitors and televisions of personal computers and portable devices because they have low voltage and low power consumption and can be reduced in size or thickness. In particular, a liquid crystal display device for television use is expected to be viewed from various angles on a large screen, and thus it is required to reduce the viewing angle dependency.

  Examples of liquid crystal cell display methods that can reduce the viewing angle dependency include an IPS (In-Plane Switching) method, an OCB (Optically Compensatory Bend) method, and a VA (Vertically Aligned) method.

  On the other hand, as an optical film capable of reducing the viewing angle dependency, a protective film for a polarizing plate (having no optical anisotropy) and a liquid crystal layer arranged thereon and having liquid crystal molecules aligned in an arbitrary direction A retardation film having been proposed (for example, Patent Document 1). In addition, a cellulose ester film containing a retardation increasing agent (for example, Patent Document 2) and a cellulose ester film containing a carbohydrate derivative in which a hydroxyl group is substituted with two or more substituents (for example, Patent Document 3) have been proposed. Yes.

  Usually, the retardation value in the in-plane direction of the cellulose ester film shows reverse wavelength dispersion. However, the retardation value in the in-plane direction of the cellulose ester film containing the retardation increasing agent exhibits forward wavelength dispersion or flat wavelength dispersion (the retardation value is constant regardless of the wavelength). The cellulose ester film whose retardation value in the in-plane direction shows forward wavelength dispersion or flat wavelength dispersion is capable of optical compensation for light of a specific wavelength, but for light of another wavelength. In many cases, optical compensation is impossible, and optical compensation in a wide wavelength band cannot be performed.

  On the other hand, a film containing a cellulose ester (for example, cellulose diacetate) having a low acyl group substitution degree has been proposed. A cellulose ester having a low acyl group substitution degree has a high intrinsic birefringence, and therefore, retardation tends to be exhibited by stretching. In addition, the retardation in the in-plane direction after stretching of a film containing a cellulose ester having a low acyl group substitution degree exhibits reverse wavelength dispersion, so that optical compensation in a wide wavelength band is easy to perform.

European Patent Application No. 0911656 JP 2004-109410 A JP 2011-94098 A

  Since the cellulose ester is usually obtained by esterifying cellulose with acetic acid, it contains a small amount of free acetic acid. In particular, a cellulose ester having a low acyl group substitution degree is easily hydrolyzed by a small amount of free acetic acid and moisture, and more easily generates free acetic acid. Moreover, the rate constant of the hydrolysis reaction of the cellulose ester greatly depends on the content of free acetic acid and the temperature. Therefore, the cellulose ester having a low acyl group substitution degree is easily hydrolyzed particularly under high temperature and high humidity, and the long-term stability is low.

  Thus, since the cellulose ester with a low acyl group substitution degree such as cellulose diacetate has low long-term stability, physical properties such as the acyl group substitution degree are likely to vary. Cellulose esters with large variations in physical properties have low compatibility with additives such as plasticizers, so there is a problem that the resulting film not only has high internal haze, but also tends to bleed out particularly under high temperature and high humidity. .

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a cellulose ester film having low internal haze and suppressed bleeding out.

（式（１）において、
Ｇは、単糖または多糖の残基を表し、
Ｌ_１は、それぞれ独立して単結合、アルキレン基、カルボニル基またはアルキレンカルボニル基を表し、
Ｒ_１は、それぞれ独立して芳香族基を表し、
Ｌ_２は、それぞれ独立して単結合またはカルボニル基を表し、
Ｒ_２は、それぞれ独立して脂肪族からなる基を表し、
ｐは、２以上の整数を表し、
ｑおよびｒは、それぞれ独立に１以上の整数を表し、かつ
ｐ＋ｑ＋ｒは、前記Ｇが、無置換の糖類であるときに含まれるヒドロキシル基の総数を表す）
［３］ 前記セルロースエステルの総アシル基置換度が１．５〜２．５である、［１］または［２］に記載のセルロースエステルフィルム。
［４］ 前記セルロースエステルの炭素原子数３以上のアシル基の置換度が０である、［３］に記載のセルロースエステルフィルム。
［５］ 前記一般式（１）において、ｑがｒよりも大きい、［２］〜［４］のいずれかに記載のセルロースエステルフィルム。
［６］ 前記一般式（１）において、Ｇは、単糖、二糖または三糖の残基である、［２］〜［５］のいずれかに記載のセルロースエステルフィルム。
［７］ 前記セルロースエステルフィルムの内部ヘイズが、０．１１％以下である、［１］〜［６］のいずれかに記載のセルロースエステルフィルム。
［８］ 下記式（Ｉ）で表される、波長５９０ｎｍでのリターデーションＲｏが３０〜１５０ｎｍであり、かつ下記式（II）で表される、波長５９０ｎｍでのＲｔｈが７０〜３００ｎｍである、［１］〜［７］のいずれかに記載のセルロースエステルフィルム。
式（Ｉ） Ｒｏ＝（ｎｘ−ｎｙ）×ｄ
式（II） Ｒｔｈ＝｛（ｎｘ＋ｎｙ）／２−ｎｚ｝×ｄ
（ｎｘは、フィルムの面内方向において屈折率が最大になる方向ｘにおける屈折率を表し；
ｎｙは、フィルムの面内方向において前記方向ｘと直交する方向ｙにおける屈折率を表し；
ｎｚは、フィルムの厚み方向ｚにおける屈折率を表し；
ｄ（ｎｍ）は、フィルムの厚みを表す） [1] A part of the hydroxyl group of the cellulose ester and the constituent sugar is respectively substituted with a substituent containing an aromatic group and a substituent not containing an aromatic group, and two or more hydroxyl groups are not substituted. And a saccharide remaining in the cellulose ester film.
[2] The cellulose ester film according to [1], wherein the saccharide has a structure represented by the following general formula (1).
General formula (1)

(In Formula (1),
G represents a monosaccharide or polysaccharide residue;
Each L ₁ independently represents a single bond, an alkylene group, a carbonyl group or an alkylenecarbonyl group;
Each R ₁ independently represents an aromatic group;
L ₂ each independently represents a single bond or a carbonyl group;
R ₂ each independently represents an aliphatic group;
p represents an integer of 2 or more,
q and r each independently represents an integer of 1 or more, and p + q + r represents the total number of hydroxyl groups contained when G is an unsubstituted saccharide)
[3] The cellulose ester film according to [1] or [2], wherein the cellulose ester has a total acyl group substitution degree of 1.5 to 2.5.
[4] The cellulose ester film according to [3], wherein the substitution degree of the acyl group having 3 or more carbon atoms of the cellulose ester is 0.
[5] The cellulose ester film according to any one of [2] to [4], wherein q is greater than r in the general formula (1).
[6] The cellulose ester film according to any one of [2] to [5], wherein G is a residue of a monosaccharide, a disaccharide, or a trisaccharide in the general formula (1).
[7] The cellulose ester film according to any one of [1] to [6], wherein an internal haze of the cellulose ester film is 0.11% or less.
[8] Retardation Ro at a wavelength of 590 nm represented by the following formula (I) is 30 to 150 nm, and Rth at a wavelength of 590 nm represented by the following formula (II) is 70 to 300 nm. The cellulose ester film according to any one of [1] to [7].
Formula (I) Ro = (nx−ny) × d
Formula (II) Rth = {(nx + ny) / 2−nz} × d
(Nx represents the refractive index in the direction x where the refractive index is maximum in the in-plane direction of the film;
ny represents the refractive index in the direction y perpendicular to the direction x in the in-plane direction of the film;
nz represents the refractive index in the thickness direction z of the film;
d (nm) represents the thickness of the film)

[9] A retardation film comprising the cellulose ester film according to any one of [1] to [8].
[10] A polarizing plate having a polarizer and the cellulose ester film according to any one of [1] to [8] disposed on at least one surface of the polarizer.
[11] A liquid crystal display device including a liquid crystal cell and a pair of polarizing plates sandwiching the liquid crystal cell, wherein at least one of the pair of polarizing plates is a polarizer and at least one surface of the polarizer A liquid crystal display device comprising the cellulose ester film according to any one of [1] to [8].

  The saccharide contained in the film of the present invention can be satisfactorily compatible with, for example, cellulose esters whose physical properties tend to vary. Therefore, the film of the present invention has a low internal haze and suppresses bleeding out.

It is a schematic diagram which shows the basic composition of one Embodiment of a liquid crystal display device.

1. Cellulose ester film The cellulose ester film of the present invention contains at least a cellulose ester and a specific saccharide.

Cellulose ester The cellulose ester contained in the cellulose ester film of the present invention is a compound obtained by esterifying cellulose with an aliphatic carboxylic acid or aromatic carboxylic acid having 2 to 22 carbon atoms, and preferably cellulose is added with carbon atoms. It is a compound esterified with 7 or less aliphatic carboxylic acid.

  The aliphatic acyl group contained in the cellulose ester may be linear or branched, and may form a ring. Usually, when the aliphatic acyl group has too many carbon atoms, retardation is hardly exhibited. Therefore, the number of carbon atoms in the aliphatic acyl group is preferably 2-7, more preferably 2-6, and even more preferably 2-4. The aliphatic acyl group may be only one type or two or more types.

  Examples of the cellulose ester include cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate propionate butyrate, and the like, preferably cellulose acetate.

  The total substitution degree of the acyl group of the cellulose ester is preferably 1.50 to 2.50, and more preferably 2.0 to 2.45 in order to develop high retardation. Among these, the substitution degree of the acetyl group is preferably 1.50 to 2.50, and more preferably 2.0 to 2.45. The substitution degree of an acyl group having 3 or more carbon atoms is preferably 1.0 or less, and more preferably 0.

  Among them, cellulose acetate having a substitution degree of acetyl group of 1.50 to 2.50, preferably 2.0 to 2.45 is preferable because of low cost and easy development of retardation.

  The acyl group substitution degree of cellulose ester can be measured according to ASTM-D817-96.

In order to obtain a film having a high mechanical strength, the number average molecular weight of the cellulose ester is preferably in the range of 3.0 × 10 ^{4 to} 7.0 × 10 ⁴ , and 4.5 × 10 ^{4 to} 6. A range of 0 × 10 ⁴ is more preferable.

The number average molecular weight of the cellulose ester can be measured by gel permeation chromatography (GPC). The measurement conditions are as follows.
Solvent: Methylene chloride Column: Three Shodex K806, K805, K803G (manufactured by Showa Denko KK) are connected and used.
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 = 1.0 × 10 ^{6 to} 5.0 × 10 ² 13 calibration curves are used. The 13 samples are preferably selected at approximately equal intervals.

  Cellulose esters can be synthesized by known methods. Specifically, cellulose is esterified in the presence of a catalyst with an organic acid having 3 or more carbon atoms containing at least acetic acid or an anhydride thereof or an anhydride thereof to synthesize a cellulose triester. Subsequently, the cellulose triester is hydrolyzed to synthesize a cellulose ester having a desired degree of acyl substitution. The obtained cellulose ester can be filtered, precipitated, washed with water, dehydrated and dried to obtain a cellulose ester (see the method described in JP-A-10-45804).

  Examples of cellulose used as a raw material include cotton linter, wood pulp (derived from conifers and hardwoods), kenaf and the like. The cellulose used as a raw material may be only one type or a mixture of two or more types.

  Examples of commercially available products include L20, L30, L40, L50 manufactured by Daicel Chemical Industries, Ltd., CA398-3, CA398-6, CA398-10, CA398-30, CA394-60S manufactured by Eastman Chemical Co., Ltd. .

About sugars In the sugars contained in the cellulose ester film of the present invention, a part of hydroxyl groups contained in the constituent sugars are respectively substituted with a substituent containing an aromatic group and a substituent not containing an aromatic group, and A compound in which two or more hydroxyl groups remain unsubstituted.

Such saccharides preferably have a structure represented by the following general formula (1).
General formula (1)

  G in the formula (1) represents a monosaccharide or polysaccharide residue. The monosaccharide or polysaccharide constituting G preferably has at least one of a pyranose structure and a furanose structure, preferably 1 or more and 12 or less, more preferably 1 or more and 4 or less, and still more preferably 1 or more and 3 or less.

  Examples of monosaccharides constituting G include glucose, galactose, mannose, fructose, xylose and arabinose, preferably glucose.

  Examples of disaccharides constituting G include lactose, sucrose, maltitol, lactitol, lactulose, cellobiose, maltose, gentiobiose and the like. Examples of the trisaccharide constituting G include cellotriose, maltotriose, raffinose, kestose, gentiotriose, xylotriose, and the like. Examples of the tetrasaccharide or more constituting G include nystose, 1F-fructosyl nystose, stachyose, gentiotetraose, galactosyl sucrose and the like. Of these, sugars having both a pyranose structure and a furanose structure are preferable, sucrose, kestose, nystose, 1F-fructosyl nystose, stachyose and the like are more preferable, and sucrose is more preferable.

-(L ₁ -R ₁ ) in formula (1) represents a substituent containing an aromatic group.

_{- (L 1 -R 1) L} 1 in a single bond, an alkylene group, a carbonyl group, an alkylene group, preferably a carbonyl group or alkylene group. The plurality of L ₁ may be the same as or different from each other.

  The number of carbon atoms of the alkylene group is preferably 1 to 5, and more preferably 1 or 2. Examples of the alkylene group include a methylene group and an ethylene group. The number of carbon atoms of the alkylene moiety in the alkylenecarbonyl group is preferably 1 to 5, and preferably 1 or 2. Examples of the alkylenecarbonyl group include a methylenecarbonyl group and an ethylenecarbonyl group.

- _{R 1} in _{(L 1} -R 1) represents an aromatic group. The number of ring carbon atoms in the aromatic group is preferably 6 to 24, more preferably 6 to 18, and still more preferably 6 to 12. Examples of the aromatic group include a phenyl group and a naphthyl group. The aromatic group may further have a substituent such as an alkyl group having 1 to 5 carbon atoms. Several R < ₁ > may mutually be the same and may differ.

Specific examples of-(L ₁ -R ₁ ) include a phenyl group, a benzyl group, a phenethyl group, a benzoyl group, and a phenylacetyl group.

Equation (1) - _(L 2 -R ₂₎ indicates a substituent containing no aromatic group.

- _{L 2} in _{(L 2} -R 2) is a single bond or a carbonyl group, preferably a carbonyl group. The plurality of L ₂ may be the same as or different from each other.

- _(L 2 -R ₂₎ in _{R 2} represents a group consisting of aliphatic (aliphatic group). The aliphatic group is a saturated or unsaturated aliphatic group, preferably a saturated aliphatic group. A saturated aliphatic group is an alkyl group or a cycloalkyl group. The plurality of R ₂ may be the same as or different from each other.

  The number of carbon atoms in the alkyl group is preferably 1 to 22, more preferably 1 to 12, and still more preferably 1 to 8. Examples of the alkyl group include methyl group, ethyl group, propyl group, t-butyl group and the like.

  The number of ring carbon atoms in the cycloalkyl group is preferably 3-22, and more preferably 5-12. Examples of the cycloalkyl group include a cyclohexyl group, a cyclopentyl group, a cyclooctyl group, and the like. The alkyl group and cycloalkyl group may further have a substituent such as a hydroxyl group.

- Specific examples of _{(L 2} -R 2), t- butyl group, an acetyl group, and the like propionyl group.

  p represents the number of (unsubstituted) hydroxyl groups. p represents an integer of 2 or more, preferably an integer of 3 or more. This is because a saccharide having p of 2 or more has high compatibility with a cellulose ester.

q represents the number of substituents (-(L ₁ -R ₁ )) containing the aforementioned aromatic group; r is a substituent (-(L ₂ -R ₂ ) not containing the aforementioned aromatic group; ). q and r each independently represent an integer of 1 or more. p + q + r represents the total number of hydroxyl groups contained when G described above is an unsubstituted saccharide. For example, when G is a group derived from sucrose, p + q + r is 8, and when G is a group derived from glucose, p + q + r is 5.

  In order to improve the retardation development property and bleed-out resistance of the cellulose ester film, the number (q) of substituents containing an aromatic group is preferably larger than the substituents (r) containing no aromatic group.

The compound represented by the formula (1) can be obtained by a known method. For example, a compound in which L ₁ in formula (1) is a carbonyl group or an alkylenecarbonyl group and L ₂ is a carbonyl group can be obtained by esterifying a sugar with a monocarboxylic acid.

  The monocarboxylic acid to be reacted with the sugar is not particularly limited, and may be a mixture of a known aliphatic monocarboxylic acid or alicyclic monocarboxylic acid and an aromatic monocarboxylic acid.

Examples of aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, lauric acid Saturated fatty acids such as acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, and laccelic acid ;
Unsaturated fatty acids such as undecylenic acid, oleic acid, sorbic acid, linoleic acid, linolenic acid, arachidonic acid and octenoic acid are included.

  Examples of the alicyclic monocarboxylic acid include cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, cyclooctanecarboxylic acid and the like.

  The aromatic monocarboxylic acid is a monocarboxylic acid having one or more benzene rings, and the benzene ring may further have a substituent such as an alkyl group or an alkoxy group. Examples of aromatic monocarboxylic acids include benzoic acid, xylic acid, hemelitic acid, mesitylene acid, prenicylic acid, γ-isoduric acid, jurylic acid, mesitonic acid, α-isoduric acid, cumic acid, α-toluic acid, hydroatropa Acid, atropic acid, hydrocinnamic acid, salicylic acid, o-anisic acid, m-anisic acid, p-anisic acid, creosote acid, o-homosalicylic acid, m-homosalicylic acid, p-homosalicylic acid, o-pyrocatechuic acid, β-resorcylic acid, vanillic acid, isovanillic acid, veratromic acid, o-veratrumic acid, gallic acid, asaronic acid, mandelic acid, homoanisic acid, homovanillic acid, homoveratrumic acid, o-homoveratrumic acid, phthalonic acid, p-coumaric acid, etc. Among them, benzoic acid is particularly preferable.

  In the process of synthesizing the compound represented by the formula (1), in order to leave two or more of the hydroxyl groups contained in the constituent sugars, the amount of monocarboxylic acid used in the esterification reaction may be adjusted, for example. .

Specific examples of the compound represented by the formula (1) include the following.

  As described above, since the cellulose ester having a low acyl group substitution degree such as cellulose diacetate contains free acetic acid, its physical properties are likely to vary over time as compared with a cellulose ester having a high acyl group substitution degree such as cellulose triacetate. Since the cellulose ester having a low acyl group substitution degree having a large variation in physical properties is not compatible with the plasticizer, the resulting film has a high internal haze, and the plasticizer tends to precipitate (bleed out) on the film surface.

  On the other hand, since the saccharide used in the present invention contains two or more unsubstituted hydroxyl groups, it is easily compatible with a cellulose ester having a low acyl group substitution degree having a large variation in physical properties.

  In addition, since the saccharide used in the present invention is partially substituted with a “substituent containing an aromatic group”, the retardation is highly expressed. In addition, since the “substituent containing an aromatic group” contained in one saccharide and the “substituent containing an aromatic group” contained in the other saccharide are likely to interact, the saccharide is less likely to bleed out. .

  Furthermore, since the saccharide used in the present invention is partially substituted with a “substituent containing no aromatic group”, a part of the hydroxyl group is substituted with a “substituent containing an aromatic group”. The compatibility with cellulose ester can be increased.

  The content of the saccharide is preferably 0.5 to 30% by mass, more preferably 5 to 20% by mass with respect to the cellulose ester. If the saccharide content is less than 0.5% by mass, hydrolysis of the cellulose ester may not be sufficiently suppressed, and if it exceeds 30% by mass, bleeding may occur.

Plasticizer Examples of plasticizers include polyester plasticizers, polyhydric alcohol ester plasticizers, polycarboxylic acid ester plasticizers (including phthalate ester plasticizers), glycolate plasticizers, ester plasticizers. Agents (including fatty acid ester plasticizers) and acrylic plasticizers. These may be used alone or in combination of two or more.

Polyester Plasticizer The polyester plasticizer is preferably a polyester compound represented by the following general formula (2).
General formula (2)

  In formula (2), A represents a divalent group derived from an alkylene dicarboxylic acid having 4 to 12 carbon atoms or a divalent group derived from an aryl dicarboxylic acid having 6 to 12 carbon atoms. G is a divalent group derived from an alkylene glycol having 2 to 12 carbon atoms, a divalent group derived from an aryl glycol having 6 to 12 carbon atoms, or an oxyalkylene having 4 to 12 carbon atoms. Represents a divalent group derived from glycol. B represents a monovalent group derived from a hydrogen atom or a carboxylic acid. n represents an integer of 1 or more.

  Examples of the divalent group derived from alkylene dicarboxylic acid having 4 to 12 carbon atoms of A include oxalic acid, malonic acid, succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, pimelic acid, A divalent group derived from suberic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid and the like is included, and succinic acid and adipic acid are particularly preferable. Examples of the divalent group derived from aryl dicarboxylic acid having 6 to 12 carbon atoms in A include phthalic acid, terephthalic acid, isophthalic acid, 1,5-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, Divalent groups derived from 2,6-naphthalenedicarboxylic acid and the like are included, and phthalic acid and terephthalic acid are particularly preferable.

  Examples of the divalent group of G derived from an alkylene glycol having 2 to 12 carbon atoms include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, , 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-didiol) Methylol heptane), 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, - nonanediol, include divalent groups derived from 1,10-decanediol, and 1,12-octadecanediol like. In particular, ethylene glycol, 1,2-propylene glycol, and 1,3-propylene glycol are preferable.

  Examples of the divalent group of G derived from an aryl glycol having 6 to 12 carbon atoms include 1,2-dihydroxybenzene (catechol), 1,3-dihydroxybenzene (resorcinol), and 1,4-dihydroxy. Divalent groups derived from benzene (hydroquinone) and the like are included. Examples of the divalent group derived from oxyalkylene glycol having 4 to 12 carbon atoms in G are derived from diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol and the like. Divalent groups are included.

  G is preferably a divalent group derived from an alkylene glycol having 2 to 12 carbon atoms. This is to increase the compatibility of the polyester compound with the cellulose ester.

  Examples of monovalent groups of B derived from carboxylic acid include benzoic acid, para-tert-butyl benzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, dimethyl benzoic acid, ethyl benzoic acid, normal propyl benzoic acid, Examples include monovalent groups derived from aromatic carboxylic acids such as aminobenzoic acid and acetoxybenzoic acid; and monovalent groups derived from aliphatic carboxylic acids such as acetic acid, propionic acid, and butyric acid. In particular, a monovalent group derived from acetic acid, propionic acid, butyric acid or benzoic acid is preferred.

  The number average molecular weight of the polyester plasticizer is preferably 300 to 1800, more preferably 300 to 600. Polyester plasticizers having a number average molecular weight of less than 300 not only easily volatilize but also easily flow out of the film into the saponification solution during the saponification treatment. A polyester plasticizer having a number average molecular weight exceeding 1800 has low compatibility with a cellulose ester having a low acyl group substitution degree, and the internal haze of the resulting film tends to be high.

  The content of the polyester plasticizer is preferably 0.5 to 20% by mass and more preferably 0.5 to 10% by mass with respect to the cellulose ester. If it is less than 0.5% by mass, the function as a plasticizer may not be sufficiently obtained, and if it exceeds 20% by mass, it may bleed out or flow out into the saponification solution.

Polyhydric alcohol ester plasticizer The polyhydric alcohol ester plasticizer is an ester compound (alcohol ester) of a divalent or higher aliphatic polyhydric alcohol and a monocarboxylic acid, preferably a 2-20 valent aliphatic. It is a polyhydric alcohol ester. The polyhydric alcohol ester compound preferably has an aromatic ring or a cycloalkyl ring in the molecule.

Examples of the divalent alcohol ester plasticizer include the following.

Examples of the trivalent or higher alcohol ester plasticizer include the following.

  The molecular weight of the polyhydric alcohol ester plasticizer is not particularly limited, but is preferably 300 to 1500, and more preferably 350 to 750. In order to make it difficult to volatilize, a higher molecular weight is preferable; in order to improve moisture permeability and compatibility with cellulose ester, a lower molecular weight is preferable.

Polyvalent carboxylic ester plasticizer The polyvalent carboxylic ester plasticizer is an ester compound of a divalent or higher, preferably 2-20 valent polycarboxylic acid and an alcohol compound. The polyvalent carboxylic acid is preferably a 2-20 valent aliphatic polyvalent carboxylic acid, or a 3-20 valent aromatic polyvalent carboxylic acid or a 3-20 valent alicyclic polyvalent carboxylic acid. .

  The molecular weight of the polycarboxylic acid ester plasticizer is not particularly limited, but is preferably 300 to 1000, and more preferably 350 to 750. The molecular weight of the polyvalent carboxylic acid ester plasticizer is preferably larger from the viewpoint of suppressing bleed-out; it is preferably smaller from the viewpoint of moisture permeability and compatibility with the cellulose ester.

  Examples of polycarboxylic acid ester plasticizers include triethyl citrate, tributyl citrate, acetyl triethyl citrate (ATEC), acetyl tributyl citrate (ATBC), benzoyl tributyl citrate, acetyl triphenyl citrate, acetyl triphenyl citrate. Benzyl citrate, dibutyl tartrate, diacetyl dibutyl tartrate, tributyl trimellitic acid, tetrabutyl pyromellitic acid and the like are included.

  The polyvalent carboxylic acid ester plasticizer may be a phthalic acid ester plasticizer. 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, dicyclohexyl terephthalate and the like.

  Examples of glycolate plasticizers include alkylphthalyl alkyl glycolates. 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 Glycolate, butyl phthalyl propyl glycolate, methyl phthalyl octyl glycolate, ethyl phthalyl octyl glycolate, octyl phthalyl methyl glycolate, octyl phthalyl ethyl Glycolate, and the like are included.

  The ester plasticizer includes a fatty acid ester plasticizer, a citrate ester plasticizer, a phosphate ester plasticizer, and the like.

  Examples of fatty acid ester plasticizers include butyl oleate, methylacetyl ricinoleate, and dibutyl sebacate. Examples of the citrate plasticizer include acetyltrimethyl citrate, acetyltriethyl citrate, and acetyltributyl citrate. 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 total content of these plasticizers is preferably 0.5 to 30% by mass and more preferably 5 to 20% by mass with respect to the cellulose ester.

Ultraviolet Absorber The cellulose ester film of the present invention may further contain an ultraviolet absorber in order to improve the durability of the film. The ultraviolet absorber is a compound that absorbs ultraviolet rays having a wavelength of 400 nm or less, preferably a compound having a transmittance at a wavelength of 370 nm of 10% or less, more preferably 5% or less, and even more preferably 2% or less.

  The light transmittance of the ultraviolet absorber can be measured with a spectrophotometer by a conventional method using a solution obtained by dissolving the ultraviolet absorber in a solvent (for example, dichloromethane, toluene, etc.). The spectrophotometer is, for example, a spectrophotometer UVIDFC-610 manufactured by Shimadzu Corporation, a 330-type self-recording spectrophotometer, a U-3210-type self-recording spectrophotometer, a U-3410-type self-recording spectrophotometer manufactured by Hitachi, A −4000 self-recording spectrophotometer or the like can be used.

  The ultraviolet absorber is not particularly limited, and is an oxybenzophenone compound, a benzotriazole compound, a salicylic acid ester compound, a benzophenone compound, a cyanoacrylate compound, a triazine compound, a nickel complex compound, an inorganic powder, or the like. Good. Benzotriazole-based UV absorbers and benzophenone-based UV absorbers are preferred for high transparency and suppression of deterioration of the actinic radiation curable resin layer, and for reducing unnecessary coloring, benzotriazole-based UV absorbers are preferred. An agent is more preferable.

  Specific examples of UV absorbers include 5-chloro-2- (3,5-di-sec-butyl-2-hydroxylphenyl) -2H-benzotriazole, (2-2H-benzotriazol-2-yl)- 6- (Linear and side chain dodecyl) -4-methylphenol, 2-hydroxy-4-benzyloxybenzophenone, 2,4-benzyloxybenzophenone, Tinuvin 109, Tinuvin 171, Tinuvin 234, Tinuvin 326, Tinuvin 327, Tinuvin Tinuvins such as 328 (manufactured by Ciba Specialty Chemicals) are included.

  Although content of a ultraviolet absorber is based also on the kind of ultraviolet absorber, it is preferable that it is 0.5-10 mass% with respect to the whole cellulose-ester film, and it is more preferable that it is 0.6-4 mass%. preferable.

Antioxidant The cellulose ester film of the present invention may further contain an antioxidant, for example, in order to prevent deterioration of the cellulose ester film that is likely to occur at high humidity and high temperature. The antioxidant has a function of delaying or preventing the decomposition of the residual solvent amount in the cellulose ester film by halogen or phosphoric acid based plasticizer.

  The antioxidant is preferably a hindered phenol compound, and specific examples thereof include 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-oxide). -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-t-butyl-4-hydroxyphenyl) propionate], octadecyl- -(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, N, N'-hexamethylenebis (3,5-di-tert-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-hydroxybenzyl)- Isocyanurate and the like are included. 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.

  The content of the antioxidant is preferably 1 ppm to 1.0% by mass ratio with respect to the cellulose ester, and more preferably 10 to 1000 ppm.

Fine Particles The cellulose ester film of the present invention may further contain fine particles in order to improve slipperiness. The fine particles may be inorganic fine particles or organic fine particles. Examples of the inorganic fine particles include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, and the like. Examples of the organic fine particles include polystyrene, polymethyl methacrylate and the like. In order to reduce the increase in the haze of the film, silicon dioxide is particularly preferable.

  The primary average particle diameter of the fine particles is preferably 20 nm or less, more preferably 5 to 16 nm, and further preferably 5 to 12 nm.

  The primary average particle diameter of the fine particles can be obtained as an average value of the particle diameters of 100 particles by observing the particles with a transmission electron microscope at a magnification of 500,000 to 2,000,000 times.

  The content of the fine particles is preferably 0.01 to 5.0% by mass and more preferably 0.05 to 1.0% by mass with respect to the cellulose ester. When the content of the fine particles is more than 5.0% by mass, aggregates can be reduced.

  The thickness of the cellulose ester film of the present invention is not particularly limited, but is preferably 10 to 200 μm, more preferably 10 to 100 μm, and still more preferably 20 to 60 μm. If the thickness of the film is too small, it is difficult to obtain a desired retardation. On the other hand, if the thickness of the film is too large, the retardation tends to fluctuate due to the influence of humidity and the like.

  When the cellulose ester film of the present invention is used as a polarizing plate protective film, the retardation Ro measured at a wavelength of 590 nm in an environment of 23 ° C. and 55% RH is 0 nm or more. Is preferable, and it is more preferable that it is 0-30 nm. Rth is preferably 70 nm or less, and more preferably 50 nm or less.

When the cellulose ester film of the present invention is used as a retardation film (for example, a retardation film used for a VA liquid crystal cell), the cellulose ester film has a wavelength of 590 nm in an environment of 23 ° C. and 55% RH. The retardation Ro measured in this way is preferably 30 to 150 nm, more preferably 35 to 65 nm. The retardation Rth measured at a wavelength of 590 nm in an environment of 23 ° C. and 55% RH is preferably 70 to 300 nm, and more preferably 90 to 180 nm. The retardations _R0 and Rth of the cellulose ester film can usually be adjusted by the stretching conditions.

Retardation _R0 and Rth are each represented by the following formula.
Formula (I) R ₀ = (nx−ny) × d
Formula (II) Rth = {(nx + ny) / 2−nz} × d
(Nx: refractive index in the slow axis direction in the film plane, ny: refractive index in the direction perpendicular to the slow axis in the film plane, nz: refractive index of the film in the thickness direction, d: film thickness (Nm))

The retardations _R0 and Rth can be determined by the following method, for example.
1) The average refractive index of the film is measured with a refractometer.
2) The retardation _R0 in the in-plane direction when light having a wavelength of 590 nm from the normal direction of the film is incident is measured by KOBRA-21ADH manufactured by Oji Scientific Instruments.
3) The retardation value R (θ) when light having a wavelength of 590 nm is incident from the angle θ (incident angle (θ)) with respect to the film normal direction is measured by KOBRA-21ADH manufactured by Oji Scientific Instruments. . θ is larger than 0 °, preferably 30 ° to 50 °.
4) From the measured R ₀ and R (θ) and the above-described average refractive index and film thickness, nx, ny and nz are calculated by KOBRA-21ADH manufactured by Oji Scientific Instruments, and Rth is calculated. The measurement of retardation can be performed under conditions of 23 ° C. and 55% RH.

  The cellulose ester film of the present invention has a slow axis or a fast axis in the film plane. The angle θ1 (orientation angle) between the slow axis and the film forming direction is preferably from −1 ° to + 1 °, and more preferably from −0.5 ° to + 0.5 °. Since the light leakage can be suppressed when the orientation angle θ1 satisfies the above range, the luminance of the display image can be increased. The orientation angle θ1 of the cellulose ester film can be measured using an automatic birefringence meter KOBRA-21ADH (Oji Scientific Instruments).

Of the cellulose ester film, JIS Z 0208 in compliance with 40 ° C. being measured, the moisture permeability 90% RH, it is preferable, 400~1500g ^/ m 2 · 24h be 300~1800g ^/ m 2 · 24h It is more preferable. In order to reduce the moisture permeability of the cellulose ester film, for example, the total acyl group substitution degree of the cellulose ester contained in the cellulose ester film is increased, the ratio of the acyl group substitution degree of 3 or more carbon atoms is increased, or plasticity is increased. A lot of additives such as an agent may be contained.

  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 internal haze of the cellulose ester film of the present invention measured in accordance with JIS K-7136 is preferably 0.11% or less, and more preferably 0.05% or less.

The internal haze of the cellulose ester film of the present invention can be measured by a method according to JIS K-7136; specifically, the following method.
A haze meter (turbidity meter) (model: NDH 2000, manufactured by Nippon Denshoku Co., Ltd.) is prepared. The light source is a 5V9W halogen sphere, and the light receiving unit is a silicon photocell (with a relative visibility filter).

1) Measurement of blank haze One drop (0.05 ml) of glycerin is dropped on the washed slide glass. At this time, care is taken so that bubbles do not enter the droplet.
Next, a cover glass is placed on the dropped glycerin. Glycerin spreads without pressing the cover glass.
A blank measurement sample (cover glass / glycerin / slide glass) obtained in this manner is set on a haze meter, and haze 1 (blank haze) is measured.
2) Measurement of haze of sample containing cellulose ester film In the same manner as in 1) above, glycerin is dropped onto the washed slide glass.
On the other hand, the humidity of the cellulose ester film to be measured is adjusted at 23 ° C. and 55% RH for 5 hours or more. Next, the conditioned cellulose ester film is placed on the dropped glycerin so as not to contain air bubbles.
Further, 0.05 ml of glycerin is dropped on the cellulose ester film, and then a cover glass is further placed thereon.
The sample for measurement (cover glass / glycerin / sample film / glycerin / slide glass) obtained in this way is set in the above-mentioned haze meter, and haze 2 is measured.
3) The haze 1 of the cellulose ester film is calculated by applying the haze 1 obtained in 1) and the haze 2 obtained in 2) to the following formula.
Internal haze (%) of cellulose ester film = Haze 2 (%) − Haze 1 (%)

  The internal haze is measured at 23 ° C. and 55% RH. The glass used for measuring the internal haze is MICRO SLIDE GLASS S9213 MATSANAMI. Glycerin is manufactured by Kanto Kagaku deer grade (purity> 99.0%) and has a refractive index of 1.47.

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

  The specific saccharide contained in the cellulose ester film of the present invention is well compatible with the cellulose ester having a low acyl group substitution degree that tends to vary in physical properties. Therefore, the cellulose ester film of the present invention has a low internal haze and suppresses bleed out of plasticizers such as sugars.

2. Cellulose ester film production method Cellulose ester film can be produced by a solution casting method or a melt casting method, and is produced by a solution casting method from the viewpoint of obtaining a thin film with high flatness. It is preferable.

  The step of producing a cellulose ester film by the solution casting method is 1) a step of preparing a dope by dissolving at least the above-mentioned cellulose ester and, if necessary, an additive in a solvent, and 2) an endless metal support for the dope. A step of casting on a body, 3) a step of drying the cast dope to form a web, 4) a step of peeling the web from the metal support, 5) a step of stretching the web to obtain a film, and 6) a film And 7) a step of winding up the obtained film.

1) Process for preparing dope The dope is prepared by dissolving the above cellulose ester and, if necessary, an additive in a solvent. The concentration of the cellulose ester contained in the dope is preferably high in order to reduce the drying load. However, if the concentration of the cellulose ester is too high, it is difficult to filter, and the filtration accuracy tends to decrease. For this reason, it is preferable that the density | concentration of the cellulose ester contained in dope is 10-35 mass%, and it is more preferable that it is 15-25 mass%.

  The solvent contained in the dope may be one kind or a combination of two or more kinds. From the viewpoint of increasing production efficiency, it is preferable to use a combination of a good solvent and a poor solvent for cellulose ester. A good solvent refers to a solvent that dissolves cellulose ester alone, and a poor solvent refers to a solvent that swells cellulose or does not dissolve alone. Therefore, the good solvent and the poor solvent differ depending on the average acyl group substitution degree (acetyl group substitution degree) of the cellulose ester.

  When a good solvent and a poor solvent are used in combination, it is preferable that the good solvent is more than the poor solvent in order to increase the solubility of the cellulose ester. The mixing ratio of the good solvent and the poor solvent is preferably 70 to 98% by mass for the good solvent and 2 to 30% by mass for the poor solvent.

  Examples of the good solvent include organic halogen compounds such as methylene chloride, dioxolanes, acetone, methyl acetate, and methyl acetoacetate, and preferably methylene chloride or methyl acetate. Examples of the poor solvent include methanol, ethanol, n-butanol, cyclohexane, cyclohexanone and the like. The dope preferably contains 0.01 to 2% by mass of water.

  The method of dissolving the cellulose ester in the solvent may be a general method, for example, a method of dissolving under heating and pressure, a poor solvent added to the cellulose ester to swell, and then adding a good solvent to dissolve. It can be a method. Especially, since it can heat beyond the boiling point in a normal pressure, the method of making it melt | dissolve under a heating and pressurization is preferable. Specifically, when stirring and dissolving while heating to a temperature in the range where the solvent is boiling or higher under normal pressure and the solvent does not boil under pressure, the generation of bulk undissolved material called gel or mamako can be suppressed.

  The pressurization can 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 is preferably higher from the viewpoint of increasing the solubility of the cellulose ester, but if it is too high, the pressure needs to be increased, and the productivity is lowered. For this reason, it is preferable that heating temperature is 45-120 degreeC, 60-110 degreeC is more preferable, and it is further more preferable that it is 70-105 degreeC. The pressure is adjusted to a range in which the solvent does not boil at the set heating temperature.

  Additives such as UV inhibitors and fine particles may be added batchwise to the dope, or an additive solution prepared separately may be added inline. The additive solution is obtained by dissolving an additive in an alcohol such as methanol, ethanol or butanol, a solvent such as methylene chloride, methyl acetate, acetone or dioxolane, or a mixed solvent thereof.

  In particular, part or all of the fine particles are preferably added in-line in order to reduce the load on the filter medium. When the additive solution is added in-line, it is preferable to dissolve a small amount of cellulose ester in the additive solution in order to improve mixing with the dope. The amount of the cellulose ester added to the additive solution is preferably 1 to 10 parts by mass and more preferably 3 to 5 parts by mass with respect to 100 parts by mass of the solvent.

  The in-line addition can be performed using an in-line mixer such as a static mixer (manufactured by Toray Engineering), SWJ (Toray static type in-tube mixer Hi-Mixer), or the like.

  The obtained dope may contain insoluble matters such as impurities contained in the cellulose ester as a raw material, for example. Such an insoluble matter can become a bright spot foreign material in the obtained film. In order to remove such insoluble matter and the like, it is preferable to filter the obtained dope.

  The dope is filtered by a filter medium such as filter paper. The absolute filtration accuracy of the filter medium is preferably small in order to highly remove insoluble matters and the like contained in the dope, but if it is too small, clogging is likely to occur. For this reason, the absolute filtration accuracy of the filter medium is preferably 0.008 mm or less, more preferably 0.001 to 0.008 mm, and still more preferably 0.003 to 0.006 mm.

  The type of the filter medium may be a normal filter medium, and may be a plastic filter medium such as polypropylene or Teflon (registered trademark), or a metal filter medium such as stainless steel. Among these, a metal filter medium is preferable from the viewpoint of less fiber dropping.

  In order to reduce the differential pressure before and after filtration, the dope is preferably filtered under heating and pressure as in the preparation of the dope. Similarly to the preparation of the dope, the heating temperature is preferably not less than the boiling point of the solvent at normal pressure and in a range where the solvent does not boil under pressure, specifically 45 to 120 ° C. It is preferably 45 to 70 ° C, more preferably 45 to 55 ° C. The filtration pressure is preferably low, specifically 1.6 MPa or less, more preferably 1.2 MPa or less, and further preferably 1.0 MPa or less.

The dope filtration is preferably performed so that the number of bright spot foreign matters in the obtained film is not more than a certain value. Specifically, the number of bright spot foreign matters having a diameter of 0.01 mm or more is 200 / cm ² or less, preferably 100 / cm ² or less, more preferably 50 / m ² or less, and still more preferably 0. -10 pieces / cm ² or less. It is preferable that the number of bright spot foreign materials having a diameter of 0.01 mm or less is also small.

The number of bright spot foreign matter on the film can be measured by the following procedure.
i) Two polarizing plates are arranged in a crossed Nicol state, and the obtained film is arranged between them.
ii) Count the number of spots (foreign matter) where light is leaked when light is applied from one polarizing plate and observed from the other polarizing plate.

2) Step of casting dope The metal support on which the dope is cast preferably has a mirror-finished surface. Preferred examples of the metal support include a stainless steel belt and a drum whose surface is plated with a casting.

  The surface temperature of the metal support on which the dope is cast is preferably high in order to increase the drying speed of the web, but if it is too high, the web may foam or the smoothness of the web may be reduced. . Therefore, the surface temperature of the metal support is preferably set to −50 ° C. or higher and lower than the boiling point of the solvent. The web temperature is preferably 0 to 55 ° C, and more preferably 25 to 50 ° C.

  The method for controlling the surface temperature of the metal support is not particularly limited, and may be a method of blowing warm air or cold air, a method of bringing hot water into contact with the back side of the metal support, or the like. From the viewpoint of efficiently transferring heat and shortening the time until the temperature of the metal support becomes constant, a method of bringing hot water into contact with the back side of the metal support is preferable.

3) About the process of drying the cast dope The cast dope is dried so that a residual solvent may become below fixed. The amount of residual solvent in the web when peeling the web from the metal support is preferably 10 to 150% by mass in order to improve the flatness of the resulting film, and 20 to 40% by mass (low residual solvent amount). Or it is more preferable that it is 60-130 mass% (high residual solvent amount), and it is further more preferable that it is 20-30 mass% (low residual solvent amount) or 70-120 mass% (high residual solvent amount).

The amount of residual solvent in the web is defined by the following formula. In the following formula, M represents the mass of a sample collected at an arbitrary point from the web being manufactured or the film after manufacture. N represents the mass of the sample after heating the sample at 115 ° C. for 1 hour.
Residual solvent amount (% by mass) = {(MN) / N} × 100

4) About the process of peeling a web Although peeling of a web is performed by a general method, it is preferable to peel with a peeling roll. Peeling with a peeling roll is preferably carried out when the web reaches the lower surface of the metal support and almost completes a round. The web peeling tension is preferably 300 N / m or less.

  The peeling of the web is not only the method of peeling after the web is dried in the step 3), but also after the step 2), the cast film is cooled without being dried and contains a large amount of residual solvent. After gelling as it is, it may be peeled off.

  The peeled web may be further dried. In general, the peeled web can be dried while the web is conveyed. Specifically, there are a roll drying method and a tenter method in which the peeled web is dried while being conveyed by a large number of rolls arranged vertically.

  The method for drying the web is not particularly limited, but in general, it may be a method of drying with hot air, infrared rays, heating rolls, microwaves, or the like, and from the viewpoint of simplicity, a method of drying with hot air is preferable. The drying temperature of the web is preferably increased stepwise from 40 ° C to 200 ° C.

5) About the process of extending | stretching a web The cellulose-ester film which has desired retardation value Ro and Rth is obtained by extending | stretching a web. The retardation values Ro and Rth of the cellulose ester film are controlled by adjusting the magnitude of the tension applied to the web at least in the direction (width direction) perpendicular to the web conveyance direction (the dope casting direction). Can do.

  The web may be stretched at least in the width direction, and may be uniaxial stretching or biaxial stretching. The web may be stretched in the width direction or in an oblique direction with respect to the casting direction of the dope. Biaxial stretching includes stretching in both the web conveyance direction (longitudinal direction) and the width direction (lateral direction). Stretching may be sequential stretching or simultaneous stretching.

  When the web is stretched biaxially in directions orthogonal to each other, the web is finally 1.1 to 2.5 times in the width direction (lateral direction) and 0.8 in the transport direction (longitudinal direction). It is preferable to set it to -1.5 times; It is more preferable to set it to 1.2 to 2.0 times in the width direction (horizontal direction) and 0.9 to 1.0 times in the conveyance direction (vertical direction).

  The web stretching temperature is preferably 120 ° C to 200 ° C, and more preferably 140 ° C to 180 ° C. The residual solvent of the stretched web is preferably 20% by mass or less, and preferably 15% by mass or less.

  The method of stretching the web is not particularly limited, and a method in which a difference in peripheral speed is applied to a plurality of rolls and the roll is stretched in the longitudinal direction using the difference in the peripheral speed of the roll (roll stretching method). The clip and pin spacing is widened in the vertical direction and stretched in the vertical direction, widened in the horizontal direction and stretched in the horizontal direction, or stretched in both the vertical and horizontal directions and stretched in both the vertical and horizontal directions (tenter stretching, etc. Law). These stretching methods may be combined.

  In the tenter stretching method, the clip portion is preferably driven by a linear drive method. This is because the movement of the clip portion is smooth, so that it is easy to stretch and the risk of web breakage can be reduced.

  It is preferable to carry out the web width maintenance and the transverse stretching by a tenter method. The tenter method may be a pin tenter method or a clip tenter method.

  The width of the cellulose ester film obtained by stretching is preferably 4 m or less, more preferably 1 to 4 m, and even more preferably 1.4 to 4 m from the viewpoint of facilitating conveyance. 1.6 to 3 m is particularly preferable. The cellulose ester film obtained by stretching is further wound as necessary and then wound.

  The cellulose ester film of the present invention is used as a functional film for various display devices such as liquid crystal displays, plasma displays, and organic EL displays. In particular, the cellulose ester film of the present invention includes a polarizing plate protective film, a retardation film, an antireflection film, a brightness enhancement film, a hard coat film, an antiglare film, an antistatic film, and an optical compensation film for expanding a viewing angle of a liquid crystal display device. Etc.

3. Polarizing plate The polarizing plate of the present invention comprises a polarizer and the cellulose ester film of the present invention disposed on one surface thereof, and a polarizing plate protective film disposed on the other surface of the polarizer as necessary. Further, it may be included.

  A polarizer is an element that allows only light having a polarization plane in a certain direction to pass therethrough. A typical example of the polarizer is a polyvinyl alcohol-based polarizing film, and there are one in which a polyvinyl alcohol-based film is dyed with iodine and one in which a dichroic dye is dyed.

  The polarizer may be a film obtained by uniaxially stretching a polyvinyl alcohol film and then dyeing with iodine or a dichroic dye, or after dyeing a polyvinyl alcohol film with iodine or a dichroic dye, A uniaxially stretched film (preferably a film further subjected to durability treatment with a boron compound) may be used. The thickness of the polarizer is preferably 5 to 30 μm, and more preferably 10 to 20 μm.

  The polyvinyl alcohol film may be a film formed from a polyvinyl alcohol aqueous solution. The polyvinyl alcohol film is preferably an ethylene-modified polyvinyl alcohol film because it is excellent in polarizing performance and durability performance and has few color spots. Examples of the ethylene-modified polyvinyl alcohol film include an ethylene unit content of 1 to 4 mol%, a polymerization degree of 2000 to 4000, and a saponification degree of 99.0 described in JP2003-248123A and JP2003-342322A. ˜99.99 mol% film is included.

  Examples of dichroic dyes include azo dyes, stilbene dyes, pyrazolone dyes, triphenylmethane dyes, quinoline dyes, oxazine dyes, thiazine dyes and anthraquinone dyes.

  The cellulose ester film of the present invention may be disposed directly on one surface of the polarizer or may be disposed via another film or layer.

  The polarizing plate protective film other than the cellulose ester film of the present invention is not particularly limited, and may be a normal cellulose ester film or the like. Examples of commercially available cellulose ester films include commercially available cellulose ester films (for example, Konica Minoltak KC8UX, KC5UX, KC8UCR3, KC8UCR4, KC8UCR5, KC8UY, KC6UY, KC4UY, KC4UE, KC8UE, KC8UY-X KC8UXW-RHA-C, KC8UXW-RHA-NC, KC4UXW-RHA-NC, manufactured by Konica Minolta Opto Co., Ltd.) are preferably used.

  A polarizing plate can usually be produced by laminating a polarizer and the cellulose ester film or polarizing plate protective film of the present invention. As the adhesive used for bonding, for example, a completely saponified polyvinyl alcohol aqueous solution is preferably used.

4). Liquid Crystal Display Device The liquid crystal display device of the present invention includes a liquid crystal cell and a pair of polarizing plates that sandwich the liquid crystal cell. And at least one is a polarizing plate which has the above-mentioned cellulose-ester film among a pair of polarizing plates, Preferably both of a pair of polarizing plates are polarizing plates which have the above-mentioned cellulose-ester film.

  FIG. 1 is a schematic diagram showing a basic configuration of an embodiment of a liquid crystal display device according to the present invention. As shown in FIG. 1, the liquid crystal display device 10 includes a liquid crystal cell 20, a first polarizing plate 40 and a second polarizing plate 60 that sandwich the liquid crystal cell 20, and a backlight 80.

  The display method of the liquid crystal cell 20 is not particularly limited, and is a TN (Twisted Nematic) method, an STN (Super Twisted Nematic) method, an IPS (In-Plane Switching) method, an OCB (Optically Compensated Birefringence Ventilating Ventilation method). There are systems (including MVA; Multi-domain Vertical Alignment and PVA; including Patterned Vertical Alignment), and HAN (Hybrid Aligned Nematic). In order to increase the contrast, the VA (MVA, PVA) method is preferable.

  A VA liquid crystal cell usually includes a pair of opposing transparent substrates and a liquid crystal layer sandwiched between the pair of transparent substrates and containing liquid crystal molecules.

  Of at least one of the pair of transparent substrates, a pixel electrode for applying a voltage to the positive liquid crystal and a counter electrode corresponding to the pixel electrode are disposed.

  The liquid crystal layer includes liquid crystal molecules, preferably positive liquid crystal molecules that are nematic liquid crystal materials having positive dielectric anisotropy. This positive type liquid crystal molecule is not applied with voltage (when no electric field is generated between the pixel electrode and the counter electrode) due to the alignment regulating force of the alignment film provided on the liquid crystal layer side surface of the transparent substrate. The major axis of the liquid crystal molecules is aligned so as to be substantially perpendicular to the surface of the transparent substrate.

  In the liquid crystal cell thus configured, an image signal (voltage) is applied to the pixel electrode, thereby generating an electric field in the horizontal direction with respect to the substrate surface between the pixel electrode and the counter electrode. Thereby, the liquid crystal molecules initially aligned perpendicularly to the surface of the transparent substrate are aligned so that the major axis thereof is in the horizontal direction with respect to the substrate surface. In this way, the liquid crystal layer is driven, and the image display is performed by changing the transmittance and reflectance of each sub-pixel.

  The 1st polarizing plate 40 is arrange | positioned at the visual recognition side, and has the 1st polarizer 42 and polarizing plate protective film 44 (F1) and 46 (F2) which clamps it. The 2nd polarizing plate 60 is arrange | positioned at the backlight 80 side, and has the 2nd polarizer 62, the polarizing plate protective film 64 (F3) and polarizing plate protective film 66 (F4) which clamps it. . One of the polarizing plate protective films 46 (F2) and 64 (F3) may be omitted as necessary.

  When the cellulose ester film of the present invention is a polarizing plate protective film, one or more of the polarizing plate protective films 44 (F1), 46 (F2), 64 (F3) and 66 (F4) are used as the cellulose ester of the present invention. It can be a film. When the cellulose ester film of the present invention is a retardation film, among the polarizing plate protective films 44 (F1), 46 (F2), 64 (F3), and 66 (F4), the polarizing plate protection disposed on the liquid crystal cell side At least one of the films 46 (F2) and 64 (F3) can be used as the cellulose ester film of the present invention.

In the following, the invention will be described in more detail with reference to examples. These examples do not limit the scope of the present invention.
1. Material preparation
1) Cellulose ester 16 parts by mass of sulfuric acid, 260 parts by mass of acetic anhydride, and 420 parts by mass of acetic acid were added to 100 parts by mass of cellulose. The resulting solution was heated from room temperature to 60 ° C. over 60 minutes with stirring, and then subjected to an acetylation reaction while maintaining at 60 ° C. for 15 minutes. Next, a mixed solution of acetic acid and water containing magnesium acetate is added to the resulting solution to neutralize the sulfuric acid, and then steam is introduced into the reaction system and kept at 60 ° C. for 120 minutes to saponify and ripen. Went. The obtained cellulose acetate was washed with a large amount of water until the odor of acetic acid disappeared, and further dried to obtain cellulose acetate 1 having an acetyl group substitution degree of 2.43.

Cellulose acetates 2 to 5 were obtained in the same manner as described above except that the addition amount of the acid was adjusted to the substitution degree of acetyl group and substitution degree of propionyl group shown in Table 1.

2) Sugars Four-headed Kolben equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen gas inlet tube was charged with 34.2 g (0.1 mol) of sucrose, 180.8 g (0.8 mol) of benzoic anhydride, 379.7 g (4.8 mol) of pyridine was charged. These materials were heated with stirring while bubbling nitrogen gas, and esterified at 70 ° C. for 5 hours. Next, the inside of the Kolben is depressurized to 4 × 10 ² Pa or less, excess pyridine is distilled off at 60 ° C., the inside of the Kolben is depressurized to 1.3 × 10 Pa or less, and the temperature is raised to 120 ° C. Most of benzoic acid, acetic anhydride, benzoic acid and acetic acid formed were distilled off. To the obtained solution, 1 L of toluene and 300 g of a 0.5% by mass aqueous sodium carbonate solution were added, stirred for 30 minutes at 50 ° C., and allowed to stand to separate a toluene layer. Thereafter, 100 g of water was added to the collected toluene layer, and after washing with water at room temperature for 30 minutes, the toluene layer was separated, and toluene was distilled off under reduced pressure (4 × 10 ² Pa or less) at 60 ° C. to obtain sucrose. A saccharide A-1 in which a part of the hydroxyl group was substituted with a benzoyl group and an acetyl group was obtained.

The saccharides A-2 to A-31, the saccharides B-1 to B-31, and the saccharide D- are the same as described above except that the type of constituent sugar, the type of acid (substituent) or the degree of substitution thereof are changed. 1-D-39 was obtained.

2. Preparation of cellulose ester film (Example 1-1)
The following components were stirred and mixed with a dissolver for 50 minutes and then dispersed with Manton Gorin to obtain a fine particle dispersion.
[Fine particle dispersion]
Fine particles (Aerosil R812 manufactured by Nippon Aerosil Co., Ltd.) 11 parts by mass Ethanol 89 parts by mass

While the methylene chloride was put in the dissolution tank and sufficiently stirred, the fine particle dispersion was slowly added, and then dispersed with an attritor so that the secondary particles had a predetermined particle size. The obtained solution was filtered with Finemet NF manufactured by Nippon Seisen Co., Ltd. to prepare a fine particle additive solution.
[Fine particle additive solution]
99 parts by mass of methylene chloride 5 parts by mass of fine particle dispersion

Preparation of dope solution A dope solution having the following composition was prepared. First, methylene chloride and ethanol were charged into a pressure dissolution tank. To these solvents, cellulose ester 1 (cellulose diacetate having an acetyl group substitution degree of 2.43) was added while further stirring. The obtained solution was dissolved while stirring under heating, and the saccharide A-1 and the fine particle additive solution were further added, and stirred to completely dissolve. The obtained solution was used as Azumi filter paper No. manufactured by Azumi Filter Paper Co., Ltd. Filtration using 244 gave a dope solution.
[Composition of dope solution]
Methylene chloride 340 parts by mass Ethanol 64 parts by mass Cellulose ester 1 (acetyl group substitution degree 2.43, cellulose diacetate) 100 parts by mass Sugar A-1 10 parts by mass Particulate additive solution 1 part by mass

  Next, the dope solution adjusted to 34 ° C. was uniformly cast on a stainless belt support of an endless belt casting apparatus so as to have a width of 1500 mm. The temperature of the stainless steel belt support was 30 ° C. After the solvent was evaporated on the stainless steel belt support until the residual solvent amount in the cast film was 75%, the paint film was applied from the stainless steel belt support at a peeling tension of 130 N / m. It peeled. The web obtained by peeling was stretched 35% in the width direction using a tenter while applying heat at 180 ° C. The residual solvent amount of the web at the start of stretching was 15%. Next, drying was terminated while the drying zone was conveyed by a number of rolls. The film obtained by stretching was dried at a drying temperature of 130 ° C. while being transported at a transport tension of 100 N / m. This obtained the cellulose-ester film with a film thickness of 40 micrometers.

(Examples 1-2 to 1-22)
As shown in Table 2, a cellulose ester film was obtained in the same manner as in Example 1-1 except that the type of saccharide was changed.

(Examples 1-23 to 1-30)
As shown in Table 3, a cellulose ester film was obtained in the same manner as in Example 1-1 except that the type of cellulose ester and the type of saccharide were changed, and the stretching temperature was 160 ° C. and the stretching ratio was 30%. .

(Examples 2-1 to 2-22)
As shown in Table 4, a cellulose ester film was obtained in the same manner as in Example 1-1 except that the type of saccharide was changed.

(Examples 2-23 to 2-30)
As shown in Table 5, a cellulose ester film was obtained in the same manner as in Example 1-1 except that the type of cellulose ester and the type of saccharide were changed, and the stretching temperature was 160 ° C. and the stretching ratio was 30%. .

(Examples 3-1 to 3-29)
As Table 6 or 7 showed, the cellulose-ester film was obtained like Example 1-1 except having changed the kind of saccharide | sugar or the kind of cellulose ester.

(Example 3-30)
As shown in Table 7, a cellulose ester film was obtained in the same manner as in Example 1-1 except that the type of cellulose ester and the type of sugar were changed, and the stretching temperature was 170 ° C. and the stretching ratio was 40%. .

(Examples 3-31 to 1-38)
As shown in Table 7, a cellulose ester film was obtained in the same manner as in Example 1-1 except that the type of cellulose ester and the type of saccharide were changed, and the stretching temperature was 160 ° C. and the stretching ratio was 30%. .

(Comparative Example 1-1)
As shown in Table 8, a cellulose ester film was obtained in the same manner as in Example 1-1 except that the type of saccharide was changed.

(Comparative Example 2-1)
As shown in Table 8, a cellulose ester film was obtained in the same manner as in Example 2-1, except that the type of saccharide was changed.

(Comparative Examples 3-1 to 3-11)
As shown in Table 8, a cellulose ester film was obtained in the same manner as in Example 3-1, except that the type of saccharide was changed.

(Comparative Example 3-12)
As shown in Table 8, a cellulose ester film was obtained in the same manner as in Example 3-1, except that the type of cellulose ester and the type of sugar were changed, the stretching temperature was 160 ° C., and the stretching ratio was 30%. It was.

(Comparative Example 3-13)
As shown in Table 8, a cellulose ester film was obtained in the same manner as in Example 3-1, except that the type of cellulose ester and the type of saccharide were changed, the stretching temperature was 170 ° C., and the stretching ratio was 40%. It was.

  The internal haze, bleed-out resistance and retardation Ro and Rth of the obtained cellulose ester film were evaluated by the following methods.

Measurement of internal haze The internal haze of the obtained cellulose ester film was measured by the above-described method based on JIS K7136. NDH 2000 manufactured by Nippon Denshoku Industries Co., Ltd. was used as the haze meter. The internal haze was evaluated based on the following criteria.
◎: 0.03% or less ○: Over 0.03% over 0.07% or less △: Over 0.07% over 0.11% ×: Over 0.11%

Measurement of Bleed-Out Resistance After the obtained cellulose ester film was stored at 60 ° C. and 90% RH for 300 hours, the presence or absence of additive precipitation (bleed-out) on the film surface was visually observed. The bleedout resistance was evaluated based on the following criteria.
◎: Bleed-out is not recognized on the film surface ○: Bleed-out is slightly observed on a part of the film surface △: Bleed-out is slightly recognized on the entire film surface ×: On the entire film surface, Clear bleed out

Measurement of Retardation Ro and Rth 1) The obtained film was allowed to stand for 24 hours in an environment of 23 ° C. and 55% RH to adjust the humidity. The average refractive index of the obtained film was measured using an Abbe refractometer (4T). Moreover, the thickness of the film was measured using a commercially available micrometer.
2) Using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments Co., Ltd.), light having a wavelength of 590 nm from the normal direction of the film is incident, and in the in-plane direction represented by the following formula (I) Retardation Ro was measured. Further, the retardation value R (θ) was measured when light having a wavelength of 590 nm was incident from an angle θ (incident angle (θ)) with respect to the film normal direction. θ was 30 ° to 50 °.
3) From the measured Ro and R (θ) and the aforementioned average refractive index and film thickness, nx, ny and nz are calculated by an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments), Rth represented by the following formula (II) was calculated. The retardation was measured under the conditions of 23 ° C. and 55% RH.
Formula (I) Ro = (nx−ny) × d
Formula (II) Rth = {(nx + ny) / 2−nz} × d
(Nx represents the refractive index in the direction x where the refractive index is maximum in the in-plane direction of the film;
ny represents the refractive index in the direction y perpendicular to the direction x in the in-plane direction of the film;
nz represents the refractive index in the film thickness direction z;
d (nm) indicates the film thickness)

The evaluation results of Examples 1-1 to 1-22 are shown in Table 2, the evaluation results of Examples 1-23 to 1-30 are shown in Table 3, and the evaluation results of Examples 2-1 to 2-22 are shown in Table 4. Table 5 shows the evaluation results of Examples 2-23 to 2-30; Table 6 shows the evaluation results of Examples 3-1 to 3-27; Table 7 shows the evaluation results of Examples 3-28 to 3-38. Table 8 shows the evaluation results of Comparative Examples 1-1, 2-1 and 3-1 to 3-13.

  The films of Examples 1-1 to 1-15, 2-1 to 2-15 and 3-1 to 3-3 containing saccharides having two or more hydroxyl groups are comparative examples 1 to 1 containing saccharides having no hydroxyl group. It can be seen that the internal haze is lower and the bleed-out resistance is higher than the films of 1, 2-1, and 3-1, or the film of Comparative Example 3-2 containing a saccharide having only one hydroxyl group.

  Moreover, even if it has two or more hydroxyl groups, the film of Comparative Example 3-8 containing a saccharide having only “substituents not containing an aromatic group” tends to cause at least bleeding out. It can be seen that the film of Comparative Example 3-9 containing a saccharide having only the “containing substituent” has at least high internal haze.

  Further, from the comparison of Examples 1-1 to 1-5, a film containing a saccharide having more “substituents containing an aromatic group” than “substituents not containing an aromatic group” is bleed-out. It turns out that tolerance is high. This is presumably because “substituents containing an aromatic group” contained in the saccharide are likely to interact with each other.

  Further, from the comparison with Examples 3-2 and 3-28 to 3-31, the films of Examples 3-2 and 3-28 containing cellulose diacetate (DAC) as the cellulose ester were obtained by using cellulose triacetate (TAC). It can be seen that the internal haze is lower and the bleed-out resistance is higher than the film of Example 3-31 including and the film of Example 3-30 including cellulose acetate propionate (CAP). This is probably because saccharides are more compatible with DAC than TAC and CAP.

  Even if the cellulose ester film of the present invention contains a cellulose ester whose physical properties tend to vary, the internal haze is low and bleeding out is suppressed.

DESCRIPTION OF SYMBOLS 10 Liquid crystal display device 20 Liquid crystal cell 40 1st polarizing plate 42 1st polarizer 44 Polarizing plate protective film (F1)
46 Polarizing plate protective film (F2)
60 Second polarizing plate 62 Second polarizer 64 Polarizing plate protective film (F3)
66 Polarizing plate protective film (F4)
80 Backlight

Claims (11)

Cellulose ester,
A part of the hydroxyl groups of the constituent sugars are each substituted with a substituent containing an aromatic group and a substituent not containing an aromatic group, and two or more hydroxyl groups remain unsubstituted,
A cellulose ester film. The cellulose ester film according to claim 1, wherein the saccharide has a structure represented by the following general formula (1).
General formula (1)

(In Formula (1),
G represents a monosaccharide or polysaccharide residue;
Each L ₁ independently represents a single bond, an alkylene group, a carbonyl group or an alkylenecarbonyl group;
Each R ₁ independently represents an aromatic group;
L ₂ each independently represents a single bond or a carbonyl group;
R ₂ each independently represents an aliphatic group;
p represents an integer of 2 or more,
q and r each independently represents an integer of 1 or more, and p + q + r represents the total number of hydroxyl groups contained when G is an unsubstituted saccharide)   The cellulose-ester film of Claim 1 or 2 whose total acyl group substitution degree of the said cellulose ester is 1.5-2.5.   The cellulose-ester film of Claim 3 whose substitution degree of the C3 or more acyl group of the said cellulose ester is 0.   In the said General formula (1), q is larger than r, The cellulose-ester film as described in any one of Claims 2-4.   In the said General formula (1), G is a cellulose-ester film as described in any one of Claims 2-5 which is a residue of a monosaccharide, a disaccharide, or a trisaccharide.   The cellulose-ester film as described in any one of Claims 1-6 whose internal haze of the said cellulose-ester film is 0.11% or less. The retardation Ro at a wavelength of 590 nm represented by the following formula (I) is 30 to 150 nm, and the Rth at a wavelength of 590 nm represented by the following formula (II) is 70 to 300 nm. The cellulose-ester film as described in any one of -7.
Formula (I) Ro = (nx−ny) × d
Formula (II) Rth = {(nx + ny) / 2−nz} × d
(Nx represents the refractive index in the direction x where the refractive index is maximum in the in-plane direction of the film;
ny represents the refractive index in the direction y perpendicular to the direction x in the in-plane direction of the film;
nz represents the refractive index in the thickness direction z of the film;
d (nm) represents the thickness of the film)   Retardation film containing the cellulose-ester film as described in any one of Claims 1-8. A polarizer,
The cellulose ester film according to any one of claims 1 to 8, disposed on at least one surface of the polarizer,
A polarizing plate. A liquid crystal display device comprising a liquid crystal cell and a pair of polarizing plates sandwiching the liquid crystal cell,
At least one of the pair of polarizing plates includes a polarizer and a cellulose ester film according to any one of claims 1 to 8 disposed on at least one surface of the polarizer. .

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