JP2014085628A - Manufacturing method for phase difference film, phase difference film, polarizer, and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device containing a phase difference film and improved in front surface contrast, in particular, with less hue change resulting from an angle of field.SOLUTION: A manufacturing method for a phase difference film comprises: a first step in which cellulose acetate with an average acetyl group substitution degree of 2.2 to 2.5 and a hydrogen-bonded chemical compound having at least a carboxy group or hydroxy group as at least a substituent group in an aromatic ring are dissolved in an organic solvent containing 90% by mass of halogen organic solvent, thereby obtaining a dope solution; a second step in which the dope solution is caused to flow and extend over a metal belt; a third step in which a film object obtained by drying the dope solution caused to flow and extend is pulled off from the metal belt; a fourth step in which the film object pulled off is stretched; and a fifth step in which the stretched film object is heated and dried to volatilize the organic solvent in the film object. The average volatilization speed of the organic solvent of the film object right before the stretching of the film object is adjusted to the range of 1.5×10to 3.0×10g/(sec cm).

Description

  The present invention relates to a method for producing a retardation film, a retardation film, a polarizing plate, and a liquid crystal display device.

  At present, a retardation film having a specific retardation value is used for liquid crystal display devices such as a television and a personal computer monitor in order to improve the viewing angle dependency of hue and the front contrast.

  That is, the liquid crystal display device includes a liquid crystal cell and a pair of polarizing plates that sandwich the liquid crystal cell. The polarizing plate has a polarizer and a pair of protective films that sandwich the polarizer; among the pair of protective films, the protective film disposed between the liquid crystal cell and the polarizer functions as a retardation film. . As described above, the retardation film is disposed between the polarizer and the liquid crystal cell, and has a great influence on the viewing angle dependency of the hue and the front contrast of the liquid crystal display device.

  It is known that the retardation film is produced from a synthetic polymer, cellulose ester, or the like. Among these, a film mainly composed of cellulose ester has an advantage that it can be directly bonded to a polarizer mainly composed of polyvinyl alcohol by immersing the surface in an alkaline aqueous solution and saponifying and hydrophilizing. doing. For this reason, the film which has a cellulose ester as a main component is widely utilized as retardation film.

  It is known that when cellulose acetate is used as a main raw material for such a retardation film containing cellulose ester as a main component, the optical properties of the film depend on the degree of acetyl substitution of cellulose acetate. In particular, since cellulose acetate having a low degree of substitution has a high intrinsic birefringence, it is considered that high retardation development suitable for a retardation film for VA can be realized by reducing the degree of acetyl substitution.

  In recent years, with the wide viewing angle and high image quality of liquid crystal display devices, there has been a demand for further improvement in the retardation compensation of the retardation film. In addition, the retardation film is required to exhibit stable optical characteristics even when the usage environment changes.

  Consider changing the Rth (retardation value in the thickness direction) of the cellulose acetate film to reduce changes in viewing angle characteristics and hue due to changes in humidity. Has been. For example, Patent Document 1 includes cellulose acylate and a compound having a functional group selected from at least a plurality of hydroxyl groups, amino groups, thiol groups, and carboxylic acid groups in one molecule, and has a humidity of 10% and a humidity of 80%. A transparent protective film in which the difference in Rth is less than a certain value is disclosed.

  Further, Patent Document 2 includes a cellulose ester film containing a cellulose ester and a polymer derived from a monomer exhibiting negative birefringence and having a reduced Rth change amount after an endurance condition of a temperature of 60 ° C. and a relative humidity of 90%. Is disclosed.

JP 2008-89860 A JP 2010-24424 A

  However, Patent Document 1 is intended to reduce the variation of Rth with respect to the humidity change in the environment in which the retardation film is used, but does not show that the variation of Rth with time immediately after production is reduced. Further, the cellulose acetate used in Patent Document 1 has a high average acetyl group substitution degree, and a large retardation required for a VA retardation film or the like could not be obtained.

  Japanese Patent Application Laid-Open No. 2004-228561 reduces the Rth fluctuation before and after the endurance condition, but does not indicate that the Rth fluctuation with time immediately after manufacture is reduced. Moreover, since the retardation development property is lowered by the addition of the polymer, a large retardation required for a VA retardation film or the like could not be obtained.

  In recent years, there has been an increasing demand for cost reduction of retardation films. As an effective means for reducing the cost, there is a method of increasing the production speed. However, when the film forming speed, the stretching speed, the drying speed, etc. are increased, there is a tendency that the variation of the retardation value (especially Rth) of the obtained film with time increases. A liquid crystal display device including such a retardation film has a viewing angle dependency; particularly, the hue changes greatly depending on the viewing angle, and the front contrast tends to be low. Therefore, even when the production speed is increased, the fluctuation of retardation value of the obtained retardation film with time can be reduced, thereby making it possible to reduce the viewing angle dependency; in particular, the hue change due to the viewing angle is small, and the front contrast is improved. It is desired to provide a liquid crystal display device.

  The present invention has been made in view of the above circumstances, and provides a liquid crystal display device that includes a retardation film and has a viewing angle dependency; particularly, there is little change in hue due to the viewing angle and the front contrast is improved. Objective.

In order to solve the above-mentioned problems, the present inventor, in the process of examining the cause of the above-mentioned problems, in the organic solvent containing 90% by mass or more of the halogen-based organic solvent, the average degree of acetyl group substitution 2.2-2.5 A first step of obtaining a dope solution by dissolving cellulose acetate and a hydrogen bonding compound having at least a carboxy group or a hydroxy group as a substituent in the aromatic ring, and casting the dope solution on a metal belt A second step, a third step of peeling the film-like material obtained by drying the cast dope solution from the metal belt, and a fourth step of extending the peeled-off film-like material. And a fifth step of heating and drying the stretched film-like material to volatilize the organic solvent in the film-like material, wherein the film-like material is stretched Is The average volatilization rate of the organic solvent, the phase difference obtained by adjusting the range of ^{1.5 × 10 -3 ~3.0 × 10 -3} g / (sec · cm 2) film of the film-like material immediately before However, it was discovered that the absolute value of the change in Rth when left to stand at 23 ° C. and 55% RH for 24 hours immediately after production was as low as a certain value. And it discovered that the change of the hue by the viewing angle of a liquid crystal display device was reduced by using this retardation film, and front contrast could be improved, and it came to this invention. That is, the said subject which concerns on this invention is solved by the following means.

（前記一般式（Ｉ）において、ｌは、１以上の整数を表し、２以上の場合、２つのカルボキシル基が互いに脱水縮合して環を形成してもよく；ｍは、０〜４の整数を表し；Ｒは、アルキル基を表し；ｎは、０〜４の整数を表し、Ｒが複数ある場合は、複数のＲは互いに同じであっても異なっていてもよく；ｌ＋ｍ≧２である）
一般式（II）

（前記一般式（II）において、Ｒ^１は、それぞれ独立にハロゲン原子または水酸基を表し；ｎは、０〜４の整数を表す）
［５］ ２３℃５５％ＲＨ下における引張弾性率が、３５００〜６０００ＭＰａの範囲内である、［３］または［４］に記載の位相差フィルム。
［６］ 下記式で定義され、２３℃５５％ＲＨ下、波長５９０ｎｍで測定される厚さ方向のリターデーション値Ｒｔｈが、７０〜４００ｎｍの範囲内である、［３］〜［５］のいずれか一項に記載の位相差フィルム。
Ｒｔｈ＝［（ｎｘ＋ｎｙ）／２−ｎｚ］×ｄ
（式中、ｎｘは、フィルム面内の遅相軸方向の屈折率を示し；ｎｙは、フィルム面内の前記遅相軸と直交する方向の屈折率を示し；ｎｚは、フィルムの厚さ方向の屈折率を示し；ｄは、フィルムの厚さを示す）
［７］ 前記位相差フィルムの遅相軸方向のフィルム幅は、７００〜３０００ｍｍである、［３］〜［６］のいずれか一項に記載の位相差フィルム。 [1] An organic solvent containing 90% by mass or more of a halogen-based organic solvent has a cellulose acetate having an average acetyl group substitution degree of 2.2 to 2.5, and an aromatic ring having at least a carboxy group or a hydroxy group as a substituent. A first step of obtaining a dope solution by dissolving a hydrogen bonding compound, a second step of casting the dope solution on a metal belt, and a film obtained by drying the cast dope solution A third step of peeling the film from the metal belt, a fourth step of stretching the peeled film, and heating and drying the stretched film to form the film And a fifth step of volatilizing the organic solvent in the product, wherein the average volatilization rate of the organic solvent in the film-like material immediately before the film-like material is stretched is 1.5. × ¹⁰ -3 ~3 0 × adjusted in the range of ^{10 -3 g / (sec · cm} 2), method for producing a retardation film.
[2] Retardation in the thickness direction of the retardation film measured at 23 ° C. and 55% RH at a wavelength of 590 nm after 0.5 hours have passed from 23 ° C. and 55% RH from the end of the fifth step. Rth (0.5), and after 24 hours at 23 ° C. and 55% RH from the end of the fifth step, in the thickness direction of the retardation film measured at 23 ° C. and 55% RH at a wavelength of 590 nm The method for producing a retardation film according to [1], wherein when the retardation is Rth (24), the following formula is satisfied.
| Rth (0.5) −Rth (24) | ≦ 2.0 nm
[3] A retardation film produced by the production method according to [1] or [2], wherein a hydrogen bonding compound having at least a carboxy group or a hydroxy group as a substituent on an aromatic ring is converted into an average acetyl group A retardation film containing 1 to 15% by mass with respect to cellulose acetate having a substitution degree of 2.2 to 2.5.
[4] The retardation film according to [3], wherein the hydrogen bonding compound is a compound represented by the following general formula (I) or (II).
Formula (I)

(In the general formula (I), l represents an integer of 1 or more, and in the case of 2 or more, two carboxyl groups may be dehydrated and condensed to form a ring; m is an integer of 0 to 4) R represents an alkyl group; n represents an integer of 0 to 4, and when there are a plurality of Rs, the plurality of Rs may be the same or different from each other; l + m ≧ 2 )
Formula (II)

(In the general formula (II), each R ¹ independently represents a halogen atom or a hydroxyl group; n represents an integer of 0 to 4)
[5] The retardation film according to [3] or [4], wherein the tensile elastic modulus at 23 ° C. and 55% RH is in the range of 3500 to 6000 MPa.
[6] Any of [3] to [5], defined by the following formula, having a retardation value Rth in the thickness direction measured at 23 ° C. and 55% RH at a wavelength of 590 nm within a range of 70 to 400 nm. The retardation film according to claim 1.
Rth = [(nx + ny) / 2−nz] × d
(Wherein nx represents the refractive index in the slow axis direction in the film plane; ny represents the refractive index in the direction perpendicular to the slow axis in the film plane; nz represents the thickness direction of the film) And d represents the thickness of the film)
[7] The retardation film according to any one of [3] to [6], wherein a film width in the slow axis direction of the retardation film is 700 to 3000 mm.

[8] A polarizing plate having the retardation film according to any one of [3] to [6].
[9] A liquid crystal display device comprising the retardation film according to any one of [3] to [6].

  According to the present invention, it is possible to produce a retardation film having a small variation in retardation value over time even at a high production rate. In addition, by using the retardation film, it is possible to provide a liquid crystal display device in which front angle is improved with less change in hue depending on viewing angle;

It is a schematic diagram which shows an example of the fundamental structure of the liquid crystal display device of this invention.

  Hereinafter, the present invention will be described in detail. In the specification of the present application, “to” is used in the sense of including the numerical values described before and after it as a lower limit value and an upper limit value.

1. Retardation film The retardation film of the present invention comprises a cellulose acetate having an average degree of acetyl group substitution of 2.2 to 2.5, and a hydrogen bonding compound having a carboxy group or a hydroxy group as a substituent at least on an aromatic ring (hereinafter, It is also characterized in that the retardation value immediately after production is small. Specifically, in the thickness direction measured at 23 ° C. and 55% RH at a wavelength of 590 nm 0.5 hours after the final drying step (fifth step) of the retardation film production process is completed. Retardation value Rth (0.5) and retardation in the thickness direction measured at 23 ° C. and 55% RH at a wavelength of 590 nm after 24 hours at 23 ° C. and 55% RH after the drying step was completed. The absolute value | Rth (0.5) −Rth (24) | of the difference from the value Rth (24) is not more than a certain value (preferably not more than 2 nm).

  Thus, the retardation film of the present invention has little variation with time in Rth. Therefore, the increase in the amount of light leakage of the polarizing plate including the retardation film of the present invention can be suppressed. Therefore, the liquid crystal display device including the polarizing plate of the present invention has little change in hue due to the viewing angle and can improve the front contrast.

  The reason why such an effect is obtained is not necessarily clear, but is presumed as follows. That is, the inventor found that the retardation film obtained immediately after production is not stable in the orientation of cellulose acetate molecules, so that the retardation value Rth in the thickness direction is likely to fluctuate even when stored at room temperature and humidity. I discovered that. In the present invention, the fluctuation of the retardation value Rth of the retardation film immediately after production is reduced by stabilizing the orientation of cellulose acetate molecules from an early stage. Accordingly, it is considered that the optical characteristics of the retardation film over time can be reduced, the change in hue due to the viewing angle of the liquid crystal display device including the retardation film can be reduced, and the front contrast can be increased.

  A retardation film having a stable orientation state of cellulose acetate molecules is obtained; that is, in order to make | Rth (0.5) −Rth (24) | In the film production process, the drying rate (average solvent volatilization rate) of the film-like material containing cellulose acetate having an average acetyl group substitution degree of 2.2 to 2.5 and the above-mentioned hydrogen bonding compound immediately before stretching. Is preferably adjusted to a predetermined range depending on the drying temperature or the air volume of the drying conditions; if necessary, the retardation film is kept at 23 ° C. 55 after 24 hours from the end of the last drying step (fifth step). It is preferable to make the film composition such that the tensile elastic modulus under% RH is in the range of 3500 to 6000 MPa (adjusting the plasticizer content and the like).

Cellulose acetate The raw material cellulose of the cellulose acetate used in the present invention may be any raw material cellulose, and examples thereof include cotton linter and wood pulp (broadwood pulp, softwood pulp). The raw material cellulose may be mixed and used as necessary.

  In particular, the raw material cellulose is preferably obtained from wood pulp from the viewpoint of good bonding properties with a polarizer.

  Glucose units having β-1,4 bonds constituting cellulose have free hydroxy groups (hydroxyl groups) at the 2nd, 3rd and 6th positions. Cellulose acetate is a polymer (polymer) obtained by acetylating part or all of these hydroxy groups (hydroxyl groups). The degree of acetyl group substitution means the ratio of acetylation of the hydroxy groups (hydroxyl groups) of cellulose located at the 2-position, 3-position and 6-position (100% acetylation has a degree of substitution of 3).

  The average acetyl group substitution degree of cellulose acetate is preferably in the range of 2.2 to 2.5. When cellulose acetate contains a plurality of cellulose acetates having different degrees of acetyl group substitution, the sum of products of the degree of acetyl group substitution and the mass fraction of each cellulose acetate is referred to as the average degree of acetyl group substitution.

  The average degree of acetyl group substitution is determined after high-performance liquid chromatography measurement of cellulose acetate by a conventional method to obtain a chart showing the degree of substitution distribution (a chart showing peaks derived from cellulose acetate for each degree of substitution); The degree of substitution can be calculated from the area ratio of the peak of cellulose acetate to the total peak.

The weight average molecular weight of cellulose acetate is preferably 1.2 × 10 ⁵ or more and less than 2.5 × 10 ^{5 in} order to obtain a film having a certain mechanical strength or more, and 1.5 × 10 ⁵ or more. More preferably, it is less than 2.0 × 10 ⁵ .

  The molecular weight distribution (weight average molecular weight Mw / number average molecular weight Mn) of cellulose acetate is preferably 1.0 to 4.5.

The weight average molecular weight Mw and molecular weight distribution 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.

  As the acetylating agent in the acetylation of cellulose, an acid anhydride or an acid chloride is used. When such an acetylating agent is used, an organic acid such as acetic acid or methylene chloride is used as the organic solvent as a reaction solvent.

As the catalyst, when the acetylating agent is an acid anhydride, a protic catalyst such as sulfuric acid is preferably used; when the acetylating agent is an acid chloride (eg, CH ₃ COCl), a basic catalyst is used. A compound is preferably used.

  The most common industrial synthesis method of cellulose fatty acid ester is a method of acylating cellulose with a fatty acid corresponding to an acetyl group (acetic acid) or an acid anhydride thereof. The cellulose acetate used for this invention is compoundable by the method described in Unexamined-Japanese-Patent No. 10-45804, for example.

(Hydrogen bonding compound)
As a result of the study by the present inventors, in the retardation film, it is possible to reduce the change in the retardation value from immediately after the production to after the lapse of 24 hours, thereby preventing the change of the hue due to the viewing angle of the liquid crystal display device, and the front contrast. It was found to be important in improving

  In order to suppress the fluctuation of the retardation value, it is necessary to suppress the fluctuation of the orientation of the cellulose acetate molecule; for that purpose, it is considered necessary to increase the hydrogen bond between the molecules of the cellulose acetate. It is done. It has been found that in order to increase the hydrogen bond between molecules of cellulose acetate, it is effective to lower the acetyl group substitution degree of cellulose acetate and to add the aforementioned hydrogen bonding compound. Thereby, it discovered that the fluctuation | variation of the retardation value of the phase difference film obtained could be suppressed.

  Hydrogen bonding is described in J. Org. N. As described in Israel Ativili, “Intermolecular Forces and Surface Forces” (Takeshi Kondo, Hiroyuki Oshima, Maglow Hill Publishing, 1991), an electrically negative atom and a covalently bonded hydrogen atom are Non-covalent attractive interaction with negative electrons (oxygen, nitrogen, fluorine, chlorine) and lone electron pairs such as π-electron system. The hydrogen bonding compound is an organic compound having a boiling point of 180 ° C. or more having a hydrogen atom covalently bonded to the electronegative atom. For example, it refers to an organic compound having a boiling point of 180 ° C. or higher that includes O—H (oxygen hydrogen bond), N—H (nitrogen hydrogen bond), and the like, and can form a hydrogen bond with an adjacent lone pair and arrange it.

  The hydrogen bonding compound applied to the present invention is a hydrogen bonding compound having at least one carboxy group or hydroxy group as a substituent in the aromatic ring. Examples of the aromatic ring include a benzene ring and a naphthalene ring.

Examples of such hydrogen bonding compounds include phenol, cresol (o-cresol, m-cresol, p-cresol), hydroxynaphthalene carboxylic acid (eg 2-hydroxynaphthalene-1-carboxylic acid), general formula (I ), A compound represented by the general formula (II), and the like.
Formula (I)

  In general formula (I), R represents an alkyl group. n represents an integer of 0 to 4. The alkyl group represented by R is preferably an alkyl group having 1 to 20 carbon atoms, more preferably 1 to 12 carbon atoms, particularly preferably 1 to 8 carbon atoms, such as a methyl group, an ethyl group, or iso-propyl. Group, tert-butyl group, n-octyl group, n-decyl group, n-hexadecyl group, cyclopropyl group, cyclopentyl group, cyclohexyl group and the like.

In addition to the above, the benzene ring of the general formula (I) may further have a substituent,
An alkenyl group (preferably having 2 to 20 carbon atoms, more preferably 2 to 12 carbon atoms, particularly preferably 2 to 8 carbon atoms, and examples thereof include vinyl, allyl, 2-butenyl, 3-pentenyl and the like);
An alkynyl group (preferably having 2 to 20 carbon atoms, more preferably 2 to 12 carbon atoms, particularly preferably 2 to 8 carbon atoms, such as propargyl and 3-pentynyl);
An aryl group (preferably having 6 to 30 carbon atoms, more preferably 6 to 20 carbon atoms, particularly preferably 6 to 12 carbon atoms, and examples thereof include phenyl, p-methylphenyl, naphthyl and the like);
A substituted or unsubstituted amino group (preferably having 0 to 20 carbon atoms, more preferably 0 to 10 carbon atoms, particularly preferably 0 to 6 carbon atoms, such as amino, methylamino, dimethylamino, diethylamino, dibenzylamino; Etc.);
An alkoxy group (preferably having 1 to 20 carbon atoms, more preferably 1 to 12 carbon atoms, particularly preferably 1 to 8 carbon atoms, and examples thereof include methoxy, ethoxy, butoxy and the like);
An aryloxy group (preferably having 6 to 20 carbon atoms, more preferably 6 to 16 carbon atoms, particularly preferably 6 to 12 carbon atoms, such as phenyloxy, 2-naphthyloxy and the like);
An acyl group (preferably having 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, particularly preferably 1 to 12 carbon atoms, such as acetyl, benzoyl, formyl, pivaloyl, etc.);
An alkoxycarbonyl group (preferably having 2 to 20 carbon atoms, more preferably 2 to 16 carbon atoms, particularly preferably 2 to 12 carbon atoms, and examples thereof include methoxycarbonyl and ethoxycarbonyl);
An aryloxycarbonyl group (preferably having 7 to 20 carbon atoms, more preferably 7 to 16 carbon atoms, particularly preferably 7 to 10 carbon atoms, and examples thereof include phenyloxycarbonyl);
An acyloxy group (preferably having 2 to 20 carbon atoms, more preferably 2 to 16 carbon atoms, particularly preferably 2 to 10 carbon atoms, and examples thereof include acetoxy and benzoyloxy);
An acylamino group (preferably having 2 to 20 carbon atoms, more preferably 2 to 16 carbon atoms, particularly preferably 2 to 10 carbon atoms, and examples thereof include acetylamino and benzoylamino);
An alkoxycarbonylamino group (preferably having 2 to 20 carbon atoms, more preferably 2 to 16 carbon atoms, particularly preferably 2 to 12 carbon atoms, such as methoxycarbonylamino);
An aryloxycarbonylamino group (preferably having 7 to 20 carbon atoms, more preferably 7 to 16 carbon atoms, particularly preferably 7 to 12 carbon atoms, such as phenyloxycarbonylamino);
A sulfonylamino group (preferably having 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, particularly preferably 1 to 12 carbon atoms, such as methanesulfonylamino and benzenesulfonylamino);
Sulfamoyl group (preferably having 0 to 20 carbon atoms, more preferably 0 to 16 carbon atoms, and particularly preferably 0 to 12 carbon atoms. Examples thereof include sulfamoyl, methylsulfamoyl, dimethylsulfamoyl, and phenylsulfamoyl. Listed);
A carbamoyl group (preferably having 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, particularly preferably 1 to 12 carbon atoms, such as carbamoyl, methylcarbamoyl, diethylcarbamoyl, phenylcarbamoyl, etc.);
An alkylthio group (preferably having 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, particularly preferably 1 to 12 carbon atoms, such as methylthio and ethylthio);
An arylthio group (preferably having 6 to 20 carbon atoms, more preferably 6 to 16 carbon atoms, particularly preferably 6 to 12 carbon atoms, such as phenylthio);
A sulfonyl group (preferably having 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, particularly preferably 1 to 12 carbon atoms, such as mesyl and tosyl);
A sulfinyl group (preferably having 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, particularly preferably 1 to 12 carbon atoms, such as methanesulfinyl, benzenesulfinyl, etc.);
A ureido group (preferably having 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, and particularly preferably 1 to 12 carbon atoms, and examples thereof include ureido, methylureido, and phenylureido);
A phosphoric acid amide group (preferably having 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, particularly preferably 1 to 12 carbon atoms, such as diethyl phosphoric acid amide and phenylphosphoric acid amide);
Mercapto group, halogen atom (eg fluorine atom, chlorine atom, bromine atom, iodine atom), cyano group, sulfo group, nitro group, hydroxamic acid group, sulfino group, hydrazino group, imino group,
Heterocyclic group (preferably having 1 to 30 carbon atoms, more preferably 1 to 12 carbon atoms, and examples of the hetero atom include a nitrogen atom, an oxygen atom, a sulfur atom, specifically, for example, imidazolyl, pyridyl, quinolyl, furyl, piperidyl , Morpholino, benzoxazolyl, benzimidazolyl, benzthiazolyl, etc.);
Examples thereof include silyl groups (preferably having 3 to 40 carbon atoms, more preferably 3 to 30 carbon atoms, and particularly preferably 3 to 24 carbon atoms, and examples thereof include trimethylsilyl and triphenylsilyl). Of these, an aryl group, a substituted or unsubstituted amino group, an alkoxy group, and an aryloxy group are more preferable, and an aryl group and an alkoxy group are still more preferable.

  In general formula (I), l represents an integer of 1 or more, preferably an integer of 1 to 3. When the compound represented by the general formula (I) contains two or more carboxyl groups, the two carboxyl groups may be condensed with each other to form a ring. m represents an integer of 0 to 4, preferably an integer of 0 to 3. However, l + m ≧ 2.

  The compound represented by the general formula (I) is preferably an o-salicylic acid derivative or an m-salicylic acid derivative.

Among the compounds represented by the general formula (I), particularly preferred examples are shown below, but are not limited to these specific examples.

Formula (II)

In general formula (II), R ¹ each independently represents a halogen atom or a hydroxyl group.

The halogen atom is not particularly limited, but is preferably a fluorine atom. That is, in general formula (II), R ¹ preferably independently represents a fluorine atom or a hydroxyl group.

n represents an integer of 0 to 4, and is preferably 3 to 4. When n is less than 4, among the carbon atoms constituting the benzene ring in the compound represented by the general formula (II), a carbon atom to which R ¹ , —NH ₂ group and —COOH group are not bonded is a hydrogen atom Are joined. That is, when n is less than 4, the benzene ring in the compound represented by the general formula (II) has no substituent other than R ¹ , —NH ₂ group and —COOH group.

In the compound represented by the general formula (II), both —NH ₂ group and —COOH group are directly bonded to carbon atoms constituting the benzene ring. Here, the bonding position of the —NH ₂ group and —COOH group in the benzene ring is not particularly limited, and any positional relationship of ortho, meta, and para may be used. Among them, the ortho or para positional relationship is preferable, and the para positional relationship is more preferable.

Further, the —NH ₂ group and —COOH group in the compound represented by the general formula (II) do not further have a substituent. That is, neither the —NH ₂ group nor the —COOH group in the compound represented by the general formula (II) forms an amide bond or an ester bond.

On the other hand, the —NH ₂ group and the —COOH group in the compound represented by the general formula (II) may be ionized in a solvent such as an aqueous solution as long as they are reversible. It may be formed.

Specific examples of the compound represented by the general formula (II) include the following, but are not limited thereto.

  Among these hydrogen bonding compounds, the compound represented by the general formula (I) or the general formula (II) is preferable because an effect of enhancing hydrogen bonding between cellulose acetate molecules can be easily obtained.

  The molecular weight of the hydrogen bonding compound is preferably 130 to 2000, more preferably 130 to 250, and still more preferably 130 to 210. By using a hydrogen bonding compound having a molecular weight in the above range, as described later, volatilization of the additive in the production process of the retardation film can be suppressed, and compatibility with the cellulose ester can be easily secured, which is preferable. .

  The content of the hydrogen bonding compound used in the present invention is preferably 0.5 to 15% by mass in the retardation film, more preferably 1 to 10% by mass, and 1 to 5% by mass. More preferably, it is particularly preferably 1-2% by mass.

  Moreover, it is preferable that it is 1-15 mass% with respect to a cellulose acetate, as for content of a hydrogen bondable compound, it is more preferable that it is 2-10 mass%, and it is further more preferable that it is 2-5 mass%. . When the content of the hydrogen bonding compound is less than 1% by mass, hydrogen bonding between cellulose acetate molecules may not be sufficiently increased. When the content of the hydrogen bonding compound is more than 15% by mass, not only the film tends to bleed out but also the Tg of the film may be lowered.

  The method for synthesizing the hydrogen bonding compound is not particularly limited, and a known method can be used. Further, the hydrogen bonding compound may be obtained commercially, and can be purchased from, for example, Tokyo Chemical Industry Co., Ltd. or Wako Pure Chemical Industries, Ltd.

Other Additives The retardation film of the present invention can appropriately contain a sugar ester compound, a plasticizer, a deterioration preventing agent, an ultraviolet absorber, a peeling accelerator, a matting agent, a lubricant, and the like as necessary.

(Sugar ester compound)
The sugar ester compound is preferably a compound represented by the following formula (1).

R _{1 to} R ₈ in the formula (1) represent a substituted or unsubstituted alkylcarbonyl group or a substituted or unsubstituted arylcarbonyl group. R _{1 to} R ₈ may be the same as or different from each other.

  The substituted or unsubstituted alkylcarbonyl group is preferably a substituted or unsubstituted alkylcarbonyl group having 2 or more carbon atoms. Examples of the substituted or unsubstituted alkylcarbonyl group include a methylcarbonyl group (acetyl group). Examples of the substituent that the alkyl group has include an aryl group such as a phenyl group.

Specific examples of the compound represented by the formula (1) include the following. R in Table 1 represents R _{1 to} R ₈ in Formula (1).

  The content of the sugar ester compound is preferably 1 to 40% by mass and more preferably 5 to 20% by mass with respect to cellulose acetate.

(Plasticizer)
Preferable examples of the plasticizer include a polyester compound represented by the following 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. B represents a monovalent group derived from a hydrogen atom or a carboxylic acid. 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. n represents an integer of 1 or more.

  Examples of the divalent group of A derived from an alkylenedicarboxylic acid having 4 to 12 carbon atoms include 1,2-ethanedicarboxylic acid, 1,3-propanedicarboxylic acid, 1,4-butanedicarboxylic acid, etc. A divalent group derived from is included. Examples of divalent groups derived from aryl dicarboxylic acids having 6 to 12 carbon atoms in A include 1,2-benzenedicarboxylic acid (phthalic acid), 1,3-benzenedicarboxylic acid, and 1,4-benzene. Divalent groups derived from dicarboxylic acids, naphthalenedicarboxylic acids such as 1,5-naphthalenedicarboxylic acid and the like are included.

  Examples of the monovalent group derived from carboxylic acid of B include a monovalent group derived from an aromatic carboxylic acid such as benzoic acid and toluic acid, an aliphatic carboxylic acid such as acetic acid, and the like.

  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.

  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 include a divalent group derived from diethylene glycol, dipropylene glycol and the like.

（２３）：コハク酸／テレフタル酸／エチレングリコール（１／１／２モル比）からなる縮合物（重量平均分子量：６０６）の両末端が安息香酸で封止された化合物
（２４）：コハク酸／テレフタル酸／エチレングリコール（１／１／２モル比）からなる縮合物（重量平均分子量：７６２）の両末端が封止されていない（両末端がエチレングリコールのＯＨ基である）化合物 Examples of the polyester compound represented by the general formula (2) include the following.

(23): Compound in which both ends of a condensate (weight average molecular weight: 606) composed of succinic acid / terephthalic acid / ethylene glycol (1/1/2 molar ratio) are sealed with benzoic acid (24): succinic acid / Condensate composed of terephthalic acid / ethylene glycol (1/1/2 molar ratio) (weight average molecular weight: 762), both ends are not sealed (both ends are OH groups of ethylene glycol)

  The plasticizer content is preferably 1 to 40% by mass and more preferably 5 to 20% by mass with respect to cellulose acetate.

(Deterioration inhibitor)
The retardation film of the present invention may further contain a known deterioration (oxidation) inhibitor. Examples of the degradation inhibitor include 2,6-di-tert-butyl-4-methylphenol, 4,4′-thiobis- (6-tert-butyl-3-methylphenol), 1,1′-bis (4 -Hydroxyphenyl) cyclohexane, 2,2'-methylenebis (4-ethyl-6-tert-butylphenol), 2,5-di-tert-butylhydroquinone, pentaerythrityl-tetrakis [3- (3,5-di- Phenolic or hydroquinone antioxidants such as tert-butyl-4-hydroxyphenyl) propionate] can be used. Further, tris (4-methoxy-3,5-diphenyl) phosphite, tris (nonylphenyl) phosphite, tris (2,4-di-tert-butylphenyl) phosphite, bis (2,6-di-tert) Phosphorous antioxidants such as -butyl-4-methylphenyl) pentaerythritol diphosphite and bis (2,4-di-tert-butylphenyl) pentaerythritol diphosphite can be used. The content of the deterioration inhibitor is preferably 0.05 to 5.0 parts by mass with respect to 100 parts by mass of cellulose acetate.

(UV absorber)
The retardation film of the present invention may further contain an ultraviolet absorber from the viewpoint of preventing deterioration of a polarizing plate or a liquid crystal display device. As the ultraviolet absorber, those excellent in the ability to absorb ultraviolet rays having a wavelength of 370 nm or less and having little absorption of visible light having a wavelength of 400 nm or more are preferably used from the viewpoint of good liquid crystal display properties.

  Specific examples of ultraviolet absorbers preferably used in the present invention include hindered phenol compounds, hydroxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex salts, and the like. Is mentioned.

  Examples of hindered phenol compounds include 2,6-di-tert-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate]. N, N′-hexamethylenebis (3,5-di-tert-butyl-4-hydroxy-hydrocinnamide), 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert) -Butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-tert-butyl-4-hydroxybenzyl) -isocyanurate and the like.

  Examples of benzotriazole compounds include 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2,2-methylenebis (4- (1,1,3,3-tetramethylbutyl) -6 (2H-benzotriazol-2-yl) phenol), (2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-tert-butylanilino) -1,3,5- Triazine, triethylene glycol-bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate], N, N′-hexamethylenebis (3,5-di-tert-butyl-4- Hydroxy-hydrocinnamide), 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene, 2 (2′-hydroxy-3 ′, 5′-di-tert-butylphenyl) -5-chlorobenzotriazole, (2 (2′-hydroxy-3 ′, 5′-di-tert-amylphenyl) -5 -Chlorobenzotriazole, 2,6-di-tert-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] and the like.

  The content of these ultraviolet light inhibitors is preferably 1 ppm to 1.0% by mass in the retardation film, and more preferably 10 to 1000 ppm.

(Matting agent)
The retardation film of the present invention contains fine particles from the viewpoint of improving scratch resistance by reducing the coefficient of friction of the film surface, preventing creaking that occurs when a wide film is wound long, and preventing film breakage. It is preferable. The fine particles are called matting agent, anti-blocking agent or anti-scratching agent and have been conventionally used. The fine particles are not particularly limited as long as they are materials exhibiting the functions described above, and may be an inorganic compound matting agent or an organic compound matting agent.

  Preferred specific examples of the inorganic compound matting agent include silicon-containing inorganic compounds (eg, silicon dioxide, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, etc.), titanium oxide, zinc oxide, Aluminum oxide, barium oxide, zirconium oxide, strongtium oxide, antimony oxide, tin oxide, tin oxide / antimony, calcium carbonate, talc, clay, calcined kaolin, calcium phosphate, etc. are preferred, and more preferably inorganic compounds containing silicon and zirconium oxide However, since the turbidity of the cellulose acylate film can be reduced, silicon dioxide is particularly preferably used.

  As the silicon dioxide fine particles, for example, commercially available products having a trade name such as Aerosil R972, R974, R812, 200, 300, R202, OX50, TT600 (manufactured by Nippon Aerosil Co., Ltd.) can be used. As the fine particles of zirconium oxide, for example, those commercially available under trade names such as Aerosil R976 and R811 (manufactured by Nippon Aerosil Co., Ltd.) can be used.

  Preferable specific examples of the organic compound matting agent are, for example, polymers such as silicone resin, fluorine resin and acrylic resin, and among them, silicone resin is preferably used. Among the silicone resins, those having a three-dimensional network structure are particularly preferable. For example, Tospearl 103, Tospearl 105, Tospearl 108, Tospearl 120, Tospearl 145, Tospearl 3120 and Tospearl 240 (manufactured by Toshiba Silicone Co., Ltd.) A commercial product having a trade name can be used.

  The thickness of the retardation film of the present invention varies depending on the purpose of use, but is usually preferably in the range of 10 to 500 μm, more preferably in the range of 20 to 200 μm, and in the range of 30 to 80 μm. Is most preferred. In adjusting the thickness of the retardation film, the concentration of solids contained in the dope liquid, the slit gap of the die die, and extrusion from the die are performed in the retardation film manufacturing process described later so that the desired thickness is obtained. What is necessary is just to adjust a pressure, the conveyance speed of a metal support body, etc.

(Thickness direction retardation value Rth)
The retardation value Rth in the thickness direction of the retardation film of the present invention measured at 23 ° C. and 55% RH at a wavelength of 590 nm can be set according to the type of liquid crystal cell to be applied, for example, 70 to 400 nm. And preferably 100 to 300 nm. The retardation film having Rth in the above range can be used as, for example, a retardation film of a VA liquid crystal cell.

  Rth (λ) of the retardation film is 10 to 50 ° on one side with respect to the film normal direction, with the slow axis (determined by KOBRA 21ADH) in the film plane as the tilt axis (rotation axis). For each degree, a total of six retardation values are measured when light having a wavelength λ (nm) is incident from the inclined direction. When the retardation film does not have a slow axis, an arbitrary direction in the film plane is set as the rotation axis. Then, KOBRA 21ADH calculates Rth (λ) of the retardation film based on the measured retardation value, the assumed value of the average refractive index, and the inputted film thickness value of the retardation film. In this specification, Rth is a value measured at 23 ° C. and 55% RH when the wavelength λ is 590 nm unless otherwise specified.

The retardation value in the thickness direction of the retardation film is obtained by the following formula.
Rth = [(nx + ny) / 2−nz] × d
(Where Rth is a retardation value in the thickness direction of the retardation film measured at a wavelength of 590 nm;
nx is the refractive index in the slow axis direction in the film plane;
ny is the refractive index in the fast axis direction in the film plane;
nz is the refractive index in the thickness direction of the film;
d is the thickness of the film)

(Tensile modulus)
The tensile modulus of the retardation film of the present invention is preferably 3000 MPa or more, more preferably 3000 to 7000 MPa, and particularly preferably 3500 to 6000 MPa. If the tensile elastic modulus is less than 3000 MPa, the retardation film may be too flexible and the orientation of cellulose acetate molecules may be easily disturbed. Thereby, the fluctuation | variation of the retardation value with time of a retardation film tends to become large. The tensile elastic modulus of the retardation film can be adjusted by the content of the plasticizer such as the sugar ester compound or the polyester compound described above.

  The tensile elastic modulus of the retardation film can be measured according to the method described in JIS K7127 after conditioning for 24 hours at 25 ° C. and 60% RH. Tensilon manufactured by Orientec Co., Ltd. can be used as the tensile tester.

2. Method for Producing Retardation Film The retardation film of the present invention can be produced by a solution casting method. Production of a retardation film by a solution casting method is as follows: 1) a first step of preparing a dope solution by dissolving cellulose acetate, a hydrogen bonding compound, and, if necessary, other additives in a solvent; ) A second step of casting the dope solution on an endless metal support; 3) a third step of peeling the film-like material obtained by drying the cast dope from the metal support; 4) The fourth step of stretching or maintaining the width of the film-like material, and 5) The fifth step of heating and drying the stretched film-like material to volatilize the organic solvent in the film-like material. Is preferred.

(First step)
The process for preparing the dope solution will be described. The concentration of cellulose acetate in the dope is preferably higher because the drying load after casting on the metal support can be reduced. On the other hand, if the concentration of cellulose acetate is too high, the load during filtration increases and the filtration accuracy deteriorates. As a density | concentration which makes these compatible, 10-35 mass% is preferable, More preferably, it is 15-25 mass%.

  The solvent used for the dope solution contains 90% by mass or more of a halogen-based organic solvent which is a good solvent. The solvents may be used alone or in combination of two or more. However, it is preferable from the viewpoint of production efficiency to use a mixture of a halogen-based organic solvent and a poor solvent of cellulose acetate.

  A good solvent is defined as one that dissolves the cellulose acetate used alone; a poor solvent can be defined as one that swells or does not dissolve alone. Therefore, the good solvent and the poor solvent differ depending on the average acetylation degree (acetyl group substitution degree) of cellulose acetate.

  The good solvent used in the present invention is not particularly limited, but an organic halogen solvent such as methylene chloride is preferable. As the halogen-based organic solvent, a solvent selected from halogenated hydrocarbons having 1 to 6 carbon atoms is preferable because it well dissolves cellulose acetate. Particularly preferred halogenated organic solvents include dichloromethane, chloroform, dichloroethane and the like.

  Although the poor solvent used for this invention is not specifically limited, It is preferable to be chosen from a C1-C10 alcohol or hydrocarbon, More preferably, it is a C1-C8 alcohol. The alcohol may be linear, branched or cyclic, and is preferably a saturated aliphatic hydrocarbon. The hydroxy group of the alcohol may be any of primary to tertiary.

  Examples of the alcohol include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, tert-butanol, 1-pentanol, 2-methyl-2-butanol and cyclohexanol.

  As the hydrocarbon, either an aromatic hydrocarbon or an aliphatic hydrocarbon can be used. Examples of hydrocarbons include cyclohexane, hexane, benzene, toluene and xylene.

  Moreover, it is preferable that 0.01-2 mass% of water is contained in dope liquid.

  Moreover, the solvent used for melt | dissolution of a cellulose acetate collect | recovers the solvent removed from the film by drying at the film-forming process, and uses this again. The recovery solvent may contain trace amounts of additives added to cellulose acetate, such as plasticizers, UV absorbers, polymers, monomer components, etc., but these are preferably reused even if they are included. Can be purified and reused if necessary.

  Various additives as described above (for example, plasticizers, UV inhibitors, deterioration inhibitors, fine particles, optical property adjusting agents, etc.) can be added to the dope solution in which cellulose acetate is dissolved. Further, the timing of the addition may be any of the first steps for preparing the dope solution, and may be performed at the end of the first step for preparing the dope solution, for example.

  As a method for dissolving cellulose acetate when preparing the dope solution, a general method can be used. When heating and pressurization are combined, it is possible to heat above the boiling point at normal pressure. It is preferable to stir and dissolve while heating at a temperature that is equal to or higher than the boiling point of the solvent at normal pressure and that the solvent does not boil under pressure, in order to prevent the generation of massive undissolved materials called gels and mamacos.

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

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

  The heating temperature with the addition of a solvent is preferably higher from the viewpoint of the solubility of cellulose acetate, but if the heating temperature is too high, the required pressure increases and the productivity deteriorates. A preferable heating temperature is 45 to 120 ° C, more preferably 60 to 110 ° C, and still more preferably 70 ° C to 105 ° C. The pressure is adjusted so that the solvent does not boil at the set temperature.

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

  Next, the cellulose acetate solution is preferably filtered using a suitable filter medium such as filter paper. It is preferable to remove and reduce impurities, particularly bright spot foreign matter, contained in the raw material cellulose acetate by filtration.

The bright spot foreign matter is arranged in a crossed Nicols state with two polarizing plates, a retardation film or the like is placed between them, light is applied from one polarizing plate side, and observation is performed from the other polarizing plate side. It is a point (foreign matter) where light from the opposite side sometimes leaks, and the number of bright spots having a diameter of 0.01 mm or more is preferably 200 / cm ² or less. More preferably, it is 100 pieces / cm < ² > or less, More preferably, it is 50 pieces / cm < ² > or less, More preferably, it is 0-10 pieces / cm < ² > or less. Further, it is preferable that the number of bright spots of 0.01 mm or less is small.

  As the filter medium, it is preferable that the absolute filtration accuracy is small in order to remove insoluble matters and the like, but there is a problem that the filter medium is likely to be clogged if the absolute filtration accuracy is too small. For this reason, a filter medium with an absolute filtration accuracy of 0.008 mm or less is preferable, a filter medium with 0.001 to 0.008 mm is more preferable, and a filter medium with 0.003 to 0.006 mm is still more preferable.

  The material of the filter medium is not particularly limited, and a normal filter medium can be used. However, a plastic filter medium such as polypropylene or Teflon (registered trademark), or a metal filter medium such as stainless steel may cause fibers to fall off. Less preferred.

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

  A preferred temperature is 45 to 120 ° C, more preferably 45 to 70 ° C, and still more preferably 45 to 55 ° C. A smaller filtration pressure is preferred. The filtration pressure is preferably 1.6 MPa or less, more preferably 1.2 MPa or less, and further preferably 1.0 MPa or less.

(Second step)
Here, the dope casting will be described. The metal support in the casting process is preferably a mirror finished surface. As the metal support, a stainless steel belt or a drum whose surface is plated with a casting is preferably used.

  The cast width can be 1 to 4 m. The surface temperature of the metal support in the casting process is preferably from −50 ° C. to less than the boiling point of the solvent, and a higher temperature is preferable because the drying rate of the cast dope can be increased. The doped dope may foam or the planarity may deteriorate. A preferable support temperature is 0 to 55 ° C, and more preferably 25 to 50 ° C. Alternatively, it is also a preferable method that the dope cast by cooling is gelled and peeled from the drum in a state containing a large amount of residual solvent.

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

(Third step)
The process of peeling the film-like material obtained after drying the dope on the metal support will be described.

  By controlling the temperature of the metal support as described above and applying the temperature-controlled drying air to the cast dope, the dope is dried to obtain a film.

  The dope drying on the metal support is generally performed by applying hot air to the surface side of the metal support (drum or belt), that is, the dope surface on the metal support, or applying hot air from the back surface of the drum or belt. There is a liquid heat transfer method in which a temperature-controlled liquid is brought into contact with the back surface of the belt or drum opposite to the dope casting surface and the drum or belt is heated by heat transfer to control the surface temperature. A thermal system is preferred. The surface temperature of the metal support before the dope is cast may be any number as long as it is not higher than the boiling point of the solvent used for the dope. However, in order to promote drying and to lose the dope fluidity on the metal support, the temperature of the liquid in contact with the back surface of the metal support is the lowest boiling point of the solvents used. It is preferable to set the temperature 1 to 10 ° C. lower than the boiling point of the solvent.

  The film-like material obtained as described above is peeled off from the metal support.

  In order for the retardation film to exhibit good flatness, the amount of residual solvent in the film-like material when peeled from the metal support is preferably 10 to 150% by mass, more preferably 20 to 40% by mass. Or it is 60-130 mass%, Most preferably, it is 20-30 mass% or 70-120 mass%.

In the present invention, the amount of residual solvent is defined by the following formula.
Residual solvent amount (% by mass) = {(MN) / N} × 100
In the above formula, M is the mass of the sample collected at any time during or after the production of the film or film, and N is the mass after heating M at 115 ° C. for 1 hour.

  It is preferable to peel at a peeling tension of 300 N / m or less while stretching in the width direction (lateral direction) by a tenter method in which both ends of the film-like material are held with clips or the like.

  Then, in at least one of the third step and the fourth step described later, the solvent in the film-like material obtained by peeling off from the metal support is further dried to a state suitable for stretching. In this drying, the film-like material tends to shrink in the width direction by evaporation of the solvent. Shrinkage increases with drying at higher temperatures. In order to improve the flatness of the obtained retardation film, it is preferable to dry while suppressing the shrinkage as much as possible. From this point, for example, a method of drying the whole drying process or a part of the process as shown in JP-A-62-46625 while holding both ends in the width direction with clips in the width direction ( Tenter system) is preferred.

(Fourth process)
In order to obtain the target retardation value Rth, it is preferable to adjust the refractive index of the film-like material by adjusting the conveyance tension or stretching operation. Hereinafter, the stretching process will be described.

  For example, the retardation value of the obtained retardation film is adjusted by lowering or increasing the tension in the longitudinal direction (casting direction) of the film-like material or the direction orthogonal to the film plane (width direction). It becomes possible.

  Further, biaxial stretching or uniaxial stretching can be performed sequentially or simultaneously with respect to the longitudinal direction (casting direction) and the width direction of the film-like material.

  It is preferable that the draw ratios in the biaxial directions perpendicular to each other are finally in the range of 0 to 1.5 times in the casting direction and 1.1 to 2.5 times in the width direction. It is preferable to carry out in the range of 0 to 1.0 times and 1.2 to 2.0 times in the width direction.

  As for the drying temperature just before extending | stretching, 140-170 degreeC is preferable. The stretching temperature is preferably 120 ° C. to 200 ° C., more preferably 150 ° C. to 200 ° C., further preferably more than 150 ° C. and 190 ° C. or less.

  The amount of residual solvent in the film-like material at the start of stretching is preferably 20 to 0%, more preferably 15 to 0%.

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

  There is no particular limitation on the method of stretching the film. For example, a method in which a difference in peripheral speed is applied to a plurality of rolls, and the roll peripheral speed difference is used to stretch in the longitudinal direction, the both ends of the film-like object are fixed with clips or pins, and the distance between the clips or pins is set in the traveling direction. And a method of stretching in the longitudinal direction, a method of stretching in the lateral direction and stretching in the lateral direction, or a method of stretching both in the longitudinal and lateral directions and stretching in both the longitudinal and lateral directions. Of course, these methods may be combined.

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

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

  In the present invention, in order to reduce the variation in retardation of the obtained retardation film over time, as described above, not only the hydrogen bonds between cellulose acetate molecules are increased, but also immediately before stretching. It is effective to reduce the amount of residual solvent in the film-like material as much as possible. In order to reduce the amount of residual solvent as much as possible, it is preferable to increase the drying rate of the film-like material immediately before stretching.

That is, the average volatilization rate of the organic solvent of the film-like material immediately before being stretched can be adjusted to a range of 1.5 × 10 ^{−3 to} 3.0 × 10 ⁻³ g / (sec · cm ² ). preferably, it is more preferably adjusted to a range of ^{1.9 × 10 -3 ~3.0 × 10 -3} g / (sec · cm 2).

  “Before stretching” means that after the film-like material is peeled off from the metal support in the third step (drying / peeling step), the film-like material starts to be drawn in the fourth step (stretching step). Time until time. For example, when stretching is started simultaneously with the start of the fourth step, “immediately before being stretched” means that after the film-like material is peeled off from the metal support in the third step until the start of the fourth step. Can be between. In addition, in the case where stretching is started after a lapse of a certain time since the fourth step is started, “immediately before being stretched” may be between the start of the fourth step and the start of stretching.

  The average volatilization rate can be adjusted by, for example, one or more of drying temperature, drying air speed, and film thickness (preferably drying temperature, more preferably both drying temperature and drying air speed). For example, the drying temperature can be preferably in the range of 140 to 170 ° C, more preferably in the range of 150 to 170 ° C. The drying wind speed can be preferably 5 m / second or more, more preferably 10 m / second or more. The thickness of the film-like material can be, for example, 25 to 45 μm.

The average volatilization rate can be measured by the following method.
(Average volatilization rate)
A total of three sample films having a size of 30 cm square are cut out from the left, center, and right in the width direction from the film-like material immediately before being stretched. Next, each sample film is immediately placed on a hot plate installed in an airtight container having a blowing function, and a mass decrease after 20 seconds (Ag) and a mass decrease after 40 seconds (Bg) while applying dry air. ) And measure. The temperature of the hot plate is set to the same value as the actual drying temperature of the film just before stretching; the wind speed of the drying air is set to the same value as the wind speed actually applied to the film just before stretching. Set; the capacity of the sealed container is 0.1 m ³ .
The measured value obtained is applied to the following equation to calculate the volatilization rate (g / sec · cm ² ).
(Ag-Bg) / (20 sec.900 cm ² )
Then, the average value of the volatilization rates of the three sample films is determined as an average volatilization rate (g / (sec · cm ² )) (mass reduction rate per unit area).

  The drying immediately before stretching is preferably performed until the amount of residual solvent in the film-like material at the start of stretching is within the above-described range (preferably 20 to 0%, more preferably 15 to 0%). The drying time immediately before stretching can be, for example, about 4 to 10 minutes.

In particular, a dope prepared by dissolving cellulose acetate having an average degree of acetyl group substitution in the range of 2.2 to 2.5 and a hydrogen bonding compound in an organic solvent containing 90% by mass or more of a halogen-based organic solvent. Is dried so that the average volatilization rate immediately before stretching is in the range of 1.5 × 10 ^{−3 to} 3.0 × 10 ⁻³ g / (sec · cm ² ). The retardation film obtained by making it possible to reduce the variation of the retardation value with time. And the change of the hue by the viewing angle of the liquid crystal display device using it is small, and front contrast can be raised.

  The reason why the retardation value of the retardation film of the present invention has a small variation over time is not necessarily clear, but is estimated as follows. That is, a film-like product containing cellulose acetate having an average acetyl group substitution degree of 2.2 to 2.5 and a hydrogen bonding compound has high hydrogen bonds between cellulose acetate molecules. For this reason, it is considered that hydrogen bonding between cellulose acetate molecules can be maintained even if the drying rate immediately before stretching is increased. Furthermore, by increasing the drying speed, a large amount of the solvent in the film-like material can be volatilized, and the amount of residual solvent in the film-like material before stretching can be reduced. By stretching a film-like material having a small amount of residual solvent, the orientation of cellulose acetate molecules can be enhanced, and it is considered that the orientation state of the cellulose acetate molecules is favorably maintained in the resulting retardation film. Thereby, it is considered that a retardation film with little fluctuation of the retardation value due to the change with time or use environment can be obtained.

(Fifth step)
A drying process is further implemented before winding up the stretched film. Thereby, the residual solvent amount of the retardation film obtained can be adjusted to the range suitable for the manufacturing process of a polarizing plate, or the manufacturing process of a liquid crystal display device.

  The drying temperature in the drying step of the film-like product after stretching is preferably 40 to 250 ° C, and particularly preferably 70 to 180 ° C. Furthermore, in order to remove the residual solvent, it is preferably dried at 50 to 160 ° C. In that case, it is preferable to dry the residual solvent by drying with high-temperature air with different temperatures. The above method is described in Japanese Patent Publication No. 5-17844. According to this method, it is possible to shorten the time from casting to stripping. The drying temperature, the amount of drying air, and the drying time vary depending on the solvent used, and may be appropriately selected according to the type and combination of the solvents used.

  The residual solvent amount of the finally obtained retardation film is preferably 2% by mass or less, and more preferably 0.4% by mass or less in order to obtain a retardation film having good dimensional stability. preferable.

  Since the retardation film of the present invention obtained immediately after finishing the fifth step (immediately after production) has a stable orientation state of cellulose acetate molecules, fluctuations in retardation values over time can be reduced.

  Specifically, after finishing the fifth step, Rth (0.5) of the retardation film after lapse of 0.5 hours at 23 ° C. and 55% RH, and 23 ° C. 55 after finishing the fifth step. The absolute value | Rth (0.5) −Rth (24) | of the difference in Rth (24) of the retardation film after 24 hours under% RH is preferably 2 nm or less, and preferably 1 nm or less. Is more preferable. Rth is a value measured under conditions of a wavelength of 590 nm under 23 ° C. and 55% RH.

  | Rth (0.5) −Rth (24) | is 1.7% or less of Rth (24) at a wavelength of 590 nm under 23 ° C. and 55% RH after 24 hours have elapsed after the fifth step. It is preferable that it is 1.0% or less.

  In order to make | Rth (0.5) −Rth (24) | within the above range, a film-form containing cellulose acetate having an average acetyl group substitution degree of 2.2 to 2.5 and the above-mentioned hydrogen bonding compound It is preferable to adjust the average volatilization rate of the product immediately before being stretched to a predetermined range; if necessary, the tensile elastic modulus of the retardation film after a lapse of 24 hours after the completion of the fifth step is predetermined. It is preferable to further adjust the film composition so as to be in the range.

  In the present invention, ending the final drying step of the production of the retardation film means a state immediately before winding. This is because the retardation film is not affected by drying by winding the retardation film.

  The winder may be a commonly used winder and can be wound by a winding method such as a constant tension method, a constant torque method, a taper tension method, or a program tension control method with a constant internal stress.

  The retardation film of the present invention can be a long film. The film width in the slow axis direction of the retardation film can improve the production efficiency as it is wider, but is preferably 3000 mm or less from the viewpoint of preventing the occurrence of creaking and folding, from the viewpoint of production efficiency. 700 mm or more is preferable.

3. Polarizing plate Since the retardation film of the present invention has high optical expression, it is preferably used as a retardation film for a polarizing plate. The polarizing plate can be obtained by attaching a retardation film to at least one surface of a polarizer. That is, the polarizing plate of the present invention has a polarizer and the retardation film of the present invention disposed on at least one surface thereof.

  As the polarizer, conventionally known polarizers can be used. For example, a hydrophilic polymer film such as a polyvinyl alcohol film is treated with a dichroic dye such as iodine and stretched. The thickness of the polarizer can usually be in the range of 0.5 to 30 μm, and preferably in the range of 5 to 20 μm.

  The retardation film and the polarizer can be bonded to each other with no particular limitation, but can be performed using a water-soluble polymer adhesive such as a completely saponified polyvinyl alcohol aqueous solution or a photo-curable adhesive.

  The photocurable adhesive may further contain a curable compound, a photopolymerization initiator, and a photosensitizer and a photosensitizer as necessary.

  The curable compound may be a radically polymerizable compound such as a (meth) acrylic compound or a cationically polymerizable compound such as an epoxy compound. The epoxy compound may be an aromatic epoxy compound, an alicyclic epoxy compound, an aliphatic epoxy compound, or the like, and is preferably an alicyclic epoxy compound. Examples of the alicyclic epoxy compounds include hydrogenated aromatic epoxy compounds, cyclohexane-based, cyclohexylmethyl ester-based, and cyclocyclohexylmethyl ether-based epoxy compounds.

  A photoinitiator is selected according to the kind of curable compound, and may be a photoradical polymerization initiator or a photocationic polymerization initiator. Examples of photo radical polymerization initiators include acetophenones such as 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 4- (2-hydroxyethoxy) phenyl (2-hydroxy-2-propyl) ketone Benzoin ether compounds such as benzoin ethyl ether; benzophenone compounds such as 3,3′-dimethyl-4-methoxybenzophenone and the like. Examples of the photocationic polymerization initiator include aryldiazonium salts, arylsulfonium salts (for example, triarylsulfonium salts), aryliodonium salts, allene-ion complexes, and the like. Content of a photoinitiator is about 0.1-10 mass parts normally with respect to 100 mass parts of curable compounds, Preferably it can be set as 0.5-5 mass parts.

  The photosensitizer includes anthracene compounds such as 9,10-dimethoxyanthracene, 9,10-diethoxyanthracene, and 9,10-dibutoxyanthracene. The photosensitizer may be 0.1 parts by mass or more and 2 parts by mass or less with respect to 100 parts by mass of the photocurable adhesive.

  The photosensitizing assistant includes naphthalene-based photosensitizing assistants such as 1,4-dimethoxynaphthalene and 1,4-diethoxynaphthalene. The photosensitizing assistant may be 0.1 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the photocurable adhesive.

  Hereinafter, an example of the manufacturing method of the polarizing plate using a photocurable adhesive agent is demonstrated. The polarizing plate is 1) a pretreatment step for easily adhering the surface of the polarizing plate protective film to which the polarizer is bonded, and 2) at least one of the adhesive surfaces of the polarizer and the polarizing plate protective film with the following photocurability. Adhesive application step for applying an adhesive, 3) a bonding step for bonding a polarizer and a polarizing plate protective film through the obtained adhesive layer, and 4) a polarizer and a polarizing plate through an adhesive layer It can manufacture by the manufacturing method including the hardening process which hardens an adhesive bond layer in the state by which the protective film was bonded together.

(Pretreatment process)
In the pretreatment step, the surface of the polarizing plate protective film that adheres to the polarizer is subjected to easy adhesion treatment. When a polarizing plate protective film is adhered to both surfaces of the polarizer, an easy adhesion treatment is performed on each polarizing plate protective film. In the next adhesive application step, the surface subjected to the easy adhesion treatment becomes an adhesion surface with the polarizer.

(Adhesive application process)
In the adhesive application step, the photocurable adhesive is applied to at least one of the adhesive surfaces of the polarizer and the polarizing plate protective film. When the photocurable adhesive is directly applied to the surface of the polarizer or the polarizing plate protective film, there is no particular limitation on the application method. For example, various coating methods such as a doctor blade, a wire bar, a die coater, a comma coater, and a gravure coater can be used. Moreover, after casting a photocurable adhesive between a polarizer and a polarizing plate protective film, the method of pressurizing with a roll etc. and spreading uniformly can also be utilized.

(Bonding process)
Thus, after apply | coating a photocurable adhesive agent, it uses for a bonding process. In this bonding step, for example, when a photocurable adhesive is applied to the surface of the polarizer in the previous application step, a polarizing plate protective film is superimposed thereon. When a photocurable adhesive is applied to the surface of the polarizing plate protective film in the previous application step, a polarizer is superimposed thereon. Moreover, when a photocurable adhesive agent is cast between a polarizer and a polarizing plate protective film, a polarizer and a polarizing plate protective film are piled up in that state. In the case where a polarizing plate protective film is bonded to both sides of a polarizer, and a photocurable adhesive is used on both sides, the polarizing plate protective film is superimposed on both sides of the polarizer via a photocurable adhesive. Is done. Usually, in this state, both sides (when a polarizing plate protective film is overlaid on one side of the polarizer, when the polarizing plate protective film is overlaid on both the polarizer side and the polarizing plate protective film side, or on both sides of the polarizer) Is sandwiched between rolls or the like from the side of the polarizing plate protective film side) and pressed. As the material of the roll, metal, rubber or the like can be used. The rolls arranged on both sides may be the same material or different materials.

(Curing process)
In the curing step, the active energy ray is irradiated to the uncured photocurable adhesive to cure the adhesive layer containing the epoxy compound or the oxetane compound. Thereby, the polarizer and the polarizing plate protective film overlapped with each other through the photo-curable adhesive are bonded. When bonding a polarizing plate protective film to the single side | surface of a polarizer, you may irradiate an active energy ray from either a polarizer side or a polarizing plate protective film side. Moreover, when bonding a polarizing plate protective film on both surfaces of a polarizer, either polarizing plate protective film in the state which laminated | stacked the polarizing plate protective film on both surfaces of the polarizer through the photocurable adhesive agent, respectively. It is advantageous to irradiate active energy rays from the side and simultaneously cure the photocurable adhesive on both sides. However, when an ultraviolet absorber is blended in one of the polarizing plate protective films and the active energy ray is ultraviolet rays, the side of the other polarizing plate protective film not usually blended with the ultraviolet absorber Is irradiated with ultraviolet rays.

  Visible light, ultraviolet rays, X-rays, electron beams, and the like can be used as the active energy rays, but ultraviolet rays are generally preferably used because they are easy to handle and have a sufficient curing rate. The light source of the active energy ray is not particularly limited, and has a light emission distribution at a wavelength of 400 nm or less. A lamp, an LED lamp, or the like can be used.

The light irradiation intensity to the photocurable adhesive is determined for each target composition and is not particularly limited, but the irradiation intensity in the wavelength region effective for activating the polymerization initiator is UV. It is preferable to adjust so that it may become the range of 1-3000 mW / cm < ² > as -B (280-320 nm medium wavelength range ultraviolet-ray). When the irradiation intensity is less than 1 mW / cm ² , the reaction time becomes too long, and when the irradiation intensity exceeds 3,000 mW / cm ² , due to the heat radiated from the lamp and the heat generated during polymerization of the photocurable adhesive, There is a possibility of causing yellowing of the photocurable adhesive and deterioration of the polarizer.

The light irradiation time to the photocurable adhesive is controlled for each composition to be cured and is not particularly limited, but the integrated light amount represented by the product of the irradiation intensity and the irradiation time is 10 to 5000 mJ / cm. It is preferably set to be in the range of ² . When the integrated light quantity is less than 10 mJ / cm ² , active species derived from the polymerization initiator are not sufficiently generated, and the adhesive layer may be insufficiently cured. On the other hand, if the integrated light quantity exceeds 5000 mJ / cm ² , the irradiation time becomes very long, which is disadvantageous for improving productivity.

  When curing the photocurable adhesive by irradiating active energy rays, it is cured under conditions that do not deteriorate the various functions of the polarizing plate, such as the degree of polarization of the polarizer, the transmittance, the hue, and the transparency of the polarizing plate protective film. It is preferable.

  In the polarizing plate obtained as described above, the thickness of the adhesive layer is not particularly limited, but is usually 50 μm or less, preferably 20 μm or less, more preferably 10 μm or less, and further preferably 5 μm or less.

  As described above, in the retardation film of the present invention, the orientation state of cellulose acetate molecules is stabilized. Therefore, it is considered that the polarizing plate including the retardation film of the present invention has little increase in light leakage over time. In addition, even under high temperature and high humidity conditions, it is considered that stable performance can be maintained for a long time because there is little fluctuation in the amount of light leakage of the polarizing plate.

4). Liquid crystal display device The retardation film of this invention and the polarizing plate using this retardation film can be used for the liquid crystal display device which has the liquid crystal cell of various display modes. That is, the liquid crystal display device of the present invention includes a liquid crystal cell and a pair of polarizing plates sandwiching the liquid crystal cell. And at least one of a pair of polarizing plates can be made into the polarizing plate containing the retardation film of this invention.

  FIG. 1 is a schematic diagram illustrating an example of a basic configuration of a liquid crystal display device. As shown in FIG. 1, the liquid crystal display device 10 of the present invention includes a liquid crystal cell 30, a first polarizing plate 50 and a second polarizing plate 70 that sandwich the liquid crystal cell 30, and a backlight 90.

  The liquid crystal cell 30 includes, for example, TN (Twisted Nematic), IPS (In-Plane Switching), FLC (Ferroelectric Liquid Liquid Crystal), AFLC (Anti-ferroelectric Liquid Crystal), OCB (Optic LiquidTypical). Various display modes such as VA (Vertically Aligned) and HAN (Hybrid Aligned Nematic) have been proposed.

  The OCB mode liquid crystal cell is a bend alignment mode liquid crystal cell in which rod-like liquid crystalline molecules are aligned in a substantially opposite direction (symmetrically) between the upper part and the lower part of the liquid crystal cell. OCB mode liquid crystal cells are disclosed in, for example, US Pat. Nos. 4,583,825 and 5,410,422. As described above, the OCB mode liquid crystal cell has a self-optical compensation function because rod-like liquid crystal molecules are symmetrically aligned at the upper and lower portions of the liquid crystal cell. The bend alignment mode liquid crystal display device has an advantage of high response speed.

  In a VA mode liquid crystal cell, rod-like liquid crystalline molecules are aligned substantially vertically when no voltage is applied. The VA mode liquid crystal cell includes (1) a narrowly defined VA mode liquid crystal cell in which rod-like liquid crystalline molecules are aligned substantially vertically when no voltage is applied, and substantially horizontally when a voltage is applied (Japanese Patent Laid-Open No. Hei 2-). 176625) (2) Liquid crystal cell (SID97, Digest of tech. Papers (Preliminary Proceed) 28 (1997) 845 in which the VA mode is converted into a multi-domain (MVA mode) for widening the viewing angle ), (3) a liquid crystal cell in a mode (n-ASM mode) in which rod-like liquid crystalline molecules are substantially vertically aligned when no voltage is applied and twisted multi-domain alignment is applied when a voltage is applied (Sharp Technical Report No. 80, page 11), And (4) a SURVAVAL mode liquid crystal cell (Monthly Display May 14th page (1999)).

  The first polarizing plate 50 includes a first polarizer 51, a protective film 53 (F1) disposed on the viewing side surface of the first polarizer 51, and a liquid crystal cell side of the first polarizer 51. And a protective film 55 (F2) disposed on the surface. The second polarizing plate 70 includes a second polarizer 71, a protective film 73 (F3) disposed on the liquid crystal cell side surface of the second polarizer 71, and the backlight side of the second polarizer 71. And a protective film 75 (F4) disposed on the surface. One of the protective film 55 (F2) and the protective film 73 (F3) may be omitted as necessary.

  And at least one of the protective film 55 (F2) and the protective film 73 (F3) may be the retardation film of the present invention.

  That is, the retardation film of the present invention comprises a protective film (F1) / polarizer / protective film (F2) / liquid crystal cell / retardation film (F3) / polarizer / protective film (F4) of the present invention, or The protective film (F1) / polarizer / retardation film (F2) / liquid crystal cell / retardation film (F3) / polarizer / protection film (F4) of the present invention can be preferably used.

  By using the retardation film of the present invention bonded to a liquid crystal cell (particularly a liquid crystal cell of TN type, VA type, OCB type, etc.), a display device having a small frontal angle and a high front contrast is provided. can do. In particular, since the retardation film of the present invention has a high retardation value, it can be preferably used for a VA mode liquid crystal display device.

  The VA mode liquid crystal display device includes a liquid crystal cell and two polarizing plates disposed on both sides thereof.

  The liquid crystal cell carries a liquid crystal between two electrode substrates. In one aspect of the transmissive liquid crystal display device of the present invention, the retardation film of the present invention is disposed between the liquid crystal cell and the polarizer of one polarizing plate, or the polarized light of both the liquid crystal cell and the polarizing plate. Two sheets are arranged between the polarizers of the plate.

  When the retardation film is used for only one polarizing plate, it is particularly preferable to use it as the liquid crystal cell side protective film (F3) of the backlight side polarizing plate of the liquid crystal cell. For the lamination to the liquid crystal cell, the film of the present invention is preferably on the VA cell side.

  The protective film may be a normal cellulose acetate film, and is preferably thinner than the film of the present invention. The thickness of the protective film is preferably 40 to 80 μm, for example. Examples of the protective film include, but are not limited to, commercially available KC4UA (Konica Minolta Opto 40 μm), KC6UA (Konica Minolta Opto 60 μm), TD80 (Fuji Film 80 μm), and the like.

  As described above, the retardation film of the present invention stabilizes the orientation of cellulose acetate molecules from the early stage in the production process, thereby reducing the variation in the retardation value immediately after production. Thereby, the fluctuation | variation of the light leakage amount of a phase difference film can be decreased, and it is thought that the front contrast of the liquid crystal display device containing it can be raised. Moreover, since the orientation of cellulose acetate molecules in the retardation film is stable, fluctuations in the orientation of cellulose acetate molecules are also reduced. Thereby, it is thought that the change of the hue by the viewing angle of the liquid crystal display device including the retardation film of the present invention is reduced.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

２）水素結合性化合物
一般式（Ｉ）で表される化合物
前述の例示化合物Ｉ−１
前述の例示化合物Ｉ−３
前述の例示化合物Ｉ−７
前述の例示化合物Ｉ−８
前述の例示化合物Ｉ−１１
一般式（II）で表される化合物
前述の例示化合物II−１
前述の例示化合物II−２
前述の例示化合物II−３
前述の例示化合物II−５
３）可塑剤
化合物Ａ：糖エステル化合物

Ｒ_１〜Ｒ_８：ベンゾイル基（置換度：４〜７、平均置換度：５．５）
残りは水素原子
化合物Ｂ：下記式で表されるポリエステル化合物（２１）

化合物Ｃ：下記式で表されるポリエステル化合物（２２）

化合物Ｄ：下記式で表されるベンゾオキサジノン化合物

1. Materials for retardation film 1) Cellulose acetate Table 1 shows the degree of acetyl group substitution and the weight average molecular weight of cellulose acetate used in the following Examples / Comparative Examples.

2) Hydrogen bonding compound The compound represented by general formula (I) The above-mentioned exemplary compound I-1
Example Compound I-3 described above
Example Compound I-7 described above
Example Compound I-8 described above
Example Compound I-11 described above
Compound represented by general formula (II)
Illustrative compound II-2 described above
Illustrative compound II-3 described above
The above exemplified compound II-5
3) Plasticizer Compound A: Sugar ester compound

R _{1 to} R ₈ : Benzoyl group (degree of substitution: 4 to 7, average degree of substitution: 5.5)
The rest is a hydrogen atom. Compound B: Polyester compound represented by the following formula (21)

Compound C: Polyester compound represented by the following formula (22)

Compound D: benzoxazinone compound represented by the following formula

2. Production of retardation film (Example 1)
Preparation of Fine Particle Additive Solution 1 The following components were stirred and mixed with a dissolver for 50 minutes, and then dispersed with Manton Gorin to obtain fine particle dispersion 1.
(Composition of fine particle dispersion 1)
Fine particles (Aerosil R812V manufactured by Nippon Aerosil Co., Ltd.): 11 parts by mass Ethanol: 89 parts by mass

The obtained fine particle dispersion 1 was slowly added to the dissolution tank charged with methylene chloride with sufficient stirring. The obtained solution was dispersed with an attritor so that the particle size of the secondary particles of the fine particles became a predetermined size, and then filtered with Finemet NF manufactured by Nippon Seisen Co., Ltd. 1 was obtained.
(Composition of fine particle additive liquid 1)
Methylene chloride: 99 parts by mass Fine particle dispersion 1: 5 parts by mass

Next, methylene chloride and ethanol were charged into the pressure dissolution tank. To this, while stirring cellulose acetate A (acetyl group substitution degree: 2.4, weight average molecular weight: 185,000), hydrogen bonding compound I-1, compound A, compound D, and fine particle additive liquid 1 were further stirred. The solution was added and completely dissolved while stirring under heating. The obtained solution was used as Azumi filter paper No. manufactured by Azumi Filter Paper Co., Ltd. It filtered using 244 and obtained the dope liquid 1 (1st process).
(Composition of dope solution 1)
Methylene chloride: 420 parts by mass Ethanol: 36 parts by mass Cellulose acetate A (acetyl group substitution degree 2.4, weight average molecular weight 185,000): 100 parts by mass Hydrogen bonding compound I-1: 2 parts by mass Compound A: 10 Part by mass Compound D: 2 parts by mass Particulate additive solution 1: 1 part by mass

  The obtained dope solution 1 was adjusted to 33 ° C. and uniformly cast on a stainless steel belt support with a width of 1500 mm using a belt casting apparatus (second step). The temperature of the stainless steel belt support was set to 33 ° C. Subsequently, the solvent in the dope was evaporated on the stainless steel belt support until the residual solvent amount became 75%. The obtained film was peeled from the stainless steel belt support with a peeling tension of 150 N / m (third step).

The obtained film was subjected to hot air having a temperature of 150 ° C. and a wind speed of 10 m / sec for 4 to 10 minutes to further evaporate the solvent in the film. At this time, the average volatilization rate of the solvent was 1.5 × 10 ⁻³ g / sec.

The average volatilization rate was calculated by the following method.
(Average volatilization rate)
A total of three sample films having a size of 30 cm square were cut from the left, center, and right in the width direction from the film-like material immediately before being stretched. Next, each sample film is immediately placed on a hot plate installed in an airtight container having a blowing function, and a mass decrease after 20 seconds (Ag) and a mass decrease after 40 seconds (Bg) while applying dry air. ) And measured. The temperature of the hot plate is set to the same value as the drying temperature of the film immediately before stretching; the wind speed of the drying air is set to the same value as the wind speed applied to the film immediately before stretching; The capacity of the container was 0.1 m ³ .
The obtained measured value was applied to the following formula to calculate the volatilization rate (g / sec · cm ² ).
(Ag-Bg) / (20 sec.900 cm ² )
And the average value of the volatilization rate of the three sample films was determined as an average volatilization rate (g / (sec · cm ² )).

  The obtained film was stretched 37% in the web width direction (TD direction) at 155 ° C. by a tenter stretching machine (fourth step). The residual solvent amount of the web at the start of stretching was 10%. The obtained film was dried at 150 ° C. while being conveyed by a large number of rolls at a conveyance tension of 100 N / m to obtain a retardation film 101 having a film thickness of 35 μm (fifth step).

(Examples 2-18, Comparative Examples 1-7)
Retardation films 102 to 125 were produced in the same manner as in Example 1 except that the types of cellulose acetate, the hydrogen bonding compound, and the plasticizer and the amounts added thereof were changed as shown in Table 2. The drying time of the film-like material immediately before stretching was the same as in Example 1.

  Rth of the obtained retardation film was measured by the following method.

[Rth]
Rth (0.5) of the retardation film after 0.5 hours in the environment of 23 ° C. and 55% RH after finishing the fifth step (drying step) in the production process of the retardation film, and 24 Rth (24) of the retardation film after the lapse of time was measured using KOBRA-21ADH (Oji Scientific Instruments). Rth was measured under conditions of a wavelength of 590 nm under 23 ° C. and 55% RH.

And the value of Rth (0.5) and Rth (24) of the obtained retardation film was applied to the following formula, and the absolute value of these differences was calculated | required.
Rth change after manufacture = | Rth (0.5) −Rth (24) |

[Tensile modulus]
A phase difference film after 24 hours from the completion of the fifth step was cut into a size of 70 × 10 mm to obtain a sample film. The sample film was then conditioned for 24 hours in an environment of 25 ° C. and 60% RH. The tensile elastic modulus of the sample film after humidity control was measured using Tensilon manufactured by Tenritsu Tenshi Tester Co., Ltd. according to the method described in JIS K7127. The measurement was performed under a distance between chucks of 50 mm and 23 ° C. and 55% RH.

The composition and drying conditions of the obtained retardation film are shown in Table 2; the evaluation results of the retardation film are shown in Table 3.

  As shown in Tables 2 and 3, the retardation films of Examples 1 to 18 in which the average volatilization rate of the solvent immediately before stretching was adjusted to a predetermined range were all the retardations of Comparative Examples 1 and 3-7. It can be seen that the change with time of Rth is less than that of the film.

  In the retardation film of Comparative Example 1, since the average volatilization rate of the solvent immediately before stretching is too low, the solvent between the cellulose acetate molecules cannot be completely removed, and it is considered that the variation in Rth is large. Although the retardation film of Comparative Example 2 can reduce the variation of Rth; since there are many micro gaps (portions from which volatile components have been removed) in the film and the area ratio of the portions having different refractive indexes increases, As shown in Comparative Example 9 in Table 4 and Comparative Example 16 in Table 5, it can be seen that the performance as a polarizing plate is low. Since the retardation film of Comparative Example 3 has a high degree of acetyl group substitution, it can be seen that the interaction between cellulose acetate molecules is small and the variation in Rth is large. It can be seen that the retardation films of Comparative Examples 4 and 5 have a high retardation expression and a relatively high Rth value because the degree of acetyl group substitution is too low; Since the retardation film of Comparative Example 6 does not contain a hydrogen bonding compound, it can be seen that the interaction between cellulose acetate molecules cannot be sufficiently maintained, and the variation in Rth is large. It can be seen that the retardation film of Comparative Example 7 has a low average volatilization rate of the solvent immediately before stretching and does not contain a hydrogen bonding compound, so that the variation in Rth is large.

3. Production of Polarizing Plate (Example 19)
Production of Cellulose Acetate Film F A cellulose acetate film F was produced in the same manner as in Example 1 except that the composition of the dope was changed as follows in the production of the retardation film 101.
(Dope solution composition)
Methylene chloride: 420 parts by weight Ethanol: 36 parts by weight Cellulose acetate F: 100 parts by weight Compound A (plasticizer): 5.0 parts by weight Compound D (plasticizer): 5.0 parts by weight Fine particle additive solution 1: 1 part by weight

Preparation of Hard Coat Film The following components were stirred and mixed to obtain a hard coat layer coating composition.
(Composition for hard coat layer application)
Byron UR1350 (polyester urethane resin, manufactured by Toyobo Co., Ltd., solid content concentration 33% (toluene / methyl ethyl ketone: 65/35)): 6.0 parts by mass Pentaerythritol triacrylate: 30 parts by mass Pentaerythritol tetraacrylate: 30 parts by mass Part Irgacure 184 (manufactured by BASF Japan, photopolymerization initiator): 3.0 parts by mass Irgacure 907 (manufactured by BASF, photopolymerization initiator): 1.0 part by mass Polyether-modified polydimethylsiloxane (BYK-UV3510, BIC Chemie Japan Co., Ltd.): 2.0 parts by mass Propylene glycol monomethyl ether: 150 parts by mass Methyl ethyl ketone: 150 parts by mass

The hard coat layer coating composition was filtered through a polypropylene filter having a pore size of 0.4 μm to obtain a hard coat layer coating solution. And the obtained coating liquid for hard-coat layers was apply | coated to the said produced cellulose acetate film F using the micro gravure coater. The obtained coating layer was dried at 80 ° C. and then irradiated with ultraviolet rays using an ultraviolet lamp to cure the coating layer. The irradiation conditions of ultraviolet rays, illuminance 80 mW / cm ^2, and the dose 80 mJ / cm ^2. Thereby, a hard coat film having a hard coat layer with a dry film thickness of 9 μm was obtained.

Production of Polarizer A polyvinyl alcohol film having a thickness of 70 μm was swollen with water at 35 ° C. The obtained film was immersed in an aqueous solution consisting of 0.075 g of iodine, 5 g of potassium iodide and 100 g of water for 60 seconds, and further immersed in an aqueous solution at 45 ° C. consisting of 3 g of potassium iodide, 7.5 g of boric acid and 100 g of water. . The obtained film was uniaxially stretched under conditions of a stretching temperature of 55 ° C. and a stretching ratio of 5 times. The uniaxially stretched film was washed with water and dried to obtain a polarizer having a thickness of 20 μm.

Preparation of photocurable adhesive The following components were mixed and then defoamed to prepare a photocurable adhesive liquid. Triarylsulfonium hexafluorophosphate was blended as a 50% propylene carbonate solution, and the solid content of triarylsulfonium hexafluorophosphate was shown below.
(Composition of photocurable adhesive liquid)
3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate: 45 parts by mass Epolide GT-301 (alicyclic epoxy resin manufactured by Daicel Chemical Industries): 40 parts by mass 1,4-butanediol diglycidyl ether: 15 parts by mass Triarylsulfonium hexafluorophosphate: 2.3 parts by mass 9,10-dibutoxyanthracene: 0.1 parts by mass 1,4-diethoxynaphthalene: 2.0 parts by mass

Production of Polarizing Plate The surface of the produced retardation film 101 was subjected to corona discharge treatment. The conditions for the corona discharge treatment were a corona output intensity of 2.0 kW and a line speed of 18 m / min. Subsequently, the adhesive liquid prepared above was applied to the corona discharge treated surface of the retardation film with a bar coater so that the film thickness after curing was about 3 μm to form an adhesive layer. The polarizer prepared above was bonded to the obtained adhesive layer.

  Similarly, the surface of the hard coat film prepared above was subjected to corona discharge treatment. The conditions for the corona discharge treatment were a corona output intensity of 2.0 kW and a line speed of 18 m / min. Next, the adhesive solution prepared above was applied to the corona discharge treated surface of the hard coat film with a bar coater so that the film thickness after curing was about 3 μm to form an adhesive layer. The adhesive layer was bonded with a polarizer on which the above-described retardation film 101 was bonded to obtain a hard coat film / polarizer / retardation film 101 laminate.

Using the ultraviolet irradiation device with a belt conveyor (the lamp uses a D bulb manufactured by Fusion UV Systems) to the retardation film 101 of the obtained laminate, ultraviolet light is applied so that the integrated light quantity becomes 750 mJ / cm ^2. Irradiated to cure the adhesive layer. Thereby, a polarizing plate 201 having a laminated structure of hard coat film / polarizer / retardation film 101 was produced.

(Examples 20 to 36, Comparative Examples 8 to 14)
Polarizing plates 202 to 225 were produced in the same manner as in Example 19 except that the retardation film 101 was changed to retardation films 102 to 125 as shown in Table 4. These polarizing plates 202 to 225 can be used as a viewing-side polarizing plate (first polarizing plate), similarly to the polarizing plate 201.

(Example 37)
A polarizing plate 226 was produced in the same manner as in Example 19 except that the hard coat film was changed to the cellulose acetate film F. The polarizing plate 226 can be used as a polarizing plate on the backlight side (second polarizing plate).

(Examples 38-54, Comparative Examples 15-21)
Polarizing plates 227 to 250 were produced in the same manner as in Example 37 except that the retardation film 101 was changed to retardation films 102 to 125 as shown in Table 5. These polarizing plates 227 to 250 can be used as a polarizing plate on the backlight side (second polarizing plate) similarly to the polarizing plate 226.

  The amount of light leakage of the polarizing plates obtained in Examples 19 to 54 and Comparative Examples 8 to 21 was measured by the following method.

[Light leakage amount]
The produced two polarizing plates were arranged in crossed Nicols, and the transmittance (T1) of light having a wavelength of 590 nm was measured using a spectrophotometer U3100 manufactured by Hitachi, Ltd.
Next, the two polarizing plates were heat-treated at 80 ° C. and 90% for 100 hours, and then placed in crossed Nicols in the same manner as described above, and the transmittance (T2) was measured.
The obtained light transmittance (T1) and transmittance T2 were applied to the following formula to calculate the amount of light leakage.
Light leakage amount (%) = T2 (%)-T1 (%)

The amount of light leakage was evaluated based on the following criteria.
◎: Light leakage amount is less than 1% ○: Light leakage amount is 1% or more and less than 4% △: Light leakage amount is 4% or more and less than 5% ×: Light leakage amount is 5% or more

The evaluation results of Examples 19 to 36 and Comparative Examples 8 to 14 are shown in Table 4; the evaluation results of Examples 37 to 54 and Comparative Examples 15 to 21 are shown in Table 5.

  It can be seen that the polarizing plates of Examples 19 to 54 have less light leakage than the polarizing plates of Comparative Examples 8 to 21. This is presumably because the variation in Rth of the retardation films contained in the polarizing plates of Examples 19 to 54 with time is small.

4). Production of liquid crystal display device (Example 55)
A pair of polarizing plates was peeled off from a liquid crystal panel (a laminate of a liquid crystal cell and a pair of polarizing plates sandwiching the liquid crystal cell) of a SONY 40-inch display KDL-40V5. And the produced polarizing plate 201 was bonded together to the surface at the side of visual recognition of a liquid crystal cell so that the adhesive layer might contact | connect a liquid crystal cell. In addition, a polarizing plate 226 was bonded to the surface of the liquid crystal cell on the backlight side so that the pressure-sensitive adhesive layer was in contact with the liquid crystal cell. Thereby, the liquid crystal display device 301 was obtained.

(Examples 56 to 72, Comparative Examples 22 to 28)
As shown in Table 6, as in Example 55, except that the polarizing plate 201 on the viewing side was changed to polarizing plates 202 to 225 and the polarizing plate 226 on the backlight side was changed to polarizing plates 227 to 250, respectively. Thus, liquid crystal display devices 302 to 325 were obtained.

  For the obtained liquid crystal display devices of Examples 55 to 72 and Comparative Examples 22 to 28, changes in hue due to viewing angle and front contrast were measured by the following methods.

[Hue change depending on viewing angle]
The change in hue depending on the viewing angle of the liquid crystal display device was measured using a measuring machine (EZ-Contrast 160D, manufactured by ELDIM). In the CIE 1976 and UCS coordinates, the hue was measured at intervals of 2 ° in a range from an angle of 80 ° upward to an angle of 80 ° downward with respect to the normal line of the display screen. Then, the measured value at each angle was applied to the following formula to calculate the hue fluctuation range. Among these, the maximum hue fluctuation range between the measured angles was determined as “maximum hue fluctuation range”.
Hue fluctuation range = [(Δu *) 2+ (Δv *) 2] * 1/2
(In the above formula, Δu * indicates the difference in u * between two measured angles; Δv * indicates the difference in v * between two measured angles)

[Front contrast]
The luminance from the normal direction of the display screen during white display of the liquid crystal display device and the luminance from the normal direction of the display screen during black display were measured using EZ-Contrast 160D manufactured by ELDIM. The obtained value was applied to the following formula to calculate the front contrast. The luminance was measured in an environment of 23 ° C. and 55% RH.
Front contrast = (brightness of white display measured from normal direction of display device) / (brightness of black display measured from normal direction of display device)

Table 6 shows the evaluation results of Examples 55 to 72 and Comparative Examples 22 to 28.

  It can be seen that the liquid crystal display devices of Examples 55 to 72 have less hue change due to the viewing angle and higher front contrast than the liquid crystal display devices of Comparative Examples 22 to 28. This is because the change over time of Rth of the retardation film included in the liquid crystal display devices of Examples 55 to 72 is smaller than the change over time of Rth of the retardation film included in the liquid crystal display devices of Comparative Examples 22 to 28. It is believed that there is.

  The liquid crystal display device including the retardation film of the present invention has less dependency on viewing angle, particularly hue change due to viewing angle, and front contrast can be improved.

DESCRIPTION OF SYMBOLS 10 Liquid crystal display device 30 Liquid crystal cell 50 1st polarizing plate 51 1st polarizer 53 Protective film (F1)
55 Protective film (F2)
70 Second polarizing plate 71 Second polarizer 73 Protective film (F3)
75 Protective film (F4)
90 backlight

Claims (9)

An organic solvent containing 90% by mass or more of a halogen-based organic solvent, cellulose acetate having an average acetyl group substitution degree of 2.2 to 2.5, and hydrogen bondability having at least a carboxy group or a hydroxy group as a substituent on the aromatic ring A first step of dissolving a compound to obtain a dope solution;
A second step of casting the dope solution on a metal belt;
A third step of peeling the film-like material obtained by drying the cast dope solution from the metal belt;
A fourth step of stretching the peeled film,
A fifth step of heating and drying the stretched film-like material to volatilize the organic solvent in the film-like material;
In the method for producing a retardation film having
The average volatilization rate of the organic solvent of the film-like material immediately before the film-like material is stretched is adjusted to a range of 1.5 × 10 ^{−3 to} 3.0 × 10 ⁻³ g / (sec · cm ² ). A method for producing a retardation film. The retardation in the thickness direction of the retardation film measured at 23 ° C. and 55% RH and at a wavelength of 590 nm after the lapse of 0.5 hour at 23 ° C. and 55% RH from the end of the fifth step is Rth (0 And 5) retardation of the retardation film in the thickness direction measured at 23 ° C. and 55% RH and at a wavelength of 590 nm after 24 hours at 23 ° C. and 55% RH from the end of the fifth step. The method for producing a retardation film according to claim 1, wherein when Rth (24) is satisfied, the following formula is satisfied.
| Rth (0.5) −Rth (24) | ≦ 2.0 nm A retardation film produced by the production method according to claim 1 or 2,
A retardation film containing 1 to 15% by mass of a hydrogen bonding compound having at least a carboxy group or a hydroxy group as a substituent on an aromatic ring based on cellulose acetate having an average acetyl group substitution degree of 2.2 to 2.5 . The retardation film according to claim 3, wherein the hydrogen bonding compound is a compound represented by the following general formula (I) or (II).
Formula (I)

(In the general formula (I),
l represents an integer of 1 or more, and in the case of 2 or more, two carboxyl groups may be condensed with each other to form a ring;
m represents an integer of 0 to 4;
R represents an alkyl group;
n represents an integer of 0 to 4, and when there are a plurality of R, the plurality of R may be the same or different from each other;
l + m ≧ 2)
Formula (II)

(In the general formula (II),
Each R ¹ independently represents a halogen atom or a hydroxyl group;
n represents an integer of 0 to 4)   The retardation film of Claim 3 or 4 whose tensile elasticity modulus under 23 degreeC55% RH exists in the range of 3500-6000 MPa. The retardation value Rth in the thickness direction, which is defined by the following formula and measured at a wavelength of 590 nm under a temperature of 23 ° C. and 55% RH, is in the range of 70 to 400 nm, according to any one of claims 3 to 5. Retardation film.
Rth = [(nx + ny) / 2−nz] × d
(Where nx represents the refractive index in the slow axis direction in the film plane;
ny represents the refractive index in the direction perpendicular to the slow axis in the film plane;
nz represents the refractive index in the thickness direction of the film;
d indicates the thickness of the film)   The retardation film as described in any one of Claims 3-6 whose film width of the slow axis direction of the said retardation film is 700-3000 mm.   A polarizing plate comprising the retardation film according to claim 3. A liquid crystal display device comprising the retardation film according to claim 3.

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