JP2009258217A - Brightness enhancing film, polarizing plate, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a brightness enhancing film being a laminate of a λ/4 wavelength plate and cholesteric liquid crystal which has no problems in coating-liquid repellent properties and contact properties and provides stable retardation at wavelengths in a wide range and has a high brightness enhancing effect. <P>SOLUTION: The brightness enhancing film is a laminate wherein a cholesteric liquid crystal layer is provided, directly or through another layer, on cellulose ester film which has a slow axis in a range from 10° to 80° with respect to a lengthwise direction of the film and has an in-plane retardation Ro of 120 to 150(nm) in measurement at a wavelength of 550 nm and satisfies formulas (i) 2.1≤X+Y≤2.8 and (ii) 0.5≤Y≤1.65 wherein: X represents a degree of substitution of an acetyl group; Y represents a degree of substitution of a propionyl group or a butyryl group; and X+Y represents a total degree of substitution of acyl groups. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a brightness enhancement film, a polarizing plate and a liquid crystal display device, and more particularly to a thin and high brightness enhancement film having a broadband λ / 4 plate function, a polarizing plate using the same, and a liquid crystal display device. .

  An elliptically polarizing plate obtained by laminating a linear polarizer and a retardation film, especially a circularly polarizing plate having a retardation value of λ / 4, prevents reflection of an organic electroluminescence display device, and is used for touch panels and liquid crystal display devices. It is used for. The circularly polarizing plate needs to exhibit its function with respect to light in the entire visible light range, and in order to obtain such a broadband polarizing plate, the retardation film needs to have broadband properties.

  A normal polymer has positive wavelength dispersion in which the refractive index decreases as the wavelength increases. As a method for obtaining a broadband λ / 4 film, it is known that it can be obtained by crossing a positive wavelength dispersion polymer film, but generally a method of crossing λ / 2 and λ / 4 is performed. (For example, refer to Patent Document 1).

  Conventionally, such a retardation film has been produced by batch bonding in order to form films stretched in one direction at different angles. In addition, oblique stretching technology is known to improve productivity, but since a wide band λ / 4 is produced using two films, the film becomes thick and is pasted twice to be pasted with a polarizer. There is a problem that an attaching process is necessary (for example, refer to Patent Document 2).

  On the other hand, in the field of liquid crystal display devices represented by liquid crystal televisions, improving the light extraction efficiency from the backlight is an important technical issue not only from the viewpoint of increasing luminance but also from the viewpoint of reducing power consumption. It has become.

  In that sense, the point is how efficiently the 50% (theoretical value) loss that is absorbed when light passes through the dichroic polarizing film normally used for polarizing plates can be used. come.

  In order to deal with such a problem, so-called brightness enhancement films having several light utilization efficiencies have been studied.

  A typical example of the brightness enhancement film for liquid crystal displays is 3M DBEF. This is because, as disclosed in Japanese Patent No. 3612415, two layers having different refractive indexes are laminated and reflected by utilizing the principle of thin film interference, and the laminated material is transmitted without any difference in refractive index. This is a mechanism that separates polarized light by having an axis and makes the transmission axis of the absorption linear polarizer and the transmission axis of DBEF parallel to increase the light utilization efficiency and exhibit the brightness enhancement effect.

  However, DBEF has problems such as transparency due to an increase in the number of members, a decrease in image quality, an increase in cost due to an increase in man-hours, and a decrease in productivity.

  Therefore, there is a polarized light separating film utilizing the circular dichroism of a cholestric liquid crystal as disclosed in Patent Document 3 which can be easily produced with a thinner film.

  Cholesteric liquid crystals with a circularly polarized light separation function have selective reflection characteristics that reflect only the circularly polarized light whose light wavelength is the helical pitch of the liquid crystal, with the rotational direction of the liquid crystal's spiral coincident with the circular polarization direction. Using the characteristics, it is possible to manufacture a polarization separation element that transmits and separates only specific circularly polarized light of natural light in a fixed wavelength band and reflects the remaining light.

  By combining this cholesteric liquid crystal with a λ / 4 wave plate, the circularly polarized light transmitted by passing through the λ / 4 wave plate is converted to linearly polarized light, and the direction of this linearly polarized light is polarized light on the backlight side in the liquid crystal display. The light transmitted through the cholesteric layer by aligning the transmission direction of the polarizer is transmitted through the polarizer, and the light reflected from the cholesteric layer is reused by the reflector to improve the light utilization efficiency and reduce the power consumption of the liquid crystal display. be able to.

  A method of laminating a circularly polarized light selective separation layer such as a cholesteric layer on a broadband circularly polarizing plate is as shown in Patent Document 4, (1) providing an alignment film on a broadband circularly polarizing plate λ / 4 wavelength plate, (2) Form a liquid crystal layer on another base film and transfer it onto the surface of a broadband λ / 4 wave plate, (3) Form a liquid crystal layer on another base film And the method of bonding the obtained laminated body with the (lambda) / 4 wavelength plate of a broadband circularly-polarizing plate is mentioned. However, in the method (1), which is the simplest and least expensive, there are some methods that cannot be produced due to the characteristics of the substrate, the alignment film, and the liquid crystal layer. In particular, the cycloolefin cyclic polymer has a problem that the repellency and adhesion of the coating solution become poor.

Liquid crystal displays are increasingly required to be thinner, and the brightness enhancement film, which is a laminate of a broadband λ / 4 wavelength plate and a cholesteric liquid crystal, has a complicated process for producing a broadband λ / 4, and is slanting. The λ / 4 wavelength plate that can be easily produced by stretching has problems of repellency and adhesion of the coating solution, and the liquid crystal layer cannot be formed directly on the alignment film. The problem is that the luminance improvement effect is reduced when the retardation is equal or lowered.
JP-A-10-90521 JP 2005-284024 A JP 2003-227933 A JP 2004-20701 A

  Accordingly, it is an object of the present invention to provide a brightness enhancement film which is a laminate of a λ / 4 wavelength plate and a cholesteric liquid crystal, and there is no problem of repellency or adhesion of the coating solution, stable retardation in a wide range of wavelengths, and brightness. The object is to provide a brightness enhancement film having a high improvement effect.

  In addition, the brightness enhancement film of the present invention can be easily produced, and is particularly transparent and thin. Therefore, the use of the brightness enhancement film provides a polarizing plate or a liquid crystal display device having low haze and high image quality such as contrast. .

  The above object of the present invention is achieved by the following configurations.

  1. It has a slow axis in the range of 10 ° to 80 ° with respect to the longitudinal direction of the film, the in-plane retardation in the wavelength 550 nm measurement is 120 ≦ Ro ≦ 150 (nm), and the following formulas (i) and (ii) A brightness enhancement film, which is a laminate in which a cholesteric liquid crystal layer is provided directly or via another layer on a cellulose ester film satisfying the above.

In-plane retardation Ro = (nx−ny) × d (nm)
(In the formula, 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, and d represents the thickness (nm) of the optical film.)
Formula (i) 2.1 ≦ X + Y ≦ 2.8
Formula (ii) 0.5 ≦ Y ≦ 1.65
(In the formula, X represents the substitution degree of acetyl group, Y represents the substitution degree of propionyl group or butyryl group, and X + Y represents the total substitution degree of acyl group.)
2. The cellulose ester film is a (meth) acrylic polymer, and an ester compound in which at least one of a pyranose structure or a furanose structure is 1 to 12, and all or part of the OH groups of the structure are esterified. The brightness enhancement film as described in 1 above, which is a cellulose ester film containing at least one kind.

  3. When measuring the film scattered light intensity of the incident light 90 ° of the scattered light profile of the goniophotometer with the cellulose ester film, the scattered light intensity at a position of 130 ° from the light source is measured, and the film is placed on the sample stage of the film. 3. The brightness enhancement film as described in 1 or 2 above, wherein a difference in scattered light intensity between the case where the installation direction is aligned with the slow axis and the direction perpendicular thereto is 0.05 or less.

  4). Any one of the above 1-3, wherein the cellulose ester film has an in-plane retardation of 0.78 ≦ Ro (480) / Ro (650) ≦ 0.96 when measured at wavelengths of 480 nm and 650 nm. The brightness enhancement film according to Item.

  5). 5. A polarizing plate having the brightness enhancement film according to any one of 1 to 4 on at least one surface.

  6). 6. A liquid crystal display device comprising the polarizing plate according to 5 above on a backlight surface side of a liquid crystal cell.

  According to the present invention, in a brightness enhancement film that is a laminate of a λ / 4 wavelength plate and a cholesteric liquid crystal, there is no problem of repellency or adhesion of the coating liquid, the retardation in a wide range of wavelengths is stable, and the brightness enhancement effect. A high brightness enhancement film can be provided.

  Moreover, since the brightness enhancement film of the present invention can be easily produced, and is particularly transparent and thin, it can be used to provide a polarizing plate or a liquid crystal display device having low haze and high image quality such as contrast. .

  The best mode for carrying out the present invention will be described in detail below, but the present invention is not limited thereto.

  The brightness enhancement film of the present invention has a slow axis in the range of 10 ° to 80 ° with respect to the film longitudinal direction, the in-plane retardation at a wavelength of 550 nm measurement is 120 ≦ Ro ≦ 150 (nm), and Luminance having a function of converting a cholesteric liquid crystal layer on a cellulose ester film having a retardation function satisfying the formulas (i) and (ii) directly or via another layer into a linearly polarized light together with a circularly polarized light separating function. It is an improvement film.

  That is, a cholesteric liquid crystal having a circularly polarized light separation function has a selective reflection characteristic that reflects only circularly polarized light in which the rotation direction of the liquid crystal spiral coincides with the circular polarization direction and the wavelength is the spiral pitch of the liquid crystal. Using this selective reflection characteristic, only a specific circularly polarized light of natural light in a fixed wavelength band is transmitted and separated, and the rest is reflected and reused by a reflecting plate or the like, so that a highly efficient polarization function is possible.

  At this time, the transmitted circularly polarized light is converted to linearly polarized light by passing through a cellulose ester film which is a λ / 4 wavelength plate having a specific composition of the present invention, and the direction of this linearly polarized light is used for a liquid crystal display. A liquid crystal display device with high transmittance can be obtained by aligning with the transmission direction of the linear polarizer. That is, when a cholesteric liquid crystal layer is provided on a film that is a λ / 4 wavelength plate and further laminated with an absorptive linear polarizer and used as an integral linear polarizer, there is theoretically no loss of light. Compared to the case where a conventional absorption polarizer that absorbs% light is used alone, it is theoretically possible to obtain a brightness improvement that is twice as high.

  As a result of intensive research on a cellulose ester film composed of a λ / 4 wavelength plate and a brightness enhancement film composed of a cholesteric liquid crystal layer, the present inventors have made wideband / 4 can be produced, and a structure capable of applying the liquid crystal layer in a simple and stable manner has been found, and the brightness enhancement film of the present invention having a thin and high brightness enhancement effect has been obtained.

  In addition, the cellulose ester film used for the brightness enhancement film of the present invention is characterized in that the angle formed by the slow axis in the film plane and the film longitudinal direction is 10 ° to 80 °. Thus, a long linearly polarizing film having an absorption axis in the longitudinal direction and the cellulose ester film are laminated with the longitudinal direction aligned to easily obtain a long elliptical or circularly polarizing film with good productivity. be able to. The inclination of the slow axis of the cellulose ester film and the longitudinal direction of the film is preferably in the range of 20 ° to 70 °, more preferably in the range of 30 ° to 60 °, and particularly preferably 40 ° to 50 °. The range of degrees is most preferred, substantially 45 degrees. Substantially 45 ° means a range of 45 ° ± 2 °.

  In order to set the angle formed by the slow axis and the film longitudinal direction within the above range, it can be achieved by using a specific cellulose ester or by adjusting using an oblique stretching apparatus described later.

  Hereinafter, the present invention will be described in detail.

<Cholesteric liquid crystal layer>
The cholesteric liquid crystal layer of the present invention is not limited to this, but a liquid crystal mixture containing a polymerizable mesogenic compound (a), a polymerizable chiral agent (b) and a photoisomerizable material (c) is subjected to ultraviolet polymerization. Is preferably obtained.

  As the polymerizable mesogenic compound (a), those having at least one polymerizable functional group and having a mesogenic group composed of a cyclic unit or the like are preferably used. Examples of the polymerizable functional group include an acryloyl group, a methacryloyl group, an epoxy group, and a vinyl ether group. Among these, an acryloyl group and a methacryloyl group are preferable. Further, by using a compound having two or more polymerizable functional groups, a crosslinked structure can be introduced to improve durability. Examples of the cyclic unit serving as a mesogenic group include biphenyl, phenylbenzoate, phenylcyclohexane, azoxybenzene, azomethine, azobenzene, phenylpyrimidine, diphenylacetylene, diphenylbenzoate, bicyclohexane, Examples thereof include cyclohexylbenzene and terphenyl. In addition, the terminal of these cyclic units may have substituents, such as a cyano group, an alkyl group, an alkoxy group, a halogen group, for example. The mesogenic group may be bonded via a spacer portion that imparts flexibility. Examples of the spacer portion include a polymethylene chain and a polyoxymethylene chain. The number of repeating structural units forming the spacer portion is appropriately determined depending on the chemical structure of the mesogenic portion, but the repeating unit of the polymethylene chain is 0 to 20, preferably 2 to 12, and the repeating unit of the polyoxymethylene chain is 0 to 0. 10, preferably 1-3.

  The polymerizable mesogenic compound (a) having one polymerizable functional group includes, for example, the following general formula (1),

(Wherein R ₁ represents a hydrogen atom or a methyl group. N represents an integer of 1 to 5).

  Specific examples of the polymerizable mesogenic compound (a) having one polymerizable functional group are not particularly limited.

The compound represented by these is mention | raise | lifted.

  Specific examples of the polymerizable mesogenic compound (a) having two polymerizable functional groups include, for example, LC242 manufactured by BASF.

  Examples of the polymerizable chiral agent (b) include LC756 manufactured by BASF.

  The blending amount of the polymerizable chiral agent (b) is preferably about 1 to 20 parts by mass, and 3 to 7 parts by mass with respect to 100 parts by mass in total of the polymerizable mesogenic compound (a) and the polymerizable chiral agent (b). The part is more suitable. The helical twisting force (HTP) is controlled by the ratio of the polymerizable mesogenic compound (a) and the polymerizable chiral agent (b). By setting the ratio within the above range, the reflection band can be selected so that the reflection spectrum of the obtained cholesteric liquid crystal film can cover the entire visible region.

  As the photoisomerization material (c), a material that causes a photoisomerization reaction can be used without particular limitation. Examples of the photoisomerizable material (c) include compounds such as stilbene, stilbenes, azobenzene, azobenzenes, spiropyrans, spirooxazines, diarylethenes, fulgides, cyclophanes, and chalcones. As these photoisomerization materials, it is preferable to use at least one selected from stilbene, azobenzene, and derivatives thereof. The addition amount of the photoisomerizable material (c) is not particularly limited, but is 0.1 to 20 mass with respect to a total of 100 mass parts of the polymerizable mesogenic compound (a) and the polymerizable chiral agent (b). About 10 parts by weight is preferable, and 2 to 10 parts by weight is more preferable.

  Various photopolymerization initiators (d) can be used without particular limitation. For example, Irgacure 184, Irgacure 907, Irgacure 369, Irgacure 651, and the like manufactured by Ciba Japan are listed. The blending amount of the photopolymerization initiator is preferably about 0.01 to 10 parts by mass, and 0.05 to 5 parts by mass with respect to 100 parts by mass in total of the polymerizable mesogenic compound (a) and the polymerizable chiral agent (b). The part is more suitable. Depending on the photopolymerization initiator (d), ultraviolet irradiation conditions, and the amount of photoisomerizable material (c) added, it is not always necessary to add them. For example, when the polymerizable mesogenic compound (a) and the polymerizable chiral agent (b) have sufficiently high reaction rates such as a combination of those having two polymerizable functional groups, a photopolymerization initiator ( The addition of d) is not necessary.

  In the present invention, a liquid crystal mixture containing a polymerizable mesogenic compound (a), a polymerizable chiral agent (b), a photoisomerizable material (c), and, if necessary, a photopolymerization initiator (d) is used as a solvent. It can be used as a dissolved solution. The solvent to be used is not particularly limited, but methyl ethyl ketone, cyclohexanone, cyclopentanone and the like are preferable. The concentration of the solution is usually about 3 to 50% by mass.

  The cholesteric liquid crystal film of the present invention is produced by applying the liquid crystal mixture to a cellulose ester film, which will be described later, and performing ultraviolet polymerization.

  Although it may be applied directly on the film, a thin film made of polyimide, polyvinyl alcohol or the like is formed, and it is rubbed with a rayon cloth or the like, a rubbing film, an oblique deposition film, or a photocrosslinking group such as cinnamate or azobenzene. A photo-alignment film may be formed by irradiating a polymer or polyimide with polarized ultraviolet rays, and coating may be performed thereon.

  Application | coating of the solution of the said liquid-crystal mixture can be performed by well-known methods, such as the extrusion coating method, the direct gravure coating method, the reverse gravure coating method, the die coating method, the inkjet method, for example.

  The liquid crystal mixture can be laminated with, for example, a thermoplastic resin after being applied to a film. When the liquid crystal mixture is a solution, the solution is applied to a film and dried, and then laminated. The drying temperature for volatilizing the solvent may be a temperature not lower than the boiling point of the solvent. Usually, the temperature may be set in the range of about 80 to 160 ° C. according to the type of solvent.

  The coating thickness of the liquid crystal mixture (in the case of a solution, the coating thickness after solvent drying) is preferably about 1 to 20 μm, and more preferably about 2 to 10 μm. When the coating thickness is thinner than 1 μm, although the reflection bandwidth can be secured, the degree of polarization itself tends to decrease, which is not preferable. On the other hand, when the thickness is larger than 20 μm, the reflection bandwidth and the degree of polarization are not significantly improved, and the cost is simply increased.

  As the ultraviolet light source, any light source that generates ultraviolet light can be used. For example, a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, a carbon arc lamp, a metal halide lamp, a xenon lamp, or the like can be used. An ArF excimer laser, a KrF excimer laser, an excimer lamp, synchrotron radiation, or the like can also be used.

Ultraviolet illuminance is preferably ^{0.1~30mW / cm 2, 1~20mW / cm} 2 is more preferable. Further, the irradiation time is preferably as short as 5 minutes or less. More preferably, it is 3 minutes or less, More preferably, it is 1 minute or less. In addition, if it heats from the direction opposite to the ultraviolet irradiation side, it is possible to broaden the band in a shorter time.

  The heating temperature at the time of irradiation with ultraviolet light or after irradiation may be higher than the liquid crystal temperature. Usually, 140 ° C. or lower is generally suitable. Specifically, about 60-140 degreeC is preferable and 80-120 degreeC is suitable. There is an effect of promoting the diffusion rate of the monomer component by heating. When the temperature is lower than 60 ° C., the diffusion rate of the polymerizable mesogenic compound (a) is very slow, and it takes a very long time to widen the band.

  In addition, about a cholesteric liquid crystal layer, the thing which reflects circularly polarized light in a wide wavelength range, such as a visible light region, can be obtained by combining two or more layers with different reflection wavelengths in combination. Based on this, transmitted circularly polarized light in a wide wavelength range can be obtained.

  In order to protect the surface of the formed cholesteric liquid crystal layer, a protective film or a protective layer may be provided. As the protective film and the protective layer, those excellent in transparency, mechanical strength, thermal stability, moisture shielding property, isotropy and the like are preferable. Examples of the material of the protective film include polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, acrylic polymers such as polymethyl methacrylate, polystyrene, acrylonitrile / styrene copolymers, and the like. Examples thereof include styrene polymers such as (AS resin) and polycarbonate polymers. Polyethylene, polypropylene, polyolefins having a cyclo or norbornene structure, polyolefin polymers such as ethylene / propylene copolymers, vinyl chloride polymers, amide polymers such as nylon and aromatic polyamide, imide polymers, sulfone polymers , Polyether sulfone polymer, polyether ether ketone polymer, polyphenylene sulfide polymer, vinyl alcohol polymer, vinylidene chloride polymer, vinyl butyral polymer, arylate polymer, polyoxymethylene polymer, epoxy polymer, or the above Polymer blends and the like are examples of polymers that form protective films and protective layers. Other examples include films made of thermosetting or ultraviolet curable resins such as acrylic, urethane, acrylic urethane, epoxy, and silicone. Among these, cellulosic polymers, particularly triacetyl cellulose, are preferable from the viewpoint of isotropic properties. Generally the thickness of a protective film is 500 micrometers or less, and 1-300 micrometers is preferable. Further, it is preferably 5 to 200 μm, and particularly preferably 5 to 100 μm from the viewpoint of thinning.

《Cellulose ester film》
The cellulose ester film of the present invention is a sample of the film in the measurement for detecting the scattered light intensity at a position of 130 ° from the light source when measuring the scattered light intensity of 90 ° incident light of the scattered light profile of the goniophotometer. It is preferable that the difference in scattered light intensity between the case where the installation direction on the table is aligned with the slow axis and the case where the direction is perpendicular to the slow axis is 0.05 or less.

<Scattered light measured by goniophotometer>
Even if the cellulose ester film of the present invention is stretched to obtain the range of in-plane retardation of the present invention, the scattered light measured by a goniophotometer is preferably within a certain range.

  In order to improve the brightness of the brightness enhancement film, it has been said that it is necessary to reduce the haze of the film, but simply reducing the haze corresponding to the straight light does not necessarily directly lead to an improvement in brightness. I understand that.

  The present inventors have found that it is necessary for luminance improvement to eliminate anisotropic scattering. Anisotropic scattering refers to the difference in scattered light intensity between the slow axis direction of the film and the direction orthogonal thereto. This anisotropic scattering is measured with a goniophotometer.

<Anisotropic scattering measurement device>
FIG. 1 shows an outline of a goniophotometer (model: GP-1-3D, manufactured by Optec Corporation). G1. Light source lamp, G2. Spectrometer, G3. Sample stage (also called stage), G4. Sample (not shown), G5. It is a light receiving part.

  The light source uses a 12V50W halogen bulb, and the light receiving section uses a photomultiplier tube (Photomaru Hamamatsu Photonics R636-10).

  (A) shows the arrangement of a light source lamp, a spectroscope, a sample stage (stage), and an integrating sphere for measuring light intensity at the time of reference measurement for measuring reference light or transmittance measurement.

  (B) shows the arrangement of the light source lamp, the spectroscope, the sample stage, and the integrating sphere when the measurement sample is placed on the sample stage and the reflectance is measured.

  The sample stage is usually a measurement sample vertical hanging type, and the measurement sample is fixed with a clamp, and the lower part of the stage is an angle indexing rotary table. The transmittance is changed by changing the angle between the sample surface and the incident surface. It is a structure that can measure the reflectance.

  The anisotropic scattered light intensity according to the present invention can be measured by the arrangement (a). That is, the measurement of the scattered light intensity of a film having an incident light of 90 ° in the scattered light profile of the goniophotometer refers to the scattered light intensity when light is applied perpendicularly to the sample from the light source of the goniophotometer.

  When measuring the scattered light intensity at a position of 130 ° from the light source, the direction connecting the normal direction of the light source, the observation point of the sample, and the integrating sphere shown in FIG. This is the scattered light intensity measured when the angle θ formed by is 130 °.

  In the present invention, in the measurement of scattered light intensity at a position where θ is 130 °, the difference in scattered light intensity between the case where the film slow axis is horizontally installed on the sample stage and the case where the film is vertically installed is 0.05. It is characterized by the following.

  In order to satisfy the horizontal and vertical conditions, a normal level can be used.

  Various angles can be selected as θ, but in the present invention, it is set to 130 °, which has the highest correlation with the front contrast as the liquid crystal display device.

  When horizontal, the scattered light intensity when vertical is preferably in the range of 0.01 to 0.25, more preferably 0.20 or less, and even more preferably 0.10 or less.

  The difference in the scattered light intensity is 0.05 or less in the present invention, but the smaller the smaller the better.

  In order to achieve the above scattered light intensity, the cellulose ester film used in the brightness enhancement film of the present invention includes at least one of the following specific cellulose ester, acrylic polymer, and pyranose structure or furanose structure. The cellulose ester film preferably contains at least one ester compound obtained by esterifying all or part of the OH groups having the structure of 12 or less.

  The cellulose ester used in the present invention is a carboxylic acid ester having about 2 to 22 carbon atoms or an aromatic carboxylic acid ester, and particularly preferably a lower fatty acid ester having 6 or less carbon atoms.

  The acyl group bonded to the hydroxyl group may be linear or branched or may form a ring. Furthermore, another substituent may be substituted. When the degree of substitution is the same, birefringence decreases when the number of carbon atoms is large, and therefore, the number of carbon atoms is preferably selected from acyl groups having 2 to 6 carbon atoms. The cellulose ester preferably has 2 to 4 carbon atoms, more preferably 2 to 3 carbon atoms.

  Specific cellulose esters include mixed fatty acid esters of cellulose in which propionate groups and butyrate groups are bonded in addition to acetyl groups such as cellulose acetate propionate, cellulose acetate butyrate, and cellulose acetate propionate butyrate. The butyryl group forming butyrate may be linear or branched.

  As the cellulose ester preferably used in the present invention, cellulose acetate propionate and cellulose acetate butyrate are particularly preferably used. Of these, cellulose acetate propionate is most preferred.

  As a cellulose ester, the total acyl group substitution degree of a cellulose ester which satisfies the following formulas (i) and (ii) simultaneously is 2.1 to 2.8.

Formula (i) 2.1 ≦ X + Y ≦ 2.8
Formula (ii) 0.5 ≦ Y ≦ 1.65
(In the formula, X represents the degree of acetyl group substitution, Y represents the degree of substitution of propionyl group or butyryl group, and X + Y represents the degree of substitution of total acyl group)
In addition, the substitution degree of an acetyl group and the substitution degree of another acyl group can be determined by a method prescribed in ASTM-D817-96.

  Further, in order to obtain optical characteristics that meet the purpose, resins having different degrees of substitution may be mixed and used. The mixing ratio is preferably 10:90 to 90:10 (mass ratio).

  The cellulose ester film used in the present invention has a slow axis in the range of 10 ° to 80 ° with respect to the film longitudinal direction, and the in-plane retardation in the wavelength 550 nm measurement is adjusted to 120 ≦ Ro ≦ 150 (nm). However, in order to impart this property, it is preferable to stretch the film in an oblique direction with respect to the longitudinal direction of the film. In order to impart stability, reproducibility, and production suitability of the stretching treatment, it is necessary to use a specific cellulose ester having the above acyl group substitution degree.

  The number average molecular weight of the cellulose ester used in the present invention is preferably in the range of 60,000 to 300,000 because the mechanical strength of the resulting film is strong. Furthermore, the thing of 70000-200000 is used preferably.

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

  The measurement conditions are as follows.

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

  In addition, this measuring method can be used also as a measuring method of the other polymer used for this invention.

  The cellulose as a raw material for the cellulose ester is not particularly limited, and examples thereof include cotton linter, wood pulp, and kenaf. Moreover, the cellulose ester obtained from them can be mixed and used in arbitrary ratios, respectively.

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

  Cellulose esters are also affected by trace metal components in cellulose esters.

  These are considered to be related to water used in the production process, but it is preferable that there are few components that can become insoluble nuclei, and metal ions such as iron, calcium, and magnesium contain organic acidic groups. Insoluble matter may be formed by salt formation with a polymer degradation product or the like that may be present, and it is preferable that the amount is small.

  The iron (Fe) component is preferably 1 ppm or less. As for the calcium (Ca) component, it is easy to form a coordination compound, that is, a complex with an acidic component such as carboxylic acid or sulfonic acid, and many ligands. Starch, turbidity).

  The calcium (Ca) component is 60 ppm or less, preferably 0 to 30 ppm. The magnesium (Mg) component is preferably in the range of 0 to 70 ppm, particularly preferably 0 to 20 ppm, since too much will cause insoluble matter.

  Metal components such as iron (Fe) content, calcium (Ca) content, magnesium (Mg) content, etc. are pre-processed by completely digesting cellulose ester with micro digest wet cracking equipment (sulfuric acid decomposition) and alkali melting. After being performed, it can be analyzed using ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometer).

<Other additives>
The cellulose ester film of the present invention preferably contains the following additives as required.

  In the present invention, an ester obtained by esterifying all or part of OH groups in a (meth) acrylic polymer, or a compound (A) having one furanose structure or pyranose structure, in addition to cellulose ester, on a cellulose ester film Containing an esterified compound or an esterified compound obtained by esterifying all or part of the OH groups in the compound (B) in which 2 or more and 12 or less of at least one of the furanose structure or the pyranose structure are bonded, It is particularly preferable for adjusting the direction of the slow axis and the retardation by stretching, and adjusting the scattered light intensity of the film.

((Meth) acrylic polymer)
The (meth) acrylic polymer used in the present invention preferably exhibits a negative birefringence with respect to the stretching direction as a function when contained in a cellulose ester film, and the structure is not particularly limited. However, it is preferably a polymer having a weight average molecular weight of 500 or more and 30000 or less obtained by polymerizing an ethylenically unsaturated monomer.

  The (meth) acrylic polymer having a weight average molecular weight of 500 to 30,000 used in the present invention is a (meth) acrylic polymer having an aromatic ring in the side chain or a (meth) acrylic having a cyclohexyl group in the side chain. A polymer may be used.

  By controlling the composition of the polymer with a weight average molecular weight of 500 to 30,000, for example, when the cellulose ester is contained, the compatibility between the cellulose ester and the polymer is improved. Can do.

  For a (meth) acrylic polymer having an aromatic ring in the side chain or a (meth) acrylic polymer having a cyclohexyl group in the side chain, preferably if the weight average molecular weight is from 500 to 10,000, The film after film formation has excellent transparency and extremely low moisture permeability, and exhibits excellent performance even when applied to a protective film for a polarizing plate, for example.

  Since the polymer has a weight average molecular weight of 500 or more and 30000 or less, it is considered to be between the oligomer and the low molecular weight polymer. In order to synthesize such a polymer, it is difficult to control the molecular weight in normal polymerization, and it is desirable to use a method that can align the molecular weight as much as possible by a method that does not increase the molecular weight too much.

  In particular, the (meth) acrylic polymer used in the cellulose ester film of the present invention includes an ethylenically unsaturated monomer Xa having no aromatic ring and hydroxyl group in the molecule, and no hydroxyl ring in the molecule. A polymer X having a weight average molecular weight of 2,000 to 30,000 obtained by copolymerization of an ethylenically unsaturated monomer Xb having Xb and a copolymerizable ethylenically unsaturated monomer excluding Xa and Xb, or an aromatic ring The polymer Y is preferably a polymer Y having a weight average molecular weight of 500 or more and 3000 or less, which is obtained by polymerizing a non-ethylenically unsaturated monomer Ya and an ethylenically unsaturated monomer copolymerizable with Ya.

[Polymer X, Polymer Y]
The method for adjusting the retardation of the cellulose ester film according to the present invention includes an ethylenically unsaturated monomer Xa having no aromatic ring and a hydroxyl group in the molecule, and an ethylenic group having no hydroxyl group and having a hydroxyl group. High molecular weight polymer X having a weight average molecular weight of 2,000 to 30,000 obtained by copolymerizing unsaturated monomer Xb and a copolymerizable ethylenically unsaturated monomer excluding Xa and Xb, and more preferably aromatic A low molecular weight polymer Y having a weight average molecular weight of 500 to 3,000 obtained by polymerizing an ethylenically unsaturated monomer Ya having no ring and an ethylenically unsaturated monomer copolymerizable with Ya; Is preferred.

  The polymer X used in the present invention includes an ethylenically unsaturated monomer Xa having no aromatic ring and a hydroxyl group in the molecule and an ethylenically unsaturated monomer Xb having no hydroxyl ring in the molecule and having a hydroxyl group, Xa and Xb. Is a polymer having a weight average molecular weight of 2000 or more and 30000 or less obtained by copolymerization with a copolymerizable ethylenically unsaturated monomer other than.

  Preferably, Xa is an acrylic or methacrylic monomer having no aromatic ring and hydroxyl group in the molecule, and Xb is an acrylic or methacrylic monomer having no aromatic ring and having a hydroxyl group in the molecule.

  The polymer X used in the present invention is represented by the following general formula (X).

Formula (X)
-[Xa] m- [Xb] n- [Xc] p-
In the general formula (X), Xa represents an ethylenically unsaturated monomer having no aromatic ring and hydroxyl group in the molecule, and Xb represents an ethylenically unsaturated monomer having no aromatic ring and having a hydroxyl group in the molecule. Xc represents a copolymerizable ethylenically unsaturated monomer excluding Xa and Xb. m, n, and p each represent a molar composition ratio. However, m ≠ 0 and m + n + p = 100.

  Furthermore, the polymer X is preferably a polymer represented by the following general formula (X-1).

Formula (X-1)
_{- [CH 2 -C (-R1)} (- CO 2 R2)] m- [CH 2 -C (-R3) (- CO 2 R4-OH) -] n- [Xc] p-
In the general formula (X-1), R1 and R3 each represent a hydrogen atom or a methyl group. R2 represents an alkyl group having 1 to 12 carbon atoms or a cycloalkyl group. R4 is _{-CH 2 -, - C 2 H} 4 - or _-C 3 _{H 6} - represents a. Xc _{is, [CH 2 -C (-R1)} (- CO 2 R2)] representing the a polymerizable monomer unit or _{[CH 2 -C (-R3) (} - - CO 2 R4-OH)]. m, n, and p represent a molar composition ratio. However, m ≠ 0 and m + n + p = 100.

  Although the monomer as a monomer unit which comprises the polymer X used for this invention is mentioned below, it is not limited to this.

  In X, the hydroxyl group means not only a hydroxyl group but also a group having an ethylene oxide chain.

  Examples of the ethylenically unsaturated monomer Xa having no aromatic ring and hydroxyl group in the molecule include methyl acrylate, ethyl acrylate, propyl acrylate (i-, n-), and butyl acrylate (n-, i-, s). -, T-), pentyl acrylate (n-, i-, s-), hexyl acrylate (n-, i-), heptyl acrylate (n-, i-), octyl acrylate (n-, i -), Nonyl acrylate (n-, i-), myristyl acrylate (n-, i-), acrylic acid (2-ethylhexyl), acrylic acid (ε-caprolactone), etc. The thing changed into acid ester can be mentioned. Among these, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, and propyl methacrylate (i-, n-) are preferable.

  The ethylenically unsaturated monomer Xb having no hydroxyl ring in the molecule and having a hydroxyl group is preferably acrylic acid or methacrylic acid ester as a monomer unit having a hydroxyl group, such as acrylic acid (2-hydroxyethyl), acrylic acid. (2-hydroxypropyl), acrylic acid (3-hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2-hydroxybutyl), or those obtained by replacing these acrylic acids with methacrylic acid. Preferred are acrylic acid (2-hydroxyethyl) and methacrylic acid (2-hydroxyethyl), acrylic acid (2-hydroxypropyl), and acrylic acid (3-hydroxypropyl).

  Xc is not particularly limited as long as it is a monomer other than Xa and Xb and is a copolymerizable ethylenically unsaturated monomer, but preferably has no aromatic ring.

  The molar composition ratio m: n of Xa and Xb is preferably in the range of 99: 1 to 65:35, more preferably in the range of 95: 5 to 75:25. P of Xc is 0-10. Xc may be a plurality of monomer units.

  When the molar composition ratio of Xa is large, the compatibility with the cellulose ester is improved, but the retardation value Rth in the film thickness direction is increased. When the molar composition ratio of Xb is large, the compatibility is deteriorated, but the effect of reducing Rth is high.

  Further, if the molar composition ratio of Xb exceeds the above range, haze tends to occur during film formation, and it is preferable to optimize these and determine the molar composition ratio of Xa and Xb.

  The molecular weight of the high molecular weight polymer X is more preferably 5,000 or more and 30,000 or less, and still more preferably 8,000 or more and 25,000 or less.

  By setting the weight average molecular weight to 5,000 or more, advantages such as little dimensional change of the cellulose ester film under high temperature and high humidity and less curling as a polarizing plate protective film are preferable.

  When the weight average molecular weight is 30000 or less, compatibility with the cellulose ester is further improved, and bleeding out under high temperature and high humidity and further haze generation immediately after film formation are suppressed.

  The weight average molecular weight of the polymer X used in the present invention can be adjusted by a known molecular weight adjusting method. Examples of such a molecular weight adjusting method include a method of adding a chain transfer agent such as carbon tetrachloride, lauryl mercaptan, octyl thioglycolate, and the like.

  The polymerization temperature is usually from room temperature to 130 ° C., preferably from 50 ° C. to 100 ° C., and this temperature or the polymerization reaction time can be adjusted.

  The measuring method of a weight average molecular weight can be calculated | required by the following method.

(Average molecular weight measurement method)
The weight average molecular weight Mw and the number average molecular weight Mn were measured using gel permeation chromatography (GPC).

  The measurement conditions are as follows.

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

  The low molecular weight polymer Y used in the present invention is a polymer having a weight average molecular weight of 500 or more and 3000 or less obtained by polymerizing an ethylenically unsaturated monomer Ya having no aromatic ring. A weight average molecular weight of 500 or more is preferred because the residual monomer in the polymer is reduced.

  Moreover, it is preferable to set it as 3000 or less in order to adjust a retardation value. Ya is preferably an acrylic or methacrylic monomer having no aromatic ring.

  The polymer Y used in the present invention is represented by the following general formula (Y).

General formula (Y)
-[Ya] k- [Yb] q-
In the general formula (Y), Ya represents an ethylenically unsaturated monomer having no aromatic ring, and Yb represents an ethylenically unsaturated monomer copolymerizable with Ya. k and q each represent a molar composition ratio. However, k ≠ 0 and k + q = 100.

  The polymer Y according to the present invention is more preferably a polymer represented by the following general formula (Y-1).

General formula (Y-1)
_{- [CH 2 -C (-R5)} (- CO 2 R6)] k- [Yb] q-
In the general formula (Y-1), R5 represents a hydrogen atom or a methyl group, respectively. R6 represents an alkyl group having 1 to 12 carbon atoms or a cycloalkyl group. Yb represents a monomer unit copolymerizable with [CH ₂ —C (—R 5) (— CO ₂ R 6)]. k and q each represent a molar composition ratio. However, k ≠ 0 and k + q = 100.

Yb is a _{Ya [CH 2 -C (-R5)} (- CO 2 R6)] and is not particularly limited as long as it is copolymerizable ethylenically unsaturated monomers. Yb may be plural. k + q = 100, q is preferably 1-30.

  The ethylenically unsaturated monomer Ya constituting the polymer Y obtained by polymerizing the ethylenically unsaturated monomer having no aromatic ring is, for example, methyl acrylate, ethyl acrylate, propyl acrylate ( i-, n-), butyl acrylate (n-, i-, s-, t-), pentyl acrylate (n-, i-, s-), hexyl acrylate (n-, i-), acrylic Acid heptyl (n-, i-), octyl acrylate (n-, i-), nonyl acrylate (n-, i-), myristyl acrylate (n-, i-), cyclohexyl acrylate, acrylic acid ( 2-ethylhexyl), acrylic acid (ε-caprolactone), acrylic acid (2-hydroxyethyl), acrylic acid (2-hydroxypropyl), acrylic acid (3-hydroxypropiyl) ), Acrylic acid (4-hydroxybutyl), acrylic acid (2-hydroxybutyl), methacrylic acid ester, the above acrylic acid ester changed to methacrylic acid ester; unsaturated acid, for example, acrylic acid, methacrylic acid And maleic anhydride, crotonic acid, itaconic acid and the like.

  Yb is not particularly limited as long as it is an ethylenically unsaturated monomer copolymerizable with Ya. Examples of vinyl esters include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, vinyl pivalate, and vinyl caproate. Vinyl caprate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl cyclohexanecarboxylate, vinyl octylate, vinyl methacrylate, vinyl crotonate, vinyl sorbate, vinyl cinnamate and the like are preferred. Yb may be plural.

  In order to synthesize the polymers X and Y, it is difficult to control the molecular weight in normal polymerization, and it is desirable to use a method that can make the molecular weights as uniform as possible without increasing the molecular weight.

  Such polymerization methods include a method using a peroxide polymerization initiator such as cumene peroxide and t-butyl hydroperoxide, a method using a polymerization initiator in a larger amount than normal polymerization, and a mercapto compound in addition to the polymerization initiator. And a method of using a chain transfer agent such as carbon tetrachloride, a method of using a polymerization terminator such as benzoquinone and dinitrobenzene in addition to the polymerization initiator, and further, Japanese Patent Application Laid-Open No. 2000-128911 or 2000-344823. Examples thereof include a compound having one thiol group and a secondary hydroxyl group, or a bulk polymerization method using a polymerization catalyst in which the compound and an organometallic compound are used in combination. Used.

  In particular, the polymer Y is preferably a polymerization method using a compound having a thiol group and a secondary hydroxyl group in the molecule as a chain transfer agent. In this case, the terminal of the polymer Y has a hydroxyl group and a thioether resulting from the polymerization catalyst and the chain transfer agent. The compatibility of Y and cellulose ester can be adjusted by this terminal residue.

  The hydroxyl values of the polymers X and Y are preferably 30 to 150 [mg KOH / g].

(Measurement method of hydroxyl value)
The measurement of the hydroxyl value is based on JIS K 0070 (1992). This hydroxyl value is defined as the number of mg of potassium hydroxide required to neutralize acetic acid bonded to a hydroxyl group when 1 g of a sample is acetylated.

  Specifically, sample Xg (about 1 g) is precisely weighed in a flask, and 20 ml of an acetylating reagent (a solution obtained by adding pyridine to 20 ml of acetic anhydride to 400 ml) is accurately added thereto. An air cooling tube is attached to the mouth of the flask and heated in a glycerin bath at 95-100 ° C. After 1 hour and 30 minutes, the mixture is cooled, 1 ml of purified water is added from an air condenser, and acetic anhydride is decomposed into acetic acid.

  Next, titration is performed with a 0.5 mol / L potassium hydroxide ethanol solution using a potentiometric titrator, and the inflection point of the obtained titration curve is set as the end point.

  Further, as a blank test, titration is performed without a sample, and an inflection point of the titration curve is obtained. The hydroxyl value is calculated by the following formula.

Hydroxyl value = {(BC) × f × 28.05 / X} + D
In the formula, B is the amount (ml) of 0.5 mol / L potassium hydroxide ethanol solution used for the blank test, C is the amount (ml) of 0.5 mol / L potassium hydroxide ethanol solution used for titration, f is a factor of a 0.5 mol / L potassium hydroxide ethanol solution, D is an acid value, and 28.05 is 1/2 of 1 mol amount 56.11 of potassium hydroxide.

  The above-mentioned polymer X and polymer Y are both excellent in compatibility with cellulose ester, excellent in productivity without evaporation and volatilization, good retention as a protective film for polarizing plates, low moisture permeability, and dimension stability. Excellent in properties.

The content of the polymer X and the polymer Y in the cellulose ester film is preferably in a range satisfying the following formulas (I) and (II). When the content of the polymer X is Xg (mass% = (mass of polymer X / mass of cellulose ester) × 100) and the content of the polymer Y is Yg (mass%),
Formula (I) 5 ≦ Xg + Yg ≦ 35 (mass%)
Formula (II) 0.05 ≦ Yg / (Xg + Yg) ≦ 0.4
A preferable range of (Xg + Yg) in the formula (I) is 10 to 35% by mass. If the polymer X and the polymer Y are 5 mass% or more as a total amount with respect to the total mass of the cellulose ester, they will sufficiently act to adjust the retardation value. Moreover, if it is 35 mass% or less as a total amount, adhesiveness with polarizer PVA is favorable.

  The polymer X and the polymer Y can be directly added and dissolved as a material constituting the dope solution described later, or can be added to the dope solution after being previously dissolved in an organic solvent for dissolving the cellulose ester.

(Ester compound in which at least one pyranose structure or furanose structure is 1 to 12 and all or part of the OH groups in the structure are esterified)
The cellulose ester film of the present invention preferably contains an ester compound in which at least one of the pyranose structure or furanose structure is 1 to 12 and all or part of the OH groups in the structure are esterified. In the present invention, the above ester compounds are collectively referred to as sugar ester compounds.

  Examples of the ester compound used in the present invention include the following, but the present invention is not limited to these.

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

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

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

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

  The monocarboxylic acid used for esterifying all or part of the OH groups in the pyranose structure or furanose structure of the present invention is not particularly limited, and known aliphatic monocarboxylic acids, alicyclic monocarboxylic acids, An aromatic monocarboxylic acid or the like can be used. The carboxylic acid used may be one type or a mixture of two or more types.

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

  Examples of preferable alicyclic monocarboxylic acids include acetic acid, cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, cyclooctanecarboxylic acid, and derivatives thereof.

  Examples of preferred aromatic monocarboxylic acids include aromatic monocarboxylic acids having an alkyl group or alkoxy group introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, cinnamic acid, benzylic acid, biphenylcarboxylic acid, and naphthalene. Examples thereof include aromatic monocarboxylic acids having two or more benzene rings such as carboxylic acid and tetralin carboxylic acid, or derivatives thereof. More specifically, xylyl acid, hemelic acid, mesitylene acid, prenylic acid, γ-isoduric acid, jurylic acid, mesitic acid, α-isoduric acid, cumic acid, α-toluic acid, hydroatropic acid, atropic acid, hydrocinnamic acid, salicylic acid, o-anisic acid, m-anisic acid, p-anisic acid , Creosote acid, o-homosalicylic acid, m-homosalicylic acid, p-homosalicylic acid, o-pyroca Succinic acid, β-resorcylic acid, vanillic acid, isovanillic acid, veratromic acid, o-veratrumic acid, gallic acid, asaronic acid, mandelic acid, homoanisic acid, homovanillic acid, homoveratrumic acid, o-homoveratrumic acid, phthalonic acid, p- Although coumaric acid can be mentioned, benzoic acid is particularly preferable.

  The oligosaccharide ester compound can be applied as a compound having 1 to 12 of at least one of a pyranose structure or a furanose structure used in the present invention.

  Oligosaccharides are produced by allowing an enzyme such as amylase to act on starch, sucrose, etc. Examples of oligosaccharides that can be applied to the present invention include maltooligosaccharides, isomaltoligosaccharides, fructooligosaccharides, galactooligosaccharides, and xylooligos. Sugar.

Moreover, the said ester compound is a compound which condensed 1 or more and 12 or less of at least 1 sort (s) of the pyranose structure or furanose structure represented with the following general formula (A). However, R < ₁₁ > -R < ₁₅ >, R < ₂₁ > -R < ₂₅ > represents a C2-C22 acyl group or a hydrogen atom, m and n represent the integer of 0-12, respectively, and m + n represents the integer of 1-12.

R _{11 to} R ₁₅ and R _{21 to} R ₂₅ are particularly preferably a benzoyl group or a hydrogen atom. The benzoyl group may further have a substituent R ₂₆ (p is 0 to 5), and examples thereof include an alkyl group, an alkenyl group, an alkoxyl group, and a phenyl group, and further, these alkyl groups, alkenyl groups, and phenyl groups. May have a substituent. Oligosaccharides can also be produced by the same method as the ester compound of the present invention.

  Although the specific example of the ester compound used for this invention below is given, this invention is not limited to this.

  The cellulose ester film of the present invention preferably contains 1 to 30% by mass of the above ester compound in order to suppress the fluctuation of the retardation value and stabilize the display quality. It is preferable to contain -30 mass%. Within this range, it is preferable that the excellent effects of the present invention are exhibited and there is no bleeding out.

(Plasticizer)
The cellulose ester film of the present invention can contain a plasticizer as necessary to obtain the effects of the present invention.

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

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

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

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

Formula (a) R1- (OH) n
However, R1 represents an n-valent organic group, n represents a positive integer of 2 or more, and the OH group represents an alcoholic and / or phenolic hydroxyl group.

  Examples of preferred polyhydric alcohols include the following, but the present invention is not limited to these.

  Adonitol, arabitol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, 1,2-butanediol, 1,3- Butanediol, 1,4-butanediol, dibutylene glycol, 1,2,4-butanetriol, 1,5-pentanediol, 1,6-hexanediol, hexanetriol, galactitol, mannitol, 3-methylpentane- Examples include 1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, xylitol and the like.

  In particular, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, sorbitol, trimethylolpropane, and xylitol are preferable.

  There is no restriction | limiting in particular as monocarboxylic acid used for polyhydric alcohol ester, Well-known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic monocarboxylic acid, etc. can be used. Use of an alicyclic monocarboxylic acid or aromatic monocarboxylic acid is preferred in terms of improving moisture permeability and retention.

  Examples of preferred monocarboxylic acids include the following, but the present invention is not limited thereto.

  As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or side chain having 1 to 32 carbon atoms can be preferably used. The number of carbon atoms is more preferably 1-20, and particularly preferably 1-10. When acetic acid is contained, the compatibility with the cellulose ester is increased, and it is also preferable to use a mixture of acetic acid and another monocarboxylic acid.

  Preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanoic acid, undecylic acid, lauric acid, tridecylic acid, Saturated fatty acids such as myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, laccelic acid, undecylenic acid, olein Examples thereof include unsaturated fatty acids such as acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid.

  Examples of preferred alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, or derivatives thereof.

  Examples of preferred aromatic monocarboxylic acids include those in which 1 to 3 alkoxy groups such as alkyl group, methoxy group or ethoxy group are introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, biphenylcarboxylic acid, Examples thereof include aromatic monocarboxylic acids having two or more benzene rings such as naphthalenecarboxylic acid and tetralincarboxylic acid, or derivatives thereof. Benzoic acid is particularly preferable.

  The molecular weight of the polyhydric alcohol ester is not particularly limited, but is preferably 300 to 1500, and more preferably 350 to 750. A higher molecular weight is preferred because it is less likely to volatilize, and a smaller one is preferred in terms of moisture permeability and compatibility with cellulose ester.

  The carboxylic acid used for the polyhydric alcohol ester may be one kind or a mixture of two or more kinds. Moreover, all the OH groups in the polyhydric alcohol may be esterified, or a part of the OH groups may be left as they are.

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

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

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

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

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

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

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

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

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

Formula (b) R2 (COOH) m (OH) n
(Wherein R2 is an (m + n) -valent organic group, m is a positive integer of 2 or more, n is an integer of 0 or more, a COOH group is a carboxyl group, and an OH group is an alcoholic or phenolic hydroxyl group)
Examples of preferred polyvalent carboxylic acids include the following, but the present invention is not limited to these.

  Trivalent or higher aromatic polyvalent carboxylic acids such as trimellitic acid, trimesic acid, pyromellitic acid or derivatives thereof, succinic acid, adipic acid, azelaic acid, sebacic acid, oxalic acid, fumaric acid, maleic acid, tetrahydrophthal An aliphatic polyvalent carboxylic acid such as an acid, an oxypolyvalent carboxylic acid such as tartaric acid, tartronic acid, malic acid and citric acid can be preferably used. In particular, it is preferable to use an oxypolycarboxylic acid from the viewpoint of improving retention.

  There is no restriction | limiting in particular as alcohol used for the polyhydric carboxylic acid ester compound which can be used for this invention, Well-known alcohol and phenols can be used.

  For example, an aliphatic saturated alcohol or aliphatic unsaturated alcohol having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. It is more preferable that it is C1-C20, and it is especially preferable that it is C1-C10.

  In addition, alicyclic alcohols such as cyclopentanol and cyclohexanol or derivatives thereof, aromatic alcohols such as benzyl alcohol and cinnamyl alcohol, or derivatives thereof can also be preferably used.

  When an oxypolycarboxylic acid is used as the polycarboxylic acid, the alcoholic or phenolic hydroxyl group of the oxypolycarboxylic acid may be esterified with a monocarboxylic acid. Examples of preferred monocarboxylic acids include the following, but the present invention is not limited thereto.

  As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. It is more preferable that it is C1-C20, and it is especially preferable that it is C1-C10.

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

  Examples of preferred alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, or derivatives thereof.

  Examples of preferred aromatic monocarboxylic acids include those in which an alkyl group is introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, and two or more benzene rings such as biphenyl carboxylic acid, naphthalene carboxylic acid, and tetralin carboxylic acid. And aromatic monocarboxylic acids possessed by them, or derivatives thereof. Particularly preferred are acetic acid, propionic acid, and benzoic acid.

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

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

  The acid value of the polyvalent carboxylic acid ester compound that can be used in the present invention is preferably 1 mgKOH / g or less, and more preferably 0.2 mgKOH / g or less. Setting the acid value in the above range is preferable because the environmental fluctuation of the retardation is also suppressed.

  In addition, an acid value means the milligram number of potassium hydroxide required in order to neutralize the acid (carboxyl group which exists in a sample) contained in 1g of samples. The acid value is measured according to JIS K0070.

  Examples of particularly preferred polyvalent carboxylic acid ester compounds are shown below, but the present invention is not limited thereto.

  For example, triethyl citrate, tributyl citrate, acetyl triethyl citrate (ATEC), acetyl tributyl citrate (ATBC), benzoyl tributyl citrate, acetyl triphenyl citrate, acetyl tribenzyl citrate, dibutyl tartrate, diacetyl dibutyl tartrate, Examples include tributyl trimellitic acid and tetrabutyl pyromellitic acid.

  The polyester plasticizer is not particularly limited, and a polyester plasticizer having an aromatic ring or a cycloalkyl ring in the molecule can be used. Although it does not specifically limit as a polyester plasticizer, For example, the aromatic terminal ester plasticizer represented by the following general formula (c) can be used.

General formula (c) B- (GA) n-GB
(In the formula, B is a benzene monocarboxylic acid residue, G is an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms, A represents an alkylene dicarboxylic acid residue having 4 to 12 carbon atoms or an aryl dicarboxylic acid residue having 6 to 12 carbon atoms, and n represents an integer of 1 or more.)
In the general formula (c), a benzene monocarboxylic acid residue represented by B and an alkylene glycol residue, oxyalkylene glycol residue or aryl glycol residue represented by G, an alkylene dicarboxylic acid residue or aryl dicarboxylic group represented by A It is composed of an acid residue and can be obtained by a reaction similar to that of a normal polyester plasticizer.

  Examples of the benzene monocarboxylic acid component of the polyester plasticizer used in the present invention include benzoic acid, para-tert-butylbenzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, dimethylbenzoic acid, ethylbenzoic acid, and normalpropyl. There exist benzoic acid, aminobenzoic acid, acetoxybenzoic acid, etc., and these can be used as 1 type, or 2 or more types of mixtures, respectively.

  Examples of the alkylene glycol component having 2 to 12 carbon atoms of the polyester plasticizer that can be used in the present invention include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1, 3-butanediol, 1,2-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol (neo Pentyl glycol), 2,2-diethyl-1,3-propanediol (3,3-dimethylolpentane), 2-n-butyl-2-ethyl-1,3propanediol (3,3-dimethylolheptane) 3-methyl-1,5-pentanediol 1,6-hexanediol, 2,2,4-trimethyl 1,3-penta Diol, 2-ethyl 1,3-hexanediol, 2-methyl 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-octadecanediol, and the like. It is used as one kind or a mixture of two or more kinds.

  In particular, an alkylene glycol having 2 to 12 carbon atoms is particularly preferable because of excellent compatibility with a cellulose ester.

  In addition, examples of the oxyalkylene glycol component having 4 to 12 carbon atoms of the aromatic terminal ester include diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and tripropylene glycol. It can be used as a seed or a mixture of two or more.

  Examples of the alkylene dicarboxylic acid component having 4 to 12 carbon atoms of the aromatic terminal ester include succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid. These are used as one kind or a mixture of two or more kinds. Examples of the arylene dicarboxylic acid component having 6 to 12 carbon atoms include phthalic acid, terephthalic acid, isophthalic acid, 1,5 naphthalene dicarboxylic acid, and 1,4 naphthalene dicarboxylic acid.

  The polyester plasticizer used in the present invention has a number average molecular weight of preferably 300 to 1500, more preferably 400 to 1000. The acid value is 0.5 mgKOH / g or less, the hydroxyl value is 25 mgKOH / g or less, more preferably the acid value is 0.3 mgKOH / g or less, and the hydroxyl value is 15 mgKOH / g or less.

  Specific examples of the aromatic terminal ester plasticizer that can be used in the present invention are shown below, but the present invention is not limited thereto.

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

  Although the ultraviolet absorber used in the present invention is not particularly limited, for example, oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, triazine compounds, nickel complex compounds, inorganic powders Examples include the body.

(Fine particles)
The cellulose ester film preferably contains fine particles in order to prevent blocking between the films.

  As fine particles, examples of inorganic compounds include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, Mention may be made of magnesium silicate and calcium phosphate.

  Fine particles containing silicon are preferable in terms of low turbidity, and silicon dioxide is particularly preferable.

  The average primary particle diameter of the fine particles is preferably 5 to 400 nm, and more preferably 10 to 300 nm. These may be mainly contained as secondary aggregates having a particle size of 0.05 to 0.3 μm, and may be contained as primary particles without being aggregated if the particles have an average particle size of 100 to 400 nm. preferable.

  The content of these fine particles in the polarizing plate protective film is preferably 0.01 to 1% by mass, particularly preferably 0.05 to 0.5% by mass. In the case of a polarizing plate protective film having a multilayer structure by the co-casting method, it is preferable to contain fine particles of this addition amount on the surface.

  Silicon dioxide fine particles are commercially available, for example, under the trade names Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600 (manufactured by Nippon Aerosil Co., Ltd.). it can.

  Zirconium oxide fine particles are commercially available, for example, under the trade names Aerosil R976 and R811 (manufactured by Nippon Aerosil Co., Ltd.) and can be used.

  Examples of the polymer include silicone resin, fluororesin, and acrylic resin. Silicone resins are preferable, and those having a three-dimensional network structure are particularly preferable. For example, Tospearl 103, 105, 108, 120, 145, 3120, and 240 (manufactured by Toshiba Silicone Co., Ltd.) It is marketed by name and can be used.

  Among these, Aerosil 200V and Aerosil R972V are particularly preferably used because they have a large effect of reducing the friction coefficient while keeping the turbidity of the polarizing plate protective film low. In the polarizing plate protective film used in the present invention, the dynamic friction coefficient of at least one surface is preferably 0.2 to 1.0.

  Various additives may be batch-added to a dope that is a cellulose ester-containing solution before film formation, or an additive solution may be separately prepared and added in-line. In particular, it is preferable to add a part or all of the fine particles in-line in order to reduce the load on the filter medium.

  When the additive solution is added in-line, it is preferable to dissolve a small amount of cellulose ester in order to improve mixing with the dope. The amount of the cellulose ester is preferably 1 to 10 parts by mass, more preferably 3 to 5 parts by mass with respect to 100 parts by mass of the solvent.

  In order to perform in-line addition and mixing in the present invention, for example, an in-line mixer such as a static mixer (manufactured by Toray Engineering), SWJ (Toray static type in-tube mixer Hi-Mixer) or the like is preferably used.

<< Method for producing cellulose ester film >>
The cellulose ester film according to the present invention can be preferably used as a film produced by a solution casting method or a film produced by a melt casting method. In this case, it is preferable to use a melt casting method in which the influence of the residual solvent need not be considered.

<Solution casting method>
Production of the cellulose ester film according to the present invention by the solution casting method is a step of dissolving a cellulose ester and an additive in a solvent to prepare a dope, casting on an endless metal support that moves the dope indefinitely, and drying It is carried out by a step of performing, a step of peeling from the metal support, a stretching step, a step of further drying, and a step of winding up the finished film.

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

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

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

  Therefore, depending on the average acetylation degree (acetyl group substitution degree) of the cellulose ester, the good solvent and the poor solvent change. For example, when acetone is used as the solvent, the cellulose ester acetate ester (acetyl group substitution degree 2.4), cellulose Acetate propionate is a good solvent, and cellulose acetate (acetyl group substitution degree 2.8) is a poor solvent.

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

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

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

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

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

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

  Moreover, after mixing a cellulose ester with a poor solvent and making it wet or swell, the method of adding a good solvent and melt | dissolving is also used preferably.

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

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

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

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

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

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

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

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

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

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

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

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

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

  Here, the dope casting will be described.

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

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

  A preferable support body temperature is 0-40 degreeC, and 5-30 degreeC is still more preferable. Alternatively, it is also a preferable method that the web is gelled by cooling and peeled from the drum in a state containing a large amount of residual solvent.

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

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

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

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

  Further, in the drying step of the cellulose ester film, the web is peeled off from the metal support, and further dried, and the residual solvent amount is preferably 1% by mass or less, more preferably 0.1% by mass or less, Especially preferably, it is 0-0.01 mass% or less. Peeling is preferably performed at a peeling tension of 300 N / m or less.

(Stretching process)
In order to obtain the target retardation value Ro in the present invention, it is preferable to further control the refractive index of the cellulose ester film having the preferred configuration of the present invention by a stretching operation.

  In the present invention, the slow axis in the film plane forms an angle of 10 ° to 80 ° with respect to the longitudinal direction of the film. For this purpose, a method of stretching by adjusting the angle is employed.

  As a method of adjusting the angle, it is preferable to stretch or regulate shrinkage in the film forming direction, and then stretch or regulate shrinkage in the inclined direction with respect to the film forming direction. For example, JP-A-2003-340916 A method using a stretching apparatus used in Example 1 of Japanese Patent Publication No. 2005-284024, a method using a stretching apparatus described in Production Example 2, a stretching method described in Japanese Patent Laid-Open No. 2007-30466, The method using the stretching apparatus used in Example 1 of JP-A-2007-94007 can be preferably used, and the film may be stretched online after casting, or may be stretched again after film formation. .

  Among them, it is particularly preferable to use the method described in JP-A-2005-30466.

Further, the following methods may be used in combination.
(1) Method of bending the left and right path by bending the conveyance (2) Method of setting the right and left clip speed difference by the spindle (3) Method of giving the right and left speed difference by giving independent left and right bending angles The embodiment will be described with reference to the drawings in the case of oblique stretching. However, the present invention is not limited to the following embodiments.

  2 and 3 show a plane and a cross section of a film stretching apparatus (oblique stretching apparatus) 1 according to an embodiment of the present invention. The film stretching apparatus 1 includes a supply device 3 that supplies the film 2, a longitudinal stretching device 4 that heats the film, and a longitudinal stretching process (longitudinal stretching process) 6 that includes an intermediate transport device 5 that transports the film 2 downstream. An oblique stretching machine 7 that is inclined with respect to the transport direction while transporting the film 2 and that stretches in the direction, and an oblique stretching heating device that is provided so as to cover the central portion of the oblique stretching machine 7 and heats the film 2 8 includes an oblique stretching process (orthogonal expansion / contraction process) 9 and a winding device 10 for winding the film 2.

  The supply device 3 is mounted with an original reel 11 around which a film 2 is wound, and the film 2 is sandwiched between a reference roll 12 and a nip roll 13 and sent out at a predetermined transport speed. The longitudinal stretching device 4 is a box made of a heat insulating material having hot air ducts (heating means) 14 for spraying hot air alternately on the film 2 from above and below. The intermediate conveyance device 5 sandwiches and conveys the film 2 between the ratio roll 15 and the nip roll 16 and stretches it in the E1 direction parallel to the conveyance direction.

  The oblique stretching machine 7 stretches the film 2 in the E2 direction inclined by an angle α with respect to the transport direction while transporting the film 2 with the stretching chains 17 disposed on both sides of the film 2. Details will be described later. The oblique stretching furnace 8 is a box made of a heat insulating material having a hot air duct 18 for blowing hot air from above and below the film 2. The winding device 10 winds the film 2 around the product reel 20 while adjusting the tension with the tension roll 19.

  FIG. 4 shows the configuration of the oblique stretching machine 7. The oblique stretching machine 7 includes two parallel stretching chains 17, a plurality of bases 21 provided in the stretching chain 17 at regular intervals, and arms 22 attached to the respective bases 21 so as to be slidable in a certain direction. , And a clip 23 provided at the tip of each arm 22. The clip 23 can grip both side edges of the film 2, and the stretching chain 17 is looped around a sprocket 24 perpendicular to the surface of the film 2. Further, the clip 23 may move on the arm or change its angle appropriately with respect to the transport direction while holding the film 2.

  FIG. 5 shows a more detailed structure of the oblique stretching machine 7. A base 21 is fixed to the extending chain 17 every other frame. The base 21 is provided with two sliding shafts 25 each inclined by 45 ° (angle α in FIG. 2) with respect to the extending chain 17, and an arm 22 is attached to be slidable along each sliding shaft 25. ing. A positioning member 26 made of a bearing is provided on the upper portion of the arm 22, and the arm 22 is projected and retracted by guiding the positioning member 26 with a guide 27. The clip 23 provided at the tip of the arm 22 is a known film gripping mechanism, and is opened and closed by the guide 28 (the film 2 is gripped or released).

  The oblique stretching machine 7 causes the arm 22 to protrude from the base 21 of the stretching chain 17, grips both side edges of the film 2 with the clips 23, and transports the film 2 as the stretching chain 17 advances. During this time, the film 22 is retracted in the direction in which the arm 22 slides (direction E2 in FIG. 1) by widening the film 22 by retracting the arm 22 while holding the film 2 with the clip 23. At the time of widening, the retreat amounts of the arms 22 facing the sliding direction of the arms 22 are equal. After the film 2 is widened, the clip 23 may be released from the clip 23 through a certain holding process and relaxation process. When the film is stretched online after casting, the holding time in the holding process varies from left to right, so that there is a possibility that the retardation in the thickness direction may vary, and the shape of the hot air supply port is preferably parallel to the inclined direction. Then, the arm 22 is further retracted so that the clip 23 does not contact the film 2 when the extending chain 17 is folded back along the sprocket 24.

  Then, the extending | stretching of the film 2 in the film extending apparatus 1 which consists of the above structure is demonstrated.

  In the longitudinal stretching section 6, when the film 2 is sent out at a predetermined speed by the reference roll 12 and is transported by the ratio roll 15 at a speed higher than that of the reference roll 12, a portion heated in the longitudinal stretching furnace 4 is transported. The film is stretched in the direction (E1 direction) at the same ratio as the ratio of the conveyance speed of the ratio roll 15 to the reference roll 12. By this stretching in the longitudinal direction, the molecules of the film 2 are arranged in the transport direction, and an orientation angle in the longitudinal direction is given.

  Further, in the oblique stretching section 9, the film 2 is stretched in the E2 direction in an inclined downward direction by an angle α with respect to the transport direction. By this stretching in the tilt direction, the film 2 is subjected to a tensile force in the E2 direction and a stress for deformation of the film 2, and a stretching force that attempts to align molecules at a larger angle with respect to the transport direction than in the E2 direction. Acts to provide an orientation angle in the tilt direction.

  As a result, the film 2 obtains an orientation angle in a direction obtained by adding the orientation angle imparted in the longitudinal stretching portion 6 and the orientation angle imparted in the oblique stretching portion 9, and the longitudinal stretching portion 6 and the oblique stretching are obtained. A retardation value (retardation) is given according to the strength of stretching (stretching ratio) in the portion 9.

  When the oriented film is produced by obliquely stretching the film 2 with the film stretching apparatus 1, the film 2 is actually stretched by the longitudinal stretching portion 6 and the oblique stretching portion 9, and the orientation angle of the obtained film 2 is measured. The stretching ratio in the longitudinal stretching section 6 is adjusted by increasing or decreasing the speed of the ratio roll 15 so that a desired orientation angle is obtained. Moreover, a desired retardation value is obtained by adjusting the stretch ratio in the oblique stretched portion 9.

  The stretching ratio in the biaxial direction is preferably in the range of 0.8 to 1.5 times in the longitudinal direction and 1.1 to 2.5 times in the width direction, respectively. It is preferable to carry out in the range of -1.0 times and 1.2-2.0 times in the width direction.

  The stretching temperature is preferably 150 ° C. to 210 ° C., more preferably 160 ° C. to 200 ° C., and further preferably 170 ° C. to 200 ° C. or less.

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

  Specifically, it is preferable that the residual solvent is stretched at 11% at 175 ° C, or the residual solvent is stretched at 2% at 175 ° C. Alternatively, it is preferable that the residual solvent is stretched at 11% at 185 ° C, or the residual solvent is stretched at less than 1% at 185 ° C.

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

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

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

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

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

<Melt casting method>
FIG. 6 is an example of a manufacturing apparatus used in the melt casting method. However, the present invention is not limited to this.

  Extruder 101, filter 102, static mixer 103, die (including thickness adjusting means) 104, touch roll 105, first cooling roll 106, second cooling roll 107, peeling roll 108, dancer roll 109, stretching machine 110, slitter 111, a thickness measuring means 112, an embossing ring and back roll 113, a winder 114, and a wound film 115.

  The cellulose ester used in the present invention is usually obtained in powder form. In the method for producing a cellulose ester film according to the present invention, powdery cellulose ester may be used, but it is preferable from the viewpoint of handling that the powder is formed into a pellet.

  When the powder is formed into a pellet, a known single-screw extruder or twin-screw extruder can be used. For example, after putting powdery cellulose ester from the hopper of an extruder, melt kneading the cellulose ester at a temperature of about (Tg + 100) ° C., extruding a strand from the die, and cooling the strand by a method such as water cooling The pellet can be obtained by cutting with a pelletizer.

  Add various antioxidants such as phenolic antioxidants and phosphorus antioxidants, lubricants such as higher fatty acid amides and higher fatty acid residual metal salts, etc. as necessary when adding powdered cellulose ester to the hopper And may be pelletized.

  The powder is preferably dried at a temperature near Tg in advance. Further, when forming into a pellet form, it is preferable to use a vented extruder while sucking the inside of the extruder.

  Pellets made of cellulose ester are preferably used after sufficiently drying at a temperature near Tg. In order to prevent the polymer from being oxidized and deteriorated during drying, drying under nitrogen is desirable.

  The cellulose ester is melt-kneaded in a single-screw or twin-screw extruder and extruded into a sheet form from a casting die. Usually, the temperature of the extruder is set so that the resin temperature is in the range of (Tg + 100) ° C. to (Tg + 200) ° C.

  In addition, the extruder hopper is sealed with nitrogen to suppress degradation of cellulose ester in the extruder, a leaf disk filter is used to suppress the generation of foreign objects such as fish eyes, and extrusion fluctuations are suppressed. For this purpose, a gear pump may be used.

  It is preferable to use a casting die having a shape in which the tip portion is processed into a sharp edge (curvature radius R = 0.1 μm or less) from the viewpoint of suppressing occurrence of a crack.

  A melted cellulose ester extruded from a casting die into a sheet is made of a cooling casting roll that is a rotating support, and a metal that is a pressing rotary body provided in pressure contact with the casting roll along its circumferential direction. A nip is formed by the elastic touch roll or endless belt, and a sheet-like molten cellulose ester is passed through the nip portion, so that the desired surface shape is sandwiched between the casting roll and the elastic touch roll or endless belt. A cellulose ester film having a thickness and optical performance is formed.

  Examples of the elastic touch roll include JP 03-124425, JP 08-224772, JP 07-1000096, JP 10-272676, WO 97-028950, JP 11-235747, JP 2002-36332. , JP-A-2002-36333, JP-A-2005-172940, JP-A-2005-280217, registered patent 3194904, registered patent 3422798, and the like can be preferably used. A commercially available product can be used for these, and a silicon rubber roll coated with a thin film metal sleeve can be used as described in the above document, but a touch roll having elasticity is preferable.

  The endless belt is a flexible metal sleeve belt that is held by a plurality of rolls arranged in parallel with the casting roll in the circumferential direction of the casting roll, and preferably has a thickness of 100 to 1500 μm. .

  If the endless belt is too thin, the strength of the belt is weak, and the belt may be deformed when the molten cellulose ester is sandwiched. If the endless belt is too thick, the pressure for sandwiching the molten cellulose ester becomes too strong, and a bank may be formed.

  The endless belt is preferably held by two or more rolls having a diameter of 100 to 300 mm. By holding the endless belt with the roll as described above, the molten cellulose ester can be pinched with a stable pressure.

  The surface temperature of the endless belt is preferably 50 ° C. or more and (Tg−5) ° C. or less from the viewpoint of peeling failure.

  In the manufacturing apparatus used in the present invention, the length (air gap) until the molten cellulose ester extruded from the lip of the casting die comes into contact with the elastic touch roll endless belt or the casting roll is 30 to 300 mm. Preferably, it is 70-200 mm.

  By producing under such conditions, an optically uniform film can be obtained. The air gap is the shortest length from the lip of the casting die until the molten cellulose ester contacts either the endless belt or the casting roll.

  For example, when the molten cellulose ester comes into contact with the endless belt first, it is the shortest length from the casting die lip to the point where the endless belt and the molten cellulose ester start to contact.

  The air gap when the molten cellulose ester comes into contact with the casting roll is also determined in the same manner. The value of the air gap can be determined by the size of the endless belt and the casting roll, the shape of the casting die tip, and the positional relationship between the casting roll, the endless belt and the casting die.

  In order to make the air gap 150 mm or less, it is preferable to use a 200 to 400 mmφ casting roll. The surface of the casting roll is preferably a mirror finish with high smoothness.

  The lower limit value of the surface temperature of the casting roll is preferably equal to or higher than the surface temperature of the elastic touch roll or the endless belt from the viewpoint of suppressing generation of wavy wrinkles and peeling, and the upper limit value is It is preferable that it is (Tg-5) degrees C or less.

  The distance for sandwiching the molten cellulose ester between the casting roll and the elastic touch roll or the endless belt is 50 to 150 mm, preferably 70 to 130 mm, from the viewpoint of the effect of improving the appearance defect such as die line. .

  The cellulose ester film sandwiched between an elastic touch roll or an endless belt and a casting roll and solidified by cooling is preferably further stretched by 1.01 to 5.0 times in at least one direction. The sharpness of the streaks becomes gentle by stretching and can be highly corrected.

  As the stretching apparatus, it is preferable to use an oblique stretching apparatus similar to the solution casting method described above.

  Thereafter, the film is taken up by a take-up machine, and after the film is slit and removed, the film is taken up in a roll by a take-up machine.

  A protective film can also be bonded using a nip roll of a take-up machine. As the protective film, a film made of a commercially available ethylene-vinyl acetate copolymer or the like can be used, and can be bonded to one side or both sides of a cellulose ester film.

  The film made of cellulose ester obtained in the present invention may be a multilayer film. In the case of a multilayer film, it is only necessary to have one or more layers made of cellulose ester.

  When using the film obtained by this invention for an optical product, it is preferable that all the layers are multilayer films which consist of a cellulose ester. When a multilayer film is produced according to the present invention, a multi-manifold type casting die or a feed block type casting die can be used. Since it is easy to accurately control the thickness of each layer, it is preferable to use a multi-manifold casting die.

<Physical properties of cellulose ester film>
The moisture permeability of the cellulose ester film according to the present invention, 40 ° C., preferably 10~1200g ^/ m 2 · 24h at 90% RH, preferably more ^{20~1000g / m 2 · 24h, 20~850g} / m 2 · 24h Is particularly preferred. The moisture permeability can be measured according to the method described in JIS Z 0208.

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

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

<< Polarizing plate, liquid crystal display >>
Since the brightness enhancement film of the present invention has a structure in which a cholesteric liquid crystal layer is provided on a cellulose ester film which is a λ / 4 wavelength plate, circularly polarized light selectively transmitted by the cholesteric liquid crystal layer is transmitted by the λ / 4 wavelength plate. It can be converted to linearly polarized light.

  Therefore, by allowing the converted linearly polarized light to enter the polarizing plate as it is with the polarization axis aligned, it is possible to efficiently transmit the polarized light while suppressing absorption loss due to the polarizing plate. Further, in the present invention, since the λ / 4 wavelength plate is a cellulose ester film, it is excellent in suitability for saponification treatment, and therefore has an advantage that it can be directly bonded to the following ordinary polyvinyl alcohol linearly polarizing film. Therefore, apart from a mode in which a brightness enhancement film is bonded to a normal polarizing plate via an adhesive layer or the like, a brightness enhancement integrated polarizing plate can be easily prepared, and a further thinning is possible.

<Linear polarizing film>
The linear polarizing film is not limited as long as it is an absorption linear polarizing film, and various known forms can be applied. In general, a film made of a hydrophilic polymer such as polyvinyl alcohol is treated with a dichroic dye such as iodine and stretched (generally called a dichroic polarizer), or polyvinyl chloride. In addition to a polarizing film formed by processing a plastic film and orienting a polyene, the polarizing film covered with a sealing film and protected can be used.

<Configuration of circularly polarizing film>
The cross-sectional structure of the circularly-polarizing film which concerns on this invention is shown with a figure. 7 to 9 are schematic views of the embodiment of the present invention, but the present invention is not limited to this.

  FIG. 7 shows that the surface of the brightness enhancement film of the present invention on the cellulose ester film side is attached to a normal polarizing plate (TAC (cellulose triacetate) / polarizer / TAC) using an adhesive or an adhesive. It is a combined circularly polarizing plate. In this case, a commercially available polarizing plate can be used as it is.

  FIG. 8 is a diagram showing one brightness enhancement film (λ / 4) according to the present invention, one conventional retardation film (λ / 2) formed only by oblique stretching, and a normal linear polarizing plate. It is a circularly polarizing plate bonded at such an axial angle.

  FIG. 9 shows a circularly polarizing plate that is laminated and bonded together with a surface of the brightness enhancement film of the present invention on the cellulose ester film side and another polarizing plate protective film with an absorption linear polarizer interposed therebetween.

  In FIG. 9, another polarizing plate protective film can be bonded to the other surface of the linearly polarizing film in which the brightness enhancement film of the present invention is disposed on one side. For example, a commercially available cellulose ester film (for example, Konica Minoltak KC8UX, KC4UX, KC5UX, KC8UCR3, KC8UCR4, KC8UCR5, KC8UY, KC4UY, KC12UR, KC4UE, KC8UE, KC8UY-HA, KC8UY-HA, KC8UY-C8 -RHA-NC, KC4UXW-RHA-NC, manufactured by Konica Minolta Opto Co., Ltd.) are preferably used.

<Liquid crystal display device>
By using the polarizing plate having the brightness enhancement film of the present invention for a liquid crystal display device bonded to at least one surface of a liquid crystal cell, the brightness can be improved and the liquid crystal display device of the present invention having excellent visibility is manufactured. be able to. The polarizing plate protective film of the present invention is a reflective, transmissive, transflective LCD or TN type, STN type, OCB type, HAN type, VA type (PVA type, MVA type), IPS type LCD etc. Are preferably used.

  FIG. 10 is a preferred example of a polarizing plate to which the brightness enhancement film of the present invention is bonded, and a liquid crystal display device using the polarizing plate.

  In the figure, light is incident on the brightness enhancement film of the present invention from the lower part of the liquid crystal display device through an edge type backlight (cold cathode tube), a reflection plate, a light guide plate, and a light diffusion plate, and selectively transmitted through a cholesteric liquid crystal layer. The circularly polarized light is converted into linearly polarized light by a cellulose ester film which is a λ / 4 wavelength plate, and led to a liquid crystal cell through a dichroic polarizer and a polarizing plate protective film.

  The direction of circular rotation of the liquid crystal spiral in the cholesteric liquid crystal layer coincides with the direction of circular polarization, and circularly polarized light whose wavelength is the helical pitch of the liquid crystal is reflected. Therefore, the reflected circularly polarized light can be reused by the reflector. A highly efficient polarization function is possible.

  The arrangement position of the polarizing plate in the liquid crystal display device is not particularly limited and can be arranged on the viewing side, but from the viewpoint of avoiding visual obstruction based on backscattering by the scattering polarizing plate, the backlight side of the liquid crystal panel It is preferable to arrange as a polarizing plate.

  Moreover, since the brightness enhancement film of the present invention also has a light scattering effect, it is possible to omit the light diffusing plate, which can contribute to reduction of members and thinning of the film.

  The backlight of the liquid crystal display device of the present invention is not particularly limited, and a flat fluorescent lamp, a flat LED lamp, an organic EL element substrate, or the like can be used instead of the cold cathode tube.

  In addition, the retardation value of the polarizing plate protective film used on the opposite side of the dichroic polarizer of the brightness enhancement film of the present invention, for example, using the polymer X and polymer Y, Ro and Rth are 0 nm ≦ Ro By adjusting the range to ≦ 2 nm and −15 nm ≦ Rth ≦ 15 nm and using the adjusted cellulose ester film, an IPS mode liquid crystal display device with excellent visibility and an expanded viewing angle can be produced. it can.

  In this manner, a liquid crystal display device having a high front contrast and a high front contrast can be obtained even when the screen is a large-screen liquid crystal display device having a screen size of 30 or more.

  Hereinafter, although an example is given and the present invention is explained, the present invention is not limited to these.

Example 1
<< Production of cellulose ester film >>
(Preparation of cellulose ester film 1)
<Fine particle dispersion>
Fine particles 11 parts by weight Ethanol 89 parts by weight The above was stirred and mixed with a dissolver for 50 minutes, and then dispersed with Manton Gorin.

<Fine particle additive solution>
The following cellulose acetate propionate was added to a dissolution tank containing methylene chloride and heated to completely dissolve, and this was then added to Azumi Filter Paper No. Filtered using 244. The fine particle dispersion was slowly added thereto while sufficiently stirring the filtered cellulose ester solution. Further, the particles were dispersed by an attritor so that the secondary particles had a predetermined particle size. This was filtered through Finemet NF manufactured by Nippon Seisen Co., Ltd. to prepare a fine particle additive solution.

Methylene chloride 99 parts by weight Cellulose acetate propionate (acetyl group substitution degree 1.65, propionyl group substitution degree 0.8, number average molecular weight 80000, weight average molecular weight 220,000) 4 parts by weight Fine particle dispersion 11 parts by weight A dope solution was prepared. First, methylene chloride and ethanol were added to the pressure dissolution tank. The following cellulose acetate propionate was added to a pressurized dissolution tank containing a solvent while stirring. This was heated and stirred to completely dissolve, and a plasticizer and an ultraviolet absorber were further added and dissolved. This was designated as Azumi Filter Paper No. The main dope solution was prepared by filtration using 244.

  In addition to adding 100 parts by mass of the main dope solution and 2 parts by mass of the fine particle additive solution, mix thoroughly with an in-line mixer (Toray static type in-pipe mixer Hi-Mixer, SWJ), and then use a belt casting apparatus to adjust the width. It was cast uniformly on a 2 m stainless steel band support. On the stainless steel band support, the solvent was evaporated until the residual solvent amount became 110%, and the stainless steel band support was peeled off. Thereafter, using the oblique stretching apparatus (oblique stretching apparatus A: FIG. 11) described in JP-A-2007-203556, the slow axis forms 45 ° with the film width direction at a temperature of 170 ° C. and a magnification of 1.5 times. In the same manner, the film was stretched in an oblique direction and dried to obtain a cellulose ester film 1 having a film thickness of 80 μm.

<Composition of main dope solution>
Methylene chloride 300 parts by mass Ethanol 57 parts by mass Cellulose acetate propionate (acetyl group substitution degree 0.8, propionyl group substitution degree 1.65, number average molecular weight 80000, weight average molecular weight 220,000) 100 parts by mass Acrylic polymer C 5 Mass parts Sugar ester compound exemplified compound 3 10 parts by mass Plasticizer (a), (b), (c) 1: 1: 1 mass ratio 0.5 parts by mass Trimethylolpropane tris (3,4,5-trimethoxy Benzoate)
1 part by mass

  The acrylic polymer was bulk polymerized by the polymerization method described in JP-A No. 2000-128911.

(Preparation of cellulose ester film 2)
From the cellulose ester film 1, the stretching apparatus is changed to the apparatus described in JP-A 2003-340916, Example-1 (oblique stretching apparatus B: FIG. 12), and the slow axis is set at a temperature of 170 ° C. and a magnification of 1.5 times. Was stretched in an oblique direction so as to form 45 ° with the film width direction to produce a long cellulose ester film 2.

(Preparation of cellulose ester film 3)
The cellulose ester film 1 is changed to a stretching apparatus (oblique stretching apparatus C) shown in FIGS. 2 to 5 and stretched 1.1 times in the longitudinal direction at a temperature of 140 ° C., and then a temperature of 170 ° C. and a magnification of 1.5. A long cellulose ester film 3 was produced by stretching in an oblique direction so that the slow axis was 45 ° with the film width direction.

(Preparation of cellulose ester film 4)
For the cellulose ester film 3, except that the oblique stretching apparatus C was used, the acrylic polymer was removed, and trimethylolpropane tris (3,4,5-trimethoxybenzoate) was changed to 5.5 parts by mass. Similarly, a long cellulose ester film 4 was produced.

(Preparation of cellulose ester film 5)
Except for the acrylic polymer and the sugar ester compound, the length of the cellulose ester film 3 was the same except that the total amount of the plasticizers (a), (b) and (c) was changed to 5.5 parts by mass. A cellulose ester film 5 was prepared.

(Preparation of cellulose ester film 6)
A long cellulose ester film 6 was produced in the same manner except that the oblique polymer stretching apparatus C was used for the cellulose ester film 3 and the acrylic polymer was changed as shown in Table 2.

(Preparation of cellulose ester film 7)
(Pellet preparation)
Cellulose acetate propionate (acetyl group substitution degree 1.23, propionyl group substitution degree 1.31, number average molecular weight 75000) 100 parts by mass Acrylic polymer C 5.5 parts by mass Sugar ester compound exemplified compound 3 5.5 parts by mass Part trimethylolpropane tris (3,4,5-trimethoxybenzoate)
1 part by mass IRGANOX-1010 (manufactured by Ciba Japan) 1 part by mass Sumitizer GP (manufactured by Sumitomo Chemical Co., Ltd.) 0.5 part by mass V-type mixing in which 0.05 part by mass of silica particles is added to the above material and nitrogen gas is enclosed After mixing with a machine for 30 minutes, the mixture was melted at 240 ° C. using a twin screw extruder (PCM30, manufactured by Ikegai Co., Ltd.) equipped with a strand die to produce cylindrical pellets having a length of 4 mm and a diameter of 3 mm. At this time, the shear rate was set to 25 (mm / s). The obtained pellets were dried at 100 ° C. for 5 hours to have a water content of 100 ppm and fed to a single screw extruder (GT-50; manufactured by Plastic Engineering Laboratory Co., Ltd.) equipped with a 300 mm wide T die. And T-die was set to 250 degreeC and it formed into a film. The surface of the T die was subjected to hard chrome plating and finished with a mirror finish with a surface roughness of 0.1S. The film from the T-die was dropped onto a first cooling roll with a chrome-plated mirror surface adjusted to 110 ° C.

  The film in close contact with the first cooling roll was pressed with an elastic touch roll after being transported around the circumference of the first cooling roll by a central angle of 10 °. At this time, it contacted with the pressure of 4 N / mm with respect to the whole width 250mm of a film. After the pressed film is brought into contact with the circumferential portion of the first cooling roll having a central angle of 150 °, a total of three cooling films, ie, a second cooling roll (temperature 110 ° C.) and a third cooling roll (temperature 80 ° C.) are cooled. The film was sequentially circumscribed on the roll, cooled and solidified to form a film, and peeled off by a peeling roll. Then, using the apparatus described in Example 1 of JP-A-2007-203556 (oblique stretching apparatus A: FIG. 11), the slow axis forms 45 ° with the film width direction at a temperature of 170 ° C. and a magnification of 2 times. In this manner, the film was stretched in an oblique direction and dried to produce a long cellulose ester film 7 having a film thickness of 40 μm.

(Production of cellulose ester films 8 to 19)
Furthermore, as shown in Table 2, cellulose ester substitution degree, acrylic polymer, sugar ester compound, casting method, oblique stretching apparatus (oblique stretching apparatus B, oblique stretching apparatus C), stretching angle, stretching temperature, Except having changed the draw ratio, it carried out similarly to the cellulose ester film 7, and produced the long cellulose ester films 8-19.

(Preparation of cellulose ester film 20)
The resin was made into triacetyl cellulose having an ester substitution degree of 2.85, and the production of a long cellulose ester film 20 was aimed in the same manner as the cellulose ester film 3, but the desired cellulose ester was broken because it was broken when stretched. A film could not be produced.

(Production of cellulose ester film 21)
The resin was made into triacetyl cellulose having an ester substitution degree of 2.5, and the production of 21 was made in the same manner as the cellulose ester film 3, but the cellulose ester film was broken when it was stretched. As in Example 20, a desired cellulose ester film could not be produced.

(Preparation of resin film 22)
A long resin film 22 having a film thickness of 100 μm was produced by forming a resin by zeonore (manufactured by Nippon Zeon Co., Ltd.) by melt casting, and stretching it obliquely using the oblique stretching apparatus A.

(Preparation of resin film 23)
Dissolve 20 parts by weight of polycarbonate having a bisphenol A skeleton in 80 parts by weight of methylene chloride, form a film in the same manner as the cellulose ester film 1, and stretch the film obliquely using the oblique stretching apparatus A to form a film thickness of 120 μm. A long resin film 23 was prepared.

(Preparation of cellulose ester film 24)
The resin was made into cellulose acetate propionate having a substitution degree of acetyl group of 0.35 and a substitution degree of propionyl group of 2.1, aiming to produce 24 long cellulose ester films in the same manner as the cellulose ester film 3, but stretched. In this case, the desired cellulose ester film could not be produced in the same manner as the cellulose ester film 20 because it was broken.

<Evaluation>
The following evaluation was implemented using the produced said cellulose-ester film and resin film.

(Difference in scattered light intensity)
Goniophotometer model: GP-1-3D, manufactured by Optec Corporation (light source: 12V50W halogen bulb, light receiving part: photomultiplier tube (Photomaru Hamamatsu Photonics R636-10)).

  The amount of light at the time of measurement was corrected with the amount of light at θ = 180 ° (photomal light receiving sensitivity: −185 V), and the measured value at this amount of light was taken as the scattered light intensity.

  The sample was measured by fixing the slow axis of the film horizontally and vertically on the sample stage, and the difference in scattered light intensity was determined.

(Measurement of retardation Ro and Rth)
A 35 mm × 35 mm sample was cut out from the obtained film, conditioned at 25 ° C. and 55% RH for 2 hours, and measured with an automatic birefringence meter (KOBRA21DH, Oji Scientific Co., Ltd.) from the vertical direction at 590 nm and the film. It calculated from the extrapolation value of the retardation value measured similarly, inclining a surface.

  Further, the same measurement was performed at wavelengths of 480 nm and 650 nm, and wavelength dispersion Ro (480) / Ro (650) was calculated.

In-plane retardation Ro = (nx−ny) × d (nm)
Thickness direction retardation Rth = ((nx + ny) / 2−nz) × d (nm)
(In the formula, 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, and d represents the thickness (nm) of the optical film.)
(Haze)
Measurement was performed according to JIS K-6714 using a haze meter 1001DP type, manufactured by Nippon Denshoku Industries Co., Ltd.

  Tables 2 and 3 show the configurations and evaluation results of the cellulose ester film and the resin film.

  It can be seen that the cellulose ester film of the present invention is an optical film having a desired retardation value and wavelength dispersibility by oblique stretching, a difference in scattered light intensity, a low haze, and excellent transparency.

  Subsequently, the brightness improvement film was produced by apply | coating a cholesteric liquid crystal on the produced said cellulose-ester film films 1-19 and the resin films 22 and 23. FIG.

Each cellulose ester film and resin film have a polyimide-treated surface (thickness: 0.1 μm) with 96 parts by mass of BASF LC242 as a polymerizable mesogenic compound (a) and BASF LC756 as a polymerizable chiral agent (b). As a photoisomerizable material (c), a methyl ethyl ketone solution (30 mass% solid content) of a mixture consisting of 5 parts by mass of stilbene was prepared. After the solution was cast and dried at 100 ° C. for 2 minutes to remove the solvent, UV irradiation at 5 mW / cm ² for 3 minutes and heating at 100 ° C. for 10 seconds were performed, resulting in a cholesteric film having a thickness of 8 μm. The intended brightness enhancement films 1 to 19, 22, and 23 having a liquid crystal layer were obtained. In addition, in the resin films 22 and 23, a repellency failure was observed on the coated surface, and there was a problem in adhesion such that the edges were slightly peeled off.

  Next, a polarizing plate and a liquid crystal display device were produced using the brightness enhancement films 1 to 19, 22 and 23 produced above.

(Preparation of polarizing plate)
A 120 μm-thick polyvinyl alcohol long film was uniaxially stretched in the MD direction (temperature: 110 ° C., stretch ratio: 5 times). This was immersed in an aqueous solution composed of 0.075 g of iodine, 5 g of potassium iodide and 100 g of water for 60 seconds, and then immersed in an aqueous solution of 68 ° C. composed of 6 g of potassium iodide, 7.5 g of boric acid and 100 g of water. This was washed with water and dried to obtain a long polarizing film (polarizer).

  Next, in accordance with the following steps 1 to 5, a polarizer, a brightness enhancement film 1-19, and a long Konica Minolta Tack KC4UY (manufactured by Konica Minolta Opto Co., Ltd.) are pasted as a polarizing plate protective film across the polarizer. A laminated polarizing plate was produced. In that case, it bonded so that the longitudinal direction of each of a polarizer, a brightness enhancement film, and KC4UY might be aligned.

  Step 1: Brightness-improving films 1-19 and cellulose ester film KC4UY, which are dipped in a 2 mol / L sodium hydroxide solution at 60 ° C. for 90 seconds, then washed with water and dried to saponify the side to be bonded to the polarizer. Obtained.

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

  Step 3: Excess adhesive adhered to the polarizer in Step 2 was lightly wiped off and placed on the brightness enhancement film and KC4UY processed in Step 1.

Step 4: The brightness enhancement film, the polarizer, and the back side KC4UY laminated in Step 3 were bonded at a pressure of 20 to 30 N / cm ² and a conveyance speed of about 2 m / min.

  Process 5: The sample which bonded together the polarizer produced in the process 4, the brightness improvement film, and the back side KC4UY in the 80 degreeC dryer was dried for 2 minutes, and the polarizing plates 1-19 were produced.

  The brightness improvement films 22 and 23 used the acrylic adhesive, and were bonded to the polarizer side to which KC4UY was bonded, and the polarizing plates 22 and 23 were produced.

(Production of liquid crystal display device)
In order to confirm the luminance improvement effect, a liquid crystal panel for measuring the luminance was produced as follows, and the characteristics as a liquid crystal display device were evaluated.

  The polarizing plate on the backlight side of the 40-inch display KLV-40J3000 made by SONY, which is a vertical alignment type liquid crystal display device, was peeled off in advance, and the above-prepared polarizing plates 1 to 19, 22 and 23 were respectively attached to the liquid crystal cell. It bonded on the glass surface of the backlight side.

  At that time, liquid crystal display devices 1 to 19, 22, and 23 were prepared so that the polarizing film was bonded to the backlight side of the retardation film of the present invention.

  The liquid crystal display device was measured for luminance, and the luminance improvement effect was evaluated. The results are shown in Table 4.

<Evaluation>
(Evaluation of brightness)
The brightness improvement degree was measured using the liquid crystal display device which bonded the brightness improvement film of this invention using the evaluation system of the brightness improvement film which consists of a structure shown in FIG.

  The measurement light quantity was set to 100% with an integrating sphere with no brightness enhancement film inserted, and measurement was performed under the same conditions with the brightness enhancement film inserted.

(Evaluation of front contrast)
The measurement was performed after the backlight of each liquid crystal display device was lit continuously for one week in an environment of 23 ° C. and 55% RH. For measurement, EZ-Contrast 160D manufactured by ELDIM was used to measure the luminance from the normal direction of the display screen of white display and black display with a liquid crystal display device, and the ratio was defined as the front contrast.

  Front contrast = (brightness of white display measured from normal direction of display device) / (brightness of black display measured from normal direction of display device)

  From the results in Table 4, it is clear that the liquid crystal display devices 1 to 17 using the brightness enhancement film of the present invention are liquid crystal display devices with improved brightness, excellent energy saving, and excellent front contrast.

Example 2
A surface treated with polyvinyl alcohol rubbing is formed on a triacetyl cellulose base material, and 96 parts by mass of BA242 LC242 is used as the polymerizable mesogen compound (a) used in Example 1, and BASF is used as the polymerizable chiral agent (b). After casting a methyl ethyl ketone solution (30 mass% solid content) of a mixture consisting of 4 parts by mass of LC756 and 5 parts by mass of stilbene as a photoisomerizable material (c), the solvent was removed by drying at 100 ° C. for 2 minutes. Then, ultraviolet ray irradiation at 5 mW / cm ² for 3 minutes and heating at 100 ° C. for 10 seconds to form a liquid crystal layer, which are formed into the cellulose ester films 1 to 19 and resin films 22 and 23 produced in Example 1. The brightness enhancement film which has a cholesteric liquid crystal layer was obtained by bonding to.

  When the same evaluation as Example 1 was performed using the obtained brightness enhancement film, the sample using the cellulose ester films 1 to 17 of the present invention was a brightness enhancement film excellent in haze, brightness enhancement, and front contrast. , A polarizing plate, and a liquid crystal display device.

It is the schematic of a goniophotometer. It is one schematic of the extending | stretching apparatus of this invention. It is one schematic of the extending | stretching apparatus of this invention. It is one schematic of the extending | stretching apparatus of this invention. It is one schematic of the extending | stretching apparatus of this invention. It is the schematic of the melt casting film forming apparatus of this invention. It is one of the embodiments of the circularly polarizing plate of the present invention. It is one of the embodiments of the circularly polarizing plate of the present invention. It is one of the embodiments of the circularly polarizing plate of the present invention. It is an example of the liquid crystal display device of this invention. It is the schematic of the extending | stretching apparatus (stretching apparatus A) used for the Example. It is the schematic of the extending | stretching apparatus (stretching apparatus B) used for the Example. It is a schematic diagram of the apparatus which verifies the brightness improvement effect of a brightness improvement film.

Explanation of symbols

G1 Light source lamp G2 Spectrometer G3 Sample stage (stage)
G5 light-receiving portion G6 Sample pressing spring G7 Angle indexing rotary table θ Angle formed by the normal direction of the light source and the direction connecting the observation point of the sample and the integrating sphere 1 Stretching device 2 Film 3 Film supply device 4 Longitudinal stretching device 5 Intermediate Conveying device 6 Longitudinal stretching step 7 Oblique stretching device 8 Oblique stretching heating device 9 Oblique stretching step 10 Winding device 11 Raw material reel 12 Reference roll 13 Nip roll 14 Hot air duct 15 Ratio roll 16 Nip roll 17 Stretch chain 18 Hot air duct 19 Tension roll 20 Winding device E1 Direction parallel to transport direction (film forming direction) E2 Direction inclined by angle α with respect to transport direction (film forming direction) 21 Base 22 Arm 23 Clip 24 Sprocket 25 Slide shaft 26 Positioning member 27 Guide 28 Guide 101 Extruder 10 Filter 103 static mixer 104 die (including thickness adjusting means)
DESCRIPTION OF SYMBOLS 105 Touch roll 106 1st cooling roll 107 2nd cooling roll 108 Peeling roll 109 Dancer roll 110 Stretching machine 111 Slitter 112 Thickness measuring means 113 Embossing ring and back roll 114 Winding machine 115 Rolled film 201 Film 210 Constant temperature chamber 211 Rail 212 Grasping means 213 Boundary between preheating zone and stretching zone 214 Boundary between stretching zone and fixed zone 221 Pulling roll 222 Winding roll 301 Film 302 Preheating zone 303 Heating stretching zone 304 Cooling zone 305 Stretched films 306, 307 Screw 308, 381 Clip 309, 391 Belt

Claims (6)

It has a slow axis in the range of 10 ° to 80 ° with respect to the longitudinal direction of the film, the in-plane retardation in the wavelength 550 nm measurement is 120 ≦ Ro ≦ 150 (nm), and the following formulas (i) and (ii) A brightness enhancement film, which is a laminate in which a cholesteric liquid crystal layer is provided directly or via another layer on a cellulose ester film satisfying the above.
In-plane retardation Ro = (nx−ny) × d (nm)
(In the formula, 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, and d represents the thickness (nm) of the optical film.)
Formula (i) 2.1 ≦ X + Y ≦ 2.8
Formula (ii) 0.5 ≦ Y ≦ 1.65
(In the formula, X represents the substitution degree of acetyl group, Y represents the substitution degree of propionyl group or butyryl group, and X + Y represents the total substitution degree of acyl group.) The cellulose ester film is a (meth) acrylic polymer, and an ester compound in which at least one of a pyranose structure or a furanose structure is 1 to 12, and all or part of the OH groups of the structure are esterified. The brightness enhancement film according to claim 1, which is a cellulose ester film containing at least one kind. When measuring the film scattered light intensity of the incident light 90 ° of the scattered light profile of the goniophotometer with the cellulose ester film, the scattered light intensity at a position of 130 ° from the light source is measured, and the film is placed on the sample stage of the film. 3. The brightness enhancement film according to claim 1, wherein a difference in scattered light intensity between the case where the installation direction is aligned with the slow axis and the direction perpendicular thereto is 0.05 or less. The in-plane retardation in the wavelength 480nm and 650nm measurement of the said cellulose-ester film is 0.78 <= Ro (480) / Ro (650) <= 0.96, The any one of Claims 1-3 characterized by the above-mentioned. Item 1. The brightness enhancement film according to item 1. A polarizing plate comprising the brightness enhancement film according to claim 1 on at least one surface. 6. A liquid crystal display device comprising the polarizing plate according to claim 5 on a backlight surface side of a liquid crystal cell.

Images