JP2010042676A - Method of manufacturing cellulose acylate film, cellulose acylate film and polarizing plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarizing plate having excellent stability with time even under a severe heat and humidity condition. <P>SOLUTION: The cellulose acylate has a glucopyranose ring in which one of hydroxides in 2-, 3- and 6-position is substituted by acylate. The method of manufacturing the cellulose acylate film includes a casting step of: casting the cellulose acylate in which substitution degree (S6) of hydroxide in 6-position by acyl is ≥0.87 and ≤0.97 and a polymer solution containing ≤35 mass% plasticizer on a base material to form a web; a heat treatment step of: stripping the web formed in the casting step from the base material and after that, heat treating the web in which a residual solvent is ≥5 mass% and ≤30 mass% at ≥160°C and ≤200°C for ≥1 min and ≤120 min. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polarizing plate having excellent temporal stability even under severe wet heat conditions.

  In general, a polarizing plate has a protective film bonded to both sides or one side of a polarizing layer having polarizing ability via an adhesive layer. As a material for the polarizing layer, polyvinyl alcohol (hereinafter referred to as PVA) is mainly used. After the PVA film is uniaxially stretched, it is dyed with iodine or a dichroic dye or dyed and then stretched. A polarizing film for a polarizing layer is formed by crosslinking with a compound. As the protective film, cellulose triacetate (TAC) is mainly used because it is optically transparent and has a small birefringence.

However, if such a polarizing plate is left in a high-temperature and high-humidity atmosphere, there has been a problem that the polarization characteristics deteriorate over time. Such deterioration with the lapse of time has conventionally been devised to reduce the moisture permeability coefficient (moisture permeability) because water has entered the polarizing plate. For example, in patent document 1 (Unexamined-Japanese-Patent No. 2002-146044), water permeability is 50-250 g / m < ² > * day (80 +/- 5 degreeC, 90 by adding a hydrophobic plasticizer in a cellulose-ester film. ± 10% RH), the effect of improving the polarization performance is confirmed visually. Also in Patent Document 2 (Japanese Patent Laid-Open No. 2002-303724), by using a cellulose ester film and an olefin film in combination, the moisture permeability coefficient is reduced to 500 g / m ² · day or less, and it is confirmed visually that the polarization ability is prevented from lowering. ing. However, it was not possible to achieve sufficient visual observation only by reducing the moisture permeability coefficient as in these polarizing films. That is, when a polarizing plate is incorporated in a liquid crystal display device and used, the absorbance when the polarizing plate is orthogonal (orthogonal absorbance) is required to be 99.8% or more. It is difficult to visually confirm the difference, and such high optical performance has not been achieved even if these prior patent documents are re-examined (by the way, it is 99.0% that the difference can be clearly recognized visually). This is the case) Furthermore, these prior patent documents all have a problem that the hue shifts with time and yellowing occurs. This was because the moisture permeability was too low.

In Patent Document 3 (Japanese Patent Application Laid-Open No. 2002-14230), a protective film having a relatively high moisture permeability of 10 to 1000 g / m ² · day at 40 ° C. and 90% RH is used. That is, since water-based glue is used as an adhesive for bonding the protective film and the polarizing layer, moisture remains in the polarizing layer unless moisture permeability is high to some extent, and this deteriorates the polarizing performance. Compared to patents, those with higher moisture permeability are used for the protective film. As a result, the occurrence of yellowishness expressed in the above two patent documents was suppressed. However, more than these patent documents, the polarization ability deterioration with wet heat aging occurred. That is, there is almost no decrease in the orthogonal absorbance under mild conditions such as 40 ° C. and 90% RH, but it is remarkable over time at a high temperature and high humidity of 60 ° C. or more and 90% RH or more, and the orthogonal absorbance after 1000 hours. Decreased to 95% or less.
Thus, it has been difficult to satisfy both the polarization ability (orthogonal polarization degree) and yellowness under high temperature and high humidity of 60 ° C. or higher and 90% RH or higher only by controlling the moisture permeability coefficient.

JP 2002-146044 A JP 2002-303724 A Japanese Patent Laid-Open No. 2002-14230

  An object of the present invention is to provide a polarizing plate excellent in durability even under extremely severe wet heat conditions, specifically, a polarizing plate having no change in polarization ability (orthogonal transmittance) and no yellowing.

1. A cellulose acylate in which at least one of the hydroxyl groups of the 2, 3, 6-position of the glucopyranose ring is substituted with an acylate group, and the substitution degree (S6) of the 6-position hydroxyl group with an acyl group is 0.87 or more. A casting step of casting a cellulose acylate of 97 or less and a polymer solution containing 35% by mass or less of a plasticizer on a substrate to form a web;
A heat treatment step in which after the web formed by the casting step is peeled from the base material, a heat treatment at 160 ° C. or more and 200 ° C. or less is performed for 1 minute or more and 120 minutes or less in a region where the residual solvent is 5% by mass or more and 30% by mass or less; A method for producing a cellulose acylate film.
2. A cellulose acylate film produced by the production method described in 1 above.
3. A polarizing plate using the cellulose acylate fill described in 2 above as a protective film for a polarizing plate.

  The polarizing plate of the present invention is excellent in durability even under extremely severe wet heat conditions.

In the present invention, the above-described polarization ability (orthogonal transmittance) and yellowness are both achieved as follows.
In conventional patent documents and the like, it is described that the polarization ability is reduced by water entering the polarizing layer, but the present inventor does not directly reduce the polarization ability, but in the following process. It was found that the polarization ability was reduced.
That is, the polarizing layer orients iodine in the gap between the stretched and oriented polyvinyl alcohol (PVA) to provide the polarizing ability. Further, the polarizing layer is obtained by crosslinking PVA with boric acid so that the orientation of PVA and iodine is not disturbed. Conventionally, it has been thought that water that has entered the polarizing layer acts on the element as if it has a polarizing ability to lower the polarizing ability, but the present inventors have cut the crosslinking between boric acid and PVA, It was also found that the cut boric acid was dissolved in water and diffused into the protective film, thereby being discharged out of the polarizing plate. In the present invention, a layer exhibiting polarizing ability (a layer obtained by stretching a pigment and polyvinyl alcohol) is called a polarizing layer, and a polarizing plate is a laminate of at least one protective film (cellulose acylate film). Distinguish between calls.
Therefore, the present invention is characterized by not only lowering the moisture permeability coefficient but also lowering the diffusion rate of boric acid. As a result, it was possible to prevent a decrease in polarizing ability even at relatively high humidity. Furthermore, the occurrence of yellowishness that is likely to occur in a region having a small moisture permeability coefficient is suppressed, thereby achieving compatibility with polarization ability.

This yellowness seems to occur as follows.
1. The compound in the polarizing layer decomposes over time. This has a yellowish color.
2. The decomposition product diffuses from the polarizing layer into the protective film and is discharged out of the system. However, when the amount of diffusion is small, decomposition products remain in the polarizing layer and become yellowish.
These degradation products are as polar as water, and films that are difficult to pass water are considered to be difficult to pass these degradation products. Therefore, in the present invention, the moisture permeability coefficient is 500 g / m ² · day to 1500 g / m ² · day, more preferably 700 g / m ² · day to 1400 g / m ² · day, more preferably 900 g / m. ² · day to 1300 g / m ² · day or less. The diffusion coefficient of boric acid is preferably 0 mmol / m ² · day · μm or more and 0.23 mmol / m ² · day · μm or less, more preferably 0 mmol / m ² · day · μm or more at 60 ° C. and 95% RH. 20 mmol / ^{m 2} · day · [mu] m or less, more preferably not more than 0 mmol / ^{m 2} · day · [mu] m or more 0.18 mmol / ^{m 2} · day · [mu] m. The content of boric acid, 2mmol / ^{m 2} · μm or more 15mmol / ^{m 2} · μm or less, more preferably 2.5mmol / ^{m 2} · μm or more 10mmol / ^{m 2} · μm or less, more preferably 3mmol / ^{m 2} · μm The above is 8 mmol / m ² · μm or less. The diffusion coefficient of boric acid as used herein refers to the amount of boric acid that has passed through the protective film through the protective film per unit area (m ² ), and further divided by time (days) per unit time. And is normalized by dividing by the thickness (μm) of the polarizing layer.

  Furthermore, in the present invention, the change in moisture permeability coefficient and diffusion coefficient of boric acid over time with wet heat (1000 hours in an atmosphere of 60 ° C. and 95% RH) is preferably 0% or more and 30% or less, more preferably 0. % Or less and 20% or less, more preferably 0% or more and 10% or less. This is the difference between before and after wet heat aging divided by the value before wet heat aging and expressed as a percentage. Thereby, higher polarization ability can be achieved. That is, it is not sufficient that these initial values are small, and the protective film itself is liable to deteriorate at high temperatures and high humidity, which tends to increase the moisture permeability coefficient and the diffusion coefficient of boric acid. Therefore, it is necessary to reduce the change in the moisture permeability coefficient and the diffusion coefficient of boric acid after aging with wet heat in order to achieve higher polarization performance. Furthermore, since the change with time of these protective films is caused by the decomposition of the protective film, this decomposed product causes an increase in yellowness. Therefore, this has the effect of significantly suppressing yellowing.

Such a polarizing plate was achieved by the following method.
(1) Diffusion coefficient of boric acid In order to reduce the diffusion coefficient of boric acid, it is effective to adjust the hydroxyl group of the cellulose acylate film. Cellulose acylate is obtained by substituting the hydroxyl groups at positions 2, 3, and 6 of the glucopyranose ring with an acylate group. If all three hydroxyl groups are substituted, the solubility is lowered, so that solution casting cannot be performed. For this reason, the degree of substitution is generally 2.7 to 2.9. For this reason, 0.1 to 0.3 hydroxyl groups are attached to each glucopyranose ring, which promotes the diffusion of boric acid. That is, since boric acid forms a weak bond with the hydroxyl group of cellulose acylate, it is presumed that it propagates and diffuses on the hydroxyl group while repeating adsorption and desorption to the hydroxyl group.
Of these three hydroxyl groups, the hydroxyl group at the 6-position is the most active. Since the hydroxyl group at the 6-position is bonded from the glucopyranose ring via a methylene group, it has high mobility and high activity, and it is easy to increase the diffusion coefficient of boric acid. On the other hand, the hydroxyl groups at positions 2 and 3 are directly bonded to the glucopyranose ring, and the hydroxyl groups at positions 2 and 3 are hydrogen bonded to each other, so that the diffusion coefficient of boric acid is not so high.
Therefore, in the present invention, the point is to reduce the hydroxyl group at the 6-position, and the degree of substitution of the hydroxyl group at the 6-position with an acyl group (S6) is 0.87 or more and 0.97 or less, more preferably 0.88 or more. It is preferably 0.96 or less, more preferably 0.89 or more and 0.95 or less. Incidentally, the substitution rate of the normal 6-position hydroxyl group is 0.7 to 0.8. In order to achieve such a cellulose acylate having a high 6-position substitution rate, the following method is used.

  The basic principle of the cellulose acylate synthesis method is described in Mita et al., Wood Chemistry pages 180-190 (Kyoritsu Shuppan, 1968). A typical synthesis method is a liquid phase acetylation method using an acetic anhydride-acetic acid-sulfuric acid catalyst. Specifically, a cellulose raw material such as wood pulp is pretreated with an appropriate amount of an organic acid, and then it is esterified by adding it to a pre-cooled acylated mixture to complete cellulose acylate (2nd, 3rd and 6th positions). The total degree of acyl substitution is approximately 3.00). The acylated mixed solution generally contains an organic acid as a solvent, an anhydrous organic acid as an esterifying agent, and sulfuric acid as a catalyst. The organic anhydride is usually used in a stoichiometric excess over the sum of the cellulose that reacts with it and the water present in the system. After completion of the acylation reaction, a neutralizing agent (for example, calcium, magnesium, iron, aluminum or zinc) is used for hydrolysis of excess organic anhydride remaining in the system and neutralization of a part of the esterification catalyst. Of carbonate, acetate or oxide). Next, the obtained complete cellulose acylate is saponified and aged by keeping it at 50 to 90 ° C. in the presence of a small amount of acetylation reaction catalyst (generally, remaining sulfuric acid), and the desired acyl substitution degree and The cellulose acylate having a polymerization degree is changed. When the desired cellulose acylate is obtained, the catalyst remaining in the system is completely neutralized with the neutralizing agent as described above, or water or dilute sulfuric acid without neutralization. The cellulose acylate solution is charged into the inside (or water or dilute sulfuric acid is added into the cellulose acylate solution) to separate the cellulose acylate, and the cellulose acylate is obtained by washing and stabilizing treatment.

  In the usual cellulose acylate synthesis method, the acyl substitution degree at the 2-position or the 3-position is higher than the acyl substitution degree at the 6-position. Therefore, in order to obtain the cellulose acylate described in the present invention, it is necessary to specifically adjust the reaction conditions. As specific reaction conditions, it is preferable to reduce the amount of the sulfuric acid catalyst and lengthen (ripen) the acylation reaction time. When the amount of the sulfuric acid catalyst is large, the acylation reaction proceeds faster, but a sulfuric ester is formed between the cellulose and the cellulose according to the amount of the catalyst, and is released at the end of the reaction to form a residual hydroxyl group. Sulfate esters are more produced at the 6-position, which is highly reactive. Therefore, when there is much sulfuric acid catalyst, the acyl substitution degree of 6-position will become small. Therefore, in order to synthesize the cellulose acylate used in the present invention, it is necessary to extend the reaction time in order to reduce the amount of sulfuric acid catalyst as much as possible and compensate for the reduced reaction rate. In addition, control of the 2-position substitution degree and 3-position substitution degree in the present invention is also possible by changing the reaction conditions.

  Further, in order to reduce the diffusion coefficient of boric acid, it is important to reduce the free volume in the cellulose acylate film, that is, to reduce the gap between cellulose acylate molecules through which boric acid diffuses. Since the cellulose acylate film is formed by solution casting, in order to dry the solution more efficiently, it is rapidly cooled after being dried at a temperature higher than the glass transition temperature (Tg). That is, the free volume is large above Tg, but when cooled rapidly from this state, the volume drop cannot follow the temperature drop, resulting in a film with a large free volume. Such a film tends to have a large diffusion coefficient of boric acid. Therefore, in the present invention, in order to reduce this, the free volume is reduced by slow cooling after film formation, thereby reducing the diffusion of boric acid. Such cooling is particularly based on a cooling rate in the temperature range between Tg and Tg-30 ° C, and it is preferable to cool at a rate between 0.01 ° C / second and 1 ° C / second. Such slow cooling is adjusted so that a zone with a temperature gradient from Tg to Tg-30 ° C is created at the outlet of the drying zone after casting, and stays in this zone for 30 seconds or longer. This can be achieved by heat treatment. Such heat treatment may be continuously gradually cooled, or may be performed stepwise and discontinuously in two or more stages.

  Furthermore, the free volume in the cellulose acylate film can be reduced by increasing the crystal content of the film. Since the free volume is a gap between cellulose acylate molecules, when this moves, the gap increases and the free volume increases. In order to prevent this, it is effective to fix the molecules so that they do not move easily. For this purpose, it is preferable to form crystals in the cellulose acylate film. Since the formation of such crystals is efficiently formed by the residual solvent, heat treatment at 100 ° C. or higher and 200 ° C. or lower is performed for 1 minute or longer and 120 minutes or shorter in the region where the residual solvent amount is 5 mass% or more and 30 mass% or less. Is achieved. That is, it can be achieved by passing the dope through a hot zone having such a temperature immediately after casting the dope on the substrate.

Such a decrease in free volume of the cellulose acylate film can also suppress yellowing. That is, such heat treatment suppresses the diffusion of boric acid but does not significantly suppress the moisture permeability coefficient. If the moisture permeability is too small, the water remaining at the time of making the polarizing layer cannot be dissipated outside the system and remains in the polarizing layer. Iodine and PVA are easily decomposed and cause yellowing. Such a decrease in free volume suppresses the diffusion of boric acid, but does not suppress the diffusion of water, and allows it to permeate appropriately. This is probably because boric acid with a large molecular radius is largely suppressed by the decrease in free volume, whereas water molecules are small and the gap can be diffused even when the free volume is reduced. On the other hand, when a barrier material is dispersed or coated, water diffusion is also suppressed, so that yellowishness is likely to occur. Therefore, the moisture permeability coefficient is preferably not too small for the suppression of yellowing, and is preferably 500 g / m ² · day or more.

(2) Moisture permeability coefficient Decreasing the moisture permeability coefficient of the cellulose acylate film used for the protective film has an effect of suppressing the diffusion of boric acid to some extent, and it is preferable from the viewpoint of deterioration of the polarizing plate. As described above, the polarization deterioration cannot be completely suppressed, and in order to fundamentally reduce the deterioration, it is essential to reduce the diffusion of boric acid). On the other hand, if the moisture permeability coefficient is too small, the yellowness increases as described above. Therefore, the moisture permeability coefficient is 500 g / m ² · day to 1500 g / m ² · day, more preferably 600 g / m ² · day to 1400 g / m ² · day at 60 ° C and 90% RH, It is preferably 700 g / m ² · day or more and 1300 g / m ² · day or less, preferably in combination with the above-described suppression of boric acid diffusion.

In order to make the moisture permeability coefficient of the cellulose acylate film in the above range, the addition of a plasticizer is effective. As a plasticizer to be preferably added,
(I) As a phosphate ester plasticizer, triphenyl phosphate (TPP), biphenyl diphenyl phosphate (BDP), tricresyl phosphate (TCP), dioctyl phthalate (DOP), tributyl O-acetylcitrate (OACTB), Acetyl triethyl citrate, substituted phenyl phosphate esters described in JP-A-11-90946, etc.),
(Ii) As fatty acid ester plasticizers, (di) pentaerythritol esters described in JP-A No. 11-124445, glycerol esters described in JP-A No. 11-246704, JP-A No. 2000-63560 Diglycerol esters described in the above, citric acid esters described in JP-A No. 11-92574, and the like.
(Iii) As phthalate ester plasticizers, diethyl terephthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, butyl benzyl phthalate, dibenzyl phthalate, butyl phthalyl butyl glycolate, methyl Examples include phthalyl ethyl gluconate.
These plasticizers may be used alone or in combination of two or more. The addition amount of the plasticizer is 10 to 35% by mass or less, more preferably 12 to 30% by mass, and particularly preferably 14 to 25% by mass or less with respect to the cellulose acylate.

  Furthermore, in order to reduce the change of the moisture permeability coefficient of the cellulose acylate film over time with wet heat, it is effective to increase the amount of the surface plasticizer as the plasticizer distribution in the thickness direction. In other words, moisture sorbs on the surface of the protective film and then diffuses inside, so it is effective to make the vicinity of the surface more hydrophobic in order to reduce the amount of moisture sorbed on the surface. It is most susceptible to changes, and the plasticizer is volatilized or oxidized to become hydrophilic. For this reason, it is effective to increase the plastic material in the vicinity of the surface in advance.

Such plasticizer distribution can be achieved as follows. That is, a cellulose acylate film is formed by casting a liquid (dope) in which cellulose acylate, a plasticizer and the like are dissolved in a solvent at a high concentration onto a substrate such as a drum or a band, and drying the film. Accompanying the volatilizing solvent, it accumulates on the surface. The plasticizer concentrated on the surface in this way re-diffuses in accordance with the concentration gradient toward the inside, and the surface concentration decreases. However, a film in which the plasticizer is accumulated at a high concentration on the surface by making the plasticizer not moveable (residual solvent: 20% by mass or less) before starting diffusion into the inside (that is, by rapidly drying). Can be formed. For this, the dope is dried at a rate of 15% by mass / min., More preferably 20% by mass / min., More preferably 30% by mass / min. Is preferred. The drying speed here means the difference between the amount of solvent immediately after casting (mass ratio of the amount of solvent with respect to the total weight of the dope: mass%) and the amount of solvent (mass%) immediately after peeling. It is indicated by the value divided by time (minutes). In the present invention, the residual solvent amount at the time of stripping was 20% by mass.
Such rapid drying can be achieved by heating the substrate and increasing the temperature of the air blown over the substrate. The substrate temperature is preferably 40 ° C. to 80 ° C., more preferably 45 ° C. to 60 ° C., and the wind temperature is 70 ° C. to 100 ° C., more preferably 80 ° C. to 95 ° C.

The present invention will be described in detail while following the manufacturing process of the polarizing plate.
1. Cellulose acylate Preferred cellulose acylates of the present invention include the following materials. That is, it is preferable that the degree of substitution with the hydroxyl group at the 6-position of cellulose acylate (S6) is 0.87 or more and 0.95 or less. Those satisfying the following formulas (I) to (IV) are more preferable.
(I) 2.6 ≦ SA + SB ≦ 3.0
(II) 2.0 ≦ SA ≦ 3.0
(III) 0 ≦ SB ≦ 0.8
(IV) 280 ≦ degree of polymerization ≦ 380
In the formula, SA and SB represent the substitution degree of the acyl group substituted by the hydroxyl group of cellulose, SA is the substitution degree of the acetyl group, and SB is the substitution degree of the acyl group having 3 to 22 carbon atoms.

Glucose units having β-1,4 bonds constituting cellulose have free hydroxyl groups at the 2nd, 3rd and 6th positions. Cellulose acylate is a polymer obtained by esterifying some or all of these hydroxyl groups with acyl groups. The degree of acyl substitution means the proportion of cellulose esterified at each of the 2-position, 3-position and 6-position (100% esterification has a degree of substitution of 1).
The acyl group (SB) having 3 to 22 carbon atoms of the cellulose acylate of the present invention may be an aliphatic group or an allyl group, and is not particularly limited. These are, for example, cellulose alkylcarbonyl esters, alkenylcarbonyl esters, aromatic carbonyl esters, aromatic alkylcarbonyl esters, and the like, each of which may further have a substituted group. These preferred SBs include propionyl, butanoyl, keptanoyl, hexanoyl, octanoyl, decanoyl, dodecanoyl, tridecanoyl, tetradecanoyl, hexadecanoyl, octadecanoyl, iso-butanoyl, t-butanoyl, cyclohexanecarbonyl, oleoyl, benzoyl , Naphthylcarbonyl, cinnamoyl group, and the like. Among these, propionyl, butanoyl, dodecanoyl, octadecanoyl, t-butanoyl, oleoyl, benzoyl, naphthylcarbonyl, cinnamoyl and the like.
Thus, the cellulose acylate having different substituents can be achieved by appropriately adjusting the type and amount of carboxylic acid added when acylating cellulose.
The substitution degree at the 6-position can be achieved by adjusting the aging time during the acylation reaction as described above.

The degree of polymerization of the cellulose acylate preferably used in the present invention is preferably a viscosity average degree of polymerization of 280 to 380, more preferably 285 to 350, still more preferably 290 to 330. The average degree of polymerization can be measured by Uda et al.'S intrinsic viscosity method (Kazuo Uda, Hideo Saito, Journal of Textile Society, Vol. 18, No. 1, pages 105-120, 1962). Further details are described in JP-A-9-95538.
The molecular weight can be adjusted by extracting a low molecular weight component from the polymerized product or by improving the polymerization method. The removal of the low molecular component can be carried out by washing the cellulose acylate with an appropriate organic solvent. In addition, when manufacturing a cellulose acylate with few low molecular components, it is preferable to adjust the sulfuric acid catalyst amount in acylation reaction to 0.5-25 mass parts with respect to 100 mass of cellulose. When the amount of the sulfuric acid catalyst is within the above range, a cellulose acylate having a uniform molecular weight distribution that is preferable in terms of molecular weight distribution can be synthesized.

2. Cellulose acylate film A cellulose acylate film is formed by casting a material (dope) obtained by dissolving a raw material in an organic solvent at a high concentration on a mirror-finished drum or band and drying the solvent.
In the cellulose acylate solution of the present invention, various additives according to the use in each preparation step (for example, the above-mentioned plasticizer, ultraviolet inhibitor, deterioration inhibitor, optical anisotropy control agent, fine particles, release agent, Infrared absorbers, etc.) can be added and they can be solid or oily. That is, the melting point and boiling point are not particularly limited. For example, both ultraviolet absorbing materials of 20 ° C. or lower and 20 ° C. or higher are used, and these are described in, for example, JP-A-2001-151901. Furthermore, examples of infrared absorbing dyes are described in JP-A No. 2001-194522. Moreover, the addition time may be added at any time in the dope preparation step, but may be added by adding an additive to the final preparation step of the dope preparation step. Furthermore, the amount of each material added is not particularly limited as long as the function is manifested. Moreover, when a cellulose acylate film is formed from a multilayer, the kind and addition amount of the additive of each layer may differ. For example, it is described in Japanese Patent Application Laid-Open No. 2001-151902 and the like, but these are conventionally known techniques.
Furthermore, for these details, materials described in detail on pages 16 to 22 in the Japan Institute of Invention Disclosure Bulletin (Public Technical Number 2001-1745, published on March 15, 2001, Japan Institute of Invention) are preferably used.

(1) Dope solvent As the organic solvent in which the cellulose acylate of the present invention is dissolved, both chlorinated solvents (dichloromethane, chloroform, etc.) and non-chlorinated solvents can be used. Is more preferably used. That is, when used in a polarizing plate, a non-chlorine solvent is more preferable because it causes less fading when wet with heat and less yellowing. This is presumably because a trace amount of chlorine-based solvent remaining in the cellulose acylate film diffuses into the polarizing layer and acts on PVA and iodine to promote fading or to promote decomposition and to become yellowish.
(I) Non-chlorine solvent When producing a solution of cellulose acylate, the non-chlorine organic solvent preferably used is preferably a solvent selected from esters, ketones and ethers having 3 to 12 carbon atoms. Esters, ketones and ethers may have a cyclic structure. A compound having two or more functional groups of esters, ketones and ethers (that is, —O—, —CO— and —COO—) can also be used as a main solvent, such as an alcoholic hydroxyl group. It may have a functional group of In the case of the main solvent having two or more kinds of functional groups, the number of carbon atoms may be within the specified range of the compound having any functional group. Examples of the esters having 3 to 12 carbon atoms include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate and pentyl acetate. Examples of ketones having 3 to 12 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, and methylcyclohexanone. Examples of ethers having 3 to 12 carbon atoms include diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, anisole and phenetole. Examples of the organic solvent having two or more kinds of functional groups include 2-ethoxyethyl acetate, 2-methoxyethanol and 2-butoxyethanol.

  The non-chlorine organic solvent used in the above cellulose acylate is selected from the various viewpoints described above, and is preferably as follows. That is, the preferred solvent of the cellulose acylate of the present invention is a mixed solvent of three or more different from each other, and the first solvent is selected from methyl acetate, ethyl acetate, methyl formate, ethyl formate, acetone, dioxolane, and dioxane. One or more, one or more selected from ketones or acetoacetates having 4 to 7 carbon atoms as the second solvent, one or more selected from alcohols or hydrocarbons having 1 to 10 carbons as the third solvent, More preferably, it is a C1-C8 alcohol. In addition, when 2 or more types of 1st solvents are used, there may not be the 2nd solvent. The first solvent is more preferably methyl acetate, acetone, methyl formate, ethyl formate or a mixture thereof, and the second solvent is preferably methyl ethyl ketone, cyclopentanone, cyclohexanone, methyl acetyl acetate, and a mixture thereof. There may be.

  The alcohol residue of the alcohol that is the third solvent may preferably be linear, branched or cyclic, and is preferably a saturated aliphatic hydrocarbon group. The alcohol may be any of primary to tertiary alcohols. Examples of the alcohol include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, t-butanol, 1-pentanol, 2-methyl-2-butanol and cyclohexanol. Moreover, a fluorine-type alcohol is also used as alcohol. Examples thereof include 2-fluoroethanol, 2,2,2-trifluoroethanol, 2,2,3,3-tetrafluoro-1-propanol and the like.

The hydrocarbon as the third solvent may be linear, branched or cyclic. Either aromatic hydrocarbons or aliphatic hydrocarbons can be used. The aliphatic hydrocarbon may be saturated or unsaturated. Examples of hydrocarbons include cyclohexane, hexane, benzene, toluene and xylene.
These alcohols and hydrocarbons as the third solvent may be used alone or in combination of two or more, and are not particularly limited. Preferable specific examples of the third solvent include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and cyclohexanol, cyclohexane, hexane, and particularly methanol and ethanol. 1-propanol, 2-propanol, 1-butanol.

  The above three kinds of mixed solvents preferably contain the first solvent at a ratio of 20 to 95% by mass, the second solvent at 2 to 60% by mass, and further the third solvent at a ratio of 2 to 30% by mass, Furthermore, it is preferable that the first solvent is 30 to 90% by mass, the second solvent is 3 to 50% by mass, and further the third alcohol is 3 to 25% by mass. In particular, it is preferable that the first solvent is 30 to 90% by mass, the second solvent is 3 to 30% by mass, and the third solvent is alcohol and 3 to 15% by mass. In addition, when the first solvent is a mixed solution and the second solvent is not used, the first solvent is preferably contained in a ratio of 20 to 95% by mass and the third solvent in a ratio of 80 to 5% by mass, Furthermore, it is preferable that a 1st solvent is 30-93 mass%, and also a 3rd solvent is contained 70-7 mass%. The non-chlorine organic solvent used in the present invention is described in more detail in pages 12 to 16 of the Japan Society for Invention and Innovation (public technical number 2001-1745, published on March 15, 2001, Japan Institute of Invention). It is described in detail. Preferred combinations of non-chlorine organic solvents of the present invention can include the following, but are not limited thereto.

-Methyl acetate / acetone / methanol / ethanol / butanol (75/10/5/5/5, parts by mass),
-Methyl acetate / acetone / methanol / ethanol / propanol (75/10/5/5/5, parts by mass),
Methyl acetate / acetone / methanol / butanol / cyclohexane (75/10/5/5/5, parts by mass),
Methyl acetate / methyl ethyl ketone / methanol / butanol (80/10/5/5, parts by mass),
-Methyl acetate / acetone / methyl ethyl ketone / ethanol / isopropanol (75/10/10/5/7, parts by mass)
Methyl acetate / cyclopentanone / methanol / isopropanol (80/10/5/8, parts by mass),
・ Methyl acetate / acetone / butanol (85/5/5, part by mass),
Methyl acetate / cyclopentanone / acetone / methanol / butanol (60/15/15/5/6, parts by mass),
-Methyl acetate / cyclohexanone / methanol / hexane (70/20/5/5, parts by mass)
Methyl acetate / methyl ethyl ketone / acetone / methanol / ethanol (50/20/20/5/5, parts by mass),
Methyl acetate / 1,3-dioxolane / methanol / ethanol (70/20/5/5, parts by mass),
Methyl acetate / dioxane / acetone / methanol / ethanol (60/20/10/5/5, parts by mass),
Methyl acetate / acetone / cyclopentanone / ethanol / isobutanol / cyclohexane (65/10/10/5/5/5, parts by mass),
Methyl formate / methyl ethyl ketone / acetone / methanol / ethanol (50/20/20/5/5, parts by mass),
-Methyl formate / acetone / ethyl acetate / ethanol / butanol / hexane (65/10/10/5/5/5, parts by mass)
Acetone / methyl acetoacetate / methanol / ethanol (65/20/10/5, parts by mass)
Acetone / cyclopentanone / ethanol / butanol (65/20/10/5, parts by mass)
Acetone / 1,3 dioxolane / ethanol / butanol (65/20/10/5, part by mass),
1,3 dioxolane / cyclohexanone / methyl ethyl ketone / methanol / butanol (55/20/10/5/5/5, parts by mass)
Etc.
In addition to the non-chlorine organic solvent of the present technology, the dope used in the present technology may contain dichloromethane in an amount of 10% by mass or less based on the total amount of the organic solvent of the present technology.

(Ii) Chlorine-based solvent In preparing the cellulose acylate solution of the present invention, a chlorine-based organic solvent may also be used. As described above, the fading property of the polarizing plate is likely to be lowered, but since cellulose acylate can be dissolved at a higher concentration, the drying process after casting can be shortened and the process cost can be reduced.
In the present invention, the chlorinated organic solvent is not particularly limited as long as the object can be achieved within a range in which cellulose acylate can be dissolved and cast and formed. These chlorinated organic solvents are preferably dichloromethane and chloroform. Particularly preferred is dichloromethane. In addition, there is no particular problem in mixing an organic solvent other than the chlorinated organic solvent. In that case, it is necessary to use at least 50% by mass of dichloromethane.

  The non-chlorine organic solvent used in the present invention is described below. That is, as a preferable non-chlorine organic solvent, a solvent selected from esters, ketones, ethers, alcohols, hydrocarbons and the like having 3 to 12 carbon atoms is preferable. The ester, ketone, ether and alcohol may have a cyclic structure. A compound having two or more functional groups of esters, ketones and ethers (that is, —O—, —CO— and —COO—) can also be used as a solvent. For example, other functional groups such as alcoholic hydroxyl groups can be used. You may have group simultaneously. In the case of a solvent having two or more types of functional groups, the number of carbon atoms may be within the specified range of the compound having any functional group.

Examples of the esters having 3 to 12 carbon atoms include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate and pentyl acetate.
Examples of the ketones having 3 to 12 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, and methylcyclohexanone.
Examples of the ether having 3 to 12 carbon atoms include diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, anisole and phenetole.
Examples of the organic solvent having two or more kinds of functional groups include 2-ethoxyethyl acetate, 2-methoxyethanol, and 2-butoxyethanol.

In addition, the alcohol used in combination with the chlorinated organic solvent may be linear, branched or cyclic, and may be a saturated aliphatic hydrocarbon. Is preferred. The alcohol may be any of primary to tertiary. Examples of the alcohol include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, t-butanol, 1-pentanol, 2-methyl-2-butanol and cyclohexanol. As the alcohol, fluorine-based alcohol is also used. Examples thereof include 2-fluoroethanol, 2,2,2-trifluoroethanol, 2,2,3,3-tetrafluoro-1-propanol and the like. Further, the hydrocarbon may be linear, branched or cyclic. Either aromatic hydrocarbons or aliphatic hydrocarbons can be used. The aliphatic hydrocarbon may be saturated or unsaturated.
Examples of the hydrocarbon used in combination with the chlorinated organic solvent include cyclohexane, hexane, benzene, toluene and xylene.

Particularly preferred non-chlorine organic solvents used in combination with the chlorine-based organic solvent that is the main solvent used in the above cellulose acylate are methyl acetate, ethyl acetate, methyl formate, ethyl formate, acetone, dioxolane, dioxane, carbon atoms Is a ketone or acetoacetate having 4 to 7 carbon atoms, an alcohol or hydrocarbon having 1 to 10 carbon atoms. Specific examples of the non-chlorine organic solvent preferably used in combination are methyl acetate, acetone, methyl formate, ethyl formate, methyl ethyl ketone, cyclopentanone, cyclohexanone, methyl acetyl acetate, methanol, ethanol, 1-propanol, 2-propanol, 1 -Butanol, 2-butanol, and cyclohexanol, cyclohexane, hexane may be mentioned.
Examples of a highly preferable combination of the chlorine-based organic solvent and the non-chlorine-based organic solvent as the main solvent include the following combinations, but are not limited thereto.

Dichloromethane / methanol / ethanol / butanol (75/10/5/5/5, parts by mass),
Dichloromethane / acetone / methanol / propanol (80/10/5/5, parts by mass),
Dichloromethane / methanol / butanol / cyclohexane (75/10/5/5/5, parts by mass),
Dichloromethane / methyl ethyl ketone / methanol / butanol (80/10/5/5, parts by mass),
Dichloromethane / acetone / methyl ethyl ketone / ethanol / isopropanol (75/10/10/5/7, parts by mass),
Dichloromethane / cyclopentanone / methanol / isopropanol (80/10/5/8, parts by mass)
Dichloromethane / methyl acetate / butanol (80/10/10, parts by mass),

Dichloromethane / cyclohexanone / methanol / hexane (70/20/5/5, parts by mass)
Dichloromethane / methyl ethyl ketone / acetone / methanol / ethanol (50/20/20/5/5, parts by mass),
Dichloromethane / 1, 3 dioxolane / methanol / ethanol (70/20/5/5, parts by mass),
Dichloromethane / dioxane / acetone / methanol / ethanol (60/20/10/5/5, parts by mass),
Dichloromethane / acetone / cyclopentanone / ethanol / isobutanol / cyclohexane (65/10/10/5/5/5, parts by mass),
Dichloromethane / methyl ethyl ketone / acetone / methanol / ethanol (70/10/10/5/5, parts by mass),
Dichloromethane / acetone / ethyl acetate / ethanol / butanol / hexane (65/10/10/5/5/5, parts by mass),
Dichloromethane / methyl acetoacetate / methanol / ethanol (65/20/10/5, parts by mass),
Dichloromethane / cyclopentanone / ethanol / butanol (65/20/10/5, parts by mass),
Etc.

(2) Additives Various additives according to applications can be added to the cellulose acylate solution in each preparation step. These additives include plasticizers, UV inhibitors and deterioration inhibitors (eg, antioxidants, peroxide decomposers, radical inhibitors, metal deactivators, acid scavengers, amines) and the like.
As the plasticizer to be preferably added, those already described can be used.
As for the deterioration preventing agent and the ultraviolet ray preventing agent, JP-A-60-235852, JP-A-3-199201, JP-A-51907073, JP-A-5-194789, JP-A-5-271471, JP-A-6-107854, 6-118233, 6-148430, 7-11056, 7-11055, 7-11056, 8-29619, 8-239509 and JP-A-2000-204173. There is a description. Preferable examples of the deterioration preventing agent include butylated hydroxytoluene (BHT).
The ultraviolet absorber is preferably one that has an excellent ability to absorb ultraviolet light having a wavelength of 370 nm or less and has little absorption of visible light having a wavelength of 400 nm or more. An oxybenzophenone compound, a benzotriazole compound, a salicylate compound, a benzophenone compound, Examples thereof include cyanoacrylate compounds and nickel complex compounds, and benzotriazole compounds and benzophenone compounds are particularly preferable. Also, JP-A-7-11056, JP-A-8-239509, JP-A-2002-79533, JP-A-6-148430, JP-A-10-237186, JP-A-2001-72782, etc. Those described in the above can also be used.
The amount of these compounds added is preferably 1 ppm to 10,000 ppm and more preferably 10 to 1000 ppm in terms of mass ratio with respect to cellulose acylate.

The in-plane retardation (Re) of the film is preferably in the range of 0 to 300 nm, more preferably 0 to 100 nm, and still more preferably 0 to 30 nm, but is adjusted according to the application. In addition, retardation (Rth) in the thickness direction of the film is also important, and Rth of cellulose acylate film is 0 nm to 300 nm per 100 μm, more preferably 0 nm to 90 nm, and particularly 0 nm to 50 nm. It is done.
Further, a release agent can be added in order to reduce the peeling stress from the band and drum during film formation. As the release agent, one selected from at least one acid having an acid dissociation index pKa in an aqueous solution of 1.93 to 4.50, an alkali metal salt of the acid and an alkaline earth metal salt of the acid is preferably used. It is done.

(3) Dissolution The cellulose acylate solution of the present invention is preferably a solution in which 10 to 30% by mass is dissolved in an organic solvent, more preferably 13 to 27% by mass, and particularly 15 to 25% by mass. A dissolved solution is preferred.
Regarding the preparation of the cellulose acylate solution (dope) of the present invention, the dissolution method is not particularly limited, and it may be room temperature, further a cooling dissolution method or a high temperature dissolution method, and further a combination thereof. Regarding these, for example, JP-A-5-163301, JP-A-61-106628, JP-A-58-127737, JP-A-9-95544, JP-A-10-95854, JP-A-10-45950, JP 2000-53784, JP 11-322946, JP 11-322947, JP 2-276830, JP 2000-273239, JP 11-71463, JP 04-259511, Special JP-A 2000-273184, JP-A No. 11-323017, JP-A No. 11-302388 and the like disclose methods for preparing a cellulose acylate solution.
The above-described method for dissolving cellulose acylate in an organic solvent can be applied by appropriately selecting these techniques in the present invention in order to achieve the object of the present invention. These details are described in detail on pages 22 to 25 in the Japan Society for Invention and Technology (Publication No. 2001-1745, published on March 15, 2001, Japan Society for Inventions), especially for non-chlorine solvent systems. Be implemented in a way that
Further, the cellulose acylate dope solution of the present invention is usually subjected to solution concentration and filtration. Similarly, the dope solution of the invention is published in the technical report of the Invention Association (public technical number 2001-1745, published on March 15, 2001, Invention Association). It is described in detail on the page. In addition, when it melt | dissolves at high temperature, it is the case where it is more than the boiling point of the organic solvent to be used, and in that case, it uses in a pressurized state.

The cellulose acylate solution of the present invention preferably has a viscosity and dynamic storage modulus within the range. The viscosity and dynamic storage elastic modulus of the solution are measured by using 1 mL of a sample solution as a rheometer (CLS 500) and a Steel Cone (both manufactured by TA Instruments) having a diameter of 4 cm / 2 °. The measurement conditions were measured by varying the range from 40 ° C. to −10 ° C. at 2 ° C./min with an Oscillation Step / Temperature Ramp, and a static non-Newtonian viscosity n * (Pa · s) of 40 ° C. The storage elastic modulus G ′ (Pa) is obtained. The sample solution is preliminarily kept at the measurement start temperature until the liquid temperature becomes constant, and then the measurement is started.
The cellulose acylate solution of the present invention preferably has a viscosity at 40 ° C. of 1 to 300 Pa · s and a dynamic storage elastic modulus at −5 ° C. of 10,000 to 1,000,000 Pa.

(4) Casting film formation A method for producing a cellulose acylate film using the above cellulose acylate solution will be described. For the method and equipment for producing the cellulose acylate film of the present invention, a solution casting film forming method and a solution casting film forming apparatus conventionally used for producing a cellulose triacetate film are used. The dope (cellulose acylate solution) prepared from the dissolving machine (kettle) is temporarily stored in a storage kettle, and the foam contained in the dope is defoamed for final preparation. The dope is passed through the filtration filter through a pressurized metering gear pump that can deliver a dope from the dope discharge port with high precision, for example, by the number of rotations, and then sent to the pressure die, and the dope is made endlessly from the die (slit) of the pressure die. It casts uniformly on the metal support (base material) of the running casting part. At this time, it is preferable to rapidly dry under the above-mentioned conditions to increase the plasticizer concentration in the vicinity of the surface.
The raw dry dope film (also referred to as a web) is peeled off from the metal support (base material) at the peeling point where the metal support has almost gone around. Subsequently, the crystallinity can be increased by drying at a high temperature as described above in a state where there is a large amount of residual solvent. At this time, it is preferable that both ends of the web are sandwiched between clips, and conveyed and dried by a tenter while maintaining the width. This is because when the residual solvent is large, the self-supporting force is weak and it is preferable to grip both ends. Subsequently, after transporting by a roll group of a drying apparatus and finishing drying, it is preferable to slowly cool and wind up according to the above conditions. The thickness is preferably 20 μm or more and 200 μm or less, more preferably 25 μm or more and 150 μm or less, and still more preferably 30 μm or more and 100 μm or less.

Further thereafter, it is also preferable to coat an undercoat layer, an antistatic layer, an antihalation layer, a protective layer and the like. Each of these production processes is described in detail on pages 25 to 30 in the Japan Society of Invention Disclosure Technical Bulletin (Public Technical Number 2001-1745, published on March 15, 2001, Japan Institute of Invention).
In such a casting process, one type of cellulose acylate solution may be cast in a single layer, or two or more types of cellulose acylate solutions may be cast simultaneously and / or sequentially. In the case of having a casting process comprising two or more layers, the composition and concentration of the solvent in each layer in the produced cellulose acylate solution and cellulose acylate film may be the same or different. The number of layers is preferably 2 to 10, more preferably 3 to 5. Although the thickness of these layers can be selected arbitrarily, the thickness of the outermost layer is preferably 0.01 to 0.3 times or less, more preferably 0.05 to 0.15 times the thickness of the innermost layer.

3. Saponification Treatment In order to increase the adhesion to the PVA forming the polarizing plate, the surface is subjected to saponification treatment by the above-described method, and the cellulose acylate is hydrolyzed to generate a hydroxyl group. Following this, sufficient water washing is performed by the above-described method.
Such a saponification treatment can be achieved by the following method.
Any saponification solution may be used as long as cellulose acylate is hydrolyzed, and an acid or alkali solution is used for this. More preferred is an alkaline solution, and sodium hydroxide, potassium hydroxide, ammonia and the like are more preferably used. The solvent is not particularly limited, and may be either water-based or organic solvent-based. More preferred are aqueous and alcoholic solvents. In the water system, the water content is 50% by mass or more, and a solvent having good compatibility with water such as alcohol may be dissolved in addition to water. The alcohol solvent is preferably an alcohol having 1 to 5 carbon atoms, more preferably methanol, ethanol or propanol, and still more preferably iso-propanol.
The pH of the saponification coating solution is preferably 10 or more, and more preferably 12 or more. The specified concentration of hydroxide ions is preferably 0.1N to 3.0N, more preferably 0.5N to 2.0N.
The saponification treatment may be immersed in a saponification solution or an alkali solution may be applied. In order to precisely control the depth of the saponification treatment as in the present invention, it is more preferable to carry out by a coating method. In the case of the coating method, an organic solvent-based coating solution that can be applied uniformly (no repellency) is more preferably used, and in the case of the dipping method, a water-based immersion solution is more preferably used.

(A) Coating saponification When saponification is performed by coating, the alkali saponification solution is preferably an alkali (KOH, NaOH, ammonia, etc.) dissolved in water or an organic solvent at a concentration of 1N or more and 10N or less. An alcohol or diol having 5 or less carbon atoms. When using water, it is preferable to suppress the repelling on the cellulose acylate film by adding a surfactant or adding a water-soluble organic solvent. The temperature of the preferred saponification solution is preferably 50 to 80 ° C., and the preferred saponification time is preferably 5 seconds to 5 minutes. The coating amount of the saponification solution is preferably 1 g / m ² to 100 g / m ² . Examples of the coating method include a dip coating method, a curtain coating method, an extrusion coating method, a bar coating method, a spray method, and an E-type coating method.
After applying the saponification solution, it may be neutralized by applying an acidic aqueous solution of 0.01N to 3.0N hydrochloric acid, nitric acid, sulfuric acid, acetic acid, formic acid, chloroacetic acid, oxalic acid, etc. It doesn't matter. That is, the film surface may be sufficiently washed to have a pH of 5 to 9 (the membrane surface pH can be measured by bringing a flat glass pH electrode into contact with the film surface). Such washing with water may be applied with water or sprayed. Then, it dries at 40 to 200 ° C.

(B) Immersion saponification A cellulose acylate film is immersed in an alkaline solution. The saponification solution is preferably an alkali (KOH, NaOH, etc.) dissolved in water, and the alkali concentration is preferably 1N or more and 10N or less. A surfactant water-soluble organic solvent may be added to such an alkaline aqueous solution. The temperature of the alkaline solution is preferably 40 to 80 ° C., and the immersion time is usually preferably 1 minute to 10 minutes.
After such saponification treatment, it may be neutralized by immersion in an acidic aqueous solution of 0.01N to 3.0N hydrochloric acid, nitric acid, sulfuric acid, acetic acid, formic acid, chloroacetic acid, oxalic acid, etc. You don't have to treat it, just wash it with water. That is, it may be sufficiently washed so that the film surface pH is 5-9. Then, it dries at 40 to 200 ° C.

4). Preparation of polarizing plate (1) Binder of polarizing layer The polarizing layer is prepared by orienting a polarizing dye dispersed in PVA in one direction. PVA is usually a saponified polyvinyl acetate, and may contain components copolymerizable with vinyl acetate such as unsaturated carboxylic acids, unsaturated sulfonic acids, olefins, and vinyl ethers. In addition, modified PVA containing an acetoacetyl group, a sulfonic acid group, a carboxyl group, an oxyalkylene group, or the like can also be used.
The saponification degree of PVA is not particularly limited, but is preferably 80 to 100 mol%, particularly preferably 90 to 100 mol% from the viewpoint of solubility and the like. The degree of polymerization of PVA is not particularly limited, but is preferably 1000 to 10,000, and particularly preferably 1500 to 5000.

(2) Dyeing PVA is dyed with iodine to obtain a polarizing film. That is, it is carried out by immersing the PVA film in an iodine-potassium iodide aqueous solution. Iodine is preferably 0.1 to 20 g / l, potassium iodide is preferably 1 to 200 g / l, and the mass ratio of iodine and potassium iodide is preferably 1 to 200. The dyeing time is preferably 10 to 5000 seconds, and the liquid temperature is preferably 5 to 60 ° C. As a dyeing method, not only immersion but any means such as application or spraying of iodine or a dye solution can be used. The dyeing step may be placed either before or after the stretching step described later, but it is particularly preferable to dye in the liquid phase before the stretching step because the film is appropriately swelled to facilitate stretching.
The effect of the present invention can be similarly exhibited in a polarizing film stained with other than iodine. This is because the present invention does not improve the resistance of the dye but improves boric acid, which is a PVA crosslinking agent fixing the dye. Examples of preferable dyes other than iodine include dye compounds such as azo dyes, stilbene dyes, pyrazolone dyes, triphenylmethane dyes, quinoline dyes, oxazine dyes, thiazine dyes, anthraquinone dyes, and the like. I can give you.

(3) Hardening In order to fix the oriented structure of PVA after stretching, it is preferable to crosslink PVA. As the crosslinking agent, those described in US Pat. No. 2,328,977 can be used, but boric acid and borax are preferably used practically. In addition, metal salts such as zinc, cobalt, zirconium, iron, nickel, and manganese can be used together.
Such a film can be achieved by immersing PVA impregnated with a dye in an aqueous solution of borax or boric acid. The content of borax and boric acid is preferably 0.1 to 10 mol / l, more preferably 0.2 to 5 mol / l, still more preferably 0.2 to 2 mol / l. The liquid temperature is preferably 10 ° C. to 40 ° C., more preferably 15 ° C. to 35 ° C. The immersion time is 10 seconds or longer and 10 minutes or shorter, more preferably 20 seconds or longer and 5 minutes or shorter. It is also preferable to put iodide salts such as sodium iodide and potassium iodide in the dura mater. This concentration is preferably 0.1 to 10 mol / l, more preferably 0.2 to 5 mol / l, still more preferably 0.2 to 2 mol / l.
Such hardening may be performed anywhere before stretching, during stretching, or after stretching.

(4) Stretching A PVA film impregnated with a dye or the like is stretched and oriented. The stretching may be performed in parallel to the transport direction, may be performed in the orthogonal direction, or may be performed in an oblique direction. Among these, a parallel direction (parallel stretching method) and a 45-degree oblique direction (oblique stretching method) are preferable. This is because the obliquely stretched polarizing film is more excellent in fading. The reason for this is estimated as follows. That is, since parallel stretching is mainly performed by two pairs of nip rolls, neck-in occurs during stretching and the width becomes narrow. On the other hand, oblique stretching does not allow neck-in because the film is stretched by a tenter. As a result, since it decreases in the thickness direction as much as it cannot be contracted in the width direction, the plane orientation proceeds. Such a plane-oriented polarizing layer has a solid alignment structure, is not easily disturbed even by a wet heat thermometer, and is presumed to have high thermo resistance.
The thickness of the polarizing layer after stretching is preferably 5 μm or more and 50 μm or less, and more preferably 10 μm or more and 40 μm or less in any stretching method.

(I) Parallel stretching method Prior to stretching, the PVA film is swollen. The degree of swelling is 1.2 to 2.0 times (mass ratio before swelling and after swelling).
Thereafter, the film is stretched at a bath temperature of 15 to 50 ° C., particularly 17 to 40 ° C. in an aqueous medium bath or a dye bath for dissolving a dichroic substance while being continuously conveyed through a guide roll or the like. Stretching can be achieved by gripping with two pairs of nip rolls and increasing the conveyance speed of the subsequent nip roll to be higher than that of the previous nip roll. The draw ratio is based on the length ratio after stretching / initial state (hereinafter the same), but the preferred draw ratio is 1.2 to 3.5 times, especially 1.5 to 3.0 times from the viewpoint of the above-mentioned effects. is there.
Thereafter, the film is dried at 50 ° C. to 90 ° C. to obtain a polarizing film.

(Ii) Diagonal Stretching Method For this purpose, a method of stretching using a tenter protruding in the tilting direction described in JP-A-2002-86554 can be used.
Since this stretching is performed in the air, it is necessary to make it easy to stretch by adding water in advance. A preferable moisture content is 5% or more. This includes immersing, coating and spraying before stretching, and applying water or the like during stretching. Since hydrophilic polymer films such as polyvinyl alcohol contain water in a high-temperature and high-humidity atmosphere, they can contain volatile components by stretching after conditioning in a high-humidity atmosphere or by stretching under high-humidity conditions. . Other than these methods, any means may be used as long as the moisture content of the polymer film can be increased to 5% or more. More preferably, it is 10% or more and 100% or less.
The temperature during stretching is preferably 40 ° C. or higher and 90 ° C. or lower, and more preferably 50 ° C. or higher and 80 ° C. or lower. The humidity is preferably 50% RH to 100% RH, more preferably 70% RH to 100% RH, and still more preferably 80% RH to 100% RH.
Further, the traveling speed in the longitudinal direction is preferably 1 m / min or more, more preferably 3 m / min or more.
After the stretching, the film is dried at 50 ° C. or higher and 100 ° C. or lower, more preferably 60 ° C. or higher and 90 ° C. or lower, and 0.5 minutes or longer and 10 minutes or shorter, more preferably 1 minute or longer and 5 minutes or shorter.
The polarizing film thus obtained is preferably substantially 45 degrees in the transport direction, and substantially 45 degrees means 45 ± 5 degrees.

(5) Bonding The cellulose acylate film after saponification and the polarizing layer prepared by stretching are bonded to prepare a polarizing plate. The laminating direction is preferably such that the casting axis direction of the cellulose acylate film and the stretching axis direction of the polarizing plate are 45 degrees.
The adhesive for bonding is not particularly limited, but examples thereof include PVA resins (including modified PVA such as acetoacetyl group, sulfonic acid group, carboxyl group, oxyalkylene group) and boron compound aqueous solution. preferable. The thickness of the adhesive layer is preferably 0.01 to 10 μm after drying, and particularly preferably 0.05 to 5 μm.

5). Application of Polarizing Plate (1) Circular Polarizing Plate The polarizing plate thus obtained and the λ / 4 plate can be laminated to produce circularly polarized light. In this case, lamination is performed so that the slow axis of the λ / 4 plate and the absorption axis of the polarizing plate are 45 degrees. At this time, the λ / 4 plate is not particularly limited, but more preferably has a wavelength dependency such that the retardation becomes smaller as the wavelength becomes lower. Further, it is preferable to use a polarizing film having an absorption axis inclined by 20 to 70 degrees with respect to the longitudinal direction and a λ / 4 plate made of an optically anisotropic layer made of a liquid crystalline compound.
(2) Liquid crystal display element When used in a reflective liquid crystal display device, in order from the bottom, the lower substrate, the reflective electrode, the lower alignment film, the liquid crystal layer, the upper alignment film, the transparent electrode, the upper substrate, the λ / 4 plate, and the polarization It consists of a board and the thing of this invention can be used for the polarizing plate in this. In the case of color display, it is preferable to further provide a color filter layer between the reflective electrode and the lower alignment film, or between the upper alignment film and the transparent electrode.
When used in a transmissive liquid crystal display device, the backlight, polarizing plate, λ / 4 plate, lower transparent electrode, lower alignment film, liquid crystal layer, upper alignment film, upper transparent electrode, upper substrate, λ / 4 are sequentially arranged from the bottom. It consists of a plate and a polarizing film. The thing of this invention can be used for the polarizing plate in this. In the case of color display, it is preferable to further provide a color filter layer between the lower transparent electrode and the lower alignment film, or between the upper alignment film and the transparent electrode.
The liquid crystal cell is not particularly limited, but more preferably, a TN (twisted nematic) type, an STN (super twisted nematic) type, a HAN (hybrid aligned nematic) type, a VA (vertically aligned) type, an ECr type, an ECr type, an ECB type, an ECB type. It is preferably a type (Optically Compensatory Bend) or a CPA type (Continuous Pinwheel Alignment).

The measurement methods used in the present invention are described below.
(1) Diffusion coefficient of boric acid A polarizing plate is cut into 4 cm × 6 cm and attached to a glass plate with an adhesive attached on one side. On this opposite surface, a 75 μm thick PVA film (Kuraray Co., Ltd. vinylon film VF-PS # 7500) cut to 4 cm × 6 cm was placed, and a plastic net was placed thereon, followed by a glass plate, a polarizing plate, and a PVA film. The plastic net is put together with a clip (this allows the PVA film and the polarizing plate to be firmly adhered, and the humidity to the polarizing plate can be sufficiently diffused).
This is put into a constant temperature bath at 60 ° C. and 95% RH for 200 hours. Thereafter, the PVA film is taken out, and boric acid therein is quantified by the following method.
-Cut out 2 cm ² of the central part of the PVA film and add 2 ml of nitric acid to make multiwave ash (wet ash by microwave).
-Make up this to 100 ml with pure water.
-Make 6 of these diluted 100 times. To this, boric acid is added so as to be 0, 1, 3, 5, 10, 20 ppm, respectively (standard addition method).
-Using these ICP-MS (HP-4500 type made by Yokogawa Analytical Co., Ltd.), the amount of boric acid is calculated | required by measuring the amount of boron.
-The addition amount is plotted on the horizontal axis, and the intensity of ICP-MS is plotted on the vertical axis. This is plotted and the concentration in the sample is determined from the straight line obtained by the least square method and the intercept on the horizontal axis. This is A (ppm).
From this, the diffusion coefficient (mmol / m ² · day · μm) of boric acid is determined according to the following formula.
Boric acid diffusion coefficient (mmol / m ² · day · μm) = 1000 × {(A × 10 ⁻⁶ × 100) /61.8} × 5000 / {2 × (200/24)} × (1 / T)

(2) Content of boric acid in polarizing layer (i) Wet ashing A polarizing plate is attached to a glass plate, 2 cm ² is exposed, and the others are masked with Mylar adhesive tape. Chloroform is added dropwise thereto to swell the protective film (cellulose acylate film), and this is rubbed off. Thereafter, the polarizing layer is scraped off, and 2 ml of nitric acid is added to the polarizing layer to ash multiwave (ashing by microwaves). This is made up to 100 ml with pure water and further diluted 100 times.
(Ii) ICP-MS measurement Using ICP-MS (HP-4500, manufactured by Yokogawa Analytical), the amount of boric acid is determined by quantifying the amount of boron in the same manner as described above.
(3) Moisture permeability coefficient A sample film is measured according to JIS Z 0208. However, after conditioning for 24 hours in a constant temperature and humidity chamber adjusted to 60 ° C. and 95% RH, the mass change was determined, and the moisture permeability coefficient was determined therefrom.
However, the moisture permeability coefficient after the aging of the thermometer was a cellulose acylate film protective film alone (not assembled on a polarizing plate) and aged for 1000 hours at 60 ° C. and 95% RH.
(4) Degree of substitution of cellulose acylate The degree of acyl substitution at the 2-position, 3-position and 6-position of cellulose acylate is described in Carbohydr. Res. Was determined by ¹³ C-NMR according to the method described in 273 (1995) 83-91 (Tezuka et al.).
(5) Degree of polymerization of cellulose acylate (DP)
-About 0.2 g of completely dried cellulose acylate was precisely weighed and dissolved in 100 ml of a mixed solvent of methylene chloride: ethanol = 9: 1 (mass ratio). This was measured for the number of seconds dropped at 25 ° C. with an Ostwald viscometer, and the degree of polymerization (DP) was determined by the following formula.
Formula: DP = [η] / 6 × 10 ⁻⁴
Here, [η] = (1nη _rel ) / C, and C is the measured concentration (g / L).
Further, the above η _rel is a value calculated by T / T0, T is the number of seconds for dropping the measurement sample, and T0 is the number of seconds for dropping the solvent alone.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
In the following, the present invention-7 and the present invention-11 will be read as “reference examples”.
1. Formation of Cellulose Acylate Film (1) Cellulose Acylate Cellulose acylates having different substituted acyl groups and different degrees of polymerization described in Table 1 were prepared. This was carried out by adding sulfuric acid (7.8 parts by mass with respect to 100 parts by mass of cellulose) as a catalyst, adding carboxylic acid as a raw material for the acyl substituent, and carrying out an acylation reaction at 40 ° C. At this time, the kind and substitution degree of the acyl group shown in Table 1 were adjusted by adjusting the kind and amount of the carboxylic acid. Moreover, it age | cure | ripened at 40 degreeC after acylation.
Furthermore, samples with different average degrees of polymerization were prepared by washing and removing low molecular weight components of the cellulose acylate with acetone.

(2) Dissolution of cellulose acylate The flakes of cellulose acylate were added to a solvent selected from the following solvents (described in Table 2) at 23 mass% and stirred.
Non-chlorine system: methyl acetate / acetone / methanol / ethanol / butanol (75/10/5/5/5, parts by mass)
Chlorine: dichloromethane / methanol / ethanol / butanol (75/10/5/5/5, parts by mass)
The plasticizer of Table 2 was added to this. Further, 2% by mass of the total amount of the dope was added to the ultraviolet absorbent (UV-9) described in Example 1 in JP-A-7-11056. The heterogeneous gel solution thus obtained was kneaded at −75 ° C. for 3 minutes. This was stirred at 50 ° C. for 2 hours to obtain a uniform solution, then returned to room temperature, filtered through 10 μm filter paper (# 63, manufactured by Toyo Filter Paper Co., Ltd.), and further 2.5 μm filter paper (manufactured by Pall, FH025) To obtain a cellulose acylate dope.
In Table 2, abbreviations for plasticizers are as follows.
TPP: triphenyl phosphate BDP: biphenyl diphenyl phosphate,
DOP: Dioctyl phthalate OACTB: Tributyl O-acetylcitrate

(3) Formation of Cellulose Triacetate Film The filtered cellulose triacetate dope at 50 ° C. was cast on a mirror surface stainless steel substrate, which was a drum having a diameter of 3 m, through a cast Gicer. The solvent volatilization rate was adjusted to the values shown in Table 2 by adjusting the temperature of the substrate and the blowing air. The volatilization rate was determined by the following method.
-The dope before casting and the film immediately after peeling off from the substrate are sampled, and the amount of the solvent contained therein is quantified by gas chromatography, which is defined as X and Y mass%, respectively.
The time from when the dope is cast on the substrate until it is peeled off is defined as t minutes.
-The volatilization rate (mass% / min) was calculated | required by (XY) / t.
The Gieseer used was similar to that described in Japanese Patent Application Laid-Open No. 11-314233. The film forming width was 200 cm.
After peeling off, both ends of this cellulose acylate film were clipped with a pin tenter. Thereafter, the cellulose acylate film held by the pin tenter was conveyed to the drying zone. Films with different crystallinity were prepared by changing the blowing air temperature here and the amount of volatile components at the time of stripping as shown in Table 2.
The crystallinity was determined as follows by X-ray diffraction (XD) measurement of the cellulose acylate film after passing through the subsequent drying zone, and is shown in Table 2. Measurement using Cu Kα ray The value obtained by dividing the area of the crystal peak appearing at 2θ = 17 degrees by the area of the halo peak appearing at 2θ = 8 degrees was taken as the crystallinity.
The cellulose acylate film was further dried at 145 ° C. for 10 minutes, and then cooled between Tg and Tg-30 ° C. under the conditions shown in Table 2. Thus, a cellulose triacetate film having a thickness described in Table 2 was obtained. The obtained sample was cut at both ends by 3 cm, further knurled at a height of 2 to 10 mm from the end, and wound into a 2000 m roll.

(4) Saponification of Cellulose Acylate Film Saponification was carried out by any of the following methods and listed in Table 3.
(I) Coating saponification • 20 parts by mass of water was added to 80 parts by mass of iso-propanol, and KOH was dissolved to 1.5 N, and the temperature was adjusted to 60 ° C. and used as a saponification solution. .
-10 g / m < ² > was apply | coated on the cellulose acylate film of 60 degreeC, and it saponified for 1 minute.
-After that, it was washed by spraying warm water of 50 ° C for 1 minute at 10 L / m ² · min using a spray.
(Ii) Immersion saponification • A 1.5 N aqueous solution of NaOH was used as a saponification solution.
-This was temperature-controlled at 60 degreeC and the cellulose acylate film was immersed for 2 minutes.
-After that, it was immersed in a 0.1 N sulfuric acid aqueous solution for 30 seconds, and then passed through a water-washing bath.

2. Production of Polarizing Plate (1) Production of Polarizing Layer A polarizing layer having a thickness of 20 μm was prepared by any of the following methods (described in Table 2).
(I) Diagonal Stretching Method A PVA film (Kuraray 9X75SR) was immersed in a dyeing solution having the following composition at 25 ° C. for 90 seconds.
<Dyeing liquid>
Iodine 1.0 part by weight Potassium iodide 60.0 parts by weight Water 1000 parts by weight This was immersed in one of the following hardeners (described in Table 3) at 25 ° C. for 120 seconds, and the initial content of boric acid Different PVA films were made.
<Hardener 1
Boric acid 40 parts by mass Potassium iodide 30 parts by mass Water 1000 parts by mass <Duracil solution-2>
Boric acid 80 parts by mass Potassium iodide 60 parts by mass Water 1000 parts by mass <Duracil solution-3>
Boric acid 120 parts by weight Potassium iodide 90 parts by weight Water 1000 parts by weight After that, according to Example 1 of Japanese Patent Laid-Open No. 2002-86554, stretching was performed using a tenter so that the stretching axis was 45 degrees obliquely. In addition, extending | stretching was made to shrink | contract to 5.3 time, after extending | stretching 7 time in 60 degreeC95% RH. Then, it was dried at 70 ° C. for 2 minutes.

(Ii) Parallel Stretching Method According to Example 1 of Japanese Patent Laid-Open No. 2001-141926, a PVA film (Kuraray 9X75SR) is immersed in the dyeing solution at 30 ° C. to give a peripheral speed difference between two pairs of nip rolls. The film was stretched 3 times in the longitudinal direction.
This was further immersed in the above hardening solution and stretched at 60 ° C. using two pairs of nip rolls 6.5 times (magnification relative to the unstretched film). This was dried at 50 ° C. for 5 minutes.

(2) Bonding The polarizing plate thus obtained and the saponified cellulose acylate film were bonded together using a 3% aqueous solution of PVA (PVA-117H manufactured by Kuraray Co., Ltd.) as an adhesive, and further at 60 ° C. A polarizing plate was prepared by heating for 30 minutes. Bonding was performed so that the polarization axis and the longitudinal direction of the cellulose acylate film were 45 degrees.

3. Evaluation of Polarizing Plate The polarizing plate was attached to both surfaces of a glass plate using an adhesive so that the polarization axis was perpendicular. This was subjected to thermo-aging for 1000 hours under two conditions of 60 ° C. and 95% RH and 70 ° C. and 95% RH. The total light transmittance (orthogonal transmittance) of this was measured, and the polarization ability was evaluated. In addition, a film in which one polarizing plate was pasted on one side of glass was prepared, and the absorbance was measured at 400 nm and 500 nm, and the yellowness was evaluated by obtaining this difference. Moreover, the polarization characteristics before thermo were also evaluated. These results are shown in Table 3.
Furthermore, the diffusion coefficient of boric acid was determined before and after the wet heat thermostat, and the diffusion coefficient before the wet heat thermometer and the rate of change thereof (the difference between them divided by the value before the wet heat thermostat) were determined according to the above method. Further, the amount of boric acid in the polarizing layer after the thermo aging was determined according to the above method. Furthermore, the moisture permeability coefficient of the cellulose acylate film of the protective film before and after the thermometer was measured, and the moisture permeability coefficient before the moist heat thermometer and the rate of change (the difference between them divided by the value before the moist heat thermometer) It was determined according to the method. These values are listed in Table 3.

From Table 3, the following is clear.
The polarizing plate using the protective film (cellulose acylate film) of the present invention-1 to 20 having a diffusion coefficient of boric acid within the range of the present invention is a long time (60 ° C. 95% RH and 70 ° C.) in a severe wet heat atmosphere. Even when exposed to 95 ° C. and 1000% RH), good polarization properties (polarization degree, yellowishness) are maintained. On the other hand, in the case of Comparative Example 1 and Comparative Example-2, the diffusion coefficient of boric acid is larger than the range of the present invention, and good polarization characteristics are not maintained.
As described above, the polarizing plate of the present invention achieves robust durability, not to mention the 1000 hour thermo treatment at 60 ° C. and 95% RH, and is good even under the severer conditions of 70 ° C. and 95% RH. The result was obtained. In addition, a good polarizing plate without yellowing was achieved.

4). Application of Polarizing Plate to Display Element The polarizing plate of the present invention is a liquid crystal display device described in Example 1 of JP-A-10-48420 and a discotic liquid crystal described in Example 1 of JP-A-9-26572. An optically anisotropic layer containing molecules, an alignment film coated with polyvinyl alcohol, a VA liquid crystal display device described in FIGS. 2 to 9 of JP-A-2000-154261, and FIGS. 10 to 10 of JP-A-2000-154261. When used in the OCB type liquid crystal display device described in No. 15, good performance was obtained.

Claims (3)

A cellulose acylate in which at least one of the hydroxyl groups of the 2, 3, 6-position of the glucopyranose ring is substituted with an acylate group, and the substitution degree (S6) of the 6-position hydroxyl group with an acyl group is 0.87 or more. A casting step of casting a cellulose acylate of 97 or less and a polymer solution containing 35% by mass or less of a plasticizer on a substrate to form a web;
A heat treatment step in which after the web formed by the casting step is peeled from the base material, a heat treatment at 160 ° C. or more and 200 ° C. or less is performed for 1 minute or more and 120 minutes or less in a region where the residual solvent is 5% by mass or more and 30% by mass or less; A method for producing a cellulose acylate film.   A cellulose acylate film produced by the production method according to claim 1.   A polarizing plate using the cellulose acylate fill according to claim 2 as a protective film for a polarizing plate.