JPH1192574A - Cellulose ester film and production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cellulose ester film which has a low optical anisotropy and is usable in optical applications by incorporating a citric ester plasticizer into the same. SOLUTION: This film contains a compd. of the formula in an amt. of pref. 0.5-30 wt.%, still pref. 1-25 wt.%, esp. pref. 2-20 wt.%. In the formula, R1 is H, 1-8C alkyl, or acyl, pref. H, 1-3C (substd.) alkyl, or 1-7C acyl; R2 to R4 are each H, 1-18C alkyl, or acyl provided the case when at least two of them are H is excluded; and the sum of the numbers of carbon atoms of R2 to R4 is pref. 3-54, still pref. 6-36, esp. pref. 9-30. The b.p. of the compd. under normal pressure is pref. 280 deg.C or higher, still pref. 300 deg.C or higher, esp. pref. 350 deg.C or higher. Pref., the compd. is selected from among triethyl citrate, tri-n-butyl citrate, acetyltriethyl citrate, acetyl-n-butyl citrate, and acetyltri(2-ethylhexyl) citrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a cellulose film and a cellulose ester film, particularly for use as a liquid crystal protective film for optical use.

[0002]

2. Description of the Related Art Cellulose triacetate film is a typical support for photographic light-sensitive materials, and is also used in liquid crystal display devices, which have recently been expanding in the market due to its optical isotropy. Specific applications of the liquid crystal display device include a protective film for a polarizing plate and a color filter.

[0003] JP-A-9-95538 describes a solution of cellulose acetate and a method for preparing the solution.
However, in the above-mentioned method, it is difficult to control the surface state at the time of drying because three kinds of mixed solvents are used, and there is a concern about safety due to mixing of a peroxide because of containing an ether-based solvent. Also, the optical anisotropy was so large that it could not be used for optical applications. On the other hand, Plastic Materials Course 17 "Cellulosic Resin" by Maruzawa and Uda, published by Nikkan Kogyo Shimbunsha, p. 121, p. 121 describes triethyl citrate, diethyl succinate and the like as a plasticizer for cellulose resin. I have.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to produce a cellulose ester film having low optical anisotropy which can be used for optical applications. Another object of the present invention is to provide a cellulose ester solution which is dissolved in an acetone or methyl acetate solvent in a stable state.

[0005]

Means for Solving the Problems The present invention has been achieved by a cellulose ester film containing at least one compound represented by the following general formula (1). General formula (1) In the formula, R ₁ represents H, an alkyl group or an acyl group having 1 to 8 carbon atoms, R ₂ , R ₃ and R ₄ may be the same or different, and H is an alkyl group or an acyl group having 1 to 18 carbon atoms. And two or more of R ₁ , R ₂ , R ₃ or R ₄ are not simultaneously H.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The compound represented by the general formula [1] (hereinafter referred to as a plasticizer) of the present invention is abbreviated. In the general formula [1], R ₁ represents H, an acyl group containing a substituted or unsubstituted alkyl group having 1 to 8 carbon atoms, an alkylcarbonyl group, an alkenylcarbonyl group, an alkynylcarbonyl group or an aroyl group. Preferably, R ₁ is H, a substituted or unsubstituted alkyl group having 1 to 3 carbon atoms,
7, specifically H, methyl, ethyl,
Examples thereof include propyl, 2-ethylhexyl, acetyl, propionyl, butyryl, caproyl, chloroacetyl, pivaloyl, cyclohexanecarbonyl, benzoyl and the like. Particularly preferred are H, acetyl, propionyl, butyroyl, pivaloyl, cyclohexanecarbonyl.

[0007] R_Two, R_Three, R_FourMay be the same or different
H, substituted or unsubstituted alkyl having 1 to 18 carbon atoms
Group, alkenyl group, alkynyl group or aryl group
R ₁, R_Two, R_Three, R_FourTwo or more become H at the same time
Never. Specifically, H, methyl, ethyl, propyl
Isopropyl, butyl, isobutyl, t-butyl,
Pentyl, hexyl, heptyl, n-octyl, 2-e
Tylhexyl, nonyl, decyl, dodecyl, hexadecyl
Octadecyl, t-octyl, cyclohexyl,
Clohexylmethyl, 4-methylcyclohexyl, full
Ruffle, aryl, oleyl, phenyl, benzyl, etc.
is there. Preferably, H, methyl, ethyl, propyl, i
Isopropyl, butyl, isobutyl, t-butyl, 2-d
Tylhexyl, cyclohexyl, dodecyl, furfuryl
Oleyl and phenyl. Also, R_Two, R_Three, R_Four
Is from 3 to 54, preferably from 6 to 3
6, more preferably 9 to 30. General formula obtained
The compound [1] has a boiling point of 280 ° C. or higher at normal pressure.
Yes, a boiling point of 300 ° C or higher is more preferable,
Above is more preferable.

Specific examples of the plasticizer represented by the general formula (1) are shown below, but it should not be construed that the invention is limited thereto. ──────────────────────────────────── Compound R ₁ R ₂ R ₃ R ₄ ───── ─────────────────────────────── PL-1 Hydrogen methyl Same as left Same as left PL-2 Hydrogen ethyl Same as left Same as left PL-3 Hydrogen methyl Same as left Dodecyl PL-4 Hydrogen methyl Same as left Oleyl PL-5 Hydrogen butyl Same as left Same as left PL-6 Hydrogen t-butyl Same as left PL-7 Hydrogen cyclohexyl Same as left PL-8 Hydrofurfuryl Same as left PL-9 Hydrogen phenyl Same as left PL-10 Acetyl Methyl isopropyl dodecyl PL-11 acetyl 2-ethylhexyl Same as left PL-12 acetyl butyl Same as left t-butyl PL-13 acetyl t-butyl Same as left PL-14 Acetyl cyclohexyl Same as left PL- 15 Piperoyl methyl Same as left Same as left PL-16 Acetyl hydrogen butyl Same as left PL-17 Acetyl hydrogen cyclohexyl Same as left PL-18 Hydrogen hydrogen butyl Same as left PL-19 Hydrogen hydrogen cyclohexyl Same as left PL-20 Methyl butyl butyl Same as left ────────── ──────────────────────────

In the above, PL-2, PL-5, PL-11,
Pfizer's trade names Citroflex- such as PL-13
2, Citroflex-4, Citroflex A-8, Citroflex A-
The plasticizer known as 4 is preferred.

The plasticizer represented by the general formula [1] of the present invention is added to the solvent in an amount of 0.2 to 5% by weight, preferably 0.5 to 5% by weight, particularly preferably 0.5 to 3% by weight. Is done. The content of the plasticizer represented by the general formula [1] of the present invention in the film is 0.5 to 30% by weight, preferably 1 to 25% by weight, particularly preferably 2 to 25% by weight, based on the solid content of the film. ~
20% by weight. The present invention is characterized in that acetone or methyl acetate or a mixture thereof is used as a solvent for preparing a cellulose ester solution. The organic solvent is substantially free of halogenated hydrocarbons such as methylene chloride. “Substantially free” means that the proportion of halogenated hydrocarbon in the organic solvent is less than 5% by weight (preferably less than 2% by weight). In particular, methyl acetate has a higher dissolving ability of cellulose acetate during cooling than acetone, and can easily dissolve cellulose ester even at a relatively high cooling temperature (-30 to -20 ° C).

The solution contains at least 50% by weight of acetone or methyl acetate or a mixture thereof,
More preferably 50 to 90% by weight, particularly preferably 55 to 90% by weight.
~ 80% by weight.

In the present invention, a branched alcohol having 3 to 8 carbon atoms (these solvents are referred to as "solvent A").
Is preferably added to the solution. For example, isopropanol, isobutanol, t-butanol, isopentanol, isohexanol, cyclohexanol and the like are preferably used. Among these, isopropanol, isobutanol, t-butanol and cyclohexanol are particularly preferred. The amount added to the solution is preferably 1 to 20% by weight, more preferably 2 to 15% by weight, and still more preferably 5 to 15% by weight. By adding these solvents, excellent viscosity of the cellulose ester solution can be imparted, and appropriate film formation can be imparted. Further, in the present invention,
The cellulose ester solution has at least one carbon atom
It is preferred that the solution contains 1 to 4 linear alcohols (these solvents are referred to as “solvent B”) in an amount of 1 to 15% by weight based on the solution. These are methanol, ethanol, propanol, and butanol, and methanol and ethanol are particularly preferably used. The content is more preferably 2 to 15% by weight, and particularly preferably 3 to 10% by weight, based on the solution.

As the ester group of the cellulose ester used in the present invention, a fatty acid group having 2 to 4 carbon atoms (for example, acetyl group, propionyl group, butyryl group, etc.) is preferable, and cellulose mixed with these esters is also used. Among them, a cellulose acetate film is particularly preferable, and is also used for a liquid crystal display device whose market is expanding in recent years due to its optical isotropy. As a specific application in the liquid crystal display device, a protective film of a polarizing plate and a color filter are typical, and the average acetylation degree of cellulose acetate is preferably 57.0 to 62.5%. It is more preferably from 5 to 62.5%, particularly preferably from 58.0 to 62.5%. Here, the degree of acetylation means the amount of bound acetic acid per unit weight of cellulose. The degree of acetylation is ASTM: D-81
The measurement and calculation of the degree of acetylation in 7-91 (test method for cellulose acetate and the like) are performed. Furthermore, the viscosity average polymerization degree (DP) of the cellulose acetate preferably used in the present invention is preferably from 150 to 500, more preferably from 200 to 400, and more preferably from 250 to 250.
It is particularly preferable that the number is 360.

The cellulose acetate used in the present invention preferably has a narrow molecular weight distribution of Mw / Mn (Mw is a weight average molecular weight, Mn is a number average molecular weight) as determined by gel permeation chromatography. Specific M
The value of w / Mn is preferably from 1.0 to 1.7, more preferably from 1.3 to 1.65, and most preferably from 1.4 to 1.6. When forming a film, the cellulose acetate to be used may be used alone, or two or more different cellulose acetates may be mixed and used.

In preparing the solution, first, the cellulose ester is gradually added to the organic solvent at room temperature with stirring. At this stage, the cellulose ester generally swells but does not dissolve in the organic solvent. In addition, even if it is a solvent which can dissolve cellulose ester at room temperature, according to the cooling dissolution method, there is an effect that a uniform solution can be obtained quickly. The amount of cellulose ester is between 5 and 2 in this mixture.
Adjust so as to contain 5% by weight. More preferably, the amount of cellulose ester is from 10 to 23% by weight. Any additive described below may be added to the mixed solvent. Next, the mixture is cooled to -100 to -10C (preferably -100 to -10C, more preferably -10C).
(0 to -20C, most preferably -90 to -30C). For cooling, for example, a dry ice / methanol bath (−75 ° C.) or a cooled diethylene glycol solution (−
30 to -20 ° C). Further, the temperature can be easily lowered by a mechanical cooling device. When cooled in this way,
The mixture of the cellulose ester and the mixed solvent solidifies.

Further, when the mixture is heated to 0 to 150 ° C., in a cooling dissolution method in which the cellulose ester dissolves in the mixed solvent, it is preferable to use a closed container in order to avoid water contamination due to dew condensation during cooling. In addition, in the cooling and heating operation, if the pressure is increased during cooling and the pressure is reduced during heating, the dissolution time can be shortened. In order to perform pressurization and decompression, it is desirable to use a pressure-resistant container. The prepared cellulose ester solution can be used for producing a film. Specifically, the solution is used as a dope in a solvent casting method. The dope is cast on a support and the solvent is evaporated to form a film. The dope before casting has a solid content of 5 to 30% by weight.
It is preferable to adjust the concentration so that The surface of the support is preferably finished in a mirror surface state. A drum or a band is used as the support.

The dope is cast on a support having a surface temperature of 10 ° C. or lower, and is dried by blowing air for 2 seconds or more. The obtained film was peeled off from the support, and further heated at 100 to 160 ° C.
It is also possible to evaporate the residual solvent by drying with a high-temperature air having a temperature which is sequentially changed up to the above. The above method is described in Tokuhei 5-178.
No. 44 discloses this. According to this method, the time from casting to stripping can be reduced. In order to carry out this method, it is necessary that the dope gels at the surface temperature of the support during casting. The dope manufactured according to the present invention satisfies this condition. The thickness of the film produced according to the present invention is preferably from 5 to 500 μm, more preferably from 20 to 200 μm, most preferably from 60 to 130 μm.
A deterioration inhibitor (eg, a peroxide decomposing agent, a radical inhibitor, a metal deactivator, an acid scavenger) or an ultraviolet inhibitor may be added to the cellulose ester film. The deterioration inhibitor is described in JP-A-5-1907073. The UV inhibitors are described in JP-A-7-11056.

In the present invention, the following 2- (2'-hydroxy) benzotriazole derivative is preferably added in an amount of 0.1 to 3% by weight based on the cellulose ester. (1
-1) 2- (2'-hydroxy-5'-t-butylphenyl) -benzotriazole (1-2) 2- (2'-hydroxy-3 ', 5'-di-t-butylphenyl) -benzo Triazole (1-3) 2- (2'-hydroxy-
3'-t-butyl-5'-methylphenyl) -5-chlorobenzotriazole (1-4) 2- (2'-hydroxy-3 ', 5'-di-t-butylphenyl) -5-chlorobenzo Triazole (1-5) 2- (2'-hydroxy-5'-isooctylphenyl) -benzotriazole (1-6) 2- (2'-hydroxy-5'-n-octylphenyl) -benzotriazole (1 -7) 2-
(2'-hydroxy-3 ', 5'-di-t-amylphenyl) -benzotriazole (1-8) 2- (2'-hydroxy-5'-dodecylphenyl) -benzotriazole (1-9) 2 -(2'-hydroxy-5'-hexadecylphenyl) -benzotriazole (1-10) 2-
(2'-Hydroxy-3'-t-amyl-5'-benzophenyl) -benzotriazole In the present invention, benzotriazole compounds may be used alone or in combination of two or more.

Further, metal oxide fine particles such as silicon dioxide, calcium oxide, titanium dioxide and zinc oxide may be added. The particles have a particle size of 0.005 to 0.2 μm,
The addition amount is preferably 0.1% to 3% by weight based on the cellulose ester.

The cellulose ester film of the present invention is useful as an optical protective film for a liquid crystal, and can be particularly used as a protective film for a TFT liquid crystal. It can also be used as a support for a silver halide photographic light-sensitive material. Optical characteristics are retardation (Rth) in the thickness direction of the film.
As a measurement method, the film thickness was multiplied by the birefringence in the thickness direction at a wavelength of 632.8 nm using an ellipsometer (Ellipsometer AEP-100: manufactured by Shimadzu Corporation). And is determined by the following equation. Rth = {(nx + ny) / 2-nz} × d nx: refractive index in the horizontal direction, ny: refractive index in the vertical direction, nz:
The smaller the refractive index in the thickness direction, the better because there is no optical anisotropy in the thickness direction. Rth of the cellulose ester film of the present invention is 10
0 nm to 0 nm is required, and Rth is more preferably 80 nm to 3 nm, and particularly preferably 60 nm to 5 nm.

[0021]

EXAMPLES In each of the examples, the properties of the cellulose ester, the solution and the film were evaluated as follows. (1) Solubility The dissolved state of the produced cellulose ester solution in a solvent was visually observed, and the following evaluation was made according to the state. ：: The cellulose ester was completely dissolved and was a transparent liquid. X: The cellulose ester was partially insoluble and was not transparent.

(2) Solution stability (solution stability) The obtained solution was observed while standing at room temperature (23 ° C.) and evaluated by the following three grades A, B and C. A: Even after 10 days, transparency and uniformity are maintained, and good solubility and solution stability are exhibited. B: At the end of stirring, the mixture exhibits transparency and uniformity and exhibits good solubility, but after a lapse of one day, phase separation occurs, resulting in a non-uniform state. C: Immediately after the completion of stirring, a non-uniform slurry is formed, and a transparent and uniform solution state is not exhibited.

(3) Gelation Characteristics The change point of the coefficient A in the following Andrade equation was determined by a viscometer (manufactured by HAAKE). Gelation was judged from the change point and the attained viscosity. Rotor: sv-DIN Shear rate: 0.1 (1 / sec) Cooling rate: 0.5 ° C./min η = Aexp (B / T) In the formula, T is the measurement temperature, and A and B are the states of the polymer, respectively. Is an arbitrary constant determined by The presence or absence of gelation was determined by the presence or absence of a changing point of the coefficient A (whether or not the graph of viscosity and temperature had a bending point). It has excellent gelation.

(4) Peelability of Film The dope was cast in a film form on a support at -5 ° C., and the properties of the film when peeled off from the support were evaluated. A: What can be peeled off within 20 seconds B: What has peeling residue even after 60 seconds or more

(5) Elastic Modulus of Film A sample having a length of 100 mm and a width of 10 mm was subjected to ISO 1184
According to the standard of -1983, the elastic modulus was measured by measuring at an initial sample length of 50 mm and a tensile speed of 20 mm / min.

(6) Film tearing load A sample cut to 50 mn × 64 mm was subjected to ISO 638.
The tear load required for tearing was determined according to the standard of 3 / 2-1983.

(7) A sample cut into a film having a folding endurance of 120 mn was subjected to ISO 8776 / 2-1.
According to the standard of 988, the number of reciprocations until cutting by bending was determined.

(8) Moisture / heat resistance of film 1 g of a sample is folded and placed in a 15 ml glass bottle.
After humidity control at a temperature of 90 ° C. and a relative humidity of 100%, the container was sealed. This was aged at 90 ° C. and taken out after 200 hours. The state of the film was visually checked, and the following judgment was made. A: No particular abnormality is observed. B: Decomposition odor or shape change due to decomposition is observed.

(9) Retardation (Rth) in the thickness direction of the film Using an ellipsometer (Ellipsometer AEP-100: manufactured by Shimadzu Corporation), the birefringence in the thickness direction at a wavelength of 632.8 nm was measured. It is obtained by multiplying the film thickness by the following formula. Rth = {(nx + ny) / 2-nz} × d nx: refractive index in the horizontal direction, ny: refractive index in the vertical direction, nz:
It is preferable that the refractive index in the thickness direction is smaller, because there is no optical anisotropy in the thickness direction.

Example 1 1-1) Preparation of Solution At room temperature, the following cellulose ester mixture was prepared. The type and content (% by weight) are as shown in Table 1.・ Cellulose ester ・ <Cellulose acetate (acetylation degree 60.9%, viscosity average polymerization degree 299)> ・ Plasticizer ・ Acetone or / and methyl acetate ・ Solvent A (ethanol 10% by weight) ・ Solvent B ・ Ultraviolet absorber a : 2- (2'-hydroxy-3 ', 5'
-Di-t-butylphenyl) -5-chloro-benzotriazole (0.5% by weight based on cellulose ester) UV absorber b: 2- (2'-hydroxy-3 ', 5'
-Di-t-amylphenyl) benzotriazole (1.0% by weight based on cellulose ester) Colloidal silica (based on cellulose ester
0.04% by weight)

At room temperature, the cellulose ester did not dissolve at room temperature but swelled in the solution to form a slurry.
Next, the swelling mixture was placed in a double-layered container. While the mixture is being stirred slowly, the mixture in the inner container is -7 with dry ice / fluorine solvent as a refrigerant in the outer jacket.
Cooled to 0 ° C. Cooling with the refrigerant was continued until the mixture was uniformly cooled and solidified (30 minutes). The refrigerant in the jacket outside the vessel was removed and warm water was instead poured into the jacket. At a stage where the solification of the contents had progressed to some extent, stirring was started and the contents were heated to room temperature over 30 minutes. The above cooling and heating operations were repeated once. The obtained dope was visually observed to determine the presence or absence of gelation.

1-2) Film Formation The dope was cast using a band casting machine having an effective length of 6 m so that the dry film thickness became 100 μm. Band temperature is 0
° C. After drying for 2 seconds, the film was peeled off from the band and dried at 100 ° C for 3 minutes at 130 ° C.
For 5 minutes and at 160 ° C. for 5 minutes while drying the film while fixing the edges of the film to evaporate the remaining solvent.
Thus, a cellulose acetate film was produced. Each film thickness was 100 μm.

1-3) Results The properties of the prepared sample solutions and the films prepared therefrom are shown in Table 1. Table 1 shows that the sample of the present invention has liquid properties,
It was found that the film was excellent in film-forming properties, had good Rth characteristics, and could be used as a retardation film of a liquid crystal display device.

[0034]

[Table 1]

[0035]

[Table 2]

Example 2 Example 1 was repeated except that, in addition to t-butanol as the solvent A, 5 parts by weight of cyclohexanol was added to the sample 1-4 of the example 1 and ethanol was changed to 5 parts by weight.
When the sample 2-1 of the present invention was prepared in exactly the same manner as in No. 4, the Rth was 9 and was remarkably excellent. Therefore, in the present invention, it is possible to provide a cellulose ester film having an unprecedented Rth by using the branched alcohol t-butanol as the solvent A in combination with cyclohexanol.

Example 3 A sample 3-1 was prepared in exactly the same manner as in Example 1-4 except that the cellulose ester was changed to cellulose diacetate monoacetate. As in the case of the cellulose ester film, it had excellent liquid properties, film-forming properties and film properties.

Example 4 Except that the triacetyl cellulose manufactured by Fuji Photo Film Co., Ltd. of Example 1 described in JP-A-7-333433 was changed to the cellulose ester film of Sample 1-4 of Example 1 of the present invention. Example 1 of JP-A-7-333433
Optical Compensation Filter Film Sample 4-
1 was produced. The obtained filter film had excellent viewing angles in the right, left, up and down directions.

Example 5 On one of the film bases obtained in 1-4,
No. 73736, the first layer and the second layer of Example 1 (back layer composition) were applied to form a back layer having a cationic polymer as a conductive layer. Further, on the opposite side of the film base provided with the back layer obtained above,
The color negative light-sensitive material layer described in Example 1 of Japanese Patent No. 287345 was coated in multiple layers to prepare a light-sensitive material sample 5-1 of the present invention having a silver halide emulsion layer. The obtained light-sensitive material was excellent in elastic modulus, tear load, and number of times of folding endurance. Furthermore, both the base surface condition and the transfer (bleed-out) of the plasticizer to the surface were excellent.

[0040]

As described above, a cellulose ester film having a small optical anisotropy which can be used for optical applications can be produced. In addition, a cellulose ester solution dissolved in a stable state could be provided.

Claims (7)

[Claims] 1. A cellulose ester film comprising at least one compound represented by the general formula (1). General formula (1) In the formula, R ₁ represents H, an alkyl group or an acyl group having 1 to 8 carbon atoms, R ₂ , R ₃ , and R ₄ may be the same or different, and H is an alkyl group or an acyl group having 1 to 18 carbon atoms. And two or more of R ₁ , R ₂ , R ₃ or R ₄ are not simultaneously H. 2. The method according to claim 1, wherein the compound is triethyl citrate, tri-n-butyl citrate, acetyl triethyl citrate, acetyl tri-n-butyl citrate or acetyl tri- (2-ethylhexyl) citrate. The cellulose ester film according to claim 1. 3. The cellulose ester film according to claim 2, wherein said cellulose ester film is a cellulose triacetate film. 4. The cellulose ester film according to claim 1, wherein Rth in the thickness direction of the cellulose ester film is 100 nm to 0 nm. 5. The cellulose ester film according to claim 3, wherein the cellulose ester film is a retardation film for a liquid crystal display. 6. The cellulose ester film according to claim 2, wherein
The cellulose ester film according to claim 1, comprising a (2'-hydroxy) benzotriazole derivative as an ultraviolet absorber. 7. The method according to claim 1, wherein the solution of the cellulose ester is -10.
Cooling to 0-10 ° C, and cooling the cooled solution to 0 ° C.
A method for preparing a cellulose ester solution, comprising a step of dissolving the cellulose ester in the solution by heating to ~ 150 ° C.