JPH0940792A - Production of cellulose acetate film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a film from a cellulose acetate which gives a dope not having a high viscosity even when prepared at a high concentration and has good moldability. SOLUTION: This process comprises casting a dope on a substrate. The dope comprises a cellulose acetate which has an average degree of acetylation of 58.0-61.5% and which has an acetone-extractable content of 5wt.% or lower or is obtained through acetylation using a sulfuric acid catalyst in an amount of 10-15 pts.wt. per 100 pts.wt. cellulose, a plasticizer, and solvents containing 75-87wt.% methylene chloride. The total concent tration of the cellulose acetate and the plasticizer is 18-35wt.%.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a protective film, a polarizing plate protective film, a color filter, and a method for producing a cellulose acetate film used as a support for a photographic light-sensitive material.

[0002]

2. Description of the Related Art A cellulose acetate film is a polarizing plate used as a support for a photographic light-sensitive material because of its toughness and flame retardancy, and as a liquid crystal display device whose market is expanding recently due to its optical isotropy. Used for protective films and color filters. This cellulose acetate film is produced by a solution casting method in which a solution of cellulose acetate dissolved in methylene chloride (hereinafter referred to as "dope") is cast on a support. In this solution casting method, the time required from casting the dope onto the support to peeling off the film on the support greatly contributes to the productivity of the film forming step. Therefore, for example, as described in Japanese Examined Patent Publication No. 5-17844, a high-concentration dope is cast on a cooling drum to shorten the time until stripping after casting to make the casting equipment compact and It has been proposed to increase the membrane speed.

However, since the dope prepared at a high concentration has a high dope viscosity, it is necessary to enhance the ability of the liquid feeding facility and the planarity of the dope cast on the support is lowered. . As a means for solving these problems, it is possible to lower the degree of polymerization of cellulose acetate, but this will reduce the mechanical properties of the molded film, such as tensile elastic modulus, folding strength, tear strength, and the protective film. However, this is not an appropriate means because it deteriorates the quality of a cellulose acetate film used as a polarizing plate protective film, a color filter and a support for a photographic light-sensitive material.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing a cellulose acetate film using cellulose acetate which has good moldability and does not easily increase the dope viscosity even when prepared at a high concentration.

[0005]

Means for Solving the Problems As a result of the examination from the above viewpoints, the present inventors have solved the present problems by the following. That is, (1) The sum of the concentrations of the cellulose acetate having an average acetylation degree of 58.0 to 61.5% and the amount of acetone extracted of 5% by weight or less and the plasticizer is 18 to 35% by weight, and the solvent composition. The ratio of methylene chloride in 75 to 8
A method for producing a cellulose acetate film, which comprises casting 7% by weight of a dope on a support. (2) When the amount of the sulfuric acid catalyst during the acetylation reaction is 10 to 15 parts by weight with respect to 100 parts by weight of cellulose, the average degree of acetylation is 58.0 to 61.5% and the concentration of the cellulose acetate and the plasticizer is The sum is 18 to 35% by weight, and the ratio of methylene chloride in the solvent composition is 75 to 8
A method for producing a cellulose acetate film, which comprises casting 7% by weight of a dope on a support. (3) Cellulose triacetate is washed with one or more solvents selected from ketones, acetic acid esters or cellosolves to obtain an acetone extracted content of 5% by weight or less. (1) The method for producing a cellulose acetate film as described above. (4) The cellulose acetate has a concentrated solution viscosity (η) according to a falling-ball viscosity method with respect to a viscosity average degree of polymerization (DP) represented by the following formula (1): (1) or (2) A method for producing the cellulose acetate film described. Formula (1) 2.814 × ln (DP) -11.753 ≦ ln (η) ≦ 6.29 × ln (DP) −31.469 [In the formula, DP is an integer of 290 or more, and η is a transit time between the marked lines (sec. ). (5) The molecular weight distribution Mw / Mn of the cellulose acetate by gel permeation chromatography is
It is 1.0 to 1.7, The manufacturing method of the cellulose acetate film of said (1) or (2) characterized by the above-mentioned. (6) The method for producing a cellulose acetate film as described in (1) or (2) above, wherein the amount of heat of crystallization (ΔH _C ) from the molten state of the cellulose acetate is 5 to 17 J / g.

The cellulose acetate used in the present invention is
The average degree of acetylation is 58.0 to 61.5%, and the acetone extract content is 5% by weight or less. Here, the degree of acetylation refers to the amount of bound acetic acid per unit weight of cellulose, and as described later, according to the measurement and calculation of the degree of acetylation in ASTM: D-817-91 (test method for cellulose acetate, etc.). It is calculated. The degree of acetylation of cellulose acetate has a correlation with the mechanical strength of the film as described above, and when the degree of acetylation decreases, the elastic modulus and the folding endurance decrease. In addition, dimensional stability and resistance to moist heat are also lowered, and the quality required for a photographic support or an optical film cannot be sufficiently satisfied. Therefore, the cellulose acetate used in the present invention preferably has an average acetylation degree of 58.0 to 61.5%. The degree of polymerization of cellulose acetate used in the present invention is 250 or more, preferably 290 or more. This is because the strength of the obtained film becomes extremely poor with cellulose acetate having a degree of polymerization of 250 or less.

The cellulose acetate used in the present invention is
The concentrated solution viscosity (η) by the falling ball viscosity method with respect to the viscosity average degree of polymerization (DP) is cellulose acetate represented by the following formula (1). Formula (1) 2.814 × ln (DP) -11.753 ≦ ln (η) ≦ 6.29 × ln (DP) −31.469 [where DP is an integer of 290 or more, and η is the transit time between the marked lines (sec) ). This formula is calculated from the plot of the viscosity average degree of polymerization and the concentrated solution viscosity of the experimental data conducted by the present inventors. That is, in the case of a cellulose acetate having a viscosity average degree of polymerization of 290 or more, the viscosity of the concentrated solution generally increases exponentially with an increase in the degree of polymerization, whereas the cellulose acetate of the present invention is a concentrated solution with respect to the viscosity average degree of polymerization. It is characterized in that the increase in viscosity is linear, and the rate of increase in the viscosity of the concentrated solution with respect to the viscosity average degree of polymerization is small as compared with the general one.

The cellulose acetate of the present invention has a molecular weight distribution M by gel permeation chromatography.
It is characterized in that w / Mn (Mw is a weight average molecular weight and Mn is a number average molecular weight) is narrow. That is, the Mw / Mn of the cellulose acetate of the present invention is 1.0 to 1.7, preferably 1.3 to 1.65, more preferably 1.4 to 1.6. When the molecular weight distribution deviates from the upper limit of the above range, the dope viscosity increases and the flatness decreases. Also, if the lower limit is not reached, the mechanical properties of the molded film will deteriorate.

The cellulose acetate of the present invention is characterized by a small amount of crystallization heat, that is, a low degree of crystallization. That is, the heating value for crystallization (ΔH _C ) from the molten state of the cellulose acetate of the present invention is 5 to 17 J /
g, preferably 6 to 16 J / g, more preferably 1
0 to 16 J / g. If the amount of heat generated by crystallization exceeds the upper limit of the above range, a large amount of fine crystal components will be present in the formed film, resulting in deterioration in processability of the film. Further, when the lower limit is exceeded, the mechanical strength of the formed film is lowered, and the method described in Japanese Patent Publication No. 5-17844, that is, a method of forming a film by casting a high-concentration dope on a cooling drum, Since the gelation of the dope is delayed, it takes a long time to peel off the dope, and the film forming speed is lowered.

The cellulose acetate satisfying the above formula (1) in the present invention can be prepared by the following two methods. That is, as one method, cellulose triacetate obtained by a conventional method is used as a ketone,
This is a method of removing low molecular weight cellulose acetate, which causes crystallization, by washing with acetic acid esters, cellosolves and the like.

The characteristic feature of the cellulose acetate obtained by this washing is that when the cellulose triacetate obtained by the conventional method is washed once, the amount of low molecular weight cellulose triacetate present in the washing liquid is 1 with respect to the raw material weight.
Although it is present in an amount of about 0 to 15% by weight, the content of cellulose acetate after washing is 5% or less even if it is washed and extracted again. That is, it is necessary that the low molecular weight cellulose acetate is washed and extracted so that the content of the low-molecular weight cellulose acetate is 5% by weight or less even if the washing and extraction are performed again.
Further, the removal of the low molecular weight substances increases the average molecular weight (degree of polymerization), but the viscosity is lower than that having the same average molecular weight (degree of polymerization) obtained by a conventional method, and also in terms of productivity. It is advantageous.

The cellulose triacetate obtained by a conventional method before washing used in the present invention may be any cellulose triacetate obtained by any method. That is, the conventional method in the present invention is to react using acetic acid-acetic anhydride-sulfuric acid. Methylene chloride is used as a solvent from cellulose acetate obtained by an extremely general industrial process, the so-called methyl chloride method, and a non-solvent of cellulose acetate, for example, benzene and toluene are added to acetylate fibrous, so-called fibrous. Cellulose acetate obtained by any method such as acetylation may be used.

In the method for removing low molecular weight cellulose triacetate in the present invention, in order to improve the extraction efficiency, it is prepared by pulverizing or sieving so that the ratio of the particles passing through the cellulose acetate particle size of 20 mesh before washing becomes 70% by weight or more. To do. Further, as the washing extraction solvent used in the present invention, there are ketones, acetic acid esters, cellosolves, etc., but when industrially performed, it is a general-purpose solvent, low boiling point acetone, methyl acetate, methyl cellosolve is effective. Is. As a washing method, a solvent circulation method such as a Soxhlet extraction method may be used, or it may be obtained by stirring with a washing extract in a usual stirring tank to remove liquid. However, in the case of main washing extraction, 10 to 15
Since the low molecular weight cellulose triacetate of weight% is dissolved, the liquid becomes viscous and the operations such as deliquoring become difficult.
It is preferable that the amount of the processing raw material with respect to the liquid is 10% by weight or less.

The cellulose acetate satisfying the above formula (1) in the present invention can also be prepared by reacting a sulfuric acid catalyst amount in an amount of 10 to 15 parts by weight with respect to 100 parts by weight of cellulose during production.

Generally, cellulose triacetate has an acetylation degree of 59% or more, while commercially available cellulose triacetate is about 61%. The major difference between cellulose diacetate and cellulose triacetate at the time of production lies in the hydrolysis step after once converting cellulose triacetate. In the case of cellulose diacetate, it is necessary to perform hydrolysis to an acetylation degree that is soluble in acetone, but in the case of cellulose triacetate, it is preferable that the acetylation degree does not decrease. In cellulose triacetate, it is bonded to cellulose. Sulfuric acid should be hydrolyzed as quickly as possible. From the above, when the amount of the sulfuric acid catalyst in the acetylation reaction is increased, the amount of sulfuric acid bound to that amount is increased, and as a result, the degree of substitution obtained at the end of acetylation is low. Therefore, in general, cellulose triacetate, which is required to have a degree of acetylation of about 61%, reacts while reducing the amount of the sulfuric acid catalyst as much as possible.

That is, it has been found that the degree of acetylation can be increased from the conventional range of commercially available cellulose triacetate to slightly increase the amorphousness. That is, like the conventional method for producing cellulose triacetate, it can be deacetylated in the hydrolysis step, but in the present invention, highly amorphous cellulose triacetate is obtained by already reducing the degree of acetylation in the acetylation step. It is something that was discovered.

The dope of the present invention is a dope having a high concentration of cellulose acetate, and the total concentration of the cellulose acetate and the plasticizer is 18 to 35% by weight, preferably 2%.
A content of 0 to 35% by weight is suitable. The plasticizer is added to improve the mechanical properties of the molded film or to improve the solvent drying rate, and examples thereof include triphenyl phosphate (TPP) and tricresyl phosphate (TC).
P) and other phosphate compounds, dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), dioctyl phthalate (DO
P), phthalate ester compounds such as diethylhexyl phthalate (DEHP), fatty acid ester compounds such as butyl oleate, methylacetyl ricinoleate and dibutyl sebacate, acetyltriethyl citrate (OACT)
E), citric acid ester compounds such as acetyltributyl citrate (OACTB), and various trimellitic acid ester compounds. However, the above compounds are merely listed as examples, and the present invention is not limited thereto.

Examples of the additive components other than the plasticizer include, for example,
Deterioration preventing agent (peroxide decomposing agent, described in JP-A-5-97073) for improving the preservability of a molded film.
There are a radical inhibitor, a metal deactivator, an acid scavenger), or an ultraviolet inhibitor described in JP-A-7-11056. However, these are merely examples and the present invention is not limited to these.

The solvent is a mixed solvent of methylene chloride and another solvent. The other solvent is an alcohol having 1 to 4 carbon atoms, such as methanol or n-butanol, and is a poor solvent for cellulose acetate such as cyclohexane. These may be used alone or in combination of two or more. The mixing ratio is 75 for methylene chloride.
To 87% by weight, and therefore 13 to 25% of other solvents.
% By weight.

The concentration and solvent composition of cellulose acetate are arbitrarily determined within the above range. Japanese Patent Fair 5-178
According to the method described in Japanese Patent Publication No. 44-44, the gelling temperature of the dope depends on the concentration of cellulose acetate and the solvent composition in the method of performing low-temperature gelation and stripping on a support at 10 ° C. or less, and therefore, as early as possible at a predetermined temperature It is set so that gelation proceeds. However, the manufacturing method of the present invention is not limited to this method.

[0021]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to this range.

[Measurement method and calculation method of acetylation degree (%)] The acetylation degree is measured by a saponification method. That is, the dried cellulose acetate was precisely weighed and dissolved in a mixed solvent of acetone and dimethyl sulfoxide (volume ratio 4: 1), and then a predetermined amount of 1N-sodium hydroxide aqueous solution was added, and the mixture was saponified at 25 ° C. for 2 hours. Turn into. Add phenolphthalein as an indicator and add 1N sulfuric acid (concentration factor:
F) Titrate excess sodium hydroxide. A blank test is performed in the same manner as described above. And
The acetylation degree (%) is calculated according to the following formula. Acetification degree (%) = (6.005 × (B−A) × F) / W (In the formula, A is the amount of 1N-sulfuric acid (m) required for titration of the sample.
1) and B are 1N-sulfuric acid amount (m
1) and F are 1N-sulfuric acid factors, and W is a sample weight. )

[Molecular Weight and Molecular Weight Distribution] A high performance liquid chromatography system (GPC-LALLS) in which a gel filtration column is connected with a detector for detecting refractive index and light scattering.
It measured using. The measurement conditions are as follows.

Solvent: Methylene chloride Column: GMHx1 (manufactured by Tosoh Corporation) Sample concentration: 0.1 w / v% Flow rate: 1 ml / min Sample injection amount: 300 μl Standard sample: polymethylmethacrylate (Mw = 188,2)
00) Temperature: 23 ° C

[Measurement method and calculation method of viscosity average degree of polymerization (DP)] About 0.2 g of absolutely dried cellulose acetate
Is precisely weighed and dissolved in 100 ml of a solution of methylene chloride: ethanol = 9: 1. This is measured for the number of seconds of dropping with an Ostwald viscometer at 25 ° C., and the degree of polymerization is determined by the following formula. η _rel = T / T ₀ T: Falling seconds of measurement sample [η] = (ln η _rel ) / C T _O : Falling seconds of solvent alone DP = [η] / Km C: Concentration (g / l) Km : 6x10 ^-4

[Measurement Method of Concentrated Solution Viscosity (η)] Cellulose acetate was dissolved in methylene chloride: methanol = 8: 2 (weight ratio) so as to be 15% by weight, and the solution was viscous tube having an inner diameter of 2.6 cm. Injected into the
Predetermined hard sphere in solution, diameter 3.15 mm, 0.135 g
Was dropped, and the number of seconds that passed between the marked lines at intervals of 10 cm was defined as the viscosity.

[Measurement Method and Calculation Method of Crystallization Calorific Value (ΔH _C )] Cellulose acetate was dissolved in a mixed solvent (methylene chloride / ethanol = 9/1 (weight ratio),
After preparing a dope having a cellulose acetate concentration of 15% by weight, pressure filtration is performed using a non-woven fabric. The dope thus obtained is cast on a smooth glass plate using a bar coater. After air-drying for 1 day, it is peeled from the glass plate and vacuum dried at 80 ° C. for 4 hours. 10 mg of the obtained film sample is packed in a standard aluminum pan and placed on a sample stand of a heat-compensated differential scanning calorimeter (DSC). The sample is melted by holding it at the melting temperature for a short time, and then cooled to room temperature at a temperature lowering rate of 4 ° C./min to crystallize.

Heat generation of the DSC curve thus obtained
From the peak area, the crystallization heat value (ΔH _C). DS
C measurement is performed in a nitrogen atmosphere, and temperature calibration is In
Point: 156.60 ° C), Sn (melting point: 231.88 ° C)
In the two-point calibration, the calorific value calibration is In (heat of fusion: 28.45).
J / g) with one-point calibration. Also crystallization
The temperature analysis method is specified in JIS K7121-1987.
The analysis method of the crystallization heat value is described in JIS K 7122-
1987, respectively.

[Acetone extract (wt%)] After measuring the weight (A) of cellulose acetate, was stirred in 10 times weight of acetone at room temperature for 30 minutes, and then was obtained by pressure filtration with a filter. Was dried, and the solid content (B) was weighed. The acetone extract was calculated by the following formula. Acetone extractables (% by weight) = (B ÷ A) × 100%

[Mechanical physical properties of film] (1) Tensile test A sample having a length of 100 mm and a width of 10 mm is ISO1184-
According to the standard of 1983, the initial sample length was 50 mm and the tensile speed was 20 mm / min, and the elastic modulus and the breaking elongation were determined. (2) Tear test The sample cut to 50 mm x 64 mm is ISO6383.
The tear load required for tearing was determined in accordance with the standard of / 2-1983. (3) Folding resistance test A sample cut to 120 mm is ISO8776-198.
According to the standard of No. 8, the number of reciprocations until bending and cutting was determined.

Example 1 The cellulose acetate of the present invention (acetylation degree: 60.9%,
Polymerization degree: 322, solution viscosity: 101.5 seconds, acetone extraction: 0.4%, crystallization heat value: 14.0 J / g) 10
Triphenyl phosphate (TPP) 16 in 0 parts by weight
Parts by weight, methylene chloride 310 parts by weight, n-butanol 60 parts by weight, and methanol 11 parts by weight with a dope having a dry film thickness of 1 m using a band casting machine with an effective length of 6 m.
It was cast so as to have a diameter of 00 μm. The band temperature was 5 ° C., and no air was blown for drying. The mechanical properties of the molded film were measured by the methods described below.
The results are shown in Table 1.

Comparative Example 1 Cellulose triacetate obtained by a conventional method (Acetification degree: 60.9%, Polymerization degree: 299, Solution viscosity 74.7)
Second, acetone extracted: 12.1%, crystallization exotherm: 1
7.5 J / g) was cast by the same method as in Example 1, and the mechanical properties were measured by the methods described above. The results are shown in Table 1.

Comparative Examples 2 and 3 Cellulose acetate obtained by a conventional method having different physical properties such as acetylation degree, a film cast by the same method as in Example 1, and mechanical properties by the above-mentioned method. It was measured. The results are shown in Table 1.

Example 2 100 parts by weight of cellulose was esterified by a conventional method using 11.7 parts by weight of sulfuric acid, 260 parts by weight of acetic anhydride and 450 parts by weight of acetic acid, and further hydrolyzed. Obtained cellulose acetate (Acetification degree: 60.2%, Polymerization degree: 313, Solution viscosity: 92.7 seconds, Acetone extraction:
0.4%), the mechanical properties of the film cast by the same method as in Example 1 were measured by the methods described above. The results are shown in Table 1.

Example 3 100 parts by weight of cellulose was esterified by a conventional method using 11.7 parts by weight of sulfuric acid, 260 parts by weight of acetic anhydride and 450 parts by weight of acetic acid, and hydrolysis longer than that of Example 2 was carried out. went. The obtained cellulose acetate (acetylation degree:
59.8%, degree of polymerization: 326, solution viscosity: 105.8
Sec., Acetone extracted: 0.4%), the mechanical properties of the film cast by the same method as in Example 1 were measured by the above-mentioned methods. The results are shown in Table 1.

[0036]

[Table 1]

Examples 1 to 4 have mechanical properties equal to or higher than those of Comparative Examples 1 to 3.

[0038]

INDUSTRIAL APPLICABILITY The cellulose acetate of the present invention has a small increase rate of the concentrated solution viscosity (η) with respect to the viscosity average degree of polymerization (DP), and thus has a lower rate of increase than the conventional method.
Dopes can be prepared using highly polymerized cellulose acetate. Therefore, a molded film having high mechanical properties can be economically manufactured.

Claims (6)

[Claims] 1. The total sum of the concentrations of cellulose acetate having an acetone content of 5% by weight or less and an average acetylation degree of 58.0 to 61.5% and a plasticizer is 18 to 35% by weight,
And the ratio of methylene chloride in the solvent composition is 75
To 87% by weight of the dope is cast on a support to produce a cellulose acetate film. 2. The amount of sulfuric acid catalyst during the acetylation reaction is cellulose 1.
The sum of the concentrations of cellulose acetate having an average acetylation degree of 58.0 to 61.5% reacted with 10 to 15 parts by weight with respect to 00 parts by weight and the plasticizer is 18 to 35% by weight,
And the ratio of methylene chloride in the solvent composition is 75
To 87% by weight of the dope is cast on a support to produce a cellulose acetate film. 3. Cellulose triacetate is a ketone,
1 selected from acetates or cellosolves
The method for producing a cellulose acetate film according to claim 1, wherein the amount of acetone extracted is 5% by weight or less by washing with at least one kind of solvent. 4. The cellulose acetate having a concentrated solution viscosity (η) according to a falling ball viscosity method with respect to a viscosity average polymerization degree (DP) is represented by the following formula (1). 2. The method for producing a cellulose acetate film according to 2. Formula (1) 2.814 × ln (DP) -11.753 ≦ ln (η) ≦ 6.29 × ln (DP) −31.469 [In the formula, DP is an integer of 290 or more, and η is a transit time between the marked lines (sec. ). ] 5. A molecular weight distribution Mw / M of the cellulose acetate by gel permeation chromatography.
n is 1.0 to 1.7, The manufacturing method of the cellulose acetate film of Claim 1 or Claim 2 characterized by the above-mentioned. 6. The method for producing a cellulose acetate film according to claim 1, wherein the heating value for crystallization (ΔH _C ) from the molten state of the cellulose acetate is 5 to 17 J / g.