JPH1045801A - Production of cellulose acetate solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the production of cellulose acetate solution useful for photographic materials, etc., by adopting the highest possible cooling temperature in a cooling dissolution method. SOLUTION: A mixture of (A) a cellulose acetate having 58.25-62.5% average acetyl content with (B) an organic solvent is cooled to a temperature (T) defined by formula I [when the average acetyl content (Dac) of the component A is 58.25-60.0%] or formula II (when the Dac is 60.0-62.5%) in a cooling step when dissolving the component A in the component B and providing the objective solution according to the step for cooling the mixture of the components A and B to <=0 deg.C and a step for heating the cooled mixture to 5-50 deg.C. Furthermore, the component A preferably has 250-400 viscosity-average polymerization degree and the content of a low-molecular component is preferably low so as to afford <=10wt.% fraction of an acetone extract.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a cellulose acetate solution.

[0002]

2. Description of the Related Art Cellulose acetate films are used for various photographic materials and optical materials because of their toughness and flame retardancy. Cellulose acetate film is a typical support for photographic light-sensitive materials. In addition, cellulose acetate films are used in liquid crystal display devices, which have been expanding in market in recent years because of their 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. Degree of acetylation and polymerization of cellulose acetate (correlated with viscosity)
Is closely related to the mechanical strength and durability of the resulting film. As the degree of acetylation and the degree of polymerization decrease, the elastic modulus, folding strength, dimensional stability and wet heat resistance of the film also decrease. In order to satisfy the quality required for a photographic support or an optical film, the cellulose acetate must have a degree of acetylation of 58% or more (preferably 59% or more). Cellulose acetate having a degree of acetylation of 58% or more is generally classified as triacetyl cellulose (TAC). It is considered that the polymerization degree is preferably 270 or more as a viscosity average polymerization degree, and more preferably 290 or more.

[0003] Cellulose acetate films are generally produced by a solvent casting method or a melt casting method. In the solvent casting method, a solution (dope) in which cellulose acetate is dissolved in a solvent is cast on a support, and the solvent is evaporated to form a film. In the melt casting method, cellulose acetate melted by heating is cast on a support and cooled to form a film. The solvent cast method can produce a good film having higher flatness than the melt cast method. For this reason, practically, the solvent cast method is generally employed. The solvent used in the solvent casting method requires various conditions in addition to simply dissolving cellulose acetate. That is, in order to economically and efficiently produce a film having excellent planarity and uniform thickness, it is necessary to prepare a solution (dope) having an appropriate viscosity and a polymer concentration and having excellent storage stability. The dope is also required to be easily gelled and easily peeled from the support. To prepare such a dope, the choice of solvent type is very important. The solvent is required to be easily evaporated and to have a small residual amount in the film.

Various organic solvents have been proposed as a solvent for cellulose acetate, but the solvent satisfying all of the above requirements has been practically limited to methylene chloride. In other words, solvents other than methylene chloride have hardly been put to practical use. Methylene chloride is a very excellent organic solvent without the above problems. However, in recent years, the use of halogenated hydrocarbons such as methylene chloride has been significantly restricted from the viewpoint of global environmental protection. Also, methylene chloride is
Since it has a low boiling point (41 ° C.), it is easy to volatilize in the manufacturing process. For this reason, it is also a problem in the working environment. In order to prevent these problems, the manufacturing process is closed, but there is a technical limit even if it is hermetically closed. Therefore, there is an urgent need to search for a solvent for cellulose acetate that can substitute for methylene chloride.

[0005] Acetone (boiling point: 56 ° C), which is a general-purpose organic solvent, has an appropriate boiling point, and the drying load is not so large. Also, for the human body and the global environment,
Less problematic than chlorinated organic solvents. However, acetone has low solubility in cellulose acetate. Acetone shows some solubility in cellulose acetate having a degree of substitution of 2.70 (degree of acetylation: 58.8%) or less.
When the degree of substitution of cellulose acetate exceeds 2.70,
The solubility of acetone is further reduced. Degree of substitution 2.80
In the case of cellulose acetate having a degree of acetylation of 60.1% or more, acetone only shows a swelling action and does not show solubility.

[0006] M. G. FIG. Cowie et al., Mak
romol, chem. 143, 105 (197
1 year) is a cellulose acetate having a substitution degree of 2.80 (60.1% of acetylation degree) to a substitution degree of 2.90 (61.3% of acetylation degree) in acetone from -80 ° C to -70 ° C. It is reported that after cooling, heating was performed to obtain a dilute solution in which 0.5 to 5% by weight of cellulose acetate was dissolved in acetone. Hereinafter, such a method of cooling the mixture of cellulose acetate and acetone to obtain a solution is referred to as a “cooling dissolution method”. However, the dilute solution of 0.5 to 5% by weight described in the same paper,
It is not suitable for producing a cellulose acetate film. The dope for producing the film requires a concentration of cellulose acetate of 10 to 30% by weight.

For dissolving cellulose acetate in acetone, see Kenji Uede et al., "Dry spinning of cellulose triacetate from acetone solution", Journal of Textile Machinery Society, 34, 57-61 (1981). ) Also has a description. This paper, as its title, applied the cooling melting method to the technical field of spinning method. In the paper, the cooling dissolution method is studied while paying attention to the mechanical properties, dyeability and cross-sectional shape of the obtained fiber. In the method described in this paper, a mixture of cellulose acetate and acetone is cooled to −70 ° C. and then heated to 50 ° C.

[0008]

The inventors of the present invention have studied the practical use of the cooling and melting method, and found that the cooling temperature (-70 ° C.) required for the cooling and melting method is too low, which hinders the practical use. It has been found. Generally used cooling equipment belongs to a class called medium temperature, and the limit is -40 ° C (preferably -30 ° C or more). Temperatures below it belong to the class called low temperatures and require special equipment. Therefore, when the cooling temperature is low, the cost of the equipment and the cost required for manufacturing (particularly, the energy required for cooling) greatly increase.
Furthermore, temperatures below -50 ° C belong to a class called ultra-low temperature,
It costs even more. For this reason, it is very difficult to commercialize at a cooling temperature (−70 ° C.) performed by the conventional cooling and melting method. The present inventor has conducted research on the cooling and melting method, and found that the cooling and melting method can be performed in a temperature range called an intermediate temperature even at an ultra-low temperature such as -70 ° C. Of course, at a very high temperature, the effect of the cooling dissolution method cannot be obtained, and a solution cannot be produced. The present inventor has further studied and found that the required cooling temperature varies depending on the average acetylation degree of cellulose acetate. An object of the present invention is to produce a cellulose acetate solution in a cooling dissolution method by using a cooling temperature as high as possible.

[0009]

The object of the present invention has been attained by the following method. A step of cooling a mixture of cellulose acetate having an average degree of acetylation of 58.25 to 62.5% and an organic solvent to 0 ° C. or lower, and a step of heating the cooled mixture to 5 to 50 ° C. A method for producing a cellulose acetate solution by dissolving cellulose acetate therein, wherein in a cooling step, the mixture is cooled to a temperature (T) defined by the following formula (1a) or (1b). A method for producing an acetate solution. (1a) Average degree of acetylation of cellulose acetate (Dac)
Is not less than 58.25% and less than 60.0% −16 × Dac + 933 ≦ T (° C.) ≦ −16 × Dac +
943 (1b) Average degree of acetylation of cellulose acetate (Dac)
Is not less than 60.0% and not more than 62.5% −Dac + 33 ≦ T (° C.) ≦ −Dac + 43

The present invention can be carried out in the following embodiments. The method according to the above item, wherein the cellulose acetate has a viscosity average degree of polymerization of 250 to 400. Cellulose acetate contains 10% by weight of acetone
The production method according to the following, which is a cellulose acetate having a low content of low molecular components as described below. The production method according to the above item, wherein the cellulose acetate has a viscosity average polymerization degree (DP) satisfying the relationship of the following formula (2) and a concentrated solution viscosity (η) by a falling ball viscosity method. (2) 2.814 × ln (DP) -11.755 ≦ ln (η) ≦ 6.29 × l
n (DP) -31.469 In the formula, DP is a value of a viscosity average degree of polymerization of 290 or more;
η is the transit time (seconds) between the marked lines in the falling ball viscosity method. The production method according to the above item, wherein the cellulose acetate has a crystallization calorific value (ΔHc) of 5 to 17 J / g.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

[Cellulose Acetate] The cellulose acetate used in the present invention has an average acetylation degree (acetylation degree) of 58.25.
To 62.5%. The degree of acetylation means the amount of bound acetic acid per unit weight of cellulose. The degree of acetylation is AST
M: According to the measurement and calculation of the degree of acetylation in D-817-91 (test method for cellulose acetate and the like). The range of the degree of acetylation of the cellulose acetate is a value required to satisfy the quality required as a photographic support or an optical film.

[0012] Cellulose acetate can be synthesized from cotton linters or wood pulp. A mixture of cotton linter and wood pulp may be used. Generally, it is more economical to synthesize from wood pulp because of its lower cost. However, the load at the time of stripping can be reduced by mixing the cotton linter. Further, when the cotton linter is mixed, even if the film is formed in a short time, the surface state of the film does not deteriorate so much. Cellulose acetate is generally synthesized by acetylating cellulose with acetic acid-acetic anhydride-sulfuric acid. Industrially, a methyclo method using methylene chloride as a solvent or a fibrous acetylation method in which a non-solvent of cellulose acetate (eg, benzene, toluene) is added to produce acetic acid in a fibrous form are used.

The viscosity average degree of polymerization (DP) of cellulose acetate is preferably 250 or more,
More preferably, it is the above. In the case of cellulose acetate having a degree of polymerization of less than 250, the strength of the obtained film deteriorates. The viscosity average degree of polymerization is determined by the following equation from the intrinsic viscosity [η] of cellulose acetate measured by an Ostwald viscometer. (1) DP = [η] / Km where [η] is the intrinsic viscosity of cellulose acetate, and Km is a constant 6 × 10 ⁻⁴ .

When the viscosity-average degree of polymerization (DP) is 290 or more, it is preferable that the viscosity-average degree of polymerization and the concentrated solution viscosity (η) determined by the falling ball viscosity method satisfy the following formula (2). (2) 2.814 × ln (DP) -11.755 ≦ ln (η) ≦ 6.29 × l
n (DP) -31.469 In the formula, DP is a value of a viscosity average degree of polymerization of 290 or more;
η is the transit time (seconds) between the marked lines in the falling ball viscosity method. The above formula (2) is obtained by plotting the viscosity average polymerization degree and the concentrated solution viscosity from the data of the experiment conducted by the present inventors, and calculating from the results. Viscosity average degree of polymerization of 29
In cellulose acetate of 0 or more, the viscosity of the concentrated solution generally increases exponentially as the degree of polymerization increases. On the other hand, in the case of cellulose acetate satisfying the above formula, the increase in the viscosity of the concentrated solution with respect to the viscosity average degree of polymerization is linear. In other words, in the case of cellulose acetate having a high viscosity average degree of polymerization, it is preferable to suppress the increase in the viscosity of the concentrated solution so as to satisfy the above formula (1).

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) 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. M
If the value of w / Mn exceeds 1.7, the dope viscosity becomes too large, and the flatness of the film may be reduced.
In addition, cellulose acetate having a value of Mw / Mn of 1.0 to 1.4 is generally difficult to produce. In order to obtain cellulose acetate having a value in this range, only a substance having a remarkably low molecular weight is actually obtained. Therefore, films produced from such cellulose acetate often have low mechanical properties due to lower molecular weight.

The crystallization heat of cellulose acetate is as follows:
Preferably, the value is small. The small heat value of crystallization means that the degree of crystallization is small. Specifically, the heat of crystallization (ΔHc) is preferably 5 to 17 J / g, more preferably 6 to 16 J / g, and most preferably 10 to 16 J / g. If the heat of crystallization exceeds 17 J / g, many microcrystalline components will be present in the film. The presence of microcrystals reduces the solubility in acetone, which is a solvent. In addition, the stability of the obtained solution (dope) is low, and microcrystals are easily generated again. Further, the workability and optical properties of the obtained film are also reduced. On the other hand, the heat of crystallization is 5 J / g.
If the amount is less than the above, the mechanical strength of the obtained film decreases. Further, when the heat of crystallization is low, there is a problem that it takes time to gel the dope.

Cellulose acetate having a small amount of low molecular components can easily adjust the relationship between the viscosity average degree of polymerization (DP) and the concentrated solution viscosity (η), the molecular weight distribution of Mw / Mn or the range of the heat of crystallization as described above. Can be satisfied.
When the low molecular components are removed, the average molecular weight (degree of polymerization) increases, but the viscosity becomes lower than that of ordinary cellulose acetate. Accordingly, the relationship between DP and η can be satisfied. Further, when the low-molecular components are removed, the molecular weight distribution becomes uniform. Further, since the low-molecular component is easily crystallized, the removal of the low-molecular component can reduce the calorific value of crystallization. Cellulose acetate having a small amount of low molecular components can be obtained by removing low molecular components from cellulose acetate synthesized by a usual method (for example, commercially available).

The removal of low molecular components can be carried out by washing cellulose acetate with a suitable organic solvent.
Examples of the organic solvent include ketones (eg, acetone), acetates (eg, methyl acetate), and cellosolves (eg, methyl cellosolve). Ketones,
Particularly, it is preferable to use acetone. When cellulose acetate obtained by a usual method is washed once with an organic solvent, about 10 to 15% by weight of low-molecular-weight cellulose acetate based on the weight of the raw material is removed from the washing solution. When the second washing is performed on the washed cellulose acetate, the amount of the low-molecular cellulose acetate removed in the washing liquid is generally 10% by weight or less. 1 acetone extract
When the content is 0% by weight or less, the cellulose acetate is a cellulose acetate having a sufficiently small amount of low molecular components. Therefore, usually, cellulose acetate having a sufficiently low content of low molecular components can be obtained by one washing. More preferably, the acetone extractable content is 5% by weight or less.

In order to increase the efficiency of removing low molecular components,
Before washing, it is preferable to control the particle size by crushing or sieving the cellulose acetate particles. Specifically, 70% of the particles pass through the 20 mesh.
It is preferable to make adjustments as described above. As a washing method, a solvent circulation system such as a Soxhlet extraction method can be employed. Further, washing can be carried out by stirring with a solvent in an ordinary stirring tank and separating from the solvent. In the first washing, 10 to 15%
The liquid tends to be viscous because a small amount of low molecular components are dissolved in the solvent. For this reason, in consideration of the treatment operation, the ratio of cellulose acetate to the solvent is preferably 10% by weight or less.

When producing cellulose acetate having a small amount of low molecular components, the amount of the sulfuric acid catalyst in the acetylation reaction is preferably adjusted to 10 to 15 parts by weight based on 100 parts by weight of cellulose. When the amount of the sulfuric acid catalyst is in the above range (relatively large), cellulose acetate which is preferable in terms of molecular weight distribution (uniform molecular weight distribution) can be synthesized.

[Organic Solvent] In the present invention, an organic solvent is used for preparing the cellulose acetate solution. Preferably, the organic solvent is substantially free of halogenated hydrocarbons such as methylene chloride. "Substantially not included"
By means that the proportion of halogenated hydrocarbons in the organic solvent is less than 5% by weight (preferably less than 2% by weight). Preferred organic solvents are selected from ethers having 3 to 12 carbon atoms, ketones having 3 to 12 carbon atoms, and esters having 3 to 12 carbon atoms. Ethers, ketones and esters may have a cyclic structure. A compound having two or more functional groups of ether, ketone and ester (that is, -O-, -CO- and -COO-) can also be used as the organic solvent. The organic solvent may have another functional group such as an alcoholic hydroxyl group. In the case of an organic 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 one of the functional groups.

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

In addition to ethers, ketones and esters, other organic solvents may be used in combination. Examples of organic solvents that can be cooled off include nitromethane and alcohols having 1 to 6 carbon atoms (eg, methanol, ethanol, propanol, isopropanol, 1-butanol, t-butanol).
Butanol, 2-methyl-2-butanol, cyclohexanol). When ethers, ketones and esters are used in combination with other organic solvents, the ratio of ethers, ketones and esters in the mixed solvent is 10 to 99.5.
%, More preferably from 20 to 99% by weight, even more preferably from 40 to 98.5% by weight, and most preferably from 60 to 98% by weight.

[Formation of Dope (Cooling Dissolution Method)] In the present invention, a solution (dope) is formed by dissolving cellulose acetate in an organic solvent by a cooling dissolution method. In forming the dope, first, cellulose acetate is gradually added to an organic solvent at room temperature while stirring. At this stage,
Cellulose acetate swells in organic solvents but does not dissolve. The amount of cellulose acetate is adjusted so that the mixture contains 10 to 40% by weight. More preferably, the amount of cellulose acetate is from 10 to 30% by weight. Optional additives described below may be added to the organic solvent. Next, the mixture was cooled to 0 ° C.
Thereafter, the cooling is performed to a temperature (T) defined by the following formula (1a) or (1b). (1a) Average degree of acetylation of cellulose acetate (Dac)
Is not less than 58.25% and less than 60.0% −16 × Dac + 933 ≦ T (° C.) ≦ −16 × Dac +
943 (1b) Average degree of acetylation of cellulose acetate (Dac)
Is not less than 60.0% and not more than 62.5% −Dac + 33 ≦ T (° C.) ≦ −Dac + 43 The above temperature range is shown in FIG. FIG. 1 is a graph showing the range of the cooling temperature where the vertical axis represents the cooling temperature (T) and the horizontal axis represents the average acetylation degree (Dac) of cellulose acetate.
The hatched area in the graph is the range of the cooling temperature defined by the present invention. As shown in FIG. 1, it is possible to perform the cooling melting method even at a cooling temperature higher than the conventional technology (at least a temperature higher than −30 ° C.). In the graph of FIG. 1, values of Examples described later are also shown as 1 to 4.

Further, when this is heated to 5 to 50 ° C., cellulose acetate is dissolved in the organic solvent. The temperature may be raised only by leaving it at room temperature or may be heated in a warm bath. In this way, a dope in a uniform solution state is obtained. If the dissolution is insufficient, the operation of cooling and heating may be repeated. Whether or not the dissolution is sufficient can be determined only by visually observing the appearance of the dope. In the cooling dissolution method, it is preferable to use a closed container in order to avoid water contamination due to 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 stability of the obtained dope is an important condition in film production. During the transfer of the dope, it is necessary to avoid the occurrence of undissolved matter in the piping and the occurrence of solidification during the downtime for maintenance of the production equipment. The stability of the dope over time is related to the storage temperature and the dope concentration in addition to the above-mentioned properties of cellulose acetate.

[Casting and drying] The dope can be cast on a support and the solvent can be evaporated to form a film. The concentration of the dope before casting is preferably adjusted so that the solid content is 18 to 35%. The surface of the support is preferably finished in a mirror surface state. A drum or a band is used as the support. The casting and drying methods in the solvent casting method are described in US Pat. Nos. 2,336,310, 2,367,603, and 24.
No. 92078, No. 2492977, No. 2492978
Nos. 2607704, 2739069 and 27
39070, UK Patents 640731, 73689
No. 2, each specification, JP-B Nos. 45-4554 and 49-56
No. 14, JP-A-60-176834 and JP-A-60-203
Nos. 430 and 62-115035.

The dope is preferably cast on a support having a surface temperature of 10 ° C. or less. It is preferable to dry it by blowing it on the cast for 2 seconds. The obtained film can be peeled off from the support and dried with high-temperature air having a temperature gradually changed from 100 to 160 ° C. to evaporate the residual solvent. The above method is described in JP-B-5-17844. 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 to be manufactured is preferably 5 to 500 μm, more preferably 20 to 200 μm, and 60 to 12 μm.
Most preferably, it is 0 μm.

[Other Additives] A plasticizer can be added to the cellulose acetate film in order to improve mechanical properties or to increase the drying speed. As the plasticizer, a phosphoric acid ester or a carboxylic acid ester is used. Examples of phosphate esters include triphenyl phosphate (TPP) and tricresyl phosphate (TCP). Representative carboxylic esters include phthalic esters and citric esters. Examples of phthalate esters include dimethyl phthalate (DMP), diethyl phthalate (DE
P), dibutyl phthalate (DBP), dioctyl phthalate, (DOP) and diethylhexyl phthalate (DEHP). Examples of citrate esters include:
Includes acetyltriethyl citrate (OACTE) and acetyltributyl citrate (OACTB). Examples of other carboxylic esters include butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, and various trimellitic esters. Phthalate ester plasticizers (DMP, DEP, DBP, DO
P, DEHP) are preferably used. DEP is particularly preferred.

[0029]

EXAMPLES In each example, the chemical and physical properties of cellulose acetate and dope were measured and calculated as follows.

(1) Degree of acetylation (%) of cellulose acetate The degree of oxidation was measured by a saponification method. The dried cellulose acetate was precisely weighed and dissolved in a mixed solvent of acetone and dimethyl sulfoxide (volume ratio: 4: 1), and a predetermined amount of a 1N aqueous solution of sodium hydroxide was added, followed by saponification at 25 ° C for 2 hours. . Phenolphthalein was added as an indicator, and excess sodium hydroxide was titrated with 1N-sulfuric acid (concentration factor: F). A blank test was performed in the same manner as described above. Then, the degree of acetylation (%) was calculated according to the following equation. Degree of acetylation (%) = (6.05 × (BA) × F) / W In the formula, A is the amount of 1N-sulfuric acid (ml) required for titration of the sample,
B is the amount of 1N sulfuric acid (ml) required for the blank test, F
Represents a factor of 1N-sulfuric acid, and W represents a sample weight.

(2) Average Molecular Weight and Molecular Weight Distribution of Cellulose Acetate A high performance liquid chromatography system (GPC) in which a gel filtration column is connected with a detector for detecting refractive index and light scattering.
-LALLS). The measurement conditions are as follows. Solvent: methylene chloride Column: GMH × 1 (manufactured by Tosoh Corporation) Sample concentration: 0.1 W / v% Flow rate: 1 ml / min Sample injection volume: 300 μl Standard sample: polymethyl methacrylate (Mw = 188,
200) Temperature: 23 ° C

(3) Viscosity Average Degree of Polymerization (DP) of Cellulose Acetate Approximately 0.2 g of absolutely dried cellulose acetate was precisely weighed and dissolved in 100 ml of a mixed solvent of methylene chloride: ethanol = 9: 1 (weight ratio). This was measured for drop seconds at 25 ° C. using an Ostwald viscometer, and the degree of polymerization was determined by the following equation. η _rel = T / T ₀ T: Falling seconds of the measurement sample [η] = (1nη _rel ) / C T ₀ : Falling seconds of the solvent alone DP = [η] / Km C: Concentration (g / l) Km : 6 × 10 ^-4

(4) Viscosity of concentrated solution of cellulose acetate (η) Cellulose acetate was dissolved in a mixed solvent of methylene chloride: methanol = 8: 2 (weight ratio) so as to have a concentration of 15% by weight. Inject into a 6 cm viscosity tube,
After adjusting the temperature to 25 ° C., the solution had a diameter of 3.15 mm, 0.13 mm.
The time (seconds) during which 5 g of a hard sphere was dropped and passed through a gauge tube at an interval of 10 cm was defined as the viscosity.

(5) Heating value for crystallization of cellulose acetate (ΔHc) Cellulose acetate was dissolved in a mixed solvent of methylene chloride: ethanol = 9: 1 (weight ratio) to prepare a dope of 15% by weight of cellulose acetate. . The dope was filtered under pressure using a nonwoven fabric, and cast on a smooth glass plate using a bar coater. After air drying for one day, it was peeled off from the glass plate and vacuum dried at 80 ° C. for 4 hours. 10 mg of the obtained film sample was packed in a standard aluminum pan and placed on a sample stage of a thermal compensation type differential scanning calorimeter (DSC). After holding the sample at the melting temperature for a short time to melt the sample, the temperature was lowered at a rate of 4 ° C./mi.
n and cooled to room temperature for crystallization. The crystallization exotherm (ΔHc) was determined from the exothermic peak area of the DSC curve thus obtained. DSC measurement was performed under a nitrogen atmosphere, and temperature calibration was performed using In (melting point: 156.60 ° C.), Sn
(Melting point: 231.88 ° C.)
This was performed by one-point calibration of In (heat of fusion: 28.45 J / g). The crystallization temperature is analyzed according to JIS
-K-7121 (1987) and the crystallization calorific value analysis method conformed to JIS-K-7122 (1987).

(6) Acetone extraction (%) of cellulose acetate After measuring the weight (A) of cellulose acetate, 10%
After stirring at room temperature for 30 minutes in double weight acetone, the mixture was filtered under pressure with a filter. The obtained filtrate was dried and the solid content weight (B) was measured. The acetone extractables were calculated by the following equation. Acetone extract = (B ÷ A) × 100

(7) Measurement of Dope Viscosity and Judgment of Gelation The change point of 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 can be determined by the presence or absence of a changing point of the coefficient A (whether or not the graph of viscosity and temperature has an inflection point).

Example 1 Average acetylation degree at room temperature:
75 parts by weight of cellulose acetate having a viscosity average polymerization degree of 60.9, 400 parts by weight of methyl acetate, and 100 parts by weight of acetone were mixed. The proportion of cellulose acetate in the mixture is 13% by weight. At room temperature, the cellulose acetate swelled in the solvent without dissolving. The resulting swollen mixture formed a slurry. Next, the swelling mixture was placed in a double-layered container. While the mixture was slowly stirred, a saturated aqueous solution of calcium chloride (−25 ° C.) was poured as a refrigerant into the outer jacket. This allowed the mixture in the inner vessel to cool to −25 ° C. over 20 minutes and hold at that temperature for another 40 minutes.

[0038] The refrigerant in the jacket outside the container was removed and warm water was instead poured into the jacket. At a stage where the sol formation of the content has progressed to some extent, stirring of the content was started. In this way, it was warmed to room temperature over 30 minutes. Further, the above cooling and heating operations were repeated once. When the obtained dope was visually observed, cellulose acetate was completely dissolved in the solvent, and a uniform dope was obtained. When the presence or absence of gelation was determined for the dope by the measurement method (7), gelation at a low temperature was recognized.

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. The band temperature was 0 ° C. After drying for 2 seconds, the film was peeled off from the band, and then stepped at 100 ° C. for 3 minutes, 130 ° C. for 5 minutes, and 160 ° C. for 5 minutes while fixing the end of the film. Dry and evaporate the remaining solvent. Thus, a cellulose acetate film was produced.

Example 2 Average acetylation degree at room temperature:
60.2, 90 parts by weight of cellulose acetate having a viscosity average polymerization degree of 323, 400 parts by weight of methyl acetate and 100 parts by weight of acetone were mixed. The proportion of cellulose acetate in the mixture is 15.3% by weight. At room temperature, the cellulose acetate swelled in the solvent without dissolving. The resulting swollen mixture formed a slurry. The swelled mixture was treated as in Example 1 to form a dope.
When the obtained dope was visually observed, cellulose acetate was completely dissolved in the solvent, and a uniform dope was obtained. Further, gelation at a low temperature was also observed. The dope was cast and dried in the same manner as in Example 1, and the thickness was 100 μm.
m of cellulose acetate film was produced.

Example 3 At room temperature, average degree of acetylation:
90 parts by weight of cellulose acetate having a viscosity average degree of polymerization of 59.5, 295, 400 parts by weight of methyl acetate and 100 parts by weight of acetone were mixed. The proportion of cellulose acetate in the mixture is 15.3% by weight. At room temperature, the cellulose acetate swelled in the solvent without dissolving. The resulting swollen mixture formed a slurry. The swelled mixture was prepared as in Example 1 except that the cooling temperature was changed to -15 ° C.
By performing the same treatment as described above, a dope was formed. When the obtained dope was visually observed, cellulose acetate was completely dissolved in the solvent, and a uniform dope was obtained.
Further, gelation at a low temperature was also observed. Doping Example 1
Then, the mixture was cast and dried to produce a cellulose acetate film having a thickness of 100 μm.

Comparative Example 1 At room temperature (20 ° C.), 75 parts by weight of cellulose acetate having an average acetylation degree of 60.9 and a viscosity average polymerization degree of 299, 400 parts by weight of methyl acetate and 100 parts by weight of acetone were mixed. . The proportion of cellulose acetate in the mixture is 13% by weight. The swelled mixture was charged into the double container used in Example 1. While stirring the mixture slowly, add room temperature (20
C) of water. The mixture was thus kept stirring at room temperature for 30 minutes. The swollen mixture still formed a slurry without dissolving. The stirring operation for 30 minutes was repeated three more times, but the swollen mixture still formed a slurry without dissolving.

Comparative Example 2 At room temperature (20 ° C.), 90 parts by weight of cellulose acetate having an average degree of acetylation of 60.2 and a viscosity average degree of polymerization of 323, 400 parts by weight of methyl acetate and 100 parts by weight of acetone were mixed. . The proportion of cellulose acetate in the mixture is 15.3% by weight. The swelled mixture was treated in the same manner as in Comparative Example 1, and an attempt was made to prepare a solution at room temperature. However, cellulose acetate is
It only swelled without dissolving in the solvent.

Comparative Example 3 At room temperature (20 ° C.), 90 parts by weight of cellulose acetate having an average degree of acetylation of 59.5 and a viscosity average degree of polymerization of 295, 400 parts by weight of methyl acetate and 100 parts by weight of acetone were mixed. . The proportion of cellulose acetate in the mixture is 15.3% by weight. The swelled mixture was treated in the same manner as in Comparative Example 1, and an attempt was made to prepare a solution at room temperature. However, cellulose acetate is
It only swelled without dissolving in the solvent.

Comparative Example 4 A solution was prepared at room temperature in the same manner as in Comparative Example 1 except that cellulose acetate having an average acetylation degree of 57.0 and a viscosity average polymerization degree of 280 was used. Cellulose acetate could be dissolved in acetone. The dope is measured by the measuring method of (7),
When the presence or absence of gelation was determined, no gelation at low temperature was observed. The dope was cast and dried in the same manner as in Example 1 to produce a cellulose acetate film.
Since there was no gelation at low temperature, the film could not be peeled from the support until the drying of the film was almost completed. Further, during the drying step, since the film was placed on the support, shrinkage occurred only in the thickness direction, and a film stretched in the plane direction was obtained. This film was easily broken and had insufficient physical strength.

Example 4 At room temperature, average degree of acetylation:
75 parts by weight of cellulose acetate having a viscosity average polymerization degree of 60.9, 300 parts by weight of methyl acetate, and 200 parts by weight of acetone were mixed. The proportion of cellulose acetate in the mixture is 13% by weight. At room temperature, the cellulose acetate swelled in the solvent without dissolving. The resulting swollen mixture formed a slurry. The swelled mixture was treated as in Example 1 to form a dope. When the obtained dope was visually observed, cellulose acetate was completely dissolved in the solvent, and a uniform dope was obtained. Further, gelation at a low temperature was also observed. The dope was cast and dried in the same manner as in Example 1 to produce a cellulose acetate film having a thickness of 100 μm.

Example 5 Average acetylation degree at room temperature:
60.2, 90 parts by weight of cellulose acetate having a viscosity average polymerization degree of 323, 300 parts by weight of methyl acetate and 200 parts by weight of acetone were mixed. The proportion of cellulose acetate in the mixture is 15.3% by weight. At room temperature, the cellulose acetate swelled in the solvent without dissolving. The resulting swollen mixture formed a slurry. The swelled mixture was treated as in Example 1 to form a dope.
When the obtained dope was visually observed, cellulose acetate was completely dissolved in the solvent, and a uniform dope was obtained. Further, gelation at a low temperature was also observed. The dope was cast and dried in the same manner as in Example 1, and the thickness was 100 μm.
m of cellulose acetate film was produced.

Example 6 Average acetylation degree at room temperature:
90 parts by weight of cellulose acetate having a viscosity average polymerization degree of 59.5, 300 parts by weight of methyl acetate and 200 parts by weight of acetone were mixed. The proportion of cellulose acetate in the mixture is 15.3% by weight. At room temperature, the cellulose acetate swelled in the solvent without dissolving. The resulting swollen mixture formed a slurry. The swelled mixture was prepared as in Example 1 except that the cooling temperature was changed to -15 ° C.
By performing the same treatment as described above, a dope was formed. When the obtained dope was visually observed, cellulose acetate was completely dissolved in the solvent, and a uniform dope was obtained.
Further, gelation at a low temperature was also observed. Doping Example 1
Then, the mixture was cast and dried to produce a cellulose acetate film having a thickness of 100 μm.

Example 7 Average acetylation degree at room temperature:
60.2, 75 parts by weight of cellulose acetate having a viscosity average polymerization degree of 323, 150 parts by weight of methyl acetate and 350 parts by weight of acetone were mixed. The proportion of cellulose acetate in the mixture is 13% by weight. At room temperature, the cellulose acetate swelled in the solvent without dissolving. The resulting swollen mixture formed a slurry. The swelled mixture was treated as in Example 1 to form a dope. When the obtained dope was visually observed, cellulose acetate was completely dissolved in the solvent, and a uniform dope was obtained. Further, gelation at a low temperature was also observed. The dope was cast and dried in the same manner as in Example 1 to produce a cellulose acetate film having a thickness of 100 μm.

Example 8 Average acetylation degree at room temperature:
75 parts by weight of cellulose acetate having a viscosity average polymerization degree of 59.5, 150 parts by weight of methyl acetate and 350 parts by weight of acetone were mixed. The proportion of cellulose acetate in the mixture is 13% by weight. At room temperature, the cellulose acetate swelled in the solvent without dissolving. The resulting swollen mixture formed a slurry. The swelled mixture was treated in the same manner as in Example 1 except that the cooling temperature was changed to -15 ° C to form a dope. When the obtained dope was visually observed, cellulose acetate was completely dissolved in the solvent, and a uniform dope was obtained. Further, gelation at a low temperature was also observed. The dope was cast and dried in the same manner as in Example 1 to produce a cellulose acetate film having a thickness of 100 μm.

Example 9 At room temperature, average acetylation degree:
90 parts by weight of cellulose acetate having a viscosity average polymerization degree of 59.8 and 250 parts by weight of acetone were mixed. The proportion of cellulose acetate in the mixture was 15.
3% by weight. At room temperature, the cellulose acetate swelled in the solvent without dissolving. The resulting swollen mixture formed a slurry. The swelled mixture was treated in the same manner as in Example 1 except that the cooling temperature was changed to -20 ° C to form a dope. When the obtained dope was visually observed, cellulose acetate was completely dissolved in the solvent, and a uniform dope was obtained. Further, gelation at a low temperature was also observed. The dope was cast and dried as in Example 1,
A cellulose acetate film having a thickness of 100 μm was produced.

Example 10 At room temperature, 90 parts by weight of cellulose acetate having an average acetylation degree of 60.2 and a viscosity average polymerization degree of 323, 350 parts by weight of acetone and 150 parts by weight of dimethyl carbonate were mixed. The proportion of cellulose acetate in the mixture is 15.3% by weight. At room temperature, the cellulose acetate swelled in the solvent without dissolving. The resulting swollen mixture formed a slurry.
The swelled mixture was treated as in Example 1 to form a dope. When the obtained dope was visually observed, cellulose acetate was completely dissolved in the solvent, and a uniform dope was obtained. Further, gelation at a low temperature was also observed. The dope was cast and dried in the same manner as in Example 1 to a thickness of 1
A 00 μm cellulose acetate film was produced.

Example 11 At room temperature, 90 parts by weight of cellulose acetate having an average acetylation degree of 59.5% and a viscosity average degree of polymerization of 295 were mixed with 500 parts by weight of 1,3-dioxolane. The proportion of cellulose acetate in the mixture is 15.3% by weight. When the mixture was stirred at room temperature for 4 hours, all the cellulose acetate was dissolved in the 1,3-dioxolane. In 30 minutes after mixing, although a part of the cellulose acetate is dissolved, most of the cellulose acetate is swollen. This was treated by the cooling dissolution method in the same manner as in Example 1 to form a dope. When the obtained dope was visually observed, all the cellulose acetate was dissolved in 1,3-dioxolane, and a uniform dope was obtained. Further, gelation at a low temperature was also observed. When the cooling dissolution method was used, the cellulose acetate could be completely dissolved in a shorter time (2 hours) than when stirring was continued at room temperature. The dope was cast and dried in the same manner as in Example 1 to produce a cellulose acetate film having a thickness of 100 μm.

Example 12 At room temperature, 90 parts by weight of cellulose acetate having an average acetylation degree of 60.2% and a viscosity average degree of polymerization of 323 and 500 parts by weight of 1,4-dioxane were mixed. The proportion of cellulose acetate in the mixture is 15.3% by weight. When the mixture was stirred at room temperature for 5 hours, all the cellulose acetate was dissolved in 1,4-dioxane. In 30 minutes after mixing, a part of the cellulose acetate is dissolved, but most of the cellulose acetate is only swollen. This was treated by the cooling dissolution method in the same manner as in Example 1 to form a dope. When the obtained dope was visually observed, all the cellulose acetate was dissolved in 1,4-dioxane, and a uniform dope was obtained. Further, gelation at a low temperature was also observed. When the cooling dissolution method was used, the cellulose acetate could be completely dissolved in a shorter time (2 hours) than when stirring was continued at room temperature. The dope was cast and dried as in Example 1,
A cellulose acetate film having a thickness of 100 μm was produced.

Example 13 At room temperature, 75 parts by weight of cellulose acetate having an average degree of acetylation of 60.9% and a viscosity average degree of polymerization of 299, 400 parts by weight of methyl acetate, and 1 part of acetone
00 parts by weight and 10 parts by weight of diethyl phthalate (DEP, plasticizer) were mixed. The proportion of cellulose acetate in the mixture is 12.8% by weight. At room temperature, the cellulose acetate swelled in the solvent without dissolving. The resulting swollen mixture formed a slurry. The swelled mixture was treated as in Example 1 to form a dope.
When the obtained dope was visually observed, cellulose acetate was completely dissolved in the solvent, and a uniform dope was obtained. Further, gelation at a low temperature was also observed. The dope was cast and dried in the same manner as in Example 1, and the thickness was 100 μm.
m of cellulose acetate film was produced.

Example 14 At room temperature, 75 parts by weight of cellulose acetate having an average acetylation degree of 60.2% and a viscosity average degree of polymerization of 323, 400 parts by weight of methyl acetate, and 1 part of acetone
00 parts by weight and triphenyl phosphate (TPP,
(Plasticizer) 10 parts by weight. The proportion of cellulose acetate in the mixture is 12.8% by weight. At room temperature, the cellulose acetate swelled in the solvent without dissolving. The resulting swollen mixture formed a slurry.
The swelled mixture was treated as in Example 1 to form a dope. When the obtained dope was visually observed, cellulose acetate was completely dissolved in the solvent, and a uniform dope was obtained. Further, gelation at a low temperature was also observed. The dope was cast and dried in the same manner as in Example 1 to a thickness of 1
A 00 μm cellulose acetate film was produced.

Example 15 The cellulose acetate (average acetylation degree: 60.9%, viscosity average polymerization degree: 299) used in Example 1 was stirred at room temperature for 30 minutes in a 10-fold amount of acetone. It was drained and dried. Cellulose acetate obtained (from which low molecular components were removed) (average acetylation degree: 6)
0.9%, viscosity average degree of polymerization: 322)
In the same manner as in Example 1, a dope was formed by a cooling dissolution method. Further, a cellulose acetate film having a thickness of 100 μm was produced in the same manner as in Example 1 using the obtained dope.

Example 16 100 parts by weight of cellulose was esterified and hydrolyzed 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 the average acetylation was carried out. Degree: 60.2%
A cellulose acetate having a viscosity average polymerization degree of 323 was synthesized. A dope was formed by a cooling dissolution method in the same manner as in Example 2 except that the obtained cellulose acetate (containing a small amount of low molecular components) was used. Further, a cellulose acetate film having a thickness of 100 μm was produced in the same manner as in Example 1 using the obtained dope.

The results of each of the above examples are summarized in Table 1 below.

[0060]

Table 1 Table 1 Sample cellulose acetate solvent 1 Solvent 2 Dissolution treatment Dissolution No.Acetification degree Concentration Kind Kind Kind Amount Temperature ──────────────────────────────────── Example 1 60.9 13.0 MA 400 Acetone 100-25 ° C melting Example 2 60.2 15.3 MA 400 Acetone 100-25 ° C melting Example 3 59.5 15.3 MA 400 Acetone 100-15 ° C Dissolution Comparative Example 1 60.9 13.0 MA 400 Acetone 100 20 ° C. Insoluble Comparative Example 2 60.2 15.3 MA 400 Acetone 100 20 ° C. Insoluble Example 3 59.5 15.3 MA 400 Acetone 100 20 ° C. Insoluble Comparative Example 4 57.0 13.0 M 400 acetone 100 20 ° C. melting Example 4 60.9 13.0 MA 300 acetone 200−25 ° C. melting Example 5 60.2 15.3 MA 300 acetone 200−25 ° C. melting Example 6 59.5 13.0 MA 300 acetone 200-15 ° C melting Example 7 60.2 13.0 MA150 acetone 350-25 ° C melting Example 8 59.5 13.0 MA150 acetone 350-15 ° C melting Example 9 59.8 15.3 Acetone 500-20 ° C dissolution Example 10 60.2 15.3 Acetone 350 DMCA 150-25 ° C dissolution Example 11 59.5 15.3 Oxolan 500-25 ° C dissolution Example 12 60.2 15.3 Oxane 500- 25 ° C. dissolution Example 13 60.9 13.0 MA 400 Acetone 100 −25 ° C. dissolution Example 14 60.2 15.3 MA 400 Acetone 100-25 C Dissolution Example 15 60.9 13.0 MA 400 Acetone 100-25 C Dissolution Example 16 60.2 15.3 MA 400 Acetone 100-25 C Dissolution ── ──────────────────────────────────

(Note) MA: methyl acetate DMCA: dimethyl carbonate oxolane: 1,3-dioxolane oxane: 1,4-dioxane Example 13: Addition of 10 parts by weight of diethyl phthalate Example 14: Addition of 10 parts by weight of triphenyl phosphate Example 15: Cellulose acetate from which low molecular components have been removed Example 16: Cellulose acetate having low low molecular components

The relationship between the average acetylation degree and the cooling temperature in each of the above examples is plotted in FIG. The points 1 to 4 in FIG. 1 correspond to the following embodiments. 1 (average acetylation degree: 59.5%, cooling temperature −15 ° C.): Examples 3, 6, 8, 112 (average acetylation degree: 59.8%, cooling temperature −20 ° C.): Example 9 3 (average acetylation degree: 60.2%, cooling temperature −25 ° C.): Examples 2, 5, 7, 10, 12, 14, 164 (average acetylation degree: 60.9%, cooling temperature −25) ° C): Examples 1, 4, 13, 15

[0063]

According to the present invention, a cellulose ester solution can be produced by a cooling dissolution method even at a relatively high cooling temperature.

[Brief description of the drawings]

FIG. 1 is a graph showing a range of a cooling temperature in which the vertical axis represents the cooling temperature and the horizontal axis represents the average acetylation degree of cellulose acetate.

[Explanation of symbols]

 1 Example 3, 6, 8, 11 2 Example 9 3 Example 2, 5, 7, 10, 12, 14, 16 4 Example 1, 4, 13, 15

Claims (5)

[Claims] 1. A step of cooling a mixture of cellulose acetate having an average acetylation degree of 58.25 to 62.5% and an organic solvent to 0 ° C. or lower, and heating the cooled mixture to 5 to 50 ° C. A method for producing a cellulose acetate solution by dissolving cellulose acetate in an organic solvent by a step, wherein in the cooling step, the mixture is treated with the following formula (1a) or (1)
A method for producing a cellulose acetate solution, comprising cooling to a temperature (T) defined in b). (1a) Average degree of acetylation of cellulose acetate (Dac)
Is not less than 58.25% and less than 60.0% −16 × Dac + 933 ≦ T (° C.) ≦ −16 × Dac +
943 (1b) Average degree of acetylation of cellulose acetate (Dac)
Is not less than 60.0% and not more than 62.5% −Dac + 33 ≦ T (° C.) ≦ −Dac + 43 2. The cellulose acetate is used in an amount of 250 to 4
The production method according to claim 1, which has a viscosity average degree of polymerization of 00. 3. The production method according to claim 1, wherein the cellulose acetate is a cellulose acetate having a small amount of low molecular components such that the acetone extractable amount is 10% by weight or less. 4. The cellulose acetate is represented by the following formula (2):
2. The method according to claim 1, having a viscosity average degree of polymerization (DP) satisfying the following relationship and a concentrated solution viscosity (η) determined by a falling ball viscosity method. (2) 2.814 × ln (DP) -11.755 ≦ ln (η) ≦ 6.29 × l
n (DP) -31.469 In the formula, DP is a value of a viscosity average degree of polymerization of 290 or more;
η is the transit time (seconds) between the marked lines in the falling ball viscosity method. 5. A cellulose acetate comprising 5 to 17 J.
The production method according to claim 1, having a crystallization heat value (ΔHc) of / g.