JPS624208B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing cellulose triacetate film by solution casting, and more particularly to a method for increasing the production speed of cellulose triacetate film. Cellulose triacetate film is transparent;
It has excellent mechanical properties and shows little dimensional change due to temperature and humidity, so it is widely used in photographic film bases and the like. Conventionally, cellulose triacetate film produced by the solution casting method is made by mixing cellulose triacetate with a degree of acetylation of 60 to 62% with methylene chloride along with a plasticizer.
90-95% by weight, alcohol 10 with 1 or 2 carbon atoms
The dope obtained by dissolving it in a mixed solvent consisting of ~5% by weight is uniformly cast onto a continuously rotating endless support, and when the solvent evaporates and the dope solidifies, it is peeled off from the support and further dried. It was obtained by doing. This method yields a transparent film with good flatness, but doping using a mixed solvent with the above composition
Since the solidification (gelation) caused by evaporation of the solvent is slow, there is a drawback that it takes a long time to peel the film from the support. In addition, if the film is rapidly dried on the support to increase the production speed by this method, the cast dope may foam, or if the film is peeled off from the support before it is sufficiently solidified, the support may Residues were left on the surface of the film, impairing the flatness and transparency of the film, and making it impossible to increase the production speed of the film. Therefore, attempts have been made to increase the film forming rate by early solidification of the dope on the support. For example, US Pat. No. 2,607,704, US Pat. The method is described. but,
When cyclohexane or n-butyl alcohol is used, the viscosity of the dope increases over time as described in Japanese Patent Publication No. 17556/1985, making it difficult to handle, and cyclohexane and n-butyl alcohol are difficult to evaporate. Therefore, even if it can be peeled off quickly from the support, drying requires high temperatures and a long time, making it inefficient.Furthermore, using cyclohexane or n-butyl alcohol means that these and methylene chloride or In order to separate alcohols having 1 or 2 carbon atoms, the recovery method and equipment are complicated and recovery costs are high, which is not industrially preferable. A first object of the present invention is to provide a method for increasing the production rate of cellulose triacetate films. A second object of the present invention is to provide a method that allows for efficient drying in a short period of time after being peeled off from a support. A third object of the present invention is to provide a method for producing cellulose triacetate film in which solvent recovery is easy and inexpensive. As a result of intensive research into a film forming method that allows for efficient drying after peeling at a high production rate and easy recovery, the inventors of the present invention have developed a film forming method that allows for efficient drying after peeling at a high production rate and easy recovery. We have found that this object can be achieved by using a mixed solvent consisting essentially of methylene chloride and an alcohol having 1 to 2 carbon atoms, and allowing the mixed solvent to contain 13 to 30% by weight of an alcohol having 1 to 2 carbon atoms. Ta. Conventionally, it has been recognized in the art that it is difficult to increase the production rate when a mixed solvent consisting of methylene chloride and an alcohol having 1 or 2 carbon atoms is used. For this reason, technology has been directed towards using a combination of the above-mentioned auxiliary solvents. However, the present inventor has discovered that unexpected results can be obtained when the solvent composition ratio is specified without using such an auxiliary solvent. That is, the number of carbon atoms in the solvent composition is 1
It has been found that using 13% or more of alcohol (2) by weight or more can dramatically shorten the stripping time; however, if the alcohol content exceeds 30% by weight, the dope becomes extremely difficult to prepare and loses its transparency. Undesirable. That is, the desired objective can be achieved by controlling the alcohol content to 13 to 30% by weight. In the present invention, cellulose triacetate is substantially dissolved in a mixed solvent consisting of 70 to 87% by weight of methylene chloride and 13 to 30% by weight of alcohol having 1 to 2 carbon atoms, and the solution is uniformly spread on an endless support. It is something that spreads. The solvent composition of the present invention is substantially 70 to 87% by weight of methylene chloride and alcohol having 1 to 2 carbon atoms.
It consists of 13 to 30% by weight, where "substantially" means that no third solvent is actively added. In other words, the solvent composition of the present invention may contain some other components, but they are not added intentionally.For example, industrial solvents generally contain other components for stabilization, antistatic, etc. For example, methylene chloride contains methyl alcohol,
Ethyl alcohol may contain benzene and alcohols with different carbon numbers, and for this reason, the inclusion of a small amount of a third solvent is of course within the scope of the present invention. Further, it is optional to include other solvents in extremely small amounts as long as they do not impair the effects of the present invention.
If the amount is less than % by weight, the effect of the present invention will not be impaired, which means that it may be included in this amount. However, from the viewpoint of solvent recovery, it is better that the amount of other solvents mixed in is as small as possible, and it is particularly preferable that the amount of other solvents mixed in is 1% by weight or less. Next, a method for preparing the cellulose triacetate dope of the present invention will be described. Cellulose triacetate preferably has an acetylation degree of 60-62%,
Using a material that has been dried to a moisture content of 1% or less, this and a plasticizer are directly dissolved in a mixed solvent of methylene chloride and an alcohol having 1 to 2 carbon atoms to form a dove. When the ratio of alcohol is high, it is preferable to divide the alcohol, dissolve cellulose triacetate and a plasticizer in a mixed solvent of one part and methylene chloride, and then add the remaining alcohol to form a dope. Note that the dope of the present invention is cyclohexane or n-
Unlike dopes containing butyl alcohol, there is no increase in viscosity over time, which is a major advantage in manufacturing because the dope is easy to handle and equipment can be simplified. The dope prepared in this way is filtered, then thoroughly degassed, and then fed into a hopper and cast to a uniform thickness onto an endless support. During one rotation, the solvent in the casting layer is removed. The film is evaporated to solidify at least until it is peelable from the support, peeled from the support, and then the remaining solvent is removed to obtain the finished film. A plasticizer is added to the cellulose triacetate film for the purpose of imparting moisture resistance or flexibility. Examples of plasticizers that can be used in the present invention include triphenyl phosphate,
Phthalate esters include dimethyl phthalate, diethyl phthalate, dimethoxyethyl phthalate, etc.; glycolic acid esters include methyl phthalyl ethyl glycolate; , ethyl phthalyl ethyl glycolate, etc. can be used alone or in combination. Furthermore, plasticizer can be used in a range of 5 to 30% by weight based on cellulose acetate, but if used in excess, the plasticizer will seep out from the film during drying, so it is recommended to use 5 to 20% by weight. is preferred. The maximum film forming speed of the dope of the present invention was determined using a conventional dope solvent composition (90 to 95% by weight of methylene chloride and 1 or 2 carbon atoms) when using a 6 m endless stainless steel band to obtain a film with a finished film thickness of 0.14 mm. (5-10% by weight of alcohol), the maximum film-forming speed is 1.4-2.6 m/min, while it is 1.0-1.1 m/min with the conventional dope solvent composition. It can be doubled. The larger the amount of alcohol, the faster the film forming speed can be increased, and the film forming speed increases rapidly from around 13% by weight of alcohol. Doping using cyclohexane or n-butyl alcohol, which is a conventional solvent composition that increases the film forming speed, increases the film forming speed by 1.8 to 2.1 times compared to the conventional method. This corresponds to a case where the alcohol having 1 to 2 carbon atoms in the solvent composition is 15% by weight or more. From the viewpoint of film forming speed, ease of dope preparation, quality of finished film, etc., the solvent composition of the present invention is more preferably in the range of 85 to 75% by weight of methylene chloride and 15 to 25% by weight of alcohol having 1 to 2 carbon atoms. Furthermore, the cellulose triacetate film obtained by the method of the present invention has a higher performance compared to a conventional film formed using a mixed solvent consisting of 90 to 95% by weight of methylene chloride and 5 to 10% by weight of alcohol having 1 or 2 carbon atoms. It was found that the mechanical properties were the same or better, and in particular, the folding strength was improved by 40 to 120%. As described above, the production method according to the present invention not only increases the film forming speed but also facilitates solvent recovery.
Moreover, the recovery cost is low, the film dries quickly after being peeled off from the support, and the drying temperature can be lower than when using cyclohexane or n-butyl alcohol, resulting in the advantage that the equipment can be simplified. This method is extremely advantageous compared to conventional methods for industrially producing cellulose triacetate films. Also, Unexamined Patent Publication 1973-
The method described in Publication No. 18361, in which monomers are incorporated into dope and ionizing radiation is carried out, is accompanied by a decrease in quality due to residual monomers, but according to the present invention, this does not occur and the above effects can be achieved. Obtainable. Examples will be shown next, but the present invention is not limited thereto. All compositions in the examples are given in parts by weight. Example (1) Cellulose triacetate 100 with acetylation degree of 61.4%
15 parts of triphenyl phosphate and 15 parts of triphenyl phosphate were completely dissolved in 738 parts of a mixed solvent consisting of methylene chloride and methyl alcohol with different composition ratios to obtain dopes. At this time, if the proportion of methyl alcohol in the mixed solvent is large, divide the methyl alcohol, dissolve cellulose triacetate in one of the mixed solvents consisting of methyl alcohol and methylene chloride, and then add the remaining methyl alcohol to form the dope. Obtained. Then pass this dope
It was uniformly cast onto a 6 m (effective length 5.5 m) endless stainless steel band that was kept at 27°C and rotated, and after the solvent had evaporated until peeling was possible, it was peeled off from the stainless steel band, and then dried until the thickness 0.14
A film of mm was obtained. Table 1 shows the solvent composition at this time, the maximum peelable film forming speed, and the folding strength of the obtained film as measured with an MIT folding durability tester. As a result, the present invention provides methylene chloride 90-95
% by weight, compared with a solvent composition of 5 to 10% by weight of methyl alcohol, the film forming speed could be increased by 1.4 to 2.4 times, and the folding strength was improved by 40 to 120%.

[Table] Example (2) Cellulose triacetate and triphenyl phosphate with a degree of acetylation of 61.8% were dissolved in 738 parts of a mixed solvent consisting of methylene chloride and ethyl alcohol in the same manner as in Example (1). A film was produced in the same manner as in 1). Table 2 shows the solvent composition, maximum film forming speed, and bending strength of the film obtained. As a result, the present invention provides methylene chloride 90~
Compared to a solvent composition of 95% by weight and 5 to 10% by weight of ethyl alcohol, the film forming speed could be increased by 1.5 to 2.6 times, and the folding strength was improved by 40 to 120%.

[Table] Example (3) Cellulose triacetate 100 with acetylation degree of 60.4%
Dopes were prepared using 15 parts of triphenyl phosphate and 15 parts of triphenyl phosphate using five types of mixed solvents shown in the table below.

[Table] Next, these dopes were kept at 27℃ and uniformly cast onto a rotating 6m (effective length 5.5m) endless stainless steel band, and the solvent was evaporated until peeling became possible. It was peeled off from the stainless steel band and further dried to obtain a film with a thickness of 0.14 mm. The drying was carried out at two different temperatures: 100°C and 120°C. The table below shows the maximum film forming speed at this time and the drying time at 100°C and 120°C required until the amount of residual solvent contained in the film after peeling became 2% by weight based on the film.

[Table] As a result, the dope compositions No. 2 and No. 3 of the present invention can increase the production speed equal to or higher than that of the dope compositions No. 4 and No. 5 using cyclohexane and n-butyl alcohol. Also, the drying time of the film after peeling is longer than that of conventional dope composition No. 1, No. 4 and No. 4 using cyclohexane and n-butyl alcohol.
While the doping composition No. 5 requires 2.1 to 2.5 times, the doping composition No. 2 and No. 3 of the present invention requires a much shorter drying time of 1.1 to 1.2 times, and is sufficiently fast at a drying temperature of 100°C.

Claims (1)

[Claims] 1. In a method for producing a cellulose triacetate film by a solution casting method, the solvent of the dope consists essentially of methylene chloride and 1 carbon atom.
A method for producing a cellulose triacetate film, characterized in that the solvent contains 13 to 30% by weight of the alcohol having 1 to 2 carbon atoms.