JPH0524808B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing a cellulose triacetate film used as a support for photographic light-sensitive materials. [Prior art] Methylene chloride or a mixed solvent of methylene chloride and about 10% alcohol is generally used as a solvent when cellulose triacetate is formed into a film by the solution casting method. Since the coagulation rate of the resulting film is extremely slow, methanol or the like, which is a poor solvent for cellulose triacetate, is further added. However, since this methylene chloride-methanol mixed solvent still has a slow coagulation rate and takes time to peel off from the support, various studies have been conducted to improve it. For example, US Pat. No. 2,607,704,
Same No. 2739069, Special Publication No. 9074 (1974), Japanese Patent Publication No. 1973 (1973)
Various specifications such as No. 48862 disclose a method of promoting gelation by adding a poor solvent such as butanol or cyclohexane. Also, US Patent No. 2221019
The issue discloses a method for stopping gelation by cooling the cast dope. It is also shown that hot air is sent to the front side of the film formed on the band in the latter half of the band to promote drying. US Pat. No. 3,793,043 discloses a method of promoting gelation using metal salts. On the other hand, a technology has also been reported that reduces the time required for peeling after casting to less than 5 minutes by casting a dope such as cellulose acetate propionate onto a cooled drum, air drying it, and peeling it off. (U.S. Patent No. 2319052). [Problems to be solved by the invention] All of the methods of promoting gelation by adding a poor solvent such as butanol or cyclohexane or a metal salt do not allow the gel to flow onto an endless band or drum (hereinafter collectively referred to as a support). After rolling, the solvent must be evaporated from the casting layer during one revolution of the support to solidify it at least until it can be peeled off from the support, and then peeled off from the support. However, it takes a considerable amount of time to dry to the point where it can be peeled off. In this method, the amount of solvent in the film at the time of peeling is proportional to the weight of the film after drying.
Generally, around 100% is the limit. Therefore, as shown in the example of JP-A No. 54-48862, the upper limit speed at which peeling is possible is about 1.0 to 1.1 m/min (with a band of 6 m per circumference) when the amount of gelling solvent is small. drying time of approximately 330 seconds), and even when an appropriate amount of gelling solvent is added, the maximum drying time is approximately 2.6 m/min (one round).
The drying time for a 6m band is only about 140 seconds).
For this reason, even if the lower limit of the film forming speed that is cost-effective in an actual manufacturing process is 10 m/min, large equipment with a circumference of the support of 20 m or more is required. On the other hand, if the drying speed is increased in order to shorten the time until peeling, foaming occurs, and if peeling is performed under insufficient drying conditions, residual peeling occurs, impairing the flatness and transparency of the film. Once these problems occur, they cause foaming and peeling one after another, so film formation must be stopped or production speed must be slowed down for cleaning, and even after restarting, these problems are close to the limit. By the way, it takes several hours because it is necessary to gradually increase the operating speed until the normal operating state is restored. Also, in the method of cooling and gelling the cast dope, it is necessary to evaporate a certain amount of the solvent before peeling off the film. The reason for this is not specifically stated in the patent publication, but in experiments conducted by the present inventors, the self-supporting properties of the peeled film deteriorated even if the film was simply gelled when most of the solvent remained. It was insufficient. In addition, nonuniform elongation and deformation tend to occur in the stripping section and subsequent conveyance section, and the film shrinks significantly during the drying process after stripping, making it impossible to obtain a film of good quality. In the method of the patent, in order to remove the solvent, hot air 16 supplied from a tube 15 is blown out from a number of pores 17 in the latter half of the band 3 to accelerate drying, as shown in FIG. This was also done. However, in this method, the evaporation rate of the solvent from the film is very slow, and it takes a considerable amount of time to remove the solvent to the extent that the problems such as elongation, deformation, and shrinkage mentioned above do not occur, and the film forming speed is reduced. It was difficult to raise it to a full height. On the other hand, no technology has been introduced to cellulose triacetate systems to date that allows the dope to be peeled off simply by casting a dope such as cellulose acetate propionate onto a cooled support and air-drying it. The reason for this is that cellulose triacetate has poor solubility in solvents, and a manufacturing method for high-concentration dope suitable for factory production has not been developed, and at low concentrations, the above-mentioned problems occur and stable stripping cannot be achieved by cooling alone. It depends. An object of the present invention is to provide a means for shortening the time from casting to stripping, thereby making the casting equipment more compact or increasing the film forming speed. Another object of the present invention is to provide a stable film forming method that does not cause foaming or peeling residue. Still another object of the present invention is to provide a film forming method in which the start-up operating conditions and steady-state operating conditions for film forming are the same and the start-up operation is easy. [Means for Solving the Problems] The purpose of the present invention is to apply air to the surface of a film cast on a support using a dope containing a mixed solvent containing cellulose triacetate at a high concentration and having a specific composition. This is accomplished by drying the surface area by applying. That is, the present invention provides a dope in which the total concentration of cellulose triacetate and other components that become solid after drying is 18 to 35% by weight, and the ratio of solvents other than methylene chloride in the solvent composition is 13 to 25% by weight. In a film forming method in which the film formed on the support is cast onto a support with a surface temperature of 10°C or less, air is applied to the surface of the film for at least 2 seconds to selectively dry the surface portion, and then the film is removed. The present invention relates to a method for producing a cellulose triacetate film, which is characterized by peeling it off from a support. A dope with a high concentration of cellulose triacetate is used, and the concentration of the sum of cellulose triacetate and other components that become solid after drying is 18
A proportion of at least 20% by weight, preferably 20 to 35% by weight, is suitable. Other components that become solid after drying include, for example, plasticizers such as triphenyl phosphate;
In addition, there are various additives that may be added as necessary. The solvent is a mixed solvent of methylene chloride and another solvent. Other solvents are _C1 - _C4 alcohols,
For example, methanol, n-butanol, etc., and cyclohexane are poor solvents for cellulose triacetate. These may be used alone or in combination of two or more. The mixing ratio is 87-75% by weight of methylene chloride and 13-25% by weight of other solvents. The concentration of cellulose triacetate and the composition of the solvent are determined within the above range so that the dope can be easily produced by the method described below and gelation proceeds as quickly as possible at a predetermined temperature of 10° C. or lower. The gelling temperature of the dope depends on the concentration of cellulose triacetate, solvent composition, etc. Cellulose triacetate concentration and The results of measuring the relationship with gelation temperature are shown in FIG. As shown in the figure, the higher the dope concentration and the higher the poor solvent concentration, the higher the support temperature can be raised, but at a dope concentration of 35%
In this case, the formation of casting beads is disturbed by melt fracture, and it is difficult to form a homogeneous dope. On the other hand, if the poor solvent content is 25% or more,
There are drawbacks such as cloudiness in the dope and increased viscosity which makes it difficult to transport the dope. The present invention was achieved for the first time by developing a technology capable of industrially producing such a high concentration dope. Such a high concentration dope, for example, is prepared by putting cellulose triacetate and the above-mentioned solvent in a pressurized container, sealing it, and heating it under pressure to a temperature above the boiling point of the solvent at normal pressure and within a range where the solvent does not boil.
Obtained by stirring. Cellulose triacetate, a solvent, and other additives added as necessary may be roughly mixed in advance and then placed in a pressurized container, or may be charged separately. The type of pressurized container does not matter, as long as it can withstand a predetermined pressure. This pressurized container needs to be able to be stirred as well as heated. Pressurization may be performed by pressurizing an inert gas such as nitrogen gas, or may be performed only by increasing the vapor pressure of the solvent by heating. In addition, it is also possible to reduce the gas phase volume within the pressurized container by injecting some or all of cellulose triacetate, a solvent, and other additives under pressure after the container is sealed. Preferably, the heating is performed from the outside, for example, a jacket type. In addition, a plate heater etc. is installed externally,
Heating can also be done by connecting and circulating through piping. It is preferable that the stirring blade has a length that reaches near the container wall, and a scraping blade is preferably provided at the end to renew the liquid film on the container wall. In addition, other gauges such as pressure gauges and thermometers should be installed as appropriate in the pressurized container. The above raw materials are placed in a pressurized container and heated under pressure. The heating temperature is a temperature above the boiling point of the solvent and within a range where the solvent does not boil. This temperature is 60℃
The temperature above is preferable, and about 80 to 110°C is particularly preferable. The pressure is determined so that the solvent does not boil at this set temperature. After melting, it is cooled and then taken out from the container, or taken out from the container with a pump or the like, cooled with a heat exchanger or the like, and then used for film formation. In this dissolution method, by applying pressure,
It can be heated above the boiling point at normal pressure, and boiling is suppressed to prevent over-concentration, thereby preventing gel formation. Heating increases solubility and dissolution rate, allowing complete dissolution in a short period of time. The dope casting method may be either a band casting method as shown in Fig. 2 or a drum casting method as shown in Fig. 3. The entire area, especially the area around the peeled part 2, is cooled. Since the interface between the support 3 and the dope 4 is mainly involved in peeling, it is important to sufficiently cool the support surface. The method of cooling is not particularly limited, and any method using a refrigerant or cold air, a method using a heat pipe, etc. can be used. The cooling temperature is such that the surface temperature of the support is 10°C or less, preferably 5°C or less. Air is applied to the surface of the film formed on the support to dry the surface portion. The temperature of the air applied to the film surface must be in a range that does not cause foaming in the base, and preferably as high as possible within this range. Especially 40℃
It is preferable to make it more than that. Air at this temperature is applied to the film surface for 2 seconds or more. As long as the wind is applied for at least 2 seconds, it may be applied for 2 seconds or more immediately after casting, for 2 seconds or more during coating on the support, or over the entire surface of the support. Preferably, the surface of the film is dried by blowing air immediately after casting. This means that the solvent component on the surface of the film immediately after casting is 1.85 on a dry basis.
In this case, only the area near the surface dries rapidly for about 10 seconds after the start of drying. Therefore, although the average solvent content does not change, the solvent content within several micrometers near the surface rapidly decreases to 1.00 or less on a dry weight basis. This is because as a result, the elastic modulus of the film surface increases rapidly and the resistance to elongation increases. The way the wind is applied to the film is perpendicular to the film.
It may be applied parallel or diagonally, but a certain amount of air velocity must be applied to effectively dry the base. For example, if the surface wind speed in the direction perpendicular to the wind film is 0.2 m/sec or more,
Or the surface wind speed of the component in the direction parallel to the film.
It is preferable to set it as 5m/sec or more. Moreover, when the wind is made to flow in a direction parallel to the film, it may be a unidirectional flow flowing from one side to the other, or a mutually facing flow flowing from both sides in opposite directions. The film is gelled on a cooled support, dried with air, and then peeled off from the support. Immediately after peeling off the film, the film may be dried by blowing air, and the surface of the film on the support side,
That is, when blowing air onto the surface that was in close contact with the support, the resistance to elongation of the surface of the film on the support side increases, similar to when blowing air immediately after casting. The tension applied to the base when peeling the film from the support must be within a range in which the film does not stretch under the tension. For example, if the width is 5 kg/m or less, there is almost no elongation, which is preferable. Next, an example of a casting apparatus for carrying out the method of the present invention will be explained based on FIG. 4. In the figure, 3 is a cooled drum that is a support, and a slit die 5 and a peeling roll 6 are provided in the vicinity of this drum 3. A wind case for guiding and holding wind 7 is provided between the slit die 5 and the peeling roll 6. 8 is provided. A slit 9 is bored in the outer peripheral surface of the wind case 8, and the wind 7 passes through the slit 9 and hits the film 10 perpendicularly. A tension pick-up roll 11 and a take-up roll 13 for winding up the film 10 are provided near the peeling roll 6. In this device, the dope cast from the slit die 5 becomes a film 10 on the drum 3,
It rotates together with the drum 3 while being cooled by the drum 3 and dried by the wind 10. When it reaches the peeling roll 6, it is peeled off from the drum 3 by the peeling roll 6, dried by air 4, and wound onto a winding roll 13 via a tension pick-up roll 11 and a roll 12. This film 10
The tension from peeling off to winding up on the winding roll 13 is adjusted by changing the winding speed of the winding roll 13. FIG. 5 shows an example of another casting apparatus.
The wind case 14 of this device is provided from the vicinity of the slit die 5 to the vicinity of the peeling roll 3 in the same way as the device shown in FIG. There is. In this device, the wind case 14 is shown as the wind 7 shown by the solid line in the figure.
Film 1 in one direction from one end to the other end
0, or let the wind 7 flow out from the other end side as shown by the chain line in the figure, so that the wind case 1
The wind 7 may be parallel to the film 10 in directions facing each other from both ends of the film 4. [Function] By increasing the concentration of cellulose triacetate in the dope to a high concentration within a certain range and by adding a poor solvent at a certain ratio, gelation is promoted and peeling from the support is facilitated, and the dope is exposed to air for a specified period of time or more. By drying at least the surface of the film, stretching of the film after peeling is prevented. [Example] Dope Composition Cellulose triacetate 100 Methylene chloride 320 Methanol 40 Butanol 25 TPP 15 Support Surface temperature 0°C Drying section From casting section to peeling section Films were formed using the above dopes and supports at various drying and peeling tensions. We investigated the growth of shiso. The results obtained are shown below.

〔Effect of the invention〕

In the method of the present invention, the adhesive force between the support and the film that is once peeled off is not rate-limiting. The rate-limiting condition in the present invention is to provide the film with a strength that can overcome the influence of its own weight and its inertia when peeled off from the support, and that force is usually 1/10 of the adhesive force. It is as follows. Therefore, a huge speed increase is possible. As a result, for example, if equipment with an effective length of 20 m was previously used, it is now sufficient to use equipment with an effective length of 2 to 3 m to maintain the same speed, significantly reducing equipment costs and running costs. I can do it. Next, in the method of the present invention, the film surface is dried by blowing air onto it, which increases the resistance to elongation of the film surface, prevents the film from stretching after peeling, and prevents sagging and This prevents deformation problems. Furthermore, the method of the present invention does not use the conventional method of solidifying the dope by drying as its main mechanism, but instead uses gel-setting of the dope under specific conditions at a low temperature as the main mechanism for stripping. No peeling remains as long as the temperature is low. As a result of the above, we do not have to worry about remaining peeling on the support, which was the biggest problem in conventional cellulose triacetate film formation.
The advantage is that the speed can be increased or decreased freely. Furthermore, in the method of the present invention, the start-up operating conditions can be made the same as the steady-state operating conditions, and as a result, troublesome adjustment operations at the time of start-up are not necessary. The present invention, which has a number of excellent effects as described above, was only made possible by the completion of a technology capable of producing a highly concentrated dope in a gel-free state.

[Brief explanation of the drawing]

FIG. 1 shows the results of measuring the relationship between cellulose triacetate concentration and gelation temperature for dopes using two mixed solvents of methylene chloride-methanol and methylene chloride-methanol-n-butanol. FIG. 2 is a schematic view of a band casting apparatus, and FIG. 3 is a schematic diagram of a drum casting apparatus. FIG. 4 is a diagram showing an example of a cooling stripping method of a drum casting apparatus embodying the present invention, and FIG. 5 is a diagram showing another example of the same. FIG. 6 is a side view showing a conventional cooling stripping method of a band casting apparatus. 1... Casting part, 2... Peeling part, 3... Support body,
4... Dope, 5... Slit die, 6... Peeling roll, 7... Wind, 8... Wind case, 10... Film, 13... Winding roll.

Claims (1)

[Scope of Claims] 1. The total concentration of cellulose triacetate and other components that become solid after drying is 18 to 35% by weight, and the proportion of solvents other than methylene chloride in the solvent composition is 13 to 25% by weight. In a film forming method in which a dope is cast onto a support whose surface temperature is 10°C or less, the surface of the film formed on the support is exposed to air for at least 2 seconds to selectively dry the surface portion, and then the film is 1. A method for producing a cellulose triacetate film, which comprises peeling the film from a support. 2. The film surface wind speed of the component in the direction perpendicular to the film is 0.2 m/sec or more, or the film surface wind speed of the component parallel to the film is 5 m/sec or more and the film is peeled off from the support. The method for producing a cellulose triacetate film according to claim 1, wherein the tension of the film is 5 kg/m width or less. 3. The method for producing a cellulose triacetate film according to claim 1, wherein the temperature of the air is 40°C or higher.