JPS61100421A - Manufacture of cellulose triacetate film - Google Patents

Abstract

PURPOSE:To shorten the time required for removing, by setting the support body temperature of a casting section and a conveying first half section at or over the gelling temperature of a dope, setting their maximum temperature between 30 deg.C and the foaming and molding temperature, and setting the temperature of the film and the support body at a removing section at or below 20 deg.C. CONSTITUTION:The temperature of a dope 16 at a casting section and the temperature of the support body and the conveying first half section on the support body for facilitating drying a cast film are set at or over the gelling temperature of the dope and their maximum temperature is between 30 deg.C and the foaming and forming temperature. The gelling temperature of the dope will depend on the concentration of the cellulose triacentate and the composition of the solvent. On the other hand, the temperature of the support body and the film at a film removing section 11 is to be at or below 20 deg.C. Accordingly, the gelling can be facilitated and the removal becomes easy. The ratio of the heating section to the cooling section for the support body is preferably such that the cooling section is the required minimum and the remaining is allotted to the heating section. As the gelling is liable to take place at higher concentrations, the more dried, the shorter the cooling operation.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) Cellulose triacetate films are widely used as supports for photographic materials. This cellulose triacetate film is generally formed by a band casting method or a drum casting method, and in either method, it is industrially important to increase the film forming speed.

The present invention relates to a method for increasing the film forming rate.

(Prior art) One of the methods to increase the film forming speed is to place the cast film on a band or drum (hereinafter collectively referred to as a support) using hot air, heat transfer from the drum, or in some cases, a band or drum. There is a method of accelerating drying by heating from the back side.

It is also known that the cast dope is kelized at low temperature to prevent peeling (USP 2221,019).
).

In this method, as shown in FIG.
After casting #-17, it is cooled by the cooler 18 through the band 3 and gelatinized. Then, the bread v3 is further cooled in the drum 5 and cooler 19 through which cold water 7 is passed, and dried while maintaining the gelled state, and when the drying progresses to a certain extent, it is peeled off. Similar methods are also known for drum casting (USP
2,319,052).

(Problems to be Solved by the Invention) The method of drying by heating on a support has a heating limit. In other words, in recent years, methylene chloride has generally been used as the main solvent for dope, but since the boiling point of methylene chloride is 40°C, heating the film above 40°C, especially in the first half of drying, may cause foaming in the film, resulting in poor product quality. can no longer be used as Therefore, heating can only be carried out within a range that does not cause foaming, and the film forming rate is limited by this heating.

Furthermore, even in the method of gelling by cooling, 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, it was found that the self-supporting properties of the peeled film were insufficient even if the film was simply gelled when most of the solvent remained. It was unsatisfactory. In addition, non-uniform elongation and deformation easily occur at the peeling section and subsequent conveyance section, and the film shrinks significantly during the drying process after peeling, making it impossible to obtain a film of good quality. In the method of the patent, hot air 4 supplied from a tube 20 is passed through a large number of pores 21 in the latter half of the band 3, as shown in FIG. 5, in order to remove the solvent.
It was also practiced to accelerate drying by blowing air out from the dryer. However, with 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 of elongation, deformation, and shrinkage mentioned above do not occur, and the film forming speed is significantly reduced. It was difficult to raise the Possible reasons for this are as follows. That is, first, the evaporation of the solvent from the cast film takes place in the decreasing rate drying stage, and the internal diffusion rate of the solvent determines the drying rate. However, the film on the band is cooled from the band surface in order to maintain a gelled state, and the diffusion rate of the solvent is very slow. Further, although latent heat of vaporization is necessary for the solvent to evaporate, much of the energy given from the hot air is taken away by cooling from the band, and the amount used as this latent heat is small. moreover,
Because the solvent evaporates on the band, the solvent concentration in the film increases toward the band, but at the band interface where this concentration is high t4, the solvent moves very slowly because it is immediately cooled and gelled after casting. It has become. As a result, the dope concentration in this part does not change even just before stripping, and in order to maintain kelization at high solvent concentrations, it is necessary to continue cooling at the initial temperature until just before stripping.

As mentioned above, this causes a self-contradiction in that the dope drying rate on the band is reduced, and in the end, energy is wasted and the upper limit of the film forming rate cannot be achieved.

An object of the present invention is to significantly shorten the stripping time by utilizing the characteristics of dope in a solution casting method.

(Means for solving the problem) The above purpose is to promote drying by actively applying thermal energy in the first half of the transfer on the support, and to some extent by cooling before stripping. This is achieved by gelling a dope that has been dried and has improved gelling properties.

That is, the present invention provides a method for manufacturing a cellulose triacetate film by a solution casting method, in which the temperature of the casting part where the dope is cast onto the support and at least the first half of the transfer of the cast film on the support and The temperature of the support in this part is set to be above the gelling temperature of the dope, and the maximum temperature is set to 30°C or above and below the foam formation temperature, and the temperature of the film and support in the film peeling part is set to 20°C.
It is characterized by the following:

The dope to be cast may be a usual one, and cellulose triacetate is dissolved in a mixed solvent of methylene chloride and methanol or a mixed solvent in which a poor solvent such as ethanol, n-phthanol, penzole, toluene, or cyclohexane is further added. It is obtained by further adding and dissolving a plasticizer such as TPP. The concentration of cellulose triacetate is about 15 to 25%, and the mixing ratio of methylene chloride and methanol is 95:5 to 80:20 by weight.
That's about it. If a poor solvent other than methanol is added, it will generally be 20% or less by weight in the mixed solvent, although it depends on the type.

The casting method may be either a band casting method or a drum casting method, but the temperature of the dope in the casting part and the temperature of at least the first half of the transferred film on the support and the temperature of the support in that part The gelation salinity of the dope must be higher than that and the maximum temperature must be 30°C or higher and lower than the foaming temperature.

The gelling temperature of the dope depends on the concentration of cellulose triacetate, solvent composition, etc. Using a mixed solvent (A) containing 92% by weight of methylene chloride and 8% by weight of methanol as a solvent and a mixed solvent (B) containing 83% by weight of methylene chloride, 7% by weight of methanol and 10% by weight of n-butanol, cellulose triacetate was prepared. FIG. 4 shows the results of measuring the relationship between concentration and celification temperature. On the other hand, the foam formation temperature is the boiling point of the solvent during casting, for example 40° C. in the case of methylene chloride, but this temperature becomes higher as the drying progresses on the support. This is thought to be because the strength of the film increased as a result of drying, making it possible to maintain a pressurized state against the solvent inside. The purpose of heating in the first half is to accelerate drying of the cast film, and the temperature is preferably as high as possible within a range that does not cause foaming.

On the other hand, the temperature of the film and support in the film peeling section is 20° C. or lower. This cooling promotes gelation and facilitates peeling.

To prevent the heating and cooling parts of the support from dying, the cooling part can be caelized to the extent that it can be easily peeled off, whereas drying using the heating part takes a relatively long time, so the cooling part should be kept to the minimum necessary size. It is preferable to allocate the remaining 9 to the heating section. Since kelization becomes more likely to occur as the concentration increases, there is an advantage that the drier the material is, the shorter the cooling time is required.

As a heating means, it is sufficient to use a heater on the front surface, the back surface, or both surfaces of the support, an infrared heater, blowing hot air, passing hot water through a drum, etc., and as a cooling means, it is sufficient to use radiation. In addition to cooling, blowing cold air,
The cooling may also be performed by forced cooling such as by passing cold water through the drum. Generally, it is preferable to raise the temperature quickly immediately after casting, and since a large amount of latent heat is required in this area due to the large amount of solvent evaporation, it is preferable to intensively heat this area. In this respect, in addition to hot air from the front surface of the support, it is preferable to use auxiliary heating means such as hot air from the back surface, a steam heater, and an infrared heater.

Since the amount of heat required gradually decreases after this point, for example, when hot air is used as a heating means, it is appropriate to flow the hot air from the casting section in parallel to the support. On the other hand, as mentioned above, it is preferable to perform cooling at a position as close to the peeled part as possible, and for this purpose, it is preferable to perform forced cooling at this position using cold air, refrigerant, or the like.

In order to maintain this temperature structure in the casting equipment, the casing can be partitioned with partition plates or the air flow can be improved to further increase thermal efficiency and shorten the stripping time. .

An example of such a casting apparatus is shown in FIGS. 1 and 2 for a band casting apparatus. The example apparatus of FIG. 1 is constructed as follows. That is, the dope is cast from a slit die 1 onto a band 3 located on the drum 2, and hot air 4 is blown onto the band 3 near this casting part. The hot air 4 travels on the band 3 in its traveling direction and leaves the band 3 just before the drum 5. On the other hand, the cold air 6 is blown onto the surface of the band 3 near the bottom of the drum 2, overflows the surface of the band 3, travels against the direction of travel, and leaves just before the drum 5. The drum 2 is cooled with cold water 7, and the drum 5 is heated with hot water 8. The cast film is peeled off from the peeling section 11. In the example shown in Fig. 2, the amount of hot air is increased by 4 compared to the example shown in Fig. 1, and it is made to flow over three quarters of the length of the band 3 surface, and the band 3 near the casting part is It is heated by a heater 9. The cold air 6 is also blown from the back side of the band.

Next, an example of a drum casting apparatus is shown in FIG. The apparatus of this example blows hot air 4 near the casting part, and
On the other hand, the cold air 6 is blown near the peeling part 11 and travels along the circumferential surface of the drum 10 in a direction opposite to the advancing direction. It is designed to leave after one minute of a lap. drum 1
0 rotates only the circumferential surface, and the internal chamber is divided at the casting part into a portion where hot air 4 flows on the circumferential surface and a portion where cold air 6 flows. Hot air 4 or cold air 6 flows through each room. 12 is a hot air inlet, 13
is an outlet, 14 is a cold air inlet, and 15 is a cold air outlet.

(Function) In the method of the present invention, the cast dope is dried at an early stage when it is easy to dry, and during this period no caking occurs, thereby preventing a drop in drying efficiency. On the other hand, gelation is performed at a stage when gelation becomes easy due to drying, thereby improving peelability.

(Example) Dope (A) Dope (B) Cellulose triacetate 17.4 parts
22-part trinoenyl phosphate (TPP)
2.6 parts 3 parts methylene chloride
66 parts 69 parts methanol
5.8 parts 6 parts n-butanol
Part 8.2 - Dope of the above composition (A
) and dope (B)'r were prepared, and each dope was subjected to the conventional hot air drying method (1), the cooling celification method (II), and the method of the present invention (g) using the apparatus shown in Figure 1. A film was formed.

The obtained peeling time is shown below.

Method (I) (n) (III) Dope A 2 minutes 3 minutes 1.5 minutes Dope B2.0
Minutes 5 minutes 1.7 minutes (Effects of the invention) The method of the present invention makes good use of the characteristics of the dope to perform drying and gelation, thereby reducing the time required for stripping, which is a bottleneck in film formation speed. It is shortened to i'. By the method of the present invention, the film forming speed can be increased, the productivity of the film forming process can be increased, and the cost can be reduced.

[Brief explanation of the drawing]

1 and 2 are side views showing an overview of an example of a band casting apparatus used in the method of the present invention, and FIG. 3 is a side view showing an overview of an example of a drum casting apparatus. . FIG. 4 shows the results of measuring the relationship between dope concentration and gelation temperature for two types of solvents. FIG. 5 is a side view showing an example of a band casting apparatus used in the conventional cooling gelling method. 1... Slit die, 2 River drums, 3... Band,
4...Hot air, 5...Drum, 6...Cold air, 7...
Cold water, 8... Hot water, 9... Heater, 1o... Drum, 11... Stripping part, 12... Hot air inlet, 13...
Hot air outlet, 14...Cold air inlet, 15...Cold air outlet,
16...Dope, 17...Honozo-, 18.19
...cooler, 2o...tube, 21...pore

Claims (1)

[Claims] In the method of manufacturing cellulose triacetate film by solution casting method, the temperature of the casting part where the dope is cast onto the support, the temperature of at least the first half of the flow of the cast film on the support, and the support temperature of that part. is higher than the gelling temperature of the dope, and its maximum temperature is 30°C or higher and lower than the foaming temperature, and the temperature of the film and support at the film peeling part is 20°C or lower. Production method