JPS61158414A - Manufacture of cellulose triacetate film - Google Patents

Abstract

PURPOSE:To enable shortening of a peeling period of time, by a method wherein the temperatures of a dope, film and support during a period of time from casting of the dope(A) and dope(B) on the support till peeling off of them are set in a specific range. CONSTITUTION:The temperature of a dope of a casting part and that of a support of the first half part of transfer and said part of a cast film on the support is made higher than the gelatinization temperature of the dope, whose maximum temperature is made lower by 30 deg.C than the foam forming temperature and the temperature of the film and support on a peeling part of the film is made lower than 20 deg.C. The dope(A) and dope(B) are cast respectively from a first casting port 1 and second casting port 2 to a band which is at positions of drums 4, 5, hot air 7 is blown against the upper part of the band 6 in the vicinity of a casting part of the dope(A) and broken away from the band when the same arrives at a position of about three quarters of a length of the band 6. Cool air 8 is blown against the surface of the band 6 in the vicinity of the lower part of the drum 4 and broken away from the band 6 when the same arrives at a position of about a quater of the length of the band 6. The drum 4 is cooled by cold water 9, the drum 5 is heated by hot water 10 and the film cast is peeled off from a peeling part 11.

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) A mixed solvent of methylene chloride and methanol has generally been used as a solvent when cellulose triacetate is formed into a film by the solution casting method, but while this solvent has excellent solubility and solution stability, etc. There was a problem in that the coagulation speed of the cast film and the peeling speed from the support were slow.

Therefore, as a method to increase the rate of coagulation and peeling, a method has been developed in which a poor solvent for cellulose triacetate other than methanol, such as ethanol, n-butanol, or cyclohexane, is added to the mixed solvent to enhance the gelling properties of the dope. (U.S. Pat. No. 2,607,
No. 704, No. 2,739,069, No. 2,739
, No. 070) For the same purpose, the same dope is used as shown in Figure 1.
A method has also been developed in which the support (band) 6 is divided into two or more parts and laminated by casting.
9 specification, Japanese Patent Application Laid-open No. 134869/1983).

Furthermore, as a method to increase the film forming speed, there is a method of accelerating drying of the cast film on a support (band or drum) using hot air, heat transfer from the drum, or in some cases heating from the back of the band. .

There is also a known method of curing the cast dope at low temperatures to prevent stripping (USP 2,221,019).
).

In this method, as shown in FIG.
After casting from step 23, it is cooled through a band 6 by a cooler 18 and gelled. Then, the band 6 is further cooled in a drum 24 and a cooler 19 through which cold water 9 is passed, and is dried while maintaining a gelled state, and when drying has progressed to a certain extent, it is peeled off. A similar method is also known for drum casting (US
P2.319,052).

(Problems to be Solved by the Invention) The first method using a poor solvent has the effect of increasing the caking property of the dope and shortening the time required to peel off the film from the support surface, but the boiling point is about 40°C. ~65℃ methylene chloride-methanol mixed solvent (mixing ratio 9228
In this case, azeotropy occurs at 40°C. ) The boiling point of poor solvents used other than methanol is generally higher than that of methanol, which poses a problem in that after stripping, it takes a long time to evaporate these solvents to form a finished film. By the way, the time required to reduce the total solvent content from 20% to 1% using hot air at about 120°C was about 20 minutes with a methylene chloride-methanol mixed solvent, but when n-butanol was added to this solvent, it took about 20 minutes. When adding 10% of
It took a minute. As a result, the drying line had to be lengthened, and the drying process became rate-limiting, making it difficult to increase the film forming rate.

Although the second split casting method is also effective in shortening the stripping time, it has been desired to further shorten the stripping time.

The method of drying by heating on the third support had a heating limit. In other words, in recent years, methylene chloride has generally been used as the main solvent for Dogue, 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, which may cause the product to deteriorate. 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.

Even in the fourth method of gelling by cooling, it was necessary to evaporate a certain amount of 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. There was a bad A. 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, band 3 is used to remove the solvent, as shown in FIG.
The hot air 7 supplied from the tube 20 is passed through a large number of pores 2 in the latter half of the
Drying has also been promoted by blowing air out from 1. 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 is at a 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, most 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. Furthermore, in order to evaporate the solvent on the band, the solvent concentration in the band lateral root film becomes high, but at the band interface where this concentration is highest, it is immediately cooled and rolled after casting, so the movement of the solvent is extremely difficult. It has slowed down. As a result, the dope concentration in this part does not change even immediately before stripping, and cooling must be continued at the initial temperature until immediately before stripping in order to maintain the ripple effect at high solvent concentrations. 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 film forming rate is not significantly improved.

(Means for Solving the Problems) The present invention provides a method for producing a cellulose triacetate film that solves the above problems. In the method for producing a cellulose triacetate film of the present invention, the cellulose triacetate dope cast from the previous casting port is provided at intervals that allow the cellulose triacetate dope to dry to some extent before reaching the next casting port. In a method for producing a cellulose triacetate film by casting and laminating cellulose triacetate doug through the casting port of a tape, cellulose triacetate is added to a mixed solvent of methylene chloride and methanol with a poor solvent for cellulose triacetate other than methanol. Dough 7″ (A) prepared using a mixed solvent of The dope Φ) prepared by The temperature of the first half of the transferred film on the support and the temperature of the support in this part is set to be higher than the dulling temperature of Dogue, and the maximum temperature is 30°C or higher and lower than the foaming temperature, and the film and support in the film peeling part are It is characterized by keeping the body temperature below 20 degrees Celsius.

The apparatus used in the method of the invention has multiple casting ports. The number of casting ports is usually 2 to 3, but there may be more. The interval between each casting port is required to be such that the cellulose triacetate dough cast from the previous casting port can be dried to some extent before reaching the next casting port. This interval varies depending on the moving speed of the support supporting the cast dope, drying conditions, solvent composition, etc., but is approximately 10 to 90% of the total amount of solvent that evaporates after being cast and before being peeled off. is set appropriately within the range in which it evaporates. For example, when two casting ports are provided, the distance between the second casting port and the stripping portion is preferably 5 to 95%, and more preferably 20 to 80%. is appropriately set in the range of 30 to 70%.

Dope (A), which is cast from the first casting port, is made by dissolving cellulose triacetate in a mixed solvent of methylene chloride and methanol, and adding a plasticizer such as TPP, like the conventional dope. The method is characterized by the use of a solvent other than methanol, which is a poor solvent for cellulose triacetate.

This poor solvent has a boiling point of 65°C or higher and hardly dissolves cellulose triacetate when used alone.
Examples include alcohols having 2 to 6 carbon atoms, aromatic compounds such as penzole and toluene, and cyclohexane. These poor solvents are added to promote the reaction, and in that respect, the appropriate proportion of the poor solvent in the mixed solvent is about 5 to 20% by weight, preferably about 5 to 15%. . One type of poor solvent may be used, or two or more types may be used in combination.

Other components constituting the solvent may be the same as conventional ones, and include methylene chloride and methanol. The ratio of 6 methylene chloride and methanol is usually 95:5 to 95:5 by weight.
The ratio is about 80:20.

On the other hand, the dope (
B) is also dissolved in a solvent mainly consisting of cellulose triacetyl-tramethylene chloride and added with a plasticizer such as TPP, but the solvent does not contain any poor solvent other than methanol or is completely free of this poor solvent. The content of Dogue (
Use one lower than A). Poor solvents generally have higher boiling points than methylene chloride and are difficult to evaporate.
It is desirable that the amount added be as small as possible, and in general, a weight percentage of 5 or less is suitable. In some cases, it may be preferable to add a small amount of the poor solvent in relation to the physical properties of the product film. The poor solvent may be the same as that of the dope, or may be different. The ratio of methylene chloride to methanol in the solvent may be the same as the ratio in the solvent of Do 7'(A), or may be different.

Even if the ratio is different, it is preferable to set the ratio within the range described for Dawg (A).

The concentration of cellulose triacetate in Dope (A) and Dogue (6) may be the same as that in normal Dope, and may be 15 to 15%.
Approximately 25% weight is appropriate.

The preparation method for both dogu may be the same as the conventional method.

Regarding the casting thickness from each casting port, an amount corresponding to 10 to 90%, preferably 20 to 80%, and more preferably 30 to 70% of the finished film thickness is cast from the first casting port. Second
The remainder may be cast from the casting port onward.

The casting method may be either a pad/dope casting method or a drum casting method, but the temperature of the dope in the casting section and at least the first half of the transferred film on the support and the support of that part It is necessary that the body temperature is equal to or higher than the dulling temperature of Dogue, and the maximum temperature is equal to or higher than 30° C. and lower than the foaming temperature.

The gelling temperature of the dope depends on the concentration of cellulose triacetate, solvent composition, etc. The solvent contains a mixed solvent of 92% by weight of methylene chloride and 8% by weight of methanol, 2024283% by weight of methylene chloride, 8% by weight of methanol, and n.
Fig. 4 shows the results of measuring the relationship between cellulose triacetate concentration and dalification temperature using a mixed solvent of -butanol 10 weight i1%). On the other hand, the foaming temperature during casting is the boiling point of the solvent, 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 through drying, making it possible to create 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 dulling and facilitates peeling.

The ratio of the heating section to the cooling section of the support should be such that the cooling section can be gelled to the extent that it can be easily peeled off, whereas drying using the heating section requires a relatively long time, so the cooling section should be kept to the minimum necessary. It is preferable that the remaining amount be allocated to the heating section. Since gelation occurs more easily 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, use may be made of a heater on the front surface, back surface, or both sides of the support, an infrared heater, blowing hot air, passing hot water through a drum, etc. As a cooling means, in addition to cooling, The cooling may be performed by forced cooling such as blowing cold air or passing cold water through the drum. Generally, it is preferable to raise the temperature immediately after casting.
Furthermore, since a large amount of solvent evaporates and a large amount of latent heat is required in this region, it is preferable to heat this region intensively. 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. .

Schematic side views of three examples of such devices are shown in FIGS. 1-3. The example in Figure 1 is a band casting device,
An endless casting band 6 made of stainless steel is suspended between the drums 4 and 5. There are two casting ports; a first casting port 1 is provided on the drum 4 on the left side of the drawing, and a second casting port 2 is provided on the drum 5 on the right side of the drawing.

Then, the dope (A) is poured from the first casting port 1, and the dope (B)
) is cast from the second casting port 2 onto the bands located on the drums 4 and 5, and hot air 7 is cast from the first casting port 1 onto the band 6 near the casting portion of the Dawg (5). Spray on top. The hot air 7 travels on the band 6 in its traveling direction, goes around the drum 5, and separates from the band 6 at a point where it reaches approximately three quarters of the length of the band 6 surface.

On the other hand, the cold air 8 is blown onto the surface of the band 6 near the bottom of the drum 4, travels along the surface of the band 6 against the traveling direction, and reaches a point where it reaches approximately one quarter of the length of the surface of the band 6. Band 6 will also leave. The drum 4 is cooled with cold water 9, and the drum 5 is heated with hot water 10. The peeling portion 11 of the cast film is also peeled off.

The example shown in Fig. 2 is also a band casting device, and the casting opening is 1° 2.3°.
The first casting port 1 is located above the drum 4 on the left side of the drawing.
, a second casting port 2 located slightly to the right of the center of Pandro, and a third casting port 2 located slightly outside the bottom of the drum 5 on the right side of the drawing.
It consists of 3 casting ports.

The hot air 7 extends over approximately three quarters of the length of the band 6 as in the example shown in FIG. Further, in this example, the band 6 near the casting part is heated from the back surface thereof by the heater 12, and the cold air 8 is also blown from the back surface of the band 6.

The example shown in FIG. 3 is a drum casting device, in which a first casting port 1 is provided at the top of the drum 13 and slightly to the left, and a second casting port 2 is provided diagonally above and to the right of the drum 13. .

The hot air 7 is blown near the casting part of the Dawg (A), travels along the circumferential surface over approximately two-thirds of the circumference of the drum 13, and then leaves. On the other hand, the current wind 8 is blown near the peeling part and travels along the circumferential surface of the drum 13 in a direction opposite to the direction of travel.
It is designed to break away after completing one-third of a lap. Only the circumferential surface of the drum 13 rotates, and the internal chamber is divided into a portion where the hot air 7 flows on the circumferential surface and a portion where the cold air 8 flows, with the casting portion as a boundary. Hot air 7 or cold air 8 flows through each room. 14 is a hot air inlet, 15 is an outlet, 16 is a cold air inlet, and 17 is a cold air outlet.

(Function) The reason why the peeling time from the support can be shortened by performing split casting is that the dope, which is thinner than the target thickness cast from the first casting port, is subjected to the second casting. This is to dry during the process and create a solidified layer containing a small amount of solvent at the interface between the Dogue and the support, and the amount of solvent contained at this interface can be reduced compared to when the entire amount is cast at once. It is.

As a result of various experiments, the present inventors discovered that the biggest factor that enables the cast film to be peeled off from the support in a short period of time is the formation of roughness at the interface. By increasing the solvent content of the dope cast from the dope, the time from casting to stripping can be shortened while suppressing an increase in the total amount of poor solvent.

Further, this divided and cast dope is dried at an early stage when drying is easy, and during that time, sludge formation is prevented from occurring, thereby preventing a decrease in drying efficiency. on the other hand,
When the coating becomes easy to form by drying, it is processed to improve peelability.

(Example) .

Dope (A) Dope (B) Cellulose triacetate) 17.4 parts 17
．． 4 parts methylene chloride 66 parts 7
3.5 parts methanol 5.8 parts
6.5 parts Butanol 8.2 parts - TPP 2.6 parts
Using 2.6 parts of the above Dodo, a film having a dry film thickness of 125 μm was formed by a conventional single-layer casting method and a split casting method of the present invention. In the case of the split casting method, the dope (
5) was cast to a thickness equivalent to 35 μm, and at the point where the drying zone reached 50 μm on the band, a second casting was performed to reduce the remaining thickness of the dope () to a thickness equivalent to 90 μm. Each film was manufactured by the conventional hot air drying method (1), but for the film formed by the split casting method, the cooling gelling method shown in FIG. 5 (ID and the method of the present invention shown in FIG. Manufactured.

The results obtained are shown below. Note that the drying time is the time required for the concentration of volatile matter to decrease from 20% to 1 ton.

Casting method Drying method Stripping time Drying time Single layer casting (Dope (A)) Hot air drying method (I) 2 minutes Approximately 50 minutes Single layer casting (Dose 7' (B)) 14 minutes Approximately 20 minutes divided Casting Hot air drying method (1) 1.
2 minutes about 30 minutes? @#a material W) 3 minutes approximately 30 minutes Present invention method ID 1 minute approximately 30 minutes (Effects of the invention) In the method of the present invention, a poor solvent is effectively used to increase the degree of gelation at the interface, and the doped Since drying and gelation are carried out by making good use of the characteristics of , the peeling time can be further shortened compared to when each of these is used alone. Furthermore, the increase in drying time after stripping due to the high boiling point of the poor solvent can be kept to a negligible level, and overall the stripping speed can be increased to an unprecedented degree. It is possible to increase process productivity and reduce costs.

[Brief explanation of drawings]

1 and 2 are side views schematically showing an example of a band casting apparatus used in the method of the present invention. FIG. 3 is a side view schematically showing an example of the drum casting apparatus. FIG. 4 shows the results of measuring the relationship between dope concentration and gelation temperature for two types of solvents. Fifth
The figure is a side view showing an example of a band casting apparatus used in the conventional cooling gelling method. DESCRIPTION OF SYMBOLS 1... 1st casting port, 2... 2nd casting port, 3... 3rd casting port, 4, 5... Drum, 6... Band, 7...
...Hot air, 8...Cold air, 11...Peeling part, 13...
・Drum patent applicant Fuji Photo Film Co., Ltd. Agent Patent attorney 1) Hiroshi Nakamasa jl'13
figure

Claims (1)

[Claims] The cellulose triacetate dope is cast from a plurality of casting holes spaced apart from each other so that the cellulose triacetate dope cast from the previous casting hole can dry to some extent before reaching the next casting hole. In the method of manufacturing cellulose triacetate film by casting and laminating cellulose triacetate, dope (A) prepared using a mixed solvent of methylene chloride and methanol and a poor solvent for cellulose triacetate other than methanol ) is cast from the first casting port, and the dope (A) is prepared using a solvent that does not contain the poor solvent or has a content lower than that of the dope (A).
B) is cast from a casting port after the second casting port, and the temperature of the casting section where these dopes (A) and (B) are cast onto the support and at least the support of the cast film. The temperature of the first half of the transfer on the body and the support in this part is set to be above the gelling temperature of the dope and the maximum temperature is 30°C or more and below the foaming temperature, and the temperature of the film and the support in the film peeling part is set to 20°C. A method for producing a cellulose triacetate film, characterized in that the temperature is below ℃