JPH0519898B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention improves the method for producing cellulose triacetate films used as supports for photographic materials.

[Conventional technology]

One of the cellulose triacetate film forming methods is a solution casting method in which a dope is cast onto a band or drum, stripped off and dried.

In general, as a drying method after peeling off in this solution film forming method, as shown in FIG.
There is a thing. ) is placed between a large number of rolls 19, 19, . . . provided in the drying chamber 18,
While moving between them, methods were used to dry them using hot air6, infrared rays, etc. (for example, U.S. Patent No.
2319053 etc.). Instead of hanging the web directly on a roll, a method has also been developed in which air is blown out and the web is floated by the pressure, thereby moving the web without contacting the hanging frame (for example, in Japanese Patent Application Laid-Open No. 1983-1996-1).
135046, etc.).

On the other hand, one of the stretching methods used to improve the mechanical strength, etc. of films made of polyester, polypropylene, etc. is a tenter method in which both side edges of the film are fixed with clips or the like and stretched 2 to 6 times. A technology has also been developed to use this tenter method to manufacture substrates for liquid crystal display panels from films such as phenoxy resin (Japanese Unexamined Patent Publication No. 59-211006), and it is known that cellulose triacetate films can also be used for this film. Some have suggested it.

[Problem that the invention seeks to solve]

A major problem with the solution casting method is that the film forming rate is slow, and increasing the drying rate in the drying process also has great industrial merits.

However, if you try to dry the web at a high temperature immediately after stripping it to increase the drying speed, wrinkles with a pitch of about 0.3 to 4.0 mm may occur on the surface of the web, or residual solvents such as methylene chloride (boiling point approximately 40°C) may occur. Since the amount is still large, foaming may appear, making it impossible to use it as a product. Therefore, in the past, after stripping, drying was carried out with care so that the film surface temperature did not exceed the boiling point of the solvent for a while, for example, drying was carried out at a high temperature only when the amount of solvent in the web was 30% by weight or less. Conditions were set. As a result, not only does drying take a long time, but the burden of managing the drying process also increases.

On the other hand, when these films are coated with photographic emulsion, cut and cut into photographic films, and perforation holes are punched to make film for motion pictures, how to prevent the perforation holes from being damaged during the motion picture. , the tear strength properties of the film are important.

An object of the present invention is to shorten the drying time in a method for manufacturing cellulose triacetate film by solution casting, thereby increasing the film forming speed and downsizing the drying apparatus.

Another object of the present invention is to simplify the management of the drying process.

Still another object of the present invention is to provide a drying method that eliminates wrinkles or foaming during the drying process and reduces the incidence of defective products.

Yet another object of the present invention is to provide a drying method that can improve the film strength (tear strength), which is particularly required for films for photographic materials.

[Means for solving problems]

The purpose of the present invention is to fix both side edges of the film during drying to control shrinkage due to drying,
This is achieved by applying tension in the width direction.

That is, the present invention is characterized in that when a cellulose triacetate film peeled from a support is transported and dried in a solution casting method, both edges of the film are fixed and the film is transported while maintaining a predetermined distance between them. The present invention relates to a method for drying cellulose triacetate film.

One embodiment of the invention is shown in FIGS. 1 and 2. Figure 1 shows film 1 peeled off from the support.
FIG. 2 is a plan view showing a state in which both side edges of the film are fixed by a width regulating device 2, and FIG. FIG.

As shown in FIG. 2, cellulose triacetate dope is cast from the casting port 3 onto the support 4,
The film 1 thus formed is stripped off by the stripping section 5, fixed at both ends by the width regulating device 2, and meandered through the drying chamber 18, during which time it is dried by hot air 6 and rolled. taken.

For example, a pin clip as shown in Fig. 3 may be used as the width regulating device for fixing both side edges of the film, or a tenter used for stretching polyester film etc. as shown in Fig. 4 may be used. You can also use paper clips. Furthermore, a nip belt system as shown in FIG. 5 can also be used.

The pin clip 7 is, for example, as shown in FIG. 3, a pin stand 8 with a large number of pins 9 planted therein.
attached to a chain (not shown) in rows. It is preferable that the length of the pin stand 8 is short in order to allow smooth movement at the turn portion of the chain. The pins 9 installed in the pin stand 8 are preferably arranged in multiple rows from the viewpoint of film retention strength.
In reality, two to three columns are sufficient. As a means for biting the pins 9 into the film, a biting roll 10 as shown in FIG. 3 having grooves cut in accordance with the rows of pins may be used, or a brush roll (not shown) may be used. You may. others,
It is also possible to make it bite by blowing air strongly.

When using clips, those used for tenters can be used as they are; for example, a large number of clips as shown in FIG. 4 may be attached to a chain or the like. This clip 11 has film 1 fixed in jaw 1.
After getting on the film 2, the lever 13 is pushed down and the film 1 is held in the shoe 14.

In the nip belt method, for example, the side edge of the film 1 is connected to a nip belt 15 and a pulley 16, as shown in a plan view in FIG.
This is a method of holding it down. In this method, as shown in the front view in FIG. 7 and in the side view in FIG. 8, it is also possible to use a large diameter drum 17 and press the peripheral edge of the drum 17 with a nip belt 15. In that case, one large-diameter drum may be used, or a plurality of large-diameter drums may be used in succession.

Both side edges of the film fixed by the width regulating device are maintained at a predetermined distance during conveyance. This interval may be constant, or it may become wider or narrower than when the width regulation started as the width is being conveyed. The range in which this interval can be widened or narrowed is usually about ±20% of the interval at the start of width regulation. Of course, it is also possible to change this interval in an arbitrary pattern during conveyance. Generally, the film shrinks during drying, so by keeping the spacing constant or gradually narrowing it, it is possible to give the film an appropriate amount of tension.

Width regulation is usually performed immediately after peeling off from the support. In that case, as shown in FIG. 9, it is also possible to connect directly to the width regulating device 2 without providing a stripping roll.

Further, depending on space constraints, it is also possible to provide the width regulating device 2 apart from the support body 4, as shown in FIG. 10. However, in that case, rapid drying must be avoided before regulating the width.

The method of the present invention is effective in drying films with a large residual amount of solvent, such as wet films with a solvent content of 30% by weight or more, particularly 50% by weight or more.

The drying means is not limited, and for example, hot air, infrared rays, etc. may be used. The drying temperature may be set immediately above the boiling point of the solvent after width regulation, for example, using methylene chloride with a boiling point of 40°C as the main solvent,
Even wet films with a solvent content of 55% can be heated to around 100°C in one go.
To speed up drying, it is best to blow drying air on both sides of the film, and the angle of the air should also be perpendicular to the film surface. The drying temperature pattern can also be freely set, but it is often set separately, for example, 100°C in the first half and 120°C in the second half.

[Operation] The main reason why wrinkles appear on the surface of cellulose triacetate film during the drying process is thought to be due to non-uniform shrinkage of the film during the evaporation process of the solvent. Therefore, if high temperature drying is performed rapidly in a state where the solvent content is high, the non-uniformity of the solvent distribution becomes large, non-uniform shrinkage occurs, and the surface quality deteriorates. This non-uniformity in solvent distribution is inherent during drying and cannot be removed. Measures can only be taken against uneven shrinkage. Although this non-uniform shrinkage occurs in all directions, the conveyance tension is acting in the shipping direction, which has a sufficient effect of suppressing the shrinkage.

Therefore, by using a conveying means that can suppress this shrinkage in the width direction perpendicular to the conveying direction where no suppressing force is acting, high temperature drying becomes possible without deteriorating the surface quality. .

In conventional transport using rolls, the frictional force between the rolls and the film can suppress this uneven shrinkage, but this frictional force is
It is extremely small and has little effect on preventing deterioration of surface quality. Also, if shrinkage occurs rapidly on the roll, it may cause scratches on the surface of the film.

One method of transporting a film is to blow air out of a nozzle, float the film using the dynamic or static pressure of the air, and transport the film in a non-contact manner. This method is normally used in the drying process after coating, but even if it is used immediately after stripping the film, it will prevent the aforementioned scratches but will have no suppressive force against shrinkage in the width direction of the film. equally,
There is no effect on preventing deterioration of surface properties.

Therefore, it is necessary to adopt a transportation method other than the above. That is, by drying the film while being transported with both sides of the film fixed so that the film cannot freely shrink in the width direction, deterioration of the surface properties can be prevented.

Furthermore, this method of regulating the width has another important effect. If the solvent content after stripping is 50% by weight or more based on the dry film, foaming will occur if the film surface temperature exceeds the boiling point of the solvent, and the film cannot be used as a product. Conventionally, this has been prevented by slowing down the drying rate so that the film surface temperature is below the boiling point of the solvent. However, by using a transport method that controls the width after drying, it has become possible to dry the film without causing foaming even when the film surface temperature exceeds the boiling point of the solvent. This is thought to be due to the fact that by fixing the width of the film so that it cannot freely shrink, a strong tension is generated in the film in the width direction, increasing the internal pressure within the film and raising the boiling point. This effect is more pronounced as the solvent content increases.

In other words, conventionally, films with high solvent content due to deterioration of film surface properties and foaming,
It was previously impossible to dry at high temperatures, but by adopting a conveying means that can suppress free shrinkage of the film, it is now possible to dry quickly at high temperatures, even for films with a high solvent content. It became possible.

〔Example〕

Cellulose triacetate 17% by weight, triphenyl phosphate 3% by weight, methylene chloride
A dope consisting of 72% by weight and 8% by weight of methanol was prepared and cast in a drum casting machine by a conventional method. The solvent content of the film in the peeled part is 55
It was in weight%.

Fix both side edges of this film with pins as shown in Fig. 3 and keep the same distance between them.
The sample was dried with dry air at a temperature of .degree. C., and the change in solvent content over time was measured, and the results shown by the white circles in FIG. 11 were obtained. This film did not exhibit any foaming, and the surface measured with a three-dimensional roughness meter was completely free of irregularities as shown in FIG. 12.

Cut this film to 40mm x 80mm, make a 5mm long cut in the center of the width along the long side,
Tear strength was measured by applying a load of 100g.
It was 380-100g/120μ.

[Comparative example]

Next, for comparison, the same film was dried with drying air at 65°C without width regulation, and the change in solvent content over time was measured, and the results shown by the black circles in Figure 11 were obtained. . This film has foamed, and the surface measured with a three-dimensional roughness meter is also
As shown in Figure 3, unevenness had occurred. When the tear strength of this film was measured under the same conditions as in the actual example, it was 340 to 50 g/120μ.

〔Effect of the invention〕

By the method of the present invention, drying time can be shortened, film forming speed can be increased, and drying equipment can be made more compact. Since a film with a high solvent content that has just been peeled off from the support can be dried immediately above its boiling point, the drying process can be easily controlled. The dried product has good flatness and no foaming, which reduces the incidence of defective products, and provides sufficient tear strength necessary for photographic films. As a result, product costs can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a state in which the film peeled off from the support is transported with both side edges fixed, and FIG. 2 is a plan view showing the film peeled off from the support and dried by the method of the present invention. It is a side view which shows a state. FIG. 3 is a perspective view showing a state in which the film is being conveyed with both side edges fixed, and FIG. 4 is a side view showing another example of the side edge fixing device. FIG. 5 is a plan view of an example in which the side edges are nipped and fixed with a belt, and FIG. 6 is a side sectional view thereof.
FIG. 7 is a front view of another example in which it is fixed with a belt, and FIG. 8 is a side view thereof. FIG. 9 is a side view of an example in which the width regulating device is directly connected to the support without providing a stripping roll, and FIG. 10 is a side view of an example in which the support and the width regulating device are provided separated from each other. FIG. 11 compares the change over time in the solvent content of the film obtained by the method of the present invention with that of the conventional method. FIG. 12 is a cross-sectional view showing the planar state of the film obtained by drying the film by the method of the present invention and FIG. 13 by the conventional method, and FIG. 14 is a side view showing the outline of the drum casting apparatus. be. DESCRIPTION OF SYMBOLS 1...Film, 2...Width regulating device, 3...Casting port, 4...Support, 5...Peeling part, 6...Hot air, 7...Pin clip, 9...Pin, 11...
Clip, 15...Belt, 16...Pulley, 1
7...Drum.

Claims (1)

[Claims] 1. A cellulose triacetate film, which is characterized in that when a cellulose triacetate film peeled from a support is transported and dried in a solution casting method, both edges of the film are fixed and the film is transported while maintaining a predetermined distance between them. drying method.