JPH1158425A - Method and apparatus for making cast film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain the deterioration of film smoothness caused by the nonuniformity of drying in a film making process in which a polymer solution melted by an organic solvent is cast on a support, and to improve productivity. SOLUTION: A polymer solution is cast on a support of a traveling belt 15 or a drum surface into a film. During drying, until the temperature of the film reaches a gelation temperature which was set up previously corresponding to the components of the polymer solution, drying air 0.1-2.0 m/s in wind velocity is supplied for the first stage drying. After that, the film is dried more speedily by the second stage drying.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a film used as a support for a photographic light-sensitive material, and more particularly to a method for casting a polymer solution dissolved in an organic solvent to form a film. Things.

[0002]

2. Description of the Related Art Conventionally, as a method of producing a polymer solution, for example, a cellulose triacetate film, a method of casting a polymer solution on a support of a running endless metal belt and drying the solution is generally used. In order to increase the production speed, various devices have been proposed.

For example, methanol or the like, which is a poor solvent for the polymer solution, is added, and further, US Pat. Nos. 2,607,704 and 2,739,695;
JP-A-9074 and JP-A-54-48862 disclose methods for promoting gelation by adding a poor solvent such as butanol and cyclohexane. U.S. Pat. No. 2,221,019 discloses a method of stopping gelation by cooling a cast dope.
JP-A-148013 discloses a method of keeping the temperature of a cast dope casting layer within a predetermined temperature range within a predetermined time, and US Pat. No. 3,793,043 discloses a method of promoting gelation using a metal salt. It has been disclosed. Further, it has been proposed to use a radiant heat source without blowing dry air to the surface of the film until the residual solvent is reduced to 35 wt% or less.
No. 6,086,045.

[0004]

In the above-mentioned method for casting a polymer solution dissolved in an organic solvent to form a film, the flatness of the film-like material cast on a support is determined by casting. It is governed by thickness unevenness generated from the die and unevenness in evaporation after the support is extended upstream. Therefore, forcing the radiant heat source drying, which is conventionally performed to increase the production speed, on the surface of the film-like material immediately after casting with high fluidity on the support, the local flow due to the drying unevenness This causes a phenomenon and deteriorates the flatness. In addition, a radiant heat source aimed at preventing the occurrence of drying unevenness due to the influence of drying air or drying similar to non-air blowing, gas transfer in the drying zone cannot be expected. There was a tendency for quality failure to occur due to condensation.

[0005] An object of the present invention is to suppress the deterioration of the planarity of a film-like material caused by uneven drying in a film forming process of a film formed by casting a polymer solution dissolved in an organic solvent on a support. Accordingly, it is an object of the present invention to provide a casting film forming method capable of suppressing deterioration in quality and improving productivity.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to provide a polymer solution dissolved in an organic solvent, which is cast on a support made of an endless belt or drum surface which runs, to form a film. In a casting method for casting a plastic film in which a polymer solution is formed into a film by drying, the temperature of a film formed by casting on a support during drying is set in advance corresponding to the polymer solution component. Until the set gelation temperature is reached, the first stage is dried by blowing dry air at a wind speed of about 0.1 to 2.0 m / s, and the second stage is further accelerated after the gelation temperature of the film is reached. By carrying out the drying step.

Here, the gelation temperature Tg and the gelation completion temperature are based on the following definitions. For the gelation temperature Tg, a polymer solution dissolved in an organic solvent is
P1 = a × 1n (b / T) in the case where the polymer solution constituting a film-like product formed by casting on a support has a temperature T <Tg between the viscosity P and the absolute temperature T; P2 when T> Tg
= C × 1n (d / T), it is assumed that this polymer solution has a gel point, and the change point Tg is defined as the gel temperature (where a, b, and c and d are constants experimentally determined).

Further, regarding the gelation completion temperature, a linear equation Tg = pN1 + qN2 + rN3... + ΑN0 + β obtained by experimentally obtaining the relationship between the gelation temperature Tg and the solvent ratio.
(Where p, q, r,..., Α, β are experimentally determined constants, N1, N2, N3,.
N0 is the polymer solid content weight ratio), and the gelation of the film-like material cast at the intersection of this formula and the curve obtained by numerically calculating the surface temperature of the film-like material on the support using the difference method is completed. Defined as temperature.

[0009] As described above, the film speed of the film-like material cast on the support until the gelling temperature Tg is reached is from 0.1 to 0.1%.
By making the wind speed weak and uniform by the first drying step of applying a drying wind of 2.0 m / s or less, the film-like material slowly gels, and the drying unevenness is suppressed to an allowable level. Dry to some extent. After the completion of the gelation, a second drying step with a higher drying rate is carried out to achieve a constant drying zone solvent gas concentration without deteriorating the flatness, thereby forming a complete plastic film. .

Here, 2.0 m /
A drying step with high drying efficiency can be performed by applying drying air of s or more. Further, as the drying in the second step, a method of heating from the back surface of the support with a radiant heat source may be employed. The drying air before reaching the gelation completion temperature in the first drying step is more preferably 0.1 to 1.0 m / s.

An apparatus for carrying out the casting film forming method includes a support comprising a running endless belt or drum surface, on which a polymer solution dissolved in an organic solvent is cast as a film. What is claimed is: 1. A casting film forming apparatus for a plastic film, comprising means for drying a film-like material and forming a polymer solution into a film by means of a film, wherein the temperature of the film-like material is preset to a polymer solution component. The moving distance corresponding to the time interval at which the temperature reaches the formation temperature is divided on the support, and an air volume adjusting means for passing a dry air having a wind velocity of 0.1 to 2.0 m / s through the divided section; And drying air supply means for passing a drying air for drying more quickly after passing through.

Next, as another structure for achieving the above object of the present invention, there is provided a film-like material which is cast on a support comprising an endless belt or drum surface which runs a polymer solution dissolved in an organic solvent. After drying, in the casting method for casting a plastic film to form a polymer solution into a film by drying, the solvent having the highest energy amount represented by latent heat of evaporation x total weight of the organic solvent contained in the solvent. The specific evaporation rate represented by (vapor pressure × molecular weight ÷ 11) is 10
In a state of about 0 to 3500, the mixture is cast on a support from a casting die, and a drying step can be performed.

The film is cast on a support from a casting die at a specific evaporation rate of about 100 to 3500, and a drying step is performed. Is larger than 3500, the occurrence of local flow caused by the difference in surface tension is suppressed, and the deterioration of flatness due to the local flow can be suppressed.

A more effective effect can be expected by using both the casting film forming method utilizing the gelling temperature and the casting film forming method for limiting the specific evaporation rate.

[0015] The polymer for solution casting that can utilize the present invention is:
In addition to polycarbonate, there are polystyrene, polymethyl methacrylate, polypropylene, polyvinyl chloride, styrene, phenylonitrile copolymer polyethylene, polyacrylate, polyether sulfone, polyphenylene oxide, diacetyl cellulose, triacetyl cellulose and the like.

The organic solvent of the polymer solution includes chlorinated hydrocarbons such as methylene chloride, ketones such as acetone and methyl ethyl ketone, and aromatics such as toluene as solvents for the above-mentioned polymer. .

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for casting a plastic film according to the present invention will be described below with reference to the drawings.
FIG. 1 shows an apparatus 1 for carrying out the casting film forming method of the present invention.
It is a figure showing an outline of an embodiment.

An endless belt 15 is stretched between the two drums 11 and 13, and a casting die 17 for flowing a polymer solution onto the belt 15 is arranged above one of the drums 11. The polymer solution is dried during substantially one round between the drums 11 and 13, returns to the vicinity of the casting die 17, and is dried in the form of a film.

Here, on the upper belt 15 between the drums 11 and 13, a windshield is provided near the position where the polymer solution is cast from the casting die 17 and comes into contact with the belt 15 and downstream in the belt 15 transport direction. A plate 19 is fixedly arranged so that the position where the polymer solution contacts the belt 15 is prevented from being blown by dry air. Further, an air volume adjusting plate 21 is arranged downstream of the drum 13 in the vicinity of the drum 13 so as to be movable in the conveying direction of the belt 15.

The drying air X is blown as the first drying step I, and the wind speed between the wind shield plate 19 and the air volume adjusting plate 21 is at least about 0.1 to 2.0 m / s. The air volume adjusting plate 21 is adjusted so that the drying air X becomes.
At this time, the position of the air volume adjusting plate 21 is set at a position where the first drying step I can be maintained until the film-like material cast on the belt 15 reaches the gelling temperature Tg.

At the downstream side of the belt 15 in the conveying direction from the air volume adjusting plate 21 after the film-like material has reached the gelation completion temperature, the wind speed of the drying air Y is increased so as to perform the second-stage drying step II for drying faster. Is set to 2.0 m / s or more, so that the film-like material is made into a completely dried film, and is stripped as described above.

These drums 11 and 13 and belt 15
Although not shown, is surrounded by a rectifying plate so that wind flows only along the belt 15. By rectifying the flow of the drying air in this manner, the atmosphere of the vaporized solvent near the film-like material adhered to the belt 15 can be kept constant.

Therefore, the drying air Y in the second drying step II
By using the wind speed, the wind speed of the drying wind X in the first drying step I is performed by the air volume adjusting plate 21, so that the drying speed is faster and there is no drying unevenness, and only one drying wind generating means is used. Can perform two drying steps. Note that the wind speed of the drying wind Y in the second drying step II is 1
About 2 m / s is appropriate.

In the second drying step II, the belt 15 may be heated from the back surface by a radiant heat source. In addition, it is more preferable that the drying air X before reaching the gelation completion temperature in the first drying step I is set to be 0.1 to 1.0 m / s, as is clear from the examples described later. In the above configuration, the belt 15 is stretched around the drums 11 and 13, but it is also possible to use only the drum having the same process distance.

[0025]

【Example】

<Example 1> In a solution casting of a polymer solution in which cellulose triacetate was dissolved in a mixed solvent of methylene chloride, methanol and butanol, a casting casting was carried out using the apparatus shown in FIG. Here, regarding the gelation completion point temperature, the gelation temperature Tg and the film-like substance (hereinafter, referred to as a base)
The relationship between temperature and time for the temperature drop is shown in FIG.

FIG. 2 shows that the base film has a thickness of 205 μm and a thickness of 8 μm.
The relationship between the gelation temperature Tg and the decrease in the base surface temperature is shown for two cases of 0 μm. The conditions for this are as follows. Initial conditions Polymer solution temperature: 34 ° C Atmospheric temperature: 40 ° C constant Drum temperature: (A) =-5 ° C (205 μm and 80 μm) constant (B) =-8 ° C (205 μm) Gelling temperature: Tg = 0.6744 CMOH + 1.2268 CBOH + 1.0599 CONC-35.148 (° C) CMOH: methanol ratio (wt%), CBOH: butanol (wt%) CONC: polymer solution concentration (wt%) Dry matter-based volatile matter : LnS (t) = ln3.25-αt (wt%) The parameter α was determined from the stripped volatile matter of the DM machine. DCL 122 μm: Converted to each thickness from α = 0.02. Boundary condition: Polymer solution temperature on drum side at time t> 0 = Polymer solution temperature Latent heat of evaporation of polymer solution: 78.7 kcal / kg Thermal conductivity: 0.13 kcal / mhr ° C Specific heat: 0.35 kcal / kg ° C Specific gravity: 1.22 × 10 ³ kg / m ³ Film heat transfer coefficient: 140 kcal / m ² hr ° C

As shown in FIG. 2, the gelation temperature Tg can be expressed by calculating and assuming a linear function of time. In this figure, it can be seen that the slope of the time change of the gelling temperature Tg differs between the base film thickness of 205 μm and the base film thickness of 80 μm. The intersection of the function of the gelling temperature Tg and the temperature drop curve of the base is the completion point of gelation (base film thickness 80 μm, drum temperature A), (base film thickness 205 μm).
m, drum temperature A) and (base film thickness 205 μm, drum temperature B).

Here, in FIG. 3, the base is cast on the belt especially when the drum temperature is set to the condition (B) and the gelation completion point is fixed for the base film thickness of 205 μm. The measurement results of the first drying step time after the completion and the thickness unevenness PV value of the base are shown.

As can be seen from FIG. 3, a comparative example in which the first drying time is shifted to the second drying before the gelation is completed with respect to the base having a fixed gelation completion point. S
1 and S2, the thickness unevenness is large. At point S3 where the first drying time reaches the completion of gelation, the point S3 where the present invention is implemented, and at point S4 where the first drying time is longer than that point S3, the thickness unevenness is smaller than at points S1 and S2. Are small and have almost the same level of unevenness. Accordingly, it can be seen that the gelation completion point is greatly related to the thickness unevenness, and that after the gelation is completed, the rapid drying does not affect the thickness unevenness.

Example 2 In the solution casting of a polymer solution in which cellulose triacetate was dissolved in a mixed solvent of methylene chloride, methanol and butanol, the latent heat of evaporation × the total weight was the highest among the three solvents constituting the solvent. When the solvent is methylene chloride, the specific evaporation rate and the evaluation results of the thickness unevenness of the obtained plastic film are shown in Table 1.
Shown in

Execution conditions Polymer solution formulation: Solid content concentration 23.5 wt% Solid content triacetate cellulose + triphenyl phosphate Solvent component weight ratio MeCl ₂ : MeOH: BuOH = 82: 16: 2 Plastic film thickness: 205 μm Casting speed ： 20m / min

[0032]

[Table 1]

As is apparent from Table 1, the specific evaporation rate 35
When the thickness is less than 00, the thickness unevenness is remarkably improved.

[0034]

According to the casting film forming method and apparatus of the present invention,
Until the gelation is completed, a gentle drying air suppresses optical nonuniformity due to drying unevenness received at a timing that is easy to flow immediately after casting, and prevents deterioration in flatness due to evaporation unevenness. Then, after the gelation is completed, by performing rapid drying, a film having high flatness can be produced with high productivity. Furthermore, it suppresses the occurrence of local flow caused by the surface tension difference generated when the specific evaporation rate becomes greater than 3500, suppresses the deterioration of flatness due to the local flow, and produces a film having high flatness with high productivity. Can be possible.

[Brief description of the drawings]

FIG. 1 is a view schematically showing an embodiment of an apparatus for performing a casting film forming method of the present invention.

FIG. 2 is a diagram showing a relationship between a gelling temperature Tg and a temperature and time relating to a decrease in a base temperature.

FIG. 3 is a diagram showing a relationship between a first drying step time and a measurement result of thickness unevenness of a base.

[Explanation of symbols]

 11, 13 Drum 15 Belt 17 Casting die 19 Wind shield plate 21 Air volume adjustment plate

Claims (6)

[Claims] 1. A polymer solution dissolved in an organic solvent is cast on a support comprising a running endless belt or drum surface to form a film, and the polymer solution is dried to form a film. In the method for casting a plastic film, a temperature of a film formed by casting on a support reaches a gelling temperature set in advance corresponding to the polymer solution component during the drying. The first stage of drying is performed by blowing dry air at a wind speed of about 0.1 to 2.0 m / s until the gelation completion temperature of the film is reached, and then the second stage of drying is performed faster. A casting film forming method characterized by the following. 2. The casting film forming method according to claim 1, wherein a drying air of 2.0 m / s or more is applied during the second stage of drying. 3. The casting film forming method according to claim 1, wherein the support is heated from the back surface of the support by a radiant heat source during the drying of the second stage. 4. The drying air for the first-stage drying is 0.1 to 1.
The casting film forming method according to any one of claims 1 to 3, wherein the casting speed is 0 m / s. 5. A support comprising a running endless belt or drum surface, comprising a support on which a polymer solution dissolved in an organic solvent is cast as a film, and a drying means for drying the film. What is claimed is: 1. A plastic film casting apparatus for forming a molecular solution into a film, comprising: a movement corresponding to a time interval at which the temperature of the film reaches a gelling temperature preset for the polymer solution component. An air volume adjusting means for dividing a distance on the support and passing a dry air having a wind speed of 0.1 to 2.0 m / s through the divided section; and a drying section for drying the film-like material more quickly after passing the section. A casting film forming apparatus, comprising: a drying air supply means for passing air. 6. A polymer solution dissolved in an organic solvent is cast on a support comprising a running endless belt or drum surface to form a film, which is then dried to convert the polymer solution into a film. In the method of casting and casting a plastic film, the solvent having the highest amount of energy represented by latent heat of vaporization × total weight among the organic solvents contained in the solvent is (vapor pressure ×
The specific evaporation rate represented by the molecular weight {11) is 100 to 350.
A casting film forming method, wherein the film is cast from a casting die onto a support in a state of 0 and dried.