JPH0915792A - Manufacture of cellulose triacetate photographic film base - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the method for manufacturing the cellulose triacetate film not causing peeling of web and to reduce a casting time on a casting surface. SOLUTION: The casting composition to be used comprises the cellulose triacetate and a plasticizer and a solvent and the concentration of the triacetate and the plasticizer is 36-72weight%. The cellulose triacetate photographic film base is manufactured by casting the casting composition at a temperature of 40-63 deg.C on the surface kept in -70-21 deg.C for a residence time of 3-8sec in accordance with the following expression: Tr/Tg<1.9, where Tg and Tr is the glass transition point (K) and the composition temperature (K) near the casting surface, and separating the film base from this surface.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to solution casting,
It relates to a method for producing a cellulose triacetate photographic film base. More particularly, the present invention relates to a method of making a cellulose triacetate film base with increased speed or thickness and reduced need for drying equipment.

[0002]

BACKGROUND OF THE INVENTION The process for making cellulose ester films, especially triacetate films, involves the step of forming a dope solution by dissolving cellulose triacetate in a suitable solvent such as dichloromethane. Conventionally, the dope has a concentration of cellulose triacetate in the solvent of about 1
5 to about 35% by weight. The dope is filtered through one or more filtration devices and then extruded as a film through a die. The film has a high polishing wheel (hi
ghly polished wheel) or cast on a moving surface such as a continuous band. The dope is "cured" by evaporation of the solvent from the exposed surface. The dope stays on the band or wheel for a sufficiently long time so that it is strong enough to be pulled away from the band or wheel. The dope is then subsequently dried through an air section and finally wound up as a roll of film.

One of the rate-determining steps of this method is that the web
The cure time required to be strong enough to be pulled away from the band or wheel without peeling. If the web is removed from the band or wheel too soon, the cohesive forces that bond the web will be less than the adhesive forces that secure the web to the casting surface. As a result, the web cannot be properly pulled away from the casting surface, and some or all of the web will again slip under the die. as a result,
Web braking and other casting obstacles occur.

If the cohesive forces in the web can be increased while the web is on the casting surface, the web can be pulled away from the casting surface relatively quickly. Therefore, if the surface hardening time is kept constant, a relatively fast method can be obtained,
Alternatively, if the velocity is kept constant, the resulting casting surface will be relatively small. The latter option is very important because the bands and wheels used in current cellulose triacetate film manufacturing processes are very large and expensive. In many cases, it takes 60 to 120 seconds to cure the web on the band or wheel. If one is inadvertently damaged, the replacement cost can be significant. Therefore, it is highly desirable to reduce the required size of the casting surface so that replacement and implementation costs can be reduced.

[0005]

As a result, there is a need for a method of making a cellulose triacetate film that has a reduced cure time on the casting surface without causing web delamination.

[0006]

The present invention provides a casting composition comprising cellulose triacetate, a plasticizer and a solvent, wherein the concentration of the cellulose triacetate and the plasticizer is 36% by weight to 72% by weight. /Tg<1.9 [in the formula, Tg
And according Tr is the temperature of the casting composition at a point near the glass transition temperature ⁽⁰ K) and the casting surface ⁽⁰ K)], 40
C. to 63.degree. C., comprising casting the casting composition on a surface held at -70.degree. C. to 21.degree. C. for a dwell time of 3 to 8 seconds and pulling the film base away from the surface. Provided is a method for producing a cellulose triacetate photographic film base.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS From a detailed experiment, the peeling between the film base and the casting surface has a Tr / Tg of 1.9 to 2.2.
It was confirmed that If this ratio is greater than 2.2, delamination occurs in all cases. If this ratio is less than 1.9, peeling does not occur. Therefore, a Tr / Tg ratio of less than 1.9 guarantees a method in which no separation occurs on the casting surface. Tg is the Fox formula:

[0008]

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It is calculated by In the formula, W _i and Tg _i are the mass fraction and glass transition temperature of the i-th component, respectively, and w _i is obtained by a number of methods including nuclear magnetic resonance, near infrared spectroscopy and the like.

When making a cellulose triacetate photographic film base according to the present invention, first, cellulose triacetate (CTA) and a plasticizer such as triphenyl phosphate, dibutyl phthalate, tricresyl phosphate, butyl stearate, tetraethylene glycol. An extremely concentrated dope solution is prepared by mixing and dissolving dimethyl ether and the like in a dichloromethane solvent. To the dichloromethane solvent, other components such as alcohols including ethanol, butanol, propanol, methanol, a mixture thereof; ketones including acetone, methyl ethyl ketone, etc .; cyclic alkanes such as cyclohexane, methylcyclohexane, cyclopentane, etc. are added. You can also do it. The plasticizer to cellulose triacetate ratio is 13 to 17% by weight. This cellulose triacetate / plasticizer ratio is mixed with the solvent to a concentration higher than 36%. Solvents are 75% to 85% by weight dichloromethane, 6% to 15% methanol, 5% to 1
0% butanol or cyclohexane and 0% to 3%
It consists of acetone. This dope solution is 7
It is pumped through a heater heated to a temperature of about 40 ° C. to about 63 ° C. with a pressure of ˜50 atmospheres and then through a fine filter. A fine filter removes particles of gelatinous material and slag. In addition, the filtration material in the said temperature range under the said pressure is -70 degreeC-21 degreeC.
Cast on the surface of a high-abrasive rotating roll or continuous belt or band maintained at the temperature of. After 3-8 seconds, the web can be removed from the surface and dried without peeling according to conventional methods known in the art of making cellulose triacetate photographic film bases. In the preferred method, the solids consist of 85% CTA and 15% triphenyl phosphate. This solid mixture is preferably combined with a solution consisting of 78% dichloromethane, 12% methanol and 7% cyclohexane or butanol (butanol being most preferred) and 3% acetone. The pressure of the solution as it passes through the heat exchanger and the filtration device is preferably about 10 to 45 atmospheres, most preferably about 1 atmosphere.
It is preferable to maintain the pressure at 5 to 40 atm. The temperature of the dope solution before casting on the highly polished surface is preferably 45 ° C to 63 ° C.
C, most preferably about 55-63C. This solution is then cast onto a surface, preferably at a temperature of about -70 ° C to 8 ° C, most preferably about 0 ° C to 8 ° C.

The dope or casting composition is mixed in a mixer
Prepared by dissolving the cellulose triacetate / plasticizer in the solvent dichloromethane or a mixture of dichloromethane and other ingredients. The dope or casting composition is discharged from the mixer through a coarse filter and then through a heat exchanger. In the heat exchanger, the pressure is maintained at 7 to 50 atm, and the temperature of the dope is 40 atm.
The temperature is raised to ℃ ~ 63 ℃. The dope is then filtered through a fine filter to remove gelatinous particles or other material. Fine filters generally have openings of about 30 micrometers. This general method is described in 1994.
US patent application Ser. No. 08/30 filed September 16, 2013
No. 8,011 and is hereby incorporated by reference into this U.S. application.

Finally, the dope still under said pressure and within said temperature range is cast onto the polishing roll at said temperature by means of conventional dies including coat hanger dies, horseshoe dies and the like. After 3-8 seconds, the web is removed from the surface of the roll, sent into an air or nitrogen dryer and finally wound into a roll.

[0013]

The present invention is further illustrated by the following examples.

EXAMPLE 1 A solution of 39.5% CTA and 6.6% triphenyl phosphate was stirred in a mixer at room temperature for 1.5% acetone, 6.3% methanol, 4.3 butanol 4.3.
% And dichloromethane (remainder), pumped out of the mixer through a coarse filter (media with openings 30 μm) and then into the heat exchanger at a pressure of 41 atm. The temperature was raised to about 63 ° C in the heat exchanger. The heated solution then delivered fines through a media filter with an absolute depth of 30 μm. 1 final dry web
A film as thick as 18 μm was extruded from the coater hanger die onto a cooled stainless steel drum with a surface temperature of 1 ° C. for 7.5 seconds. Tg and Tr are measured to be 1
It was 58.8 ⁰ K and 284.9 ⁰ K, and the Tr / Tg ratio was 1.79. The web was easily removed from the casting surface without peeling.

Example 2 (Comparative) Example 1 was repeated except that the cooling drum temperature was raised to 21.1 ° C. According to Tg and Tr are measured to be 158.8 ⁰ K and 304.9 ⁰ K, Tr / Tg ratio was 1.92. The web could not be removed cleanly from the casting surface, resulting in delamination of the cellulose triacetate web.

Example 3 (Comparative) Example 1 was repeated except that the temperature of the cooling drum was 7.2 ° C. and the residence time on the drum was 5.2 seconds. Tg and Tr
Are measured to be 157.6 ⁰ K and 305.3 ⁰ , respectively.
K, and the Tr / Tg ratio was 1.94. The web could not be removed cleanly from the casting surface, resulting in delamination of the cellulose triacetate.

Example 4 CTA 49.8%, triphenyl phosphate 6.3%, acetone 1.35%, methanol 5.
7%, butanol 4.1% and dichloromethane (remainder)
Example 1 was repeated except that According to the measurement, Tg and Tr were 165.9 ⁰ K and 286.0 ⁰ K, respectively, and the Tr / Tg ratio was 1.72. The web was easily pulled away from the cooling drum surface.

Example 5 CTA 44.4%, TPP7.
Example 1 was repeated except that 0%, Acetone 0%, Methanol 4.7%, Cyclohexane 2.7% and Dichloromethane (remainder) were changed and cast on a cooling drum at 7.2 ° C for 4.7 seconds. It was According to the measurement, Tg and Tr are each 16
6.1 a ⁰ K and 198.2 ⁰ K, Tr / Tg ratio is 1.
It was 8. The web was easily pulled away from the cooling drum surface.

Claims (1)

[Claims] 1. A casting composition containing cellulose triacetate, a plasticizer and a solvent, wherein the concentration of the cellulose triacetate and the plasticizer is 36% by weight to 72% by weight is prepared.
Formula Tr / Tg <1.9 [where Tg and Tr are glass transition temperatures ( ⁰
K) and the temperature of the casting composition at a point near the casting surface ( ⁰
K)], the casting composition at 40 ° C. to 63 ° C. is cast on the surface kept at −70 ° C. to 21 ° C. for a residence time of 3 to 8 seconds, and the film base is cast from the surface. A method of making a cellulose triacetate photographic film base, comprising: