US 3805402 A
A process for preparing a plastic film of controlled curl comprising blowing hot moistened air onto the surface of said plastic film.
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Description (OCR text may contain errors)
United States Patent [1 1 Aono et al.
[111' 3,805,402 1 Apr. 23, 1974 PROCESS FOR PREPARING A PLASTIC FILM  Inventors: Masazumi Aono; Goro Uehara, both of Kanagawa, Japan  Assignee: Fugi Photo Film Co., Ltd.,
Kanagawa, Japan 22 Filed: Aug. 26, 1971 21 Appl. No.: 175,248
 Foreign Application Priority Data Aug. 26, 1970 Japan 45-74739  US. Cl 34/23, 34/26, 34/30, 34/46, 34/50, 34/151  Int. Cl. F26b 3/00  Field of Search 264/235, 346; 34/22, 23,
CURLING VALUE (K) Primary ExaminerCarroll B. Dority, Jr.
Assistant Examiner-Larry I. Schwartz Attorney, Agent, or Firm-Sughrue, Rothwell, Mion, Zinn & Macpeak [5 7] ABSTRACT A process for preparing a plastic film of controlled curl comprising blowing hot moistened air onto the surface of said plastic film.
10 Claims, 4 Drawing Figures 'ggggmummnv 0.5 Kg STEAM/Kg, DRY AIR) ggo mumnm 0.2Kg STEAM/Kg DRY AIR) PMEHI'EH km 2 3 m4 mum; VALUE W W m A v m W "M II. [I M M A A E E V g m m M 0 W m m m m M U W "My W 59 6 4 2 c; w3 @5413 FIG. 3
5! BLOWING TIME (MINUTES) 7oc-02 Kg STEAM/Kg DRY AIR 150c-2.0 Kg STEAM/Kg DRY AIR L 2 4 6 CURLINGV VALUE (K55) :55: I? was @223 s 225% BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for preparing plastic films. More particularly, the present invention relates to a process for controlling the curl of a plastic film to a desired extent.
2. Description of the Prior Art Cellulose esters, for example, cellulose nitrate, cellulose acetate, cellulose propionate, cellulose butyrate, and mixed esters thereof, are generally manufactured into a film base by a casting method. It is known that plastic films obtained by said process have some extent of curl. And the extent of curl (curling value) varies depending on the variation of the humidity of the atmosphere.
It is considered that this variation of curling value is due to the fact that the density and plasticizer have certain distributions along the direction of film thickness. These distributions vary as conditions of film formation change, and accordingly, change the curling value; thus, the change of curling value presents a serious hindrance in the case of changing the condition of the film casting and drying process.
It is also well known that, in the process for preparing photographic films, if a silver halide photographic emulsion is applied to one side of said film, the film curls to the side of the emulsion layer because of the tension which is generated in the emulsion layer during the drying step of said emulsion layer.
To prevent the curls which occur due to the many causes as above-mentioned, some processes have been hitherto employed such as a process to balance the curl of the emulsion layer with a curl of a gelatin layer applied on the other side of the film; a process to apply some layers of certain substances other than gelatin in order to achieve the curling balance corresponding to the swelling or shrinking of the emulsion layer during the developing step; and a process to apply a layer which balances the curl corresponding to the swelling or shrinking of the emulsion layer during development and may be removed during that step.
There are also processes of curling the film base to the side opposite the emulsion layer in advance in order to balance the curling value of the film. For example, a process of curling the film base to the side opposite the emulsion layer by applying a swelling material thereto (such as acetone, for cellulose triacetate) and then drying the layer; and a process of curling the support to the other side opposite emulsion layer by lowering the speed of drying the back layer in a drying step of the undercoating layer and back layer, which are applied before the applying of the emulsion, are known, as well as other processes.
These processes, however, are not desirable industrially, because of accompanying defects such as the limited range of curl controlling, the increase of thickness of the layers, or the increase of drying steps of the layers.
The aim ofthe present invention is to provide a process for overcoming said defects and for controlling the curl of plastic films with a simple treatment.
aim, the present inventors have found out that a very industrially favorable result can be obtained when one prescribes three for conditions the humidty, the temperature and the blowing time of moist hot air that is blown onto the film; in order to control the curling value (K) and the variation of the curling value (A K), depending on the change of humidity of the air.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a piece of film indicating the method to measure the curl.
FIG. 2 is a graph which shows the relation between humidity and the curling value.
FIG. 3 is a graph which shows the relation of the curling value, humidity and times in Example 1.
FIG. 4 is a graph which shows the relation between the curling value and the variation of the curling value with humidity in Example 4.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Said aim can be attained by blowing moist hot air, which is adjusted in temperature and humidity, for a fixed time onto the concave plastic film surface which is to be curled.
The higher the temperature and humidity of the moist hot air are, the larger the results are; and the longer the blowing time is, the more effective the process is. These three factors can be combined suitably according to the conditions of the respective processes.
For example, if a short time process is emphasized, the temperature and humidity should be higher; and if making the error of curlingvalue small is emphasized, the humidity should be lower and the time longer.
The desirable range of temperature is from 40 C to the point where the film begins to soften (softening point), and the desirable humidity is higher than that corresponding to the dew point at 40 C (10 vol. percent humidity). Of course, even if the temperature and the humidity are out of said ranges, the aim of the present invention can be attained by controlling the blowing time. I
It is desirable to treat each of the: films under the following conditions:
Film Temperature Humidity Fixed time rang (C) range Vol. range (sec.)
Cellulose ester film 60 150 I0 I00 5 600 Celluose triacetate film 150 10 5 300 Polyethylene terephthalate 100 200 40 I00 l0 I200 Cellulose ester, used as a support for photography, is formed into a film by a casting method, sothe film contains residual solvent. Although the process according to the present invention is also effective when films contain much residual solvent, the effect is greater when the amount of residual solvent is less.
The curling value of the plastic film which is processed according to the process of the present invention once,.seems to change superficially as the film is exposed to severe changes of humidity and temperature during the developing process.
It has, however, been determined that the degree of curl does not decrease, but remains to the last.
It is also well known that the curling value of a film which is formed by a solution process varies according to the change of humidity of the atmosphere.
The above phenomenon results from the fact that differences occur in the distribution of dope density and that of plasticizer along the direction of thickness of the finished film because the film is dried only from one side when the dope is applied on the surface of an applicating casting velt. Therefore, the variation of curling (A K) due to humidity variation is almost fixed by the drying conditions on the surface of the casting velt. If this A K can be varied as is desired, a very favorable effect can be sometimes obtained. For example, if a film is desired to remain flat regardless of the humidity of the atmosphere, the dependence of the film on the humidity had better be small, and as for a film support for a photographic element, a great dependence, of curling to the other side, on humidity is desired in order to cancel the curl due to moistening and swelling the gelatin film, as the film suffers an extremely great change of humidity during the developing process.
As is stated above, the control of curl of a plastic film according to the present invention permits a suitable combination of temperature, humidity and time of blowing moist hot air according to each condition. Further, combining these three factors suitably, one can produce films having the variations of the curling value (A K) different from one another in spite of having the same curling value.
It is known that to make A K large, a long time process with low temperature is more effective than a short time process with high temperature and high humidity. As is stated above, it is very favorable to be able to vary the dependence of curling value on humidity, considering films as photographic supports.
As is stated above, a desired curling value can be obtained by the control of curl of plastic films according to the present invention, selecting temperature, humidity and time of blowing moist hot air suitably. Moreover, thecurling value variation depending on the variation of humidity of the atmosphere can be varied by the combination of these three factors. The process according to the present invention is simpler, cheaper and more stable than processes hitherto known.
and a humidity of 0.2 or 0.5 kg steam/kg dry air, was blown at the surface of a cellulose triacetate film having a thickness of 140 microns and a curling value of 0 whishsyt ass w s d red Q. b curled concave for various periods. After drying said film at 105C for eight hours, 3 X mm pieces of said film (cf. FIG. 1) were cut out to measure the curl. After leaving the pieces in the atmosphere at 23C, 55% RH (Relative Humidity) for more than 24 hours, the curling values of these pieces of film were measured. The results are shown in FIG. 3. FIG. 3 shows that a higher temperature, a higher humidity and a longer blowing time yield a greater effect.
To get the curling value 1, 60 seconds of blowing were required at 60C and 0.08 Kg steam/Kg dry air. but only one second was required at 150C and 10.0 Kg steam/Kg dry air. As is seen above, if a short'time process is emphasized, temperature and humidity should be high, and if making errors in curling values small is emphaszied, low temperature, low humidity and long blowing time should be favored.
Similar results can be obtained with other cellulose esters, that is, esters or mixtures of esters of nitric acid, acetic acid, propionic acid, butyric acid and the like.
EXAMPLE 2 Polyethylene terephthalate film, having a thickness of 100 micro secs. and stretched three times biaxially by the fusion process of film formation was processed in the same way as in Example 1. By blowing air at 140C and 5 Kg steam/Kg dry air for600 seconds, the
It has also been confirmed that the control of curl of film surface had a curling value of 1.
Effects of curling differ according to the kind and thickness of polymers. Desirable curl can be obtained by selecting suitable temperature, humidity and time.
Similar results were obtained with other plastic films, that is, polyvinyl chloride, polystyrene, and the like.
EXAMPLE 3 Cellulose triacetate was dissolved in a mixture of so]- vents consisting chiefly of methylene chloride. A plasticizer was added to the resulting solution to obtain a dope. The dope, having a concentration of 20.0 wt. was flowed onto the surface of a support. The prepared film was stripped from the surface of the support when 25 wt.% of the solvent remained in the film, and was introduced into a drying chamber.
In succession to the above step, when the residual solvent in the film reduced to 20.0 wt.%, the surface of the film opposite to the support was treated by the process according to the present invention and the film EXAMPLE 1 5 dried. The results obtained are shown in the following Moist hot air having a temperature of C or 130C t bl Residual solvent Process conditions Curling At the value time of After curl to the process drying Humidity* casting velt No. (wt (wt Temp (C) Time (sec.) side) From this, it can be seen that the process is effective when residual solvent remains in the film, (cf. No. 1 and No. 3). However, the effect is smaller, compared with when a small amount of residual solvent remains. (cf. No. l and No. 2)
EXAMPLE 4 Cellulose triacetatefilm. having a thickness of 140 microns was processed under two conditions,"( 1) 70C and 0.2 Kg steam/Kg dry air, and (2) 150C and 2 Kg steam/Kg dry air, with the time being varied, in the same way shown in Example 1. The curling values of the processed films were measured at 23C, and 25,55 and 85% RH (these values being denoted by K K K respectively). By taking the variation K (AK=K -K as the ordinate, and K as abscissa, the relationship is shown in FIG. 4.
As is seen above, if the curling value (K of the processed film is the same, the variation of the curling value (AK) due to humidity variation can be changed. it can be seen that the process with low temperature and low humidity is more effective than the process with high temperature and high humidity to make the variation of the curling value (AK) due to the humidity variation range.
What is claimed is:
1. in a process for preparing a plastic film of controlled curl useful as a support for a photographic materialcomprising producing said plastic film and treating it to control the curl thereof, the improvement comprising controlling the curl by blowing hot moistened air onto the surface of said plastic film for a period of time sufficient to obtain a plastic film of desired curl.
'2. The process of claiml wherein the plastic film is a cellulose ester, polyvinyl chloride, polystyrene or polyethylene terephthalate film.
3. The process of claim 2 wherein said cellulose ester is cellulose nitrate, cellulose acetate, cellulose propionate, cellulose butyrate or a mixture theseof.
4. The process of claim 1 wherein the hot moist air, adjusted in temperature and humidity, is blown for a fixed time onto the plastic film surface, said surface being concave.
5. The process of claim 4 wherein the temperature is 1 within the range of from 40C to the softening temperature of the film.
6. The process of claim 4 wherein the humidity is more than the dew point at 40C.
7. The process of claim 4 wherein the time varies from 1 second to 1200 seconds.
8. The process of claim 2 wherein the air, at a temperature of from 60C. to C..a:nd having a humidity of from 0.1 to 1 kilogram of steam per kilogram of dry air, is blown onto the surface of said cellulose ester film for a period of time of from 5 seconds to 600 seconds.
to 1,200 seconds.