Ultrasonic Cleaning Of A Web Of Film

Abstract

Dirt particles are cleaned from a web of flexible material, such as photographic film or paper, by applying ultrasonic vibrations to a web in a direction transversely of the web while applying a solvent liquid to the web. The liquid can be applied by immersion of the web and ultrasonically vibrating apparatus in a pool, or by spraying the liquid onto the web as it passes over the apparatus in air. Vibrations are imparted by passing the web between a pair of shoulders defining a circular channel for the films.

Parent Case Text

This application is a continuation-in-part of our application, Ser. No. 879,680 filed Nov. 25, 1969.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a novel method of and apparatus for ultrasonically cleaning dirt from a web of flexible material such as photographic film or paper.

During the manufacture of webs of photographic film or paper, it is important that dirt particles be prevented from accumulating on a web because such particles will adversely affect the quality when photographic emulsions are coated over such particles. Moreover, if dirt particles should accumulate on the top of the finished web (before or after exposure and development) the quality of the photographs may be impaired, and the film may be scratched as it passes through a projector.

Dirt particles can accumulate from the ambient atmosphere, or can result from slitting and punching operations normally employed during the manufacture of photographic film and paper.

2. The prior Art

In the past, photographic film has been cleaned by immersing it in a liquid bath, which is then subjected to ultrasonic vibrations, cleaning being accomplished by cavitation of the liquid. (See U.S. Pat. Nos. 2,967,119 and 3,422,479.) This requires the introduction of bulky equipment into the production line for the cleaning operation. Moreover, cavitation does not do as thorough a job as desired.

SUMMARY OF THE INVENTION

In our copending application, Ser. No. 879,680 we have described the ultrasonic dry cleaning of a web by passing it in a dry condition over an ultrasonic horn having shoulders which impart vibrations to the edges of the web. This is especially advantageous for cleaning webs of materials which may be harmed by volatile liquid solvents ordinarily used for cleaning baths.

We have now found that the principles of our copending application can be employed to good advantage by applying a volatile liquid to a web during ultrasonic vibration thereof, where the web material will not be harmed by contact with the liquid. Moreover, the efficiency of the operation is improved by increasing the mass of dirt particles by wetting them so that they will be jarred off the web. Additionally, the particles shaken off are readily transported away from the web in the washing liquid.

The liquid can be applied, advantageously, by dipping the web below the surface of a pool, or by spraying the liquid on one or both surfaces of the web in air, or by wiping a liquid-laden roller against one or both web surfaces in air.

THE DRAWING

FIG. 1 is an end view, partly broken away, showing apparatus for transporting a web through a pool of liquid while ultrasonically vibrating the web;

FIG. 2 is a side elevational view, partly in section, of the apparatus as seen from the right in FIG. 1;

FIGS. 3, 4 and 5 are side elevational views, partly in vertical section, of three modified forms of apparatus wherein a web is transported through a pool of liquid.

FIGS. 6 and 7 are end views of two modified forms of apparatus wherein liquid is sprayed against a web; and

FIG. 8 is an end view, partly in section, of still another modification for applying liquid to a web by a rotating roller.

THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 and 2, there is shown a nonrotating ultrasonic horn 11 having two oppositely tapered annular flanges 13 and 15 projecting laterally therefrom at positions spaced longitudinally from each other, thus forming a pair of opposed circular shoulders or abutments which define a circular channel C of generally cylindrical or slightly frustoconical shape therebetween.

The horn is operatively connected to an ultrasonic transducer 17 which may be of the electrostrictive (piezoelectric) or magnetostrictive types, such as have been described in many United States patents, for example in U.S. Pat. Nos. 2,748,298 (Calosi et al.--magnetostrictive); 3,022,814 (Bodine--both types); and 3,328,610 (Jacke et al.--piezoelectric). The major direction of vibration should be along the longitudinal axis of the horn, as shown by the double pointed arrow. Of course, the transducer 17 should be clamped in a suitable holding device 19.

The end of horn 11 is of much greater diameter than the main body of the horn, and dips down into a pool 21 of cleaning liquid in a vessel 23. This large end permits a substantial length of web of large area to dip into pool 21 during vibration thereof.

In operation, a web 25 of flexible material, shown as moving picture film having perforations along one side, is transported from a source to the ultrasonic horn. Film 25 is bent around the horn within channel C and is taken up on a motor driven spool 27. As the film moves continuously through channel C, the transducer 17 is energized to impart back-and-forth vibrations to the flanges 13 and 15 which engage both edges of the film and impart the vibrations to the film in the film plane, thus shaking off from both top and bottom surfaces any dirt particles present.

Among suitable liquids for the pool 21 are methyl chloroform, freons, trichloroethylene, trichloromonofluoromethane, perchloroethylene, carbon tetrachloride, dichlorodifluoromethane, dichloromonofluoromethane, monochlorotrifluoroethane, and dichlorotetrafluoroethane.

The success of our method results from so rapidly accelerating the web relative to the dirt particles (which have extremely small inertia) that the particles are torn loose from the web. In one example, an ultrasonic horn as shown was operated at 20 kHz. with a longitudinal excursion of 0.001 inch, providing a web acceleration transversely approximately 40,000 times gravity. Thus the forces exerted on dirt particles relative to the web were approximately 40,000 times the weights of the particles. This, coupled with the fact that the force is reversing its direction 20,000 times per second, explains the ability of our apparatus to rip dirt particles loose from the web.

In the embodiment of FIG. 3, a nonrotating ultrasonic horn 31 having two flanges is connected to a transducer 33 which projects through an aperture 34 in a sidewall of a container 35 and is sealed by a circular mounting plate 37 pressing against a gasket 39. Horn 31 is of smaller diameter than that of FIG. 1, and is fully immersed in the liquid 41. Mounting plate 37 is clamped between parts of the transducer by a central bolt 41 which bears against the outer end of the transducer and is threaded into the front or horn end of the device.

In FIG. 4 vibrations are imparted to the web by a flexing-type nonrotating piezoelectric crystal element 43 consisting of two face-shear plates or two transverse-expander plates secured together face-to-face in such a manner that a voltage applied to the electrodes in a known way causes the plates to deform in opposite directions. Suitable elements are sold under the trade name "Bimorph" by the Clevite Corporation Piezoelectric Division, Cleveland, Ohio. Element 43 is mounted on a rigid support 45 and can be revolved thereon to present new guide surfaces as the old are worn. Only the lower portion of the element is immersed in liquid.

FIG. 5 is similar to FIG. 4 except that the element 43 is fully immersed in liquid.

In FIG. 6 a web 45 is passed over a horn 47 like that of FIG. 3, but instead of being immersed in a pool of liquid the horn and web are in the ambient atmosphere such as air, and the under surface of the web is sprayed with a stream of solvent liquid from a nozzle 49.

FIG. 7 is like FIG. 6, but two liquid sprayers are applied, one to each surface of the web from nozzles 49 and 51.

In FIG. 8 the web 45 is wiped on its undersurface with a liquid laden roller 53 having a nap, which dips down into a pool 55 of liquid. Roller 53 can be motor driven, or can be an idler roller which is actuated by friction with the web.

In all the devices described above it is to be understood that the web can be sprayed or flushed with clean solvent after the vibration treatment. Also liquid can be removed from the web in any desired way prior to windup, as is well known.

Among the advantages of the various forms of apparatus described above are:

a. the shear forces on the dirt particles are many times more effective in removing surface dirt than the forces normal to the web surface generated in cavitation.

b. the energy is far more efficiently used in directly vibrating the web transversely than in vibrating the liquid.

c. effective cleaning is obtainable with a small portable unit.

d. the nonrotating flanged devices can be revolved periodically to present new unworn surfaces to the web.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims

We claim:

1. A method of cleaning dirt particles from a web of flexible material comprising moving said web in a direction lengthwise thereof, contacting at least one edge of said moving web with a solid ultrasonically vibrating abutment, and ultrasonically vibrating said contacting abutment in a direction transversely across the width of said moving web while simultaneously applying a volatile liquid solvent to said moving web at the location of contact with the ultrasonically vibrating abutment.

2. A method in accordance with claim 1 wherein said liquid is applied by immersing said web in a pool thereof.

3. A method in accordance with claim 1 wherein said liquid is applied by spraying onto at least one surface of said web.

4. A method in accordance with claim 1 wherein said liquid is applied by spraying onto both surfaces of said web.

5. A method in accordance with claim 1 wherein said liquid is applied by rotating a liquid-laden roller in contact with a surface of said web.

6. Apparatus for cleaning dirt particles from a web of flexible material by applying ultrasonic vibrations to said web in a direction transversely across the width thereof comprising, in combination: a longitudinally extending ultrasonically vibratable device having abutment means extending transversely from a side surface thereof; mechanism for advancing a web to be cleaned in a lengthwise direction transversely across said device with at least one edge of said web contacting said abutment means; means for ultrasonically vibrating said device in a direction longitudinally thereof to impart ultrasonic vibrations to said advancing web through said contacting abutment means in a direction transversely across the width of said advancing web; and, means for simultaneously applying a volatile liquid solvent to said advancing web at the location of contact with said ultrasonically vibrating abutment means.

7. Apparatus in accordance with claim 6 wherein said liquid applying means is a tank containing a pool of said liquid, and wherein said abutment means is immersed in said pool whereby said web is immersed in said liquid.

8. Apparatus in accordance with claim 6 wherein said liquid applying means comprises means for spraying said liquid on said web.

9. Apparatus in accordance with claim 6 wherein said liquid applying means comprises a roller engaging a surface of said web, and means for conveying liquid to said roller and thence to said web.