US3110593A

US3110593A - Low temperature clayden prescreening

Info

Publication number: US3110593A
Application number: US69152A
Authority: US
Inventors: John A C Yule
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1960-11-14
Filing date: 1960-11-14
Publication date: 1963-11-12
Anticipated expiration: 1980-11-12
Also published as: GB923226A; BE610140A; DE1149986B

Description

Nov. 12, 1963 J. A. c. YULE 3,110,593

LOW TEMPERATURE CLAYDEN PRESCREENING I Filed Nov. 14. 1960 l E2191 I I 1 l7 (f [fl/Il/I/l/I/l/l/I/l/l/ l/l/l/l/j/l/l; IcE.\ P12 /////////////y// L V3 JbhmAU. Yu l e IN VEN TOR.

BY WM M MTORNEYS United States Patent 3,110,593 I LGW TEMPERATURE CLAYDEN PRESCREENENG John A. C. Yule, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed Nov. 14, 196i), Ser. No. 69,152 6 Claims. (Cl. 96-45) This invention relates to the prescreening of film for use in halftone reproduction work. A prescreened film'is one which has variations in sensitivity distributed in halftone pattern.

Clayden prescreening of film is described in US. Patent 2,691,586, to J. A. C. Yule and R. E. Maurer. Cross reference is made to two cofiled applications, Serial No. 69,153 by Donald J. Howe, entitled Prescreening Film by Clayden and Herschel Exposure, and Serial No. 69,154 by Donald J. Howe and Richard E. Maurer, entitled Continuous Prescreening of Film.

The present invention is based on a discovery of a relationship between the temperature of the silver halide emulsion layers and the Clayden effect.

I have found that when the temperature of film is lowered to C. or lower, for example by the presence of Dry Ice or liquid air, two things happen to the Clayden sensitivity. Clayden sensitivity refers to the amount of desensitization produced 'by a short duration pre-exposure, and is measured in terms of the relative log exposure (low intensity, long duration) required to produce a latent image with and without the desensitization preexposure. Even films which show a very low Clayden sensitivity exhibit a much higher sensitivity at these lower temperatures. However, the present invention is concerned primarily with those materials which already show a fairly high Clayden sensitivity at room temperature, say 20 C. specifically which show at least 0.3 log E units Clayden effect to a high intensity exposure of 0.001 second at 20 C. All such materials when cooled to below 10 C. show a greatly enhanced Clayden effect, some materials have actually shown over 1.6 log E units Clayden chest at -40 v C., but this is beyond that required by ordinary prescreening procedures although it may be useful for special pur- The second effect, and this is perhaps the more poses.

important one, is that the low temperature extends the exposure time which is permissible without losing the Clayden effect.

Thus one object of the invention is to provide greater scale than previously obtainable by Clayden prescreening and another object is to provide a manner of continuously Clayden prescreening.

Historically Clayden effects require brief exposures, usually less than a 50th of a second. At temperatures below 10 C. the Clayden effect is still observed in a useful amount up to one second exposure time and even up to a few seconds, say four. Because of this longer duration, the use of the term Clayden effect under these circumstances might, at first sight, be questioned, but it is proper and applicable since the effect is the same, although the difference was not predicted. While the upper limit of exposure duration at room temperature is on the order of second, this upper limit increases by a factor of two for about every 10 C. drop in temperature. Dropping the temperature from +20 C. to 10 C. increases the time limit about 8 times. However, temperatures of 40 C. or lower are preferred; the drop from +20 C. to 40 C. increases the time limit about 64 times. This means that exposure in excess of /2 second can be used and this in turn lends itself admirably to continuous Clayden prescreening of film. Thus a preferred embodiment of the invention moves a chilled photosensitive layer through an exposure station synchronously with a halftone exposing image while giving an exposure of sufficiently high intensity and sufficiently short duration (in this case less than 4 seconds) to produce Clayden desensitization in a useful amount, say at least 0.6 log E units. So that the exposure station will not be impractically narrow in the direction of movement of the film and so that the film will not have to move impractically fast, an exposure lasting at least /2 second is preferable. Thus one preferred embodiment of the invention has an exposure between /2 second and 4 seconds, the film being sufficiently chilled to give Clayden effect for exposures of such duration. The moving exposing image is provided either by a moving screen (ruled or contact type) with a fixed light source or by a fixed ruled screen and a moving source or exposing aperture.

There appears to be nothing peculiar in the emulsion I selected for this purpose. Any photosensitive silver halide emulsion which shows at least 0.3 log E units of desensitization when given an exposure of 0.001 second (and of proper intensity) at a temperature of 20 C., will give the added effects necessary for the operation of the present invention. As is known, total exposure (intensity times time) is just below threshold for maximum Clayden effect. The briefness of the duration requires the intensity to be high even though threshold is barely reached.

The operation of the invention will be more fully understood when read in connection with the accompanying drawing in which:

FIG. 1 schematically illustrates one embodiment of the invention and,

FIG. Zschematically illustrates continuous prescreening according to the invention.

In FIG. 1 a silver halide emulsion layer 10 which at 20 C. will show 0.3 log E units Clayden effect to brief exposure, is carried on a support 11 which in turn rests on a metal container 12 containing Dry Ice 13 to bring the emulsion layer 10 to the temperature of Dry Ice which is about 56 C. The operation must be performed in a dry atmosphere to prevent condensation of moisture on the emulsion layer 1 Light from a lamp 16 as indicated by arrows 17 exposes the layer 10 through a ruled halftone screen illustrated schematically at 18. The exposure at the emulsion layer it at halftone distance behind the ruled screen 18 is in an undulating pattern due to the size of the source 16 and diffraction effects at the apertures in the screen 18. This is a normal halftone exposure step. If the lamp 16 is a flash lamp giving exposures of fl of a second say, the Clayden desensitization in the areas-of the layer 10 which are exposed, will be very high, about 1.2 to 1.6 or 1.8 log E units. This is an excellent way to get a high degree of Clayden prescreening. If the lamp to is an ordinary tungsten lamp for example the exposure may be permitted to continue for about 1 secondand the film 1% still receives a useful degree of Clayden prescreen- In FIG. 2, the ability to getClayden prescreening with relatively long duration of exposure is put to use to provide continuous prescreening. A film 20, emulsion side down, is rolled from a supply roll 21 and is passed through a cooling chamber 22. Chilling rollers come in contact with the emulsion or the back of the film or, as shown, with both sides of the film. These chilling rollers are kept very cold by the circulation of a low temperature liquid (say liquid air) from a supply 26 by means or" a pump 27. Alternatively the rollers may be chilled by direct contact with Dry Ice. Again the film is preferably kept in a dry atmosphere during and following chilling to the low temperature. transparent roller 30 carrying a contact halftone screen 31 on the surface thereof. Lig it from a lamp 32 exposes the film while it passes from the point 33 to the point 34. A mask or reflector 35 confines the light to this area of The film is then passed over a the drum. The exposure station between points 33 and provides about /2 second exposure as the film moves to a talteup roll This contact halftone screen 31 on a transparent roller is similar to those used in the continuous preparation of contact halftone screen material. Projection printing is less preferable because of the added dir'liculty in obtaining suhiciently high intensity. The drum or roller 33 moves relative to the mask 35. The driving mechanism (which may engage the ends of the drum) is not shown. Preferably the edges of the film are held by pressure rollers to an easily rotated drum and the film itself then drives the drum to insure that tl ere is no slippage between the film and the drum. The main drive for the film is provided on the takeup roll by any suitable drive means, not shown. it is preferable to use a contact halftone screen in this continuous prescrcening form of the invention, but a sharp screen spaced from the film by a glass drum (or in a fiat exposure station by air) may be used. in the case of a flat station, the film may be ctually spaced from the halftone screen with the film support in contact with rollers or t er means for maintaining the spacing of the film from therscreen. The Herschel clean-up features described in the copending applications referred to above may be combined with this low temperature Clayden prescreening to provide the advantages of both.

Various systems in which a halftone screen is held stationary and a film is moved continuously relative thereto are described in US. latent 2,211,345, Murray. in these systems an exposing image (behind the screen) moves synchronously with the film by the simple expedient of moving the exposing light aperture. Such arrangements are directly useful with the present invention which lengthens the permissible time of the Clayden exposure so that the film can move completely across the exposing station during the brief (eg. one second) exposure at which Clayden effect (at -40 C.) occurs. Thus, cooling Clayden sensitive film to C., preferably to 40 (3., and exposing it as shown in US. 2,211,345, produces a prescreened (desensitized) film according to the present invention instead of producing the contact screen of Murray.

Having thus described preferred embodiments of my invention I point out that it is not limited thereto but is of the scope of the appended claims.

I claim:

1. The method of making a halftone sensitive material which comprises cooling to a temperature below l0 C. a photosensitive silver halide emulsion layer of the type which at C. temperature shows at least 0.3 log E units (Hayden ellect to high intensity exposures of 0.001 second, erqzosins said layer at said low temperature through a halftone screen to a high intensity, short duration, uniform exposure of suiiicient intensity and sufiiciently short duration to produce a Clayden desensitization of at least 0.6 log E units, the illumination at the emulsion being dist 'buted in an undulating halftone pattern.

2. The method according to claim 1 in which said exposin includes continuously moving the layer and exposli ht pattern past an exposure area, the duration bein g between /2. second and 4 seconds.

3. The method of continuously prescreening a photosensitive silver halide emulsion layer of the type which at 20 C. temperature shows at least 0.3 log E units Clayden effect to high intensity exposures of 0.001 second, which comprises cooling the layer to a temperature below l0 C., moving the layer while so cooled through an exposure stationsynchron usly with a light image having an undulating halitone pattern caused by an adjacent halftone screen and exposing the layer by said image through the screen to a high intensity, short duration, uniform exposure of sufficient intensity and sufiiciently short duration to produce a Clayden desensitization of at least 0.6 log E units.

4. The method according to claim 3 in which the layer is in contact with a contact halftone screen and the two move together through the exposure station.

5. The n ethod according to claim 3 in which the halftone screen is a stationary ruled screen at halftone spacing in front of the exposure station and an illuminated area moves transversely in front of the screen so that the halftone image formed by li ht from the illuminated area in the exposure area moves synchronously with the layer.

6. The method according to claim 3 in which said cooling is to a temperature below 40 C. and the exposure is between /2 second and 4 seconds.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES James et al.: Fundamentals of Photographic Theory, 2d

ed., Morgan and Morgan 1110., New York, pages -57, 7374 and 77-79.

Claims

1. THE METHOD OF MAKING A HALFTONE SENSITIVE MATERIAL WHICH COMPRISES COOLING TO A TEMPERATURE BELOW -10*C. A PHOTOSENSITIVE SILVER HALIDE EMULSION LAYER OF THE TYPE WHICH AT 20*C. TGEMPERATURE SHOWS AT LEAST 0.3 LOG E UNITS CLAYDEN EFFECT TOGHITH INTENSITY EXPOSURES OF 0.001 SECOND, EXPOSING SAID LAYER AT SAID LOWER TEMPERATURE THROUGH A HALFTONE SCREEN TO A HIGH TENSITY, SHORT DURATION, UNIFORM EXPOSURE OF SUFFICIENT INTENSITY AND SUFFICIENTLY SHORT DURATION TO PRODUCE A CLAYDEN DESENSITIZATION OF AT LEAST 0.6 LOG E UNITS, THE ILLUMINATION AT THE EMULSION BEING DISTRIBUTED IN AN UNDULATING HALFTONE PATTER.