Technical Field

This invention relates to a diazo film devel¬ oping apparatus and method.

Background Art

Diazo sensitized papers have been used for making duplicate copies from originals by means of contact printing and development of the exposed diazo paper in an aqueous ammonia vapor atmosphere. Diazo sensitized films have been used as a medium for making microfilm or microfiche masters and duplicates thereof because of the low cost, the high resolution and the increased speed of operation. Increasing demands are made on the film developing process, especially as to the speed of developing so as to enable an efficient and high volume production of diazo film copies from a master.

One common problem encountered with prior art apparatus and methods of this kind is that, owing to the presence of water vapor in the developing chamber of the apparatus, moisture spots may form on the film dur¬ ing development which may interfere with the reading of the data which is on the developed film.

Also, some prior art apparatus and methods utilize high temperatures for developing diazo film. Thus, U.S. Patent No. 4,099,868 discloses an apparatus including a developing chamber and an evaporator, or separation chamber, connected therewith by a short pipe, both chambers being equipped with separate heaters and being heated to a temperature greater than 100°C.

Aqueous ammonia introduced into the evaporator is caused to evaporate by heating and the ammonia vapor spreads into the developing chamber and develops the exposed film moved therethrough. This prior art apparatus has the disadvantage of high heating costs and that the high

temperatures used may cause damage to certain types of diazo film.

Disclosure of the Invention

It is an object of the invention to provide an apparatus and method for developing diazo film which enable the problem of moisture spots on the film to be avoided without the disadvantages associated with the use of very high developing temperatures.

Thus, according to the invention, there is provided a diazo film developing apparatus including a developing chamber; heating means for heating said de¬ veloping chamber; transport means for moving exposed film through said developing chamber; and a separation chamber connected with said developing chamber and adap- ted to evaporate aqueous ammonia introduced thereinto and to supply ammonia vapor to said developing chamber to contact the emulsion side of said film moving there¬ through so as to develop said film, characterized in that a thermal control means is provided between said developing chamber and said separation chamber to main¬ tain a temperature differential therebetween, said sep¬ aration chamber having a temperature lower than the temperature of said developing chamber.

According to another aspect of the invention, there is provided a method of developing a diazo film as it is moved through a developing chamber heated to a predetermined temperature, by introducing aqueous am¬ monia into a separation chamber connected with said de¬ veloping chamber, and causing the ammonia to separate from the water and spread into said developing chamber so as to contact therein the emulsion side of said film, characterized in that said separation chamber is main¬ tained at a temperature which is lower than said pre¬ determined temperature. In a preferred embodiment of the present inven¬ tion, a diazo film developing apparatus has a separation

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chamber in the form of a cavity in the wall of the de¬ veloping chamber at the-lower part thereof. In operation of the apparatus, heat is conducted from the developing chamber to the separation chamber via a thermal resistor so that the evaporation chamber is at a lower tempera¬ ture than the developing chamber, both chambers being maintained at temperatures substantially less than 100°C, preferably in the range of 77°C. to 88°C. It is found that by virtue of the temperature differential between the two chambers the formation of moisture drops on the diazo film in the developing chamber is avoided. Also, the apparatus has the additional advantages of relative¬ ly low heating costs and that only one heating element is required. Moreover, the fact that the developing chamber is at a higher temperature than the separation chamber ensures faster dispersal of the ammonia vapor in the developing chamber.

The film is developed in ammonia vapor at a pressure which does not substantially exceed atmospheric pressure. The pressure may be only slightly higher than atmospheric pressure by an amount no more than that re¬ quired to introduce the vapor into the developing cham¬ ber.

Brief Description of the Drawings One embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 is a block diagram of the major parts of a film developing apparatus; Fig. 2 is a front elevational view, partially in section, of the film developing apparatus;

Fig. 3 is a side elevational view, partially in section, taken on the plane 3-3 of Fig. 2; and

Fig. 4 is an enlarged sectional view taken on the plane 4-4 of Fig. 2.

Best Mode for Carrying Out the Invention

Referring now to the drawing-, the film devel¬ oping apparatus comprises a plurality of major parts as shown in Fig. 1 and wherein the enclosure structure 10 and the various major parts of the developing apparatus are shown in block form. The major parts of the devel¬ oping apparatus include a drive system 12 associated with a preheating chamber 14 and a developing chamber 16, which chambers are in communication with a heater control 18 for the purpose of providing the desired temperatures in the respective chambers. The drive system 12 is also in communication with an ammonia pump 22 which receives ammonia from a reservoir 24 and con¬ veys the ammonia in aqueous form into a separation chamber 20.

In Fig. 2 is shown a front elevational view of the developing apparatus and in Fig. 3 is shown a partial sectional and side elevational view thereof with certain of the parts being placed for accommodation on the drawing. A base assembly 32 provides support for the various parts of the developing apparatus and a cover assembly 34 is secured to the top of the unit in suitable manner. A portion of a diazo film 36 is shown entering at the right side in Fig. 2 and a portion of the film 38, after developing thereof, is shown leaving at the left side. The diazo film 36 is caused to be moved in a path between a pair of rollers 40 into and through the preheating chamber 14 and further caused to be moved by a pair of rollers 42 into and through the developing chamber 16 and finally, a pair of rollers 44 convey the developed film 38 from the developing appara¬ tus.

The preheating chamber 14 includes an upper plate 46 and a lower plate or block 48 which are spaced apart by means of a spacer 50 on each side of the film path a distance sufficiently to enable passage of the film 36 as it is moved from the right to the left in

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Fig. 2. A heater 52 in the form of a rod is embedded in the lower plate 48 for heating thereof and of the upper plate 46 through the spacers 50 for the purpose of preconditioning the emulsion on the film. The developing chamber 16 includes an upper plate 54 and a lower plate or block 56 which are likewise spaced from each other by means of a spacer 58, one of which is positioned on either side of the path of the film 36. A heater 60 and a thermal resistor 62 are associated with the developing chamber 16 so as to maintain a desired temperature in the developing chamber 16 and also to control the amount of heat to the aqueous ammonia separation chamber 20. A suitable thermometer 108 (shown in Fig. 4) is preferably located at the front of the developing chamber 16 for viewing the temperature therein.

A motor 64, shown in Fig. 3, is provided to drive the various pairs of rollers by means of a drive chain 66 trained around a series of pulleys 68, 70, 72,. 74 and 76, as seen in Fig. 2, for driving or traveling in a clockwise direction so as to cause the diazo film 36 to be moved from right to left. The drive system also accommodates the pump 22 to cause the pump to move the aqueous ammonia from the reservoir 24 through a bulkhead fitting by means of a tubing 80 and from the fitting by a tubing 81 to the pump. The ammonia is moved from the pump 22 to the separation chamber 20 through a tubing 82 extending into one side of the chamber 20. A tube 83 has one end thereof disposed for draining the separation chamber 20 of accumulated water and to deposit such water into a container or bottle 84.

In Fig. 4 is shown a sectional view through the developing chamber 16 and through the separation chamber 20 which is located at the entrance end of the developing chamber and is in the shape of a deep cavity or trough to accommodate the temperature differential

between the aqueous ammonia being introduced into the lower chamber 20 and the upper part of the developing chamber 16. The developing chamber 16 includes the side walls 92 and 94 which are covered by the cover assembly 34 so as to provide a closed container for the develop¬ ing portion of the processor. The separation chamber 20 includes the side or end walls 96 and 98 and a lower base 100 and which forms an elongated cavity at the entrance end of the developing chamber 16 for enabling the vaporized ammonia to rise and thereby make contact with the emulsion side of the diazo film 36. An edge seal 102 in the form of an O-ring is placed adjacent the spacers 58 and between the upper plate 54 and the lower plate 56 of the developing chamber 16 to arrest the ammonia vapors and prevent escape thereof into the surrounding atmosphere. Additionally, seals 104 and 106 are provided adjacent the pair of rollers 42 and rollers 44 to contain the ammonia vapor within the chamber 16. The thermometer 108, mentioned earlier, is on the left side in Fig. 4 with its probe extending about midway through the lower plate 56.

In the operation of the developing apparatus, the diazo film 36, in an exposed and cut-to-length condition and with the emulsion side of the film dis- posed in a downward direction, is caused to be moved by rollers 40 into the preheating chamber 14 wherein the emulsion on the film is preconditioned by the elevated temperature through heating the plate 48 by use of the heater 52 and which heat is caused to be moved by thermal conduction through the spacers 50 and to the upper pla'te 46. The second pair of pinch rollers 42 then trans¬ port the conditioned film 36 into the developing cham¬ ber 16 where the emulsion on the lower side of the film is exposed to and contacted by the ammonia vapors which react with the emulsion and thereby develop the film. ^l The third pair of rollers 44 then convey the developed film 38 from the chamber 16 and onto a tray (not shown)

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on the side of the processor. In similar manner, as in the case of the preheating chamber 14, the heater 60 provides the desired heat in the developing chamber 16 to the elevated temperature in heating the lower plate 56 and through the spacers 58 to also heat the upper plate 54. The aluminum plates 46, 48 in the preheating chamber 14 and also the aluminum plates 54, 56 in the developing chamber 16, along with the aluminum spacers 50, 58 between the plates distribute the heat by thermal conduction and the aluminum plates in each of the chambers are coated with suitable thermoplastic mater¬ ial on the surfaces which are adjacent the film path. The aqueous ammonia is introduced into the separation chamber 20 and with a certain amount of heat being transferred from the plate 56 through the thermal resistor 62 and to the walls of the separation chamber 20, the separation chamber is caused to be heated a desired amount which is lower than the temperature of the upper chamber. The thermal resistor 62 is a con- trolling factor in determining the desired temperature differential between the two chambers 16 and 20 and is made of stainless steel to provide and maintain a tem¬ perature differential between the two chambers. As the aqueous ammonia is caused to be introduced at substan- tially ambient temperature into the separation chamber 20, which chamber is at a temperature slightly above the ambient temperature, the ammonia separates from the water in extremely fast or rapid manner and the ammonia vapor spreads rapidly and rises by reason of the elevated temperature of the developing chamber 16. The higher temperature environment at the top of the separating chamber 20 is saturated with ammonia vapor in a uniform manner so that when the film passes across the open chamber 20 the contact with the emulsion causes develop- ment of the film within a period of one to two seconds. The water is accumulated and drains off after the ammonia has separated and because the water is only in the

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cooler portion of the chamber 20, the water does not enter and does not appear on surfaces in the developing chamber 16. Summarily, when the aqueous ammonia is injected or introduced into the separation chamber or trough 20 below the film developing area, the ammonia separates from the water and the ammonia vapors rise with the warm air to contact the preheated emulsion on the underside of the diazo film 36 for developing thereof

^~ as the film passes over the open chamber 20. In this manner the water is prevented from contacting the film and thus the film is free of water spots.

In actual operation, it was found that the optimum temperature in the developing chamber 16 was 82°C. and that an 18 tooth sprocket in the ammonia pump 22 provided the correct amount of ammonia vapor for superior development of the film and thereby consuming a minimum amount of aqueous ammonia. The thermal resistor or spacer 62 was made of 18 gauge stainless steel which proved in the final design to uniformly control the heat flow from the lower plate 56 in the developing chamber 16 to the separation chamber 20 so as to provide the optimum temperature differential between the developing area 16 and the bottom of the trough 20. When the thermometer 108 read 82.2°C, typical observed tempera- tures of the upper plate 54, the lower plate 56, and the bottom of the trough 20 were 80.2-80.4°C. , 82.4-84.8°C. , and 81.4-82.0°C. , respectively, to provide a temperature differential of 1-2.8°C. between the lower plate and the bottom of the trough with a desired figure of 1.67-2.78° C. for proper separation of the ammonia and water.

It should be clear from the foregoing that the invention provides a high speed, low temperature, substantially atmospheric pressure, and low aqueous am¬ monia consumption apparatus and method which is extremely reliable and efficient for developing the diazo film.