AU1781592A

AU1781592A - A system for producing a photographic dispersion

Info

Publication number: AU1781592A
Application number: AU17815/92A
Authority: AU
Inventors: Carlos Roberto Fernandes Esteves; Kiyoaki Kawakami; Roberto Kendi Okuda
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1992-05-21
Filing date: 1992-05-21
Publication date: 1993-12-13
Also published as: JPH06510371A; EP0595821A1; WO1993023791A1

Description

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Title: A SYSTEM FOR PRODUCING A PHOTOGRAPHIC DISPERSION

The present invention relates to a new system for producing a photographic dispersion. The term

"photographic dispersion" relates to dispersions utilized for producing both photographic dispersions and for

5 negative, positive or X-ray films.

The system comprises producing a photographic dispersion with a constant mixing ratio and estimate of excess aqueous solution, implemented in a control algorithm, by using a load cell as a main sensor element 10 and turbine-type disperser for performing mixing and under the conditions of: reactor of oily solution pressurized under controlled pressure and nitrogen atmosphere and constant dispersion flow rate.

The system comprises the following equipments: 15 a pressurized reactor, load cells, an open reactor, flowmeters, turbine-type pump, check valves and computer.

The term "computer" (1) herein means a process digital computer or controller, which may be a programmable logical controller. The term "dispersion" (2) means a 20 compound resulting from mixing the aqueous solution and the oily solution at a determined mixing ratio and constant pressure. The term "turbine" (3) refers a turbine-type pump.

The process for producing a photographic v

25 dispersion consists basically in mixing two solutions, an aqueous solution and an oily solution. The aqueous solution which has gelatin as a main element, is prepared at a temperature between 70 and 80 degrees Celsius. The oily solution, which has as its main element, a solvent having a viscosity close to that of oil, is prepared at a temperature between 100 and 141 degrees Celsius. Because both solutions have different viscosities and chemical characteristics, they are not easily miscible with each other. In order to achieve dispersion, it is usually employed an injector or "eductor". In this case, the aqueous solution is injected at the inlet of the injector at a constant pressure of 1.24 kPa, through a positive displacement pump. The oily solution is sucked through the suction inlet of the injector. A check valve is utilized at the suction inlet in order to control the flow rate of oily solution, thus maintaining the mixing ratio constant. In this scheme, mixing of the two solutions takes place in the injector chamber. The thus obtained dispersion is homogenized and cooled to between 30 and 40 degrees Celsius. An essential condition for producing the dispersion, is that the aqueous solution should not be depleted before the oily solution due to the characteristics of rapid crystallization.

The conventional process for producing dispersions was carried out in two open reactors, a positive displacement pump, a check valve and an injector. Said process was characterized by high losses of product for being a discontinuous or batchwise process. The absence of an inert atmosphere of nitrogen within the reactor of oily solution entrained constant risks of product loss because of the oxidation of this solution in contact with air. Mixing ratio was not constant throughout mixing of both solutions because the valve controlling the flow rate of oily solution was manually adjusted to a constant opening at the beginning of the batch. Because a controller of mixing ratio and end of oily solution was not utilized, changes in the product characteristics such as viscosity, specific gravity and volume may dangerously affect the condition of the oily solution ending before the aqueous

I solution. When this occurred, the following problems were usual: (1) loss of oily solution and (2) crystallization of

'■ the products in those portions of the line wherein oily

5 solution circulates and consequently the production has to discontinued for the lines to be cleaned; this contributes for increasing the production losses.

The new system (as depicted in figure 1) which is the object of this invention, comprises a pressurized

10 closed reactor having therein an inert atmosphere of nitrogen, for oily solution, an open reactor for aqueous solution, a turbine-type pump, load cells, check valves, computer and control algorithm. The reactors, both for oily solution and for aqueous solution, are supported on load

15 cells, so as to achieve a constant reading for the mass of product within the reactors. Mixing of the two solutions takes place within the turbine. A control algorithm which is implemented in a digital computer is utilized for meeting the following conditions: (1) maintaining the

20 mixing ratio of two solutions constant throughout the batch and (2) depleting the oily solution before the aqueous solution.

Utilizing a turbine provides for advantages that a process utilizing injector could hardly offer, such

25 as: (1) low amplitude pressure pulses in the flow of aqueous solution: high amplitude pulses such as those caused by the positive displacement pump bring about disturbances in the control algorithm. In this case, use of dampeners would not be a definitive solution since, several -_t 30 types of dispersions are produced which have different fluidic characteristics and this also would jeopardize the x need for the process to be of the sanitary type. (2)

Uniformity in particle size: pulses in the flow of aqueous solution adversely affects mixing ratio, causing changes in

35 particle size. (3) Absence of line clogging as caused by product crystals, diverse impurities and waste of sealing joints for sanitary piping: this clogging usually occurs at the injector nozzle. (4) Reduction of particle size of some dispersions, thus increasing mixing efficiency. Such characteristics are extremely beneficial for increasing product quality and throughput, imparting savings in the use silver in the final product.

Changes in the product amounts in terms of volume and changes in the fluidic characteristics of the products contribute for the mixing ratio and the excess of aqueous solution not being constant from batch to batch. The utilization of load cell allows to know the actual amount of product existing in the reactors, so that the mixing ratio and excess of aqueous solution are adjusted at every batch through the control algorithm. With the control based on the mass information, it is possible to obtain an increase in quality of the mixing ratio, production uniformity and depletion of the oily solution prior to the aqueous solution. Both open and closed reactors are supported on load cells so that the signals from the bulk are continuously transmitted to the computer. Pressure signals, aqueous solution flow rate signals and dispersion flow rate signals are also transmitted to the computer for monitorizing and full control of the process.

The inside of the closed reactor is subjected to pressurized inert atmosphere of nitrogen gas.

Mixing of the two solutions takes place in a turbine type disperser. Since the turbine has solely a suction inlet, a device has been devised for enabling suction of the two solutions at the same time. Such device can be seen in figure 2. The line portion of the oily solution reactor is heated in order to - prevent crystallization of the solution due to cooling caused by the line. Mixing ratio and excess of aqueous solution are

--. continuously controlled through a computer-implemented control algorithm. Excess in this case means as the amount

'■-> of gelatin existing in the aqueous solution vat at the

5 moment in which depletion of oily solution occurs. This signifies that from this moment on, only aqueous solution will flow until depletion thereof. The algorithm also provides for the possibility of the excess being null, that is to say, aqueous solution will be also depleted

10 simultaneously with the oily solution. In order to this to occur, it is enough to make Ro approaching zero in equations (1) and (2) below.

The algorithm takes into account the initial mass of the reactors, that is, the total mass of product 15 prior to starting mixing, see equation (1) . During mixing, the mass present in the reactors is constantly monitored and is supplied to the algorithm for the calculation of the estimate of the excess of aqueous solution, see equation (2) . If the estimate is within the desired range, the 20 mixing ratio will be as well. Is it is not, the flow rate of oily solution will be increased or reduced by actuation of the check valve VC-1. Control of the flow of the dispersion is effected through check valve VC-2. Control algorithm:

E(k)-E(k-1)

+AB.40.95 dt wherein:

C flow rate constant;

Mgo total mass of aqueous solution [kg];

Mco total mass of oily solution [kg] ;

Ro desired excess of aqueous solution [kg] ;

Rk estimated excess of aqueous solution [kg] ;

Mgk instantaneous mass of aqueous solution at instant t= k, [kg];

Mck instantaneous mass of oily solution at instant t= k, [kg];

E error value, [kg]; OP output value of controller, signal to check valve VC-1;

Kp proportional constant; Ki integrating constant; Kd derivative constant; AB initial opening of check valve VC-1, [%] .

In order to prevent initial perturbations from occurring, the computes positions valve VC-1 with an initial opening AB and starts execution of the algorithm, fifteen seconds after starting mixing. Such time proved to be empirically suitable for the implemented plant.

Claims

CLAIMS ■? 1. A system for producing a photographic dispersion by mixing two solutions, one aqueous solution and one oily solution, characterized by comprising: a 5 closed and pressurized reactor for oily solution, an open reactor for the aqueous solution, a turbine-type pump, load cells, control valves, and a computer means associated to a control algorithm.
2. A system in accordance with claim 1, 10 characterized in that both the open and the closed reactors are supported on the load cells so that mass signals are continuously sent to the computer means.
3. A system in accordance with claim 2, characterized in that signals of pressure, of flow rate of

15 aqueous solution, and flow rate of dispersion are also sent to the computer means.
4. A system in accordance with claim 1, characterized in that the closed reactor is internally subjected to a nitrogen gas inert atmosphere.
20 5. A system in accordance with claim 1, characterized in that mixing of the solutions takes place in the turbine.
6. A system in accordance with claim 5, characterized in that, since the turbine has only one

25 suction inlet, a device for enabling suction of two solutions at the same time is provided.
7. A system in accordance with claim 1, characterized in that, during mixing, the mass present in the reactors is constantly monitored and supplied to the

-v 30 algorithm for calculating an estimate of aqueous solution excess, said estimate being controlled by a valve (VC-1) and the flow rate of dispersion is controlled by a valve

(VC-2) .