Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1996-06-07
2002-04-16
Tung, T. (Department: 1743)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S435000, C205S778500, C205S780000, C205S789500, C430S030000
Reexamination Certificate
active
06372105
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method of producing a silver halide photographic emulsion, an apparatus for the same, and also a method of measuring a silver or halogen ion concentration of an emulsion during or after the formation of a silver halide photographic emulsion, and an apparatus for the same.
2. Description of the Related Art
As a prior art technique, U.S. patent specification No. 3,031,304 discloses a method of producing a fine particle emulsion which has a mean particle diameter of 0.06 &mgr;mm. In the specification, a convenient method is disclosed in which particles are formed in a pAg range of about 2 to 6 by using a method of simultaneously mixing a silver nitrate solution and a potassium bromide solution which are reaction liquids, and four pumps are used for injecting the reaction liquids so as to automatically control the pAg. Specifically, the silver nitrate solution and the potassium bromide solution are separately provided with a pump so as to be injected in a substantially stoichiometrically equivalent amount. A potentiometer circuit has a limit switch which, when a silver ion concentration of an emulsion in a precipitation solution is raised to pAg of 5 or more, functions so as to decrease the amount of potassium bromide pumped to be injected, by 1% by means of a third pump. When pAg reaches to 5 or more, the third pump is stopped. When pAg is lowered to a predetermined level, usually 4.3 or less, potassium bromide to be injected is added by the third pump.
The fourth potassium bromide injecting pump is used for a manual addition. In accordance with the reading of the potentiometer or a recorder, the operator can adequately adjust the addition of potassium bromide.
Furthermore, U.S. patent specification No. 3,821,002 discloses a control apparatus and a method of producing a silver halide emulsion. In the apparatus and method, pAg in a precipitation bath is made constant or changed, and the flow rates of a silver nitrate solution and a halogen sale solution to be added are changed in accordance with a program so that the required accuracy of pAg is maintained.
Furthermore, Photogr. Korresp. 101, 37 (1965) teaches relationships of crystal diameters of silver halide and the number of particles which are obtained by maintaining the temperature, and adjusting valves for adding a silver nitrate solution and a halogen salt solution, by an electrical control, thereby controlling pAg and pH.
All the three publications relate to a control of a preset target value, and teach only that several minutes must be elapsed in the period from the uncontrolled state at the start of reaction to the control of the pAg value stabilized at the preset target value, and the controlled state is unstable. The publications say nothing about a control method on apparatus-for causing the pAg value to rapidly reach a preset target value and conducting a control at the preset target value.
Japanese Patent Unexamined Publication No. SHO 61-65305 discloses an optimum control method in which a defect of the conventional PID control is eliminated and a computer control is done in accordance with a mathematical model. Japanese Patent Unexamined Publication No. HEI 5-181504 discloses an adaptive control method having a feedforward element in which a sequential plant model in the control of a physical quantity of a system is estimated, the control is conducted on the basis of the plant model, a variation quantity at an elapse of a dead time with respect to a variation externally applied to the system is predicted by using a variation pattern of a physical quantity which causes the external variation, and the external variation at an elapse of a dead time is previously canceled. U.S. patent specification No. 4,933,870 discloses a method of producing a silver halide emulsion which employs an apparatus and method of converting an output signal of a nonlinear ion sensor into a linear signal. U.S. patent specification No. 5,248,577 discloses an apparatus and method of producing a silver halide emulsion in which the density of halogen ions and flow rates of added halogen salt and silver nitride solutions are periodically measured, the measured data are accumulated, an internal calculation is conducted by an equation estimated on the basis of the accumulated data, and the flow rates of the added halogen salt and silver nitride solutions are controlled. In these disclosed techniques, complex calculations are done, and hence it is difficult for a controller or computer which is commercially available, to conduct processing with a short period. These publications make no mention of a method or apparatus which is used for starting the control from the uncontrolled state. When the pAg distribution in a precipitation vessel is uniform, a conventional PID control can sufficiently cope with the control at a steady state far as disturbance is not extremely produced.
However, relationships between a potential E
Ag
corresponding to the silver ion activity and ion concentrations of silver nitride and halogen salt (e.g., potassium bromide) in a liquid containing silver halide crystals are linear and abruptly changed at the equivalence point as shown in FIG.
1
. In the E
Ag
range of −50 mV to +150 mV where precipitation of a silver halide emulsion is often conducted while controlling the silver ion concentration, a very small change in concentration of silver ions or halogen ions causes the potential to be abruptly changed. Even when, in the uncontrolled state at the start of precipitation, the control is to be conducted at the preset target E
Ag
potential, pAg in a conventional precipitation bath is largely changed in an initial period of precipitation and hardly converged into the target value, with the result that several minutes must be elapsed before pAg is stabilized. Furthermore, the potential locus of E
Ag
obtained until the controlled state is attained cannot be reproduced.
As the scale of a precipitation bath is increased, the control is further unstabilized, and hence it is difficult to stably produce a silver halide emulsion of constant quality.
Also, conventionally, in order to obtain desired photographic characteristics, it is essential to control the silver or halogen ion concentration during or after the formation of a silver halide photographic emulsion, and a technique is widely employed in which reference and indicator electrodes for the above-mentioned control are directly inserted into a precipitation vessel in which a halogen salt aqueous solution reacts with a silver nitrate aqueous solution and which contains a gelatin aqueous solution.
The relationships between a silver or halogen ion concentration and an electrode potential is described in “The Theory of the Photographic Process, Third edition or Fourth edition (Macmillan Publishing Co., Inc.)”.
Silver and halogen ion concentrations are respectively defined by equations (1) and (2):
pAg=−log[Ag
+
] (1)
pX=−log[X
−
] (2)
where [Ag
+
] indicates the silver ion activity, and [X
−
] indicates the halogen ion (Br
−
, Cl
−
, or I
−
) activity.
The electrode potentials E
Ag
and E
X
in relation to the silver or halogen ion activity in silver halide crystals are expressed as follows:
E
Ag
=E°
Ag
−2.30259×(RT/F)×pAg (3)
where E°
Ag
indicates the standard potential for a silver half cell, R indicates the gas constant, F indicates the Faraday constant, and T indicates an absolute temperature.
In a silver halide emulsion which is practically used, halogen halide is often in excess, and hence a silver indicator electrode is covered by a silver halide layer and saturated with silver halide salt. Therefore, the silver ion and halogen ion activities on the surface of the electrode have the relationship of equation (4) below,
[Ag
+
][X
−
]=Ksp (4)
where Ksp indicates the
Saito Hirokazu
Tada Sugihiko
Fuji Photo Film Co. , Ltd.
Tung T.
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