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Description  |
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FIELD OF THE INVENTION
The invention relates to a method of regenerating and maintaining the
activity of a photographic processing solution, more particularly a lith
developing solution, in a continuous processing machine intermittently
supplied with exposed photographic material.
When photographic materials are processed in automatic machines, care must
be taken that the activity of the individual processing baths remains
constant, so that the quality of processing stays constant over relatively
long periods. Over a prolonged period, the activity of the bath is
determined mainly by the following two factors:
(a) Chemical exhaustion due to the actual processing, and
(b) Chemical changes due not to the processing but to other factors, e.g.
the action of atmospheric oxygen, gradual decomposition of individual
components, accumulation of by-products, etc.
Change (a) usually depends directly on the amount of processed material,
whereas change (b) is generally independent of the amount of processed
material but depends on the time in use and the bath temperature.
In many cases, therefore, it is not sufficient to regenerate the processing
bath by making up used components in proportion to the amount of processed
material. On the contrary, particularly after relatively long inoperative
periods, it is also necessary to allow for the age of the bath liquor and
renew any components which have deteriorated, either spontaneously or
through action of atmospheric oxygen.
Variations during operation occur particularly in those processing baths
which contain substances having an action based on reduction and
oxidation. Photographic developing baths are particularly easy to oxidize
by atmospheric air. Another example is colour bleaching baths used in the
silver colour-bleaching process, the action of the baths being dependent
on the relatively sensitive redox equilibrium of the bleaching catalysts
and oxidizing agents therein. It is particularly difficult to regenerate
lith developing agents used to develop high-contrast materials. Apart from
a single developing substance (hydroquinone), these developing agents
contain only a very little sulphite and are therefore easily oxidized by
atmospheric oxygen. The activity of lith developing agents is also
critically influenced by other factors such as the pH and the
instantaneous concentration of bromine ions. During the developing of
photographic material, hydroquinone and sulphite are used up and bromine
ions are simultaneously liberated. It is therefore particularly difficult
to maintain a constant activity in the aforementioned baths, and both the
changes caused by continuous developing of photographic material and the
changes caused by variations in the time in use must be exactly
compensated.
PRIOR ART
Lith developing agents are commonly regenerated by using two or more
different solutions having compositions matched to one another so that, by
varying the mixing ratios, all changes in activity occurring during
operation can be compensated. Various methods of measurement are
conventionally used for accurately determining the nature of the changes
in activity and regenerating the bath by adding suitable components. The
following two fundamentally different methods are used:
1. Chemical analysis of bath composition and
2. Measuring the area and blackening of the developed material.
Both methods are relatively expensive and are not of real value unless they
can be performed with sufficient accuracy. The first method and its use in
an automatic lith developing-agent regenerating system is described e.g.
in German Offenlegungeschrift No. 2 119 069, and the second is described
e.g. in German Offenlegungeschriften Nos. 2 343 242 and 2 343 318. In the
method described in the last-mentioned publications, it is normal to use
three different solutions, the total amount and proportion of the
regenerating constituents being calculated from (a) the amount and
blackening of the processed film material and (b) from the time during
which the contents of the tank has been in use. A relatively expensive
automatic measuring device is used, and the constituents are added at
periodic intervals.
U.S. Pat. No. 3,162,534 discloses a method of regenerating lith developing
agents wherein only two solutions are used, the less concentrated solution
being added for compensation, depending on the amount of developed film
and the more highly concentrated solution being used for periodically
compensating the changes occurring during use. Neither solution contains
hydroquinone, and consequently their activity can be maintained only for a
limited time.
The normal regeneration method, more particularly in automatic developing
machines, is as follows: Measured quantities of regenerator fluid are
poured into the tank, either periodically or at intervals controlled in
accordance with the amount of processed material, and at the same time a
corresponding quantity of fluid from the tank is discharged through an
overflow to a waste-water pipe. The volume of processing fluid thus
remains constant during the entire period of operation and the activity is
kept constant by continuously supplying the regenerator fluid.
OBJECT OF THE INVENTION
The object of the invention is to provide a particularly simple method of
regenerating lith developing agents, more particularly suitable for
automatic developing machines and requiring only one regenerator,
containing the active components in a constant ratio. More particularly,
the method according to the invention does not require any complicated
methods of determining the bath composition or the area of blackened film,
but is capable of maintaining the activity of the lith developing agent
constant for a very long period.
SUMMARY OF THE INVENTION
In accordance with this invention therefore we provide a method of
regenerating and maintaining the activity of a photographic processing
solution in a continuous processing machine intermittently supplied with
exposed photographic material, comprising adding a regenerator of
concentrated substances and diluting water to the processing solution
before, simultaneously or after the introduction of photographic material
the proportion of concentrates in the regenerator being made higher or
lower depending on whether the expected throughput of photographic
material is relatively small or relatively large respectively during a
given period.
In practice, the regenerator is preferably divided into two concentrated
solutions, one at a pH below 7 and containing hydroquinone, sulphite and
sodium formaldehyde bi-sulphite and the other at a higher pH and
containing alkali, buffer substances and, if required, other components
such as complexing agents and aromatic amines, both concentrates being
free from bromine ions. The two concentrates are simultaneously but
separately poured into the developing tank together with the water for
dilution whenever a piece of photographic material for development is
placed in the tank. The blackened portion of material can be determined
simply by using an empirical value. The throughput is estimated from the
amount of regenerator converted per unit time, relative to the contents of
the processing tank.
As a result of the method according to the invention, both the
concentration of bromine ions, which determine the activity of the
developing solution, and the concentration of hydroquinone, which is acted
upon by atmospheric oxygen, can be kept substantially constant. It is
known that when exposed photographic material is developed, bromine ions
are liberated in an amount proportional to the exposed area and the silver
bromide present in the photographic film. Consequently, if the machine
throughput is large, the developing fluid will contain a higher proportion
of bromine ions unless case is taken to remove them from the fluid at the
same rate as they are produced. Since the volume of replenishing liquid
which is added per unit area of exposed and processed film is kept
constant, the number of bromine ions generated by the development process
will be equal to the number of bromine ions removed by overflow as soon as
the process has reached its equilibrium. On the other side, the
concentration of hydroquinone is kept constant by variation of the
replenisher concentration: with low throughput, the part of hydroquinone
rendered inactive by aerial oxidation tends to be higher, whereas this
part will be lower with high throughput. Accordingly a higher
concentration of the replenisher has to be chosen for low throughput and,
logically, a lower concentration for high throughput, the total volume of
replenisher solution per unit area of exposed film being kept constant for
the reasons explained above.
If the machine is long inoperative, hydroquinone is used up by atmospheric
oxidation without bromine ions being simultaneously liberated. This can be
compensated by adding an amount of concentrated regenerator proportional
to the expected loss. If the regenerator concentrates do not contain
bromine ions, the concentration of bromine ions in the developing fluid
changes only very slightly, e.g. in proportion to the amount which has
been discharged, and this amount can be kept very small if no diluting
water is added.
If A and B are the two regenerator concentrates and W is the water for
dilution, the change in concentration is preferably brought about as
follows. The total amount of regenerator fluid per unit area of blackened
film and the proportions of each regenerator concentrate are kept
constant, the only variation being made in the amount of diluting water,
depending on the proportions of the two regenerator concentrates, i.e.
A+B+W=constant
A:B=constant
Preferably the regenerator concentration is varied in steps, corresponding
to the throughput. The minimum concentration, i.e. the minimum amount of
concentrate in proportion to the total amount of regenerator, can be
approximately 2:6, associated with a maximum throughput of 60% or more of
the volume of the developing tank. The maximum concentration depends on
the minimum throughput occurring in practice, e.g. approximately 10%
consumption of regenerator, and can be approximately 2.5:6 to 3:6. Of
course the most favourable values depend on the nature and composition of
the processing solution and regenerator.
The invention also relates to a device for performing the method comprising
a control system, three storage containers for the two concentrates and
the diluting water, and three proportioning pumps for the concentrates and
water, the pumps being connected by lines between the storage containers
and the processing tank. The control system comprises first input means
for inputting the area, the exposed portion and characteristic variable
dependent on the nature of the photographic material, and a second input
means for the expected throughput. The control system determines the
amount of regenerator on each occasion from the parameters supplied by the
first input means and the concentration of regenerator on each occasion
from the parameters input by the second means, and actuates the
proportioning pumps accordingly.
BRIEF DESCRIPTION OF THE DRAWINGS
A method and a device according to the invention will now be described in
detail with reference to the drawings, in which:
FIG. 1 is a diagram of a device for carrying out the method in accordance
with this invention; and
FIG. 2 is a block circuit diagram of the control system of the device shown
in FIG. 1.
As shown in the drawings, the device comprises three storage vessels, 1.2,
3 for concentrate A, concentrate B and water for dilution W, three
proportioning pumps 5,6,7 driven by a common motor 4; a three-way valve 8,
a control system 10 for motor 4 and valve 8, and a processing machine
comprising a developer tank 11, a fixing agent tank 12 and a washing tank
13.
The regenerating concentrates A and B and the water W are conveyed from
containers 1,2,3 through lines 14, 15, 16, pumps 7, 6, 5 and additional
lines 17, 18, 19 to the developer tank 11. The input and one output of
valve 8 are in line 19. Its other output is connected to a line 20 which
when the 3-way valve is inoperative, returns the water to the water
reservoir 3.
The control system 10 comprises first adjusting means 21, 22, 23 for
allowing for the area of film, the exposed portion and the film
characteristics (the amount of silver per unit area), a second adjusting
means 24 allowing for the machine throughput, and a start button 25.
System 10 generates pulses t.sub.1 and t.sub.2 which actuate the motor 4
and consequently the three proportioning pumps during a time t.sub.1 and
actuate the three-way valve during a time t.sub.2, during which time the
regenerator concentrates and the water can flow from vessel 3 into tank
11.
The second adjusting means 24 is used to adjust the lengths of pulses
t.sub.1 and t.sub.2 in opposite directions. System 10 is designed so that
when means 24 is in the position corresponding to maximum throughput of
the machine, the lengths of pulses t.sub.1 and t.sub.2 are equal to one
another and to a basic control pulse t.sub.0, when the regenerator is most
highly diluted.
The required length of the basic control pulse t.sub.0 follows directly
from the capacity of the proportioning pumps and the constant total
quantity A+B+W of regenerator fluid required at a given time. This total
quantity is an empirical value and, as previously mentioned, depends inter
alia on the characteristics (the silver content) S, the exposed portion E
and the area F of film material being processed. t.sub.0 is chosen in
accordance with the maximum expected dilution of the regenerator fluid,
i.e. when the three-way valve is actuated all the time the pumps are
switched on, so that no water is recirculated through line 20. In that
case, the proportion of regenerating concentrate to water (A+B):W is at a
minimum and will hereinafter be called X. This ratio is adjusted by
suitably dimensioning or adjusting the proportioning pumps.
Means 24 is used for increasing the proportion of regenerating concentrate
(A+B) to the water W, depending on the machine throughput. To this end,
pulse t.sub.2 can be shortened relative to t.sub.0 by a factor Z
adjustable in five steps between 1 and approximately 0.85 by means 24,
i.e.
t.sub.2 =t.sub.0 .multidot.Z; 0.85.ltoreq.Z.ltoreq.I (I)
To ensure that the aforementioned total amount A+B+W of regenerating fluid
remains constant, the duration of pulse t.sub.1 must satisfy the following
condition:
t.sub.1 =t.sub.0 .multidot.(1+1/X-Z/X) (II)
In the special case of maximum dilution, i.e. Z=1, conditions (I) and (II)
for t.sub.1 and t.sub.2 return to t.sub.1 =t.sub.2 =t.sub.0.
FIG. 2 shows a block circuit diagram of control system 10. It comprises the
aforementioned start button 25 and means 21 to 24 and four multipliers 101
to 104, an integrator 105, an adder 106 and two comparators 107 and 108.
To simplify the drawing, the input means are denoted by potentiometer
signs. Potentiometers can be used for continuously inputting the area F of
processed material, the exposed portion E, the type of film S and the
throughput Z. In practice, however, step switches have been found a
completely adequate substitute for potentiometers and are even more
advantageous in some cases.
Multipliers 101 and 102 produce the products E.F. and E.F.Z. from the input
variables E,F and Z. Multipliers 103 and 104 multiply these products by
the terms (1+1/x) and (-1/x), the values of x usually being fixed in
accordance with their definition given previously. The output signals of
multipliers 103 and 104 are summed in adder 106 and then supplied to an
input of comparator 107. The output signal of multiplier 102 is conveyed
to an input of the second comparator 108.
The input means 23 (film type S) goes immediately into the time constant of
integrator 105. After being reset by button 25, integrator 105 integrates
a constant signal such that its output signal is
##EQU1##
wherein k represents all system constants of integrator 105 and t denotes
time. The output signal is supplied to the second inputs of comparators
107 and 108 and is compared with the output signals of adder 106 and
multiplier 102.
If a piece of photographic material for developing is fed into the machine,
the film type S, the area F and the exposed portion E are set and button
25 is pressed. If desired, the start pulse can be triggered automatically
by a microswitch or the like whenever a piece of film is introduced. The
estimated machine throughput Z during the day is set at the beginning of
the day. After the integrator has been released by the button its output
signal is zero, i.e. the comparator outputs become positive and thus
actuate the proportioning pumps and the solenoid valve via
servo-amplifiers (not shown). As soon as the integrator output voltage
##EQU2##
becomes as great as the voltages applied to the other comparator inputs,
the comparator in question flips over and thus puts an end to pulses
t.sub.1 and t.sub.2, thus inactivating the proportioning pumps or the
solenoid valve. The comparators remain in the same state until they are
again flipped by actuating the start button.
As FIG. 2 shows, the durations of pulses t.sub.1 and t.sub.2 are:
##EQU3##
If
##EQU4##
is denoted by t.sub.0, these formulae merge directly into formulae (I) and
(II).
Of course, the integrator system constants k must be designed so that the
required proportioned volume is obtained if the feed pumps are suitably
dimensioned. This, however, does not have to be spelt out to the skilled
addressee.
In the prior art methods, the activity of lith developers can be kept
constant only by continuous, expensive monitoring of the bath activity or
operating conditions, allowance also being made for the time in use. It
has surprisingly been found that the method according to the invention and
the device for performing the method can obtain the same result in simple
manner, by varying only the dilution of the regenerator fluid or the
amount of diluting water added with the concentrates, in dependence on the
machine throughput.
The direct use of concentrates and direct supply of water to the processing
tank also simplifies the processing work, in that there is no need to
prepare dilute regenerator solutions from the components or the
concentrates.
The following example will illustrate the method and operation of the
device according to the invention. Of course, it is not intended to
restrict the invention to the composition of the components given in the
examples.
EXAMPLE
A photographic high-contrast material containing a silver halide emulsion
film containing 6 grams of developable silver (i.e. 70 mol % silver
chloride and 30 mol % silver bromide) per m.sup.2 emulsion, was exposed in
conventional manner, after which individual sheets of the material were
supplied to a continuous processing machine.
The first tank of the machine contained 64 liters of a developing solution
containing the following substances per liter:
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Hydroquinone 15 g
Triethylene glygol 40 g
Sodium sulphite 2.5 g
Sodium formaldehyde bisulphite
50 g.
Sodium carbonate 33 g
Sodium metaborate 1.5 g
EDTA tetrasodium salt 1.5 g
Diethanolamine 25 g
Potassium bromide 2 g
Potassium hydroxide approx. 3 g*
Water Made up to 1 liter
______________________________________
*The amount of potassium hydroxide was chlosen so that the pH of the
developing solution was exactly 10.2.
The developing time was 1.8 min. at a temperature of 25.degree. C.
In order to keep the activity of the solution constant for a long period, a
regenerator solution having the following composition was added whenever a
new sheet was placed in the machine:
Regenerator concentrate A
______________________________________
Hydroquinone 120 g
Triethylene glycol 400 g
Sodium sulphite 40 g
Sodium formaldehyde bisulphite
300 g
Boric acid 9 g
Water Made up to 1 liter
______________________________________
Regenerator concentrate B
______________________________________
Sodium carbonate 200 g
EDTA tetrasodium salt 9 g
Diethanolamine 150 g
Potassium hydroxide Approx. 20 g*
Water Made up to 1 liter
______________________________________
*The amount of potassium hydroxide was made such that the pH of the 1: 1:
4 (A : B: water) dilute regenerator was 10.3.
1 liter of dilute regenerator solution was added to the developer for each
square meter of exposed surface of photographic material. Components A and
B were diluted with water in accordance with the following Table, in
dependence on the machine throughput. According to the invention,
components A and B and the water were introduced individually,
simultaneously and in equal portions into the developing tank, using a
proportioning pump in each case.
TABLE I
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Machine throughput per
24 hours
m.sup.2Surface in Exposed
contents % of tankregenerator as Volume of
##STR1## A :B : WregeneratorComposition
______________________________________
of
38.4 .gtoreq.60
1.00 1.00 1.00 4.00
28.8 45 0.98 1.04 1.04 3.92
19.2 30 0.94 1.12 1.12 3.76
9.6 15 0.90 1.20 1.20 3.60
6.4 10 0.87 1.26 1.26 3.48
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If the machine is expected to stop more than 48 hours after the heating
(for keeping the developing agent at a predetermined temperature) has been
switched off and without circulating the developing agent, 160 ml of each
concentrate A and B (i.e. 0.25% of the tank contents) will be poured into
the tank after each 24 idle hours.
Provided the developing time and temperature are kept constant, the results
obtained by this method remain unchanged even after six months.
* * * * *
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