This invention relates to the processing of radiation sensitive devices comprising a radiation sensitive coating on a substrate and is concerned with the processing of such devices using an apparatus comprising a container for developer liquid and a means for contacting the devices with the liquid.
Such radiation sensitive devices are used in the production of, for example, printing plates, in particular lithographic printing plates printed circuits; and integrated circuits. Radiation sensitive devices for use in the production of lithographic printing plates usually consist of a substrate in the form of a metallic support sheet, which is mechanically and/or chemically treated to provide a suitable working surface and which carries the radiation sensitive coating. In use, the device is image-wise exposed to actinic radiation using either a negative or a positive transparency of an appropriate subject. The effect of actinic radiation is to alter the solubility of the radiation-sensitive coating. The image-wise exposed device is then processed. The processing step involves contacting the image-wise exposed device with a developer liquid to selectively dissolve unwanted areas of coating from the support sheet to leave an image constituted by the areas of the coating remaining on the support sheet. Other types of printing plates and printed and integrated circuits are produced in a similar manner.
The negative or positive transparency commonly comprises a silver halide layer which forms and provides a line image or a half-tone image or a continuous tone image, or any combination of such images. Of the numerous radiation sensitive coatings that can be used for the devices, poly(vinyl cinnamate) and diazo resins are typical of those that can be used in conjunction with negative transparencies, whilst quinone diazides optionally in combination with novolak resins are representative of those that can be used when exposure is carried out beneath a suitable positive transparency.
The precise processing routine, and the developer liquids used, depend on the solubility and chemical characteristics of the radiation sensitive coating being processed. Whilst the processing may be done manually it is increasingly being carried out automatically using apparatus such as those described in British Patent Specifications No. 1,253,026 and No. 1,299,864 and United States Patent Specifications No. 3,552,293 and No. 4,001,854.
Some radiation sensitive coating/developer combinations are significantly affected by the developer temperature and variation from the predetermined temperature results in incorrect development and unsatisfactory reproductions of the transparency. Thus in accordance with GB 1253026 the developer bath temperature is adjusted by heating and cooling to ensure uniform development. It is also known from BE 771221 to determine the temperature of the developer bath by means of thermistors and to vary the dwell time of a photographic film in the bath in dependence on the temperature. DE 1271545 discloses a similar technique wherein the bath temperature is determined by measuring its viscosity. As is well known, a measure of the ability of a radiation sensitive plate to reproduce a transparency may be obtained by exposing the plate through an exposure guide known as a "grey-scale" or "step-wedge". A typical example of such an exposure guide consists of a number of steps of increasing optical density, the first step being clear. The actual steps that are reproduced on the plate depend on the particular radiation sensitive coating/developer conditions. However it is desirable that for a given set of conditions the reproduction of the step-wedge is always the same. Variation in the temperature of the developer could prevent such results being obtained.
It is an object of this invention to provide an apparatus for processing image-wise exposed radiation sensitive devices which compensates for any changes in the operating temperature of the developing liquid.
Because of the variations in the processing routines, there are problems in providing apparatus capable of processing different radiation sensitive devices. Thus, a processing apparatus with a developer bath length of, for example, 12 inches (about 31 cm) will have an optimum plate speed of 35 inches (about 90 cm) per minute when used for developing a negative working radiation sensitive plate with an organic solvent developer and an optimum plate speed of 20 inches (about 51 cm) per minute when used for developing a positive working radiation-sensitive plate with an alkaline developer.
It has been found that if an image-wise exposed positive working radiation sensitive device is processed by including the step of giving it a brief overall uniform exposure to actinic radiation before or during the development, the development time can be decreased. When this exposure is given manually, it is difficult to obtain predictable and repeatable results because the exposure conditions are difficult to control. This problem can be solved by giving the device an overall exposure to relatively less intense actinic radiation for a relatively longer time whilst the plate moves along a path past the source of radiation. However, it has been found that the degree to which a given device needs to be subjected to an overall exposure in order to obtain a given result is dependent on the temperature of the developer liquid.
It is another object of the invention to provide an apparatus for processing an image-wise exposed radiation sensitive device by giving the device an overall exposure, before or during development, which overall exposure is controlled in dependence on the temperature of the developer liquid.
According to the present invention there is provided an apparatus for processing an image-wise exposed radiation sensitive device which apparatus comprises a container for developer liquid, a means for contacting the device with the developer liquid, and a temperature sensitive member for sensing the temperature of the developer liquid and for producing an output signal in dependence on that temperature characterised in that the apparatus additionally includes a roller for agitating the developer liquid in contact with the device and a motor for driving the agitating roller, said temperature sensitive member being operably connected to the motor for driving the agitator roller so that said output signal controls the speed of the motor whereby the degree to which the developer liquid is agitated in contact with the device is dependent on the temperature of the developer liquid.
In one embodiment the apparatus includes a means of moving the device with respect to the developer liquid, the output signal being used, in addition to controlling the agitating roller motor, to control a motor for driving the device moving means. In one form of this embodiment, the device moving means comprises a pair of rollers for feeding the device at an appropriate speed along a path through the developer liquid. In an alternative embodiment the device moving means comprises a mechanism for dipping the device into the developer liquid in the container and for withdrawing the same after an appropriate time interval. In either case not only the degree of agitation but also the residence time of the device in the apparatus is dependent upon the output signal i.e. upon the temperature of the developer liquid. In an alternative embodiment the developer liquid is fed to the device for a period of time dependent on the output signal, which of course is also used to control the speed of the agitator roller motor. Thus in this case also the device and the developer liquid are in contact for a time dependent on the temperature of the developer liquid.
In a further embodiment, the apparatus additionally includes a source of actinic radiation arranged so that the processing also involves the step of subjecting the device to an overall uniform exposure prior to or during its contact with developer liquid. In this case, in addition to the degree of agitation, the degree to which the device is subjected to radiation from said source may be controlled in dependence on said output signal. This may conveniently be effected by interposing a variable aperture between the source and the device and regulating the size of the aperture in dependence on said output signal.
Positive working radiation-sensitive devices typified by quinone diazide sensitised devices are used in the technique known as 'screen(ess lithography' i.e. the technique in which the device is exposed directly through a continuous tone master, without the use of the conventional half tone screen. Processing the plate by subjecting it to an overall exposure before developing increases the range of tones that can be obtained. Again, however, it is difficult to obtain predictable and repeatable results when this is done manually. An apparatus of the invention including a source of actinic radiation as aforesaid can be used to process these plates, variations in the tonal range being produced by varying the duration or the intensity of the overall exposure. Alternatively if it is desired to keep these parameters constant, the tonal range can be varied by altering the speed at which the plates pass the radiation source. Clearly, variation of exposure duration and intensity and variation of plate speed can be combined to give better control of the tonal range.
For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:
Referring to Figure 1, the apparatus includes a pair of rubber covered input rollers 20 and 20a, a pair of rubber covered output rollers 30 and 30a, and a d.c. electric motor 40 for driving the rollers 20 and 20a. The apparatus includes a separate container 21 for developer liquid and a pump 25 for delivering developer liquid to a spray bar 26 located between a pair of plush covered rollers 23 and 23a driven by a separate motor 24. A planar member 22 is located under the rollers 23 and 23a and bar 26 and a catch tray 27 is provided to return developer liquid to the container 21. The apparatus includes a temperature sensitive member in the form of a probe 28 containing a thermistor and this is preferably located in the container 21 as shown. The apparatus also includes an electrical control circuit as shown in Figures 2 and 3; the output from the servo device of the circuit is fed to motor 24 and, optionally, to motor 40.
Referring to Figure 2, the electrical control circuit consists of a constant voltage source 9 in the form of an integrated circuit voltage regulator, a temperature voltage converter 10 incorporating the thermistor, and a servodevice 11 in the form of a d.c. thyristor controller, the output of which controls the speed of the motor 24.
Referring to Figure 3, the regulated voltage from the source 9 (Figure 2) is fed through the thermistor 12 to a pair of d.c. amplifiers 13 and 14. Variation in the temperature of the thermistor 12 causes a change in its resistance which in turn produces a change in the input voltage to the amplifier 13. The output of the amplifier 14 is connected to the servo device 11 (Figure 2). A variable resistor 15 is provided to vary the gain of the amplifier 13.
In use of the apparatus shown in Figure 1, an image-wise exposed radiation sensitive plate is fed face upwards along a path between the input rollers 20 and 20a, between the rollers 23 and 23a and the member 22, and then between the output rollers 30 and 30a. The exposed radiation sensitive coating of the plate is contacted by the rollers 23 and 23a and development, i.e. removal of the more soluble areas of the image-wise exposed radiation sensitive coating of the plate, is carried out by a combined scrubbing and solvent action. The arrangement of the apparatus as shown is such that with increased developer liquid temperature, (i) motor 24 (and hence rollers 23 and 23a) rotate slower and hence the developer liquid on the exposed coating is subjected to a less severe agitation; and (ii) motor 40 (and hence rollers 20 and 20a) rotate faster and hence the residence time of the plate in the apparatus is shorter. The degree to which the plate is processed is thus dependent on the temperature of the developer liquid. This relationship can be adjusted as desired.
Clearly, the temperature compensation that will be suitable for one combination of radiation sensitive coating and developer liquid will not necessarily be suitable for another. Suitable variation of the change in motor speed with temperature may be obtained by adjusting the variable resistor 15. Further, in the case of a given radiation sensitive coating/developer liquid combination the variable resistor 15 may be adjusted to vary the contrast of the developed plate. Moreover, the setting of the variable resistor 15 may be varied to allow for an alteration in the activity of the developer liquid as a result of partial exhaustion.
The scope of the invention also includes a method of processing a radiation sensitive device which comprises passing the device through an apparatus as defined above.
Devices which may be processed in the apparatus of the invention using particular developers include for example positive working presensitised plates consisting of a grained and anodised substrate such as aluminium coated with a radiation sensitive mixture of a naphthoquinone diazide sulphonic acid ester and a novolak resin using aqueous sodium metasilicate developer, optionally with polyethylene glycol; deep-etch plates consisting of an anodised substrate having a radiation sensitive coating based on dichromated gum arabic using aqueous calcium chloride developer; smooth surfaced sheets of photoengraving zinc coated with positive working radiation sensitive compositions using aqueous sodium metasilicate developer; negative working presensitised printing plates consisting of a grained and anodised substrate having a radiation sensitive coating comprising the cin- namylidene-malonic acid half ester of poly(2,3,- epoxy-propyl methacrylate) using aqueous sodium silicate developer; film such as "alus X" panchromatic film (Kodak Ltd) using "Microdol X" developer (Kodak Ltd); and silver halide diffusion transfer materials such as exposed silver halide diffusion transfer negative paper in conjunction with positive receiving sheet in the form of an ADT aluminium lithographic plate (supplied by the Howson-Algraphy Group of Vickers Ltd) using ADT monobath developer/ fixer (Howson-Algraphy Group of Vickers Limited).
The apparatus of the present invention provides several advantages over conventional processors. It is possible to obtain repeatable plate processing accurately without having to monitor and adjust the working temperature of the developer, which thus can always be at the ambient temperature. Time is saved when the developer temperature is low e.g. at the start of processing in a cold environment, as it is not necessary to wait until the developer is heated to the normal working temperature as is the case with conventional developers. Further, in the case where the ambient temperature is higher than the normal working temperature, there is no need to provide a means of cooling the developer. This is particularly important in the case of large processors containing 30 or 40 litres of developer.