GB2046931A - Method of developing positive- acting photosensitive lithographic printing plate precursor - Google Patents

Abstract

A method of using an aqueous solution of an alkali metal silicate to develop an imagewise exposed positive- acting photosensitive lithographic printing plate precursor having on an aluminium support a photosensitive layer containing an o-quinonediazide compound, wherein (1) a decrease in the activity of said developer resulting from development is compensated for by adding to said developer a first replenisher composed of an aqueous solution having an alkalinity higher than that of said developer and (2) a second replenisher composed of an aqueous solution having an alkalinity higher than that of said developer is added to said developer either (a) continuously in a predetermined amount or (b) at a predetermined interval in a predetermined amount. Preferably in each solution at least 20% of the alkali metal is potassium; this prevents formation of a deposit which would clog filters in an automatic developing machine. Equations are given for determining the amounts of replenishers.

Description

SPECIFICATION Method of developing positive-acting photosensitive lithographic printing plate precursor This invention relates to a method of developing a positive-acting photosensitive lithographic printing plate precursor (also known as a presensitized plate or simply PS plate) and, more particularly, to a method of maintaining the developer activity at a constant level during automatic development of a great number of positive-acting PS plates having a photosensitive layer that contains an ~quinonediazide compound as the photosensitive material.

The positive-acting PS plate that has been most widely used comprises an aluminum support having disposed thereon a photosensitive layer containing an oquinone-diazide compound. The oquinonediazide compound contains a structural unit of the formula (I) below, and it is already known that when exposed to actinic radiation, the compound forms a carboxyl-containing compound of the formula (II) below (see 0. Süs, Liebigs Annalen der Chemie, Vol. 556, page 65(1944)).

Thus, when a positive-acting PS plate having an aluminum support coated with a photosensitive layer containing an oquinonediazide compound is exposed to actinic radiation through a positive transparency, the oquinonediazide compound present in the exposed area of the photosensitive layer changes to the corresponding carboxylic acid. Therefore, development of the exposed PS plate with an aqueous alkaline solution results in the removal of only the exposed area of said photosensitive layer, thereby revealing the surface of the support in that area. Since the surface of the aluminum support is hydrophilic, the non-image area or the area where the surface of the support has become revealed upon development retains water and repels greasy ink used in lithography.On the other hand, the image area of the area from which no photosensitive layer has been removed upon development is lipophilic and, therefore, it repels water and is receptive to said greasy ink.

Various aqueous alkaline solutions are known for use as developer for such positive-acting PS plate. An aqueous solution of sodium silicate is particularly preferred, because it has a low ability to etch the aluminum support, and its developing capacity can be controlled within a range by varying the ratio of silicon dioxide (SiO2) to sodium oxide (Na2O) in the sodium silicate (said ratio being generally expressed as the SiO2/Na2O molar ratio) and the concentrations of these two components.

To meet the demand for a streamlined and standardized photomechanical process, an automatic developing machine is now widely used in the printing industry for processing PS plates. A common automatic processor of the type that sprays a processing solution is schematically shown in cross-section in the figure of the accompanying drawing. The processor comprises a transport section where a PS plate is transported by such means as feed rollers 1 in the direction of arrow 2 and which has a plurality of overhanging nozzled pipes 3. As the PS plate is transported, a developer 5 in a tank 4 is sprayed by means of a pump 7 through said pipes 3 onto the surface of the photosensitive layer. If required, the surface of the photosensitive layer may be rubbed by brush rollers (not shown) or like means.The used developer is passed through a filter 6 to remove any insoluble matter before it is returned to the tank 4. The processor has sensing means 8 for sensing the start and finish of the processing of the PS plate in the machine; if it detects the insertion of the plate into the processor, spraying of the developer through the nozzles starts, and when the plate leaves the processor, such spraying is terminated .

U.S. Patent Application Serial No. 954,033, filed October 23, 1978 (which corresponds to German Patent Application (OLS) 2,846,256) teaches a method of developing a great number of positive-acting PS plates without replacing the developer in the tank of an automatic developing machine of the type described above.The method uses as the developer an aqueous solution of an alkali metal salt having an rSiO2 ] / [ M ] ratio of from 0.5 to 0.75 and an SiO2 concentration of from 1 to 4% by weight based on the total weight of the developer, where [ SiO2# represents the concentration of SiO2 per unit volume expressed as gram-molecules, and [M] represents the concentration of the alkali metal per unit volume expressed as gram-atoms, and to compensate for the change (primarily the decrease in alkalinity) in the developer caused by repeated processing and/or aging, the developer is replenished with an aqueous solution of an alkali metal silicate having an [ SiO2 ] / [ M ] ratio of from 0.25 to 0.75.

A specific method of adding such a replenisher to the developer comprises first processing a PS plate of a predetermined area, determining by actual calculation the amount of a replenisher required for compensating for the resulting decrease in the alkaline component thereby preventing a possible reduction in the apparent sensitivity of the PS plate in the subsequent processing, converting said amount to one required per unit area of the plate under processing, and adding the replenisher either at each processing in an amount corresponding to the area of the PS plate to be processed or at a given interval based on the average amount necessary.

However, it has been found that such method involves the following defects: when a number of PS plates must be processed in a short period of time, the addition of a predetermined amount of replenisher results in an increased proportion of the alkaline component, causing an apparent increase in the sensitivity of the PS plate. If the apparent increase in sensitivity is excessive, the number of reproductions that can be printed by a plate prepared from the PS plate is decreased or the plate becomes less receptive to ink. On the other hand, when only a small number of PS plates are processed over an extended period of time, an apparent decrease in the sensitivity of the PS plate results, and if such decrease is excessive, a lithographic printing plate prepared from the plate gives a stained reproduction.The present inventors have found that such defects are due to the fact that, in the conventional technique, the stated average necessary amount of replenisher has been considered jointly from both the amount necessary to compensate for the decrease in the developer activity resulting from processing a positive-acting PS plate and the amount to compensate for the decrease in the developer activity caused by carbon dioxide gas absorbed during exposure to air.

Therefore, the primary object of this invention is to eliminate the defects in the replenishing method described above.

The present invention relates to a method of maintaining the activity of an alkaline developer constant during development of an imagewise exposed positive-acting photosensitive material having disposed on a support a photosensitive layer that contains an oquinonediazide compound, in which a first replenisher having a higher alkalinity than that of said alkaline developer being used for development is added to said developer at each processing of said photosensitive material and a second replenisher having a higher alkalinity than that of said developer is added to said developer either continuously in a predetermined amount or at a predetermined interval in a predetermined amount.

More specifically, this invention relates to a method of using an aqueous solution of an alkali metal silicate to develop an imagewise exposed positive-acting photosensitive lithographic printing plate precursor having a photosensitive layer containing an ~quinonediazide compound, and in this method, (1) a decrease in the activity of said developer resultin#g from development is compensated by adding to said developer a first replenisher composed of an aqueous solution of an alkali metal silicate having an alkalinity higher than that of said developer and (2) adding a second replenisher composed of an aqueous solution of an alkali metal silicate having an alkalinity higher than that of said developer to said developer either (a) continuously in a predetermined amount or (b) at a predetermined interval in a predetermined amount.

Still more particularly, this invention relates to the above methods in which each of said developer, said first replenisher and said second replenisher contains at least 20% of potassium based on the gram-atoms of all the alkali metals present.

We will first describe the photosensitive material used.

Basically, the positive-acting PS plate to which the developing method of this invention applies has disposed on an aluminum support a photosensitive layer containing an o- quinonediazide compound. Suitable aluminum supports include a pure aluminum plate and aluminum alloy plate. Plastics films laminated or metallized with aluminum can also be used.

The surface of the aluminum plate is preferably subjected to surface treatments such as graining, immersion in an aqueous solution of sodium silicate, potassium fluorozirconate or phosphate, and anodization. Other suitable examples are an aluminum plate first grained and then immersed in aqueous sodium silicate as taught in U.S. Patent 2,714,066, and an aluminum plate first anodized and then immersed in aqueous alkali metal silicate as taught in U.S. Patent 3,181,461. Anodization is performed in an electrolyte consisting of at least one aqueous or non-aqueous solution of an inorganic acid such as phosphoric acid, chromic acid, sulfuric acid or boric acid, or an organic acid such as oxalic acid or sulfamic acid, or a salt thereof, with a current applied through an aluminum anode.

Another effective surface treatment is electro-deposition of silicate as taught in U.S. Patent 3,658,662. An aluminum support anodized in the manner described above after it is electrolytically grained as taught in U.S. Patent 4,087,341, British Patent 1,208,224 and Japanese Patent Application (OPI) No. 30503/77 (the term "OPI" as used herein refers to a published unexamined Japanese patent application") is also useful. Another preferred support is an aluminum plate chemically etched and anodized after it is grained in the manner described in U.S. Patent 3,834,998.The purposes of these surface treatments are not limited to rendering the surface of the support hydrophilic; other purposes are to prevent undesirable reaction with the photosensitive composition disposed on the support as well as to provide intimate contact with a photosensitive layer.

The photosensitive layer disposed on the support contains an oquinonediazide compound.

Preferred quinonediazide compounds are the onaphthoquinonediazides disclosed in U.S.

Patents 3,046,110, 3,046,111, 3,046,115, 3,046,118, 3,046,119, 3,046,120, 3,046,121, 3,046,122, 3,046,123, 3,061,430, 3,102,809, 3,106,465, 3,635,709, and 3,647,443 and many other prior publications. These compounds can be used in this invention with advantage. Preferred examples are an naphthoquinonediazide sulfonate ester or an o naphthoquinonediazide carboxylate ester of an aromatic hydroxy compound. Particularly preferred are a pyrogallol/acetone condensate which is esterified with onaphthoquinonediazide sulfonic acid as described in U.S. Patent 3,635,709; a polyester having a terminal hydroxyl group which is esterified with onaphthoquinonediazide sulfonic acid or #naphthoquinonediazide carboxylic acid as described in U.S.Patent 4,028,111; a homopolymer of Rhydroxystyrene or a copolymer thereof with another copolymerizable monomer, which is esterified with #naphtho- quinonediazide sulfonic acid or #naphthoquinonediazide carboxylic acid, as described in U.S.

Patent 4, 139,384.

These oquinonediazide compounds may be used alone, but they are preferably mixed with an alkali-soluble resin and the resulting admixture disposed as a photosensitive layer. Advantageous alkali-soluble resins include phenolic novolak resins, for example, phenolformaldehyde resin, ~ cresol-formaldehyde resin and m-cresol-formaldehyde resin. More preferably, these phenolic resins may be used in combination with a condensate of alkyl (CS 8)-substituted phenol or cresol and aldehyde (e.g., t-butylphenol-formaldehyde resin), as taught in U.S. Patent 4,123,279.

Such alkali-soluble resin is incorporated in the photosensitive layer in an amount of from about 50 to about 85 wt%, preferably from 60 to 80 wt%, based on the total weight of the photosensitive layer.

The photosensitive layer containing an #quinonediazide compound may further contain a dye, plasticizer and other additives such as a component providing printing-out property.

The photosensitive composition containing such o-naphthoquinonediazide compound is coated on the support as a solution in a suitable solvent. Illustrative solvents include glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether and 2-methoxyethyl acetate; ketones such as acetone, methyl ethyl ketone and cyclohexanone; and chlorinated hydrocarbons such as ethylene dichloride. The dry weight of the coated photosensitive layer is in the range of from about 0.5 g to about 7 g, preferably from 1.5 g to 3 g, per square meter of the support.

A number of commercial lithographic "PS" plates are available, and they can be used in the practice of this invention. Illustrative positive-working "PS" plates are "GAP-Il", "SGP-ll" and "SGP-KII" all of which are manufactured by Fuji Photo Film Co., Ltd.; "P-7", "P-7s", "P-3" and "P-3s" all of which are manufactured by Hoechst, West Germany; and "Alympic Gold" and "Spartan" both of which are manufactured by Hawthorn Allography, England.

When these positive-acting PS plates are exposed through an image-bearing transparency to an abundance of actinic radiation from a suitable source such as a carbon-arc lamp, mercury vapor lamp, metal halide lamp, xenon lamp or tungsten lamp, the exposed portion of the photosensitive layer becomes alkali-soluble. Therefore, the exposed portion is washed away when the surface is treated with an aqueous alkaline solution, revealing the hydrophilic surface of the support at that portion.

We now describe the development method of the invention.

A fresh developer can process a positive acting PS plate and provide the intended proper development, but the developer activity decreases with the increase in the number of PS plate developed, the time spent after the preparation of the developer, and other factors. To prevent such decrease in the developer activity, a replenisher is added to the original developer. The most characteristic feature of this invention is in the method of adding the replenishers.

According to this invention, a first replenisher having an alkalinity higher than that of the developer being used in development is added to the developer during the development processing of the photosensitive materials, and a second replenisher, also having an alkalinity higher than that of said developer, is added during processing to the developer either continuously in a predetermined amount or at a predetermined interval in a predetermined amount.

According to this invention, (1) the first replenisher is added to the developer to compensate for any decrease in its activity resulting from the processing of positive-acting PS plates, and (2) the second replenisher is added to the developer either (a) continuously in a predetermined amount or (b) at a predetermined interval in a predetermined amount.

The alkaline developer is composed of an aqueous solution of an inorganic alkali substance such as sodium silicate, potassium silicate, sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium tertiary phosphate, sodium secondary phosphate, ammonium tertiary phos phate, ammonium secondary phosphate, sodium metasilicate, sodium bicarbonate or ammonia water. The concentration of the inorganic alkali may range from 0.1 to 10 wt%, preferably from 0.5 to 5 wt%. The developer containing an inorganic alkali in these concentrations has a pH in the range of from 12.5 to 13.5, which is suitable for development of a positive-acting photosensitive material.

Each of the developer and first and second replenishers in the most preferred embodiment of this invention is an aqueous solution of an alkali metal silicate and contains at least 20% of potassium based on the total gram-atoms of all alkali metals present in the aqueous solution.

One advantage of using an aqueous solution of silicate that contains the specified amount of potassium is that even if a number of positive-acting PS plates have been processed the solution does not form any insoluble matter in the developer that clogs the spray nozzles of an automatic developing machine and the filter through which the used developer is passed for recovery. This is a very surprising advantage that can be obtained even when a number of positive-acting PS plates using an anodized aluminum support are processed. So far, this type of positive-acting PS plate has suffered from the excessive formation of insoluble matter. The above-described aqueous solution of alkali metal silicate preferably contains from 20 to 90%, more preferably from 30 to 80% of potassium.

Preferred supply sources of potassium include potassium hydroxide, potassium borate, potassium pyrophosphate, potassium tertiary phosphate, potassium polyphosphate and potassium silicate. These potassium sources may be used independently or as a mixture. Scarcely any effect is observed if potassium salts having relatively high dissociation constants are used, for example, potassium chloride, potassium iodide, potassium nitrate, potassium citrate and potassium acetate.

The alkali metal in the alkali metal silicate includes lithium and sodium as well as potassium.

Preferred alkali metals are potassium and sodium.

A preferred developer for use in this invention is an aqueous solution of an alkali metal silicate which contains at least 20% of potassium based on the total gram-atoms of all alkali metals present, has an SiO2/M2O molar ratio (M representing an alkali metal in the following description) of from 1.0 to 1.5 (or an [ SiO2 ] / [ M ] ratio of from 0.5 to 0.75, wherein [ Si02 ] represents the concentration of SiO2 per unit volume as expressed in gram-molecules, and [ M ] represents the concentration of M per unit volume as expressed in gram-atoms, and this definition will also apply to the description hereunder), and which has an SiO2 concentration of from 1 to 4 wt%.Particularly preferred is an aqueous solution of an alkali metal silicate having an [ SiO2 ] / [ M ] ratio of from 0.5 to 0.75 and an SiO2 concentration of 1 to 3 wt%.

Both first and second replenishers have an alkalinity higher than that of the developer, and they are composed of an aqueous alkaline solution as is the developer. Each replenisher may contain the same or a different alkali than that contained in the developer. Alternatively, the formulation of each replenisher may be the same or different from that of the developer. The first replenisher may contain the same or a different alkali than that contained in the second replenisher. Again, both replenishers may consist of the same or a different formulation.

Replenishers having the desired alkalinity can be prepared by adjusting the concentration of alkali in the range of from about 0.5 to 30 wt%.

Particularly preferred first and second replenishers are each an aqueous solution of an alkali metal silicate which contains at least 20% of potassium as defined above and which has an SiO2/M2O molar ratio of from 0.5 to 1.5 (or an [ SiO2 ] / [ M ] ratio of from 0.25 to 0.75). These first and second replenishers are added to the developer for the purpose of compensating for the component (primarily alkali component) of the developer that has been consumed by processing a positive-acting PS plate and the alkali component that has been neutralized with carbon dioxide gas in the air.Therefore, the first and second replenishers may be any aqueous solution of an alkali metal silicate that is added to the developer and is capable of maintaining the above specified composition of the developer which would otherwise change as a result of repeated processing of positive-acting PS plates or the progress of time; to be more specific, an aqueous solution of an alkali metal silicate having an alkalinity higher than that of the developer may be used as the first and second replenishers of this invention. For instance, if the first and/or the second replenisher is an aqueous solution of an alkali metal silicate having the same [ SiO2 ] / [ M ] ratio as that of the developer, it may be so controlled as to have a higher SiO2 concentration than that of the developer. On the other hand, if the first and/or second replenisher is an aqueous solution of an alkali metal silicate having the same SiO2 concentration than that of the developer, it may be so controlled as to have a lower [ SiO2 ] / [ M ] ratio than that of the developer. The first and second replenishers may have the same or a different composition.

They may also have the same or a different concentration of SiO2.

Thus, those skilled in the art will find it easy to determine the respective compositions of the developer, the first and second replenishers. The first or second replenisher may be divided into two or more portions which are combined together when they are added to the developer.

Alternatively, a concentrated stock replenisher may be diluted with water when it is added to the developer. It is to be emphasized again that whatever composition it has, the aqueous solution of an alkali metal silicate of which the developer, the first and second replenishers are made should preferably contain at least 20% potassium based on the total gram-atoms of all alkali metals present.

If the developer, first and second replenishers contain less than 20% of potassium based on the total gram-atoms of all alkali metals present, the processing of positive-acting PS plates can be accompanied by the formation of insoluble matter in the developer which clogs the spray nozzles or the filter through which to recover the used developer. Therefore, it is critical that the concentration of potassium in the developer always be held at 20% or more, otherwise special precautions must be taken. The developer is usually supplied to the user in a concentrated form, and the user dilutes it with water before processing.When a concentrated aqueous solution of sodium silicate having an [ SiO2 ] / [ Na ] ratio of not more than 0.75 is diluted with water containing a divalent or higher metal ion such as calcium, magnesium or aluminum (e.g., water having a German hardness of 36 ), the solution turns white and forms a precipitate that will clog the filter of an automatic developing machine that uses such solution as a developer. In contrast, none the concentrated developer, first and second replenishers used in this invention will turn white even when they are diluted with hard water of the type described above.

Accordingly, the diluted developer or replenisher can be used in an automatic developing machine without any adverse effect. When positive-acting PS plates having an anodized aluminum support are processed in an automatic developing machine using an aqueous solution of sodium silicate in accordance with the conventional technique, a great amount of white deposit that mainly consists of silicic acid is formed on the surface of lower transport rollers of the machine. However, such phenomenon is minimal in development according to the method of this invention.

The developer, first and second replenishers to be used in this invention may contain an organic solvent. Illustrative suitable organic solvents include benzyl alcohol, 2-butoxyethanol, triethanolamine, diethanolamine, monoethanolamine, glycerin, ethylene glycol, polyethylene glycol, and polypropylene glycol. The developer, first or second replenisher may contain such an organic solvent in a controlled amount of not more than 5 wt% based on the total weight of the developer.

The developer, first or second replenisher used in this invention may further contain a surfactant. This helps increase the developing capacity (the amount of a photosensitive layer that can be washed away by a unit volume of the developer) and broaden the range of the developing conditions (e.g., temperature and processing time) that will give optimum results.

Preferred surfactants include anionic and amphoteric surfactants. Illustrative preferred anionic surfactants are alkylbenzenesulfonic acid salts (with the alkyl group having 8 to 18, preferably 12 to 16 carbon atoms) such as sodium dodecylbenzenesulfonate, alkylnaphthalenesulfonic acid salts (with the alkyl group having 3 to 10 carbon atoms) such as sodium isopropylnaphthalenesulfonate, a condensate of formalin and a naphthalenesulfonic acid salt, dialkyl sulfosuccinic acid salts (with the alkyl group having 2 to 18 carbon atoms), and dialkylamidosulfonic acid salts (with the alkyl group having 11 to 17 carbon atoms).Illustrative preferred amphoteric surfactants are imidazoline derivatives, and betaine-type compounds such as N-alkyl-N,N,N-tris (carboxymethyl)ammonium (with the alkyl group having 12 to 18 carbon atoms) and N-alkyl-Ncarboxymethyl-N,N-dihydroxyethylammonium (with the alkyl group having 1 2 to 18 carbon atoms). There is no particular limitation on the amount of the surfactant to be used, but the developer or the replenisher generally contains such surfactant in a controlled amount of from 0.003 to about 3 wt%, preferably from 0.006 to 1 wt%, based on the total weight of the developer.

The developer, first and second replenishers used in this invention may further contain an antifoamer. Suitable antifoamers are described in U.S. Patents 3,250,727 and 3,545,970, British Patents 1,382,901 and 1,387,713, and other prior art references. Organic silane compounds are preferred.

A second characteristic feature of this invention is in the method of adding the first and second replenishers defined above to the developer also defined above. One embodiment of the method is hereunder described by reference to processing with alkali silicate solutions in an automatic developing machine of the spray type illustrated in the figure. It is to be understood that the method of this invention is not limited to this particular embodiment.

In this invention, the first replenisher is added to the developer in an amount that will compensate for the decrease in the developer activity resulting from the processing of imagewise exposed positive-acting PS plates. In case of processing in an automatic developing machine of the spray type, this amount equals to the sum of an amount (C) that compensates for the developer that has been neutralized upon its washing away the exposed area of the photosensitive layer of the PS plate and an amount (A) that compensates for the sprayed developer that has been neutralized upon its absorbing carbon dioxide gas in the air.

Determination of the amount (A) presents no difficulty in practice because it is automatically determined from the type of an automatic developing machine and the formulations of the developer and first replenisher. On the other hand, the amount (C) varies with the areas of the imagewise exposed portions of the plates even if positive-acting PS plates of the same brand are processed in great numbers. Therefore, to determine the amount (C), the area of the non-image portion of a lithographic printing plate prepared by developing an imagewise exposed positiveacting PS plate is measured by, for example, optical means, and an analog signal for the measurement delivered from a photoelectric converter is processed electrically to provide an amount proportional to the measured area of the non-image portion.

The inventors researched a simpler way to determine the sum of amounts (A) and (C), and have found that effective development can also be realized by substituting the value Rt(l) determined by the following equation ( for the amount of the first replenisher to be added upon processing of each PS plate having an individual length L in the direction it runs through an automatic developing machine.

cZWn + aTTn Rtfl) = #---- x L (t) ZLR wherein EWn is the total weight of the photosensitive layers of n sheets of positive-acting PS plates processed within 2 given period of time; c is a proportional factor to be determined by the type of positive-acting PS plate (e.g., the brand of a commercial product) and the formulation of the first replenisher; ETn is the total operating hours of the spray required for processing the n sheets of positive-acting PS plates; a is a proportional factor to be determined by the type of automatic developing machine, the formulation of the first replenisher, and the concentration of carbon dioxide gas in the atmosphere where the developing machine is installed. ELn is the total length of the n sheets of positive-acting PS plates in the direction in which they run in said developing machine. The symbol T.Wn can be expressed as an area when the PS plates processed have a photosensitive layer of the same composition if the same weight of photosensitive layer is coated on a given area of the support.

It is desired that the size and number of the positive-acting PS plates processed be known before using the equation (t} to determine the amount of the first replenisher to be supplied to the developer. But the inventors have found that the object of this invention can also be reasonably achieved by determining the value of R,(I) through the multiplication of L by a proportional factor (a) which is the average of cS.Wn + aXTn 2;Ln obtained on the basis of an accumulated record of processing operations.According to this empirical technique, the amount of the first replenisher supplied is proportional to the length in the travelling direction of a positive-acting PS plate to be processed. Therefore, this technique can be readily implemented by supplying the first replenisher at a given rate as long as microswitch and other sensing means provided on the automatic developing machine detects the running of a PS plate through feed rollers in the machine.

The object of this invention can also be achieved by substituting the value R1(ll), to be determined by the following equation (II), for the amount of the first replenisher to be added at processing of each. PS plate having an area of S: c;Wn + aETn R1,(II)=----------- XS (II) ESn wherein l;Sn is the total area of n sheets of positive-acting PS plates processed within a given period of time; and #Wn, c, 2,Tn and a have the same meaning as defined in the equation (I).

Again, it is desired that the size and number of the positive-acting PS plates being processed be known before using the equation (Il) to determine the amount of the first replenisher to be supplied to the developer. But the object of this invention can also be reasonably achieved by determining the value of R,(ll) through the multiplication of S by a proportional factor (p) which is the average of c#Wn + aXTn #Sn obtained on the basis of an accumulated record of processing operations. According to this empirical method, the amount of the first replenisher to be supplied is proportional to the area of a positive-acting PS plate to be processed.Therefore, the method can be readily implemented by supplying, at processing of each PS plate, the first replenisher in an amount proportional to the area of the plate that is calculated using both means for detecting the travel of the PS plate and means for detecting the transversal length of the plate. This method provides uniform development because there is higher accuracy of developer replenishment than is obtained with the aforementioned method that adds the first replenisher in an amount proportional to the length in direction the PS plate runs in the automatic developing machine.

An alternative method is to determine the supply of the first replenisher on the basis of two independent factors, the amount proportional to the length L in travelling direction of the positive-acting PS plate and the amount proportional to the spray operating time T. To do this, the equation (I) is expanded and rearranged to give the following equation (I'): cXWn R,(l') = -#- X L + aT (I') l;Ln wherein l;Wn, c, ZLn and a have the same meaning as defined in the equation (I).

If the average (a') of cZWn #Ln is known by calculation from an accumulated data of processing operations, the first replenisher may be supplied at a given rate as long as a microswitch or other sensing means provided on the automatic developing machine detects the running of a PS plate through feed rollers in the machine, while at the same time, the switch may be coupled to a spray actuating mechanism so that the first replenisher is added at another rate as long as the spray is operating.The advantage of this alternative method is its capability of assuring even higher accuracy in replenishment than the method based on the equation (I) because in this alternative method, the amount of sprayed developer that deteriorates upon absorbing carbon dioxide in air is considered as an independent factor to be compensated for by the first replenisher.

The same concept can be used to provide a method that is a modification of the method based on the equation (II) but which assures even higher accuracy in replenishment by basing on two independent factors, i.e., the amount proportional to the area S of the PS plate and the amount proportional to the spray operating time T. To do this, the equation (II) is expanded and rearranged to give the following equation (II').

cSWn R,(ll') = > cS+aT (it') 2;Sn wherein ZWn, c and a each have the same meaning as defined in the equation (I) and > ;Sn has the same meaning as defined in the equation (II).

As described in the foregoing, the first replenisher may be added at processing of each positive-acting PS plate. Instead, supply of the first replenisher may be continued until it reaches a predetermined level, whereupon the first replenisher that compensates for that level may be added.

The second replenisher compensates for developer neutralized by carbon dioxide in the air while the developer is standing in the developer machine. As equation (I) above illustrates, the first replenisher compensates for neutralization which results from development and during the spraying operation which is a function separate and distinct from that of the second developer.

By using two replenishers in the present invention the activity of the developer can be more accurately and more closely controlled which in turn means continuous ultra-high quality development is possible. This is not the case where only one replenisher is used.

The amount of the second replenisher supplied in the method of this invention is proportional to the length of time the developer is in the developer tank absorbing CO2X (b), and the proportional factor (b) is determined by the type of automatic developing machine, the amount of developer exposed to the air, the formulation of the second replenisher and the concentration of carbon dioxide gas in the atmosphere where the machine is used. Therefore, with the factor (b) predetermined, the second replenisher may be added either continuously in a given amount or at pre-set intervals in a given amount.For continuous replenishment, a metering pump or a chemical supply pump may be used, and for intermittent replenishment, a measuring cup may of course be used, but a more reliable method is to couple a metering pump with a timer that provides a supply of a given amount of the replenisher at a given interval.

The proportional factors (a), (b) and (c) can be determined by the following method. As mentioned already, these factors are determined from a specific combination of the developer, first replenisher, second replenisher and automatic developing machine, as well as specific environments for processing a specific type of positive-acting PS plate. Therefore, the suppliers of an automatic developing machine and processing agents should predetermine these factors based on the combinations they recommend for a processor as follows.

First prepare positive-acting PS plates each composed of a specific photosensitive material (coating weight: X g-/plate). Charge a specific automatic developing machine with a specific developer the standard charge of which is H liters. Process the PS plates in the developing machine, with the spray being operated continuously. Every time the photosensitive material is dissolved in the developer in an amount of 1 to 2 g per liter of the developer, check for a decrease in the plate sensitivity by processing a positive-acting PS plate on which a PS step guide (grey scale manufactured by Fuji Photo Film Co., Ltd.) has been printed. When the decrease in sensitivity is about one step less than the sensitivity at the commencement of the development, replenish the developer until the initial sensitivity is obtained. If the initial sensitivity is regained, re-start processing.Replenish the developer when there is another decrease in sensitivity of about one step. Repeat such procedure, and when sH/X plates (wherein S is an estimated weight of the photosensitive material per unit developer charge processable with a given system of processing agents) have been processed, determine the total amount of replenisher Mx supplied during the running experiment. Let the running time for this first operation be Tx.

For the second running experiment, charge an automatic developing machine the same as used in the first running experiment with H liters of a developer the same as used in the first running, and run the machine to continuously process PS plates (coating weight: X g) the same as used in the first running in the same manner as in the first running. When sH/X plates have been processed, determine the total supply of replenisher My. It is desired that the second running time Ty be much shorter than Tx. In the third running, follow the usual practice to process PS plates (coating weight: X g) the same as used in the first running (the spray in the developing machine operating only when the plates are being processed).When sH/X plates have been processed, determine the spray operating time Ts, total running time Tz (including the spray operating time), and the total supply of replenisher Mz. It is desired that Ts be much shorter than Tz (preferably Ts is about one-half of Tz). The proportional factors (a), (b) and (c) for the case where both first and second replenishers have the same composition can be determined by substituting into the following equations the respective values obtained in the three running experiments:: Ts(Mx - My) + Tx(My - Mz) + - Mx) a= (Tx - Ty)(Tz - Ts) Tz(Mx - My) + Tx(My - Mz) + Ty(Mz - Mx) b = (Tx - Ty)(Tz - Ts) MyTx -MxTy c = sH(Tx-Ty) If the second replenisher has a different composition than that of the first replenisher, supply the first replenisher according to the factors (a) and (c) determined above, and check for a decrease in sensitivity every one or two hours. If any decrease is found, supply the second replenisher to compensate for it. In this way, any decrease in sensitivity due to the progress of time is compensated by the second replenisher during running experiment of processing.Divide the total supply of second replenisher Mw by the total running time Tw, and the quotient (Mw/Tw) is the proportional factor (b) for supply of the second replenisher.

In the practice of this invention, if processing is interrupted for many hours, it is advantageous to suspend the supply of the second replenisher, too. Before restarting development, check the activity of the developer in a developing tank and supply a sufficient amount of the second replenisher to regain the desired activity. To be more specific, expose a positive-acting PS plate through a step tablet under standard conditions, develop the exposed plate, count the number of solid black steps to know the degree of loss in the developer activity, and supply a sufficient amount of the second replenisher to compensate for such loss.

As will be apparent from the foregoing description, in the method of this invention, the developer activity is maintained constant by the addition of the first and second replenishers.

Therefore, it is desired that provision be made against time-dependent deterioration of the two replenishers; more specifically, the first and second replenishers are preferably stored in air-tight containers to prevent contact with carbon dioxide gas.

As described hereinabove, in the developing method of this invention, the decrease in the developer activity due to processing of positive-acting PS plates is compensated independently of the compensation of activity loss due to the lapse of time. For this reason, the invention assures a constant level of developer activity regardless of the number of positive-acting PS plates to be processed in a given period of time. The result is a stable processing operation that gives uniform development over an extended period of time without replacing the original developer in the developing tank of an automatic developing machine.

As a further advantage, each of the developer, first and second replenishers to be used in this invention is made of an aqueous solution of an alkali metal silicate containing a specified amount of potassium and, therefore, no insoluble matter is formed in the developer that clogs the spray nozzles or filter of the automatic developing machine. This advantage, coupled with the above-described separate compensations of developer activity loss, provides uniform development for an even longer period.

This invention is now described in greater detail by reference to the following examples, wherein unless otherwise specified, all percents are by weight.

EXAMPLE 1 A 2S aluminum plate 0.24 mm thick was degreased by immersing it for 3 minutes in a 10% aqueous solution of sodium tertiary phosphate held at 80 C. After graining with a nylon brush, the plate was etched with sodium aluminate for 10 seconds, and desmutted in a 3% aqueous solution of sodium hydrogensulfate. The so-treated aluminum plate was anodized in 20% sulfuric acid at a current density of 2 A/dm2 until an oxide coating was formed in 2.5 g per square meter.

The thus prepared support was coated with a photosensitive solution of the formulation indicated below, and dried to provide a positive-acting PS plate having a photosensitive layer in a dry weight of 2.5 g/m2.

Photosensitive Solution Esterified product of naphthoquinone- 0.63 g (1 ,2)-diazide-(2)-5-sulfonic acid chloride and pyrogallol/acetone resin (as described in Example 1 of U.S.

Patent 3,635,709) Cresol-novolak resin 1.98 g p-t-Butylphenol resin 0.05 g Tetrahydrophthalic anhydride 0.15 g Thymol Blue 0.04 g Naphthoquinone-(1 ,2)-diazide-(2)-4- 0.03 g sulfonic acid chloride Ethylene dichloride 18 g 2-Methoxyethyl acetate 1 2 9 An automatic developing machine "1 300 RU" (manufactured by Fuji Photo Film Co., Ltd. for development of PS plates) of the construction illustrated in the figure was charged with 21 liters of a 7-fold (by volume) aqueous dilution (pH: 1 3.1 0) of a stock solution of the formulation indicated below.

Formulation of Stock solution (developer) Aqueous solution of JIS No. 3 sodium 332 g silicate (comprising 29.5% SiO2 and 9.5% Na20) Aqueous solution of potassium 191 g hydroxide (48%) Aqueous solution of N-alkyl-N,N- 3.2 g dihydroxyethyl betaine amphoteric surfactant (36%) "Amogen K" ' as antifoamer (organic 0.72 g silicone compound manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) Water 688 g A stock solution of the following composition was diluted 5-fold {by volume) with water to make first and second replenishers (pH: 13.41), which were supplied to the respective replenisher tanks attached to an automatic developing machine.

Formulation of Stock Solution (replenisher) Aqueous solution of JIS No. 3 sodium 238 g silicate Aqueous solution of potassium 328 9 hydroxide (48%) Water 645 g The development temperature was adjusted to 35 C, and the automatic developing machine was so adjusted that it required 50 seconds to develop a positive-acting PS plate passing through it. The so-adjusted developing machine was supplied with 30 imagewise exposed positive-acting PS plates (639 X 939 mm in size and prepared in the manner described above) which were processed at suitable intervals over a period of 6 hours. The developer was supplied with 390 ml of the second replenisher every hour from the commencement of the development, whereas the developer was supplied with 37 ml of the first replenisher at processing of each PS plate.The 30 plates were developed to substantially equal extent, and this fact indicates that the activity of the developer was held almost constant during processing. The step tablet printed to each PS plate (with 15 steps, the first one having an optical density of 0.10 with a density of 0.15 as a difference between two adjacent steps) indicated a difference of less than one step between the number of solid black steps for the plates processed by the used and fresh developers.

After the 6 hour processing, the developer and replenishers in the automatic developer were let stand for 18 hours. Before restarting development, the positive-acting PS plates to each of which a step tablet was printed were processed, and the developer activity was found to have decreased. Therefore, 3.4 liters of the replenisher was supplied. This cycle of processing and replenishment was repeated for 6 days, and the difference between the number of solid black steps for the plate processed by the fresh developer and that for the plate processed by the developer used on the 6th day was less than one step. This demonstrates the prolonged effectiveness of the method of this invention.

The developer and the replenisher used in Example 1 contained potassium in amounts of 62.6% and 79.5%, respectively, based on the total gram-atoms of all alkali metals present. The ratio of silicon dioxide to alkali metal, or [ SiO2 ] / [ M ] for the developer was 0.61, and that for the replenisher was 0.33. The supply rate of the first replenisher was calculated by the equation (II), wherein the proportional factors (a) and (c) were 2.5 ml/min and 16 ml/g, respectively.

Throughout the 6-day development, no nozzle clogging occurred in the automatic developing machine, nor was observed insoluble matter in the developer.

EXAMPLE 2 The procedure of Example 1 was repeated using an automatic developing machine "1 300 RU", except that a stock solution of the following formulation was used for developer and replenisher: Formulation of Stock Solution Aqueous solution of JIS No. 3 sodium 497 g silicate Aqueous solution of potassium 272 g hydroxide (48%) Amphoteric surfactant (the same as 3.2 g used in Example 1) Organic silicone antifoamer 0.72 g Water 760 g The developing machine was charged with 21 liters of a 7-fold (by volume) aqueous dilution (pH: 13.07) of the stock solution, and the respective replenisher tanks were fed with a 34old (by volume) aqueous dilution (pH: 13.40) of the same stock solution. The heat-insulating container was adjusted to hold the developer at 25 C, and the developing time was set at 40 seconds per PS plate.

The positive-acting PS plates used in this example were the same as used in Example 1. The size and number of the plates were as follows: 1310 X 1050 mm (size A) 30 plates 1003 X 800 mm (size B) 100 plates 650 X 525 mm (size C) 80 plates The developing machine had a mechanism that used a microswitch to measure the length of one side in travelling direction of each PS plate, and in operative association with the mechanism, an amount of the first replenisher substantially proportion to the measured length was supplied to the developer. With a development time of 40 seconds used in this example, 33 ml of the first replenisher was supplied per 0.892 m of one side of PS plate. Based on this reference value, 48.5 ml, 29.6 ml and 19.4 ml of the first replenisher were supplied for the processing of size A, size B and size C, respectively.The developer was supplied with 840 ml of the second replenisher every two hours after the commencement of the processing.

The three sizes of PS plates were processed without determining the order of processing.

Continuous or intermittent processing for a period of 22 hours showed that the difference between the number of solid black steps for the plate processed by the fresh developer and that for the plate processed by the developer in any stage of processing was less than one step.

Again, the effectiveness of this invention was apparent. Both the developer and replenisher contained potassium in an amount of 61 % based on the total gram-atoms of all alkali metals present. The ratio of silicon dioxide to alkali metal, or [ Si02 ] / [ M ] for the developer and replenisher was 0.585. The supply rate of the first replenisher was calculated by the equation (II), wherein the proportional factors (a) and (c) were 2.5 ml/min and 14 ml/g, respectively.

EXAMPLE 3 The procedure of Example 1 was repeated, except that the developing tank of the automatic developing machine was charged with 21 liters of a 7-fold (by volume) aqueous dilution of a stock solution of the formulation specified below. The dilution had 210 g of potassium pyrophosphate dissolved therein.

Formulation of Stock Solution Sodium metasilicate nonahydrate salt 360 g JIS No. 3 sodium silicate 66 g Amphoteric surfactant (the same as used 3.2 g in Example 1) Organic silicone antifoamer 0.72 g Water 784 g First and second replenishers were prepared from a 3-fold (by volume) aqueous dilution of the above stock solution, plus 23.3 g of potassium pyrophosphate dissolved per liter of the dilution.

Eighty positive-acting PS plates (1,003 X 800 mm in size) were processed at suitable intervals over a period of 6 hours. The developer was replenished with 25 ml of the first replenisher at processing of each plate, whereas 400 ml of the second replenisher was supplied every hour from the commencement of the development. The step tablet printed on each PS plate indicated a stable processing operation wherein the difference between the number of solid black steps for the plates processed by the used fresh developers was less than one step. Hence, the developer activity was held almost constant throughout processing according to the method of this invention.

The developer and replenisher contained about 24% of potassium based on the total gramatoms of all alkali metals present. The supply rate of the first replenisher was calculated by the equation (II) wherein the proportional factors (a) and (c) were 2.2 ml/min and 12.5 ml/g, respectively. The exhausted developer was let stand in the automatic developing machine for 4 days, and no insoluble matter was formed.

EXAMPLE 4 An automatic developing machine "1 300 U" (manufactured by Fuji Photo Film Co., Ltd. for development of PS plates) of the construction illustrated in the figure was charged with 21 liters of a developer composed of a 7-fold (by volume) aqueous dilution of a stock solution having the same formulation as used in Example 2. A stock solution of the same formulation was diluted 3fold (by volume) with water to prepare first and second replenishers. The development temperature was adjusted to 25 C, and the automatic developing machine was so adjusted that it required 40 seconds to develop a positive-acting PS plate passing through it.The thusadjusted developing machine was supplied with the below indicated number of imagewise exposed positive-acting PS plates I (the same as used in Example 1) and positive-acting PS plates II (to be described below), which were processed at suitable intervals over a period of 10 hours.

The positive-acting PS plates 11 were prepared in the following manner. A 2S aluminum plate û.24 mm thick was degreased by immersing it for 3 minutes in a 10% aqueous solution of sodium tertiary phosphate held at 80QC. After graining with a nylon brush, the plate was etched with sodium aluminate for 10 seconds, and desmutted in a 3% aqueous solution of sodium hydrogensulfate.

The thus-prepared support was coated with a photosensitive solution of the formulation indicated below, and dried to provide a positive-acting PS plate II having a photosensitive layer in a dry weight of 2.5 g/m2.

Photosensitive Solution Esterified product of naphthoquinone- 0.63 g (1, 2)-diazide-(2)-5-sulfonic acid chloride and pyrogallol/acetone resin (as described in Example 1 of U.S.

Patent 3,635,709) Cresol-novolak resin 1.98 g p-t-Butylphenol resin 0.05 g Tetrahydrophthalic anhydride 0.15 g Thymol Blue 0.04 g Naphthoquinone-(1 ,2)-diazide-(2)-4- 0.03 g sulfonic acid chloride Ethylene dichloride 18 g 2-M ethoxyethyl acetate 12 9 Positive-Acting PS Plate I 1310X 1050 mm (size A) 15 plates/day 1003 X 800 mm (size B) 30 plates/day Positive-Acting PS Plate 11 1310X 1050 mm (size A) 15 plates/day 1003 x 800 mm (size B) 20 plates/day 700 X 550 mm (size C) 30 plates/day At processing of each PS plate, the developer was supplied with the first replenisher in an amount of 50 ml per square meter of the plate.Therefore, 62 ml, 40 ml and 19 ml of the first replenisher were supplied for processing size A, size B and size C, respectively. The developer was also supplied with 400 ml of the second replenisher every two hours after the commencement of the processing. After completion of the processing, the developer and replenisher in the automatic developing machine were held overnight (i.e., for 14 hours). This resulted in a decrease in the developer activity. The developer was supplied with 2.5 liters of the replenisher and used to develop the same number of positive-acting PS plates as processed the previous day. The 2-day processing demonstrated the effectiveness of this invention. The supply rate of the first replenisher was calculated by the equation (II), wherein the proportional factors (a) and (c) were 2.5 ml/min and 16 ml/g, respectively.

EXAMPLE 5 An automatic developing machine "400S" (manufactured by Fuji Photo Film Co., Ltd. for use in development of PS plate) was charged with 5 liters of a 7-fold dilution (pH: 1 3.10) of a stock solution of the following formulation: Formulation of Stock Solution (developer) Sodium metasilicate nonahydrate salt 341.Q g Potassium tertiary phosphate 14.8 g Aqueous solution of potassium hydroxide 50.2 g Water 764 g The respective replenisher tanks were charged with first and second replenishers both of which were a 7-fold dilution (pH: 13.45) of a stock solution of the following formulation: Formulation of Stock Solution (replenisher) Sodium metasilicate nonahydrate salt 341.0 9 Potassium tertiary phosphate 46.0 g Aqueous solution of potassium hydroxide 162.5 g (48 wt%) Water 690.5 g The temperature of the developer was adjusted to 25 C, and the development time was set at 50 seconds. The so-adjusted automatic developing machine was supplied with 250 PS plates "GAP-II" (254 X 391 mm in size, manufactured by Fuji Photo Film Co., Ltd.) that were processed continuously or intermittently over a period of 8 hours. The developer was supplied with 75 ml of the second replenisher every hour after the commencement of the development, whereas 2.2 ml of the first replenisher was supplied at processing of each PS plate.

The step tablet through which each PS plate was exposed indicated that difference between the number of solid black steps for the first processed plate and that for the last processed plate was less than one step.

EXAMPLE 6 An automatic developing machine "1 300 RU" was charged with a 7-fold dilution (pH: 12.93) of a developer stock solution of the following formulation.

Formulation of Stock Solution (developer) Sodium metasilicate nonahydrate salt 360 9 Aqueous solution of JIS No. 3 sodium 65.6 g silicate "Amogen K" 32 g Organic silicone anti-foamer 0.72 g Water 784 9 The respective replenisher tanks were fed with a 74old dilution (pH: 13.42) of a replenisher stock solution of the following formulation: Sodium metasilicate nonahydrate 360 g Aqueous solution of JIS No. 3 sodium 65.6 g silicate Aqueous potassium hydroxide solution 140 g (48%) Water 784 g The temperature of the developer was adjusted to 25 C, and the development time was set at 50 seconds per plate. The developing machine was supplied with 150 PS plates "SGP-ll" (1,003 X 800 mm in size) that were processed continuously or intermittently over a period of 8 hours. The developer was supplied with 720 ml of the second replenisher every two hours after the commencement of the development, whereas 25.5 ml of the first replenisher was supplied at processing of each plate. Again, all the PS plates were developed to equal extent.

Claims (14)

1. A method of developing imagewise exposed positive-acting photosensitive lithographic printing plate material, wherein plates are developed in an aqueous alkaline developing solution and to maintain the activity of developer constant during development, a first replenisher having a higher alkalinity than that of said alkaline developer is added to said developer at each processing of a plate of said photosensitive material and a second replenisher having a higher alkalinity than that of said developer is added to said developer either continuously in a predetermined amount or at a predetermined interval in a predetermined amount.

2. A method according to Claim 1, wherein the photosensitive material has a photosensitive layer containing an o-quinone diazide compound coated on an aluminium support, and each of said replenishers is an aqueous solution of an alkali metal or ammonium silicate having an alkalinity higher than that of said developer.

3. A method as claimed in Claim 2, wherein each of said developers, said first replenishers and said second replenisher contains at least 20% of potassium based on the gram-atoms of all the alkali metal (and ammonium) present.

4. A method according to Claim 3, wherein said content of potassium is 30 to 80%.

5. A method according to Claim 3 or 4, wherein said developer is an aqueous solution of an alkali metal silicate which has an [ SiO2 ] / [ M# ratio of from 0.5 to 0.75, wherein [ SiO2 ] represents the concentration of SiO2 in a unit volume as expressed in gram-molecules, and EMI represents the concentration of an alkali metal in a unit volume as expressed in gram-atoms and has an SiO2 concentration of from 1 to 4 wt% based on the total weight of the aqueous solution, and each of said first and second replenishers is an aqueous solution of an alkali metal silicate having said [SiO2][M] ratio from 0.25 to 0.75.

6. A method according to any preceding claim, wherein said first replenisher is added to said developer in a predetermined amount proportional to the length of one side of the plate of photosensitive material to be processed.

7. A method according to any preceding claim, wherein said development is performed in an automatic developing machine.

8. A method according to Claims 6 and 7, wherein said first replenisher is added to said developer in a predetermined amount proportional to the length in the travelling direction of the plate of photosensitive material processed by the automatic developing machine.

9. A method according to any preceding claim, wherein said first replenisher is supplied at each processing of said positive-acting photosensitive lithographic printing plate precursor in an amount expressed by the following equation (I) or (II): can + afln XL XL L (I) ELn c;Wn + aXTn XS us (li) "Sn wherein EWn is the total weight of the photosensitive layers of n positive-acting photosensitive lithographic printing plates within a given period of time; c is a proportional factor determined by the type of the plate and the formulation of the first replenisher; ETn is the total operating hours of the spray required for processing the n positive-acting plates; a is a proportional factor determined by the type of the automatic developing machine, the formulation of the first replenisher, and the concentration of carbon dioxide gas in the atmosphere where the developing machine is installed; FLn is the total length of said n positive-acting plates in the direction in which they run in said developing machine; XSn is the total area of said n positiveacting plates; L is the length of one positive-acting photosensitive lithographic printing plate in said running direction, and S is the area of one positive-acting plate.

10. A method according to Claim 9, wherein said first replenisher is supplied at each processing of said positive-acting photosensitive lithographic printing plate in an amount expressed by the following equation (I') or (II'): c#Wn XL+aT (I') Ln c#Wn XS+aT XS S + aT (11') Sn wherein EWn, c, ELn, a, T.Sn, L and S each have the same meaning as defined in the equations (I) and (II), and T is the time for which the spray is operated during the processing of one positive-acting photosensitive lithographic printing plate material.

11. A method according to Claim 7 or 8, wherein said development is performed by an automatic developing machine comprising means for transporting the exposed photosensitive lithographic printing plate material, a nozzle pipe through which the developer is sprayed onto the photosensitive layer of the photosensitive lithographic printing plate material being transported by said transport means, a developing tank and means for supplying the developer from said developing tank to said nozzle pipe, and said first replenisher is supplied in two separate amounts, (a) an amount proportional to the length of said imagewise exposed plate in the direction in which it is moved by said transport means or proportional to the area of said plate, and (b) an amount proportional to the time during which said developer is sprayed through said nozzle pipe.

12. A method as claimed in Claim 11, wherein said machine is substantially as shown in the accompanying drawing.

13. A method of developing as claimed in Claim 1, substantially as hereinbefore described with reference to any of the Examples.

14. Lithographic printing plate material when processed by a method as claimed in any preceding claim.