JPH06241996A - Method for detecting concentration of developer and developing device - Google Patents

Abstract

PURPOSE:To provide the title method and device always accurately detecting the concentration of the developer to keep in a fixed concentration range, and making high-grade developing possible without exchanging a developer even in the developing of many sheets over a long term, about the developing device for exchanging an electrostatic latent image on the photoconductive layer of a form plate into a visible toner image by the developer, after charging with electricity and exposing an electrophotographic surface printing plate providing the photoconductive layer on a conductive backing. CONSTITUTION:A light emitting element 20a and photodetector 20b are disposed facing each other in a developer. A pulse of an infrared LED is modulated and it is emitted by the light emitting element 20a, the transmitted light through the developer is received by the photodetector 20b, and the photocurrent output is made to correspond to the solid part concentration of the developer, and the concentration measurement and control of a developer toner are carried out. By this method, a gap between the light emitting element and photodetector can be spread out.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an electrostatic latent image on a printing plate photoconductive layer formed by a liquid developer after charging and exposing an electrophotographic lithographic printing plate having a photoconductive layer on a conductive support. A method for detecting a density in a liquid developer that converts a visible toner image,
And a developing device accompanied by a liquid developer concentration control unit including a liquid developer concentration measuring unit, wherein the concentration of the liquid developer is always accurately detected and is maintained in a constant concentration range, and it is possible to develop a large number of sheets over a long period of time. Even in this case, the present invention relates to a method for detecting the concentration of a liquid developer and a developing device that enable high-quality development without liquid exchange.

[0002]

2. Description of the Related Art A method of developing an electrostatic latent image formed by imagewise exposing an electrophotographic photosensitive material provided with a photoconductive layer on a conductive support and developing the latent image is roughly classified into dry type and wet type. Be divided. Wet development methods include electrophoresis, chargeless development, conductive ink development, selective wet development,
And the mist developing method, etc., but the most commonly used method is the electrophoresis method. As the wet developer, that is, a liquid developer, a dispersion of electrically charged toner particles in an insulating dispersion medium is used. Generally, the development obtained by the wet development method has a higher resolution and a better gradation reproducibility than the dry development. This is because the particle size of the toner is small, the amount of charge is large, and the conductive ions in the liquid reduce the edge effect, and the counter electrode can be made closer than in the dry method. It is considered as a factor.

In wet development (electrophoresis), charged toner particles are electrophoresed by an electric field formed between an electrostatic latent image on a surface to be developed and a developing electrode, and are attached to the electrostatic latent image to be visualized. It The image quality of the visible image obtained by developing in this way, particularly the image density of the visible image, decreases as the development proceeds, the concentration of toner particles in the liquid developer, which substantially contributes to the development, decreases. To fall. Therefore, conventionally, in order to maintain good image quality, the concentration of toner particles in the developer is optically detected, and when the concentration of toner particles is lowered, a replenisher is replenished to obtain a good development image. (Hereinafter, it is referred to as an appropriate concentration range).

The optical toner particle concentration is detected by arranging a light emitting element and a light receiving element in a liquid developer so as to face each other, receiving light from the light emitting element by the light receiving element, and transmitting the amount of transmitted light. The toner particle concentration in the liquid developer is detected by associating with the toner particle concentration. As the light emitting element, a tungsten lamp, a semiconductor laser, and an L are conventionally used.
ED and the like are known as light receiving elements such as photodiodes, phototransistors, CdS photoconductive cells, and Si photocells. And the wavelength of light used for concentration detection is
A wavelength which is not so far from the maximum absorption wavelength in the visible region of the liquid developer is used.

However, in the above-mentioned optical density detection method, the surface in contact with the liquid developer on the light path between the light emitting element and the light receiving element (hereinafter referred to as the surface of the detecting portion) after long-term use or when the liquid is replaced. Contamination occurs due to the adherence of toner particles to the liquid developer), and foreign matter in the liquid developer may be caught due to the narrow space between the light emitting element and the light receiving element. When such a situation occurs, the amount of transmitted light changes, and the toner particle concentration obtained from the amount of transmitted light differs from the actual toner particle concentration. There is a problem that the toner particle concentration of the agent deviates from the proper concentration range and a good image product cannot be obtained.

The influence of contamination on the surface of the detecting portion can be reduced by widening the gap between the light emitting element and the light receiving element to increase the optical path length in the liquid developer. The longer the optical path length, the lower the possibility that foreign matter will be caught and the greater the attenuation of the transmitted light by the liquid developer, but the attenuation by dirt will not change, so the above-mentioned effect can be reduced. However, in general, a liquid developer in an appropriate concentration range has a low equivalent transmittance, so that the amount of transmitted light is greatly attenuated. Therefore, in order to increase the optical path length in the liquid developer, it is necessary to increase the output of the light emitting element. On the other hand, when the output of the light emitting element is increased, the heat of light emitted from the light emitting element makes it easier for the toner particles to adhere to the surface of the detection portion of the light emitting element, resulting in a substantial decrease in the amount of light emission.

Therefore, the following method has been proposed as a measure against the above problem. In other words, (1) a method of suppressing toner sticking by forming a detection portion surface with a molded article of a plastic composition containing a substance having a low surface energy, as disclosed in JP-A-55-27350. . (2) Toner concentration is determined by freely discharging a liquid developer in air in the form of a liquid layer as disclosed in JP-A-56-82437 and measuring the light transmittance and capacitance of the liquid layer. How to improve detection accuracy. According to this, since the surface of the detection unit and the liquid developer are held in non-contact with each other, the surface of the detection unit is not contaminated. (3) As disclosed in JP-A-3-83074, a low-volatile silicone oil is mixed with a conventionally known petroleum-based aliphatic hydrocarbon as a dispersion medium of a liquid developer, and the light-emitting element receives light during liquid exchange. A method for suppressing liquid developer sticking to the gap (about 0.5 mm to 1.0 mm) between elements. In addition, (4)
Japanese Patent Laid-Open No. 293070/1992 proposes a method of widening the gap between the light emitting element and the light receiving element at the time of non-detection of density to remove dust and sludge-like toner.

However, in the case of (1), it is possible to suppress the fixation of toner particles at the time of exchanging the developing solution or in the developing solution, but a substance having an extremely low surface energy such as fluororesin is opaque or translucent. If the transparency of the plastic composition is low, the optical path length in the developing solution must be shortened in order to improve the detection sensitivity as described above, and foreign matter is easily caught. On the other hand, when used in combination with another highly transparent plastic in order to improve the transparency of the plastic composition, the surface tension is also increased accordingly, so that there is a limit to the effect of suppressing contamination.

Further, in (2), the capacitance measurement is for calculating the liquid layer thickness and correcting the light transmittance, and it is necessary to perform the light transmittance measurement and the capacitance measurement at the same site. The device becomes complicated. Furthermore, not only the vibration of the device but also the liquidity (viscosity) and flow rate of the developer fluctuate, so that the liquid layer (film thickness) at the measurement site easily fluctuates, and it is considerably difficult to perform highly accurate measurement. It was

In the case of (3), the drying and solidification of the toner at the time of liquid exchange can be suppressed, but the problem that foreign matter in the developer is caught in the gap on the transmitted light path cannot be solved. Furthermore, if contamination occurs on the surface of the detection portion, the optical path length in the developing solution is short, so that the effect on the developing solution concentration becomes large. In the last (4), when the apparatus is stopped, the gap is widened and foreign matters caught therein are removed, but the prevention of the foreign matter caught during the development and the malfunction due to it is still unsolved.

[0011]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to charge and expose an electrophotographic lithographic printing plate having a photoconductive layer on a conductive support and then charge the liquid on the printing plate photoconductive layer with a liquid developer. A method for detecting a density in a liquid developer for converting an electrostatic latent image into a visible toner image, and a developing device accompanied by a liquid developer density control unit including a density measuring unit for the liquid developer. Provided is a method for detecting the concentration of a liquid developer and a developing device, which are always detected with high precision and are kept in a constant concentration range, and which enable high-quality development without changing the liquid even when developing a large number of sheets over a long period of time. It is to be.

[0012]

Means for Solving the Problems The present invention has been earnestly studied in order to achieve the above object, and as a result, a liquid developer was obtained after charging and exposing an electrophotographic lithographic printing plate having a photoconductive layer provided on a conductive support. A method for detecting the density in a liquid developer that converts an electrostatic latent image on a photoconductive layer of a printing plate into a visible toner image by developing the transmitted light intensity between a light emitting element and a light receiving element installed in the liquid developer. In a method of detecting the concentration of a liquid developer by an optical detection method corresponding to the concentration of solid content of a developer, the concentration of the liquid developer is detected by a light receiving element by emitting light from the light emitting element by pulse modulation of an infrared LED. Achieved by the method.

Further, a developing device equipped with a mechanism embodying the present method, which is a liquid developer developing mechanism for supplying and developing a liquid developer for circulation and reuse to a developing means, infrared LED
Optical liquid developer concentration measuring means by pulse-modulated luminescence and the measured liquid developer concentration are compared with the desired setting range, and the liquid developer replenisher is replenished in the circulating reuse liquid developer to obtain the desired value. The above object has been achieved by developing using a developing device having a liquid developer concentration control means which is maintained in a set range.

First, an optical liquid developer concentration measuring mechanism by pulse-modulated light emission of an infrared LED and a concentration measuring method thereof relating to the liquid developer concentration detecting method of the present method will be described in detail. The optical liquid developer concentration measuring means according to the present invention and the measured liquid developer concentration are compared with a predetermined setting range, and the recycle liquid developer is replenished with a replenishing solution and kept in the predetermined setting range. FIG. 1 shows a basic structure of a toner developing section of an electrophotographic printing plate making machine equipped with a liquid developer concentration control means for controlling the electrophotographic printing plate. The optical liquid developer concentration measuring means comprises a detecting section 20 and an instrument section 21, and the liquid developer concentration controlling means comprises a comparator 30, a pump drive circuit 31, and a replenishment supply pump 71 in addition to the measuring means.

As shown in FIG. 2, the detecting section 20 constituting the liquid developer concentration measuring means is composed of a light emitting element 20a and a light receiving element 20b which are a pair of elements facing each other.
It is installed inside. An infrared emitting LED is used for light emission according to the present invention. The instrument unit 21 includes a pulse oscillator 22 and an amplifier 2 for pulse-driving the light emitting element as shown in FIG.
3 and an AC amplifier 24, a detector 25, and a DC amplifier 26 for converting the signal from the light receiving element into a photocurrent output. The light emitting element 20a is configured to emit light after being pulse-modulated by transmitting a signal from a pulse oscillator in the instrument section 21 through an amplifier.

Light reception in the detection unit according to the present invention is carried out in synchronization with the light which is pulse-modulated and emitted, but it is also possible to receive light without being synchronized. In general, pulse-modulated light emission can increase the light intensity, reduce the influence of incident light from the outside that is not related to light emission, and significantly improve the S / N ratio. Therefore, the gap (optical path length) of the detection unit can be made sufficiently wider than in the conventional case, and even if foreign matter is mixed in the liquid developer, the drop in detection accuracy is significantly suppressed.

By setting the emission wavelength to the infrared wavelength, absorption of a dye component existing in the liquid developer which does not contribute to development (usually in the visible region) is not affected. When the dye is slightly soluble in the dispersion medium of the liquid developer, the dye component that does not contribute to the development gradually accumulates as the development is repeated, and contributes to the development when light is emitted and received in the visible region where the dye is absorbed. Not strongly affected by dye components. The use of infrared light does not cause the above problem. There is also an effect that the distance between the light emitting element and the light receiving element can be expanded as compared with the case of using visible light.

The gap between the light-receiving element and the light-receiving element depends on the optical density of the dye in the emission wavelength range of the liquid developer, but is sufficiently larger than the size of foreign matter that may be generated in the liquid developer. In the meantime, the liquid developer flows sufficiently,
It is desirable that the distance is such that the cooling effect for suppressing the fixation of the toner particles due to the uniformization of the liquid components and the heat generation of the element due to the light emission is sufficiently exhibited. The gap between the elements according to the present invention is preferably 2 mm or more, more preferably 5 to 80 mm.
However, it is more preferably 10 to 50 mm.

Further, it is desirable that the light emitting element and the light receiving element are coated with a low surface energy substance in order to suppress the fixation of the toner particles. As described above, even if the low surface energy substance is opaque or semi-transparent, the light intensity and the amount of transmitted light of the light emitting device according to the present invention are large, so that measurement can be performed without narrowing the gap between the devices. . Suitable materials for coating the light emitting element and the light receiving element used in the detecting section according to the present invention are ester resin, silicone resin, fluororesin, polyethylene, polypropylene and the like, and among these, particularly preferable ones are silicone resin and fluororesin. It is a resin. In order to ensure the transparency of the coating material, it is preferable to make the coating thickness thinner than mixing a material having high transparency but not low surface energy with these materials.

In light emission and light reception by pulse modulation according to the present invention, the duty ratio expressed by pulse width / pulse period is important. In other words, a larger duty ratio means a longer lighting time, and the light intensity per emission generally decreases. Therefore, it is difficult to widen the gap between the light emitting element and the light receiving element and to maintain the measurement accuracy together. become. On the other hand, when the duty ratio becomes small, the responsiveness deteriorates. The duty ratio in the pulse modulation according to the present invention is preferably 1/2 to 1/100, more preferably 1/5 to 1 /
A range of 20 is preferably used. The pulse current is generally 0.1 mA to 100 mA, though it depends on the duty ratio.
It is carried out in the following range, and 0.5 mA to 10 mA is preferably used.

Next, the liquid developer in the concentration detecting method according to the present invention will be described. The liquid developer according to the present invention is obtained by dispersing toner particles, which are substantially a developed image and have an electric charge, in a highly insulating hydrocarbon medium. The highly insulating hydrocarbon medium in which the toner particles are dispersed is an organic solvent having a low dielectric constant and high electrical insulation, and for example, n-paraffin hydrocarbon, isoparaffin hydrocarbon, aliphatic hydrocarbon, aromatic hydrocarbon, Examples thereof include halogen-based aliphatic hydrocarbons and silicone oils, but isoparaffin-based hydrocarbons are preferably used. Although the characteristics of the isoparaffin hydrocarbons are slightly different depending on the fraction, for example, Shell Sol 71 (manufactured by Shell Petroleum), Isopar G, Isopar H,
Isopar K, Isopar L (above, manufactured by Esso Petroleum), IP solvent (made by Idemitsu Petroleum) and the like are preferably used.

The toner in the liquid developer according to the present invention has good fixability to at least the photoconductive layer of the electrophotographic lithographic printing plate by heat and / or light, and further has a photoconductive layer in the non-image area. It is composed of a resin component having a resist property with respect to a treatment liquid (so-called eluate) for removing. Examples of the resin component include methacrylic acid, acrylic acid, and acrylic resins composed of esters thereof, vinyl acetate resins, copolymers of vinyl acetate and ethylene or vinyl chloride, vinylidene chloride resins, vinyl chloride resins, polyvinyl butyral, etc. Vinyl acetal resin, polystyrene, styrene and butadiene, styrene and acrylic resin, copolymers of methacrylic acid ester and the like, polyethylene, polypropylene and its chlorides, polyester resin such as polyethylene terephthalate, polyamide resin, phenol resin, xylene resin, Examples thereof include alkyd resins, vinyl-modified alkyd resins, and other waxes.

A method for producing toner particles is disclosed in Japanese Patent Application Laid-Open No. Sho 5
9-83174, 59-177,57, 59-
No. 212850, No. 59-212851, No. 60-1
No. 64757, No. 60-179751, No. 60-18
As described in JP-A-5962 and JP-A-60-185963, in the presence of a polymer soluble in the above-mentioned highly insulating medium by the so-called dispersion polymerization method, the polymer soluble in the medium but Those obtained by polymerizing monomers that become insoluble when formed are preferably used. Also, JP-A-62-231266
No. 62-231267, No. 62-232660.
No. 63-178258 and No. 63-17936.
The liquid developers described in Japanese Patent No. 8 and the like can also be preferably used. These liquid developers are excellent in industrial production stability and dispersion stability.

The toner particles in the liquid developer according to the present invention can be colored with a colorant within a range that does not impair the particle dispersion stability and the charge stability over time. The colorant is
What is generally known as a colorant for wet developers can be used, for example, oil-soluble dyes such as oil black and oil red, basic azo dyes such as Bismarck brown and chrysoidine, wool black, amido black green,
Acid azo dyes such as blue black HF, direct day black E, direct dyes such as Congo red, anthraquinone dyes such as Sudan violet and assid blue,
Examples thereof include carbonium dyes such as auramine, malachite green, crystal violet and Victoria blue, rhodamine dyes such as Rhodan B, and quinoneimine dyes such as safranine, nigrosine and methylene blue.

As a method for coloring the dispersed resin particles, there is a method in which the colorant to be used is dissolved in advance in a solvent that dissolves it, and this colorant solution is dropped into the dispersed resin particle liquid and stirred. In particular, the oil dye can be preferably colored by dissolving it in an aromatic solvent such as toluene or xylene and stirring with dropping. At that time, it is desirable that the solvent that dissolves the colorant is miscible with, for example, an isoparaffin hydrocarbon solvent used as the medium. Further, as a solvent for dissolving the dye, it is desirable to use a solvent having a relatively insulating property and a high boiling point. As an example, when an oil-soluble dye is used, if xylene or the like is used in a small amount in the case of an aromatic hydrocarbon, Even without removing the solvent, it is possible to produce a liquid developer for electrophotography that can be sufficiently used. Therefore, when a dye having a relatively large solubility in an organic solvent such as an oil-soluble dye is used, it is necessary to remove the solvent after coloring the dispersed resin particles if the amount of the solvent that dissolves the dye is reduced. Disappears.

The liquid developer according to the present invention can produce a toner having a positive charge property or a negative charge property by selecting a charge control agent and a dye for dyeing. Examples of the charge control agent of the liquid developer according to the present invention include cobalt octanoate, copper oleate, aluminum stearate, zinc naphthenate, cobalt naphthenate, manganese naphthenate, lecithin, sodium dioctylsulfosuccinate, and steberite rosin. Aluminum salts and the like, Japanese Patent Publication Nos. 49-26594 and 49-26595, and JP-A-60-173558 and 60-17.
No. 5060, No. 60-179750, No. 60-182
No. 447, No. 60-218662, No. 61-2788.
No. 67, No. 62-30260, No. 62-34170.
And the charge control agents described in JP-A-63-124056 and the like can be used, and a toner having a positive charge property can be produced by using them.

Similarly, to produce a toner having a negative charge, a monomer soluble in the medium and having a base (for example, a copolymer of lauryl methacrylate and N, N-dimethylaminoethyl methacrylate) is used. Acids insoluble in the medium, such as pyromellitic acid, trimellitic acid, trimesic acid, and benzoic acid, can be used in combination, but are not limited thereto. In any case, at least in the wavelength region of pulse-modulated light according to the present invention, the toner particles in the produced liquid developer are more than the toner dispersion medium and the liquid developer composition other than the toner particles such as the dissolved product thereof. Also, it should have strong absorption.

As described above, it is possible to widen the gap between the light emitting element and the light receiving element which constitute the detecting section and improve the emission intensity by emitting infrared light by modulating the light emitting element. When the optical density of the liquid developer is measured by the density detecting method of the present invention, the influence of the incident light from the outside which is not related to the light emission in the detecting portion can be reduced, and the S / N ratio can be greatly improved. . Further, even if foreign matter is mixed in the liquid developer, the drop in detection accuracy is significantly suppressed, and the concentration of the liquid developer can always be detected accurately over a long period of time.

The developing device for developing the electrophotographic lithographic printing plate having the optical liquid developer concentration measuring means, which can make the most suitable use of the liquid developer concentration detecting method, with the liquid developer will be described in detail. FIG. 1 shows a schematic view of the developing device according to the present invention. The developing device according to the present invention includes a liquid developer developing mechanism for supplying a liquid developer to be recycled and used for developing to a developing means, and an optical liquid developing by pulse-modulated light emission of an infrared LED according to the density detecting method of the present invention. Liquid developer concentration measured by the agent concentration measuring means and the measured liquid developer concentration is compared with the predetermined setting range, and the liquid developer replenisher is replenished in the circulating reuse liquid developer to maintain it in the predetermined setting range. It consists of control means.

The liquid developer developing mechanism in the developing device according to the present invention further includes a developing electrode portion 14 and a liquid developer 2 in which the electrophotographic lithographic printing plate 1 is disposed so as to oppose the transport plane.
For storing liquid developer, a liquid developer supply pump 72 for supplying the liquid developer 2 in the liquid storage tank 12 to the developing electrode section 14, and a liquid developer squeezing means for removing excess solvent after development. It consists of 13. The electrophotographic lithographic printing plate 1 which is charged and exposed by a charging device and an exposure device (not shown) and provided with an electrostatic latent image like an image is carried between the developing electrodes filled with the liquid developer 2 by a conveying means (not shown). It is supposed to be done.

The developing electrode 14 used in the present invention is composed of an upper developing electrode 14a arranged above the conveying plane of the electrophotographic lithographic printing plate 1 and a lower developing guide plate 14b arranged below the conveying plane. It is configured. At least the upper developing electrode 14a is partially or entirely formed of a conductor to which a bias voltage of 0 to 300 V can be applied, and the charged toner particles in the liquid developer 2 filled between the upper developing electrode 14a and the printing plate 1 are charged. Is electrophoresed by an electric field formed by the bias potential of the developing electrode and the surface potential of the electrostatic latent image on the plate surface, and imagewise adheres to the plate surface. Upper developing electrode 14
The arrangement of a and the lower guide plate 14b is set so that the distance between the upper developing electrode and the plate surface is kept constant. The distance between the upper developing electrode and the plate surface is preferably 0.05 to 10 mm, more preferably 0.1 to 2.5 mm.

The liquid developer 2 supplied into the developing electrode section 14 is developed under the developing electrode and the toner particles are consumed. On the other hand, in the printing plate 1 which has been developed and carried out from the developing electrode portion 14, the excess liquid developer 2 remaining on the plate is removed by the liquid developer squeezing means 13. The removed liquid developer 2 is once collected in the tray 17 and then returned to the liquid developer storage tank 12, and is circulated for reuse.

In the liquid developer storage tank 12, there is provided a detecting section 20 which constitutes an optical liquid developer concentration measuring means. The photocurrent obtained by the detector light-receiving element 20b is converted into a voltage corresponding to a predetermined proper concentration range by the comparator 30 after the photocurrent output is obtained by the AC amplification, detection, and DC amplification in the instrument unit 21. It is designed to be compared with the threshold value. The photocurrent output obtained by the optical liquid developer concentration measuring means increases as the amount of transmitted light increases as the concentration decreases. Now, it is appropriate to define a pre-verified limit range of the image quality of the liquid developer according to the present invention in the initial charging liquid due to the fluctuation of the developer concentration as a threshold value in the developer concentration. The threshold value on the low density side of the density range is the upper limit value of the photocurrent output voltage value.

In the comparator 30, the measured photocurrent output voltage value is compared with the upper limit value and the lower limit value of the voltage value corresponding to the predetermined proper concentration range threshold value. . Then, when the measured photocurrent output voltage value is higher than the upper limit value (that is, low concentration), the pump drive circuit 31 is operated to operate the replenisher solution supply pump 71 to operate the replenisher solution 3 with the liquid developer. The liquid is supplied to the liquid storage tank 12. In addition, the measured photocurrent output is the comparator 3
When it is compared by 0 and is below the lower limit value, the replenisher supply pump 71 is stopped by the control of the pump drive circuit 31.

As the replenisher 3 according to the present invention, a solid content concentrate of an unused liquid developer is preferably used, and more preferably a concentrate having a solid content concentration of 10 to 20 times. Also,
The amount of the charge control agent contained in the replenisher does not have to be the same concentration ratio as the solid content concentration.
% To 80% is more preferably used. In the liquid developer storage tank 12, when a replenisher 3 is supplied, a circulation pump and a circulation pump are provided to promote mixing and diffusion of the liquid developer 2 and the concentrated replenisher 3 in the liquid developer storage tank 12. Forced mixing and stirring means such as stirring blades may be provided.

When the developing device having the optical liquid developer concentration measuring means constructed as described above is used for developing an electrophotographic lithographic printing plate, the infrared LED emits light by pulse modulation, so that heat is generated in the light emitting portion. A high output can be obtained without toner adhesion, the gap between the light emitting element and the light receiving element can be widened, and abnormal density detection due to foreign matter being caught can be prevented. Even if dirt adheres to the surface of the detection unit, the effect of dirt is suppressed because the optical path length of the transmitted light in the liquid developer is long, and even if a large number of sheets are developed over a long period of time,
The toner concentration in the liquid developer can be detected stably. In addition, the surface of the detection unit can be easily cleaned even when the liquid is replaced. The effect of widening the gap and the effect of preventing toner sticking due to heat generation on the surface of the detection portion can be achieved by pulse-modulated light emission.

The present invention is most preferably used for the development of an elution type electrophotographic lithographic printing plate, in which the non-image area is removed by an elution solution after toner development. In the elution type electrophotographic lithographic printing plate, the toner particles after development and fixing act as a resist against the elution liquid, so the effect as a resist varies slightly depending on the toner adhesion state, and as a result, the quality of the printing plate after elution Have a significant impact on. When printing is performed with a lithographic printing plate obtained by developing the electrophotographic lithographic printing plate in a state where the toner concentration is not appropriate, line thinning occurs, printing durability deteriorates and printing stains occur. Therefore,
In developing an elution type electrophotographic lithographic printing plate, it is particularly important to control the toner concentration, and by performing development using the developing device of the present invention, a lithographic printing plate free from the above troubles can be obtained. You can

Finally, the electrophotographic lithographic printing plate and the method for producing the same according to the present invention will be described. The electrophotographic lithographic printing plate according to the present invention has a photoconductive layer provided on a conductive support and can form a toner image by a usual electrophotographic development method. As the electroconductive support used in the electrophotographic lithographic printing plate, a plastic sheet having an electroconductive surface, paper having solvent impermeability and electroconductivity, or aluminum, zinc, copper-aluminum, copper-stainless steel, chromium -Conductivity based on a metal plate such as bimetal such as copper, chrome-copper-aluminum, trimetal such as chrome-lead-iron, chrome-copper-stainless, etc., and at least the photoconductive layer forming surface being hydrophilically treated. A support is mentioned. The thickness of these is preferably 0.07 to 2 mm, more preferably 0.1 to 0.5 mm. Among these substrates, the aluminum plate is preferably used. This aluminum plate may contain aluminum as a main component and a slight amount of a foreign element, and conventionally known and officially used materials can be appropriately used.

In order to form a desired surface property on the surface of the support on which the photoconductive layer is provided, graining or anodic oxidation may be performed by a known method. Prior to the graining treatment, a degreasing treatment with a surfactant or an alkaline aqueous solution may be carried out, if desired.
The graining treatment method includes a mechanical surface roughening method, an electrochemical surface roughening method, and a chemical surface selective dissolution method. As the mechanical surface roughening method, known methods such as a ball polishing method, a brush polishing method, a blast polishing method and a buff polishing method can be used.
The electrochemical graining method includes a method of performing alternating current or direct current in a hydrochloric acid or nitric acid electrolytic solution. Further, as disclosed in Japanese Patent Application Laid-Open No. 54-63902, a method of combining the two can be used. The substrate thus roughened is
If necessary, alkali etching treatment and neutralization treatment are performed before use.

The substrate that has been subjected to the above treatment is anodized to form an oxide film on its surface. As the electrolyte used for the anodizing treatment, sulfuric acid, phosphoric acid, oxalic acid or the like, or a mixed acid thereof or the like is used, and the concentration thereof is appropriately determined depending on the kind of the electrolyte. The anodizing condition cannot be unconditionally specified because it varies greatly depending on the electrolyte used, but the amount of anodizing film is preferably 0.10 to 10 g / m ² , more preferably 1.0 to 6.0 g / m ^2. Is preferred.

A desired electrophotographic photoconductive layer is provided on the electroconductive support thus obtained to obtain an electrophotographic lithographic printing plate. The photoconductive layer of the electrophotographic lithographic printing plate according to the present invention contains at least a photoconductive compound, and known photoconductive compounds exemplified below can be used. a) Triazole derivatives described in U.S. Pat. No. 3,112,197, etc., b) Oxadiazole derivatives described in U.S. Pat. No. 3,189,447, etc., and c) JP-B-37-16096. Imidazole derivatives described in publications, etc. d) US Pat. Nos. 3,542,544 and 3,615,40
2, No. 3,820,989, Japanese Patent Publication No. 45-55
5, 51-10983, and JP-A-51-93224.
No. 55-108667, No. 55-156953.
And polyarylalkane derivatives described in JP-A-56-36656, e) US Pat. Nos. 3,180,729 and 4,278,74
6, JP-A-55-88064, JP-A-55-88
065, 49-105537, 55-5108.
No. 6, No. 56-80051, No. 56-88141,
Pyrazoline derivatives and pyrazolone derivatives described in JP-A-57-45545, f) US Pat. No. 3,615,404, JP-B-46
-3712, 47-28336, JP-A-54-8
No. 3435, No. 54-110836, No. 54-119
Phenylenediamine derivatives described in Japanese Patent No. 925, etc., g) US Pat. Nos. 3,567,450 and 3,180,70
No. 3, No. 3,240,597, No. 3,658,520,
4,232,103, 4,175,961, 4,
012,376, West German Patent (DAS) 1,11
0,518, Japanese Patent Publication No. 49-35702, 39-2
7577, JP-A-55-144250 and JP-A-56-1.
19132 and 56-22437, etc., h) Amino-substituted chalcone derivatives described in U.S. Pat. No. 3,526,501, i) U.S. Pat. No. 3,542,546 Described N, N-
Bicarbazyl derivative, j) Oxazole derivative described in US Pat. No. 3,257,203, k) Styrylanthracene derivative described in JP-A-56-46234, l) JP-A-54-110837, etc. The fluorenone derivative described in m. U.S. Pat. No. 3,717,462, JP-A-54
-59143 (corresponding to U.S. Pat. No. 4,150,987), No. 55-52063, No. 55-52064.
No. 55, No. 55-46760, No. 55-85495, No. 57-11350, No. 57-104144, No. 57.
Hydrazone derivatives described in JP-A-148749, n) U.S. Pat. Nos. 4,047,948 and 4,047,94
No. 9, No. 4,265,990, No. 4,273,846,
Benzidine derivatives described in JP-A Nos. 4,299,897 and 4,306,008, etc., o) JP-A-58-190953 and 59-95540.
No. 59-97148, 59-195658,
Stilbene derivatives described in JP-B No. 62-36674, p) Polyvinylcarbazole and derivatives thereof described in JP-B-34-10966, and q) Polyvinyl compounds described in JP-B-43-18674 and 43-19192. Vinyl polymers such as bilene, polyvinyl anthracene, poly-2-vinyl-4- (4'-dimethylaminophenyl) -5-phenyloxazole and poly-3-vinyl-N-ethylcarbazole, r) JP-B-43-19193 Polymers such as polyacenaphthylene, polyindene, and acenaphthylene / styrene copolymers described in JP-B No. 56-13940, and the like.
Condensation resins such as formaldehyde resin and ethylcarbazole / formaldehyde resin, t) JP-A-56-90883 and 56-161550.
Various triphenylmethane polymers described in Japanese Patent Publication No. 1989, u) U.S. Pat. Nos. 3,397,086 and 4,666,80
No. 2, Japanese Patent Publication No. 49-4338, No. 49-17535
JP-A-64-2061, JP-A 64-4389, JP-A 1-144057, 1-153757, and 1
-217362, 1-221459, 1-25
2967, 1-285952, 1-312255.
No. 1, No. 2-8256, No. 2-16570, etc., and metal-free or metal phthalocyanines and naphthalocyanines, and derivatives thereof.

The photoconductive compound used in the electrophotographic lithographic printing plate according to the present invention is not limited to the compounds listed in a) to u), and the photoconductive compounds known so far and, if desired, two or more kinds may be used. Can be used as a mixture, but a metal-free or metal phthalocyanine pigment having photoconductivity is advantageously used in the electroconductive planographic printing plate photoconductive layer used in the present invention.

As the metal phthalocyanine, the central metal of the phthalocyanine ring is lithium, beryllium, sodium, magnesium, aluminum, potassium, calcium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, molybdenum, ruthenium,
Rhodium, palladium, silver, cadmium, indium,
Tin, antimony, barium, hafnium, osmium,
Platinum, mercury, lead, and the like, and complex salts in which oxygen or halogen is axially coordinated to these metals are known, and metal-free phthalocyanines are those in which those metals are replaced by hydrogen. In addition, for the purpose of improving electrophotographic properties and dispersibility, the hydrogen of the benzene ring in the phthalocyanine molecule is halogen, cyano group, nitro group, carboxyl group, sulfonic acid group, alkoxy group, alkylamino group, alkylamide group, substituted Alternatively, a derivative substituted with an unsubstituted aliphatic or aromatic group is also known. Furthermore, the presence of various different crystal forms is known by measuring the X-ray crystal diffraction of these phthalocyanines.

The photoconductive layer in the electrophotographic lithographic printing plate used in the present invention includes, among them, α type, β type, γ type,
Metal-free phthalocyanines such as π-type, τ-type, χ-type, and ε-type, copper phthalocyanine such as α-type, β-type, γ-type, ε-type, and η-type, titanyl phthalocyanine such as α-type and β-type, and halogeno A metal phthalocyanine such as aluminum phthalocyanine is preferable, and a χ-type metal-free phthalocyanine having excellent photosensitivity even in a long wavelength region corresponding to a light source such as a He-Ne laser and a semiconductor laser, and titanyl phthalocyanine are further preferable. .

A binder resin is used in combination with the photoconductive layer of the electrophotographic lithographic printing plate used in the present invention to improve the film-forming property and the adhesion to the support. When used as a printing plate, it is necessary to finally remove the photoconductive layer other than the image area. This step depends on the relative relationship between the solubility of the photoconductive layer in the eluate and the resist property of the toner in the eluate. Although it cannot be unconditionally expressed because it is determined, the binder resin is preferably a polymer compound that is soluble or dispersible in the eluate described below. In addition, all the reagents that can be used in the charge holding layer can be used as the binder resin for the photoconductive layer. Even when the charge retention layer and the photoconductive layer are composed of the same type of reagent, the molecular weight, the acid value, etc. may be appropriately changed and used.

The mixing ratio of the photoconductive compound and the binder resin in the photoconductive layer of the electrophotographic lithographic printing plate used in the present invention is
It may be determined so as to satisfy various characteristics such as desired electrophotographic characteristics and plate-making characteristics, but generally, when the content of the photoconductive compound is small, the sensitivity becomes low. It is preferable to use a mixture of 5 parts by weight or more, more preferably 15 parts by weight or more. However, since dispersibility, coating liquid stability, liquid properties such as coating properties and further improvement of electrophotographic properties cannot be expected, etc.,
Usually, it is not desirable to use more than 40 parts by weight. If the thickness of the photoconductive layer is thin, the electric charge necessary for toner development cannot be charged and induces a cover due to leakage. Conversely, if it is thick, it not only accelerates the deterioration of the eluate but also induces side etching during elution. Since good image reproducibility cannot be obtained, 0.10 to 30 μm
However, it is more preferably 0.50 to 10 μm, further preferably 1.5 to 6.0 μm.

The electrophotographic lithographic printing plate according to the present invention can be obtained by coating a photoconductive layer on a conductive support according to a conventional method. In producing the photoconductive layer, a method of containing the components constituting the photoconductive layer in the same layer, or a method of separately containing two or more layers, for example, the lower layer (support side) is easy to dissolve, A method in which a strongly adhesive binder resin is placed and a resin having good chargeability and ink acceptability is placed in the upper layer, or the content of the photoconductive compound is increased, etc., and the layers are separated into different layers, etc. Are known and can be produced by any method. The coating liquid is prepared by dissolving and dispersing each component constituting the photoconductive layer in a suitable solvent, but when the photoconductive compound uses a component insoluble in the solvent such as phthalocyanine, a ball mill, a dynomill, an atom. Using a lighter, paint shaker, or other disperser, the average particle size is 0.4 μm or less,
More preferably, it is dispersed in a particle size of 0.2 μm or less before use. In addition to the photoconductive compound and the binder resin, if necessary, the photoconductive layer may include a plasticizer, a surfactant, and other plasticizers in order to improve film properties such as flexibility of the photoconductive layer and coating surface state. Additives can be added. The additives used in the photoconductive layer can be added during or after the dispersion of the photoconductive compound.

The coating solution thus prepared is spin coated,
An electrophotographic lithographic printing plate can be obtained by coating and drying on a conductive support by a known method such as blade coating, knife coating, reverse roll coating, dip coating, rod bar coating, spray coating, extrusion coating. As the solvent for the coating liquid, various solvents described above as the solvent for the charge retention layer can be used. Further, the concentration (or viscosity) of the coating liquid and the mixing ratio of the solvent are appropriately selected depending on the coating method and the drying device.
In the drying of the photoconductive layer-forming coating liquid, the electrophotographic characteristics may be deteriorated particularly due to the drying conditions (temperature and air volume) in the initial drying zone, and therefore it is preferable to set mild drying conditions.

The electrophotographic lithographic printing plate according to the present invention can form a toner image by a known operation. That is, charging is performed substantially uniformly in a dark place, an electrostatic latent image is formed by imagewise exposure, and then toner development is performed.
Examples of the exposure method include reflection image exposure using a xenon lamp, tungsten lamp, fluorescent lamp, or the like as a light source, contact exposure through a transparent positive film, and scanning exposure with laser light, a light emitting diode, or the like. The light source in the scanning exposure is He-Ne laser, argon ion laser, krypton ion laser, ruby laser, YAG laser, nitrogen laser, dye laser, excimer laser, GaAs /
Laser light sources such as semiconductor lasers such as GaAlAs and InGaAsP can be used, or scanning exposure using light emitting diodes and liquid crystal shutters (including line printer type light sources using light emitting diode arrays, liquid crystal shutter arrays, etc.) Is also good.

In the electrophotographic lithographic printing plate on which the toner development has been completed, at least the non-image area photoconductive layer is eluted and removed with an alkaline elution solution in the elution section. The eluent used for elution of the electrophotographic lithographic printing plate according to the present invention is preferably an aqueous solution containing an alkaline agent and having a buffering capacity near the liquid pH after the preparation of the eluate. The alkali agent to be contained is an inorganic material such as a silicate represented by the general formula SiO ₂ / M ₂ O (M represents an alkali metal atom), an alkali metal hydroxide, an alkali metal such as phosphoric acid or carbonic acid, and an ammonium salt. Alkaline agents, ethanolamines, ethylenediamine, propanediamines, triethylenetetramine,
Organic alkaline agents such as morpholine, and mixtures thereof can be used, but in particular, the above silicates are advantageously used because they show appropriate alkaline strength and strong buffering capacity at high pH.

In the above silicate-based eluate, it is desirable to further add an appropriate amount of alkali metal hydroxide to adjust it to a desired pH range. The final molar ratio of the total amount of alkali metal oxides (M ₂ O) to silicic acid (SiO ₂ ) in the eluate is Si.
The range of O ₂ / M ₂ O = 1 to 2.6 is preferable, and further 1.3 to 2.
2 is preferred. In addition, the concentration of the alkaline agent in the eluate is one of the main factors that determine the elution rate, and its concentration ranges from 1 to
The range of 10% by weight, more preferably 2 to 8% by weight,
It is more preferably 3 to 5% by weight. The pH of the eluate is
12.0 to 13.5, and more preferably 12.3 to 13.0.

The printing plate from which at least the non-image area photoconductive layer has been eluted and removed is then rinsed to remove the solubilized photoconductive layer component remaining on the plate by rinsing the plate surface. The rinse liquid used for the rinse is adjusted so that the eluent soluble resin used in the electrophotographic lithographic printing plate precursor according to the present invention does not reaggregate. That is, unless the initial pH of the rinse liquid promotes the insolubilization of the resin to a minimum, the resin flowing in together with the eluate is kept in the solubilized state, and therefore the trouble due to the reinsolubilization of the resin can be prevented. However, on the contrary, if the pH of the rinse liquid is high, not only the elution effect is exhibited and the side etching is deteriorated, but also a slight amount of the rinse liquid flows into the protective gum liquid for the plate surface protective treatment which is usually performed thereafter. The pH of the rinse liquid inevitably rises at an early stage and the plate surface protection effect is also attenuated.

The printing plate whose plate surface has been rinsed by the rinsing treatment is subjected to a protective gum treatment for the purpose of improving scratch resistance of the plate surface and desensitizing the non-image area. The protective gum solution that can be used in the present invention, other than hydrophilic polymer compounds such as gum arabic, organic and inorganic acids, acidic buffers, lipophilic substances,
Alternatively, known agents can be used for all these agents including a surfactant and the like.

[0054]

EXAMPLES The present invention will be described in more detail with reference to the accompanying drawings, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

FIG. 1 is a schematic view showing an example of a toner developing unit in a wet developing type electrophotographic lithographic printing plate making machine equipped with a liquid concentration toner concentration detecting apparatus according to the present invention. A liquid developer used for this toner development was prepared as follows.

(Synthesis of Emulsion) n-Hexyl methacrylate / methacrylic acid (monomer weight ratio 95/5) was polymerized by a known solution polymerization method to obtain a 40% xylene solution of the copolymer. 30 g of this solution was added to 1 L of hexane to obtain a copolymer precipitate as a slurry. n-
The slurry decanted with hexane several times,
1L equipped with nitrogen gas inlet tube, thermometer, stirrer, cooling tube
Into a 4-necked flask of No. 4, 450 g of IP solvent (manufactured by Idemitsu Petrochemical Co., Ltd.) was added.

Next, 130 g of vinyl acetate and 30 g of lauryl methacrylate were added and well stirred to obtain a uniform transparent solution. After purging with nitrogen gas at 80 ° C., 1 azobisisobutyronitrile (AIBN) was used as a polymerization initiator.
g was added to start the polymerization, and the inside was distilled under reduced pressure to remove the remaining vinyl acetate monomer. The resulting white emulsion had no precipitate and almost no monomer odor. When the particle size was measured with an electron microscope, it was 0.20 μm, and the particle size was extremely uniform.

(Production of Positively Charged Liquid Developer) 2 g of oil black HBB (manufactured by Orient Chemical Co.) dissolved in 20 g of xylene was dropped into 70 g of the emulsion obtained above while irradiating with ultrasonic waves. , The emulsion particles were colored. Next, 0.6 g of a 1% xylene solution of steberite resin salt was added as a charge control agent to obtain a conc (concentrated) toner. This contact toner was diluted with Isopar G to a total amount of 10 L to obtain a positively charged liquid developer.

(Preparation of original plate for electrophotographic planographic printing) JIS
1050 aluminum (0.3mm thickness) at 60 ℃, 10%
It was dipped in a sodium hydroxide aqueous solution and etched so that the amount of aluminum dissolved was 6 g / m ² . 30% after washing with water
It was immersed in a nitric acid aqueous solution for 1 minute for neutralization, and then thoroughly washed with water. Next, electrolytic surface roughening was performed in a 3% hydrochloric acid aqueous solution at 35 A / dm ² for 50 seconds, and the surface was washed by immersing the surface in a 20% sulfuric acid aqueous solution at 50 ° C., followed by washing with water. Furthermore, an anodizing treatment was performed in a 20% aqueous solution of sulfuric acid to form an oxide film on the surface, followed by washing with water and drying to prepare a printing plate support. On the surface-treated surface of the support, a photoconductive layer-forming coating liquid described in Table 1 dispersed for 1 hour with a paint shaker was applied at a solid content of 4.2 g / m ² and then at 90 ° C. After drying for 3 minutes, an electrophotographic lithographic printing plate was obtained.

[0060]

[Table 1]

The obtained electrophotographic lithographic printing plate was printed at 398 mm
It was cut into × 560 mm, shielded from light and heated at 50 ° C. for 2 hours, and then allowed to cool to room temperature. The surface potential of this is about +2 in the dark.
Charged to 80V, semiconductor laser (780nm)
Scanning image exposure was carried out using, and immediately in the toner developing section shown in FIG. 1, reversal development was carried out as follows using the liquid developer prepared as described above.

Electrophotographic planographic printing 1 on which an electrostatic latent image is formed
Is transported into the developing electrode section 14 by a transport device (not shown) that transports the plate at a constant speed in the direction indicated by the arrow.
The liquid developer 2 is supplied into the developing electrode portion 14 by the liquid developer supply pump 72, and the liquid developer 2 is filled between the upper developing electrode 14 a and the printing plate 1 conveyed into the developing electrode portion 14. A voltage of 180 V is applied to the upper developing electrode 14a, and an electric field formed by the upper developing electrode 14a and the electrostatic latent image on the plate surface forms an uncharged portion (that is, a laser exposure portion) of the electrostatic latent image on the plate surface. The positively chargeable toner in the liquid developer 2 adheres. In this way, reversal development was performed.

Excess liquid on the plate surface of the plate 1 developed by the developing electrode section is removed by the squeeze roll 13, then dried by cold air, and then heat-fixed by an infrared lamp in a fixing section (not shown). The photoconductive layer in the non-image area was removed by alkali elution in the elution section (not shown). After that, it was gummed to make a lithographic printing plate.

As described above, 2000 per month
Plate making was performed. Meanwhile, the liquid developer 2 in the liquid developer storage tank 12 is supplied to the developing electrode portion 14 by the liquid developer supply pump 72, is provided for development, and is then removed from the plate surface by the squeeze roll 13 to receive the tray 17 The liquid was recovered in the above step and returned to the liquid developer storage tank 12 again and circulated for reuse.

During that time, the liquid developer concentration control means was kept operating at all times. That is, the infrared LED continues to emit pulsed light with a duty ratio of 1/9 from the light emitting element 20a of the detection unit 20, and the photocurrent from the light receiving element 20b is compared with the comparator 30.
Thus, the comparison with the upper limit value and the lower limit value of the voltage value corresponding to the threshold value in the proper concentration range was continuously performed. As the development is repeated, the toner concentration in the liquid developer 2 becomes thin, and when the photocurrent value in the light receiving element 20b reaches the low concentration side threshold value in the proper concentration range, the replenisher liquid supply pump drive circuit 31.
As a result, the replenisher supply pump 71 was operated, and the replenisher 3 was supplied into the liquid developer storage tank 12. When the photocurrent output value from the light receiving element drops due to the supply of the replenishing liquid and reaches the high concentration side threshold value in the proper concentration range, the replenishing liquid supply pump 71 is controlled by the comparator 30 and the pump drive circuit 31.
Stopped.

The light emitting element 20a and the light receiving element 20b of the detecting portion of the liquid developer concentration measuring means are separated from the liquid developer by the coating material 20c. The coating material 20c was made of FEP resin (tetrafluoroethylene-6-fluorinated propylene copolymer resin), and no stain was observed on the surface of the detection portion even after the 2000 plate-making. Further, the light emitting element 20a and the light receiving element 20b are arranged at a distance of 3 cm. 200
No troubles such as malfunctions due to the entrapment of foreign matter were found in the 0th edition.

As the replenisher, a solution having a solid content concentration of 10 times that of the initially charged liquid developer and a charge control agent concentration of 5.5 times that of the initially charged liquid developer were used. The amount of replenisher replenished per plate was 5 cc / plate on average. The number of plate making was 200 when it was large and 0 when it was small.

As a result of carrying out plate making for 2000 plates for one month, clear plate-making images having good image density, reproducibility of halftone dots and fine lines were obtained over 2000 plates.

[0069]

As described above, by pulse-modulating the light emitting element to emit light, it is possible to widen the gap between the light emitting element and the light receiving element constituting the detection section and to improve the emission intensity. If the optical density of the liquid developer is measured by the density detecting method of No. 3, the influence of the incident light from the outside which is not related to the light emission in the detecting portion is reduced, and the S / N ratio is reduced.
The ratio can be greatly improved. Further, even if foreign matter is mixed in the liquid developer, the drop in detection accuracy is significantly suppressed, and the concentration of the liquid developer can always be detected accurately over a long period of time.

Further, by developing with the developing device equipped with the density measuring means and the density control means embodying the density detecting method of the present invention, even if a large number of sheets are developed over a long period without changing the liquid, it is always good. The developed image can be maintained.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of a toner developing unit of an electrophotographic lithographic printing plate making machine according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a configuration of a detection unit of the liquid developer concentration detection means according to the exemplary embodiment of the present invention.

FIG. 3 is a functional block diagram of the inside of the instrument portion of the liquid developer concentration detecting means according to the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrophotographic lithographic printing plate 2 Liquid developer 3 Replenisher 13 Liquid developer squeezing means 14 Development electrode 20 Liquid developer concentration detecting means detecting section 20a Light emitting element 20b Light receiving element 20c Coating material 21 Liquid developer concentration detecting means Instrument section 22 Pulse Oscillator 23 Amplifier 30 Comparator 31 Pump Drive Circuit 71 Replenisher Liquid Supply Pump 72 Liquid Developer Supply Pump 73 Liquid Circulation Pump

Claims (2)

[Claims] 1. An electrostatic latent image on a photoconductive layer of a printing plate is converted into a visible toner image by a liquid developer after charging and exposing an electrophotographic lithographic printing plate having a photoconductive layer provided on a conductive support. A method for detecting the concentration of a liquid developer, which is an optical detection method in which the intensity of transmitted light between a light emitting element and a light receiving element installed in the liquid developer is made to correspond to the solid concentration of the developer. A method for detecting the concentration of a liquid developer, characterized in that light emission from the light emitting element is performed by pulse modulation of an infrared LED. 2. A wet electrophotographic developing device for developing an electrophotographic lithographic printing plate, which has been charged and exposed on a photoconductive layer to form an electrostatic latent image like an image, with a liquid developer, the developing device comprising: A liquid developer developing mechanism for supplying and developing a liquid developer to be recycled and reused, an optical liquid developer concentration measuring means by pulse modulation emission of an infrared LED, and a measured liquid developer concentration in a predetermined setting range. In comparison with the above, the developing device is provided with a liquid developer concentration control means for replenishing the liquid developer replenisher in the circulating reuse liquid developer and holding the liquid developer replenisher in a predetermined setting area.