JPH08262811A - Controlling method of concentration of liquid developer for developing device of electrophotographic planographic printing plate - Google Patents

Abstract

PURPOSE: To always obtain a good developing state just after the electric power is turned on by detecting the concn. of a liquid developer at the time when the power is turned off and controlling the developer in such a manned that if the detected concn. is lower than the threshold of the higher concn. side in the preliminarily determined initial concn. range, the concn. of the liquid developer is increased to the threshold of the higher concn. side of the determined initial concn. range. CONSTITUTION: Light beams from a light emitting element 20a of an optical detecting means 20 for the concn. of a liquid developer is transmitted through the liquid developer 2 and received by a light receiving element 20b. The light receiving element 20b generates a photocurrent according to the intensity of the transmitted light, which is then sent as the photocurrent output to a comparator 30. The photocurrent output is compared with the upper and lower limits of the photocurrent output corresponding to the preliminarily determined threshold of the proper concn. range in the comparator 30. If the detected photocurrent output is higher than the upper limit, a pump driving circuit 31 is operated to operate a supply pump 71 for a replenisher to supply a replenisher 3 to a liquid developer reservoir 12. If the detected current is lower than the lower limit, the pump 71 is stopped.

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. The present invention relates to a liquid developer concentration control method for an electrophotographic lithographic printing plate development processing apparatus which converts a toner image.

[0002]

2. Description of the Related Art Many methods for producing a lithographic printing plate are already known. For example, a printing original plate is brought into close contact with an original made of a silver salt film, and the photosensitive layer of the original plate is directly exposed to ultraviolet rays or the like,
This is a plate making method in which a cured portion corresponding to the image portion of the original and a non-cured portion corresponding to the non-image portion are formed, the non-cured portion is washed and removed with alkali or water, and the cured portion is made ink-receptive. . The printing plate produced by this method is called P
It is called S version and is widely used.

On the other hand, due to advances in computer image processing technology, memory development of large-capacity data, and data communication technology, etc., in recent years, a computer is consistently operated from original input, correction, editing, layout to page setting, and a high-speed communication network. An electronic editing system that can immediately output to a terminal plotter in a remote place by satellite communication has been put to practical use. In particular, in the field of newspaper printing where immediacy is required, not only electronic editing systems but plate making systems that can directly obtain printing plates from data from the electronic editing systems are being put to practical use. Currently, in such a plate-making system, a system using a laser light source (semiconductor laser, He-Ne laser, etc.) exposure utilizing an electrophotographic process is being studied from various aspects.

In such a system, an elution type electrophotographic lithographic printing plate as described below can be printed under the same printing conditions as the PS plate used conventionally, which is advantageous. Can be used for As the main plate making process, the electrophotographic lithographic printing plate is charged, exposed, and toner-developed to form an image, and the non-image part where the toner particles are not adhered is eluted and removed by an eluent, and the support is preliminarily hydrophilized. The body surface is exposed to make a printing plate. Here, since the image portion protected by the toner particles is lipophilic, offset printing can be performed.

The electrophotographic lithographic printing plate is prepared from an electrophotographic photosensitive member having a photoconductive layer containing a photoconductive substance coated on a conductive support such as aluminum. As a material forming the photoconductive layer of the electrophotographic photosensitive member, an organic photoconductive compound / binder resin material is excellent in practical sensitivity and printing durability.

In the plate making process of the electrophotographic lithographic printing plate,
On the photoconductive layer of the electrophotographic photosensitive member, a predetermined charging process is first performed to apply a uniform charge. The exposure then forms an electrostatic latent image corresponding to the image. Subsequently, toner development and fixing processing are performed using an electrophotographic developer, and a toner image corresponding to the electrostatic latent image is formed.
The non-image area other than the toner image is eluted and removed by a solution containing an alkaline agent, etc., followed by washing with water or adjusting the apparent pH of the plate surface with an acidic rinse, and if necessary, a plate surface protective solution ( A final printing plate is obtained by applying a treatment such as coating with a protective gum solution).

A development processing device (or a development processing section) for performing a development process for converting an electrostatic latent image into a toner image using a liquid developer includes a development electrode, a liquid developer supply port, a liquid developer squeezing means, It is composed of a plate conveying means, a liquid developer circulating system and the like. The developing electrode is used when an electrophotographic planographic printing plate (hereinafter also simply referred to as a printing plate) on which an electrostatic latent image is formed enters.
It is installed so that it faces the surface of the electrostatic latent image of the printing plate with a gap. On the other hand, the liquid developer is stored in the liquid developer storage tank and is piped from the liquid developer storage tank to the liquid developer supply port of the developing electrode section, and the circulation pump installed in the middle is operated. Thus, the liquid developer is supplied to the developing electrode section. The liquid developer supplied to the developing electrode section fills the gap between the printing plate and the developing electrode, and the toner of the electrostatic latent image on the printing plate is developed. After the printing plate has passed through the developing electrode, the excess liquid developer on the printing plate is removed by the liquid developer squeezing means. The removed liquid developer is collected by the tray installed under the developing electrode section and is collected again in the liquid developer storage tank. As the liquid developer squeezing unit, a squeezing liquid formed by a pair of rubber rolls is used.

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

If the toner particle density of the liquid developer exceeds the threshold value on the high density side of the proper density range and becomes high,
There is a risk of non-image areas such as fog and halftone dot clogging, and when the thickness becomes thinner than the threshold value on the low density side, it continues after the development processing area due to insufficient adhesion of toner particles to the image area. The eluate cannot be sufficiently resisted in the elution part, resulting in insufficient density in the image part. In any case, when printing is performed using the printing plate, the printed matter suffers from a defect such as a non-image area covering or a blank area in the image area, which significantly deteriorates the print quality. I will end up. Therefore, in such an elution type electrophotographic lithographic printing plate, it is particularly important to control the toner particle concentration of the liquid developer in the developing section within an appropriate range.

There are various means for detecting the concentration of the liquid developer depending on the physical quantity of interest, and an optical detecting method for detecting the concentration by the amount of transmitted light in the liquid (for example, Japanese Patent Laid-Open No. 56-
No. 167162), a method of detecting the concentration by the capacitance of a parallel plate capacitor in liquid (Japanese Patent Laid-Open No. 5-188).
No. 785), a method in which a specific gravity detector is provided in the liquid to detect the concentration based on the specific gravity of the liquid (JP-A-55-147650), and a method in which the electrical conductivity is measured and correlated with the toner particle concentration.

In the optical detection method, a light emitting element and a light receiving element are arranged in a liquid developer so as to face each other, light from the light emitting element is received by the light receiving element, and the amount of transmitted light and the toner particle concentration are detected. By making it correspond, the toner particle concentration in the liquid developer is detected. A tungsten lamp, a semiconductor laser, an LED and the like are conventionally known as the light emitting element, and a photodiode, a phototransistor, a CdS photoconductive cell, a Si photocell and the like are known as the light receiving element. The optical detection method is an excellent liquid developer concentration detection method capable of simply and accurately detecting the toner particle concentration.

By the way, in general, the density detecting means as described above does not always provide a stable and proper output immediately after the power is turned on. Therefore, the density detecting means itself may be warmed up to some extent. It is desirable to do it.
Therefore, there is a possibility that proper concentration control of the liquid developer by the concentration detection means cannot be expected for a certain period after the power is turned on. Also, the temperature of the liquid developer itself is often in a relatively low state immediately after the power is turned on immediately after the power is turned on and during the steady plate making work thereafter, and the physical quantity to be the target of the concentration detection means has temperature dependence. If there is any, or if a part or all of the concentration detecting means is adversely affected by the temperature of the liquid, the normal concentration cannot be detected for a while immediately after the power is turned on.

For example, in the case where the density detecting means detects a density higher than the actual liquid developer density until the warming up is completed, if a large number of plates are made immediately after the power is turned on, the liquid is Although the toner particles in the developer are being consumed, the actual liquid developer concentration may exceed the low concentration side threshold value of the proper concentration range even if the output of the concentration detecting means is within the proper concentration range. Often, the image quality is deteriorated due to insufficient image density.

Further, even when the warming-up time of the concentration detecting means itself is sufficiently short and there is no problem, when the liquid temperature of the liquid developer itself is lower than the liquid temperature at the time of steady use immediately after the power is turned on, There is a risk that the developing ability of the liquid developer itself may be reduced. Further, when the concentration detecting means has a liquid temperature dependency, the actual developing ability of the liquid developer is deteriorated immediately after the power is turned on even if the output from the concentration detecting means is within the proper concentration range. There are many cases. In such a case, similarly to the above, when a large number of continuous plate making is performed immediately after the power is turned on, the same quality deterioration as described above may occur.

Particularly when the density detecting means having a light emitting element and a light receiving element is used as the density detecting means, the toner particle density of the liquid developer is accurately detected and stable density control is enabled, but the light emitting element is used. The light-receiving element usually has temperature dependency, and when performing continuous plate making immediately after power-on, quality deterioration such as insufficient image density as described above often occurs.

[0016]

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. Regarding a liquid developer concentration control method for an electrophotographic lithographic printing plate development processing apparatus for converting an electrostatic latent image into a toner image,
It is an object of the present invention to provide a liquid developer concentration control method for an electrophotographic lithographic printing plate development processing apparatus, which can always obtain a good development state immediately after power-on.

[0017]

The above object can be achieved by the following liquid developer concentration control method. That is, electrophotographic lithographic printing in which an electrostatic latent image on the printing plate photoconductive layer is converted into a toner image by a liquid developer after charging and exposing the electrophotographic lithographic printing plate having a photoconductive layer on a conductive support. A liquid developer concentration control method for detecting a liquid developer concentration using a concentration detection means of a plate development processing device to maintain the liquid developer concentration within a predetermined set concentration range. When the power supply is turned off, the liquid developer concentration is detected, and if the liquid developer concentration is lower than the preset threshold on the high concentration side of the preset concentration range, the liquid developer concentration is set to the desired value. This was achieved by increasing the set concentration on the high concentration side of the set concentration range and then turning off the power supply.

The above method is extremely effective when the concentration detecting means is an optical detecting means having a light emitting element and a light receiving element.

[0019]

In the present invention, the electrostatic latent image on the printing plate photoconductive layer is tonered by the liquid developer after charging and exposing the electrophotographic lithographic printing plate having the photoconductive layer on the conductive support. In the electrophotographic lithographic printing plate development processing apparatus for converting into an image, in the liquid developer concentration control method for detecting the liquid developer concentration using the concentration detection means and keeping the liquid developer concentration within a predetermined set concentration range, When the power of the electrophotographic lithographic printing plate development processing device is turned off, the concentration of the liquid developer is detected, and when the concentration of the liquid developer is lower than the set threshold value on the high side of the intended set concentration range, , When the power of the electrophotographic lithographic printing plate development processing device is turned on next time, by turning off the power supply after raising the liquid developer concentration to the set threshold value on the high concentration side of the intended set concentration range, Even if a large number of continuous plates were made immediately after, No decrease in the quality of the insufficient density, etc., is always good development state obtained immediately after the power is turned on. Moreover, it can be performed by a simple method without adding equipment such as temperature control and temperature compensation.

Further, in the above method, when the density detecting means is an optical detecting means having a light emitting element and a light receiving element, it is possible to more effectively and stably maintain a good developing state.

The present invention will be described in more detail. First, an electrostatic latent image on the printing plate photoconductive layer is charged with a liquid developer after charging and exposing an electrophotographic planographic printing plate (hereinafter also simply referred to as a printing plate) having a photoconductive layer provided on a conductive support. An electrophotographic lithographic printing plate development processing apparatus (hereinafter, also simply referred to as a development processing unit) for converting toner into a toner image will be described.

The development processing section is provided with a liquid developer supply port for discharging the liquid developer and a development electrode, which is partially or entirely opposed to the electrostatic latent image surface of the printing plate with a predetermined gap. , Liquid developer squeezing means, liquid developer storage tank, and the like.

The printing plate passes by a conveying means with a predetermined gap from the developing electrode. At this time, the liquid developer is supplied and filled in the gap between the printing plate and the developing electrode. The liquid developer is stored in the liquid developer storage tank,
The liquid developer storage tank and the liquid developer supply port are connected by a pipe, and a circulation pump for supplying the liquid developer is installed in the middle of the pipe. Just before the plate making starts and the printing plate carrying the electrostatic latent image enters the developing electrode section, the circulation pump for supplying the liquid developer starts to operate, and when the printing plate faces the developing electrode, A sufficient amount of liquid developer for toner development is supplied to the gap between the printing plate and the developing electrode. A bias voltage can be applied to the developing electrode. Due to the electric field created by the potential of the developing electrode and the electrostatic latent image on the printing plate, the charged toner particles in the liquid developer in the gap cause electrostatic charge on the printing plate. An electrostatic latent image is attached imagewise to the latent image surface, and toner development is performed. Excess liquid developer on the printing plate is removed from the printing plate by the liquid developer squeezing means provided immediately after the developing electrode.

The liquid developer is supplied from the liquid developer storage tank to the gap between the developing electrode and the printing plate passing therethrough by a circulation pump, and then removed from the printing plate by the liquid developer squeezing means. The liquid is collected in a tray provided under the developing electrode section and then collected again in the liquid developer storage tank, forming one circulation system. When plate making is continuously performed, the circulation pump for supplying the liquid developer continues to operate, and the liquid developer is circulated for use.

A liquid developer concentration detecting means is provided in the liquid developer storage tank or in the middle of the pipe of the liquid developer circulation system so that the concentration of the liquid developer can be detected. Accordingly, it is possible to control the concentration of the liquid developer within an appropriate range where good development is performed.
Further, in addition to the above position, the concentration detecting means can be installed in any place where the liquid developer can be sufficiently exchanged.

The liquid developer concentration control method according to the present invention will be described below. The liquid developer concentration control method according to the present invention detects the toner particle concentration of the liquid developer by using the concentration detecting means, and when the concentration of the liquid developer is lowered, the liquid developer is replenished with a replenisher. By doing so, the concentration of the liquid developer is always maintained within an appropriate concentration range.

As the concentration detecting means according to the present invention, any means can be used as long as it can detect the toner particle concentration of the liquid developer. For example, it is possible to use an optical detecting means having a light emitting element and a light receiving element, an electric conductivity measuring means for applying an AC or DC voltage, or a means utilizing electrodeposition. In each means, the physical quantity of the liquid developer to be detected is different. For example, when an optical detection means is used, the toner particle concentration (solid (Concentration) can be the object of detection, and in the case of conductivity measurement, the electrical characteristics of the liquid developer are the object of detection.
In any case, if the physical quantity to be detected by the detecting means has a correlation with the toner particle concentration of the liquid developer, the detecting means can be used. Since the toner particle concentration has a good correlation with the degree of the actual developing ability, the actual developing state can be stably maintained by controlling the toner particle concentration within the proper concentration range. The degree of developing ability can be determined by the image density (optical reflection density) of the solid image area (solid area) when toner development is actually performed. In particular, the optical detecting means can detect the toner particle concentration with high accuracy, and thus is preferably used.

In order to perform the density control by detecting the density by the density detecting means, the proper density range for properly performing the toner development is determined in advance. Based on the appropriate concentration range, a high concentration side threshold (high concentration side setting threshold) and a low concentration side threshold (low concentration side setting threshold) are set, and the liquid developer concentration is set between the two setting thresholds. Set the concentration control range to maintain (desired concentration range). When the concentration of the liquid developer falls below the set threshold value on the low concentration side of the desired set concentration range, the liquid developer is replenished with a replenisher to bring the liquid developer back within the desired set concentration range. As the replenisher, a concentrated liquid developer or a liquid in which the ratio of constituent components of the liquid developer is changed is used. or,
It is also possible to replenish a plurality of replenishers by using a plurality of concentration detecting means.

As a method of replenishing the replenisher, it is possible to use a method of performing replenishment while continuously or intermittently detecting the concentration and performing replenishment until the set threshold value on the high concentration side is reached. At this time, if it takes time after the replenisher is replenished until the concentration detecting means detects an increase in the liquid developer concentration due to the replenisher, the replenisher is intermittently replenished or agitated. It is also possible to accelerate the homogenization of the liquid developer concentration by feeding or liquid.

Further, the replenishment solution replenishment can be controlled by time without using the set threshold value on the high concentration side of the intended set concentration range. That is, as a result of performing the concentration detection, when the liquid developer concentration decreases to the set threshold value on the low concentration side of the intended set concentration range, replenisher replenishment is continuously or intermittently replenished for a certain period of time. is there. Even in this case, if the replenishment time of the replenisher is set so that the concentration of the liquid developer falls within an appropriate concentration range as a result of the replenishment, the concentration of the liquid developer at the end of the replenishment is defined in the present invention. It corresponds to the setting threshold on the high density side of the desired density setting range.

The liquid developer concentration control in the development processing section during the plate making process is performed as described above, but when the plate making process is completed and the electrophotographic lithographic printing plate development processing apparatus is powered off, the following process is performed. Density control is performed. That is, when the power-off operation of the electrophotographic lithographic printing plate development processing apparatus is performed,
Immediately, the power is not shut off, the replenisher is replenished to the liquid developer, and the power is shut off after the liquid developer concentration is increased to the set threshold on the high concentration side of the intended set concentration range. Be seen. This replenishment solution replenishment is performed by detecting the concentration when the power is turned off, and even if it is not less than the set threshold value on the low concentration side of the preset set concentration range If it is a concentration, it is done.

The toner development according to the present invention may be either normal development or reversal development. In particular, in the case of reversal development, it is more important to control the concentration of the liquid developer for the following reasons. Therefore, the present invention is particularly effective in the case of reversal development. That is, when performing toner development by reversal development, a bias voltage having the same polarity as the electric charge of toner particles and a lower absolute value than the charging potential (surface potential) of the non-image area of the printing plate is usually applied to the developing electrode. However, when developing a solid image portion, charged toner particles may move toward and adhere to the printing plate by the force of an electric field formed by applying a bias voltage on the surface of the printing plate having a surface potential of about 0V. Becomes According to the reversal development, a high quality image can be obtained in a short development time by selecting an appropriate bias voltage.
At this time, the developing speed or the image density of the solid image portion after development largely depends on the density of the liquid developer, particularly the toner particle density. That is, when the toner particle concentration decreases, the number of toner particles reaching and adhering to the surface of the printing plate decreases within a certain developing time, so that the image density of the solid image portion decreases. On the other hand, when the solid image portion is developed by the positive development, the solid image portion is a portion which retains an electric charge and substantially has a surface potential on the surface of the printing plate by the positive development. Since the development proceeds in such a manner that the toner particles of No. 2 neutralize the charge on the surface of the printing plate, the number of toner particles necessary for neutralization does not change even if the concentration of toner particles in the liquid developer slightly changes. In many cases, the influence of the toner particle concentration is not so strong as the above-mentioned reversal development. Therefore,
Particularly in the case of reversal development, concentration control of the liquid developer becomes more important.

The liquid developer according to the present invention will be described below. 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 characteristics of isoparaffinic hydrocarbons are slightly different depending on fractions, for example, Shell Sol 71 (made by Shell Petroleum), Isopar G, Isopar H, and Isopar L
(Above, manufactured by Exxon Chemical), IP Solvent 1620
(Made by Idemitsu Petroleum) and the like are preferably used.

The toner particles in the liquid developer according to the present invention have good fixability to at least the photoconductive layer of the electrophotographic lithographic printing plate by heat and / or light, and further have a photoconductive property in the non-image area. It is preferably composed of a resin component having a resist property with respect to the eluent for removing the layer. As the resin component, methacrylic acid, acrylic acid, and acrylic resins composed of esters thereof, vinyl acetate resins, copolymers of vinyl acetate with 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 with methacrylic acid ester, polyethylene, polypropylene and its chlorides, polyester resin such as polyethylene terephthalate, polyamide resin, phenol resin,
Examples thereof include xylene resin, alkyd resin, vinyl-modified alkyd resin, and other waxes.

Next, the electrophotographic lithographic printing plate relating to the present invention and the processing method after toner development thereof will be described.
The electrophotographic lithographic printing plate according to the present invention comprises a photoconductive layer provided on a support, and the support is a metal support known to form a desired surface property on the support surface provided with the photoconductive layer. Graining or anodic oxidation may be performed by the method. If desired, prior to the graining treatment, a degreasing treatment may be carried out with a surfactant or an aqueous alkaline solution.

A desired electrophotographic photoconductive layer is provided on the support thus obtained to obtain an electrophotographic lithographic printing plate. In the electrophotographic photoconductive layer, an organic or inorganic photoconductive compound can be used, and if desired, a mixture of two or more of these can be used. In the electrophotographic lithographic printing plate photoconductive layer used in the present invention. Among them, organic photoconductive compounds are preferable, and among them, metal-free or metal phthalocyanine pigments having photoconductivity are advantageously used. As the binder resin for the photoconductive layer,
In the case of a printing plate that finally elutes and removes the photoconductive layer other than the image area, a polymer compound that is soluble or dispersible in the eluate is preferable.

The electrophotographic lithographic printing plate is subjected to toner development and fixing of the electrostatic latent image using a liquid developer by the electrophotographic method as described above to convert the electrostatic latent image into a toner image, which is then subjected to alkaline elution at the elution portion. The non-image area photoconductive layer is eluted and removed by the liquid. Next, the plate surface is rinsed to wash and remove the solubilized photoconductive layer components remaining on the plate, and then, for the purpose of improving scratch resistance of the plate surface and desensitizing non-image areas, lithographic printing The plate is completed.

[0038]

The present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited thereby.

First, a plate making machine including the electrophotographic lithographic printing plate development processing apparatus used in this embodiment will be described.
The plate-making machine used consisted of a plate feeding section, charging / exposure section, development processing section (development processing unit), elution section, and plate ejection section. It is designed to be fed to the next charging / exposure unit one by one. In the charging / exposure section, the surface of the electrophotographic lithographic printing plate is subjected to corona charging to form a surface potential of about 220 V, and then image exposure is performed using a semiconductor laser. The electrophotographic lithographic printing plate on which an electrostatic latent image has been formed by imagewise exposure is sent to the next development processing section for toner development, and then the non-image area is eluted and removed at the elution section to form a lithographic printing plate. A series of processes such as discharging to the plate discharging section is continuously performed.

Next, the development processing apparatus (development processing section) of the plate making machine used in this embodiment will be described with reference to FIG. The development processing section includes a development electrode section 14 including a development electrode 14a and a lower guide plate 14b, a liquid developer squeezing means 13, a liquid developer discharge port 80, a liquid developer storage tank 12, a replenisher storage tank. 16 is installed, the liquid developer storage tank 12 is connected to the liquid developer discharge port 80 by a pipe 74, and a liquid developer supply pump 72 is installed in the middle of the pipe to store liquid in the liquid developer storage tank 12. The liquid developer 2 being discharged is discharged from the liquid developer discharge port 80.
Through the developing electrode 14a and the lower guide plate 14b (developing electrode portion 14). Further, the replenisher storage tank 16 is connected to the liquid developer storage tank 12 by a pipe 75, and the replenisher 3 in the replenisher storage tank 16 is sent to the liquid developer storage tank 12 along the way. Replenisher supply pump 7
1 is installed.

There is a tray 17 at the bottom of the development processing section.
The liquid collected in the saucer flows along the pipe 76 under the saucer 17 and flows into the liquid developer storage tank 12. In this way, by operating the liquid developer supply pump 72, the liquid developer storage tank 12 and the developing electrode portion 14 are circulated and used.

In the liquid developer storage tank 12, an optical liquid developer concentration detecting means 20 is arranged. The optical liquid developer concentration detecting means 20 has a light emitting element 20a and a light receiving element 20b, and the light from the light emitting element 20a emits light to the liquid developer 2
The light passes through the inside and is received by the light receiving element 20b. Light receiving element 2
At 0b, a photocurrent corresponding to the amount of transmitted light is generated, and the photocurrent output is sent from the optical liquid developer concentration detecting means 20 to the comparator 30. The comparator 30 is configured to compare with a set threshold value corresponding to a predetermined proper density range. The photocurrent output obtained by the optical liquid developer concentration detecting means 20 increases as the amount of transmitted light increases as the concentration of the liquid developer 2 decreases. So, for example,
The set threshold value on the low concentration side of the proper concentration range of the liquid developer is the upper limit value for the photocurrent output.

In the comparator 30, the detected photocurrent output value is compared with the upper limit value and the lower limit value of the photocurrent output value corresponding to the preset threshold value of the proper concentration range. There is. Then, when the detected photocurrent output value is equal to or higher than the upper limit value (that is, the liquid developer concentration is equal to or lower than the set threshold value on the low concentration side of the predetermined set concentration range), the pump drive circuit 31 is operated to supply the replenisher. The pump 71 is operated to supply the replenisher 3 to the liquid developer storage tank 12. If the measured photocurrent output is compared by the comparator 30 and is lower than the lower limit value (that is, the liquid developer concentration is higher than the set threshold value on the high concentration side of the predetermined set concentration range), the pump drive circuit 31 controls The pump 71 for supplying the replenisher is stopped.

During operation of the plate making machine, the liquid developer having a relatively low concentration used for toner development flows into the liquid developer storage tank 12 from the tray 17. Replenisher supply pump 7
When No. 1 is operating, a high-concentration replenisher is supplied, so that the concentration of the liquid developer 2 can be made uniform and the concentration detecting means 20 can always detect the made uniform liquid developer concentration. In order to do so, a liquid circulation pump 73 is provided, and the operation thereof causes the liquid developer 2 in the liquid developer storage tank 12 to be stirred.

Charged and exposed electrophotographic lithographic printing plate 1
Is conveyed into the developing electrode portion 14 by a conveying means (not shown) which conveys the plate at a constant speed in the direction of the arrow. Before the printing plate 1 enters the development processing section 14, the circulation pump 72 for supplying the liquid developer starts to operate, and the liquid developer 2 is supplied to the development electrode section 14. The liquid developer fills the gap between the printing plate 1 and the developing electrode 14a, and toner development is performed. After that, the excess liquid developer on the printing plate 1 is squeezed by the liquid developer squeezing means 13, and then the printing plate 1
After being dried and fixed, it is sent to the next elution part (not shown), where the non-image part other than the toner adhering part is elute and removed, and the lithographic printing plate is completed after the subsequent rinse and protective gum treatment.

Example As an electrophotographic lithographic printing plate 1, ODP.ND-300
(OPC plate manufactured by Mitsubishi Paper Mills, 0.3 mm thick, 398 mm x 1110 m
m) was used to perform plate making with the above plate making machine. As the liquid developer 2 in the development processing section, a positively chargeable liquid developer O
DP-TW (manufactured by Mitsubishi Paper Mills Ltd.) was used. Further, as the replenishing liquid 3, the replenishing liquid ODP-TR (Mitsubishi Paper Mills, Ltd.)
Manufactured) was used. The bias voltage applied to the developing electrode 14a in the development processing section was set to 180V.

During plate making, the liquid developer 2 in the liquid developer storage tank 12 is supplied to the development processing section 14 by the liquid developer supply circulation pump 72, and after being supplied for development, the liquid developer squeezing means 13 is provided. Was removed from the surface of the plate by means of, and recovered in the tray 17 and returned to the liquid developer storage tank 12 again, and was always circulated and used during plate making.

The 200th printing plate was prepared as described above.

After the plate making of 200 plates, the power supply of the plate making machine was turned off, and the plate making machine was stopped (stopped) for 12 hours. After stopping for 12 hours, the power was turned on, and the 200th plate was made in the same manner as above. Thereafter, in the same manner, the plate-making machine power was turned off, the machine was stopped for 12 hours, and then the 200-plate making was repeated 10 times as described above, and a total of 2000 plates were made.

When performing the power-off operation of the plate making machine, the density is detected by the density detecting means 20 before the power is turned off.
The comparator 30 compares the photocurrent output value with the lower limit value of the photocurrent output corresponding to the set threshold value on the high concentration side of the desired preset concentration range of the liquid developer concentration, and if the photocurrent output value is lower than the lower limit value. If it is larger, the replenisher supply pump 71 is operated by the control of the pump drive circuit 31 and the supply of the replenisher 3 to the liquid developer 2 is started. After that, when the photocurrent output value from the concentration detecting means 20 reaches the lower limit value of the photocurrent output corresponding to the set threshold value on the high concentration side of the desired set concentration range of the liquid developer 2, the replenisher supply pump 71 is provided. Was stopped, and then the power supply to the plate making machine was cut off.

As a result of making the 2000 plate, good plate making was carried out without problems in all 2000 plates. The image quality of the plate-making image, the line width of the image lines, and the image density were almost unchanged even when the continuous plate-making was performed immediately after the power was turned on, and the plate-making was performed stably.

Comparative Example In the same manner as in Example 2 except that the concentration control (replenisher replenishment) was not performed at all during the power-off operation in Comparative Example 2.
20 plates are made 10 times with a 12-hour stoppage.
00 plate making was performed.

As a result, when the continuous plate-making process was carried out immediately after the power was turned on after the stop for 12 hours after the first 200-plate plate making, the plate-making process in which the image density was insufficient around the 30th plate after the continuous plate-making process was started. Things appeared. During that time, as a result of observing the operating state of the replenisher supply pump, it was found that the pump was not operating at all. When the plate making was continued thereafter, the pump for supplying the replenisher started to be operated after the plate making and the image density of the plate-making product returned to the normal state. Good plate making was performed until the power was turned off thereafter.

After that, when the plate making was continued, during the plate making of 2000 plate, the image density was further reduced several times during the continuous plate making after the power was turned on. At that time, the toner particle concentration of the liquid developer immediately after the power is turned on is measured by electrodeposition and the weight is measured, and it is slightly lower than the toner particle concentration corresponding to the set threshold value on the low concentration side of the proper concentration range. It was in the state of.

Therefore, if the density control during the power-off operation of the present invention is not performed, the image density of the plate-made product may decrease when continuous plate making is performed immediately after the power is turned on, and good plate-making can be stably continued. I couldn't do it.

[0056]

As described above, the concentration of the liquid developer is detected at the time of power-off operation, and when the concentration of the liquid developer is lower than the set threshold value on the high concentration side of the intended set concentration range, By increasing the liquid developer concentration up to the set threshold value on the high concentration side of the desired set concentration range, the next time when the electrophotographic lithographic printing plate development processing device is turned on, a large number of continuous plates are produced immediately after the power is turned on. Even if the above is performed, there is no deterioration in quality such as insufficient image density, and a good development state can always be obtained immediately after the power is turned on. It can be performed by a simple method without adding equipment such as temperature control and temperature compensation.

Further, when the optical detecting means having the light emitting element and the light receiving element capable of stably measuring the toner particle concentration is used as the density detecting means, the above method is used to make the method more effective and stable. A good development state can be maintained.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the configuration of an electrophotographic lithographic printing plate development processing apparatus used in an example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrophotographic planographic printing original plate 2 Liquid developer 3 Replenisher 13 Liquid developer squeezing means 14 Developing electrode part 20 Liquid developer concentration detecting means 20a Light emitting element 20b Light receiving element 31 Pump drive circuit 71 Replenisher supplying pump 72 Liquid developing Agent supply pump 73 Liquid circulation pump

Claims (2)

[Claims] 1. An electron for converting an electrostatic latent image on a printing plate photoconductive layer into a 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 controlling the concentration of a liquid developer, which detects the concentration of the liquid developer by using the concentration detecting means of a photolithographic printing plate development processing apparatus to maintain the concentration of the liquid developer within a predetermined set concentration range. When the power of the development processing device is turned off, the concentration of the liquid developer is detected, and if the concentration of the liquid developer is lower than the preset threshold value on the high concentration side of the preset preset concentration range, the liquid developer concentration A liquid developer concentration control method for an electrophotographic lithographic printing plate development processing apparatus, characterized in that the power is turned off after the temperature is raised to a set threshold value on the high density side of a desired set density range. 2. A liquid developer concentration control method for an electrophotographic lithographic printing plate development processing apparatus according to claim 1, wherein said concentration detection means is an optical detection means having a light emitting element and a light receiving element.