JPH10254077A - Exposure control method for planographic plate for scanning exposure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and accurately control exposure without being influenced by photographic gradation characteristic by measuring the density of a dotted image and a black solid image on a paleographic plate and controlling the exposure so that a density difference between them may be within a specified range. SOLUTION: The exposure is controlled by measuring the blackened image of the dotted image and the black solid image formed on a plate surface. The black solid image means an image whose entire surface is blackened to a some-extent wide range with respect to the dotted image. A part (outside of a printing area) which is not submitted for printing generally exists on the surface of the planographic plate made. For example, the peripheral part 3 of the printing area 2 on the paleographic plate 1 corresponds to such a part. By forming the dotted image 4 and the black solid image (ordinarily, the part which is not submitted for printing becomes a non-image part in printing, so that it is blackened by exposure and chemical development and necessarily becomes the black solid image in the case of a silver salt printing plate) on the part 3 which is not submitted for printing at the time of making the plate, the density of the dotted image and the black solid image around the dotted image is measured regularly or every time the plate is made so as to control whether appropriate exposure is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling an exposure amount when a lithographic printing plate is scanned and exposed by a silver salt diffusion transfer system.

[0002]

2. Description of the Related Art In the printing operation of a lithographic printing plate in the plate making process, the degree of printing must be within an appropriate range in order to prevent fluctuations in image reproducibility due to fluctuations in light sources and slight fluctuations in sensitivity of the printing plate. It is necessary to periodically determine whether or not the plate making process is in progress and manage the plate making process. As a method of controlling the printing degree of the plate, a transparent gray scale with a stepwise change in density is made in close contact with the film original and the plate is made, and the part of the gray scale with a specific density is reproduced on the printing plate If it is, a method of determining that the exposure amount is appropriate is generally used. In addition, a method has been widely used in which a specific image is put in a manuscript to make a plate, and the degree of printing is controlled from the reproducibility of the image on a printing plate.

A lithographic printing plate is provided with a silver salt diffusion transfer method (DTR).
), Particularly those having a physical development nucleus layer on a silver halide emulsion layer.
No. 8,114, No. 4,134,769, No. 4-1
No. 60,670, No. 4,336,321, No. 4,
Nos. 501,811, 4,510,228 and 4,4621,041. In such a printing plate, the exposed silver halide crystal becomes blackened silver by chemical development to form a hydrophilic non-image portion, while the unexposed silver halide crystal is a silver salt in a developing solution. The complexing agent forms a silver salt complex and diffuses to the physical development nucleus layer on the surface. Due to the presence of the nucleus, physical development is caused to form an image area mainly composed of physically developed silver having ink receptivity.

A lithographic printing plate prepared by the silver salt diffusion transfer method has a high photographic sensitivity.
There is an advantage that plate making can be performed directly from a reflection original by camera exposure, and is widely used. In the case of making such a printing plate by camera exposure, the method of controlling the exposure is basically the same as in the case of close contact exposure. Appropriate exposure is determined based on the reproduction up to the density portion.

A printing plate according to this method is disclosed in US Pat.
No. 1,811, JP-A-59-71055 and JP-A-60-7
By adjusting the photosensitive characteristics as in 5838 and 60-001448, it is possible to easily cope with a scanning exposure method using a laser or the like, and the advantage that a printing plate can be directly output from digital information using an image setter or the like. Have. Lithographic printing plates used in these scanning exposure systems are required to have a particularly high spectral sensitization sensitivity, so that sensitivity fluctuation between production lots and sensitivity fluctuation during storage are likely to occur, and therefore, an appropriate exposure amount Management is becoming increasingly important.

However, there is a problem in applying the conventional exposure amount management method to the scanning exposure method. That is, since the scanning exposure method is performed only by turning the exposure beam ON / OFF, it is not possible to change the exposure amount stepwise using a gray scale and control the exposure amount based on reproduction on the plate surface as in the related art. Can not.

Further, a method of controlling the exposure so that the density of the blackened image, that is, the density of the solid black image area falls within a predetermined range has been tried. It is necessary that the densification density be changed to a certain degree or more, and the gradation of the lithographic printing plate requires a certain degree of softness. However, in a scanning exposure digital output in which an image is constituted only by ON / OFF, in order to improve image reproducibility, it is desirable that photographic characteristics be as high as possible.
In particular, recently, in order to reduce the cost of a scanning exposure apparatus using a red LD or the like, simplification of an exposure beam has been performed. In order not to appear, demands for higher contrast of lithographic printing plates are increasing. Therefore, it is impossible to apply the conventional exposure management method.

[0008] Furthermore, the above-mentioned method of managing only the blackening density is as follows.
There has been a problem that the blackening density fluctuates due to a change in development conditions due to fatigue of the developer or the like, so that accuracy is lacking.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of making a lithographic printing plate in a scanning exposure system using a silver complex salt diffusion transfer method, which is simple and accurate without being influenced by the photographic gradation characteristics of the lithographic printing plate. To provide a method for controlling the amount of exposure.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for controlling an exposure amount in a scanning exposure of a lithographic printing plate utilizing a silver salt diffusion transfer method, wherein a halftone image and a black solid image are formed on the lithographic printing plate. Is formed, the density of the halftone dot image and the solid black image are measured, and the exposure is controlled so that the density difference between the two is within a predetermined range. Was.

In order to accurately control the amount of exposure, it is necessary to provide a numerical reference for determining the amount of exposure. The reference numerical value is a measured amount that changes in accordance with the change in the exposure amount and the sensitivity of the lithographic printing plate, and the measured amount must be a stable one with little fluctuation. Therefore, the inventor paid attention to the halftone dot image as the former requirement, that is, the measurement amount that changes according to the change in the exposure amount and the sensitivity of the lithographic printing plate, and as a result of testing, confirmed that the requirement was satisfied. . Further, with respect to the latter fluctuation of the measured amount, by performing a relative comparison with the solid black image density, it was possible to avoid the problem of the fluctuation due to development conditions and the like.

More specifically, in the absolute value of the density of the image on the printing plate, there may be fluctuation due to development conditions and the like, but in the relative value of the density of the two types of images on the same printing plate, We found that the effects of such swings were offset. In particular, due to the characteristics of the silver salt diffusion transfer printing plate and general optical characteristics, it was found that the measured value of the density was more stable as the area ratio of the blackened area was larger for the halftone dots. For this reason, by using the density difference between the halftone image having an area ratio of 70% or more and the solid black image as the criterion for the exposure amount, the exposure amount is not influenced by the photographic gradation characteristics of the plate and unique management of the exposure amount Became possible.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The present invention manages the exposure amount by measuring the blackening density of a halftone image and a solid black image formed on a printing plate. In the present invention, a solid black image refers to an image in which the entire surface is blackened to some extent over a halftone dot image (at least an area larger than the measurement unit of the optical densitometer).

There are portions (outside the printing area) that are not generally used for printing on the plate surface of the lithographic printing plate that has been made. For example, the printing area (2) in the printing plate (1) shown in FIG.
(3) corresponds to this. The halftone image (4) and the solid black image (usually, the non-printable portion is a non-image portion of the print, so that the portion (3) not used for printing during plate making is exposed to light in the case of a silver halide printing plate. The density of a halftone dot image and its surrounding black solid image is formed every plate making or periodically (for example, at the start of daily work) by forming a black image by chemical development and inevitably forming a black solid image. Is measured, and whether or not the exposure is appropriate can be managed. Instead of the above method, plate-making may be performed only for controlling the exposure amount.

In the present invention, it is advantageous that the halftone dot area ratio of the halftone dot image is large in order to reduce the deflection at the time of density measurement. Therefore, the halftone image used for exposure control (exposure management halftone image) has as large an area ratio of the exposure region as possible,
It is also desirable that the number of lines be high. However, when the image becomes close to the limit of the reproducibility of the exposure apparatus, the density value becomes conversely unstable. Therefore, in practice, the number of lines from 133 lines used in normal output to 200 lines is used. 85% ~
It is preferable that halftone dots having an area ratio of about 97% are used as exposure control halftone dots. Particularly preferably, it is 90% to 95%.

The halftone image for exposure management can be formed by a dedicated algorithm from an output device or halftone generation software and output as a management image. Also, using the same algorithm used in normal image output work,
As described above, the image may be periodically output as the management image. More preferably, at the time of outputting all the plates, an exposure control halftone dot is generated outside the printing area of the plate (portion not used for printing) or attached to a print control patch image, and the To determine the appropriateness of Note that the dot image has attributes of shape and angle in addition to the number of lines and area ratio, and the shape and the like also vary depending on the type of its generation algorithm. is there.

The method for obtaining the proper exposure amount is not particularly limited. For example, the following method is generally used.
As a specific work procedure, first, according to the performance of the output device and the lithographic printing plate, an exposure determination pattern composed of a specific minute image (negative / positive fine line, minute checkerboard pattern, etc.) and an appropriate image reproduction state thereof are determined. It is determined in advance. When each output device and lithographic printing plate are introduced, the exposure judgment pattern is output by changing the exposure dial value stepwise, and the dial value whose reproduction on the plate surface is closest to the most appropriate state is determined as the appropriate exposure amount. I do.

More specifically, the silver halide printing plate has a period of 10 lines.
/ mm square wave image is output, the obtained square wave image is read with a microdensitometer, and a method is adopted in which the appropriate exposure is performed when the reproduction width of the exposed portion and the unexposed portion on the plate is equal. it can.

When the proper exposure amount is determined by the above method, the control halftone dot and the solid black image at the proper light amount are output, and the density difference between them is measured and used as a reference value. Thereafter, when the printing plate is output on a daily basis, the management halftone dots are periodically output under the same setting conditions, and the density difference from the solid black image is measured. Then, it manages whether or not the density difference falls within a predetermined range with respect to the reference value. If not, the exposure amount is adjusted by changing the exposure dial value.

By using the above exposure amount management method of the present invention, once the appropriate exposure conditions are set according to the type of the output device and the type of the lithographic printing plate, it is easy to carry out the routine work thereafter. It is possible to accurately determine whether the exposure is proper.

In the present invention, managing the density difference between a halftone dot image and a solid black image to be within a predetermined range means that a predetermined value is determined with respect to a predetermined reference value for proper exposure as described above. Means within the range. The predetermined range with respect to the reference value differs depending on the type of halftone image used (difference in halftone dot area ratio) and the type of printed matter (high-definition printed matter or coarse printed matter), etc. Therefore, it cannot be determined unconditionally, but it is preferable to substantially match the reference value. Here, “substantially coincide” means that a measurement error of the optical densitometer is included. That is, a commonly used optical densitometer has a minimum measurement density of 0.0
The difference is a maximum of ± 0.01 with respect to the reference value, and is managed as substantially matching.

When stricter control is required, a high-precision densitometer, for example, VIPlate 115 of VIPtronic, is used.
It can be controlled within the range of ± 0.005.

The management method according to the present invention can also be used as a unique method for determining an appropriate amount of light. That is, the reference value is determined in advance after clearly specifying the types of halftone dots for each type of output device and printing plate, and the density difference between the control halftone dots when each output device and lithographic printing plate is introduced is determined as the reference value. Exposure dial value is set to match.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an example of the exposure dose control method of the present invention will be described, but the present invention is not limited to this.

Two types of lithographic printing plates for scanning exposure (silver salt printing plates (SDP-FR175, manufactured by Mitsubishi Paper Mills, Ltd., PET base)) having a relative sensitivity different by 10% and corresponding to red LD are prepared (printing plates A and B). did. Printing plate A is 7% more sensitive than printing plate B. A flat scanning exposure type image setter using a red LD light source, Dainippon Screen FT-R3050 was used as the output device.

First, for the printing plate A, the period 10
Line / mm rectangular wave images were output, and the appropriate exposure conditions were determined by a method of reading the images with a microdensitometer.
The appropriate light intensity dial at that time was 110.

Next, an image obtained by outputting a halftone dot image for management with an area ratio of 95% to the center of the output device under the above-mentioned proper exposure condition was used. As detailed conditions, the generation algorithm was AD-RIP, the shape was a square dot of an alpha logic screen, the screen angle was 45 °, and the number of lines was 175 lines. VIPtr for densitometer
The density difference between the management halftone dot image and the surrounding solid black image was measured using VIPlate 115 manufactured by onic Corporation. as a result,
The density difference was 0.060, which was used as a reference value.

Next, a rectangular wave image having a period of 10 lines / mm was outputted from the printing plate B under the same exposure conditions as the printing plate A, and it was determined whether or not the exposure was proper. As a result, no proper image was obtained. The density difference between the halftone dot image and the solid black image was measured in the same manner as described above, but it was 0.105, which was considerably deviated from the reference value of 0.060.

From this, the method of the present invention can be applied to the case where lithographic printing plates having different sensitivities are used, even if the lithographic printing plates have different sensitivities.
Even if a ne / mm rectangular wave image is output and it is not necessary to determine whether or not the exposure is proper, the density can be determined based on the density difference between the halftone dot image and the solid black image, so that it can be easily introduced into daily work.

Next, the proper exposure conditions for printing plate B were determined in the same manner as for printing plate A. As a result, in the proper exposure, the exposure dial value was 150. Under these exposure conditions, 95%
A halftone dot image and a solid black image were output, and the density difference was measured. The result was 0.065, which substantially coincided with the reference value. This also indicates that the method of the present invention can accurately determine the proper exposure.

[0031]

According to the present invention, appropriate exposure management in scanning exposure can be performed simply and accurately.

[Brief description of the drawings]

FIG. 1 is a diagram showing a halftone image and a solid black image on a printing plate.

[Explanation of symbols]

 1 Lithographic printing plate after plate making 2 Printing area 3 Non-printing part 4 Halftone image

Claims (2)

[Claims] In an exposure amount controlling method for scanning exposure of a lithographic printing plate utilizing a silver salt diffusion transfer method, a halftone image and a solid black image are formed on the lithographic printing plate, and the halftone image and the black solid image are formed. A method of managing exposure in scanning exposure of a lithographic printing plate, comprising measuring the density of a solid black image and managing the exposure so that the difference between the two is within a predetermined range. 2. An exposure area of the halftone dot image having an area ratio of 70
2. The method according to claim 1, wherein the exposure amount is not less than 0.1%.