JPH0221941B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image quality control method in a small-sized offset printing machine with a relatively small number of ink mixing rollers, and more specifically, to optically controlling the water content of ink on the ink mixing roller or inking roller. The present invention relates to a method of detecting the amount of water and controlling the amount of water supplied to the ink to control the density of the printed image.

As illustrated in FIG. 1, an offset printing machine includes an ink supply system 1, a plate cylinder 2 around which an original plate (not shown) is wound, and an ink image on the original plate transferred onto the surrounding surface. Transfer cylinder 3, impression cylinder 4, and paper feed system 5
It is mainly composed of. Then, by feeding the printing paper between the transfer cylinder 3 and the impression cylinder 4 from the paper feed system 5, the printing paper is printed, and the printed paper is discharged to the paper discharge tray 6. It will be done.

Here, ink is supplied to the original plate on the plate cylinder 2 as follows. First, ink is supplied to an ink pot 9 formed between a doctor blade 7 and a duct roller 8, and the duct roller 8 rotates intermittently in the direction of the arrow while ink is kneaded into a predetermined property.
The ink on the circumferential surface of is transferred to a calling roller 11 that reciprocates in the direction of the arrow, and is further applied to an ink mixing roller 12 by this calling roller 11. The ink on the ink mixing roller 12 is transferred to the inking roller 13 while being mixed, and the ink on the roller 13 is further supplied and applied to the original plate on the printing cylinder 2.

On the other hand, at the bottom of the ink supply system 1, a water tray 14 containing water W, a fountain roller 15 whose peripheral surface is partially immersed in water W, and a water priming roller 16 for supplying water are arranged. The water W is supplied from the fountain roller 15 via the water priming roller 16 to the ink mixing roller 12, where it is kneaded and mixed into the printing ink inside.

The water in the water tray 14 mainly serves the function of keeping the grease-insensitive portion of the etched original plate in a grease-free state during continuous printing, and is essential in the printing process.

By the way, in such a small offset printing machine with a small number of ink mixing rollers, it is necessary to appropriately control the image density of the printed matter. Conventionally, when controlling the image density, the operator observes the image density of the printed material every moment and manually adjusts and controls the amount of ink feed, water supply, etc., or goes one step further. In this model, the image density of the printing paper discharged from the printing section is measured using, for example, a reflective densitometer, and the amount of change in density is fed back to the ink supply system, and the adjustment screw of the ink duct is turned, for example. The amount of ink supplied was adjusted and controlled by moving the ink.

Conventionally, such methods have been used to stabilize the quality of printed images, but these methods have the following drawbacks.

1 The image density of the printed paper is measured and detected by a density detection sensor such as a reflective densitometer, so either set the sensor manually to a certain detection position or set the sensor to the entire range of the printed paper. need to be placed. Especially when printing using a small offset printing machine or when printing short runs, the original plate must be replaced frequently, and the density detection sensor must be moved artificially every time the pattern changes due to a plate change. I have to let it happen. This is because the character image position differs depending on the version.

2. Since the density is measured near the paper discharge section of the printing press and the measurement and detection results are fed back to the ink supply system, it takes a considerable amount of time from the detection until the density adjustment is actually made. In other words, even if the above-mentioned detection is performed, only printed matter with the previous image density will be obtained for a while. In addition, since the final printed image density is detected and this detection result is fed back to the ink supply system, a corresponding feedback system that takes time is required, making the device bulky. With,
It is easy to pick up various types of noise that can disrupt control in the feedback system.

The present invention is a small-sized offset printing machine that performs printing by supplying dampening water from a water supply means and ink from an ink supply means to an ink mixing roller, an inking roller, and a plate cylinder. This method solves the problems with the conventional detection method, and the amount of ink on the ink mixing roller or inking roller is constant for each original, and the amount of water on the ink layer on the inking roller or inking roller is fixed. The detected amount of water is optically detected and compared with a predetermined reference amount of water for the original plate, and the amount of water supplied is controlled according to the difference. The image quality is controlled by maintaining the water amount at the above-mentioned reference water amount.

Hereinafter, the present invention will be explained specifically and in detail with reference to the drawings.

For example, the present invention detects and measures the degree of dispersion of drops formed by dampening water on the ink mixing roller 12 (see FIG. 1) using an optical method, and feeds back the change to the water supply system. For example, by changing the contact time of the water priming roller 16 with the ink mixing roller 12 and keeping the degree of dispersion of droplets on the ink mixing roller constant, the printed image density is stabilized. In the present invention, the degree of dispersion of the droplets on the inking roller may be made constant, but in the following description, for convenience, an ink mixing roller will be used.

In an offset printing machine in which a water priming roller 16 is rotated in contact with an ink kneading roller 12 to supply water to the ink on the roller 12 and simultaneously moisten the original plate and knead the ink to a predetermined property, the water supply is Changes in the amount have a considerable effect on the density of the printed image; as the amount of water supplied increases, the density decreases, and conversely, as the amount of water supplied decreases, the density increases.

In general, the response of density changes to increases and decreases in water supply is extremely fast, and within the range of practical printing speeds,
After printing about 2 or 3 sheets, the change in density can be visually determined. On the other hand, for example,
When the water priming roller 16 is rotated in contact with the ink mixing roller 12, drops of dampening water are dispersed and adhered to the ink film on the roller 12. The average diameter of the droplets is determined primarily by the interfacial tension of the dampening solution with the ink film, and the degree of droplet dispersion is dependent on the amount of dampening solution supplied.

That is, on the ink kneading roller that the water priming roller 16 rotates in contact with, droplets of dampening water with an appropriate diameter are dispersed over the entire surface, and these droplets pass through the inking roller to the non-image on the original plate. Due to the hydrophilic nature of the original surface, the droplets adhering to the ink film surface first expand to the surface and prevent the ink from adhering there. The opposite phenomenon occurs, and only ink adheres to the image area.

The thickness of the ink film on the ink mixing roller is irrelevant to the formation of a droplet on the ink mixing roller. Therefore, in this printing method, the thickness of the ink film, that is, the amount of ink supplied can be kept constant as an initial condition. If the ink supply amount is constant and a water priming roller with dampening water of a specific formulation is rotated in contact with the surface of the ink film on the mixing roller for a certain period of time, the particle size and dispersion will be determined by the conditions. A thick droplet will be deposited on the inking roller.

Assuming that the droplet diameter is constant, the required degree of dispersion is determined by the area ratio of the non-image area to the image area of the original. For example, if the printed image is text,
It is known that the above area ratio is about 5 to 8%, and if the degree of dispersion of droplets corresponding to this area ratio can be maintained, printed matter with a constant density can always be obtained.

However, when performing printing, there are various variable factors that affect the degree of dispersion of droplets, and even under the same water supply conditions, the degree of dispersion of droplets changes due to the above-mentioned uncertain variable factors. . Conventionally, as mentioned at the beginning, changes in the degree of dispersion of the droplets were detected by changes in the density of the printed matter and the amount of water supplied was artificially adjusted. The response speed until the density adjustment is actually made is slow and the response is uncertain, making it necessary to constantly monitor the print tone of the printed matter. The present invention monitors the dispersion of drops on an inking roller, such as an inking roller or an inking roller, and uses the resulting monitoring signal to determine the dispersion of the drops, so to speak, the water content of the ink. It is characterized by adjusting and controlling the water supply system so as to maintain it at an appropriate value. Note that the water content referred to here refers to the amount of water contained under the condition that the amount of ink supplied is constant.
This is the absolute water content for this fixed amount of ink. By the way, detailed theoretical formulas have been proposed by Rayleigh, Mie et al. regarding the scattering of light by droplets, but they are only effective when the particle size is 10 microns or less, and they are effective only when the particle size is 10 microns or less. If the diameter is large, such as a droplet (10 microns or more), the reflected light from the droplet is approximately proportional to the density of the droplet, and since the ink is a black body, it is treated as if there is no reflection. There's no problem with it. Therefore, if a roller such as an ink mixing roller on which droplets are formed is irradiated with light from one direction, and the amount of specular reflection or diffuse reflection is received by an appropriate light receiving sensor, the light at this time can be detected. The magnitude of the current is taken as the degree of dispersion of the droplets, which is proportional to the water content of the ink.

In order to experimentally confirm the above points, the present inventors set the photo sensor and light source of a mimeograph machine F500 manufactured by Ricoh Co., Ltd. on the inking roller provided in an autoprinter 1310 also manufactured by Ricoh Co., Ltd. Then, the output voltage of the photo sensor was measured using the water supply scale in the water supply system of the printing press as a parameter. The results are shown in FIG. The vertical axis shows the output voltage expressed on a logarithmic scale, and the horizontal axis shows the number of water supply scales.

As understood from FIG. 2, as the number of water supply scales increases, that is, as the water content of the ink increases, the output voltage increases in proportion. From this result, determine the standard water content corresponding to a certain desired and appropriate print image density, measure the output voltage at a certain point to understand the water content at that point, and compare this water content with the standard water content. By extracting the difference and feeding it back to the water supply system to adjust the ink water content to the reference water content, it is possible to maintain a constant density of the printed matter.

In this way, the detection and measurement of ink water content is performed quickly in the ink supply system, so
Water supply amount control can be performed immediately. In other words,
The responsiveness is fast, and there is no risk of printing several pages with undesired density. That is, it is possible to continuously and constantly obtain printed matter with a desired density.

FIG. 3 conceptually shows a control block diagram from water content detection to water supply control, and the water content sensor corresponds to a photo sensor. FIG. 4 shows a specific circuit example, and this circuit includes a water content sensor 24, a comparator 25,
Amplifier 26 and a solenoid 27 that controls the water supply amount
It is mainly composed of.

FIG. 5 shows a specific example of a device for adjusting and controlling the water supply amount. Using the solenoid 27 that is controlled on and off by the circuit described above, the lever 26
is intermittently oscillated about the shaft 15a. Then, the water priming roller 16 comes into contact with and separates from the ink mixing roller 12. Then, the amount of water supplied is adjusted and controlled by changing the contact time of the water priming roller 16 with the ink mixing roller 12. Figure 6 shows that by controlling the solenoid 27 on and off,
This shows an example of a device in which the immersion time of the fountain roller 15 in the water W is changed by moving the water tray 14 up and down. Even in this case, water supply amount control can be performed appropriately and smoothly.

In this way, the present invention detects and measures the amount of light reflected from the ink on the ink mixing roller or inking roller to grasp the current water content of the ink, and adjusts this ink water content and, for example, the print image density to an appropriate level. The method is characterized in that the water content of the ink is adjusted and maintained at the reference water content by mutually comparing the obtained water content with a predetermined reference water content, and controlling the amount of water supplied according to the detected difference in water content. .

According to the present invention, there is no need for an image density detection sensor as used in the conventional example, and therefore there is no need for moving the sensor. From this point of view, it is particularly suitable for printing in which the original plate is frequently replaced, and the structure can be greatly simplified since no means for moving the sensor or the like is required.

Furthermore, in the conventional example, the print image density is measured near the paper discharge section of the printing machine, and the measurement results are fed back to the ink supply system, so density adjustment is virtually impossible from detection. It takes a considerable amount of time to complete the process, and there is a risk that several prints with undesired image density may be printed. In contrast, in the present invention, detection and measurement are performed at the time of the ink supply system before sending the printing paper, so the time from detection to the actual density adjustment is extremely short. , the responsiveness is good, and the printed matter can be made to the desired density immediately after detection. In other words, printed matter with a predetermined image density can be obtained continuously. Further, since a simple configuration of simply installing a simple detection sensor in an ink supply system such as an ink mixing roller is sufficient, the device can be made more compact.

By the way, as a method of managing the print image density, a method of adjusting the amount of ink feed and water supply can be considered. The present invention adjusts and controls the amount of water supplied, which is much simpler than adjusting and controlling the amount of ink supplied itself. This is because ink has a predetermined viscosity, and it is difficult to immediately change its supply amount. Then, for the image area ratio,
This is because the amount of change in water contributes more than that of ink.

As described above, according to the present invention, printed matter with a desired constant density can always be obtained continuously without any manual operation. In addition, since the response time to image density adjustment is quick, there is no need to strictly monitor the printed matter, and furthermore, printing does not require much skill, and it can cope well with short run printing. be able to.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram of an example of an offset printing machine to which the present invention is applied, and Fig. 2 shows the correlation between the output voltage and the water supply scale when measuring the amount of reflected light of ink in an embodiment of the present invention. Figure 3 is a control block diagram for adjusting and controlling the water supply amount based on the detection of water content, and Figure 4 is a specific circuit for adjusting and controlling the water supply amount based on the detection of water content. FIG. 5 is a diagram showing an example of the water supply amount adjusting device, and FIG. 6 is a side view showing another example of the water supply amount adjusting device. 2... Plate cylinder, 12... Ink kneading roller, 13
...Inking roller, 14...Water tray, 15...Fountain roller, 16...Water priming roller.

Claims (1)

[Scope of Claims] 1. In a small offset printing machine that performs printing by supplying dampening water from a water supply means and ink from an ink supply means to an ink mixing roller, an inking roller, and a plate cylinder, for each original plate. The amount of ink on the ink mixing roller or inking roller is kept constant, the amount of water on the ink layer on the ink mixing roller or inking roller is optically detected, and the detected water amount and the original plate are determined in advance. An image quality control method for an offset printing press in which the amount of water on the ink mixing roller or the inking roller is maintained at the reference amount by comparing the amount of water supplied with the reference amount of water and controlling the amount of water supplied according to the difference.