JP2000085093A - Doctoring device for printing press - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extend the life of a plate surface or a doctor blade by keeping the pressing force of the doctor blade to the plate surface almost constant and preventing the pressing force from becoming unnecessarily large. SOLUTION: In the doctoring device of a printing press constituted so as to bring a doctor blade 1 into slide contact with a plate surface to apply scraping action to a plate surface, the doctor blade pressing means pressing the doctor blade 1 to the plate surface and the up and down moving shaft means 8 for moving the doctor blade 1 along the plate surface are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a doctoring device used in a printing machine, and more particularly to a doctoring device for preventing printing defects such as fog and streaks due to abrasion of a doctor blade during long lot coating in gravure printing / coating. Related to a ring device.

[0002]

2. Description of the Related Art In gravure printing, a cylinder having a large number of minute concave portions called cells corresponding to images on a cylindrical surface is used as a plate, and a relatively low-viscosity ink layer is formed on the surface. A method is used in which the ink is scraped off using a scraping tool called, and the web is brought into contact with the ink remaining in the cells on the plate surface to transfer the ink. This doctor blade is usually made of an elastic metal sheet, but in order to improve the scraping effect, it is indispensable to apply a certain pressure to the plate surface and print while pressing the tip of the doctor blade. For this reason, if printing is performed continuously for a long time, several defects that affect image quality occur due to the progress of abrasion at the tip (edge) of the doctor blade.

[0003] A typical example of the defect is a phenomenon called "fog" in which ink remains in a portion of the plate surface where there is no image, and as a result, the ink is transferred to a position where a pattern of a printed material should not exist. . Further, there is a phenomenon called “streak” in which a continuous linear pattern is formed in the flow direction due to partial wear and loss of the blade edge of the doctor blade. These phenomena occur more or less with the progress of continuous printing, but have been a serious problem particularly in printing inks having a large friction coefficient such as aqueous inks.

[0004] In a conventional gravure printing machine, a method for reducing the wear of a doctor blade is to reduce the pressure (doctor pressure) applied between the blade edge of the doctor blade and the plate surface by changing the material of the doctor blade to a hard material with little wear. A reverse angle doctor or the like in which the contact angle (doctor angle) of the blade edge of the doctor blade to the plate surface is reversed from the normal angle (trailing) has been put into practical use.

[0005]

However, in the method of reducing the doctor pressure, the pressure actually required for scraping is smaller than the pressure normally set, but the variation in the roundness of the printing plate and the rotation of the printing plate are reduced. Unnecessary pressure is applied because eccentricity and undulation in the width direction of the doctor blade are inevitable, and as a result, the degree of reduction in the wear of the doctor blade is not large.

When the doctor blade is made of a material having high hardness with little wear, the wear of the plate surface is accelerated when the hardness of the cutting edge is larger than that of the plate surface, usually in relation to the wear of the plate surface coated with a chrome plating layer. As a result, the quantity that can be printed on one plate is reduced.

[0007] The reverse angle doctor is similar to the case where the doctor pressure is reduced, but the effect of promoting the replacement of air and ink in the cell, which is another function of the doctor blade, is remarkably reduced. There have been problems such as a reduction in the amount of ink transfer and instability.

The present invention has been made to solve such a problem, and can maintain the pressure of the doctor blade against the printing plate almost constant, and the pressure becomes unnecessarily large. It is an object of the present invention to prolong the life of the printing plate or the doctor blade by preventing such a situation.

[0009]

A doctoring device for a printing press according to the present invention is a doctoring device for a printing press in which a doctor blade is slid into contact with a printing plate to scrape off the doctor blade. It is characterized by having a doctor blade pressing means for pressing and a vertically moving shaft means for moving the doctor blade along the plate surface.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Among the factors affecting the wear of a doctor blade, the present inventor regards the doctor angle and the doctor pressure as having a gradation curve (continuously reducing the cell volume from the minimum). When it was changed to the maximum, the examination was made based on the curve of the reflection density of the printed image corresponding thereto. The range in which the variation of all the reflection density values in this gradation curve falls within 5% is approximately the doctor angle of 45 to 75 degrees. Further, the doctor pressure is from 0.07 kg / cm to 0.58 k
g / cm.

Further, as a result of examining the relationship between the cross-sectional shape of the blade of the doctor blade after abrasion and the printing defect, it has been found that, along with the amount of abrasion of the blade, minute chipping of the blade and generation of burrs are caused by printing such as "streaks" and "fog". It has been found that the correlation with the defect is large, and in order to prevent these defects, it is necessary not only to suppress the amount of wear of the cutting edge but also to make the state of wear uniform. Therefore, the wear leveling method based on the premise that the image quality does not fluctuate is to change the contact angle of the doctor blade as the wear progresses. It is effective in preventing.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of the apparatus of the present invention. The printing press shown in FIG. 1 is a gravure printing press, and as is well known, the ink in the ink pan 13 is supplied to the surface of the gravure plate 10 and the unnecessary portion is scraped off by the doctor blade 1. It is transferred to the web 12 by the impression cylinder 11 and is dried and wound up by the subsequent drying device. In FIG. 1, the drying device is omitted.

In the doctoring device for a printing press according to the present invention, the doctor blade 1 is attached to the doctor holder 2 at the tip of a doctor holder holder 3 whose angle can be adjusted. A pressurizing means for the air cylinder 5 for pressing with a constant pressure is provided.

Next, in order to change the contact angle 14 of the blade edge of the doctor blade 1, a holder up / down movement shaft 8 serving as up / down movement means for supporting the doctor holder holder 3.
Is periodically moved up and down by a doctor vertical movement cam 9 which rotates in conjunction with the doctor swinging device. Next, the doctor holder holder 3 rotates around the holder rotation shaft 7. In other words, when the doctor holder holder 3 is rotated while the pressure of the air cylinder 5 as the pressurizing means is kept constant, the contact point between the gravure plate 10 and the blade edge of the doctor blade 1 moves along the plate surface. In that range, the pressure on the plate falls within the range of 0.07 kg / cm to 0.58 kg / cm, so that the printing quality is not affected by the fluctuation of the doctor pressure.

FIG. 2 is an enlarged view of the doctor blade 1 and the gravure printing portion, showing that the doctor blade has moved. For example, a case where the doctor blade 1a is moved to the doctor blade 1b will be described.
First, the doctor blade 1b is raised by the holder up / down movement shaft 8 as the up / down movement means, and at the same time, the pressure of the air cylinder 5 as the pressurization means is kept constant to rotate the doctor holder holder 3, and the doctor blade 1a It will be moved along the printing plate to the position. Therefore, when the doctor blade moves up and down, the contact angle becomes 1
The contact angle changes from 4b to 14a. The same applies to the case where the doctor blade 1a is moved to the position of the doctor blade 1b.

As described above, according to the present invention, the vertical movement means of the holder vertical movement shaft 8 may be any as long as the contact angle of the doctor blade can be changed in the range of 45 to 75 degrees. It is not limited to the illustrated device. Further, the contact angle of the blade of the doctor blade with the plate is 45 °.
If it is less than the degree, the ink is scraped off at the flat portion of the lower surface of the cutting edge, not at the tip of the cutting edge, resulting in "fog". On the other hand, when the contact angle is larger than 75 degrees, the air in the cells is not sufficiently replaced with the ink, resulting in a decrease in print density.

In the conventional method for making the contact angle of the blade edge of the doctor blade constant, the wear of the blade in contact with the plate proceeds at the same position in the cross section, and the unevenness of the wear is not averaged. Marks appear and appear as printing defects. In the apparatus of the present invention, the wear of the cross section is leveled out by periodically changing the position of the cross section where the cutting edge of the doctor blade wears, and the above-mentioned defect can be prevented from occurring.

The material and shape of the doctor blade 1 are not particularly limited. However, for the purpose of the present invention, a material having a high hardness cutting edge such as a ceramic coat is desirable.

In order to confirm that the present invention can greatly extend the timing of occurrence of printing defects caused by a doctor in continuous printing of a long lot, the following example will be described.

[0021]

EXAMPLE 1 In Example 1, the contact angle of the blade edge of the doctor blade was 50 to 70 degrees, and the contact angle of the blade was 500 m.
A water-based ink was printed on a plastic film using a gravure printing machine using the doctoring apparatus of the present invention set so as to change in a cycle. As the ink, white of the water ink "Aqua Ecole" manufactured by Toyo Ink Mfg. Co., Ltd. was used. As the film, a stretched polyester film having a thickness of 12 μm (corona treated) was used. As the gravure plate, a solid plate with a surface chrome plating having a cell depth of 12 μm was used. In addition, a silicon carbide-coated steel doctor having a blade edge thickness of 0.07 mm was used as the doctor blade. The printing speed is 20,000 m continuously at 100 m / min, and the time when the unevenness of the printed matter is produced, and 20000 m
The cross-sectional shape of the blade of the doctor blade after printing was observed. As a comparative example, the same evaluation was performed by printing under the same conditions, except that a gravure printing machine using a doctoring device in which the contact angle of the blade edge of the doctor blade was fixed at 60 degrees was used. As a result, when the contact angle of the doctor blade was fixed, the unevenness in the form of a streak was 600 minutes from the printing start.
Although it occurred at 0 m, it did not occur up to 20000 m when the contact angle of the doctor blade was changed periodically.
When observing the cross-sectional shape of the blade edge of the doctor blade before and after 20000M printing with a laser microscope, when the contact angle of the doctor blade was fixed, the contact surface to the plate was cut almost linearly and the length of several μ Many were found with the burr turned up. On the other hand, when the contact angle of the doctor blade was changed periodically, the cross section of the blade tip was slightly circumferential and almost no burrs were observed. From these results, the apparatus of the present invention has the effect of equalizing the wear of the doctor blade and extending the number of continuous prints without "streaks" to about three times or more. In addition, it has been confirmed that there is an effect that enables continuous printing of a long lot of aqueous ink having a large coefficient of friction.

In the second embodiment, the gravure using the doctor ring apparatus of the present invention is set so that the contact angle of the blade edge of the doctor blade changes in one cycle to the plate circumferential length of 500 m between 45 degrees and 70 degrees. A water-based ink was printed on a plastic film by a printing machine. As the ink, water ink "Aqua Ecole" manufactured by Toyo Ink Mfg. Co., Ltd. was used. As the film, a stretched polyester film having a thickness of 12 μm (corona treated) was used. A gravure plate used was a chrome-plated picture plate having a cell depth of 12 μm, and a doctor used was a silicon carbide-coated steel doctor with a 0.07 mm-thick cutting edge. The printing speed was 100 000 m / min and 20,000 m continuously, and the time when "fogging" of the printed matter occurred and the cross-sectional shape of the blade of the doctor blade after printing 20,000 m were observed. As a comparative example, printing was performed under the same conditions except that the contact angle of the blade edge of the doctor blade was fixed at 60 degrees, and the same evaluation was performed. As a result, when the contact angle of the blade edge of the doctor blade was fixed, “fog” occurred at 3000 m from the start of printing, but 15,000 m when the contact angle of the doctor blade was changed periodically.
Did not occur until. 200 of the blade of the doctor blade
Observation of the cross-sectional shape before and after the printing of 00m with a laser microscope. When the contact angle of the blade edge of the doctor blade was fixed, the contact surface to the plate was cut almost straight, and burrs with a length of several μm turned up. Many were raised in the raised state. On the other hand, when the contact angle of the doctor blade was changed periodically, the cross section of the blade edge was somewhat circular, and the burrs were clearly smaller than when the contact angle of the blade edge of the doctor blade was fixed.

According to the above embodiment, the apparatus of the present invention can be used in the same manner as in the case of the white ink of the first embodiment.
It has been confirmed that this method is effective in preventing the occurrence of ink droplets, and that this has the effect of enabling long-lot continuous printing even with aqueous ink having a large coefficient of friction.

[0024]

By using the apparatus of the present invention, it is possible to greatly extend the timing of occurrence of printing defects caused by a doctor in continuous printing of a long lot. In particular, water-based inks with a large coefficient of friction and consequently high doctor abrasion are typical ones in which "fogging" is likely to occur due to the slow drying on the plate surface, but the same as oil-based inks Enabled continuous printing.

[0025]

[Brief description of the drawings]

FIG. 1 is a conceptual sectional view of a doctoring device according to the present invention.

FIG. 2 is a view showing a state where a doctor blade is moved up and down.

[0026]

[Explanation of symbols]

1 Doctor blade 1a Doctor blade moved 1b Doctor blade moved 2 Doctor holder 3 Holder holder 4 Air cylinder connection shaft 5 Air cylinder 6 Air cylinder connection shaft 7 Holder rotating shaft 8 Holder vertical movement shaft 9 Doctor vertical movement cam 10 Gravure Plate 11 Impression cylinder 12 Web 13 Ink pan 14 Contact angle of blade edge of doctor blade 14a Contact angle of blade edge when doctor blade is moved up and down 14b Contact angle of blade edge when doctor blade is moved up and down 14b

Claims (4)

[Claims] A doctor blade presser for pressing a doctor blade against a printing plate in a doctor ring device of a printing press, wherein the doctor blade is pressed against the printing plate by scraping the ink adhering to the printing plate surface by sliding the doctor blade against the printing plate surface. And a vertically moving means for moving a doctor blade along a printing plate surface. 2. The doctoring device for a printing press according to claim 1, wherein the contact angle of the doctor blade of the gravure printing press with the printing plate changes periodically. 3. The doctoring device for a printing press according to claim 2, wherein said contact angle is an angle in a range of 45 degrees to 75 degrees. 4. The doctoring device for a printing press according to claim 2, wherein the cycle of changing the contact angle is interlocked with the lateral swing of the doctor blade. A doctoring device for a printing press.