JP2001080230A - Doctor, gravure printer and method for printing using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent occurrence of a defect called 'backing of a spatula' of printing faults caused by a doctor in a gravure continuous printing by using a gravure printer having a doctor preventing backing of a spatula in which a fluorine-containing treatment is executed on at least one side surface of a knife. SOLUTION: The gravure printer supplies an ink in an ink tank 9 to a surface of a printing plate 8, scrapes an unnecessary part by a doctor 4, then brings an impression cylinder 2 into a raw fabric 3, and transfers it. The doctor 4 is mounted at an end of a doctor holder 5 capable of regulating at its angle, and urged at its edge to the plate 3 at a predetermined pressure. For example, polytetraethylene coating is executed on one side surface of the edge of the doctor 4, and a plastic film is coated with an aqueous ink. Thus, a growth of an ink droplet on a rear surface of the doctor 4 is microminiaturized, a number of a continuously printing meter which eliminates backing of a spatula is remarkably extended, and continuous coating having few coating defects can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mechanism for preventing a coating surface defect from occurring when a coating liquid is scraped off by a doctor in gravure printing / coating.

[0002]

2. Description of the Related Art In gravure printing, a cylinder is used in which a number of small concave portions called cells corresponding to images are formed on a cylindrical surface as a printing plate, and a relatively low-viscosity ink layer is formed on the surface of the cylinder. A method is used in which the ink is scraped off with a removing tool, and the web is brought into contact with the ink remaining in the cells on the plate surface to transfer the ink.

[0003] This doctor is usually made of a thin metal plate having elasticity and applies a constant pressure to the plate surface to scrape the coating liquid while pressing the tip of the doctor. The coating liquid accumulates on the back side of the tip (edge) of the surface, and the grown droplets are irregularly transferred onto the raw material, causing spots or streaks to form a defect called Heraula that affects the image quality .

[0004] These phenomena occur more or less with the progress of continuous printing, but have been a serious problem that the uniformity of the coated surface is impaired, especially when the growth of droplets is large.

In order to alleviate this, there has been a conventional method in which the state of accumulation on the blade edge is made uniform by polishing the blade edge of the doctor, and a condition for minimizing the Heraula by changing the angle and pressing pressure of the blade edge. Had been taken.

However, the blade edge of the doctor wears unevenly due to friction between the plate surface and the coating material. Therefore, it is necessary to interrupt the coating in the continuous coating. To avoid this, it is necessary to increase the hardness of the blade edge. However, the limitation of this method is that the hardness of the cutting edge is greater than that of the plate, which is usually related to the wear of the plate coated with the chrome plating layer. The workable quantity will decrease.

Also, the method of changing the angle of the blade edge and the pressing pressure affects the transfer of the coating material beyond a certain range and causes a change in the film thickness. It was something.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a novel means for preventing a coating defect caused by a heraula of a doctor in gravure coating.

[0009]

Means for Solving the Problems The present inventors have studied in detail the mechanism of occurrence of the Heraula phenomenon in gravure coating, and as a result, have reached the present invention.

[0010] It is considered that the back of the coating agent at the time of gravure coating is generated by elasticity in the thickness direction at the moment when the pressure applied by the doctor to the coating agent on the plate surface rotating at high speed is released. Has the viscoelasticity of the coating agent, the rotational speed of the plate and the shape of the doctor blade, but the former two are industrially difficult to set arbitrarily from the quality and productivity of the coating film. Continuous control is difficult for the reasons already mentioned.

[0011] Since it is difficult to completely prevent back running, the practical solution is to prevent the growth of the liquid droplets accumulated on the back and move it to the coating surface in a small time to reduce the quality defect. As a result, it is possible to prevent such large thickness unevenness.

As a method for this, a method of removing the droplets grown by using a vacuum near the tip of the doctor and a method of controlling the cross section in an equilibrium state between the tip of the doctor and the liquid surface can be considered.

The first method is a general-purpose method that does not depend on the viscoelasticity of the coating agent, the shape of the doctor tip, and the rotation speed of the plate, but the additional mechanism including position control is complicated. It is difficult to easily deal with plates of various diameters.

The second method is a simple method and a practical method if control within a required range is possible. Based on this idea, we studied means to suppress the growth of droplets on the back surface of the doctor tip. As a result, it was effective for this purpose to reduce the droplet diameter in the equilibrium state by lowering the surface tension of the doctor surface near the tip. And completed the present invention.

As a method for lowering the surface tension of the doctor surface near the tip, a commonly known method of coating a low surface energy substance such as a fluorine compound or codeposition by composite plating is typical, and the method of coating is simple. And has a large effect, but has poor resistance to polishing and cleaning. The method of eutectoid plating provides a stable doctor blade and excellent resistance. The embodiment can be selected according to the purpose.

A first aspect of the present invention is a doctor for preventing heraura, characterized in that at least one surface of a blade is subjected to a fluorine-containing treatment.

According to a second aspect of the present invention, there is provided a doctor for preventing heraura, wherein the fluorine-containing layer is a metal plating layer in which polytetrafluoroethylene particles are eutectoid.

According to a third aspect of the present invention, there is provided a gravure printing machine including the doctor according to any one of the first to second aspects, wherein a gravure printing machine can be prevented during printing.

According to a fourth aspect of the present invention, there is provided a printing method using the doctor according to any one of the first and second aspects or the gravure printing machine according to the third aspect to prevent heraura during printing. Is the way.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The mechanism of the present invention is a heraura prevention mechanism in which at least one surface of a doctor blade of a gravure printing machine is treated with a fluorine-containing compound. This will be described below with reference to the drawings.

FIG. 1 is a sectional view showing an outline of the mechanism of the present invention. The ink in the ink tank is supplied to the surface of the plate, the unnecessary portions are scraped off by a doctor, and then contacted and transferred to the raw material by an impression cylinder, dried and wound up by a drying device thereafter. In this figure, the drying device is omitted. The doctor is attached to the doctor holder at the tip of the doctor holder holder whose angle can be adjusted, and further includes a pressurizing device such as an air cylinder for pressing the blade edge against the plate at a constant pressure.

[0022]

The present invention will be described below with reference to examples.

<Example 1> A water-based ink was applied to a plastic film by a gravure printing machine using a steel doctor having a 0.07 mm-thick cutting edge having a polytetrafluoroethylene coating on one surface of the cutting edge. The ink used was an aqueous ink "Aqua Ecole" manufactured by Toyo Ink Mfg. Co., Ltd. The film used was a stretched polyester film having a thickness of 12 μm (corona treated). As the gravure plate, a solid plate with a surface depth of 12 μm and chrome plating was used. Printing speed 100
The printing was carried out continuously at 20,000 m at a speed of m / min, and the occurrence of Heraula in the printed matter and the state of droplets at the doctor blade were observed.

As a comparative example, printing was carried out under the same conditions using a steel doctor having a blade edge thickness of 0.07 mm without a polytetrafluoroethylene coating, and the same evaluation was performed.

The results show that when a steel doctor with a 0.07 mm-thick blade not coated with polytetrafluoroethylene was used, a Heraula having a width of 0.5 mm or more was 200 mm thick.
From the point when it passed 0 m, it occurred at a rate of 1 place / 400 m, but when a steel doctor with a 0.07 mm-thick cutting edge coated with polytetrafluoroethylene was used, Heraura with a width of 0.3 mm or more occurred up to 20,000 m. Did not.

When a steel doctor having a 0.07 mm-thick steel blade without a polytetrafluoroethylene coating was used, the droplet at the doctor blade was visually observed after 200 m. When a steel doctor having a blade edge thickness of 0.07 mm was used, droplets which could be visually confirmed as dots were not visually observed.

From these results, the mechanism of the present invention has the effect of minimizing the growth of ink droplets on the back of the doctor in the case of continuous printing of water-based ink and dramatically increasing the number of continuous printing meters free of herabra. It was confirmed that there was an effect of enabling continuous coating with few coating defects.

Example 2 An oil-based ink was applied to a plastic film by a gravure printing machine using a 0.07 mm-thick steel doctor having a 5-μm-thick nickel plating containing polytetrafluoroethylene on one side of the cutting edge. . The ink is oil-based ink "N" manufactured by Toyo Ink Manufacturing Co., Ltd.
The film used was a 12 μm-thick stretched polyester film (corona-treated) using “ewLP Super” black ink. The gravure plate used was a chrome-plated picture plate with a cell depth of 12μ. Printing is continuous 2 at a speed of 100 m / min.
000 m was performed, and the state of occurrence of herabra in the printed matter and the state of droplets at the doctor blade were observed.

As a comparative example, printing was performed under the same conditions using a steel doctor having a blade edge thickness of 0.07 mm and the same evaluation was performed. The results show that when a steel doctor with a blade edge thickness of 0.07 mm was used, a heraura having a width of 0.5 mm or more was generated at a rate of 1 location / 600 m from the time when it passed 3000 m, but the thickness including polytetrafluoroethylene was 5 μm. In the case of using a nickel doctor-plated steel doctor with a blade edge thickness of 0.07 mm, no Heraura with a width of 0.3 mm or more occurred up to 20,000 m. When a steel doctor having a blade edge thickness of 0.07 mm was used, the droplet at the doctor blade edge was visually observed from a point of time exceeding 200 m. In the case of using a 0.07 mm steel doctor, droplets that could be visually confirmed as dots were not visually observed.

From these results, it can be seen that the mechanism of the present invention has the effect of minimizing the growth of ink droplets on the back of the doctor in the case of continuous printing of oil-based ink and dramatically increasing the number of continuous printing meters free of heraula. It was confirmed that there was an effect of enabling continuous coating with few coating defects.

[0031]

By using the mechanism of the present invention, it was possible to prevent the occurrence of a defect called Heraula among printing defects caused by a doctor in continuous gravure printing. In particular, a stable prevention effect can be easily obtained without using a complicated mechanism for both the water-based and oil-based coating agents, and continuous coating without defects has been made possible.

[Brief description of the drawings]

FIG. 1 is a conceptual sectional view showing a state of occurrence of heraula.

FIG. 2 is a conceptual diagram showing the vicinity of a cutting edge.

Claims (4)

[Claims] 1. A doctor for preventing heraula, wherein at least one surface of a blade is subjected to a fluorine-containing treatment. 2. A doctor for preventing heraula, wherein the fluorine-containing treatment layer is a metal plating layer in which polytetrafluoroethylene particles are eutectoid. 3. A gravure printing machine comprising the doctor according to claim 1, wherein a gravure printing press can be prevented during printing. 4. A printing method using the doctor according to claim 1 or the gravure printing machine according to claim 3, wherein a heraura during printing is prevented.