KR101089658B1 - Method for controlling of film thickness around rotating roller partially immersed in liquid - Google Patents

Abstract

A method of controlling the liquid film thickness of a portion in contact with a printing surface by mounting a blade for blocking air inflow at the rear of a rotating roller immersed in liquid and controlling the position and angle of the blade is disclosed.
A method of controlling the liquid film thickness of a roller rotating at high speed in a liquid, the method comprising: installing a blade immersed in the liquid at the rear of the roller and extending in the longitudinal direction of the roller; And controlling the liquid film thickness on the upper circumferential surface of the roller by moving the blade on the lower circumferential surface of the roller.
In the liquid film thickness control method according to the present invention, the thickness of the liquid film can be stably controlled by controlling the position of the blade installed to prevent air inflow.

Description

Method for controlling film thickness around rotating roller partially immersed in liquid

The present invention relates to a liquid film thickness control method of a roller that rotates at high speed in a liquid, and more particularly, to a printing surface by mounting a blade to block air inflow at the rear of the roller and controlling the position and angle of the blade. It relates to a method of controlling the liquid film thickness of the portion in contact with.

In general, in gravure printing or coating operations using a roller, the thickness of the ink on the rotating printing roller is a very important factor in determining the quality of printed matter.

1 shows a schematic configuration of a printing process using a roller.

As can be seen in the drawing, printing using a roller is performed between the pressure roller 4 and the printing roller 3 while the printing roller 3 is rotated while partially submerged in the ink 2 filled in the fan 1. The ink 2 is transferred to the raw material 5 which is the printed matter passing through.

In the printing process using the roller, the air is sucked into the ink along the rotational direction of the roller when the rotational speed of the roller exceeds a predetermined limit (threshold speed), and the introduced air makes the liquid film flow on the roller unstable. The print quality will be degraded.

In order to prevent this, the present applicant discloses to install a blade for blocking the air at the rear of the roller through the patent application of the application number 10-2008-0077494 (air inflow blocking device of the high-speed rotating roller immersed in liquid) have.

On the other hand, it is required to stabilize the liquid film flow and to control the thickness of the liquid film. Liquid film thickness is the factor that has the biggest influence on print quality during the printing process, and if the roller rotation speed exceeds the critical speed, it is more expensive to use other means than controlling the film thickness only by controlling the roller rotation speed. And more efficient in quality.

An object of the present invention for solving the above problems is to provide a method for controlling the liquid film thickness of the portion in contact with the printing surface by using a blade for blocking the air inlet to the rear of the roller.

In the liquid film thickness control method of the printing roller according to the present invention for achieving the above object in the method for controlling the liquid film thickness of the roller rotating at high speed in the liquid,

Installing a blade submerged in the liquid at the rear of the roller and extending in the longitudinal direction of the roller and moving the blade on the lower circumferential surface of the roller to control the liquid film thickness at the upper circumferential surface of the roller.

The present invention has the effect of improving the quality and productivity of the printed matter by controlling the liquid film thickness by controlling the position and angle of the blade is installed to block the inflow of air into the ink.

1 is a cross-sectional view showing a schematic configuration of a printing process using a roller,
2 is a view showing a flow situation generated in the vicinity of the roller when the printing roller rotates above the critical speed,
3 is a view showing a state in which a blade for preventing air inlet is installed in an embodiment according to the present invention,
FIG. 4 shows the configuration of the blade 6 shown in FIG. 3 and
5 is a graph showing the change of the liquid film thickness according to the position of the blade in the embodiment according to the present invention.

The terms or words used in this specification and claims are not to be construed as limiting in their usual or dictionary meanings, and the inventors may properly define the concept of terms in order to best explain their invention in the best way possible. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention.

Hereinafter, the liquid film thickness control according to the present invention will be described in detail with reference to the accompanying drawings.

Mass and momentum conservation equations, which are governing equations for analyzing liquid flow on a roller rotating at high speed, partially submerged in liquid, are represented by Equations 1 and 2 below.

Where F _SF is the surface tension.

The density ρ is calculated as in Equation 3 below.

Here, α _k is a volume fraction of the k (= 1, 2) th fluid in the calculation region and has a value of 0 ≦ α _k ≦ 1. If α _k = 0, there is no k th fluid in the computational domain. If α _k = 1, only k th fluid is present.

And the viscosity (μ) is computed like following formula (4).

The volume ratio of the second phase (α ₂ , fluid) is obtained by the volume fraction equation of Equation 5 below,

The first phase (α ₁ , air) is calculated by the following equation (6).

The surface tension F _SF uses a continuous surface force (CSF) model such as the following Equations 7 to 9.

Where n is the vertical vector of the surface and κ is the curvature.

And, the adhesion condition (wall adhesion) between the ink and the roller is defined as in Equation 10 below.

와

는 각각 접선 및 법선 벡터이다.Where θ _w is the contact angle between the fluid and the wall,

Wow

Are the tangent and normal vectors, respectively.

The boundary and initial conditions applied for numerical analysis of the model are as follows.

First, the boundary conditions for numerical analysis are as follows.

Interface between fluid and roller:

Interface between the fluid and the wall:

Next, initial conditions are as follows as volume ratio in an analysis area | region.

Filled with air: α ₁ = 1

Filled with ink: α ₂ = 1

Interface: α ₁ = α ₂ = 0.5

Computational numerical analysis is performed by the VOF method using the governing equations, boundaries, and initial conditions as described above.

Pressure implicit with splitting of operator (PISO) algorithm is used to analyze the flow field combined with pressure and velocity, and 2-order upwind difference scheme for mass and momentum equations to improve accuracy in space. The first-order implicit method is used for time, and the accurate body force-weighted equation for VOF calculation of fluids with large differences in density for pressure interpolation. scheme).

The time interval was based on 10 ^-4 , and it was determined that the convergence of the dependent variables converged when the relative variable relative error was less than 10 ^-5 at each time interval.

As a result of this analysis, as described in the literature (Bolton, B., and Middleman, S., 1980, Air entrainment in a roll coating system.Chemical Engineering Science, 35, 597-602.) An analysis result showing that the air flows into the liquid occurs when rotating above the critical speed.

FIG. 2 is a diagram illustrating a flow situation generated around a roller when the printing roller rotates at a critical speed or more by computer numerical analysis.

2 shows a state in which air flows into the ink on the surface of the printing roller when rotating at a critical speed or more, as can be seen from the drawing, the rotational force of the roller when the roller rotates clockwise. Due to this, air is introduced into the liquid, and the air thus introduced is attached to the roller surface and moves together, thereby preventing the ink liquid film on the roller from being properly formed. This causes instability of the liquid film flow and causes a deterioration in print quality.

As a way to prevent this, it has been proposed to install an air-blade behind the roller. The blade is to prevent the inflow of air at the source to ensure that the liquid film is formed stably even if the roller rotates at a high speed.

Figure 3 shows a state in which a blade for preventing the inflow of air in the embodiment according to the present invention installed.

The blade 6 is installed so as to be spaced apart from the liquid surface of the ink 2 at the rear of the roller 3 by a predetermined distance from the circumferential surface of the roller 3, and on a line extending radially from the center of the roller 3. Is placed. The blade 6 extends along the longitudinal direction of the roller 3.

Factors that may affect the thickness of the liquid film depending on the position of the blade 6 include the distance that the blade 6 is spaced from the liquid surface of the ink 2, and the blade 6 is spaced apart from the circumferential surface of the roller 3. Distance and angle, the length of the blade 6 and the like. In addition, as a result of careful observation and experiment on the thickness of the liquid film, the thickness of the liquid film is best obtained when the blade 6 is installed on the circumferential surface of the roller 3 and its direction coincides with a line extending radially from the center of the roller 3. It can be seen that it can be controlled stably. Moreover, it turned out that the position of the blade 6, ie, the circumferential position of the roller 3, is the most important element which controls the thickness of a liquid film.

4 shows the configuration of the blade 6 shown in FIG. 3. As shown in Fig. 4A, the blade 6 is composed of a connecting portion 6a, a fixing portion 6b and an exchange blade 6c.

A connection 6a is provided for securing the blade 6 to the fan in which the ink is submerged.

Since the exchange blade 6c can be easily worn due to friction with the air and the roller surface, for easy replacement, as shown in Figs. 4A and 4B, the fixing blade 6b It is configured to be quarried against.

5 is a graph showing the change of the liquid film thickness according to the position of the blade in the embodiment according to the present invention.

In FIG. 5, the rotation speed of the roller 3 is 20 rad / s, and the position of the blade 3 represents the position on the circumferential surface of the roller 3. The position of the blade 3 is represented by the radial angle seen from the center of the roller 3. For example, 90 degrees indicate the position directly under the roller 3, and 0 degrees represents the position immediately after the roller 3.

Referring to FIG. 5, it can be seen that the thickness of the liquid film changes and shows a constant correlation as the position of the blade 6 is changed. Moving the position of the blade 6 from 0 °, i.e., immediately after the roller 3, to 90 °, i.e., directly below the roller 3, changes the thickness of the liquid film as shown by the solid and dashed lines. Here, the thickness of the liquid film is measured on the upper circumferential surface of the roller 3, the position 8 is on 45 ° and the position 9 is on 90 °, that is, directly above the roller 3.

It can be seen that the liquid film thickness decreases as the blade 6 is installed farther from the surface of the ink 2.

This is understood to be achieved by controlling the starting position at which the ink 3 adheres to the roller 3. Referring to FIG. 3, when the blade 6 is directly below the roller 3, the length of the ink 3 adhering to the roller 3 is short (the circumferential length of the roller / 4) and thus the thickness of the liquid film. It is also thin. In contrast, it can be seen that the longer the blade 6 moves directly below the roller 3, the longer the length of the ink 3 adheres to the roller 3, and accordingly, the thickness of the liquid film becomes thicker.

Therefore, when it is necessary to control the thickness of the liquid film thickly, it is preferable to provide it close to the surface of the liquid film, and when it is necessary to control the liquid film thickness thinly, it is preferable to install it far from the surface of the liquid film.

Preferably, the blade 6 is preferably located in the range of 90 ° to 15 ° below the roller 3. When it exceeds 90 °, that is, when the blade 6 is positioned forward than directly below the roller 3, the position at which the ink 3 starts to stick is too short, making the liquid film flow unstable and less than 15 °. In this case, the effect of blocking the inflow of air is reduced.

Therefore, the liquid film thickness control method according to the present invention can stably control the thickness of the liquid film by controlling the position of the blade installed to prevent air inflow, thereby not only stabilizing the liquid film but also improving the productivity of the product.

The liquid film thickness control method according to the present invention can stabilize the quality of printed matter by using in parallel with the method of limiting the roller rotation speed as in the prior art.

Although the present invention has been described in detail only with respect to the described embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made within the technical scope of the present invention, and such modifications and modifications belong to the appended claims.

1: fan 2: ink
3: printing roller 4: pressure roller
5: material 6: blade
7: inflow air

Claims (3)

A method of controlling the liquid film thickness at the upper circumferential surface of a roller which is partially locked in a liquid and rotates at high speed,
Installing a blade immersed in the liquid, the blade extending in the longitudinal direction of the roller adjacent to a portion where the roller enters the liquid to prevent air accompanying the roller from entering the liquid; And
And moving the blade along the circumferential direction of the roller on the lower circumferential surface of the roller to control the liquid film thickness on the upper circumferential surface of the roller. The method of claim 1, wherein the blade is installed on a line extending radially from the center of the roller. The thickness of the liquid film according to claim 2, wherein the thickness of the liquid film ranges from 90 ° to 15 ° in the circumferential direction of the blade from the center of the roller, where 90 ° is an angle when the blade is directly below the center of the roller. Means that the smaller the angle is, the closer the roller is to the part entering the liquid).

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