The requirements for the water conveyance are uniform, stable, and continuous water supply to the plates. This is an important condition for ensuring the balance of ink and water. Because of the small viscosity of the water, it is easy to beat evenly, so the water roller, the string water roller, the water transfer roller, the clutch of the water roller and the pressure regulating mechanism. The function of each part is described in detail below.
1. Bucket and fountain ink
The function of the bucket is mainly to hold the water. The role of the bucket roller is to transfer the water in the bucket to the string water roller. The water bucket roller and the bucket are not as strict as required between the ink fountain and the ink roller. Normally, the thickness of water on the roller is constant (by affinity adsorption). Changing the volume of water can only be achieved by changing the angle of the roller. There are two intermittent and continuous types of rotation of the fountain roller:
Intermittent transmission of water, the water is easy to flow on the fountain roller, that is, when the rotation and stop, the state of the water in the fountain roller is not the same, but also affected by the temperature is relatively large. If the speed is low and the temperature is high, the water is easily volatilized, resulting in non-uniformity of the water, so this structure is now tending to be eliminated.
Continuous water supply, as long as the speed is certain, the state of water on the bucket is the same, and because the air around the bucket roller is always in a flowing state, the temperature is relatively low, which is conducive to water conjunctiva on the bucket roller. Ensure the water supply is stable. When the water supply needs to be adjusted, it can be changed to the speed of the roller. Due to the elimination of impact caused by speed changes, the operation is smooth and the structure is more reasonable.
At present, almost all multi-color offset presses use a continuous water supply device. The speed of the water fountain roller is driven by a DC speed control motor and a reduction gear mechanism.
Since the pH of the fountain solution is generally between 4-6, ie slightly acidic, it is easy to react with the surface of the bucket, causing corrosion of the bucket. Therefore, when it is not working, it is best to remove the water from the bucket.
2. Water transfer roller
The role of the water transfer roller is to transfer the water from the roller roller to the roller. The requirement for the roller is that it must be in a parallel state when contacting the roller and the roller to prevent the water from flowing unevenly. The pressure of the water transfer roller must be moderate when it comes into contact with both sides, that is, it can play the role of water transfer, and it can not cause a large impact. Due to the oscillating motion of the water transfer roller, there are always some inertial impacts. In order to solve this problem, some equipments currently use metering roller water supply, eliminating the swing type water transfer roller. This water supply method utilizes the speed difference between the fountain roller and the metering roller to control the amount of water.
3. String water roller
The role of the string of water rollers is to balance the water in both the circumferential and axial directions, ensuring that the water on the water roller is always distributed evenly. It is much easier to evenly distribute the ink. Therefore, the requirements for the string water roller are not as stringent as the string ink roller. The requirements for the material on the surface of the skewer roll are hydrophilic and ink repellent to prevent the ink from returning to the bucket. Otherwise, if the ink sticks to the skewer roller or fountain roller, the water cannot reach the ink due to the repulsion of the ink, and the uniformity of the water supply is destroyed. The movement of the string water roller is driven by the ink string roller.
4. Water roller
There are four roles for the water roller:
(1) Water supply to the surface of the printing plate This is its main function. The water on the printing plate is lost in the following forms:
a. Ink emulsification: Ink emulsification is an important source of water loss. From the ink transfer point of view, ink emulsification is a must. When the water roller comes into contact with the ink-receiving image portion or the ink roller comes into contact with the non-graphical portion of water, water may be pushed into the ink to form a water-in-oil emulsion. In color printing, when one color is printed, two colors of ink may be printed on the paper where there is water. If the ink is not emulsified, the ink cannot be transferred to the paper.
b. Paper Absorption: The water on the printing plate is transferred to the printed sheet through the blanket. Due to the good hydrophilicity of the paper, most of the water on the blanket is absorbed by the paper, and the paper expands after absorbing water, bringing a series of printing difficult.
c. Evaporation: Since both the water roller and the ink roller are driven by friction between the plate and the ink roller. Friction heat, one of the heat generated is transmitted through the air, and the other is absorbed by water, so that the water evaporates. When the room is relatively dry, the water on the plate can also be lost to the surrounding air.
d. Loss: During printing, due to vibration and impact, the water on the water roller is sometimes thrown off, and a special water receiving device is generally installed under the water bucket of the printing machine. If the water in the bucket fails to be replenished, the ink and water balance is destroyed and the printing cannot be performed normally.
(2) to make up for the errors of the surface of the printing plate and the skewer roller. The outer layer of the water roller is made of water glue, which is easy to deform, so its ability to make up for errors is very strong.
(3) The shock absorbing water roller forms an impact every week and on the surface of the printing plate. If its surface is easily deformed, it can absorb the energy of the impact, thereby achieving the purpose of absorbing vibration.
(4) Safety function When foreign matter enters between the water roller and the printing plate, since the surface of the water roller is deformed, the printing plate is subject to a small amount of damage.
5. Adjustment of the water roller
The adjustment of the water roller and the adjustment of the ink roller are basically the same, but it is necessary to pay attention to the mutual influence between the upper and lower water rollers.
When the pressure between the inker roller and the skewer roller is too large, the water may not be pushed down and the amount of water applied to the down roller will be reduced. The amount of water applied to each water roller can be calculated to be 50% each. When the water roller is on the water, it can also function as a uniform water and does not need to be as complex as the ink path. When two water rollers are on the water, they can complement each other and it is easier to keep the water even. For general quality prints, two water rollers are required, and the quality of the prints is not as high as a water roller.
The water roller is sometimes used in common with the first ink roller. This saves a water roller, which is generally used for alcohol wetting. The lifting mechanism of the water roller and the lifting mechanism of the ink roller are basically the same, and will not be described in detail here.
6. Water glue line
The function of the water velvet is to absorb water, store water, and make water, and the water is sucked onto the surface by a sucking phenomenon. Hydrogel glue is not selective to water and ink, which is the first one, which is adsorbed on the first, so the first water must be printed, so that the surface of the water roller has enough water, because of the ink repulsion, the ink will be difficult to transfer to Water roll up. If the surface of the water roller is stained with ink, it is difficult to transfer water, and the glue should be washed in a timely manner. Water glue can not be reversed, otherwise it will be uneven water supply, wear plate.
Taixing Chaobang Adhesive Co., Ltd.
