How to control the dot enlargement in the offset printing process

The expansion of outlets does have a negative impact on offset printing. So, how to control network expansion? We talk about specific operational measures from the following aspects.

1. Master offset printing exposure time
Control of the exposure time, development time, developer humidity, concentration ratio is one of the ways to reduce dot gain. Separation of four-color film through the printing, the graphic network transferred to the printing plate, requiring the network to expand as little as possible, 3% to 5% outlets are not lost, 5% of the outlets do not expand, 95% -98% of the outlets are not Paste version, strong outlets, positive and neat particle circles, no white spots, burrs, and rich and clear tone levels. This requires the accurate preparation of PS version of the developer, according to the specification of the formula proportion, exposure time with gray ladder ruler, printing plate signal to data control, after printing plate out of the sun with a 5-10 times the magnifying glass inspection in the ladder and The level of the signal bar is missing the situation of stencil and network expansion.

2. Reasonable choice of lining material and printing pressure
Offset printing is a kind of indirect printing method. It needs an intermediate elastic body of a rubber roller to transfer the printing plate image dot to the surface of the paper. The blanket and its backing are the intermediate media for graphic transfer. Without the padding, there is no printing pressure. By adjusting the thickness of the lining of the offset printing press, the best printing pressure can be obtained, and the uniformity of the ink shades and the sharpness of dots of the printed product can be enhanced. The printing pressure is obtained by the two methods of lining thickness and roller center distance adjustment, and the pressure should be based on the premise that the printed product has strong dots, clear graphics, vivid colors, and dark and light, and the smaller the amount of application, the better the control point expansion. Deformation, adjusting accurate printing pressure is critical. Accurately calculate and use the micrometer to measure the thickness of the rubber roller lining during work, adjust the center distance between the two rollers, and evenly use the minimum printing pressure within the allowable range of the dot expansion.

3. Control ink balance to reduce dot gains
Controlling the balance of ink and ink can improve the quality of printed products. Advocate to use as little water as possible on the premise of not contaminating the plate and pasting plate. The ink balance is also a measure of the level of the offset printing operator's technology. Only when the ink is balanced, the paper is small in stretch and deformation, the overprint accuracy is high, and the color is bright. The hue and hue are consistent with the ink color shades of a batch of proofs. The printed dots are round Strong. Avoid large ink and large ink layers during offset printing. Extend the dot expansion of the ink layer too thick. Control 3% to 5% of bright dots. Small dots are not lost. 5% of intermediate dots do not expand, do not expand, darken 95% -97% of large outlets do not overlap, and the control standard for ink volume is: the graphic network points are solid and clear, and the ink color hue is accurate, using as little ink as possible.

Source: Zhongyuan Printing Network