Five Simple Steps to Easily Change Colors on Printing Presses

Posted on 05-08-2024 by

Changing colors on a printing press involves switching the ink color of a particular unit or transitioning from regular base color inks to spot color inks. Nowadays, using spot color inks for printing is very common, and sometimes a shift to four or five spot colors is required in just one shift. Frequent washing of the press can be quite bothersome, especially when dealing with poor roller quality or light shades of spot color inks. Sometimes, even after repeated washing and color changes, the process fails, disrupting production. Therefore, color changing is a crucial task that requires attention to detail and some techniques to ensure spot color printing is hassle-free. Through years of practical experience, the following points have been summarized:

1. Firstly, one must learn about the theory of subtractive color and understand the basic principles of color change inks. This knowledge should be applied practically and flexibly through repeated practice.

2. Upon receiving a print job requiring spot colors, it's essential to analyze the composition of the spot color. Which primary color inks should be mixed to create the desired spot color? What are the approximate proportions? For instance, orange-red typically requires more yellow ink and less red ink, while teal generally requires more red ink and less blue ink. Brown usually consists of equal parts of yellow and red ink with some black ink, and lighter spot colors may require a significant amount of extender.

3. Choose a color group for washing and color changing that closely resembles the hue of the spot color. Nowadays, four-color machines are prevalent, offering flexibility, particularly with the cyan color group. Choosing the wrong color group will undoubtedly lead to undesired results. For instance, never select the cyan group for orange-red ink; instead, opt for the yellow or magenta group. Similarly, for silver ink, avoid the magenta group and choose the black group. This ensures easier color changes, even if the washing process is not entirely thorough, minimizing visual effects that could impact product quality.

4. Before preparing for washing and color changing, it's crucial to pre-coat the rollers with other primary inks present in the spot color, based on the hue analysis of the spot color. For example, if the spot color is golden-red, apply some yellow ink over the existing red ink on the roller. If it's brown, apply some yellow ink and a small amount of black ink over the red ink. Then, let the machine run for a while before rinsing with washing solution. This pre-coating helps approximate the color on the rollers to the spot color before washing, making the washing process easier. Usually, one or two washes are sufficient, even if some residue ink remains, it won't significantly affect the color of the print.

5. It's crucial to thoroughly clean the rollers within a short timeframe, ensuring the correct pressure between rollers, rubber strips in the washing unit, and ink transfer rollers. Additionally, pay extra attention to thoroughly wash the ends of the rollers. Over time, rollers tend to develop an olive shape, and their ends are more prone to aging, leading to cracks and spots that retain ink residue, affecting the hue of the print. If necessary, specialized cleaning agents like water and paste removers can be used, albeit at slightly higher costs.

In conclusion, accumulating knowledge and experience, mastering effective work methods and techniques, and judiciously using appropriate additives are essential to save time, effort, and money while achieving optimal results. This ensures that spot color printing becomes less troublesome and more efficient.