Determining the General Principles of Flexographic Printing Color Sequence
Since the color sequence significantly impacts the printing outcome, how should the color sequence in flexographic printing be determined? In general, the following principles can be followed:
Arrange the Sequence Based on the Content and Characteristics of the Original Manuscript:
Consider the content and characteristics of the original manuscript.
Choose the color sequence based on the overall tone of the design.
For warm tones (e.g., red, orange, yellow), consider printing black and cyan first, followed by magenta and yellow. For cool tones (e.g., green, blue), consider printing magenta first, followed by cyan.
Determine the Sequence Based on the Transparency of Inks:
Yellow ink typically has the highest transparency, followed by magenta and cyan, with black having the lowest.
Consider printing black first, followed by cyan or magenta, and finally yellow.
Consider the Characteristics of the Image:
Place the main color plate toward the end of the sequence to enhance the color atmosphere.
For landscape-dominant images, consider a sequence of black, magenta, cyan, and yellow.
For portrait-dominant images, consider a sequence of black, cyan, magenta, and yellow.
Determine Based on the Characteristics of the Printing Process:
Consider the angle between adjacent screen sets to minimize moiré effects.
When using both screen plates and solid plates, consider printing the screen plates first and then the solid plates.
Consider the Ink Absorption Properties of the Substrate:
If the substrate has high ink absorption, start with the first color using a high-viscosity ink.
For lower-quality paper, consider printing yellow first to compensate for paper defects.
Arrange Based on the Difficulty of Trapping:
In flexible plate printing, where substrates may deform, place the main colors of high trapping requirements in adjacent color groups.
Take into Account the Cost of Inks:
Consider the price of inks when arranging the sequence.
Start with cheaper inks like black and cyan and end with more expensive ones like magenta and yellow.
Consider the Difficulty of Overprinting in Multi-color Printing:
Due to decreasing printing adaptability from the first to the last color, consider placing dark plates at the beginning and light plates at the end.
These principles provide a foundation for determining the color sequence in flexographic printing. However, artistic considerations and the specific characteristics of the printing content, equipment, substrate, and desired effects may lead to variations in the color sequence arrangement.
Determining the Color Sequence in Flexographic Printing on Plastic Film
Choosing a rational color sequence is a crucial step in flexographic printing on plastic film. Due to differences in the composition and operation of inks used for surface printing (表印) and reverse printing (里印), the color sequence determination varies. The key differences in surface and reverse printing include:
Binder Composition:
Surface inks primarily use polyamide resin as a binder, offering good adhesion and gloss but poor resistance to high temperatures.
Reverse inks use chlorinated polypropylene as a binder for non-cooking types and polyurethane for high-temperature-resistant reverse inks.
Solvent Selection:
Surface inks commonly use xylene and isopropanol as solvents.
Reverse inks use toluene and ethyl acetate, with high-temperature-resistant reverse inks using acetone and ethyl acetate.
Abrasion Resistance:
Surface inks with polyamide resin are more flexible and have better abrasion resistance.
Reverse inks with chlorinated polypropylene resin are more rigid and have lower abrasion resistance.
Additive Selection:
Different additives are used in surface and reverse inks to enhance properties like adhesion, gloss, and viscosity.
Printing Process:
The plate-making process is the same for both, but surface printing produces a reversed image on the plate.
Considering these differences, the color sequence for surface printing on plastic film is typically arranged as white → yellow → magenta → cyan → black. For reverse printing, where a visual effect similar to surface printing is desired, the color sequence should be reversed, i.e., black → cyan → magenta → yellow → white.