Analysis of Printing Color Sequence in Flexographic Printing

In color printing, the typical approach is to use four colors: yellow, magenta, cyan, and black, which are printed in a specific sequence. Theoretically, there are twenty-four different printing color sequences possible with these four colors, and any sequence should yield satisfactory results. However, different sequences can lead to varying color effects on the printed material. A rational printing color sequence enhances the colors, makes the image closer to the original, and can improve clarity and depth. Additionally, it protects the paper surface, increases product gloss, and facilitates registration. This is particularly important in color printing, especially in packaging, when using more than four colors, spot colors, or full coverage.

In flexographic printing, color plates often use solid colors, and the water-based inks typically have lower transparency. Therefore, when determining the registration order of the color plates, it’s essential to consider whether the overlapping colors meet the original requirements and achieve a good registration effect, as this directly impacts the product’s quality. The printing color sequence is mainly determined by the design of the original and the chosen plate-making order but can also vary based on product characteristics and process requirements.

In general, the color sequence in flexographic printing is determined by the following factors:

1. Inks with strong coverage should be printed first. Typically, light colors are printed first, followed by darker colors.
2. When printing multiple colors without a dark outline, the dark outline should be printed first.
3. If a dark color is needed to cover the edges of the image outline to eliminate fringing, it must be printed last. However, if this dark color also serves as the registration standard, it can be partially printed first and then registered with the other colors, with the dark outline printed last.
4. The main color tone of the image is generally arranged to be printed last.
5. For images containing both halftones and full-color solids, the halftone and solid colors should be printed separately to adjust pressure and use different inks, ensuring print quality.

In three-color printing, the typical color sequence is: cyan – magenta – yellow, with solid densities around 1.6 for cyan, 1.4 for magenta, and 1.2 for yellow.

Next, let’s discuss an important application area of flexographic printing: the color sequence in plastic flexible packaging printing.

Plastic flexible packaging printing usually starts with a white ink base to enhance other colors. This method has several advantages: first, white ink has the best affinity for polyolefin films (PE, PP), providing strong adhesion; second, white reflects all colors, making the printed colors more vibrant; third, it thickens the ink layer, enriching the print’s depth and dimensionality.

Flexographic printing on plastic flexible packaging can be categorized into “inner printing” and “surface printing.” Inner printing involves using a reverse image plate to transfer ink to the inner side of a transparent film, producing a correct image on the film’s outer surface. Surface printing, in contrast, has the opposite color sequence. For surface printing, the typical sequence is: white – yellow – magenta – cyan – black. For inner printing, it is: black – cyan – magenta – yellow – white.

Comparatively, inner printed materials are brighter, more colorful, fade-resistant, moisture-proof, wear-resistant, durable, long-lasting, non-stick, and non-breakable. Since the ink is printed on the inner side of the film (sandwiched between two film layers), it does not contaminate the packaged items, complying with hygiene regulations.

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Flexographic printing machines are multi-color printers, using a wet-on-dry overlay method with at least six colors, typically ten, and can reach up to twelve colors, including UV and infrared glossing. The printed products primarily consist of decorative printed materials featuring text, images, halftones, and solids, with some requiring metallic inks and gloss. Therefore, the color sequence in flexographic printing is highly flexible. When determining the printing color sequence, one must analyze specific product requirements to achieve the best sequence. For example, halftones might be printed first, followed by solids, then metallic inks, and finally gloss. In some cases, if the ink color is too dark and the anilox roller cannot provide the necessary thickness, the color may need to be reprinted using another unit. The sequence for four-color halftones should not be changed arbitrarily. For spot color printing, the general rule is to print lighter colors first to enhance the brightness of the darker colors when overlaid. For spot colors printed using the overlay method, the sequence should have the secondary color printed first, followed by the primary color.