What to do when color deviation occurs in label printing?

How Do Color Differences Occur in Label Printing?

Color difference, the variation between printed colors and the design file or standard color, is nearly impossible to eliminate entirely in label printing, but it can be controlled within an acceptable range. Understanding the sources of color difference is the first step to solving the problem.

According to industry experience, color differences mainly come from five aspects: the color gamut differences inherent in different printing methods, color performance variations between different material batches, accuracy in color matching, stability control during the printing process, and the impact of post-processing on color. Only by breaking down each one can the right solution be applied.

Different Printing Methods Produce Different Color Differences

Different printing methods have fundamental differences in color gamut range and color reproduction capability. Offset printing offers excellent color reproduction with clear dots and precise spot color control; digital printing has zero plate-making cost but a narrower color gamut than offset, and large solid color areas may show uniformity variations. Flexography and screen printing also have their own color gamut characteristics.

If the same label design is proofed digitally and then produced in bulk using offset printing, color differences between the paper proof and the final production run are inevitable. The solution is to use the final mass production method for proofing. Digital proofs can only serve as a reference for effect and structure, while the bulk production color should be based on the offset press color matching.

Material Differences Are an Invisible Variable

For the same label material, different batches may have subtle differences in surface coating thickness, smoothness, and whiteness, all of which directly affect color performance. Coated paper prints well and does not interfere with color difference control. However, non-absorbent materials such as synthetic paper and PET have different ink adhesion properties, and their color performance differs significantly from paper-based materials.

When switching material batches or suppliers, an on-press color matching test must be performed first; the previous color parameters cannot be used directly.

Key Control Points in Color Matching

Color matching is the process where the press operator adjusts the colors on the printing machine to match the customer's approved sample, and it is a critical step in color difference control. Several things need attention during color matching:

First, confirm the standard light source. Compare colors under D50 or D65 standard lighting to avoid visual judgment under different color temperatures. Second, use a densitometer or spectrophotometer to measure DeltaE. The industry typically requires DeltaE not to exceed 3, with strict applications requiring no more than 1.5. Third, retain the customer-signed approved sample as the sole color standard for batch production. It is recommended to specify the color difference standard range in the contract.

Stability Control During the Printing Process

During printing, ink viscosity, printing pressure, press speed, and ambient temperature and humidity all affect color stability. For large-quantity label runs, it is recommended to perform color spot checks at regular intervals during printing, using a densitometer to measure and record DeltaE values, so that deviations can be detected and corrected promptly. Color difference control in digital printing depends more on the device's ICC color management profiles and routine calibration maintenance.

Impact of Post-Processing on Color

Lamination will make colors appear darker and deeper, with matte film having a greater effect than glossy film. Hot foil stamping must be registered with the printed pattern. The color in spot UV-coated areas will appear more vivid than in non-coated areas. Post-processing factors should be considered during color matching: finalize the post-processing plan first, then perform color matching under those conditions.

Practical Recommendations

Establish a color difference management workflow: proof approval and color swatch signing, DeltaE standard setting, first-article inspection, in-process sampling inspection, and final inspection comparison. Record color difference data for each production run and gradually build a color difference database for different materials and equipment. Digital printing and offset printing each have their suitable scenarios: digital printing for small batches requiring fast delivery, offset printing for large batches requiring high precision.