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In everyday life, we often see food packaging such as pizza boxes, burger wrapping paper, and bakery packaging boxes produced by flexo printing machines. Some designs appear pale and fail to accurately reproduce skin tones, while others look solid with vibrant, eye-catching colors. This difference is largely due to the use of white underprinting. So, what is white underprinting? Which materials is it suitable for? What are the common issues and solutions? This article will answer these questions one by one.

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What Is White Underprinting

White underprinting is a process used in printing to enhance visual impact, prevent show-through, and protect specific areas. It involves applying a layer of white ink to the substrate first, followed by printing colors on top of it. Though it may seem like just a thin layer of white, it effectively solves two major problems.

When packaging materials are transparent or light-colored, printing colors directly can result in dull, grayish tones. On dark substrates, light-colored designs are even more likely to appear unclear and lack definition. White underprinting acts like a “white canvas” beneath the design, allowing subsequent colors to appear more vibrant and accurate. It is a standard technique in flexographic printing for products such as snack packaging bags, bottle labels, and baking paper, widely used in flexible packaging, labeling, and tobacco packaging applications.

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Which Materials Are Suitable for White Underprinting

Based on the need for white underprinting, materials can be divided into two categories: those that require white underprinting and those that do not.

Materials That Require White Underprinting

Transparent substrates: Films such as BOPP, PET, and NY used for sandwich packaging wrapping film and frozen food packaging. When printed on a flexo label printing machine without a white base, colors appear washed out due to show-through.

Metallized materials: VMCPP and VMPET. Direct printing on these surfaces can cause metallic glare that distorts color accuracy.

Dark-colored paper: Black cardstock and colored paper used for luxury packaging boxes, black business cards, and premium gift boxes. When printed on a high-speed flexo printing machine, a white underlayer is essential; otherwise, colors will be absorbed by the dark background.

Window designs: Selective white underprinting creates contrast between transparent and opaque areas.

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Materials That Do Not Require White Underprinting

Materials with a white base or sufficient opacity (such as high-opacity titanium white ink), or designs that intentionally require a transparent or see-through effect, do not require white underprinting.

In addition to the cases mentioned above, white underprinting is also widely used for special-effect substrates such as silver paperboard and holographic paper. Today, commonly used UV white ink can also create a subtle embossed or tactile effect by controlling the thickness of the white layer.

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Common Issues with White Underprinting

White underprinting is highly practical. By understanding common issues and mastering the right solutions, it can bring significant added value and branding benefits to food packaging such as kraft paper bags and burger boxes. The most common problems include bubbling in the white layer, color deviation in overprinted areas, white ink delamination after lamination, and jagged edges in window designs.

Bubbling in White Underprinting Areas

During white underprinting, if the white ink is not fully dried, residual solvents may remain on the substrate, leading to bubbling in the white layer.

This issue can be improved by reducing the printing speed, increasing the temperature of the drying system, and adjusting the solvent formulation.

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Color Deviation

Uneven gloss of the white ink can cause inconsistent light reflection, resulting in color deviation in prints produced by a flexo printing press.

This issue can be resolved by using a consistent batch of white ink and adjusting the doctor blade pressure to ensure uniform application.

White Ink Delamination After Lamination

The primary causes of white ink delamination are insufficient adhesion or adhesive penetration.

This issue can be minimized by increasing the corona treatment level, using barrier-type white ink, and optimizing the adhesive coating weight.

Jagged Edges in Window Areas

Misregistration between the white ink and transparent areas can lead to jagged edges in window sections of products such as takeaway food boxes, fast food packaging bags, and French fries boxes.

Common solutions in production include applying trapping design and reducing white ink shrinkage.

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White underprinting is widely used in the flexographic printing of products such as cake boxes, wine labels, and chocolate wrapping film. By mastering its working principles, suitable materials, common issues, and corresponding solutions, it can significantly enhance production in industries like flexible food packaging, beverage label printing, pharmaceutical packaging, and cosmetic packaging printing—ultimately elevating brand value.