Corrugated boxes are commonly made using several types of base papers, such as cardboard, liner paper, kraft paper, tea board paper, white paper, and single-sided coated white paper. Due to differences in the papermaking process, materials, and surface properties, these base papers exhibit varying physical and chemical characteristics, including printability. This article explores the challenges that arise when printing on corrugated cardboard using different types of base papers.
First, issues caused by low grammage base paper
When corrugated cardboard is made with low grammage paper, it can lead to surface imperfections. These defects make it difficult to achieve clear prints, especially in areas where the surface is uneven or has low gloss. The uneven surface may cause ink to settle unevenly, leading to poor print quality. To address this, it's recommended to use a flexible resin plate with good resilience, which can help reduce printing flaws. In particular, A-type corrugated boards made from low grammage paper are more prone to damage during the printing process. The pressure from the printing and embossing rollers can significantly weaken the structural integrity of the board.
If there is a large variation in the grammage across the surface of the corrugated board, it can result in warping. Warped corrugated boards can cause misalignment during printing and slotting. Therefore, it's essential to flatten warped boards before printing. Forcing print on uneven boards may lead to misregistration and a decrease in board thickness, further affecting the final product quality.
Second, problems caused by surface roughness differences
The surface roughness of the original paper plays a significant role in print quality. On rough paper with a loose structure, ink tends to absorb quickly, causing it to dry faster. In contrast, smooth paper with dense fibers absorbs less ink, resulting in slower drying times. Therefore, more ink should be used on rougher surfaces, while less ink is needed for smoother ones. Unsized paper allows for quicker ink drying, whereas sized paper dries more slowly but offers better color reproduction. For example, coated whiteboard paper typically has lower ink absorption than cardboard or tea board paper, leading to slower drying and higher smoothness. This makes it ideal for high-resolution printing, offering better pattern clarity and consistency compared to other base papers.
Third, issues caused by differences in paper absorption
The absorption capacity of the base paper varies depending on the raw materials and the sizing, calendering, and coating processes. For instance, when overprinting on single-sided coated whiteboard paper or kraft card, the ink dries more slowly due to lower absorption. To compensate, the previous ink concentration should be reduced, and the viscosity of the overprint ink should be increased. It’s also advisable to place lines, text, and small patterns in the first color, while reserving full-color images for the final pass. This helps improve the overall overprint quality.
Additionally, dark colors should be printed first, followed by lighter ones. Dark colors have stronger coverage, making them more effective for achieving accurate overprints. Lighter colors, on the other hand, have weaker coverage and may not hide minor misalignments after the second print. This is why careful planning of the printing sequence is crucial for achieving professional results.
The surface sizing of the base paper also affects how much ink it absorbs. Papers with less sizing tend to absorb more ink, while those with more sizing absorb less. Therefore, the gap between the ink rollers should be adjusted based on the paper’s sizing condition. This ensures proper ink distribution and enhances print quality. It’s important to test the absorption performance of incoming paper at the factory, so that the printing and ink technicians can adjust equipment settings accordingly. They should also monitor and control the ink’s viscosity and pH level based on the absorption characteristics of each type of base paper.
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