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Measures to Reduce Paper Shrinkage and Variation During UV Printing

Release time:

2024-07-10 17:23

Measures to Reduce Paper Shrinkage and Variation During UV Printing
Measures to Reduce Paper Shrinkage and Variation During UV Printing

In the UV printing process, the shrinkage and deformation of paper stem from a multitude of complex factors, including the paper’s intrinsic physical properties, the requirements of the UV printing process itself, and variations in external environmental conditions. These shrinkage and deformation effects significantly impact print quality and the appearance of the finished product. To effectively control these changes, mitigate their potential adverse effects on print quality, and ensure the precision and overall quality of the final products, control measures are particularly critical.

To reduce the impact of paper shrinkage and deformation during UV printing, we can take the following measures:

I. Material Selection and Formula Adjustment

1. Use materials with low shrinkage rates:

In the UV printing process, to effectively control shrinkage of paper and other substrates, it is an effective strategy to select oligomers and monomers with lower shrinkage rates as printing materials. The reason these materials exhibit lower shrinkage rates lies largely in their relatively high molecular weights. Generally speaking, materials with higher molecular weights have tighter interactions among their molecular chains during the curing process, thereby reducing deformation caused by volume shrinkage. Consequently, during formulation design, priority should be given to using materials with higher molecular weights.

2. Add filler:

By adding an appropriate amount of filler to the UV coating, it is possible to control and reduce the coating’s shrinkage rate in specific application scenarios. Although the addition of fillers may to some extent affect the coating’s transparency, making it less transparent, in many practical applications this trade-off is acceptable—especially when the coating’s primary function does not entirely depend on its transparency.

3. Use non-reactive resin:

The introduction of non-reactive resins aims to reduce internal stresses within the coating film, thereby minimizing shrinkage during the curing process. Non-reactive resins do not participate in chemical reactions during UV curing; hence, they can serve as “diluents” or “buffers” within the coating, helping to disperse and alleviate volume shrinkage and localized internal stress caused by chemical reactions. However, when selecting non-reactive resins, it is essential to conduct thorough testing and evaluation to ensure their compatibility and synergistic performance with other components in the coating formulation. Particular attention should be paid to their compatibility with active ingredients such as monomers and oligomers. Poor compatibility may lead to phase separation, delamination, or degradation of coating performance during curing, seriously compromising the overall effectiveness of the UV coating.

II. Process Improvement

1. Optimize formatting:

During typesetting, the spacing between products is incrementally adjusted before printing, taking into account differences in paper grain direction and deformation patterns. Since paper typically exhibits a higher shrinkage rate in the transverse direction, appropriately increasing the lateral spacing during typesetting can offset this shrinkage effect, ensuring that after UV printing is complete, the spacing between products remains within the design specifications.

2. Control printing parameters:

a. Since the paper undergoes high-temperature baking during UV printing, one important measure to ensure stable print quality is to properly control the temperature inside the printing machine and prevent excessive temperature increases that could cause the paper to shrink excessively.

b. Appropriately reducing the printing speed can extend the heating time of the paper during the printing process, ensuring more uniform heat distribution and minimizing shrinkage caused by sudden high temperatures.

c. Although excessively high irradiation intensity or prolonged irradiation time can accelerate the curing speed, they may also cause the paper surface temperature to rise too high, speeding up moisture evaporation and fiber shrinkage. It is necessary to adjust the irradiation intensity and duration of the UV lamp according to the actual situation, ensuring that while achieving the desired drying effect, the adverse impacts on the paper are minimized as much as possible.

3. Allow for overprinting tolerance:

When designing post-printing plates (such as hot-stamping plates, embossing plates, and die-cutting plates), predict the actual dimensional changes of the paper after printing and leave sufficient margin for registration errors to ensure accurate overprinting.

III. Environmental Control

The printing workshop and storage warehouse should be equipped with temperature and humidity control devices to maintain stable environmental conditions. Based on factors such as paper type, ink characteristics, and equipment requirements, a reasonable temperature and humidity range should be set to ensure that the temperature and humidity within the workshop and warehouse remain within an appropriate range. This helps minimize paper expansion and contraction caused by fluctuations in temperature and humidity.

4. Optimize storage

1. Regularly inspect stored paper to promptly identify and address issues such as dampness, mold, and insect damage. For paper stored for extended periods, it should be periodically turned over and air-dried to maintain its excellent physical and printing properties.

2. As much as possible, avoid long-term storage of paper in the warehouse. By adopting the “first-in, first-out” inventory management principle, you can ensure that the paper that was received first is used first, thereby effectively reducing the storage time of paper in the warehouse and minimizing risks such as fiber aging, strength degradation, and localized moisture buildup caused by prolonged storage.

As can be seen from the above, measures to reduce paper shrinkage and deformation during UV printing involve multiple aspects, including material selection, process optimization, environmental control, and post-processing. By comprehensively applying these measures, it is possible to effectively control paper shrinkage and deformation during UV printing, thereby enhancing the quality of printed materials and improving production efficiency.

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