Corrugated cardboard, due to its multi-layered corrugated structure and relatively poor surface smoothness, has pores formed by interwoven fibers that become the main channels for ink penetration. Excessive ink penetration leads to blurred prints, dull colors, and even ink showing through to the back of the cardboard; insufficient penetration can cause poor drying and back-side smudging. Therefore, controlling ink penetration on the surface of corrugated cardboard requires a comprehensive approach encompassing ink formulation, printing processes, cardboard pretreatment, and auxiliary technologies.
Ink formulation is fundamental to controlling penetration. Water-based inks are the mainstream choice for corrugated cardboard printing, and their binders are typically formed by resin and water in the presence of surfactants, creating an oil-water miscible system. The penetration of these inks is significantly affected by viscosity, pH value, and pigment dispersibility. For example, appropriately increasing ink viscosity can slow down the penetration rate, but this must be balanced with print smoothness; maintaining a pH value within the weakly alkaline range of 8-9 maintains ink stability while avoiding excessive fiber swelling or excessively rapid ink film formation due to acidity or strong alkalinity. Furthermore, selecting pigments with fine particle size and uniform distribution can reduce the mechanical retention of ink in the pores of the cardboard, thereby reducing the penetration depth.
Optimization of printing process parameters is crucial for penetration control. Flexographic printing, which uses anilox rollers for ink transfer, allows control of the amount of corrugated cardboard ink transferred by adjusting the cell depth and angle. Printing pressure must be precisely matched to the thickness and elasticity of the corrugated cardboard; excessive pressure will cause ink to be excessively forced into the cardboard, leading to bleed-through; insufficient pressure may result in a hollow or incomplete print. The coordinated design of printing speed and drying method is equally critical. High-speed printing requires infrared or hot air drying equipment to accelerate the surface curing of corrugated cardboard ink, reduce free penetration time, and prevent ink diffusion due to drying lag.
Cardboard pretreatment is an effective means of reducing penetration differences. Pre-calendering can compress the surface fibers of the cardboard, reducing porosity and creating a denser printing surface. For example, pre-calendering TMP (thermomechanical pulp) paper can reduce the number of large pores and increase the proportion of small pores, thereby limiting the ink penetration channels. Furthermore, adding water-resistant components to the pulp or surface sizing the base paper can enhance the bonding force between fibers and reduce ink absorption under capillary action. However, it should be noted that excessive sizing may affect the reproducibility of the printed pattern, requiring a balance between water resistance and printability.
Nano-coating technology provides an innovative solution for penetration control. Coating the surface of cardboard with nanomaterials can form a hydrophobic structure similar to an air cushion layer, significantly improving the oil and water resistance of the cardboard. Experiments show that corrugated cardboard treated with nano-coating can remain free of penetration marks for more than 12 hours when exposed to highly penetrating liquids such as machine oil and wood oil, with no oil stains spreading on the back. This type of coating can also penetrate into the fibers without increasing the weight of the cardboard, while meeting the anti-fouling requirements of harsh environments such as long-term sea transport. Although nano-coating is more expensive, it has significant advantages in increasing the added value of cardboard and extending the service life of packaging.
The rational use of ink additives can further refine penetration control. For example, adding a drying agent can shorten the ink oxidation and film-forming time, reducing the free penetration stage; adding an anti-settling agent can prevent pigment particle sedimentation, maintain the uniformity of corrugated cardboard ink, and avoid uneven penetration caused by local concentration differences. Furthermore, considering the dark yellowish-brown characteristics of corrugated cardboard's face paper, selecting a high-opaque base color ink can reduce the ink layer thickness required to cover the base color, thereby reducing the risk of penetration.
Controlling the ambient temperature and humidity is a hidden factor in penetration control. High temperatures accelerate ink drying and shorten the pressure penetration time, but may cause excessively rapid free penetration; high humidity conditions may cause the cardboard to absorb moisture and expand, altering the pore structure and affecting penetration behavior. Therefore, the printing workshop needs to maintain constant temperature and humidity, controlled through air conditioning systems or dehumidification equipment, to ensure the stability of the penetration process.
In terms of results, the comprehensive application of the above methods can significantly improve the printing quality of corrugated cardboard. For example, by optimizing ink formulation and printing pressure, ink penetration can be reduced to below 5%; combining pre-calendering and nano-coating technologies can reduce ink absorption on the cardboard surface by 30% to 50%, while maintaining the clarity and color saturation of the printed pattern. In the future, with advancements in materials science and printing technology, penetration control will develop towards greater precision and intelligence, providing stronger support for the high-quality application of corrugated cardboard packaging.
