Printed product smearing is a common problem in printing. This problem can impact print quality at best, or even lead to mass product scrapping, resulting in significant losses for the company. There are many reasons for printed product smearing, including excessively thick ink layers, a glossy backing of the paper, improper ink mixing, and inappropriate printing pressure. Smearing is related to 

both ink properties and ambient temperature and humidity.

1. Understanding the Relationship between Printing Pressure and Ink Layer Thickness

Appropriate printing pressure is crucial for achieving uniform ink transfer across the printing plate. Insufficient or uneven printing pressure can affect this uniformity. Insufficient or uneven printing 

pressure can cause the ink on the printed product to blend and the ink thickness to vary across the entire printing plate. Increasing the ink volume can indeed compensate for poor contact between 

the ink layer and the substrate caused by insufficient printing pressure, but it can also easily cause smearing. Therefore, the printing pressure should be adjusted first, followed by the ink volume, to 

achieve optimal printing results.

2. Addressing the Relationship Between Paper Printability and Ink Layer Thickness

Paper with poor surface smoothness absorbs ink quickly and absorbs large amounts of ink. When printing on this type of paper, insufficient or uneven printing pressure can easily lead to the bottom 

layer showing through and creating a blur. Increasing the ink volume and resulting in a thicker ink layer can also slow the print from drying, leading to smearing. For paper with poor surface 

smoothness, the printing pressure should be increased accordingly. For smoother papers like coated paper and glass paperboard, the ink layer should be kept as thin as possible to avoid smearing. 

To prevent smearing, large-area printing plates should adopt a "dark ink, thin print" approach: darken the ink hue and apply a correspondingly thinner ink layer. This approach achieves the desired 

hue while preventing smearing.

3. Understanding the Relationship Between Plate Properties and Ink Layer Thickness

A certain relationship exists between plate quality, ink layer thickness, and printing pressure. Poor plate smoothness requires a greater ink layer and pressure, while poorer plate smoothness requires

 less. For example, when printing on zinc plates, due to their poor ink affinity and surface gloss, a full ink layer can only be achieved by increasing printing pressure and ink layer thickness. However, 

this is very prone to smearing, so zinc plates are not suitable for color prints larger than 8-mo. Photosensitive resin plates offer a high surface gloss, soft texture, good flatness, and ink affinity. A 

slightly thinner ink layer can still achieve good printing results and is less prone to smearing. Therefore, photosensitive resin plates should be used when printing large images.

Fourth, Avoiding Backside Smearing Caused by Improper Printing Ink Layer Thickness

The key criteria for determining whether the printing ink layer is adequate are uniform pressure on the printing plate, uniform ink distribution across the plate to prevent underprinting or voids, and 

the color of the printed product matches the original. Uneven or insufficient printing pressure, poor paper gloss, dark original color, or lightly adjusted ink hues can all lead to inaccurate 

determination of the ink layer thickness. If you blindly increase the ink volume at this point, the ink layer will be too thick, causing smudges on the back of the printed product.

5. Avoiding Smudges on Prints Caused by Improper Operation

(1) Improper Ink Roller Adjustment, Excessive or Uneven Ink Volume

When the ink roller head and shaft hole have a large gap or eccentricity due to wear; or when the elasticity of the ink roller colloid deteriorates, the ink roller will contact the plate unevenly as it rolls 

along the plate, easily causing uneven ink application and a thin ink layer on some areas. Furthermore, if the ink roller is adjusted too high or one end is too high, it can also easily cause insufficient 

or uneven ink application on the plate. In this case, blindly increasing the ink volume will cause a thicker ink layer on some areas, leading to smudges on the printed product. Therefore, when printing 

large-area graphic products, high precision in the ink roller assembly, good roller roundness, appropriate roller colloid hardness, uniform contact between the ink roller and the inking roller, and 

accurate height adjustment are required to minimize smudges on the printed product.

(2) Improper paper collection

When collecting paper during printing, the angle and height of the paper should be accurately adjusted according to the size of the printed product and the hardness of the paper. Otherwise, the 

edge of the printed sheet can easily rub against the previous sheet, damaging the ink on the printed product. Additionally, printed sheets should be handled with care to prevent movement and 

friction between the upper and lower sheets, which can cause smearing. The amount of paper airing should be adjusted according to the ink absorption of the printing plate to prevent heavy 

pressure and smearing.

(3) Insufficient plate support and uneven pressure

Plywood is not a solid material and has a high coefficient of deformation under pressure. Using this material as a plate support requires increased printing pressure and ink layer thickness, which can 

easily cause smearing of the printed product. Therefore, it is best not to use plywood as a plate support when printing solid areas. Instead, use a magnetic plate table or other metal plate support to 

ensure a thin, uniform ink layer, which helps prevent smearing.

5. Highly acidic paper and humid climates

When printing on offset paper or some domestic coated papers, the thick ink layer and the high acidity of the paper make it difficult to dry and prone to smearing. In this case, add an appropriate 

amount of all-purpose ink to the ink to prevent smearing.

6. Tapping the paper creases, causing friction in the printed product

When printing on coated paper, the surface is smoother. Prominent creases can easily rub against the printed product, causing smearing. Therefore, the amount of tacking should be determined based on the layout and paper characteristics. For thicker coated paper, avoid tacking as much as possible; instead, use upward or downward rubbing to smooth and firm the paper.