The base silver ink layer of the printed matter is not fully dry.
Excessive white ink is used as a diluent on light-colored ink layers.
Control the interval between printing and anodized aluminum stamping. This requires proper dosage of drying oil during printing. For printed matter to be stamped, the amount of drying oil should be appropriately increased compared with non-stamped products (e.g., red drying oil at about 0.5%), but not excessively, to avoid crystallization and emulsification of the ink layer, which would also cause stamping problems.
Prohibit using white ink alone as a diluent. Although white ink has a good dilution effect, complete elimination is unrealistic.
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02 2026.04
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How to solve the problem of back pull / offset printing?
How to Solve Back-Pulling Problems in Fully Automatic Hot Stamping Machines?
Back-pulling is a common fault in hot stamping. Back-pulling in fully automatic hot stamping means that after hot stamping, the anodized aluminum foil does not firmly adhere to the base ink layer or the white paper surface of the printed matter; instead, part or all of the base ink layer is pulled away by the anodized aluminum.
In actual production, back-pulling and poor adhesion are not easy to distinguish visually, and back-pulling is often mistaken for poor adhesion. However, they are completely different faults. If back-pulling is misjudged as poor or insufficient adhesion without analysis, and measures are taken blindly such as increasing stamping temperature and pressure, or even replacing anodized aluminum with stronger adhesion, it will be counterproductive and worsen the back-pulling problem. Therefore, it is necessary to strictly distinguish back-pulling from poor adhesion first. A simple method is to observe the anodized aluminum base film after stamping: if traces of base ink remain on it, it can be determined as back-pulling.
Causes of Back-Pulling in Fully Automatic Hot Stamping Machines
According to manufacturers of fully automatic hot stamping machines, hot stamping with anodized aluminum is different from ordinary overprinting. A peeling force is generated during the stamping process, which is much greater than the separation force in ink printing. After ink is transferred to the paper surface, it can achieve strong adhesion only when fully dried. Before the ink layer is completely dry, the peeling force during anodized aluminum separation is far greater than the adhesion of the ink layer, causing the base ink layer to be pulled away by the anodized aluminum. Therefore, the anodized aluminum stamping process requires the ink layer on the printed surface to be fully dry to ensure good adhesion to the paper.
In operation, it is often found that dark ink layers are easier to stamp than light ones. As explained by manufacturers, this is because light inks are mostly diluted with white ink. Due to the relatively coarse pigment particles of white ink, the bonding force between the particles and the vehicle is poor. After printing, the ink vehicle is easily absorbed by the paper, while the pigment tends to float on the surface and chalking occurs, which can even be wiped off by hand. Under such conditions, stamping is very difficult: the anodized aluminum cannot be separated and adhered to the paper; instead, the chalked layer is pulled away by the anodized aluminum.
Fundamental Measures to Prevent Back-Pulling
A compromise solution, according to manufacturers, is to mix No. 991 Reducing Agent with white ink, with the proportion of white ink controlled within a reasonable range. Of course, if the process permits, to avoid back-pulling (including poor stamping), it is best to leave blank areas on the base ink layer during plate making, so that the anodized aluminum adheres to the blank paper instead of the ink layer.
Solutions to Existing Back-Pulling Faults
If back-pulling is caused by insufficiently dried ink layers, place the products in a ventilated and dry area and delay the stamping time appropriately.If caused by chalking of the base ink layer or excessive white ink, apply a base coat with No. 991 Bright Reducing Agent mixed with 3% white drying oil first, then perform hot stamping.
