3 Real Causes of Digital Printing „Curling“ — Paper Edge Curling / Skewed Web Feeding / Excessive Drying: The Cause Print Shops Most Often Misdiagnose by Adjusting Only One Parameter

In early October 2026, a print shop producing premium cards and invitation cards received an order for 5000 foil-stamped cards. Immediately after digital printing, the paper looked smooth and clean. The next day, the client inspected the samples and said, “The paper looks wrinkled, like a shirt that has not been ironed.” The print shop retrieved the printing conditions used for the batch and found that the drying temperature, line speed, and paper orientation had not changed. However, the wrinkling described by the client was not present when the cards left the press.

The difficulty in diagnosing this issue is that curling often becomes visible only after the printed product leaves the press, or even 1-2 days after it leaves the print shop, while print shops tend to focus only on the moment immediately after printing. Because the problem may arise from 3 completely different causes, focusing exclusively on the cause most familiar to the operator can lead to a cycle in which “it is adjusted today but returns tomorrow.”

Cause 1: Paper Curls Due to the Environment — Most Often Misdiagnosed as an Equipment Problem

Paper, particularly untreated neutral paper and matte-coated paper, expands and contracts according to the relative humidity of its surroundings. If one side of a sheet is exposed to an open workshop entrance while the other is next to a wall, uneven moisture absorption can create slight curling or waviness. The high-temperature drying process used in digital printing can set this curl, making it more noticeable when the sheet leaves the press.

Diagnostic method: Turn off the dryer and gently run your fingers across the paper to feel the direction of the undulation. If the direction of the waves matches the orientation of the sheet on the loading table, which is usually across the web, the defect is most likely environmental paper curling rather than skewed web feeding.

Correction: This cause cannot be resolved through equipment adjustment. Instead, allow the paper to acclimate to the workshop environment. Paper taken from the warehouse should lie flat in the workshop for a period before use. Do not feed paper directly into the dryer immediately after it has been removed from a temperature-controlled environment. Also inspect the loading area for heat sources and temperature variations, including air-conditioning outlets, heaters, and densely occupied areas.

Cause 2: Skewed Web Feeding — Fixed Wave Patterns Caused by Uneven Heating

If the web path is misaligned, or the sheet is slightly twisted on the transport rollers, the distance and travel time from each edge to the drying zone will differ. One side then receives more heat than the other. This form of curling has a characteristic pattern: the waves are fixed and directional, usually running parallel to the web direction or appearing as regular diagonal lines.

Diagnostic method: Hold the finished product against the light. If the waves form regular straight lines parallel to the web direction, skewed web feeding is likely. Irregular, randomly distributed fine undulations are more consistent with Cause 1 or Cause 3.

Correction: Correct the web alignment, remove paper debris and adhesive residue from the transport rollers, and check whether an earlier process has curled the paper. This problem is often unrelated to die cutting or converting. The misalignment may already be present when the paper enters the press for printing.

Cause 3: Excessive Drying Energy — The Most Frequently Misdiagnosed Cause

If digital printing dryer energy, whether hot air or infrared, is excessive, the temperature is too high, or the line speed is too slow because the unit area remains under heat for too long, moisture migration within the paper may become uneven. The sheet can look flat when it leaves the press while internal stresses remain. Several days later, the paper may “spring back” and curl.

The key distinction between this cause and the first 2 is that the severity of the wrinkling should visibly change after the drying parameters are adjusted. If lowering the temperature by 5-10℃ or increasing the line speed by 10-20% reduces the wrinkles, Cause 3 is the primary factor. If changing these parameters produces no visible improvement, the issue lies in the paper or web handling rather than the dryer.

Correction: Set the dryer within a range that is “dry enough but not excessive,” while maintaining adequate ink drying and adhesion. Digital ink films are thin and often do not require high temperatures. However, thicker papers and areas with greater ink coverage, such as solid backgrounds, require more drying energy. This balance must be established through testing rather than guesswork.

How to Systematically Investigate the 3 Causes

Because the 3 causes require fundamentally different corrections, some involving equipment and others involving paper handling, blindly adjusting only one parameter at a time is inefficient. A more effective investigation sequence is:

• Step 1: Identify the pattern. Examine the curling waves against the light. Regular parallel waves indicate a greater likelihood of skewed web feeding. Irregular fine undulations indicate environmental paper behavior or drying issues.
• Step 2: Run a variable-control test. Take sheets from the same batch, print one with the front side facing up and another with the back side facing up. If the two sheets curl in clearly different directions, the issue is associated with paper orientation or edge curling. If they curl in the same way, the issue is associated with web feeding or drying.
• Step 3: Adjust the dryer to verify. Print a small batch at a lower temperature or higher line speed, then compare the results after several days. If the defect improves significantly, drying is the main cause.
• Step 4: Check web handling and paper storage. If the drying adjustment has no effect, inspect the cleanliness of the transport rollers and the paper’s acclimation time after entering the workshop.

This 4-step process will usually identify the primary cause. Print shops that standardize this investigation sequence as a small SOP can avoid starting the diagnosis from scratch every time curling occurs.

How Print Shops and Clients Should Discuss the Issue

If curling is caused by the print shop, such as clearly inappropriate drying parameters, the print shop should accept responsibility. If it results from the paper environment or client storage conditions, the print shop should also be able to explain the cause clearly. The key is recordkeeping. For every batch, retain the paper grade, time it entered the workshop, drying parameters, line speed, and sheet orientation. Together, these records can reconstruct the conditions present at the time of printing.

In addition, premium thin-paper products such as cards and invitation cards have virtually no tolerance for curling, and clients may reject an entire production run because of a single sheet. When accepting such orders, print shops can leave proof samples in both the workshop and a simulated client storage environment for 24-48 hours and inspect them again. This exposes curling risks during the proofing stage rather than after the printed products have already been delivered.

Further Reading

• 3 Major Post-Printing Pitfalls in Digital Printing: Lamination / Die Cutting / Converting
• 3 Real Boundaries of Static-Curl in Digital Printing Cold Lamination
• 3 Real Types of Color Shift in Digital Printing White Ink Underlays
• 3 Real Boundaries of Reverse White Text and Solid Black in Digital Printing