Why Do Corrugated Plastic Sheets Need Corona Treatment?

When printing a logo, text, or graphic on a corrugated plastic sheet made from polypropylene (PP), ink may spread unevenly or fail to adhere well. One possible reason is the sheet’s naturally low surface energy, which makes it difficult for many inks to wet the surface.

Corona treatment changes the surface of a corrugated plastic sheet to improve ink wetting and support adhesion. The need comes from the printing requirements and the properties of the PP surface.

This guide explains what treatment changes, when it is useful, and how to check whether a treated sheet is ready for your printing process.

Recommended Reading: Corona Surface Treatment: 8 Essential Things to Know

Why Is an Untreated Corrugated Plastic Sheet Difficult to Print?

Low Surface Energy Makes Ink Wetting Difficult

A corrugated plastic sheet has a surface that many inks do not wet easily. In simple terms, the attraction between the ink and the untreated PP surface may be too weak for the ink to spread evenly.

Instead of covering the intended area, the ink can form beads or pull back into smaller patches. Polyreflex identifies the difficulty of printing on untreated PP as a reason for corona treatment for a corrugated plastic sheet.

This is a surface issue, not a problem caused by the hollow channels inside the sheet. Ink is applied to the outer face, so that face needs to suit the chosen ink.

A clean, smooth-looking sheet may still be difficult to wet. Appearance alone cannot tell you whether it is ready for printing.

Poor Wetting Can Affect Print Adhesion

Good wetting helps ink make close contact with the sheet. If the ink pulls away from parts of the surface, it becomes harder to form a continuous, well-bonded print.

However, three terms describe different things:

• Wetting: Liquid ink spreads across the sheet’s surface.
• Absorption: Liquid enters the material.
• Adhesion: The finished ink layer remains attached to the surface.

Corona treatment does not make a corrugated plastic sheet absorb ink through its face or into its hollow channels.

Uneven coverage during printing and peeling after drying are also different symptoms. Poor surface preparation may contribute to either, but peeling alone does not prove that corona treatment is missing.

When Does a Corrugated Plastic Sheet Need Corona Treatment?

Direct Printing on a Corrugated Plastic Sheet

Corona treatment is commonly relevant when a corrugated plastic sheet will carry printed graphics, such as signs, displays, or identification graphics. The objective is to prepare the face that receives the ink.

Both UV digital printing and screen printing require a suitable combination of sheet surface, ink, and process conditions. Coropak discusses surface treatment specifically for printing on a corrugated plastic sheet.

Buying blank sheets does not remove the need to discuss printing requirements. If you plan to print them later, confirm the treatment requirements before ordering.

For example, a buyer ordering blank sheets for double-sided signs should tell the supplier that both faces will be printed. The printer then needs to verify both faces with the intended ink.

Labels and Adhesive Bonding on the Sheet Surface

Surface preparation may also matter when labels or glued components must remain attached to a corrugated plastic sheet. Some adhesive systems can benefit from improved contact with the PP face.

However, not every label or tape requires corona treatment. Ask the adhesive supplier whether its system is suitable for the sheet’s existing surface, and validate it on a sample.

Keep the decision tied to the actual attachment task. A label used briefly for handling may have different acceptance requirements from one that must remain attached during repeated use.

When Treatment May Not Be Necessary

A corrugated plastic sheet used only as an unprinted divider or protective pad may have no printing, labelling, or adhesive-bonding requirement. In that case, those uses alone do not justify adding corona treatment.

Similarly, additional treatment should not be automatic when the existing surface and chosen process already meet the required performance.

Is Corona Treatment Alone Enough for Reliable Printing?

The Ink and Printing Process Still Matter

A treated sheet still needs a suitable ink and correctly controlled printing conditions. Dust, handling contamination, or inadequate drying or curing can affect the result.

If a print fails, review the complete combination:

• The sheet and its surface condition.
• The ink’s suitability for the corrugated plastic sheet.
• The printing, drying, or curing conditions.

Increasing treatment is not a reliable response to every defect. First identify which part of the process is falling short.

Treatment Levels Can Change Before Printing

A treated surface can change during storage. Additives may migrate to the surface, and the polymer surface itself can rearrange, reducing the treatment effect.

The rate depends on the material formulation and conditions. Vetaphone discusses these differences in its guidance on treatment durability.

There is no single six-month or one-year period that guarantees print readiness for every corrugated plastic sheet. A factory test records the condition at that time.

If sheets have been stored before printing, check their current condition. Use surface-test and trial-print results to decide whether retreatment is needed and suitable.

How Can You Check Whether a Treated Corrugated Plastic Sheet Is Ready to Print?

Check the Correct Surface and Treatment Level

Start by identifying the face that will receive the print. Ask how treated faces are marked or identified, especially when only one side has been prepared.

For double-sided printing, confirm the preparation and condition of both faces.

Dyne liquids or pens help assess the current wetting behaviour of an unprinted surface. The test fluid either remains spread out or pulls back during the specified observation period, as described in Tantec’s dyne testing guide.

Set the target according to the actual ink and process, rather than borrowing a number from another sheet supplier.

Follow the chosen test method and record the tested face, positions, time, and result. Check representative areas of the sheet rather than relying on one mark.

Run a Print and Adhesion Test

Trial-print a representative sheet using the intended ink and actual drying or curing conditions. Assess two things separately:

• Print coverage: Does the ink cover the intended area evenly?
• Print adhesion: Does the finished ink layer meet the agreed adhesion or rub-resistance requirements?

A dyne test helps assess the surface; a finished-print test checks the result of the whole process. Enercon explains why dyne level alone does not guarantee adhesion.

A corrugated plastic sheet needs corona treatment when its surface requires preparation for the intended printing or bonding task. Confirming the printing method, ink, treated faces, and sample results helps turn that requirement into a practical specification.

At JIANXIN PLASTIC, our corrugated plastic sheet can be supplied with corona treatment for printing applications. Share your printing requirements so the treatment needs can be discussed before production, and verify a sample with your actual printing process.

For wider purchasing considerations, including thickness, sheet size, MOQ, and lead time, see our custom corrugated plastic sheet buying guide.