Wisdom For Polyethylene vol.33

33. Why Do Poly Bags Get Damaged?

2025-12-04

Small Scratches, Big Problems

Scratches and pinholes in poly bags may seem minor, but they can lead to serious complaints.

Poly bags are versatile containers used widely—from food packaging to inner liners for chemical drums—due to their safety, cost-effectiveness, and resistance to acids, alkalis, and certain chemicals.

However, once damaged, the bag’s functionality is compromised and it cannot serve its intended purpose.

This article organizes the typical causes of bag damage occurring during manufacturing, transport, filling, and packing, along with practical countermeasures. It provides knowledge useful for preventing recurrence.

Scratches on bags are a relatively frequent complaint.
Analyzing the types of scratches reveals various forms:

Scratches or punctures from outside to inside
Scratches or punctures from inside to outside

If detected before filling, complaints are minor; if discovered after filling, complaints can become major and investigations are difficult. The impact is especially significant when the contents are liquids or viscous materials.

Main Causes of Poly Bag Damage

We will discuss scratches in poly bags by dividing them into two stages: “before filling the bag with contents” and “during/after filling the bag with contents.”

1. Causes of Damage Found Before Using the Bag (Transport and Packing Related)
First, we explain scratches discovered before use, after opening the outer packaging of the bag.
The most likely cause is improper handling during transportation. Cases in which scratches occur due to impacts or drops during transport are relatively common.

In such cases, investigation is relatively straightforward. Poly bags are usually folded lengthwise for packaging, and the position of scratches often coincides with the crease positions of the packaging material.

In these cases, scratches appear consecutively in the same position across 2–3 layers, becoming weaker toward the inner layers.

Corners of packages are particularly prone to scratches, and occasionally the bottom surfaces may also be scratched.

In some investigations, it was found that wooden pallets or truck beds had splinters that penetrated the packaging material, causing scratches on the bottom surfaces of the bags.

2. Scratches in the Manufacturing Process and Their Signs
Next, we consider scratches that occur on the manufacturing line before transportation.

Poly bags are generally produced through the following three processes:

Inflation Line: Melting the resin, forming polyethylene tubing, and winding
Bag-Making Line: Heat-sealing and cutting the tubing
Packing Line: Packaging and bundling the finished bags

In these processes, based on past experience and lessons learned, many measures are taken to prevent scratches.

Thus, scratches rarely occur on the production line itself, but they mainly arise due to human error during the packing process.

It is common to accidentally damage the film with scissors, cutters, or tape dispensers.

In particular, if a scratch occurs on one side of an unfilled bag, it is likely that the damage occurred during manufacturing.

Often, such scratches are caused by carbonized resin particles or pinholes, requiring inspection of the entire production line.

3. Scratches Occurring During or After Filling
Next, we discuss scratches found during or after filling.

Poly bags for drum liners are very large, so scratches may occur if they collide with something during handling.

Additionally, if there are burrs on the inner surface of the drum when setting the bag, these may damage the film, or the contents may rub and create holes during transport.

Surprisingly, even cardboard, which appears soft, can cause scratches when it rubs against the film during transportation.

There have been past cases where unexpected leaks occurred during transport of noodle soup products in cardboard packaging.

This was due to the hardness or sharp cut edges of laminated bags causing friction with the film and resulting in scratches.

4. Special Case: Scratches from the Inside Out
Here, special attention should be paid to scratches that enter “from the inside to the outside.”
These are considered scratches that occur after filling, as they often appear on one side of the bag after the contents have been filled.

The presence of scratches only on one side is evidence of post-filling damage.

Using a digital scope, it is possible to determine the direction from which the scratch occurred.

5. Case of Pinholes Due to Folding of Poly Bags
While we have discussed various causes, there is another factor causing scratches during the packing process: the way poly bags are folded.

Bags are usually folded only along the length, but if the bag is wide, folding along the width may be necessary.

In such cases, scratches may occur.

If a bag is folded along the mouth opening and then folded along the length, a “corner” always forms at the folded section along the length.

In the industry, this is called “forming a horn.” Folding the R-section along the mouth direction again along the length causes a difference in dimensions between the inner and outer angles, resulting in sharp points at the folded sections.

These “horns” are very hard and sharp, and even thin poly bags can feel prickly when touched with a finger.

If this part rubs against packaging materials during transportation, the tip may tear due to friction, causing pinholes.

In the case of thin films, pinholes may occur through several layers starting from the outermost bag.

In such cases, scratches may develop from the outside to the inside on one film layer and from the inside to the outside on the other.

Moreover, the scratches occur at the same positions on both sides, so when folding bags along both width and length, careful consideration of packaging units is required.

Summary: Scratches in Poly Bags Are Not a “Minor Issue”

As described, scratches in poly bags are extremely diverse and a very deep issue.

Both customers and we as manufacturers must verify each cause carefully. Otherwise, any countermeasures or report submissions will only be temporary measures.

Focusing solely on assigning responsibility, such as “the manufacturer is at fault!” or “the scratch occurred during use!” will not resolve the problem. Continuous attention to identifying the actual causes is necessary for proper resolution.

Indeed, it is a case of “scratches are not to be underestimated.”

Note: *This article summarizes actual cases of scratches and pinholes that frequently occur in poly bags and drum liners, as well as countermeasures, from the perspective of manufacturing, transportation, and packing operations.

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