What's the common issue in PE Coated Paper?

1. Printing defects

Printing problems are often found in laminated paper products. These problems usually appear as unclear images, uneven colors, or missing small dots in the printed design.

There are several common reasons for these printing defects:

1. Poor quality of the Base Paper – If the surface of the paper is not smooth or has marks like nail holes, the ink may not stick well, which causes bad print results.
2. Too thin coating layer – A very thin coating on the paper surface can lead to low smoothness. This makes it hard to get a clear and clean print.
3. Wrong printing plate or incorrect pressure – If the printing plate is not made correctly or if the printing machine applies uneven pressure, the final print may look blurry or incomplete.

These factors can all affect the quality of the printed material. So, it's important to use good-Quality Paper, apply the right amount of coating, and make sure the printing equipment works properly.

2. Paper sticking

Paper sticking happens when paper sheets stick together during cutting or stacking, making it hard to separate them.

The main reason for this problem is that the paper contains a lot of starch-based additives. These materials can easily absorb moisture, especially in humid conditions, and become sticky.

In winter, static electricity becomes stronger. This makes the paper sheets stick together even more, making the problem worse.

3. Peel-off

"Peel-off" means that the laminated layer (the thin plastic or film layer) separates from the base paper during the lamination process. This can greatly reduce the strength and usefulness of the final product.

There are several main reasons for peel-off:

1. No corona treatment on the base paper – If the paper has not been treated with a special process called corona treatment, its surface will not be active enough, so the coating or film doesn't stick well.
2. Worn or damaged rubber roller – During coating, a rubber roller helps press the film onto the paper. If the roller is worn or deformed, the film may not stick evenly to the paper.
3. Die head temperature is not correct – The die head is used to apply the coating. If it's too hot or too cold, the coating may not dry or stick properly.
4. Cooling roller is too hot – After coating, the paper passes through cooling rollers. If these rollers are too hot, the film may come off the paper easily.

These problems can all lead to poor quality laminated paper. So, it's important to control each step carefully during production.

4. Layer separation

Layer separation happens when the paper layers come apart from the coating layer when the paper is pressed or folded.

This problem usually happens when the base paper has too much moisture. If the paper is stored in a wet or damp place, it can absorb water. This weakens the bond between the layers.

Also, if the cutting knife angle is not set correctly, stress can build up at the edges of the paper. This can cause the layers to separate.

Another reason is unstable temperature control during cooling. If the cooling roller is not at the right temperature, the coating won't stick well to the paper. This also leads to layer separation.

All these factors can affect the quality of laminated paper products. That's why it's important to control the storage conditions and machine settings carefully during production.

5. Missing coating

"Missing coating" means that some parts of the paper do not get fully covered with the coating during production. As a result, those areas lose their waterproof and oil-proof abilities.

Here are some common reasons:

1. Wrong paper feeding: If the paper is not fed properly into the machine or moves out of place during the process, some parts may not get coated.
2. Unstable die head edge: If the edge of the die head (the part that spreads the coating) is not stable, the coating may not spread evenly on the paper.
3. Machine speed changes: When the machine starts or stops, it may speed up or slow down. These changes can cause the coating to be applied unevenly or skip some areas.

These problems can lead to poor product quality. So, it's important to run the machine carefully and check everything during production.

6. Wave edges

"Wave edges" are wavy or uneven edges that appear on laminated paper. They can make cutting and shaping the paper more difficult.

Here are the main reasons for wave edges:

1. Moisture causes paper to bend: If the base paper absorbs moisture, it may warp or bend, especially at the edges.
2. Die head edge is too hot: If the temperature at the edge of the die head (the machine part that applies the coating) is too high, the coating can build up there.
3. Coating is too thick: A very thick coating can also cause extra material to collect at the edges, making them wavy.
4. Trimming knife angle is not correct: If the cutting blade is not set properly, the edges may be cut unevenly, leading to a wave-like shape.

To prevent this problem, it's important to store the base paper in a dry place and control its moisture level carefully.

    7. Black spots

Black spots refer to small black spots on the laminated paper, affecting appearance and hygiene standards. These black spots may originate from impurities in the base paper itself or from residual substances carbonizing due to inadequate cleaning of the die head during coating.

8. Cup seal (seal film adhesion)

In real life, some laminated papers are used to make single-use paper cups or lunch boxes. These products often need to be sealed with a plastic film lid.

However, there can be problems when sealing: Not enough adhesion (too loose): This usually happens when the surface of the roller or the base paper is too smooth. Then, the heat seal is not strong enough, and the lid may come off easily.

Too much adhesion (too tight): This may happen if the PE material (the plastic layer) doesn't match the material of the cup lid. As a result, the lid becomes very hard to open after sealing.

These problems can affect how well the product works. So it's important to choose the right materials and settings during production.