A Guide to Solving the Problem of Yellowing of PET Laser Marking

The book provides a complete guide to the problem of PET materials turning yellow after being marked with a laser, from analysis of the cause to solutions.The company's laser technology includes techniques for adjusting laser parameters, pre-processing material, and post-processing, which help customers solve problems with discoloration and extend the beauty of their products.It is suitable for technicians and operators who need to optimize PET laser marking.

Why does PET turn yellow after printing?

Many friends who use laser marking machines to mark PET plastic often find that the material turns yellow after the marking is done, as if the material had been "burned."The problem is that PET is sensitive to heat. If the laser energy is too high or the focus time too long, it will cause carbonization.Furthermore, if the paper contains impurities or additives, that can also accelerate the yellowing process.

Three steps to solving yellowing.

Adjusting the laser parameters is the key.

Don't start out at the highest power setting. First try using a low power setting (for example 20 %) and a high frequency (above 50 kilohertz). Then gradually adjust the settings.Watch the color of the marking: Ideally, it should be very slightly whitish, not yellow.Parameters for laser equipment from different manufacturers vary widely. It is recommended that you do a small test for every batch of material.

The material is given a "pre-treatment.

Some PET materials have anti-adhesive coatings or oil films, and direct marking can cause uneven heating.Try wiping the surface with rubbing alcohol or using a specialized cleaning agent.If the PET is transparent, you can attach a matte film to the back side. This will reduce the heat buildup caused by the laser reflection.

Don't forget to cool off after a game.

The temperature of the freshly coated area is high, so cold air can be blown over it with an air gun to assist cooling.If conditions permit, a water cooling system should be installed on the marking machine.Don't touch the hot areas with your hands, or you might get burned!

Everyday tips to prevent yellowing.

Choosing the right material is very important.

When purchasing PET sheets, be sure to ask if they are suitable for laser processing.Some factories specialize in making laser-grade PET that contains yellowing inhibitors. Although this material is more expensive, it can save a lot of trouble down the road.Don't be tempted to buy recycled materials, there are too many impurities to be worth it!

Regular maintenance is essential.

The laser lenses need to be cleaned at least once a month. Dust can affect the quality of the beam and cause uneven energy distribution.Make sure to lubricate the rails. If the machine is not moving smoothly, the time it takes to mark the item will be longer. Even a 0.1-second delay may cause the material to turn yellow.

The humidity has to be controlled.

The workshop must be kept at the right humidity. Too dry and static electricity will attract dust; too wet and the laser beam will be affected.The ideal relative humidity is between 40 and 60 percent, so buy a hygrometer and keep an eye on it.

How can they be saved?

If you notice any yellowing, don't panic. Use fine-grit sandpaper (2000 or finer) to lightly sand the yellowed area, then apply a plastic repair agent.For products with high requirements, you can try double printing--but remember to adjust the power down 10 %!

Finally, we should note that the characteristics of PET from different batches may vary. If you run into problems, do some experiments before mass production.If you use these techniques properly, you can be sure that your PET labels will be bright and white, and your customers will give you two thumbs up!