How to Eliminate Static Electricity in Adhesive Labels? How Is Static Electricity Generated?
Static electricity is almost omnipresent in the production and labeling processes of adhesive labels, bringing great troubles to label printing companies. Especially with the arrival of winter, when the air humidity gradually decreases, the “static problem” in the printing process becomes more and more evident. How is static electricity generated? What are the common problems in label printing caused by static electricity? And how can static electricity be eliminated? Let's discuss these issues together in this article.

Generation of Static Electricity

Under normal circumstances, various materials all have the same number of positive and negative charges. The positive and negative charges neutralize each other, so that the materials themselves do not show electric properties. However, if a material absorbs extra electrons from the outside, it will show negative electricity. On the contrary, if it loses some electrons, the material will show positive electricity. These two ways can both be called the generation of static electricity. In the actual production environment, the generation of static electricity is mainly due to two different materials coming into contact and then separating, successively losing and gaining electrons, and the transfer of electrons within the material, thus generating the static electricity effect.

Specifically in the label printing production process, theoretically, static electricity will be generated wherever there is friction and separation in the production process, such as at the unwinding and winding positions, the press roller positions, the die-cutting waste removal positions, the laminating positions, the labeling positions, etc. Static electricity will be generated at these positions. Therefore, static electricity problems will accompany the entire life cycle of labels, from material unwinding, printing, die-cutting, winding to the final use, static electricity problems may occur.

External Factors Affecting Static Electricity

The external factors that lead to the generation of static electricity mainly include environmental humidity, raw material properties, and problems with printing equipment itself.
1.  Environmental Humidity
•  In winter, the environmental humidity decreases. The surface resistance of objects will increase with the decrease of humidity, thereby generating static electricity problems.
2.  Raw Material Properties
•  Under the same environmental conditions, film materials are more likely to generate static electricity problems than paper materials. This is because film materials are insulators themselves. Once static electricity is generated, it is difficult to conduct away the positive and negative charges like paper materials.
3.  Equipment Factors
•  The anti-static capability of the equipment itself is also an important influencing factor. The grounding condition of the equipment directly affects whether the static electricity generated can be smoothly conducted out. If the surface of the drive roller is smooth, the static electricity generated will be relatively less. On the contrary, if the surface of the drive roller is rough, worn, or contaminated with dirt, the static electricity generated will be more.

Hazards of Static Electricity

1.  Burr Phenomenon
•  In the printing process, if static electricity is generated during the contact and separation of the printing plate and the ink roller, the pattern and text edges will fly out due to adsorption, forming ink whiskers, similar to burrs.
2.  Static Mottle
•  When printing solid areas, motting appears. It looks like the ink has poor fluidity and the ink is not evenly applied. But in fact, the ink has been affected by static electricity before drying and has shifted.
3.  Leak Printing
•  For two-color overprinting inks, due to static electricity repulsion, there will be white edges of ink that cannot be printed between each color, such as the white ink background around some text areas with repulsion gaps.
4.  Dirt Points
•  If the raw materials carry a large amount of static electricity, they will adsorb dust in the environment, leading to the appearance of printing dirt points, white points, fish eyes and other problems.
5.  Static Adsorption
•  In the process of single-sheet material printing or single-label collection, static adsorption will cause the materials and labels to fail to separate normally. In the labeling process, the label is affected by static electricity. After being peeled off from the backing paper, it will be adsorbed on the bottle body in a disorderly manner, causing the label to wrinkle and bubble.

Methods to Eliminate Printing Static Electricity

After static electricity is generated, a static electricity tester can be used to measure the size of the static electricity. The operating method is: bring the test port of the static electricity tester close to the material within 150 mm, and the real-time static electricity value can be detected. Next, let's take a look at some methods to reduce or eliminate printing static electricity.

1.  Physical Elimination Method

•  Using the physical properties of static electricity to eliminate it. There are mainly two methods: grounding elimination method and humidification elimination method.
•  Grounding Elimination Method: By using metal conductive materials, one end contacts the printed matter and the other end is connected to the equipment that has been grounded, the static electricity is directed to the ground, thereby eliminating the static electricity in the equipment. At present, the common grounding methods in printing factories mainly include adding anti-static ropes and anti-static copper wires. Compared with each other, since the anti-static copper wire is exposed to the air and is prone to oxidation and weakened conductivity, the anti-static rope with strong conductive copper wire wrapped in nylon has a better anti-static effect.
•  Humidification Elimination Method: By increasing the environmental humidity to reduce the surface resistance of the printing material, at the same time, the increase in environmental humidity will also improve the conductivity of the material surface, thereby reducing static electricity problems. In addition, the increase in environmental humidity can also reduce the floating objects in the environment, which will greatly reduce dust problems. At present, the simplest humidification method is to frequently mop the floor with water, but it is more recommended to use a spray humidifier to humidify the entire workshop environment.

2.  Chemical Elimination Method

•  By applying a layer of anti-static agent coating on the printing material to make the printing material conductive, static electricity generation can also be effectively reduced. This method can be used before printing, or the anti-static agent can be added to the varnish and used after printing.

In summary, this article has briefly discussed the causes, hazards, and solutions of printing static electricity. It is hoped that it can help label printing companies that are also encountering similar confusion in actual production. In short, the simplest solution is to directly seek anti-static raw materials or improve the equipment grounding and environmental humidity conditions to reduce or eliminate the troubles caused by static electricity.