Burrs, missed prints, graphic and text dots...... How can static electricity in printing be effectively resolved?

Burrs, missed prints, graphic and text dots...... How can static electricity in printing be effectively resolved?

In the modern printing industry, with the continuous development of printing technology and increasing printing speeds, static electricity issues have become increasingly prominent, bringing numerous difficulties to the printing process, seriously affecting print quality and production efficiency, and even posing threats to production safety. Therefore, in-depth research on the impact of static electricity on printing and the search for effective solutions are of great significance for the development of the printing industry.

The impact of static electricity on printing

01/ Impact on print quality

(1) Burrs

When printing graphic or text parts, actual areas, or large characters with thick lines, static electricity causes hairy ink to splash, resulting in a thread-like 'whisker-like ink splatter.' This is because during printing, ink particles carry static electricity and repel each other, preventing ink from evenly transferring to the substrate, which leads to burrs forming at the edges of the text and images, seriously affecting the clarity and appearance of the printed product. For example, in some packaging printing, burrs appear on the text and patterns on the product surface, which lowers the product's grade and market competitiveness.

(2) Missing stamp

During printing, some images and text around the text may not be printed or inaccurate due to static electricity, resulting in missed prints; When applying white ink as a base, repulsion occurs, creating gaps. This is because static electricity on the substrate surface repels ink, hindering normal ink transfer and preventing complete printing of the graphic and text parts. For example, in label printing, if there is a missed print, it can result in incomplete label information, affecting product identification and sales.

(3) Graphic and textual highlights

Static electricity causes dust and impurities to adhere to films and other substrates, resulting in many uneven dots on the images and texts after printing. These dots can damage the integrity and consistency of the text and images, reducing the quality of the print. In high-end brochure printing, the appearance of graphic and decorative dots can seriously affect the texture and artistic effect of the image.

(4) "Tear-like" water droplets

When printing full-sheet, multicolor overlays show droplets like 'tears,' some light, some heavy. This is because static electricity causes uneven distribution of ink on the substrate surface, causing ink to accumulate into droplet-like shapes that affect the color uniformity and saturation of the printed product. In poster printing, these "tearful" water droplets distort the colors of the image and fail to achieve the intended promotional effect.

02/ Impact on production safety

During printing, due to high-speed friction and peeling, strong static electricity is generated. When static electricity accumulates to a certain level, it can easily cause air discharge, resulting in electric shock or fire. For example, in environments where ink and solvents are evaporating, charged inks or substrates may cause fires, seriously threatening the personal safety of operators and the property of enterprises. At the same time, static electric shocks can frighten operators, affect work efficiency, and may even lead to operational errors and other safety incidents.

03/ Impact on production efficiency

When paper is electrostatically charged, charges of the same polarity repel each other, causing inaccurate paper feeding positioning and affecting the stacking of paper on the transfer and paper collection tables; However, when different charges attract each other, the paper and printing equipment attract each other, causing difficulties in paper feeding, uneven paper collection, and inaccurate registration, which can lead to production interruptions and delays. On automated printing production lines, these issues occur frequently, requiring operators to constantly stop the machine to adjust, severely reducing production efficiency. Additionally, static electricity can cause materials to stick to drive rollers and guide rollers, affecting printing and die-cutting registration and further reducing production efficiency.

Causes of static electricity

01/ Material properties

The conductivity of materials has a dual effect on static electricity. If the material is a conductor, charges move freely and evenly on its surface, causing only a relatively low voltage, and the conductive material contacts the ground to transfer charge to the surface; Insulating materials such as paper and plastic film generate static electricity and generate higher voltages, which cannot be eliminated through grounding. The chemical composition, internal structure, stress-strain mechanical characteristics, and shape of the material also affect the generation of static electricity. For example, different types of paper generate different degrees of static electricity due to differences in fiber structure and chemical composition. For example, smooth plastic films are more prone to static electricity generation than rough ones.

02/ Mechanical effects

Mechanical action includes the type, time, area, separation speed, and properties of the forces acting on the two materials. Generally, the closer the two materials come into contact or the faster the separation speed, the greater the static electricity generated. During printing, paper frequently contacts and separates from parts such as rollers and guide rollers of the printing equipment, especially during high-speed printing, where the separation speed is fast and a large amount of static electricity is easily generated. Additionally, uneven printing pressure can cause different friction and contact between materials, which in turn affects static electricity generation.

03/ Ink characteristics

The composition and properties of the ink also affect the generation of static electricity. Some inks contain volatile solvents, which evaporate during printing, changing the ink's conductivity and making static electricity more likely. The viscosity and flowability of the ink also affect the generation of static electricity. Ink with excessive viscosity experiences strong friction during transfer, making it prone to static electricity; Ink with excellent flowability may generate static electricity when flowing through the ink fountain and ink path, due to friction with pipes and components.

04/ Environmental factors

Temperature and humidity have a close impact on static electricity. When paper is stored in paper warehouses and workshops, moisture content changes significantly due to large temperature and humidity variations. Once the relative humidity drops to a certain level (below 40%), static electricity is easily generated; When the ambient temperature rises, the paper is subjected to friction, and the movement of charge accelerates, increasing the generation and accumulation of static electricity. In the dry and cold winter environment, static electricity issues in printing workshops are often more prominent. In addition, dust and impurities in the environment can also affect the generation and accumulation of static electricity. Dust adsorbing on the surface of the substrate may alter its surface charge distribution, thereby exacerbating static electricity.

Solutions for static electricity

01/ Physical Elimination Method

(1) Grounding

By connecting printing equipment and metal conductors to the earth, creating a potential difference between the object and the earth, charge can leak through the earth. This is the simplest physical method to eliminate static electricity, but it has almost no effect on insulators. In the printing workshop, it is necessary to ensure good grounding of equipment, regularly inspect grounding circuits and grounding resistance, generally requiring resistance less than 10Ω. For example, the metal frame, ink fountain, and guide roller of the printing machine can be connected to the ground via grounding cables, allowing static electricity on the equipment to be promptly transmitted to the ground.

(2) Humidity regulation

The surface resistance of printing materials decreases as the relative humidity of air increases; increasing the relative humidity of the air can improve the conductivity of the paper surface and accelerate charge leakage. Generally, the relative humidity in the printing workshop should be controlled between 40%~60%. Humidity in the workshop can be adjusted by installing humidifiers or dehumidifiers. In dry seasons, use humidifiers to increase air humidity; During humid seasons, use a dehumidifier to lower the air humidity and maintain a suitable printing environment.

(3) Static eliminator

The induction-type static eliminator, also known as the induction-type static elimination brush, works by the principle that when the tip of the suppressor approaches a charged body, it can induce an electric charge with polarity opposite to that on the charged body, forming a strong electric field near the tip. After ionizing the air, the generated positive and negative ions move toward the tips of the charged body and the suppressor, thereby neutralizing the static electricity. During printing, a combination of induction and high-voltage discharge electrostatic elimination methods can be used. The static eliminator can be installed in areas prone to static electricity such as the paper feed section, printing drum, and paper collection of the printing machine, which can thoroughly and effectively eliminate static electricity.

02/ Chemical elimination method

Chemical elimination generally involves applying an antistatic agent to the surface of the substrate to make it conductive. However, because chemical components are added to paper during papermaking, it may negatively affect its quality, such as reducing paper strength, adhesion, tightness, and tensile strength, so it is generally not commonly used. For printing materials such as plastic films, appropriate antistatic agents can be selected for treatment. When selecting antistatic agents, determine the type and amount of antistatic agent based on the material's characteristics and printing requirements, to avoid affecting other properties of the material.

03/ Optimize production processes and management

Arrange the process flow reasonably to avoid prolonged material stacking and friction, reducing static electricity buildup. For example, moisture control is applied to the paper before printing to ensure uniform and stable moisture content; During the printing process, control the printing speed and pressure to avoid static electricity generated by excessive speed and pressure; Provide employees with static electricity protection training to enhance their awareness of static hazards and safety operations; Develop detailed operating procedures to standardize employee behavior during the printing process, such as avoiding direct contact with substrates and ink to prevent static electricity caused by friction; Regularly inspect and maintain equipment to ensure normal operation and avoid static electricity caused by equipment failures.

Case Study

A large printing company, while producing high-end food packaging boxes, experienced serious quality issues with printed products due to static electricity issues, such as burrs, missed prints, and dots in the text, resulting in a large number of products being scrapped and causing significant economic losses. At the same time, static electricity has triggered several small-scale fires. Although they were extinguished in time, they pose significant safety risks to the company's production.

After investigation and analysis, it was found that the company's printing workshop had low humidity, with an average relative humidity of around 30%, and there were issues with the grounding system of the printing equipment, with some equipment having excessive grounding resistance. In addition, the quality of the paper and ink used is unstable and can easily generate static electricity.

To address these issues, the company has taken a series of measures:

First, a humidifier was installed to raise the relative humidity in the workshop to about 50%;

Second, a comprehensive inspection and maintenance of the grounding system of the printing equipment was conducted to ensure the grounding resistance met the requirements;

In addition, paper and ink with more stable quality were replaced, and employees were trained on static protection knowledge to standardize operating procedures.

Through the implementation of these measures, the company's static electricity problem was effectively resolved, printing quality was significantly improved, production safety was ensured, scrap rates were greatly reduced, and production efficiency was markedly enhanced.

Static electricity has multiple impacts on the printing industry; it not only reduces print quality and impacts product market competitiveness, but also threatens production safety and lowers production efficiency. Understanding the causes of static electricity-such as material properties, mechanical effects, ink characteristics, and environmental factors-is crucial for taking effective solutions. By comprehensively applying physical elimination methods, chemical elimination methods, and optimizing production processes and management, static electricity generation and hazards can be effectively reduced, ensuring smooth printing production and improving product quality and economic benefits. In future printing production, as technology continues to advance, printing companies should keep exploring and applying more advanced electrostatic protection technologies to meet increasingly complex printing environments and higher quality requirements.