In high-speed computer gravure printing machines, electrostatic interference (ESD) is a critical issue affecting print quality and production safety during film printing. ESD primarily originates from friction between the film and guide rollers/impression rollers, as well as charge separation of ink during high-speed flow. Especially in dry environments, ESD accumulation can easily lead to ink splatter, misregistration, dust adsorption on the film, and even fires due to ESD. To avoid these interferences, a comprehensive solution needs to be developed from multiple dimensions, including equipment design, material handling, environmental control, and process optimization.
Grounding is the fundamental measure for eliminating ESD in high-speed computer gravure printing machines. Metal components of the machine, such as guide rollers, impression rollers, and the frame, must be reliably connected to the ground via conductive materials to form an ESD discharge path. For non-conductive components, such as some rubber rollers, conductivity can be enhanced by spraying a conductive coating or wrapping them with conductive materials. Furthermore, installing anti-static brushes at the film unwinding and rewinding positions, with bristles in contact with the film surface, conducts charge to the grounding terminal, effectively reducing ESD accumulation during film movement. The material of the antistatic brush must possess high conductivity and abrasion resistance, and its installation location must avoid ink splatter areas to prevent contamination.
The electrostatic properties of the film itself are a core factor affecting printing results. Materials such as PET and NY, due to their molecular structure, are prone to generating high static electricity during friction, requiring antistatic treatment before printing. Chemical antistatic methods, by adding antistatic agents during film production or coating the finished film, can significantly reduce surface resistance. Antistatic agents are typically ionic surfactants; their hydrophilic groups absorb moisture from the air, forming a conductive water film and accelerating charge leakage. Coating treatment requires selecting a suitable antistatic agent based on the film material and controlling the coating thickness and uniformity to avoid affecting printability.
The antistatic properties of the ink in high-speed computer gravure printing machines are equally crucial. Adding antistatic agents to the ink formulation can improve the ink's conductivity and reduce charge accumulation during printing. The selection of antistatic agents must consider compatibility with the ink system to avoid affecting ink drying speed, adhesion, and other properties. Furthermore, adjusting ink viscosity is also an effective means of controlling static electricity. Ink viscosity that is too low is prone to splashing due to centrifugal force, increasing the risk of static electricity generation; while viscosity that is too high may lead to increased friction due to poor flow. In practice, the optimal viscosity range needs to be determined through experimentation based on factors such as film material and printing speed.
Ambient temperature and humidity have a significant impact on the generation and dissipation of static electricity. Dry environments reduce air humidity, decreasing the conductive water film on the film surface and exacerbating static electricity accumulation. Therefore, humidification equipment is needed to control the humidity in the printing workshop between 55% and 65%, while maintaining the temperature between 18 and 28°C to optimize the film's conductivity. The humidification method should be selected according to the workshop size; dry steam humidifiers are suitable for centralized air conditioning systems, while high-pressure spray humidifiers are suitable for localized areas. Care must be taken to avoid excessive humidity, which can cause the film to become damp and deformed, affecting printing accuracy.
Static eliminators are key equipment in the printing process. High-voltage corona discharge static eliminators ionize air with high voltage, generating a large number of positive and negative ions to neutralize the static charge on the film surface; inductive static eliminators utilize the principle of electrostatic induction to create a reverse electric field on the film surface, canceling out the existing static electricity. These devices need to be selected based on parameters such as printing speed and film width, and installed in key locations such as unwinding, printing, and rewinding to ensure continuous electrostatic control. In addition, the discharge needles and collecting electrodes of the electrostatic eliminator should be cleaned regularly to prevent dust accumulation from affecting performance.
Optimizing process parameters can also indirectly reduce electrostatic interference. Reducing the printing speed can decrease the friction frequency between the film and the guide rollers, but production efficiency must be balanced; adjusting the pressure of the impression roller can prevent excessive film stretching and reduce frictional static electricity; optimizing the doctor blade angle and pressure can reduce ink splatter and lower the risk of static electricity generation. The optimal combination of these parameters needs to be determined through experimentation to achieve a balance between electrostatic control and printing quality.
