PVC ink, a key material widely used in printing on plastic products, directly affects the core properties of printed materials, such as color uniformity, gloss, and adhesion, due to its pigment dispersibility. Poor pigment dispersibility can easily lead to problems like clumping, sedimentation, and uneven coloring, resulting in decreased print quality. To address this issue, a comprehensive approach is needed, encompassing pigment selection, dispersant application, grinding process optimization, ink formulation adjustment, equipment improvement, storage condition control, and production process management, to achieve efficient pigment dispersion and stable suspension in PVC ink.
The properties of the pigment itself are fundamental to the dispersion effect. Different pigments exhibit significant differences in crystal structure, particle size distribution, and surface polarity, directly impacting their ease of dispersion in ink. For example, organic pigments, due to their complex molecular structure and high surface energy, are prone to agglomeration; inorganic pigments, although having larger particle sizes, have stronger surface polarity, requiring surface modification to reduce their hydrophilicity. Therefore, selecting pigments with uniform particle size and proper surface treatment is the primary step in improving dispersibility. Pre-dispersed pigments, or those with surface-coating technology to reduce surface energy, can significantly improve their initial dispersibility in inks.
The selection and dosage of dispersants play a crucial role in pigment dispersion. Dispersants prevent pigment particles from re-aggregating by adsorbing onto the pigment surface and creating steric hindrance or charge repulsion. For PVC ink systems, dispersants with good compatibility with PVC resin and strong temperature resistance should be selected. For example, high molecular weight dispersants can form a thick adsorption layer on the pigment surface, providing a stronger steric hindrance effect; while low molecular weight dispersants stabilize pigment particles through charge repulsion. In actual production, the amount of dispersant needs to be adjusted according to the pigment type and ink formulation. Excessive dispersant may increase ink viscosity, while insufficient dispersant will not effectively prevent agglomeration.
The grinding process is the core step that determines the final dispersion state of the pigment. Equipment such as three-roll mills and sand mills use mechanical shearing force to refine pigment particles to the micron level and destroy their initial agglomerated structure. During the grinding process, it is necessary to control the particle size, filling rate, and grinding time of the grinding media (such as zirconium beads) to avoid incomplete dispersion due to insufficient shear force or damage to the pigment structure due to over-grinding. Simultaneously, employing a segmented grinding process to gradually reduce the pigment particle size can improve dispersion efficiency and reduce energy consumption. Furthermore, controlling the grinding temperature is crucial; excessively high temperatures may accelerate the decomposition of dispersants, reducing their stabilizing effect.
The interactions of other components in the ink formulation also affect pigment dispersibility. As the film-forming substance of the ink, the resin's molecular structure and polarity must match the pigment to provide good wetting properties. The choice of solvent must balance solubility and volatility to avoid pigment re-aggregation due to excessive solvent evaporation. Additives such as leveling agents and defoamers, although not directly involved in dispersion, can indirectly improve the dispersion effect by improving ink flowability. For example, leveling agents can reduce the surface tension of the ink, promoting uniform distribution of pigment particles; defoamers can eliminate bubbles generated during grinding, preventing bubbles from encapsulating pigment particles and affecting dispersion.
The precision and maintenance of production equipment have an indirect impact on pigment dispersibility. Wear and tear on grinding equipment leads to decreased shear force, affecting pigment refinement. Uneven mixing in the mixing equipment can cause localized excessive pigment concentration, resulting in agglomeration. Therefore, regularly inspecting equipment for wear, replacing worn parts promptly, and ensuring the equipment is clean and residue-free are crucial measures for maintaining pigment dispersion stability. Furthermore, using an automated control system to monitor parameters such as temperature and viscosity during the grinding process allows for precise control of process conditions, further improving dispersion quality.
Storage conditions are critical to the long-term stability of pigment dispersion. During storage, excessively high temperatures or humidity can cause dispersant migration or pigment hygroscopicity, leading to re-agglomeration. Therefore, ink should be stored in a cool, dry place, avoiding direct sunlight and high temperatures. Storage containers must be well-sealed to prevent solvent evaporation, which can increase ink viscosity and affect pigment dispersion. For inks stored for long periods, thorough stirring and testing of viscosity and dispersibility are necessary before use to ensure they meet printing requirements.
Production process management is a systematic measure to ensure pigment dispersion. From raw material inspection and formulation design to process execution, each step requires strict control. For example, pigment particle size and dispersibility indicators need to be tested before raw materials are put into storage; small-scale tests are required when adjusting the formula to ensure the compatibility of the dispersant with other components; key parameters need to be recorded during process execution for traceability and optimization. In addition, strengthening employee training and improving their understanding of dispersion mechanisms and process control is also an important guarantee for achieving efficient pigment dispersion.
