Ink additives are auxiliary materials used to adjust ink to adapt to different printing conditions. There are many types of ink additives, and the commonly used ones include leveling agents, varnishes, drying agents, retarders, thinners, anti-friction agents, and overprint varnishes. Below is a brief introduction to the functions and usage methods of common ink additives.

 1. Leveling Agent  
A leveling agent is a functional additive that improves the flow and surface smoothness of liquid materials after application. Its core functions include:  
- Eliminating surface defects: By reducing the surface tension of the coating, it minimizes issues like pinholes and fish eyes caused by uneven tension.  
- Promoting spreading: Enhances the wetting ability of the liquid on the substrate, ensuring even coverage on complex surfaces.  
- Extending leveling time: Slows down surface drying, allowing the coating to flow fully before curing, reducing brush or roller marks.  
- Balancing fluidity: Works synergistically with thixotropic agents to prevent sagging while avoiding leveling difficulties caused by excessive viscosity.  

 2. Varnish  
Varnish is an essential auxiliary material in offset printing inks. Commonly used varnishes are made by refining and blending synthetic resins, drying vegetable oils, and high-boiling-point mineral oils. They are primarily used to adjust the fluidity of the ink and reduce its viscosity, with a typical dosage of 3–5%. Adding varnish does not affect the gloss or adhesion of the ink and has minimal impact on drying performance.  

 3. Drying Agent  
Drying agents are one of the most important ink additives in printing. Depending on the printing conditions and paper type, the amount, type, and usage method of drying agents vary. Commonly used drying agents include red drying oil and white drying oil. Red drying oil dries from the outside in, while white drying oil dries uniformly throughout. The type of drying oil is selected based on the drying requirements and ink color during printing. Generally, the dosage of drying oil is 2%–3%. Excessive amounts can have the opposite effect, slowing down the drying speed.  

 4. Retarder  
Retarders, also known as anti-oxidants, are the opposite of drying agents. During the printing process, machine stoppages often occur due to various reasons. When the stoppage time is long, the ink on the machine may dry and form a skin. To address this issue, an appropriate amount of retarder is added to the ink on the machine, and the machine is run briefly to prevent the ink from drying too quickly.  

 5. Thinner  
During printing, issues such as paper linting or plate wear may occur due to excessive ink viscosity or poor paper quality, disrupting the printing process. In such cases, besides adding an appropriate amount of tack reducer to lower the ink viscosity, a small amount of thinner can also be added to reduce the ink viscosity and ensure smooth printing. There are many types of thinners, with low-viscosity No. 6 varnish being the most common.  

 6. Anti-Friction Agent  
Anti-friction agents, also known as smoothing agents, are primarily wax-based substances. When printing with coarser ink particles, such as white ink or metallic ink, adding an appropriate amount of anti-friction agent can enhance the print's resistance to friction and smoothness.  

 7. Overprint Varnish  
High-end printed products like trademarks and picture albums often require overprint varnish treatment to achieve a high-gloss finish. Overprint varnish can be mixed into the ink before printing or applied as a final coat after printing. However, prints treated with overprint varnish may yellow over time and have poor light resistance. As a result, many new varnishes have been developed as alternatives to traditional overprint varnish.