Ink additives have a significant impact on printing performance, stability, and the lifespan of printing equipment. Therefore, selecting the appropriate additives during the ink production process is crucial.
1. What are Ink Additives?
Additives, also known as auxiliary agents, are supplementary materials added during ink manufacturing and the printing process to optimize performance. Generally, when an ink formulated with basic components cannot meet specific performance requirements, or when printing performance declines due to changing conditions (such as temperature, printing substrate, paper conditions, or deterioration from long-term storage), adding appropriate additives is beneficial for improving printing efficiency and quality. Almost every type of ink has its specific additives, though some are universal.
2. Types and Functions of Ink Additives
There are numerous types of ink additives. Below are the common types and their functions:
1. Fillers (填充剂)
Fillers are generally white solid materials that can be uniformly dispersed in the binder. Common fillers include chemical components such as aluminum hydroxide, magnesium carbonate, and calcium carbonate. They regulate ink properties like consistency, viscosity, flowability, and yield value, while also adjusting ink concentration.
2. Driers (干燥剂)
Driers are key additives for printing inks. Their dosage, type, and application method depend on the printing conditions and the paper used. Common driers include “Red Drier” (cobalt-based) and “White Drier” (lead/manganese-based); the former facilitates drying from the outside in, while the latter achieves simultaneous drying of the surface and core. The choice depends on the drying requirements and ink color. Typically, the dosage is 2%-3%; excessive use may actually slow down the drying speed.
3. Thinners / Diluents (稀释剂)
Without affecting the pH value of the ink, the primary function of a thinner is to reduce viscosity and prevent film formation. For thick water-based inks, thinners can lower viscosity, but the amount should not exceed 5% of the total ink volume. Low-viscosity oligomer linseed oil thinners mix well and are mild; mineral oil thinners have a significant thinning effect but must be used sparingly to avoid poor printing results. Typically, low-viscosity No. 6 varnish is chosen.
4. Anti-skinning Agents (防结皮剂)
These prevent coatings from forming a gel-like skin on the surface due to oxidative polymerization during storage. The mechanism involves capturing free radicals produced during the film-forming process, interrupting oxidative polymerization, and preventing organic substances from aggregating at the surface.
5. Reducers / Extenders (撤淡剂)
Also known as tinting bases, these are used in large doses in offset printing to reduce color concentration. Common types include transparent oil (for gloss inks) and resin-based reducers (for resin inks). If the ink color is too dark to accurately reproduce the original, a reducer is added. To ensure proper drying, it is essential to add about 2% white drier when using reducers.
6. Anti-set-off Agents (防反印剂)
These prevent the ink layer from transferring (setting off) to the back of the next sheet of paper. The most common agent is corn starch, which offers good adhesion, flowability, and stability, effectively reducing the set-off phenomenon.
7. De-tackifiers (撤粘剂)
De-tackifiers have very low tackiness and are used in offset and letterpress inks to reduce stickiness. In offset printing, changes in paper properties (high oil absorption, low surface strength) or environmental factors (too much drier, low room temperature) can cause “picking” (tearing the paper surface) or “piling” on the plate. Adding an appropriate amount of de-tackifier can eliminate these faults.
8. Retarders / Anti-oxidants (慢干剂)
The opposite of driers, these are used when printing stops for an extended period. They prevent the ink on the press from drying and forming a skin. Adding a retarder and running the machine briefly helps slow down the drying speed and maintain print quality upon restart.
9. Abrasion-resistant Agents (耐摩擦剂)
Also called slip agents, these are primarily composed of wax-like substances. When using inks with coarse particles (such as white, gold, or silver inks), adding these agents improves the rub resistance and smoothness of the printed product.
10. Varnishes (罩光油)
High-quality prints like trademarks and albums often require a varnish treatment to achieve a high-gloss effect. Varnish can be mixed with the ink before printing or applied as a topcoat afterward. However, some traditional varnishes may yellow over time or have poor lightfastness, leading to the development of many modern gloss oil alternatives.
11. Dispersants / Anti-settling Agents (分散/防沉剂)
These are modern interface materials that act as a bridge by coupling with filler surfaces and cross-linking with polymer bases. They are superior to surfactants in terms of bonding strength, reducing interface free energy, and improving dispersion. Unlike surfactants, they do not migrate (which can affect gloss and adhesion). They shorten grinding time, reduce solvent use, lower viscosity, and improve substrate wetting and mechanical properties.
12. Adhesion Promoters (附着力促进剂)
Mainly used in water-based coatings and inks, these improve the bond between the ink and the substrate while providing some dispersion and anti-settling capabilities.
3. Choosing the Right Ink Additive
Selecting the right additive becomes more efficient once the types are understood. However, one must also consider the following practical factors:
- Substrate Material: Different materials have different surface properties. For example, plastics may require flow improvers, while paper may require adhesion enhancers.
- Printing Process: Requirements vary by process. Offset printing may require anti-piling agents, while screen printing often requires drying accelerators.
- Quality Requirements: High-definition prints require flow improvers to ensure uniform ink dispersion.
- Environmental Factors: Temperature and humidity significantly affect ink performance.
Furthermore, once the type of additive is determined, it is important to compare different brands based on performance indicators, safety, and price to choose the most cost-effective product.