Screen Printing Ink Introduction (Part 1)
Screen printing inks, like other types of inks, are made of pigments, resins, solvents, and additives. The various screen printing ink types can be categorized into four types based on their curing methods:
1. Solvent-based ink: As the solvent evaporates, the ink film adheres to the substrate.
2. Oxidative polymerization type: An oxidation reaction occurs, forming the ink layer.
3. Two-component reaction type: This involves a chemical reaction between two components.
4. UV ink: A chemical reaction is triggered by UV irradiation.
Additionally, screen printing ink types can be classified into five categories based on their applications:
1. Screen printing ink for fabric
2. Screen printing ink for plastic
3. Screen printing ink for metal
4. Screen printing ink for paper
5. Screen printing ink for glass
According to the type of ink binder, screen printing ink can further be divided into several types, including epoxy resin ink, polyurethane ink, polyester ink, vinyl ink type, acrylic ink type, and rubber type. It is important to choose the appropriate ink based on the substrate’s material to ensure optimal adhesion. Using the same resin type ink helps avoid poor adhesion issues. For uncertain materials, it is advisable to determine the selected ink after conducting a printing test.
Selecting the manufacturer's recommended solvent is critical, as different solvents have varying solubility properties, which can influence the printing effect.
During the screen printing ink process, several common problems may arise along with their solutions:
1. Foaming: This issue can occur if the printing viscosity is too high, drying occurs too quickly, or the plate separates from the substrate too fast. A suitable solution is to add an appropriate amount of defoaming agent or to replace the ink with another type.
2. Screen Blocking: This problem often arises from fast drying while the printing speed is too slow, high printing viscosity, or poor-quality diluents. Additionally, the printing surface being blown by wind or containing impurities can contribute to this issue.
3. Pinhole: This defect can be caused by a smooth printed object or if the printing surface has a protective layer of grease or impurities. To resolve this, the printed object's surface should be pre-treated, and a leveling agent or high-quality ink should be used.
4. Poor adhesion: This problem may stem from improper ink selection, insufficient pre-treatment, dust on the object, or inadequate drying temperature and time. Adjusting the dosage of additives, curing agents, and driers can also help improve adhesion.
When printing with two-component ink and overlapping colors, excessive solidification of the background color can lead to issues. Materials like PE, PP, PET, and aluminum foil often require treatments such as corona, flame, or strong acid dipping to increase surface tension for better ink adhesion. Once cured, the ink film becomes dense and resistant to solvent erosion, allowing for multiple color applications after the base color has dried.
5. Drawing: This issue may result from high viscosity, fast drying, or improper solvent use. Adjusting the solvent and viscosity or opting for high-quality ink can help solve this problem.
6. Migration and fading: The use of inappropriate pigments in the ink can cause this issue, especially if plasticization is excessive. Selecting the right ink is crucial.
7. White or foggy printing surface: This occurs when the diluent contains water, air humidity is high, or the ink itself is defective. During drying, the solvent evaporates and absorbs heat, leading to local condensation that causes white fog.
To prevent this, it is essential to choose an appropriate drying speed, reduce humidity, or use high-quality ink.
Screen printing ink additives include defoaming agents, leveling agents, anti-friction agents, and matting agents, which should be used according to the manual instructions. Improper use of screen printing ink additives can result in poor printability, diminished gloss, slow drying, and reduced adhesion.
The curing agent and drier must be added accurately according to the recommended ratios, as incorrect amounts can lead to increased ink condensation.
