Applications of Pigment Paste in Papermaking
Pigment paste is widely used in papermaking to achieve various color effects.
Below are the key application methods:
1. Whitening Blue and yellow are complementary colors. By reducing yellow light reflection or increasing blue light reflection, a whitening effect is achieved. Paper mills commonly use blue-violet pigment and fluorescent whitening agents to enhance whiteness. Ideal for papers requiring high whiteness levels.
2. In-Pulp Dyeing Used for producing colored papers such as cultural paper, food paper, noodle paper, and kraft paper. Works on the same principle as whitening pastes. Challenges include high cost, low retention rate, and complex wastewater treatment. Pigment retention depends on production factors like fillers, retention aids, and filter aids.
3. Coating A common method for coloring paper that requires coating formulations. Popular coating techniques: roller coating, metering rod coating, and air knife coating. Color paste should be compatible with the coating formula to maintain stability in pH, viscosity, and water resistance, especially in large-scale applications.
4. Glue Dipping Primarily used for decorative paper production. Requires good compatibility with glue, minimal bubbles, strong adhesion to the decorative base paper, and uniform application. Ensures stable viscosity and pH levels for high-quality results.
5. Pre-Sizing Dyeing A more complex coloring technique, mainly applied in cultural paper manufacturing. Helps optimize production costs while achieving the desired color effects.