1、Source of water-based ink wastewater
Water-based inks are mainly used in low-end printing such as books and magazines, in printing industries with low requirements such as corrugated paper, in flexographic printing fields such as product packaging for cigarette factories, breweries, pharmaceutical factories, cosmetics, children's toys, and in composite paper packaging for milk and beverages, as well as in other carton packaging industries. During the production and application of water-based ink, due to equipment cleaning, a certain amount of water-based ink wastewater is generated. The main source of wastewater in the application field of water-based inks is the drainage water that needs to be cleaned for printing related equipment such as ink replacement, such as wastewater generated from washing sticks, sinks, buckets, and operating rooms.
Waterborne inks can be divided into three categories: water soluble, alkali soluble, and diffusible. Currently, alkali soluble ink is widely used in research and development.
(1) The connecting materials for water-soluble inks include polyvinyl alcohol, hydroxyethyl cellulose, and polyethylene chromate ketone. This type of connecting material can be permanently dissolved by water, so the formulated ink can only be used in situations where it is not in contact with water.
(2) The connecting material for alkali soluble ink is an alkali solution of an acidic resin, with an appropriate amount of ammonium hydroxide added. The two chemically react to form a soluble resin salt. During the ink drying process, ammonia volatilizes and turns the ink into a water insoluble substance.
(3) The connecting material of diffusive ink is fine resin particles suspended in water, called latex. Compared to dissolved resin, latex has the following advantages: it can have a high density and low viscosity, forming a high-quality thin coating, and can contain considerable polymer molecules. The coating is hard, wear-resistant, heat resistant, and has good adhesion; The disadvantage is that printing is difficult and difficult to clean.
2、Characteristics and hazards of water-based ink wastewater
The main pollutants in the wastewater from the production of water-based inks are water-soluble acrylic resins (color carriers), cyclic organic compounds (pigments) containing colored groups, and alcohol or phenyl dispersants with high molecular weight. Acrylic resins are the main component of CODcr in the wastewater, accounting for over 80%. There are various types of pigments, among which inorganic pigments include salts, oxides, and carbon; Organic pigments include azo pigments, phthalocyanine pigments, nitro pigments, lake pigments, reducing pigments, nitroso pigments, heterocyclic pigments, and many other types. In addition, it also contains more than ten additives such as stabilizers, defoamers, blockers, surfactants, and preservatives.
The wastewater from water-based ink production is a weakly alkaline, high concentration, high chroma, and difficult to biodegradable industrial wastewater, which is difficult to treat.
3、Treatment method of water-based ink wastewater
1. Chemical oxidation coagulation process
2. Ultrafiltration technology
3. Coagulation Air Floatation Contact Oxidation Combined Process
4. Iron chip micro electrolysis process
5. Chemical coagulation process
6. Coagulation Air Floatation Microelectrolysis SBR Process