Nitrocellulose Lacquers
Nitrocellulose (cellulose nitrate) lacquers are a mixture of binders (nitrocellulose and resins), plasticizers, and pigments dissolved or dispersed in organic solvents.
The components of nitrocellulose lacquers are :
a. Nitrocellulose
Nitrocellulose is an outstanding film-forming substance which displays rapid solvent evaporation (short drying time). Nitrocellulose is characterized by its nitrogen content and solubility. The nitrogen contents are :
- Ester-soluble nitrocellulose 11.8 - 12.2 wt%
- Alcohol-soluble nitrocellulose 10.9 - 11.3 wt%
Based on its viscosity nitrocellulose classified into three category : high-viscosity, medium-viscosity, and low-viscosity.
High-viscosity nitrocellulose have good flexibility combined with a high crack resistance. It is used where high mechanical stress is to be expected (e.g., in leather coatings, putty, adhesives). Only lacquers with low solids contents can be obtained from high-viscosity nitrocellulose.
Medium-viscosity nitrocelluloses have the broadest application range, such as furniture lacquers, paper and metal coatings.
Low-viscosity nitrocellulose is used to prepare high-solids lacquers. The low-viscosity nitrocellulose produces hard to brittle coating films, plasticizers and plastifying resins must be added to the lacquer formulation. They are used in putty, dipping paints, and printing inks.
b. Resins
Many synthetic resins such as alkyd, ketone, urea, maleate, and acrylic can be combined with nitrocellulose to make nitrocellulose lacquers. Selection of the resins based on price, color, influence on solvent release, gloss, hardness, sandability, yellowing, and durability of the final coating.
c. Plasticizers.
Plasticizers are used in coatings for the following purposes:
- To improve adhesive strength and gloss
- To improve mechanical properties such as elongation, pliability, buckling strength, crease resistance, and deep-drawing ability
- To increase resistance to light, heat, cold, and sudden temperature changes (cold-check test)
Plasticizers may be solvents such as dibutyl phthalate, dioctyl phthalate, dicyclohexyl phthalate, tricresyl phosphate, and triphenyl phosphate. Or nonsolvent such as crude and blown vegetable oils, stearates, and oleates.
d. Pigment
The use of pigment in nitrocellulose lacquers is same with other type of paint.
e. Solvents
The mixture of solvents has influence specially in drying time. The last solvent that evaporate should be a true solvent (can disslove) all material from the formula. Some solvents that are used are acetate esters (such as : ethyl acetate, butyl acetate, or propyl acetate) and ketones (such as : acetone, methyl ethyl ketone, methyl isobutyl ketone).
Uses
Nitrocellulose lacquers is used in printing inks employed in flexographic, gravure, or silk-screen printing. The most important uses of nitrocellulose lacquers are for coating wood, metal (automotive repair), paper, foil (cellophane, aluminum), leather, textiles, and in nail polish.
