Chlorinated Rubber Coatings

Chlorinated Rubber Coatings

Chlorinated rubber (CR) is manufactured from natural or synthetic rubber such as polypropylene, polyethylene, or polyisoprene which is degraded to low molecular mass compounds by mastication or addition of radical formers and dissolved in carbon tetrachloride. Chlorine gas is than introduced into the solution and will reacts with the raw material to form CR. The solution is then introduced into boiling water. The CR is than precipitated and vaporized. It is separated from water, rinsed, dried, and ground to form a white powder.
CR has some properties :
- high resistance to oxidizing agents (such as ozone or peroxide), water, inorganic salts, acids, alkalis, and gases.
- good solubility in almost conventional ssolvents except water, aliphatic hydrocarbons, and alcohols.
- good compability with a wide range of paint resins and plasticizers.
- low flammability.
- fungistatic and bacteriostatic behavior.
- compatible with almost all inorganic pigments and extenders, as well as many organic pigments.

Chlorinated rubber has high water resistance, it is used for underwater coatings on steel and concrete.

Oil-Based Coatings

Oil-Based Coatings

Oil-based paints (oil paints) are the oldest organic coating materials. The content of Oil paints is natural drying oils such as linseed oil, tung oil, and soybean oil which will undergo autoxidative polymerization in the presence of catalytic driers and atmospheric oxygen. The catalytic driers are metallic soaps such as cobalt, lead, and manganese naphthenates or octoates.

During curing of paint, the atmospheric oxygen reacts with the oil to form hydroperoxides which will decompose into radicals and then initiate polymerization of the binder. The drier will catalyze the formation and decomposition of the hydroperoxides and thereby accelerate film formation.

The thickness of film will influence the curing process. If the film is too thick, the oxygen will penetrates the film very slowly and the inside of paint will remain soft. The thickness of paint ussually 25-30 micron on vertical and 40-50 micron on horizontal surfaces. The drying time is depent on the room temperature, higher temperature will increase the speed of drying.
Oil-based paints are tough but not excessively hard. It has limited weather resistance. It will lose its gloss and tend to yellow much more than otehr binders (ca. two years).
The use of oil paint has decrease and have been replaced by other types of binder. Its renewable natural oil are environment friendly as long as toxic pigment and solvent are not used.

Nitrocellulose Lacquers

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.