SURFACE COATING INDUSTRIES

CHE 432

INDUSTRIAL PROCESS

Introduction

• Divided into:– Paints: opaque solid coatings applied as thin

layers, formed by polymerization of polyunsaturated oil

– Varnishes: clear coatings– Enamels: pigmented varnishes– Lacquers: films formed by evaporation only– Printing inks– Polishes

Functions

• Decorative - paints decorate by its colors, textures, finishes and its different levels of gloss

• Protective – different paints offer protection to different types of substrates depending on formulation, paints can protect against high humidity, chemicals, oil, corrosion, algae, abrasion, etc.

Paint Composition

• Liquid phase (vehicle) : dispersion of finely divided pigment composed of resin or binder and volatile solvent

• Characteristics of pigment:- inorganic substance or pure insoluble organic dye (toner)- opaque to ensure good covering power and chemically inert to secure stability- non toxic or low toxicity- wet by the film-forming constituents and low cost

Classification of paints

• Emulsion-based paints: emulsion of binder in water, binder can be oil, acrylic or polyvinyl acetate resin

• Water-thinned paints• Casein-based paints• Resin-emulsion paints• Latex-based paints: eased of applications-

quick drying, low odor, easy cleaning, great durability and impermeability to dirt.

Paint formulation

• Specific requirements such as:- hiding power- color- weather resistance- washability- gloss- metal anticorrosive properties- consistency

Manufacturing Procedures

• Involved chemical conversions• Step 1: weighing, assembling and mixing

pigments and vehicles• Step 2: further grinding and mixing • Step 3: Tinting and thinning of paints in agitated

tanks• Step 4: transfer to hopper, centrifuge, screened

and filtered to remove nondispersed pigments• Step 5: filling in cans or drums, labeled, packed

and moved to storage (automated)

Paint failure• Chalking: progressive powdering of the paint film

from the surface caused by continued and destructive oxidation of the oil after the original drying of the paint

• Erosion: rapid chalking• Flaking/peeling: poor attachment of the paint to

the surface due to dirt or grease on surface• Alligatoring: type of peeling in which center

portion of section starting to peel remains attached to the surface

• Checking: fine type of surface cracking