by mrs. adetoun tijani head, quality control laboratory, portland paints...
TRANSCRIPT
By Mrs. Adetoun Tijani
Head, Quality Control Laboratory,
Portland Paints & Products Nig. Plc
Quality control is a procedure/set of procedures carried out to ensure that a manufactured product/performed service adheres to a defined set of criteria/standard values, before, during and after manufacturing, to ensure customer satisfaction and conformance with statutory regulations.
The raw materials, manufacturing process and finished products undergo stringent QC checks.
Paints can be defined as a liquid, paste, or powder products which when applied on a substrate, dries to form a thin layer and serves for informative, decorative and protective purposes.
Paints is a mixture (not a compound).
Paint is different from DYE.
The term colorant is often used for both Dyes and Pigments. i.e. substances that impart color.
Dyes are chemicals /organic compounds, that are dissolved in a medium, to impart color and are absorbed into the material to which they are applied.
Coating is a general term denoting a material that is applied to a surface (e.g. Paint, Varnish)
Paint is pigmented, while varnish refers to clear lacquer/pigment-free coating.
Paints is made up of numerous components which are PEARS. i.e.
◦Pigment
◦Extender
◦Additives
◦Resins/Binder
◦Solvent
Pigments are responsible for color, covering power and anti-corrosive properties.
Pigments are finely ground crystalline solids that are dispersed/ suspended in the paint. They may be organic, in-organic and metallic.
The most widely used pigment is TiO2, due to its excellent hiding property. Other e.g. are carbon black, FeO, CdS for red, metallic salts for yellow and orange.
Extenders, also known as Fillers are largely finely ground crystalline solids that are dispersed in the paint, added to reduce cost of production, by replacing expensive pigments in paint.
Fillers give the paint body / make the paint bulky and improves flow ( i.e. less sagging on application).
They are used as matting agents (control gloss level), to provide matt or semi-gloss finishes e.g. are CaCO3, kaolin, talc, clay (Al silicates), sand, marble dust etc.
Additives are added to modify certain properties of paint. Examples are:
Driers – accelerate drying of paints. They are basically metals, which catalyses the oxidation and polymerization of film in solvent-based paints. E.g. Pb, Ca, Co, Mn driers. However, Pb is no longer in use due to high toxicity; but zirconium is now used instead.
Anti-settling Agent - to prevent pigment settling.
Anti-Skinning Agent- control skinning (ensures paint do not skin). i.e. oximes
Defoamers - reduce formation of bubbles during manufacturing, and breaks bubbles as they are formed in the paint
Biocides / Preservatives (IN-CAN/DFP) - prevents smelling of paint while in the container and growth of moulds /algae/fungi on paint after it has been applied.
Wetting & Dispersing Agent - are surfactants, that assists in moistening (wetting) the pigment, hence, easier to grind & disperse. They prevent flocculation of the pigment particles {ensuring uniformity}
Thickeners- makes the paint easy to apply.
Neutralizing Agents- are used in waterborne paints to neutralize and stabilize paints. E.g Ammonia
Co-Solvent- increases the hardness of the film, enhances flow. E.g in water-based paints, the co-solvent is texanol; Butyl Glycol- gloss paints.
Binder is a polymeric substance, mostly gummy in nature. They bind components together & make it stay on the substrate.
Binder is the actual film-forming component of a paint.
Binders improve the paints resistance to moisture permeability, sunlight exposure, staining, cracking, damage from abrasion & adhesion to the surface.
Binder/Resin may be natural or synthetic. Examples of natural resins are: linseed oil,
soya beans oil, coconut oil.
Examples of popular synthetic resins are: Alkyds, Acrylics, Epoxies, Polyurethane etc.
◦ Alkyd resins: most commonly used in solvent-based paints, e.g. gloss paints, heat cured stoving enamel paints.
◦ Poly Vinyl Acetate & Acrylic binders: are water-based binders.
◦ Epoxy resins: Epoxy resins are applied as base – coats, which prevents corrosion (tanks (fuel)and prevents friction (factory floor). Epoxy resins are also useful in marine application.
◦ Polyurethanes: Polyurethane - based paints are tough, with durable films that retain their gloss & are easy to clean. Polyurethane paints are applied as topcoats and are often used for painting aircraft.
◦ Silicon resin: are used for chiming machine (generates lots of heat)
◦ Polyester resin: used for roofing sheet.
Note: Epoxies/ Polyurethane paints are two-packed coatings that polymerize by way of a chemical reaction initiated by mixing the paint & curing agent/hardener at the point of use and which cure by forming a hard plastic structure.
Solvent is also known as CARRIER / DILUENT /THINNER
Solvents are low viscosity, volatile liquids.
They dissolve the binder & hold it in suspension with the paints’ pigment.
Ensures even-mixing of the paint components& makes the paint easy to apply.
They are used to reduce the viscosity of paint for better flow & application.
Examples of solvents are water, MEK- methyl-ethyl-ketone, MIBK- methyl-iso-butyl-ketone, Xylene, Toluene, Butyl-acetate, Butyl-glycol, kerosene. e.t.c.
Paint manufacturing process is just like making semo / amala at home.
The 1st thing should be ensuring that foodstuff (raw materials) are available.
Then, work instruction/batch sheet is issued, based on the quantity of raw materials available & sales request.
Next thing is to ensure that the pot/container and HSD/Grinding machine is very clean.
However, manufacturing instruction has to be adhered to in order to achieve the desired results. {For instance, if u want to make amala, u don’t pour your elubo in an empty pot on fire and start adding water; rather u put little quantity of water, allow to boil & then add your elubo}
Water based paints is processed in a HSD (high-speed dispersion) tank, in which a circular, toothed blade attached to a rotating shaft agitates the mixture of pigment, extenders, wetting & dispersing agents, little quantity of water, and defoamer; until the pigment particles are fully dispersed.
Once the dispersion is certified okay, by the Quality Control, the temperature of the mixture is controlled to 300c, before adding the binder & other raw materials remaining in the Batch sheet.
The paint is then mixed and sampled to the laboratory to check Quality Control parameters (viscosity, S.G, Colour, Opacity, drying, texture -consistency, gloss/sheen, NVC etc) to ensure conformance with the set standard.
Thinning & Tinting occurs.
Once the paint is certified okay by QC, it is then PASSED & PACKED as finished product. However, QC ensures that packaging containers are properly labelled, free from dirt & that products are packed to level.
The first step in making oil-based paint involves mixing the pigment/fillers with little resin, little solvent, wetting and dispersing agent to form a paste.
It is then routed into a sand mill/grinding machine (a large cylinder that agitates/grinds the pigment/filler particles, making them smaller and dispersing them throughout the mixture).
After about 30minutes, the fineness of grind is checked by the Quality Control Personnel. If okay, the paint is discharged & made-up. At this stage, the remaining raw materials yet to be added are added.
Thinning & Tinting then starts.
Quality Control parameters (viscosity, S.G, Colour, Opacity, drying, gloss/sheen, NVC etc.) are checked to ensure conformance with the set standard.
Once the paint is certified okay by QC, it is then PASSED & PACKED as finished product. However, QC has to ensure that packaging containers are properly labelled, free from dirt and that products are packed to level.
Specific gravity
PH: 7.5 – 9.0
Dispersion/ Fineness of Grind
Viscosity determined by Ford Cup/B4 cup (seconds) for low viscous products and Rotothinner (Poises) for highly viscous products.
Bleed resistance/ flocculation
Drying
The Texture of the paint is determined by applying it on the wall using a Texcote roller to check for sagging.
Color – using spectrophotometer
Opacity/ Hiding power is measured by painting it over a black surface and a white surface. The ratio of coverage on the black surface to coverage on the white surface is then determined.
Non-volatile matter
Gloss/Sheen is measured by determining the amount of reflected light given off a painted surface, using a Gloss meter.
Adhesion is tested by making a crosshatch on a dried paint surface. A piece of tape is applied to the crosshatch, and then pulled off. A good paint will remain on the surface.
Resistance to soapy water is tested by a machine that rubs a soapy brush over the paint's surface. – Wet Abrasion Scrub Tester
Weathering/ Resistance of the color to fading is determined by exposing a portion of a painted surface to outdoor conditions i.e. sunlight, water, extreme temperature, humidity, and comparing the amount of fading to a painted surface that was not exposed.
Stability Test
Coarse particle/ foreign matter – stick, rope, sack etc.
Flash Point is the temperature at which the mixture of the paint vapour and air, can ignite in the presence of a spark. The higher the flash point, the safer a solvent-based paint is considered for storage.
S/N DEFECTS CAUSES
1. Settling Low dispersion
2. Paint Separation Incompatibility
3. Foaming Mixing at high speed,
insufficient defoamer.
4. Foul smell/
Mould growth
Micro-organisms
5. Sagging, no
texture/ pattern
Too much water, sand omitted
6. Low viscosity Excess solvent
7. High Viscosity Insufficient solvent
S/N DEFECTS CAUSES
8. High Specific
gravity
Insufficient solvent
9. Low Specific
gravity
Excess solvent, foaming
10. Foreign matter Adding foreign contaminants
without manufacturers
specification (lead to film defect)
11. Chalking (is the
progressive
powdering of the
paint film on the
painted surface).
Polymer degradation of the paint
matrix, due to exposure from UV
radiation.
S/N DEFECTS CAUSES
12. Erosion (Erosion
is a very quick
chalking)
due to external agents like
rainfall
13. Peeling/Blisterin
g
Improper surface treatment
before application& dampness
present in the substrate.
14. Cracking
When paint coatings are not
allowed to cure/dry completely
before the next coat is applied.
S/N DEFECTS CAUSES
15. Pigment
Flocculation
The pigment, after
dispersion, reverts to a
greater or lesser degree,
when rubbed. (Colour
change)
16. Tacking/ not
drying
Insufficient drier
17. Skinning Absence of anti-skinning
agent, excess drier
18. Low sheen Excess pigment/extender
Quality control is the process of finding out the outcome of the product produced if it conforms to the standard procedures or not and if it will meet up with market demands. It is the heart of every organization.
Note that a poor or adulterated raw material and a wrong manufacturing process will never produce a good product hence quality checks on raw materials and finished products are very essential in order to get the desired benefits from such products.
Quality checks says a lot about the image of any organization. Above all the quality of a product should NEVER be compromised.
