To most people, paint is the colour on the walls of their home, the colour of their car, boat or caravan.
Paint is more than just the colour though; it is a material that is applied as a liquid and dries by a variety of chemical processes to a solid.
We apply paint for:
Paint typically consists of pigment, resin, solvent and additives:
Pigments are usually divided into two groups. One called ‘Prime Pigments’ includes pigments such as Titanium Dioxide (white), Chrome Green Oxide, Yellow and Red Iron Oxides, etc. The other group of pigments is called ‘Extender Pigments’ and includes Calcite (Calcium Carbonate), Talc (Magnesium Silicate), Mica, Barytes (Barium Sulphate), etc.
Waterborne paints most often use acrylic emulsion polymers as binders. These come in a wide variety of types and combinations. Common acrylic polymer types are based on monomers such as methyl methacrylate and butyl methacrylate. Traditionally, lower cost paints have been formulated on PVA (Poly Vinyl Acetate) binders.
Solventbased resins come in a very wide range of types. The most common solventbased resins are termed ‘alkyd resins’ that are normally used in enamel paints. Urethane alkyds often used in clear varnishes. Protective coating resins include types such as Epoxy, Urethane, Polysiloxane and Moisture Cured Urethane.
Our paint is generally manufactured in batch lots from 200 litres for special products and colours to 10,000 litres for mainline white products.
The manufacturing process involves five critical parts:
Ingredients are typically measured by weight on scales, and in some cases by volume in calibrated vats and graduated measuring containers. For batches larger than about 4000 litres the vats are loaded onto load cells connected to accurate electronic scales. The scales allow addition of ingredients with a measurement accuracy of +/- 5 kg in 20,000 kg. Where greater accuracy of small additions is required highly accurate floor scales are used.
Pigments are powders of typically small size that tend to stick together to form clumps or agglomerates. These must be broken down into separate particles that must then be wetted by resin and additives to stop them sticking together again. This is the process of dispersion.
High speed mixers are used for combining materials and dispersing most pigments. These machines rotate stainless steel serrated discs of up to 60cm diameter, at up to about 1000 rpm. The largest machine also has rotating scraper blades to ensure material doesn’t stick to the sides of the mill-base vat.
Pigments are added slowly, from containers of 10 kg up to 1000 kg, to a portion of the liquid paint components, with the mixer running, to form the mill-base.
Certain pigments are more difficult to disperse and require ball milling, bead milling or bar milling.
Ball mills are used for small batches of difficult to disperse mill-bases. Ball mills are large porcelain lined rotating drums containing golf ball sized porcelain balls. Rolling and tumbling of the balls provides sufficient force to break up agglomerates.
Bead mills are used for large batches and can maintain semi-continuous output. Operation is similar to a ball mill but the vessel is smaller and balls are 3mm diameter zirconium dioxide beads, and mixing is at a higher speed producing more rapid output.
Bar mills are especially useful for highly viscous (thick) mill-bases. The mill-base is forced through a small clearance between a rotating water cooled roller and a bar pushed against the roller.
In a separate, larger, vat the rest of the paint (resin, solvent and additives) is combined and mixed. This is called the let-down. When the let-down and the mill-base are completed, the mill-base is added with stirring to the let-down. At this stage, if required by the formulation, any final additions are made and added in.
Product quality is monitored throughout the manufacturing process by the Product Verification Laboratory. Critical ingredients are tested before manufacturing starts. The mill-base may be tested for dispersion; if necessary further processing may be required. The let-down may be tested to ensure it is sufficiently mixed.
The completed batch (mill-base plus let-down and any final additions) is thoroughly tested by the Product Verification Laboratory. These final tests evaluate properties such as degree of dispersion, viscosity (consistency), density, hiding, tint strength and colour, application, dry time, gloss and dry film appearance.
When testing is completed the batch is passed for canning. During canning two samples are taken; a retain sample, which is stored in case it is needed for future reference, and a Final Inspection sample. The Final Inspection sample is tested in the Resene Final Inspection Laboratory to guarantee conformance to relevant standards and specifications, such as APAS, Environmental Choice, etc. After this final stage of testing is complete the batch is passed for use in the warehouse and dispatch to branches as required.
The simplest types of paint are lacquers that form a film by evaporation of solvent.
Waterborne paints, such as Resene Hi-Glo, are usually based on emulsion resins that consist of trillions of tiny resin particles, about 1/100th of the diameter of a human hair. As the water in these paints evaporates the resin and pigment particles get closer and closer together until they begin to touch each other. When the resin particles touch each other and the pigments, they stick together and fuse into a tough elastic solid, which we recognise as the paint film.
Solventborne enamel paints, such as Resene Super Gloss, are based on alkyd resin dissolved in solvent (mineral turps). When the solvent evaporates the first stage is the formation of a tacky lacquer. The alkyd resin progressively reacts with oxygen from the atmosphere and polymerises to form a hard, tough coating.
Two component protective coating paints are unreactive on their own, but when mixed together undergo a chemical reaction. The chemical reaction takes a few hours (depending upon temperature) and results in an extremely tough, hard coating with great adhesion. These paints generally require specialist surface preparation and application, and are often used in extreme environments.
The boundaries between waterborne paints and solventborne enamels, and other reactive coatings, are becoming blurred as new technologies develop. For example, Resene Enamacryl and Resene Lustacryl consist of waterborne emulsion resins and chemistry that produces polymerisation of the dried film similar to solventborne enamels.
Mill-base: High speed mixer
|1.||Water, propylene glycol, surfactants, dispersants, defoamer and biocide are measured out and added to a dispersion vat. This is the start of the mill-base.|
|2.||The liquid measure is premixed for about five minutes.|
|3.||White pigment (titanium dioxide) and extender pigment (calcite, talc, barytes) are added in a predetermined order with the disperser running. The disperser blade speed is gradually increased as pigment is loaded. Water is also added in stages to maintain optimum viscosity for mill-base dispersion. The finished mill-base is then tested.|
|4.||Remaining additives ad some thickener and water are added and mixed.|
|5.||Meanwhile in a larger let-down vat, the emulsion resin component is measured out. This has defoamer, thickener and coalescent solvent added with stirring and is mixed for about 30 minutes.|
|6.||When both mill-base and let-down are completed, the mill-base is pumped into the let-down, while the hydraulic mixers attached to the vat maintain good agitation.|
|7.||Once all the mill-base is added, and the mill-base vat washed out, the nearly completed paint is mixed for about 30 minutes. Then additional thickeners and remaining additives are measured out and mixed into the batch.|
|8.||A sample of the batch is taken to the laboratory for analysis.|
|9.||Depending upon the results of testing, the batch may be fine tuned for viscosity and mixed for a further period of time.|
|10.||A predetermined series of tests are carried out on a sample of the batch. Where tint strength and colour are specified, the batch will also be tested for properties such as tint acceptance and compatibility with tinters.|
|11.||When the batch passes through the primary stage of testing it is approved for canning and then packed into a specified series of containers. Retain and Final Inspection samples are collected.|
|12.||If the product is APAS and EC approved it is held in quarantine while a sample if subjected to further tests in our Final Inspection Laboratory.|
|13.||When all tests are completed, and results recorded and checked, the Final Inspection Laboratory issues a release from quarantine to the warehouse.|
|14.||When the Final Inspection Laboratory request is received the batch is moved into warehouse general stock for dispatch as required to meet orders.|
The normal production time for steps 1-14 is about two days.
Mill-base: High speed mixer and bead mill
|1.||Check organic bright red pigment for quantity and grade.|
|2.||Solvents, alkyd resin, dispersing resin, dispersants and anti-settling aids are added to the mill-base vat.|
|3.||The liquid mixture is premixed for about five minutes.|
|4.||The organic bright red pigment is added very carefully and mixed in to form the mill-base.|
|5.||The mill-base is dispersed by the high speed mixer for about 20 minutes to predisperse the pigment.|
|6.||After premixing, the mil-base is pumped through a horizontal bead mill. A sample is taken to test dispersion. Depending on the result the mill-base may be further bead milled. Typically several passes are required to ensure all the agglomerates are broken up.|
|7.||Meanwhile in a larger let-down vat, alkyd resin, solvent, driers (metal soaps) and anti-skinning agents are measured out and mixed together to form the let-down.|
|8.||When both mill-base and let-down are completed, the mill-base is pumped into the let-down while the mixture is stirred. Stirring continues for about 30 minute to ensure a uniform mixture.|
|9.||Final additions of solvents and additives are made and mixed into the batch.|
|10.||A sample is taken to the laboratory for analysis.|
|11.||The batch is fine tuned to viscosity as necessary based on the results of the tests.|
|12.||Further samples are taken and the batch is tested for properties including gloss, colour, tint acceptance and drying.|
|13.||When the primary stage of testing is completed the batch is passed for straining and canning. While being strained the batch is periodically sampled to ensure satisfactory straining is maintained. Retain and Final Inspection samples are collected.|
|14.||If the product is APAS approved it is held in quarantine while a sample if subjected to further testing in our Final Inspection Laboratory.|
|15.||When all tests are completed, and results recorded and checked, the Final Inspection Laboratory issues a release from quarantine to the warehouse.|
The normal production time for steps 1-15 is about four days.
|Agglomerate:||A clump of many small particles that are stuck together.|
|Alkyd resin:||A synthetic resin used in oil based paints. An alkyd resin is made by reacting a natural drying oil with a hard, synthetic material.|
|Biocide:||A chemical used in very small amounts to control the growth of bacteria and fungi in paint. Biocides are used to prevent spoilage of paint in the can and to prevent fungal attack of the dried paint film.|
|Coalescent:||A solvent used to soften emulsion resin particles so that they stick together properly when the water evaporates and the film forms.|
|Defoamer:||A specially formulated additive to break down foam bubbles and prevent the formation of bubbles during mixing and application.|
|Dispersant:||Most often a salt (e.g. sodium) of a poly-acrylic acid. Used to help break up agglomerates.|
|Organic pigment:||Pigments based on carbon chemistry are described as ‘organic’. In contrast pigments based on minerals (such as titanium dioxide and calcium carbonate in calcite) are described as inorganic. Examples of organic pigments are: Quinacridone (magenta), Diketo Pyrrole (red), Copper Phthalocyanine (blue and green), Arylamide (yellow), etc.|
|Polymerisation:||A chemical reaction where molecules grow larger and longer. The result is to produce a polymer that is tougher and harder than the starting point.|
|Surfactant:||A detergent or soap used to stabilise emulsions and dispersions of pigment. Surfactants help prevent particles sticking together.|