Manufacture of paints

Manufacture of paints

• 1.
  PAINTS oPaints are fluidmaterial that after applying over a surface forms a solid, cohesive, decorative and protective film. oIt is primarily used for decorative purposes but also as a protecting agent for the surface. oIts use has been investigated in ancient Egypt where artist would use paints for making paintings. oPaint has three main ingredients oPigment oBinder osolvent
• 2.
  Pigments (& Extenders) oPigments are solids which are responsible for giving color to the paint system. o Pigments are primarily opaque and provide opacity to paints while Extenders are practically transparent and does not impart color. o Pigments – organic and inorganic. o Most organics are manufactured, have brilliant color but their opacity varies very much. o Inorganic – natural and manufactured. o Natural inorganics are oxides and hydroxides of Iron. o Manufactured inorganics cover a wide range of colors including whites.
• 3.
  Table Representing concentrationof oxides of iron to obtain different colors
• 4.
  o Binders arethe continuous phase in which pigments are dispersed. o It is responsible for the mechanical and protective properties the paint has. o Can be dissolved in solvents or suspended to form emulsion. o Provides adhesion to the surface o Binders – organic and inorganic o Organics include resins containing fatty acids, polymers. o Inorganics include silica based materials like ethyl silicate, alkali silicates and quaternary ammonium silicates. o Convertible (thermoset binders) and non-convertible. BINDER
• 5.
  o Solvents areused to render the pigment-binder system. o It reduces the viscosity to ensure uniform coating o After application, it is no longer required and should vaporize quickly. o Majority of solvents are toxic or are harmful, which is a cause of concern. o Solvents chosen are organic in nature. o Plasticizers are taken in case of non-convertibles and are mostly oils. o Apart from these ingredients, additives might also be added to impart or improve one or more properties. SOLVENTS
• 6.
  POINTS TO KEEPIN MIND o Interaction of solvent with other ingredients is important. o It should provide appropriate rheological properties before and during application. o Solvent release after application is an important criteria o If solvent remains in paint film after application, it may cause internal tension and shrinkage. o Selection of binder – based on compatibility with solvents, type of drying etc.
• 7.
  Manufacturing of paints oStarts with paste grinding process – where pigments are broken down into fine particles. o This is then introduced in mixer where binder and solvents are added. o It is then sent to another tank where further materials are added to make it a finished product. o Quality checking and testing follows after. Color intensity, matching, viscosity, gloss etc. are being tested. o Paint is then filtered to remove any unwanted particles before being packed.
• 8.
  PASTE MAKING  Itis an important part. Milling machines are preferred for this.  High-Speed Disperser (HSD) – Tank jacketed for cooling, a motor & a shaft with blades bent at 900C.  Dispersion is near or at the surface of blades.  Operates at 915-1921.5 m min-1.  Low maintenance, low labor, easy to operate.  High power dissipation, needs easily dispersible pigments.  Latex, primers, plastisols, PU etc.
• 9.
  CONT…  Continuous MillingMachine – based upon shearing action.  Have high speed shafts with multiple discs.  Have high rates, easy to clean and large batch sizes.  Expensive to maintain, cannot grind tough pigments, requires premix tanks.  Primers, PU, lacquers etc.  Ball Mill – In use from earlier times. Has a steel cylinder and filled with 1/3 of it’s volume with steel balls which are responsible for the grinding action.  Up to 40% vol. should be of pigments, no solvent loss, low maintenance, easy handling.  Takes long time, discoloration from metal may occur, becomes difficult to clean.  Primers, alkyds, Polyesters, Acrylics, Lacquers.
• 10.
  DISPERSION/DISSOLVING  Roller Mills– One to five rollers can be used with three roll mill being preferable.  First roller is slowest, second rotates at moderate speed and third rotates fastest.  Hopper is above first roller.  Nip gap between first and second roller is small which further shears the pigments. The other nip gap ensures dispersion.  Provides finish, removes dust and other unwanted particles. Continuous process of pigment breaking and dispersion.  Very slow process; unsuitable if volatile solvents are used.
• 12.
   After paste-making,it’s dispersion into binder comes.  Kneaders are first choice because of the variety it can produce (highly viscous, putties, rubbery composition).  It can also be used for those systems which are difficult to wet.  Batch-wise or continuous operation.  Pug Mixers are also used.  Heavy-duty machines; provide high consistency.  Horizontal and vertical arrangements  Horizontal provides high consistency, while vertical is used primarily for heavy pastes & putties.
• 13.
  Vertical Pug MixerHorizontal Pug Mixer
• 14.
  FILTER SYSTEM  Beforefilling, cleanliness must be ensured of the end product.  Sieves – Mesh or gauges made from steel (or metals).  Paints are poured onto a vibrating screen. It vibrates either horizontally or vertically, allowing paint to pass through sieves.  Bag Filters – metal filter with closable and/or sealable covers.  Filter Cartridge – multiple cartridges are aligned on after other through which paint passes. Synthetic micro fibers are used as filter material (5-100 µm).
• 15.
  References • Outlines ofPaint Technology – W.M. Morgans • Paints, Coatings and Solvents – D. Stoye & W. Freitag. • Paint Technology Handbook – Rodger Talbert. • Wikipedia • Google (For pictures).