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The chemistry of painting cars and the recent development of water based paints

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The chemistry of painting cars and the recent development of water based paints Why paint cars? It is necessary to paint cars because the paint protects the steel of the car from corrosion, paint fills and smooths out any imperfections in the steel surface and it provides a durable, decorative, glossy appearance. If rusting continually takes place the car becomes unsafe. When water and oxygen come in contact with the metal of the car surface, several redox reactions happen. The oxygen is reduced to hydroxide ions and iron is oxidized to Fe2+ ions which pass into solution. More reactions happen which ultimately produce rust - Fe2O3H2O. The components of car paint There are three components of car paint, each one has different roles: * The pigment provides a barrier to protect car from atmosphere slowing the rate of corrosion. It disguises appearance of the steel car body, gives colour and other effects which enhance the appearance of the car. * The polymers in paint protect the metal from damage that may be caused by the paint sticking to the surface. ...read more.


an electrolysis cell is made (car body is cathode). The polymer then becomes electrically neutral and therefore insoluble in water. This means the car has better coverage of paint and is consequently protected, due to amine groups in the polymer. Aromatic ether units in the polymers mean the paint adheres to the steel surface better and therefore gives better protection against rusting. A greater mechanical flexibility is achieved by Three-Carbon aliphatic links. Hydroxyl groups allow cross-linking when the paint is heated, therefore improve the strength of the paint. The diagram below (Fig. 1) shows the structure of part of a polymer of an epoxy resin present in primers. Properties Of The Surfacer Layer Branched mixed polyesters have unreacted hydroxyl groups which help the surfacer stick to the primer and promote cross-linking during heating. This increases the strength of paint. The structure of one polymer often present in surfacers is shown in the diagram below - Fig. 2. CH2 __ OH l HO __ CH2 __ C __ CH2__ OH l CH2 __ OH Fig. ...read more.


* Higher Solid Products - These use existing equipment but unfortunately have poor flow properties, are sticky and not good in metallic colours. * Water Based Systems - Can use existing equipment but difficult to control flow in variable humidity conditions. Have high boiling points and enthalpy changes of evaporation, which prevents the paint thickening in the air between the gun and metal surface. Aquabase Aquabase began when it was realised that polymer particles could be dispersed in water in a similar way to oil and grease being dispersed by soap. This led to Alan Blackhouse realising that polymer particles surrounded by a special layer could make a water based paint. Further research and development created a paint which has many advantages over the original method of painting cars, as it can be applied in a range of humidities and requires less baking (consequently saving energy). The resulting paint has theseproperties:- * Does not release organic molecules. * Resistance to the clear coat on top. * Toughness. * Flexibility. * Durability (due to a high mr of the polymer). * Chemical resistance (from cross-linking). * Adhesive * Control of flow properties. ...read more.

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