The objective in applying a paint coating is to provide a film which will give Protection and decoration to surface being painted . The success of any paint Application will be governed by a number of parameters, including:
- Film thickness applied
- Mon the method of application
- Condition during application
There are discussed below;
The importance of surface preparation to the success of a paint system can not Be overemphasized. A separate section on surface preparation has been include In this manual.
An adequate film thickness is essential for the success of any coating system. Under application will generally result in premature failure for obvious reason. However , the old age of “the more paint, the better “ can be equally dangerous The gross over application of modern high technology paint coatings can lead Either to solvent entrapment and subsequent loss of adhesion, or to splitting Of primer coats. With the majority of coatings, the limits of acceptable dry film Thickness allow for reasonable practical variation, but the correct thickness Should always be the target during application.
The actual dry film thickness recommended for a particular surface will depend On the type of paint system being used and the nature of the surface . Recommended dry film thickness for individual products given on the Production Data Sheet and System Specification Sheets .
Methods of application :
The accepted methods applying the protective coating described in this manual Are by brush, roller, conventional spray and airless spray . The advantages of Each method are briefly discussed below:
Brush application :
Brush application is relatively slow, but is generally used for decorative paints And for coating small areas . It is particularly suitable for coating complex areas It is particularly suitable for coating complex areas where the use of spray Methods would lead to considerable losses due to over spray and associated dry Spray problems.
However, most high build coatings are designed for application by airless spray, And high film build will generally not be achieved by brush application. In General, twice as may coats will have to be applied by brush to achieve a similar Build when compared to airless spray.
Roller application :
Roller application is faster than brush on large, even surface and can be used For the application of most decorative paints .
However, control of film thickness is not easily achieved. As with brush, high Film build will generally not be attained. Care must be taken to choose the Correct roller pile length, depending on the type of paint and degree of Roughness of the surface.
Conventional Spray :
This is a widely accepted, rapid method of paint application in which paint is Atomized by a low pressure air stream . Conventional spray equipment is Relatively simple and inexpensive, but it is essential to use the correct Combination of air volume, air pressure and fluid flow to give good atomisation and a paint film free from defects. If conventional spray application is not controlled correctly, large losses of paint can result from overspray and rebound from the surface, in addition to problems such as poor flow, sagging and pinholing. The major disadvantage of conventional spray is that high build coatings can generally not be applied by this method, as most paints have to be thinned to a suitable viscosity for satisfactory atomization, and so lose their high build properties.
Airless spray :
Unlike conventional spray, air is not mixed with the paint to form a spray, Hence the name airless spray . Atomization is achieved by forcing the Paint through specially designed nozzles or tips, by hydraulic pressure. The required hydraulic pressure is usually generated by an air powered Pump having a high ratio of fluid pressure to air input pressure. Pumps With ratios between 20:1 and 60:1 are available, perhaps the most common Being around 45:1
The chief advantages of airless spray are:
- High build coating can be applied without thinning.
- Very rapid application possible, giving an economic advantage.
- Compared to conventional spray , over spray and bounced-back reduce,
Leading to reduce losses of material and lessening dust and fume hazards.
The tips, through which the paint is forced to achieve atomization , are precisely constructed from tungsten carbide. The atomized “fan” of paint by the fluid pressure reqired to give atomization coupled with the orifice size needed to give the correct fluid delivery rate. The fluid delivery Rate controls the film thickness applied.
Different slot angles produce spray fans of different widths. The selection of a particular fan width depends on the shape and size of the structure to be painted. Choice of fan width is also related to orifice size-for the same orifice size, but paint applied per unit area will be less, the wider the spray fan.
Generally tips with an orifice size 0.009” -0.013” are suitable for coating to be applied at approximaterly 50 micros(2mils) wet film thickness. Tip sizes from 0.013”-0.019” for wet films of 100-200 micros(4-8)mills and 0.019”-0.013” for 200 micros (8mils) and above. Heavy-duty mastics, which are applied at very high film thickness , may need tips with orifices as largely as 0.040”to0.060”. spray data given in our data sheets are indicative subject to final adjustment depending on pump pressure, tips sizes, thickness of coating and type of the coating, etc.
There are several designs of tips available, the choice of which depends upon the finished , the ease of application and ease of cleaning blockages from tips.
When some products, the decorative effect achieved with airless spray is not as
good as can be achieved by conventional spray application is now widely accepted
as a convenient method of applying high performance and decorative coatings.