Most coated surfaces encounter the same inevitable problems - imperfections, scratches, nicks and other damage from production and assembly, all of which can cause customer dissatisfaction. What is the best way to handle these issues?
Scrapping the part means losing the material and labor spent making the part. Recoating means extra labor, time and materials. The fastest and most cost-effective way to cover hook marks, faraday cage issues, scratches and other blemishes is to use touch-up paint. Touching up the part allows you to save on materials and labor, and touch-up paint can cost as little as pennies per use. However, using the right supplier and application method, ensuring an exact match to the original coating, and perfecting the required skills are crucial to optimizing the final results.
Select a Supplier and Application MethodThe first step is finding a reliable a touch-up paint supplier. Once you have selected a supplier you are comfortable with, you should then determine your application needs. Touch-up paint should be quick and easy to apply. Your supplier should be able to help guide you to the correct application method, depending on the surface and type of blemish you are trying to fix.
The most common application methods include aerosols, brush-in-cap bottles and paint pens. Aerosols are capable of applying a high-quality paint film that can most closely match the OEM coating, but masking is required to keep the touch-up paint off the rest of the part. Brush-in-cap bottles offer portability but are better suited for smaller nicks and dents. Paint pens are portable and provide a great way to cover scratches, but they apply a very thin film.
One additional way of applying touch-up is with bulk containers, such as pints and quarts. These can be used with an air brush or cup gun and can offer a great quality film, but the area needs a lot of masking and preparation.
Ensure an Exact MatchAfter the application type for touch-up has been decided, what does your touch-up provider need from you? The only thing worse than a blemish on a product is a blemish covered by touch-up paint that doesn’t match the original coating. To ensure an exact match, you should provide the supplier with a color standard that is an exact representation of the color and gloss you need. This standard should be considered the master standard. You should always have at least two master standards - one to keep, and the other to send to the touch-up provider. This way you can be assured that both standards match.
A master standard is usually prepared by the manufacturer of the original coating. Another option is to use a batch standard or a piece of your coated product as the master standard. However, this isn’t always the best way to match color, as it only represents the color of one batch of your original coating. Since batches are required to match the standard within certain tolerances, a batch standard may not represent the color at the center of that tolerance. Approximately half of all color match problems occur when the original coatings change in color.
An additional way to provide color and gloss information is with a spectrophotometer (or colorimeter) and glossmeter reading. In most cases, these instruments are the last resort for information because of the variation in measurement that exists from one color measurement instrument to another. This way of providing information prevents visual evaluation of the color match since no physical standard is available. Quality touch-up providers prefer to evaluate color matches both visually and instrumentally.
Another important point is the type of light in which your product is typically viewed by the consumer. The touch-up vendor you choose should evaluate the color match under all three principle light sources - daylight, fluorescent and incandescent. These three light sources have been standardized by the International Commission on Illumination. The visual evaluation of the color match under these light sources is carried out in a light booth. The color most likely will look different and match differently in one light source compared to another. The touch-up supplier should optimize the color of the touch-up to match best in the primary light source.
Perfect Your Touch-Up SkillsAfter you have finalized the application method, sent in a standard for matching and decided on a light source, you are ready to order your paint. But is the touch-up task as simple as just spraying an aerosol can or applying paint from the pen? Applying touch-up, even paint that exactly matches your original coating, is a skill that requires practice. Experimentation with different steps, methods and tools will ensure the best results.
If you are unsure about how the touch-up should be applied, it is always best to test it on a scrap part or in an inconspicuous area first to determine whether the results will be acceptable. The following tips will help you achieve a blemish-free coating.
Preparation:Clean the surface that needs to be repaired. The most effective technique will depend on what is being cleaned. A water-based hard-surface cleaner such as glass cleaner is good for removing loose surface soil. For oily residue, use a solvent wipe with a weak solvent, such as mineral spirits, that won’t hurt the original finish. Test it on a scrap part first. The cleaner shouldn’t leave a residue that could interfere with the adhesion of the touch-up.
To remove rust or other undissolvable contaminates, 200- to 600-grit sandpaper can be used. Sand an area slightly bigger than the blemish so that the touch-up can be blended into the original finish. If the area being touched up is bare metal, priming the metal will result in better adhesion.
When using aerosols or spray guns, mask any areas where touch-up is undesired. Masking tape or paper/plastic sheeting is typically used. Aluminum foil also offers an impermeable barrier that can be pressed into place.
Application: If using an aerosol, always shake the can for at least one minute after the mixing ball begins to rattle. The color and gloss might not match if you do not shake the can properly. Always hold the can upright 10 to 12 in. from the surface. Consider applying several light coats instead of one heavy coat. Apply just enough paint to achieve a wet, glossy, continuous film. Wait for the paint to set up and then apply another coat until the desired amount of hiding is obtained.
Aerosols or spray guns often have a wider spray pattern than desired to do touch-up. One solution to this problem is to cut a 1/4 to 1 in. hole in a stiff paper card and hold the card between the spray tip and part surface to restrict the amount of spray that reaches the surface. You will still get the fine mist that a wide spray produces while limiting the area covered. Make sure to wear the appropriate personal protective equipment, such as respirators and eye protection.
If using a brush-in-cap bottle, always shake the bottle for one minute after the mixing ball rattles. Dip the brush into the bottle as far as it will go. Slowly remove the brush. (Some bottles have an opening with a built-in brush wiper to help wipe excess paint from the brush.) Brush the paint on the surface with smooth strokes. Avoid retouching the wet film with the brush after it is applied.
Paint pens usually have a spring-loaded tip that actuates the valve. To use the pen for the first time, remove the cap and prime the tip with paint by pressing it a few times against an inconspicuous flat surface. However, keep in mind that pressing the tip continuously may result in too much paint being dispensed. The tip should only be pressed when additional paint is required to cover the repair area.
Most touch-up is formulated to dry quickly and is sensitive to high heat and humidity. For the best results, make sure to use the touch-up at room temperature in conditions with less than 50% relative humidity.
Metallic Colors: When applying metallic colors, you are actually applying tiny flakes of metal in the coating. These flakes reflect light. The more light they reflect, the brighter the coatings appear. When metallic touch-up is applied too heavily, the flakes are buried under the paint, and the finish seems dark. When it is not applied heavily enough, the flakes lie on top of the paint and reflect too much light. By varying your application technique, you can achieve the color you want. There is no substitute for experience when applying a metallic color.
A Cost-Effective SolutionTouch-up paint, when chosen and used correctly, is one of the fastest and most cost-effective solutions to blemishes in coatings. Following a successful touch-up strategy will help to ensure that you can easily fix even seemingly impossible nicks, scratches or faraday cage issues.
Raabe Co.’s website is at www.raabeco.com.