What are the proper procedures and various techniques used when painting on ACRYLITE® acrylic sheet products?

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What are the proper procedures and various techniques used when painting on ACRYLITE® acrylic sheet products?

Procedures

Be sure to follow the manufacturers’ safety recommendations for equipment and materials used with ACRYLITE® extruded (FF) acrylic sheet.

Fabrication Techniques

If you fabricate ACRYLITE® extruded (FF) sheet prior to painting, incorrect technique may cause heat build-up, resulting in crazing (numerous tiny cracks in the material) after painting.

Cleaning

Clean ACRYLITE® extruded (FF) acrylic sheet before painting to remove dust and assure paint adherence. Since acrylic sheet is sensitive to solvents such as aromatic hydrocarbons, concentrated alcohol, and ketones, use care in cleaning. Clean parts with a 25% solution of denatured alcohol and distilled water. However, for stains such as oil or grease, use a stronger cleaning agent such as hexane, aliphatic naphtha, or kerosene. Be sure the sheet is fully dry and clean before painting.

Static Neutralization

Before painting, it’s important to neutralize electric or static charges that accumulate on the sheet’s surface. Dust on the sheet causes paint agglomeration and uneven layers. Since tearing the masking off the sheet will create a static charge, all acrylic pieces should be treated.

One common way to do this is with an ionizing air gun. These guns safely and effectively neutralize electric charges. Alternate techniques, such as wiping the sheet with a damp, lint-free cloth or cleaning with a diluted alcohol-water solution, are also effective.

Avoid anti-static cleaners since they may leave a residue and cause paint adhesion problems.

Maskants

The protective paper masking is usually used as a protective layer for spray painting flat signs. However, many paint manufacturers also distribute liquid maskants, which are commonly used to spray paint designs onto ACRYLITE® extruded (FF) sheet. Maskant is supplied as a thick liquid consisting of water-soluble latex resins in solution. Because they are water solutions, maskants must be stored above 32°F to prevent freezing. Application is through the use of air or airless atomizing spray equipment – see the drawing on the first page of this brief.

Clogging may occur due to dried film mixed with the solution. To prevent this, obtain a special nozzle that reverses the flow of product and cleans out the build-up. These nozzles are available from the suppliers of painting equipment listed at the end of this brief. Spray the film on evenly to a wet thickness of 10-12 mils, which will dry to above 4-5 mils.

Maskant Drying

Drying time is usually about 2 hours, although it’s better to plan overnight drying to assure complete evaporation. Drying can be accelerated by using forced-air heating at 110°F – don’t go above this temperature as doing so might dry the surface and prevent evaporation of the water in the layers beneath.

Leave the dried film in place until you’re ready to paint to prevent dust accumulation on the plastic surface. Just before painting, score the design on the film using an X-Acto knife (available in art supply stores), giving it just enough pressure to cut the film without scratching the plastic. After painting, leave the film in place until the paint is thoroughly dry. Otherwise, you’ll get smeared paint and uneven edges.

Painting

Before painting, practice on a few test pieces to be sure that paint viscosity and air pressure are correct. Too high a delivery rate will result in too much paint and cause paint sag. It may also cause crazing due to too much solvent. Too low a delivery rate will result in “dry spray”, a matte surface caused by too much dusting.

As a rule, use the lowest pressure at which you obtain correct results. Hold the gun 12-14 inches from the workpiece – too close or too far will cause the above listed defects. Move the gun at an even pace and in a straight line. Its movement should never start or stop directly on the sheet surface.

Vary the direction of the spray, horizontally and vertically, to assure uniform coverage. Usually, four or five passes with several seconds between coats will provide sufficient paint. As mentioned, a light box behind the ACRYLITE® extruded (FF) sheet will help in judging the uniformity and intensity of color.

Screen Printing

Screen-printing is used for volume production. It is fast, and economical. For beginners, it is best to purchase a screen from a local screen supply house. After setup, apply paint with the squeegee in a uniform, even motion in one direction. It will pass through the open mesh on the screen, transferring the pattern onto the acrylic. The most important factors in the screening process are the paint’s viscosity and the size of the mesh openings. These will determine paint flow through the screen and the paint’s appearance on the acrylic.

Since many different fabrics are used for screening, and paint viscosity depends on the application and temperature conditions, it’s difficult to generalize what these conditions should be. Paint manufacturers give advice on thinning paint. Consult these companies should you need information.

Paint Removal

If you need to remove paint from the surface of ACRYLITE® extruded (FF) sheet, take it off immediately with the paint manufacturer’s recommended cleaner. Apply the remover using a rag; wipe off paint using a clean rag. Because paint removers contain organic solvents, minimize the time the remover is in contact with acrylic to reduce the chance of crazing.

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