The Basic Materials of Masking
by Kevin Harman
Harman Corp. Rochester Mich
Masking, a critical component of many inorganic and organic finishing operations, is aterm covering a variety of materials, products, and applications.Masking includes use of protective caps to cover raised areas and/or the grounding area around studsand holes during painting, powder coating, electro-coating, electroplating, anodizing, and many more finishing operations.The materials and products of masking also include plugs used, as their name implies, to plugthreaded and nonthreaded holes, the groundingarea around such holes, tube and pipe ends, andother depressed areas during powder coating, electrocoating, painting, anodizing, and sandblasting.In addition the materials and products of mask-ing comprise a wide variety of pull tabs, tapes, disks,masking squares, cords, sheets, tubing, and lipmasks designed to meet the specific needs of almostany manufacturer. (See Fig. 1.) There is a widevariety of materials and processes on the markettoday used to mold the masks in literally thousandsof shapes, sizes, styles, and colors.The ideal mask for each application depends uponthe type of finishing process; the temperature,fumes, and chemicals inherent in the process; theimportance of achieving sharp and distinct line separation; the need for excellent sealing capability; theease of fitting and removing the mask; the ability tomask an irregular shape; the desire to reuse themask; the mask’s durability and resistance to flame,aging, and cracking; and many more factors The qualifications of the mask maker obviouslyhave an important role in matching mask, material,and application. When comparing mask manufacturers look into the cost of tooling (for example, adip-molded mask will usually incur tooling costsbelow l/o those for an injection-molded part). Compare the mask maker’s experience, flexibility, abilityto provide a custom shape if needed, and ability toprovide quick turnaround.
FEATURES OF WIDELY USED MASKING MATERIALS
Although the selection of masking is an exactingprocess, it becomes easier by gaining a basic understanding of the most widely used materials, theirability to withstand high temperatures, and the fin-Figure 1. Masking supplies come in a variety of shapes, sizes,and colors.ishing processes for which they are best suited.Among the leading materials are the following.
Standard Vinyl -PVC
Standard or regular polyvinyl chloride (PVC) mate-rial contains a plasticizer for enhanced softness andwithstands temperature maximums up to 35O”F/ 177°C on an intermittent basis. Standard vinyl isrecommended for caps and plugs in masking applications such as painting (air dry, as well as bakingup to 350”F), electroplating, electroless nickel plating, anodizing, hard anodizing, chrome plating, beadblasting, and chemical milling
High-Temperature Vinyl -PVC
This material is specially formulated with heat stabilizers, enabling it to withstand intermittent temperatures up to 45O”F/232”C. Normally used for capsand plugs that function as paint masks, the materialalso is appropriate for caps and plugs in electrocoating applications. Caps and plugs of this material arerecommended for one-time use because the hightemperatures tend to withdraw the plasticizer fromthe vinyl, causing the cap or plug to harden.
Neoprene [50” (+5”) durometer Shore Al
Caps and plugs of this synthetic rubber polymer areresistant to temperatures up to 225”F/107”C for continued usage and up to 35O”F/177”C for one hour orless. Neoprene masking is appropriate for finishingoperations such as painting, electrocoating, electro-plating, electroless nickel plating, lower-temperature (375”F/19O”C!) plating, hard anodizing, beadblasting, and chemical milling. Neoprene is not to beused for chrome plating
Silicone Rubber [55” (25”) durometerShore Al
Caps and plugs of high-strength silicone rubber arethe ultimate high-temperature mask. Silicone is resistant to temperatures up to 600”F/315”C for intermittent use and up to 5OO”F/26O”C for normal use forone hour or less. The soft material enables caps tostretch to fit over unusual sizes. Paint will not adhere to the caps, making them reusable as paintmasks. Silicone resists hardening, cracking, andbleeding. The material is recommended for highertemperature powder coating applications and is alsoapplicable for painting/baking, electrocoating, electroplating, electroless nickel plating, anodizing,hard anodizing, chrome plating, and chemical milling
Polyester (2-mil film with 1.5-mil siliconeadhesive system)
This thin film with silicone adhesive is widely usedin tape and disk forms as masks in powder coating,plating, anodizing, coating, bead blasting, andchemical milling. These masks withstand temperatures up to 425”F/218”C and also are resistant tofumes and chemicals. Tapes and disks of this material leave sharp and distinct line separation, and thetapes are easily removed without leaving residue
Kapton Thin Film
Tapes, disks, and die-cuts of Kapton with silicone adhesive are known for their ability to withstand temperatures up to 5OO”F/26O”C continuously, making them popular masks for powder coating. The silicone adhesive system leaves sharp and distinctline separation without leaving residue.
NEW TECHNOLOGY
New technology and new applications continue tomake masking a viable manufacturing component inthe 21st century.Dip MoldingDip molding, one of the leading mask-making processes, is an example. Its origins are as old as candlemaking, but computer technology and evolving manufacturing processes have provided the masking accuracy, reliability, and turnaround required in today’s finishing operations.Films Capture Contaminants in CuringOvensAnother example is the new generation of heat activated films for the curing ovens of metal coaters,powder coaters, and platers. Until recently, dust andairborne particles that marred painted or powdercoated surfaces usually resulted in a temporary shutdown of the contaminated oven. Now, finishers canuse thermal cast films to remove dust and otherparticles from ovens that remain in operation. Thefilm softens and becomes sticky at 250”F, capturingdust and airborne contaminants that pass over itssurface.
SUMMARY
Tomorrow will bring new masking materials, products, and applications. The finishing industry willbecome increasingly sophisticated, and the trend ofbuying from masking sources that provide the bestcombination of quality, delivery, technological expertise, tooling support, customization capability,price, and customer service will continue.
BIOGRAPHY
Kevin Harman is Vice President, Sales for HarmanCorp., a Rochester, Michigan-based manufacturer ofmolded products for protective and decorativeapplications.
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