Industrial & Specialty Printing - July/August 2012 - 25

0 N/INCH ABS Aluminum MDF Plate PC PE treated >38 mN/m PMMA PS Hard PVC SS

35.2 39.4 38.5 32.6 35.9 34.6 32.9 32.2 36.5
Figure 5 (Left) Twenty-four-hour peel adhesion, 180°, on various substrates Figure 6 (Right) Examples of adhesive thickness for white goods ickness achieved 115 m 160-165 m maximum U.S. ( reads/in. thread diameter in m) 25-260 20-300 Metric ( reads/cm thread diameter in m) 10-260 8-300

usual front panel standard, for technical applications, is 2 mil (50 m) of dry coating thickness. For special applications where greater thickness is required, it is possible to lay down maximum 6.4 mil (160-165 m) White goods (appliances) are one of the special applications often requiring a higher deposit (Figure 6). At the extreme end—maximum adhesive thickness— both the overlay and the housing are made of molded plastics. When the overlay and housing are assembled, small gaps are normal and inevitable. Thick adhesive is required to bridge the variances/gaps, and water-based PSAs t the speci cations. Membrane-switch manufacturers print PSAs to create pressure sensitive overlays, for identi cation and control of the underlying circuits. In the same manner, PSA is screen printed to the underside of the nished membrane switch, to facilitate positioning and bonding to the intended housing. Instrument panels are still a leading application for printable PSAs, primarily for the electronics and automotive industries. Optical display panels of polyester and polycarbonate, imprinted with graphic colors and transparent inks creating windows, text and dial, are nish printed with PSAs. These are then bonded to molded housings and ber optics made from PMMA, PS, ABS, PA, etc. Printable acrylic dispersions are the primary contenders because their high solids content enables very high

coating thicknesses. UV formulations are increasingly making inroads towards this application; however, the water-based acrylics have the aggressive tack, important for successful bonding of dif cult substrates, as well as the required heat and UV light resistance. Finally, it is appropriate to mention a few of the non-technical applications that represent a considerable portion of printable PSA use. A decal transfer is a special application historically made only with printable, solvent-based PSAs. Used for decorative purposes, or in the advertising business, only solvent-based rubber and acrylic resin formulations were used. Where transparency and UV resistance are required, acrylic resin printable PSAs are traditionally used. Today, however, a new UV-curable, printable PSA can also be used for permanent lm and reverse-print glass displays, as well as for wet and dry color-transfer applications. Except for the UV-resistance applications, solvent-based products are still often used for the sake of economy, though UV products are gaining in the market. Typical applications are: permanent advertising displays, ink transfers for bicycle and vehicle decoration, and labels and stickers for indoor and outdoor use. Plastic lm printed on both sides with PSA is used for short-term advertising in fast-food restaurants. When used in glass applications, the lm has to remain remov-

able without residue—best achieved with a cohesive and UV-resistant acrylic. Foam bonding of mouse pads, screen dot/line-shaped transfer-adhesive lm for photo albums, tacky document-security systems, and rub-off letters or designs for things such as scrap booking are popular applications as well. SUMMARY The advantages of printable PSAs are compelling. Like the electronic devices they hold together, the new generation of printable PSAs, whether UV curable or water based, provide easier processing, environmental advantages, simpli ed processing, and greater performance. They are capable of providing the strength and permanence for demanding appliance and automotive applications. These versatile adhesives save processing time and offer signi cant cost savings.

LISA KRUEGER CASTILLO
KIWO
Lisa Krueger Castillo is the product manager, industrial adhesives, KIWO (Kissel + Wolf). She has been involved in technical, marketing, and sales capacities in the screen-printing industry for two decades. Castillo holds a bachelor’s degree from California University of PA and a master’s degree from Clemson University. JULY/AUGUST 2012 | 25

Industrial & Specialty Printing - July/August 2012

Table of Contents for the Digital Edition of Industrial & Specialty Printing - July/August 2012