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Graphics With Pull

A look at magnetic-sheet material and its applications

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Magnets have evolved tremendously since my grade-school and junior-high science classes, when the teacher would wow the class by picking up iron filings. Fabricated into vulcanized rubber, flexible magnetic sheet has emerged as a viable source for short-term, removable, vehicle-graphic and promotional applications. Several magnetic-material companies offer background about how they fashion printable magnetic sheets, plus tips for ensuring that they last their projected lifetimes of up to two years.

Background

Akron-based tire and rubber-product manufacturing giant BF Goodrich developed the first magnetic materials in the early ’60s for use as refrigerator-door gaskets — the older "icebox" model fridges were potentially hazardous because small children could lock themselves inside.

Fabricating the sheets entails mixing magnetic powder, thermoplastic elastomers and binders with ferrite. The vast majority of sheet used for vehicle and promotional graphics contains polyethylene binders, which are more rigid than nitrile (a copolymer that withstands higher temperatures, but doesn’t resist oxidizing acids). The mixture is blended into a dough-like material, which endures high pressures as it progresses through large, stainless-steel cylinders pre-set to control thickness and temperature (naturally, each manufacturer’s formula, like a prize-winning chili recipe, is a closely guarded secret).

After passing quality-control checks, the material is married to a paper, vinyl or adhesive laminate. While paper backing is sufficient for indoor use, a vinyl or adhesive is required for a vehicle graphic. Each sheet batch is tested for tensile strength. A durometer measure the sheet’s hardness, and peel tests ensure laminate adherence. Further, sheet tests verify ample flexibility.

In addition to offering flexibility, magnetic sheet offers ample fabrication options; the material can be readily slit, die-cut, scored or punched. Available thicknesses range from 8 to 70 mils; 30-mil, vinyl-backed magnetic sheet has been the standard for vehicle graphics since their inception.

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However, emerging products will utilize thinner-grade materials. Manufacturer input Ralph and Gary Murphy founded Magnetic Specialties Inc. (MSI), Marietta, OH, in 1972. They devised magnetic, rubber-based material while working for BF Goodrich, and departed when that company halted further development. Magnetic Specialty

According to Jeff Stern, the company’s director of sales and marketing, screenprinting was the first graphics method applied to magnetic sheet, on white material, for vehicle-graphic applications. Eventually, ad-specialty companies demanded mutli- and full-color screening processes. Vinyl magnets remained the industry standard until UV laminates and coatings enhanced the performance of paper-backed magnetics. Flexographic printing emerged as an option as its quality improved in recent years, making runs of 25,000 magnetic sheets cost effective.

Offset printing capabilities allowed the printed laminate to be married to the magnetic sheet, which further eased the production of new, thinner magnetic that readily peels away from the laminate. Such applications have become popular for mailers and publication inserts. MSI introduced JetMag™, the first inkjet-printable, magnetic sheets, approximately six years ago. A photo-quality laminate converts the 8-mil magnet to a 12- to 14-mil substrate suitable for most desktop, dye-based printers.

First-generation inkjet magnetics were limited to approximately 8 1/2 x 11-in., paper stocks. Now, the widest material commonly used is 26 in. (24-in. printable space). Stern noted that existing 39-in. material is much weaker and more expensive. For larger applications, he suggests binding larger sheets together.

Ruth Wyckoff, director of marketing for Magnum Magnetics (Marietta, OH), said the company offers magnetic sheet with vinyl, paper, polyolefin and additional specialty materials, such as brushed-foil and luminescent. The company offers DigiMag® for inkjet printing, as well as materials suitable for lithographic, offset, hot-stamp, screenprinting and flexographic processes. Wyckoff noted that, although each process has its niche market, inkjet printing is quickly gaining overall acceptance. Magnum Magnetics

Greg Block, an account specialist for Magnet Sales and Manufacturing Inc. (Culver City, CA), said sheets for vehicle graphics and other outdoor applications typically measure 30 mils, whereas those used for indoor promotions generally measure 15 mil. The company has recently introduced sheets comprising Mylar™, die-plate and designer vinyls.

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For paper-stock materials, only dye-based inks work; other inks are too aggressive. When vinyls and other laminates are applied to magnetic sheet, UV- and pigment-based inks can be used. Mike Jouver, Flexmag’s (Marietta, OH) director of marketing, said magnetic-sign makers commonly don’t realize that only one side is magnetized; they’ll adhere a laminate to the wrong side of the material.

"Some mistakenly believe that it’s like a bar or horseshoe magnet, and that the only magnets are on the north and south poles," Jouver said. "The truth is, there are 12 magnetic poles in every square inch across the sheet." $image2

Further, if a user runs a magnetic sheet through a standard printer, which has steel rollers, the sheet will pull towards the rollers and not track properly through the machine. To counter this, the user may need to use unmagnetized sheet and activate the magnet after printing.

While the manufacturing process has remained relatively constant, printable-sheet enhancements have included longer rolls (up to 100 ft. for white materials), which allow longer runs and fewer chances for splicing, and customized binder systems, which allow magnetics to be more rigid or flexible than standard material.

Storing magnetic materials requires a climate-controlled environment not exceeding 110°F. Otherwise, the magnetism could weaken. A vehicle graphic’s surface must stay reasonably clean to prevent dirt from contaminating the magnet. Wth modern, porous clearcoats, moisture can readily accumulate behind the graphic. Also, avoid folding the sheet against itself; if the magnets come into direct contact with one another, significant magnetism is lost.

The printing perspective

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Will Curtis, public relations manager for Roland DGA Corporation (Irvine, CA), said that magnetic sheets pose unique challenges to printers. Specifically, the sheets can stick to printer beds or rollers. For instance, some machines can’t accommodate 30-mil material. Also, Curtis noted that magnetic material can’t be completely punched through without a backer sheet, because it will weaken the magnetic pull. Roland DGA

Dye- and pigment-based inks require topcoated materials. Yet, solvent-based, magnet-compatible inks may offer a wider range of acceptable substrates and better performance for outdoor graphics.

Companies Mentioned

Flexmag Industries
Marietta, OH
800-543-4226
www.arnoldmagnetics.com

Magnet Sales & Manufacturing
Culver City, CA
800-421-6692
www.magnetsales.com

Magnum Magnetics
Marietta, OH
800-258-0991
www.magnummagnetics.com

Magnetic Specialty Inc. (MSI)
Marietta, OH
800-848-6330
www.magspec.com
 

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