MP-4 Rejuvenates A Century-Old Technology…Metal Particulate Tape - Technology Information

Computer Technology Review,  May, 2001  by Christine Chudnow

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Tape media terms can be confusing. I was researching MP-4 for this article (not the music tape, but metal particulate tape's development path) and left a message with a well-known tape media company's PR department. I soon received a snippy reply that they don't make MP-4 music tapes and wouldn't necessarily talk to me about their development if they did.

Well, fine.

I wrote back to describe that of course I meant metal particulate tape, which in fact forms the backbone of their own tape media products, and perhaps they should be aware of that? However, I really cannot blame the PR department, as most of the comments from experts about MP-4 came with the warning that if they told me, they'd have to kill me. But I did get them to confirm that yes, MP-4 is the next stage in development for metal particulate tape. And I'm not dead yet.

MP technology has been around a long time (how does 100 years sound to you?) and has proved reliable against other coating properties. For the last 30 years, data storage manufacturers have known that thin metallic high coercivity films on flexible substrates produce excellent performance in high frequency recording. They adopted it for their own needs in order to increase the areal density of their digital tape media.

Metal particulate (MP) in this case refers to microscopic magnetic particles incorporated in a polymeric binder that form the magnetic layer on a magnetic tape. This surface is in turn coated onto a flexible substrate. An analogy of the coating layer is Jell-O: remember all those potlucks where a Jell-O dish featured fruit suspended in green gelatin? The green color aside, this is quite similar to the magnetic layer, where the metal particles are grapes and pineapples and the binder is the quivering stuff.

MP media is manufactured by double-coating a thick nonmagnetic underlayer and an extremely thin magnetic outerlayer, resulting in a thin and smooth recording layer which is covered with tiny magnetic metal particles. The binder material consists of organic polymers of various types, and must also include additives to reduce sedimentation and clumping. Manufacturers also add solvents to help deposition, and lubricating materials to assure long tape life.

Substrates for tape or flexible media are typically polyester. These materials are classified into PET (polyethylene terephthalate), PEN (polyethylene naphthalate), and PA (polyamid). PET is primarily used in low performance particulate tapes, PEN is used in several advanced MP and ME products. PA is at the high end and quite expensive, but as the particulate tapes move towards greater areal density, even mid to low range MP media may move in PA's direction, especially if the material becomes more economical.

The Competition

Metal Evaporated (ME) and Advanced Metal Evaporated (AME) are important competing technologies to MP AME sports a film of metallic recording material deposited by an evaporative process. This allows an extremely thin coating, good for high density recording. Sony's AIT, Exabyte's Mammoth, and Ecrix's VXA all use AME formulations for their media.

Which is better, ME or MP? That depends on who you're talking to as well as the tape's intended use. Trust me, Sony and Quantum will give you entirely different answers. That is not so surprising, like most technology manufacturers they'll report test results largely on their products' best qualities.

It is true that AME's sensitive material must be separated from the read heads by a nonmagnetic carbon layer. The resulting phenomenon, called spacing-loss, reduces the signal strength available to the read/write head. On the other hand, the AME media recording layer contains a 90-100% magnetic cobalt material while MP uses 45% magnetic material (made of pure iron) mixed with a binder and other additives The highly metallic surface of AME media allows higher recording densities with 50% lower tape tension than MP. This highly metallic surface allows a high recording density and improved signalto-noise ratio while still employing a lower tape tension than some MP tapes.

Later versions of MP have narrowed this performance gap by incorporating a mixture of organic acid and lubricants with the binder formulation. Unlike ME tape's separate layer of liquid lubricant, MP's lubricant blooms to the surface as the tape is used, thus minimizing friction.

Both technologies are perfectly acceptable under normal usage. Under the terms of catastrophic failure and extreme environmental problems, test results differ. Peter Brothers, president of data recovery firm Specs Bros., reports that he has not witnessed a statistically significant difference in the percentage of catastrophic failure of compromised ME as opposed to MP tapes. However, catastrophic failure in ME tapes seems to be more extensive than failure in MP tapes. This may be due to the fact that since the protective coating in MP tapes is applied to individual recording matter rather than to the entire tape surface, failure of the coating may be isolated.