#4 from R&D Innovator Volume 1, Number 2          September 1992

Inventing a Tape that Breathes
by Frank Copeland, Ph.D.

Dr. Copeland is Quality Manager, Medical Devices Division, 3M Health Care.

The problem had been around as long as people have been binding wounds with adhesive tape.  The adhesive blocked perspiration, and its chemical constituents often irritated the area surrounding the wound.  The result?  The tape often caused a new wound.

Back in 1955, a gastroenterologist, Dr. Theodore Golden, suggested that 3M produce a tape with a non-irritating acrylate medical adhesive he'd been using.  At the time, 3M was a tiny presence in medical products.  But Dr. Golden stressed the value of a breathable tape for people who had to wear a sac after a colostomy--and for other long-term uses. 

Adhesive tape did seem a natural extension of our specialties, adhesives and tapes, but there was one reality standing in the way--the company was determined to exit the medical device market.  3M had entered the market with surgical drapes in 1948, but it had continually lost money.  In spite of earlier directives to steer clear of the area, I was assigned to look at the possibility of developing a superior medical tape that used acrylate adhesive. 

I had a personal interest in the area as well:  after knee surgery in high school, the adhesive tape had attacked my skin.  There were days when the tape caused more pain than the surgery itself.

Because cloth-backed adhesive tape was already on the market, and because cloth would be too expensive, we opted for the new, non-woven technology.  The fibers in non-woven materials are held together with a chemical binder rather than the traditional over-under weave.  3M had created and used one of the first non-woven materials for ribbons.  Today, non-wovens are used in scouring pads, packaging materials, surgical drapes and dust masks, to name a few products.

So the problem came down to this: how to make a breathable tape, with acrylate adhesive, on a non-woven backing?  As I narrowed my search for a solution, I took advantage of 3M's policy requiring a free flow of ideas and inventions throughout the corporation.   I talked with people in our ribbon-making business and spread the adhesive using a patterned coating technique they'd used for decorating ribbons.  Although this increased breatheability somewhat, the four or five of us in the group I led realized we'd need to make the adhesive even stronger to compensate for the large voids that allowed the moisture to travel. 

For months, we tested many ideas in the laboratory.  We tried applying liquid adhesive through perforated metal drums, we tried spraying a "spider-web" pattern through nozzles--anything to prevent the adhesive from plugging up every little hole in the non-woven backing.

Surprising Value from Baseline Data

But nothing worked well enough to give us a product that would overwhelm the market, so I suspended my experiments and began gathering baseline data on the actual porosity of the various acrylate adhesives I had been using.  Maybe they were more porous than we assumed, and would need less improvement than we figured.

To test for moisture vapor transmission, I wanted to measure a layer of adhesive without backing.  But it was too easy to fracture or tear the unsupported adhesive, so I finally decided to put adhesive first on a temporary backing, then press that against another backing.

After several attempts using this approach, I saw exactly what I had searched for with all those other fancy but feckless techniques--millions of microscopic holes formed as the adhesive finished drying on the tape.  And these holes allowed moisture to migrate freely, meaning that the tape could be left in place for long periods without irritating the skin.

So in the course of that tangential search for baseline data, we stumbled on the right process.  But I might have missed the fact that the two-step application worked had I not been focusing so much time and energy on the porosity problem.  At any rate, we quickly dropped the other approaches and concentrated on the two-step application.

By manipulating time, temperature, and air flow in the process, we could control how much solvent remained in the adhesive when it was pressed onto the backing.  This, it turned out, was a critical factor, because it's the evaporation of solvent and resultant shrinkage of the adhesive on the backing that opens those microscopic pores.  And it's those pores that allow you to blow smoke right through Micropore® brand tape.

Varying the types and quantities of adhesives and the types and amounts of materials in the backing allowed us to create more than 300 different variations.  With help from our customers, we finally chose a formulation for marketing.  Unfortunately, we had to discard one formulation because it smelled too much like a martini!

We applied for a patent and started marketing the tape in 1960, about four years after I'd started my efforts.  Since that time, 3M has made enough Micropore tape to reach the moon and back 15 times.  3M Health Care, which had Micropore as its first "super-product," now includes several divisions, with combined sales of more than $2 billion annually.  And it's 3M's fastest-growing business.

What Did I Learn?

Obviously, luck was on our side, because a testing process turned out to solve our problem.   But chance, as usual, favored a prepared mind.  Had I not spent more than a year focusing on porosity, I might not have recognized the value of what I'd done.  This taught me again the importance of immersing myself in a project, of not making it just one goal among many.  To put it another way, if you direct people to work 5 percent on something, you're essentially telling them to ignore it.

Another lesson is to keep in motion.  When you run into an absolute roadblock, try something completely different. Work on a related project, or go back to the basics and start over.

We also needed a bit of accounting legerdemain to finance the project.  On the books, we were improving Scotch brand transparent tape, not working on a medical product (the medical business, remember, was on the point of being phased out as unprofitable).  But my effort was sanctioned under a 3M policy that asks technical employees to devote 15 percent of their time and money to projects of their own choosing.  (After several months of this "bootleg" work, my supervisors decided to establish the project as a "legal" one.)

Thus I must give credit to 3M's corporate research policy.  Not only did we have convenient access to expertise throughout the organization, but there was also an expectation that we'd be innovating, not resting on our laurels.  As employees at 3M put it, "Don't ask permission--ask forgiveness."