Tikalon Blog by Dev Gualtieri

Silly Putty

August 6, 2014

There's a saying, " Build a better mousetrap, and the world will beat a path to your door." This saying is a mélange of two 19th century quotations by Ralph Waldo Emerson. The phrase is popular, since it's a paean to innovation. Inventors have heeded the call, since a search of the US Patent and Trademark Office yields 187 patents from 1790 to the present with "mouse trap" or "mousetrap" in their title. Ninety-two of these were granted from 1976 to the present.

Figures from US Patent No. 5528853, 'Magnetic computerized mouse trap,' by Donald W. Dufaux and George Spector, June 25, 1996.

Figures one and two from Donald W. Dufaux and George Spector, "Magnetic computerized mouse trap," US Patent No. 5,528,853, June 25, 1996. (Google Patents.)[1]

Not all innovations are patent-worthy, since it's important to look at the economics of practicing the invention. There's a considerable cost in prosecuting a patent application, the cost of maintenance fees, and the possible cost of defending the patent against infringers. In the mousetrap case, why would anyone want to buy your particularly effective mousetrap when they can buy a package of several conventional, spring traps for a dollar at many stores?

Some patented inventions make a lot of money. Chester Carlson's invention of xerography is one example.[2] I wrote about Carlson and his invention in a previous article (PARC Turns Forty, September 28, 2010). A more recent example is Pfizer's cholesterol-lowering drug, Lipitor. Lipitor's 1993 patent, which expired in 2011, resulted in more than $100 billion in revenue for Pfizer. The Lipitor patent is considered to have been the most lucrative patent.[3]

Most companies don't rely on just a single patent to protect their product line. They're constantly patenting improvements, or possible alternatives to what they manufacture. They sometimes license these in a package to other companies, such patent portfolios increasing the value of fundamental patents with added fortification against infringers.

About a decade ago, NTP, Inc. was able to extract a $612.5 million payment from Research in Motion (now, BlackBerry Limited, manufacturer of the BlackBerry) for infringing its patents on a wireless email system. The settlement came only after protracted litigation, which, as I mentioned earlier, is another cost center for patents.

As scientists will admit, failures in the laboratory sometimes turn into unexpected successes. This is often the case when a failed industrial process becomes a consumer product. One example of this was the early attempt by American scientist, Thomas Adams (1818-1905), to use chicle, the natural gum of Manilkara trees, as a replacement for rubber. Instead, he went on to invent chewing gum.

Sculpey is a popular polymer clay used for sculpting by Children and artists. It has the desirable property that it's soft, and easily worked, but it can be hardened in a low temperature oven. The Sculpey composition was originally intended as a thermal transfer compound, since it could be formulated to contain a high proportion of thermally conducting fillers. A composition similar to Sculpey contains the following:[4]

Polyvinylchloride, 5 - 95 weight-%
Phthalate-free softener, 5 - 30 weight-%
Stabiliser, 0 - 10 weight-%
Co-stabiliser, 0 - 10 weight-%
Fillers, 0 - 75 weight-%
Colorant, 0 - 5 weight-%
Other additives, 0 - 5 weight-%

Sculpey sculpture, "Butterfly on a Flower," created by my daughter when she was an elementary school student.

(Photo by the author.)

Play-Doh is another popular children's modeling compound originally manufactured for another purpose; namely, a wallpaper cleaner. The original formulation was wheat flour, water, salt, boric acid, and mineral oil. A modern composition is as follows:[5]

Sodium chloride, 3% to ~10%
Calcium chloride, ~3% to ~10%
Aluminum sulfate, ~0.5% to ~1.1%
10 molar borax decahydrate, ~0.35% to ~0.80%
Sodium benzoate, ~0.1% to ~0.5%
Wheat flour,~30% to ~38%
Waxy corn starch, ~3.5% to ~7.0%
Polyethylene glycol (PEG 1500) monostearate, ~0.4% to ~1.0%
Mineral oil, ~2.5% to ~4.0%
Vanilla fragrance, ~0.05% to ~0.25%
Water, balance (~45%)

In this composition, the amounts of aluminum sulfate and borax decahydrate are adjusted to give a pH in the range of about 3.5 to about 4.5. Now you know that the Play-Doh smell is vanilla. The composition can be pigmented.

Silly Putty is another example of a failed rubber substitute becoming a popular consumer play item. The Silly Putty trademark is owned by Crayola, but there are similar materials sold under different names. That's because the original research goes back to World War II, when the US was looking for alternative rubber materials.

The original starting composition was just polydimethylsiloxane, [C₂H₆OSi]_n, a silicone oil, reacted with boric acid.[6-7] The unusual mechanical characteristic of this material is that it can be slowly worked, like a clay, but it behaves as an elastic solid when the rate of applied force is large. This characteristic is a result of the viscoelasticity of the polydimethylsiloxane.

The structure of polydimethylsiloxane.

(Via Wikimedia Commons.)

According to Wikipedia, this is the composition of Silly Putty:

Dimethyl siloxane polymer, terminated with boric acid, 65%
Silica (crystalline quartz), 17%
Thixatrol ST (castor oil derivative), 9%
Polydimethylsiloxane, 4%
Decamethyl cyclopentasiloxane, 1%
Glycerine, 1%
Titanium dioxide, 1%

Over the years, inventors have developed improved compositions.[8] More than four thousand tons of Silly Putty have been sold since 1950.[9] The package size is 0.46 ounce (13 grams); so, doing the math, more than 278 million units have been sold.

Silly Putty

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