acrylics and polycarbonates

Acrylics and Polycarbonates

Plastics

Remember this scene from the 1967 Dustin Hoffman classic movie “The Graduate”?

Mr. McGuire: I just want to say one word to you. Just one word.
Ben: Yes, sir.
Mr. McGuire: Are you listening?
Ben: Yes, I am.
Mr. McGuire: Plastics.
Ben: Exactly how do you mean?
Mr. McGuire: There’s a great future in plastics. Think about it. Will you think about it?
Ben: Yes, I will.
Mr. McGuire: ‘Nuff said. That’s a deal.

McGuire had one thing right. Forty-two years have passed since that memorable bit of advice was offered, and there’s still a great future when it comes to making signs with plastics—all sorts of plastics. The problem is there are so many kinds of plastics that keeping them straight can be a chore in itself.

There is a unique type of plastic formulated for just about any purpose you can think of, and laboratories develop new ones every day. Calling them all “plastics” may be convenient in offering career advice to a young college graduate, but the word plastic doesn’t communicate much about UV resistance, impact strength, clarity, weight, dyne levels, compatibility with other materials, fabrication methods, decoration options—and any number of other properties materials need to be suitable for a sign project. And that doesn’t even take into account the many types of signs placed in diverse environs: P.O.P., backlit, channel letters, dimensional letters…

McGuire must have known how complicated it could get, which might be why he cut short his bit of advice to Ben with, “’Nuff said.”

REINING IT IN
Adding confusion to the mix is how plastics are named. Word roots, prefixes and suffixes like “ethyl,” “meth,” “acry,” “poly,” “oxy,” “plas,” “phen,” “ate,” “ite,” “hyde,” “tone,” “ether” and many other terms with exact chemical definitions are perfectly logical to any chemist but wreak havoc on the lay person’s practical understanding of which plastic is good for what. (The same problem contributes to the inefficiency of recycling programs, but that’s another story.)

Plastics used in sign making include vinyls, urethanes, polyesters, polystyrenes, polyethylenes, acrylics and polycarbonates—to name just a very few. Still, one need not be over intimidated by a few hundred-dollar words. 
Let’s rein it in a bit and take a look at two similar but not interchangeable plastics that are often used in sign making: acrylics and polycarbonates. It may be useful to understand how they are similar and different.

PROPERTIES
What we call acrylic is formally known as polymethyl methacrylate or PMMA. With a name like polymethyl methacrylate, it’s easy to see why even chemists might want to use the simpler acrylic, which comes from the acrylate portion of the word. Polycarbonates are called polycarbonates, but both materials are more frequently called–albeit often mistakenly—by some of the better known brand names.

Both acrylics and polycarbonates are thermoplastic polymers, which means they can be re-heated and re-shaped, as opposed to thermosettingpolymers, which cure to a hard material and remain so even as new heat is applied. Being thermoplastic, both are suitable materials for thermoforming processes. Acrylics generally soften at lower temperatures than polycarbonates.

Both polycarbonates and acrylics transmit light efficiently and are used to make specialty lenses, including polycarbonate eyeglass lenses and acrylic contact lenses. These optical properties also make them both excellent materials for backlit sign faces and lenses for LED lamps.

Physically, the density of PMMA is just under 1,200 kg/m3; the density of PC is just over 1,200 kg/m3. Essentially, this means either material is about half as heavy as an equally sized piece of glass. Acrylics and polycarbonates will scratch easier than glass but, to an acceptable level, can be buffed out.

Compared to glass, acrylic is much more impact resistant, but not nearly as much so as polycarbonate. Polycarbonates are stronger than acrylics but also more expensive.

But these all are general characteristics and in no way a comprehensive summation of the properties of either material. Actually, such a summation would be difficult, if not impossible, as the nature of plastics manufacturing includes constant new formulations and redevelopment to suit specific needs and meet the demands of other constantly changing technologies. For example, within just one manufacturer’s acrylic product offerings may be cast, extruded or co-extruded, all of which affect properties such as hardness, melt temperature, impact resistance, etc. Some of those same manufacturers offer polycarbonate product lines, as well.

A SHORT HISTORY
The first acrylic was discovered in 1877, and the first acrylic product, Plexiglas, was sold in the 1930s. The first polycarbonates, GE’s Lexan and Bayer’s Makrolon, discovered within weeks of each other, were brought to market in the early 1950s. Since then, a series of modifications have been added to the original formulas, resulting in a wide variety of specialized products with even more unique names.

There also have been some modifications regarding which corporation owns which brand. For example, in 2007, Saudi Basic Industries Corporation acquired GE’s plastics division. The division now is called SABIC Innovative Plastics, headquartered in Pittsfield, Mass.

Röhm & Haas, the company that originally introduced the Plexiglas brand, sold its Plexiglas division in 1998 to the Arkema Group. The American company DuPont and the British company ICI combined to form Lucite International. In 2007, Plaskolite purchased Lucite International’s Mississippi and Monterrey, Mexico facilities, and, in 2007, Evonik Industries acquired Degussa (CYRO). Dow Chemical now owns Röhm & Haas.
In other words, there have been changes.

OPTIMIZED
The result of this dynamic progression is a parade of new products, optimized for specific purposes in a wide range of industrial, commercial and household settings. For example, Bayer has optimized its Makrolon LD polycarbonate sheet product with a proprietary diffuser to eliminate hot spots from LEDs when used for channel letter faces; in a similar way, Plaskolite’s Optix LD light-diffusing acrylic sheet is optimized to allow maximum light transmission with minimum hot spots. There are many other examples relating to color matching, impact resistance and other properties for specialty applications that demonstrate the versatility of both materials. So, just as all plastics are not the same, on another level, all acrylics and all polycarbonates are not the same, either.

FABRICATION NOTES
Polycarbonates and acrylics can be fabricated economically and efficiently for various signage applications, using the tools found in many sign shops, including mills, saws, drills, thermal forming equipment, CNC routers, engravers and laser engravers. Polycarbonates and acrylics are available in a range of sizes and thicknesses, making them suitable not only for sign faces but also individual cut letters and other graphic and architectural elements.

Extruded acrylics and polycarbonates in the 3/16-inch thickness range are most suitable for vacuum-formed sign faces and are sometimes pre-decorated. The decision of which material to use is determined mostly by how strong it needs to be. As one wholesale thermoforming provider told me, “If you really don’t want it broken, use polycarbonate.”

Both materials fall in the “seven” category on the Society of the Plastics Industry’s recycling chart, which means they are considered more permanent materials that are better suited for re-use than recycling and usually are accepted in most municipal recycling programs. There are, however, specialty companies that collect clean pre-sorted fabrication scraps.

In the end, the material choice for any given project will be determined by a number of factors, including but not limited to appearance, performance, durability, cost and availability. If it’s acrylic or polycarbonate, there are plenty of knowledgeable resources online and among the many distributors supplying the sign industry.