Introduction to Acrylics

Acrylic sheet has been on the market for more than 75 years, ever since Rohm & Haas introduced it as Plexiglas® in 1936.  Yet, as commonplace as acrylic is, its chemistry has evolved. Sheet manufacturers typically modify the Poly Methyl Methacrylate (PMMA) with additives to change the performance properties of the plastic. Today, a wide range of acrylic products are available to sign makers, most of which are modifications of the original formula.  

Acrylic History. The development of acrylic spans nearly one hundred years, before the product was  commercial. This plastic product owes its creation to the pioneering work of German scientists. Here is the timeline of the developmental process:

·         1843. Chemists first created acrylic acid.

·    1865. Scientists created methacrylic acid, which is the monomer building   block for the acrylic polymer.  

·        1877. German chemists, Fittig and Paul, were credited with the development of the polymerization process, in which methanol is combined with methacrylic acid to form PMMA.

·         1928. The German company, Rohm and Haas, developed acrylic  fiber.

·         1936. Rohm and Haas introduces the Plexiglas® brand to the market.

As the world prepared for war, new applications were discovered.  As an alternative to glass, acrylic was used for the canopies of fighter aircraft and the bubble turrets of bombers.  While pure acrylic can be brittle, it provides much better shatter resistance than glass. In fact, the impact strength of acrylic is at least five times greater than that of glass.   It also possesses good optical clarity, nearly as good as glass, and is non-yellowing.

Today, popular brand names, such as Lucite® and Plexiglas®, are household words. Because it is nearly water clear, resists chemicals and provides exceptional outdoor durability, acrylic is ideal for many sign applications, such as internally illuminated signs and P.O.P displays.   Compared to polycarbonate and flexible-signface material, it’s also an economical alternative for sign faces.

Manufacturing Acrylic. In the sign industry, leading manufacturers of acrylic sheet include the Arkema Group, CYRO Industries and Plaskolite.  The family of acrylic sheet products is divided into three major categories: “cell cast”, extruded,  and “continuous cast”.  Each manufacturing process is unique.  And the finished products produced in each process results in distinctive characteristics.  

Cell Cast. Cell cast is manufactured between two sheets of tempered glass.  Along the perimeter of the glass a gasket separates the two pieces of glass, acting as a spacer.  The thickness of the gasket determines the thickness of the sheet.  A syrupy acrylic resin is poured into the mold.  To control the heat, which the acrylic syrup generates, the mold is immersed in water. 

As the resin cools, it transforms from a liquid state into a solid sheet.  After being removed from the mold, the sheet undergoes a post cure process, as the acrylic monomers continue to polymerize.  During this post cure phase the cast acrylic sheet can shrink significantly, as much as 20%.  The shrinkage, however, occurs in the thickness of the sheet.

The casting process produces acrylic sheet with the best optical clarity, compared to extruded and continuous cast sheet. The plastic itself is also harder and more scratch resistant.  The cell cast method is a very traditional way to make acrylic, but it is also a very costly process.  Variations in gauge are common.  Nevertheless, for custom thickness, custom finishes and custom colors along with the highest quality materials, cell cast sheet has no equal. 

Extrusion. In the extrusion process, the manufacturer receives resin in the form of tiny plastic pellets. In the extruder barrel, the pellets are heated, after which they form a molten mass.  This molten mass of plastic is forced through a thin slot die. The hot extruded mass is then fed between metal rollers which squeeze the plastic down to its finished thickness. The distance between the rollers and the opening gap of the die determines sheet gauge. 

An advantage of this process is that extrusion maintains much tighter tolerances of sheet thickness than in the casting process.  More importantly, this is a high speed production process, making it a very cost-effective way to manufacture acrylic sheet.   A disadvantage of extruded sheet is that, because it is pressed between the metal rollers, it induces some mechanical stress, which can result in shrinkage in machine direction. 

Continuous Cast.  Another form of mass producing acrylic sheet is the continuous cast method. In this process, the polymerized acrylic syrup is poured between two polished metal belts. Much of what is used in the sign industry is continuous cast acrylic.  To control the gauge of the sheet, gaskets along the edge of the web separate the metal belts. To regulate the curing of the resin the belts pass through a series of heating and cooling chambers.

The continuous cast process produces sheet exhibiting very good optical clarity, consistent gauge, and minimal shrinkage during thermoforming. 

Both extrusion and the continuous cast processes are very economical production methods compared to cell cast acrylic.  In the continuous cast process the raw materials costs are lower for the resin syrup versus the pellets used in extrusion.  The equipment cost of the extrusion equipment, however, is significantly lower than the investment required for continuous cast equipment. As a result, extrusion is the more common production equipment used.

Conclusion. Each acrylic sheet manufacturer makes a variety of products, designed to satisfy particular application requirements. Some additives, such as butyl acrylate, increase impact resistance.  Other additives, such as methacrylic acid, increase glass transition temperature for high temperature applications.

The addition of plasticizers, on the other hand, can lower the glass transition temperature, which can make acrylic easier to bend and thermoform, as well as improving the sheet’s impact resistance.

Some modifications have made acrylic products, many of are stronger to resist breakage. Other acrylic products are more heat resistant and can withstand the high temperatures of illuminated sign cabinets. Still other acrylics form at lower temperatures, when   thermoforming sign faces.

While these chemical modifications have greatly improved the performance characteristics of acrylic, different chemistries may not be compatible with the other materials that you are using in production. For this reason, as a sign maker or printer, you are ultimately responsible for understanding the raw materials used for a particular application and determining their suitability.

Regardless of how you chose to fabricate or decorate acrylic sheet, the important rules are basically the same:

1.    Read and heed the manufacturers’ technical bulletins. If you have questions, don’t hesitate to call your distributor for additional information or call the manufacturer directly for advice.

2.    Test, don’t guess. Test your raw materials for compatibility before going into a production run. When you find a combination that works, stick with it.

3.    To control your results in production, control your shop environment.

4.  Proper surface preparation prevents printing, painting and vinyl application problems.

5.    Document your results. That way, you hopefully won’t repeat any mistakes of the past, when you run a repeat order. What’s more you can reproduce those repeat orders with consistency and control. That way, you will keep your customers happy, so they keep coming back.

NEW INSTRUCTIONAL VIDEOS.  Five new videos have been added to RTape’s  YouTube channel. The following is a description of the new videos:

Squeegee Technique. Nothing is more basic in vinyl application than the squeegee. But some squeegees work better than others. And there are right ways and wrong ways to use this simple tool. This video clip reviews squeegee selection, squeegee care and squeegee technique. Click here to view the Squeegee Technique video.

Wet Applications. Dry applications are typically recommended for most vinyl applications. For those exceptions to the rule, this instructional video explains the right way to perform a wet application. Click here to view the Wet Applications video.

Introducing AT65. Installing multiple color overlays with a paper application tape is not much easier than driving in the dark without your headlights. For these challenging applications, RTape developed its AT65, the universal high tack film. This video clip explains the features and benefits of this remarkable new film application tape. Click here to view the Introducing AT65 video.

Application of Window Graphics. Installing vinyl graphics on glass can be challenging, because the adhesive aggressively grabs onto this high energy surface. Repositioning graphics on window is generally difficult, if not impossible. This instructional video explains how to dry apply window graphics right the first time. It also describes the necessary steps required for surface preparation. Click here to view the Application of Window Graphics video.

Transferring Frosted Window Graphics Films.  Because frosted window films are highly textured, transferring cut vinyl graphics can be problematic. This video provides direction in selection of the right application tape and how to apply these films quickly, easily and without problems. Click here to view the Transferring Frosted Window Graphics Films video.

About Jim Hingst: After fourteen years as Business Development Manager at RTape, Jim Hingst retired. He was involved in many facets of the company’s business, including marketing, sales, product development and technical service.

Hingst began his career 42 years ago in the graphic arts field creating and producing advertising and promotional materials for a large test equipment manufacturer.  Working for offset printers, large format screen printers, vinyl film manufacturers, and application tape companies, his experience included estimating, production planning, purchasing and production art, as well as sales and marketing. In his capacity as a salesman, Hingst was recognized with numerous sales achievement awards.

Drawing on his experience in production and as graphics installation subcontractor, Hingst provided the industry with practical advice, publishing more than 150 articles for  publications, such as  Signs Canada, SignCraft,  Signs of the Times, Screen Printing, Sign and Digital Graphics and  Sign Builder Illustrated. He also posted more than 325 stories on his blog (hingstssignpost.blogspot.com). In 2007 Hingst’s book, Vinyl Sign Techniques, was published.

© 2015 Jim Hingst