Does vinyl film have a shelf life?

Rolls of plastic

Yes, it does.

Polyvinyl chloride, or PVC, is the primary resin that makes up the vinyl sheeting used by the sign industry for computer-cut graphics as well as printed decals. The manufacture of vinyl sheet involves the blending of PVC resin with other ingredients, such as UV absorbers, heat stabilizers, pigments, fillers—and plasticizers.

Plasticizers are the reason for vinyl’s shelf life. Or rather, it is due to the phenomenom of “plasticizer migration.”

 

Plasticizers—What are they?

Plasticizers are generally clear liquid components that, when mixed with PVC, soften it, making it flexible, so that it can be formed, welded, etc.

There is an almost bewildering variety of vinyl films used in sign work—with a wide range of quality and cost. Some of the differences in the vinyls are due to the quality level of the raw materials used. The manufacturing process is also a factor. Less expensive vinyls are produced by an extrusion process called calendering, which uses heated rollers to process softened PVC into a thin film. Calendering lends itself to high production and lower manufacturing costs. More expensive vinyls are produced by casting, a process that starts with the PVC as a molten liquid which is then spread out or cast onto a moving web, a flat sheet that carries the layer of vinyl through a series of ovens that evaporate the solvents, leaving behind a thin dry film. Cast films are inherently more stable (they shrink less) and they are more durable. They retain color better and are more UV resistant longer.

The choice of plasticizers has an affect on quality, too. Cast vinyls, generally, are produced with higher grade plasticizers, allowing them to be more flexible and conformable. This allows for better performance over rivets, corrugations and complex curves. These plasticizers are also more stable, not as prone to migration. This is because their molecular weight is greater; the molecular chain is longer, more complex. It makes them more durable.

 

Plasticizer migration

A tech sheet from Arlon (April, 2014), a vinyl manufacturer since 1958, indicates that the reason for vinyl’s limited shelf life is usually contamination of the adhesive by the plasticizer in the PVC. As vinyl ages, the plasticizer “migrates” to the surfaces front and back, and eventually saturates the adhesive, gradually “deadening” it. Adverse storage conditions, such as a hot supplier warehouse, can accelerate plasticizer migration. Also, cheaper vinyls use cheaper plasticizers that are less stable. They transfer to the adhesive more easily. Other vinyls have plasticizers that are more resistant to migration. Adhesives vary, too. Some are more resistant to plasticizer contamination than others.

Not all plastics rely on plasticizers the way PVC does. Most manufactured plasticizers are, in fact, made for PVC products. Vinyl sheeting for sign work may contain as much as 20-25% plasticizer.
Plasticizer migration is a cause of concern in some industries that use PVC extensively. This is because the plasticizer, though necessary, can also become a contaminant.  Examples of areas of concern are the manufacture of PVC products made for food storage and packaging, medical equipment (tubing, bags, etc), and the plastic sheet used as liners in landfills and water treatment plants.

 

 

Acrylic plastic—How is it made?

Starbucks channels

 

Polymethyl methacrylate is a plastic containing one or more derivatives of acrylic acid.
We know it simply as acrylic.
It is sold under many trade names: Plexiglas, Lucite, Acrylite, Perspex, Acrilex and Crystallite.

There are two types of acrylic sheet commonly used by the sign industry—cast and extruded.

CAST ACRYLIC

Cast acrylic is made by injecting the ingredients into molds as a molten liquid, about the consistency of syrup, in one of two ways. The “cell cast” or “batch cell” method is made in sheets in a mold made of two plates of polished glass with gaskets at the edges. The liquid plastic fills the cavity between the two plates of glass and may be heated. Several plates may be stacked to produce multiple sheets of acrylic. After curing, the molds are disassembled and cleaned for reuse.

“Continuous cast,” is a higher production method. The molten mixture is cast between two continuous sheets of polished metal in much longer runs as it goes through a series of heaters for curing. Again, gaskets seal the edges.

Cast acrylic is polished and is known for optical clarity. It is harder than extruded acrylic and less prone to scratch. It is also more heat resistant, which is why cast acrylic cuts so much cleaner when machined, whereas extruded acrylic tends to melt behind a saw blade.

EXTRUDED ACRYLIC

Extruded acrylic is a less costly process and provides the larger share of acrylics used in the sign industry. It is manufactured by forcing the semi-molten acrylic mixture through forms and rollers.

Acrylite FF is an example of an extruded acrylic sheet. Acrylite GP is cast.

Airplane and helicopter canopies are made from cast acrylic because of its optical clarity.
Plastic sign faces are mostly extruded acrylics.