(Editor’s Note: In the March issue of ST, Jim discussed the integral components that comprise cast and calendered materials, plus the advantages and shortcomings of each.)
Film manufacturers often force signmakers to determine a vinyl’s suitability for a particular application, and then hold them responsible for problems. However, you might not have a lab outfitted with up-to-date testing equipment.
Several criteria arise when making your material selection. Always study the manufacturer’s product data sheets and other technical information. Generally, cast vinyl is referred to as high-performance, and calendered vinyl is known as intermediate material.
But, buyers must beware and take what some manufacturers publish about their products with a grain of salt. Some manufacturers play name games. For example, a "high-performance" label doesn’t necessarily mean the film is cast vinyl.
Shop and compare
When conducting your tests, research the following:
Vinyl manufacturers perform cutting and weeding tests to evaluate their own and competitors’ products. Cut letters of various sizes, such as 1/4, 1 or 2 in. Some manufacturers cut the entire alphabet, whereas others cut letters only in the top row of keyboard keys.
Conduct your cutting and weeding tests side by side for easier vinyl comparison. You’ll find that the facestock’s brittleness or softness may impact cutting. Further, colors in a vinyl series may cut differently than others. Facestock’s caliper variations can also complicate cutting. Often, cast vinyl cuts more easily than calendered, because it’s thinner and provides better caliper control during manufacturing.
When testing a vinyl, pay attention to its weedability. To a large extent, a film’s release characteristics determine how well it weeds. Release values, which many vinyl manufacturers publish, measure the force required to remove a release liner from a pressure-sensitive material, including vinyls.
Without standardized industry procedures, test results from one lab to another would vary widely and have little meaning. Vinyl manufacturers conduct their tests according to accepted industry standards, such as those created by the Pressure Sensitive Tape Council (PSTC) and the Tag & Label Manufacturers Institute (TLMI).
Remember that release values can gradually grow. This happens because time and environmental conditions can wear on the liner and facestock, requiring more force to separate them.
To gauge this, testers commonly use a TLMI test instrument. Using this implement, the facestock of a 2 x 10-in. material sample is attached to the sled of a release tester, while the sample’s liner attaches to the tester’s stationary arm. As the sled travels its track at 25 ft. per min., the test equipment measures (in grams) the force required to peel and separate the sample’s two parts.
The tester may calculate a release value of 100gm per 2-in. width after coating. One week later, the reading could measure 140gm. In a few months, the value may grow to 160gm.
When evaluating vinyl, make sure the liner paper lies reasonably flat; excessive edge curling makes handling more difficult. High release values — such as those in the 200- to 500-gram range — indicate poor graphic transfer from the liner, making application difficult. Low release values, such as 60-70 grams, can indicate poor film stability on the liner, which causes problems for screenprinting, die-cutting and plotter-cutting applications.
If you’re working in a humid environment, such as Florida or Houston, you’ll want to note how flat the liner stays. As it gains or loses moisture, liner paper can expand or contract. Vinyl manufacturers measure these changes and the paper’s moisture content. Liner growth can cause curling, which makes plotter cutting difficult.
Test, don’t guess
To assess a vinyl’s durability, vinyl manufacturers will perform a variety of tests, including outdoor weathering at perhaps a Florida or Arizona test site, as well as simulated weathering tests in a weatherometer, such as a UV tester — for instance, an accelerated-weathering tester from Q-Lab Corp. (Cleveland) — or a xenon test chamber.
A UV tester exposes vinyl to fluorescent UV rays. Although UV light represents only 5% of the sun’s rays, it causes the most damage. This type of testing measures worst-case environmental scenarios, and spectrophotometers gauge color weathering after 500, 1,000 and 2,000 hours of exposure under such intense conditions.
Xenon test chambers expose samples to both infrared and UV light using a filtered, xenon arclight. Although more accurate than UV testing, this method is considerably more expensive.
The results obtained with test equipment often don’t correlate with real-time outdoor exposure. A sample can fail in a QUV tester and pass in the real world, and vice versa.
Very few sign companies and screenprinters can afford expensive weathering equipment, but that’s OK. Nothing beats the time-tested method of exposing a sample to the elements. Mother Nature can tell you more about how a vinyl performs than costly equipment. A friend in Minnesota conducts his own weathering tests by applying vinyl samples to banners he hangs outside his shop.
Still, test equipment is useful as a pass/fail exam to screen new vinyl formulations. Weathering tests measure gloss and color loss visually, as well as tangibly, with a gloss meter. These tests compare weathered samples against a control sample.
Technicians also look for water spots, chalking, dirt retention and corrosion between the adhesive and substrate (and the film, if it’s either a reflective or metallic specialty vinyl). In evaluating a vinyl film’s dimensional stability, the technician will cut an "X" in the center of the sample and measure the shrinkage from the cut line.
Manufacturers often test new material against "aged" vinyl that’s been baked in an oven for a specified period, such as seven days at 120