Printing Coroplast Signage

If you're producing signage (to announce a political campaign, or even to direct the members of your nonprofit organization to their tables for a summer picnic), consider Coroplast rather than cardboard.

I recently encouraged a client of mine to choose this product for her signs because it's easily printable, light, durable, weather resistant, and inexpensive.

If you can imagine a piece of cardboard with paper fluting between two parallel flat sheets, you've got the idea of Coroplast. But instead of paper, Coroplast is made of plastic.

You would most likely choose one of two options for printing your signage on Coroplast: inkjet and screen printing. Why not offset lithography? For the same reason you wouldn't run a sheet of corrugated board through an offset press. The intense pressure of the rollers would crush the fluting between the top and bottom plastic layers.

If you have a longer press run for your signs, it may be worth the preparation cost for screen printing. There's considerably more set-up work to be done for screen printing than for inkjet printing, so you would need to distribute this cost over a number of Coroplast signs to make it worthwhile. For instance, if you're printing four signs, as my client is doing, you'd want to select inkjet printing rather than screen printing. On the other hand, if you're printing 500 signs, you would choose screen printing. Ask your printer where the cut off would be to make one technology or the other more cost-effective in your particular case.

To be cost-effective, keep in mind that screen printing would usually be best for single-color or two-color signs. Your printer would use a different screen for each color of ink, and preparation would still get expensive, even on longer runs, if you were to opt for four or five ink colors. Nevertheless, such an option is possible, and I have even seen outstanding halftone work done with screen printing using four color imagery. The printer just uses slightly coarser screen frequencies in the halftones due to the thicker screen printing ink. He can still print four colors, setting the halftone screens at angles to one another to produce the printed effect of full color just as he would do with process color on an offset press.

If you choose inkjet printing for a shorter press run, you will have the option of full-color imagery. This is because inkjet printing is a four-color printing process that uses CMYK inks. Something to keep in mind, however, is that you will therefore need to build process color equivalents of any match colors you might want to use. For instance, my client uses a PMS match blue in her corporate printing work (PMS 2995). Her four Coroplast signs will have the name of her organization printed in blue on a field of white. On her offset printing work, my client would use the PMS color as a single match ink, but for the inkjet printed signs, she will need to build the nearest equivalent color to the blue using CMYK inks, and this may be slightly inaccurate. Keep this in mind for your own design work.

Consider using a Pantone Bridge to avoid an unwelcome surprise due to a variation between the PMS color you're trying to match and the actual PMS ink. This swatch book lists all the Pantone inks along with a color image of each ink. Side by side with each match color, the Pantone Bridge includes the closest process color build (including a color swatch and the percentage components of cyan, magenta, yellow, and black ink). If your process color build will not exactly match the PMS ink, you'll see this immediately in a Pantone Bridge swatch book, and you can make your design decisions accordingly.

Finally, how do you inkjet print Coroplast? Since Coroplast is a rigid material (not bendable), you would use a large-format (or grand-format) inkjet printer with a flat bed. Early versions of inkjet presses for the most part printed on rolls of printing media (such as paper, film, or vinyl), but many of the newer inkjet presses have support tables that attach to the printing equipment and allow flat substrates to be guided under the inkjet heads. Conceivably, you could print directly on a window or door this way, depending on the thickness of the printing surface.

Avoid Communicating Paper Weights and Coatings by Telephone

A print brokering client of mine is producing a swatch book similar to the PMS book I just mentioned. It will include swatches of various colors that go well together to create a particular look. You've probably seen similar books in paint stores, intended to showcase brands of paint and give consumers an idea of which colors to use together when painting their houses.

My client described the thickness of the cards used in the color deck, but since she was almost halfway across the country from me, it was difficult for us to communicate accurately. Describing the thickness of the paper was problematic, and describing the coating used to protect the paper color swatches was also difficult.

To bridge the communication gap, we got creative. I asked if her samples were thicker than a business card. I noted that some business cards are much thicker than others, but that a lot of business cards are printed on an 80# uncoated cover stock.

Then we both looked at our Pantone Color Bridge books, and I asked about the thickness of the covers. She noted that the covers and text pages in her color swatch book should be of the same thickness and not as thick as the covers of the Pantone Color Bridge.

This was particularly useful information. My client wanted the covers and text to be the same thickness. I was still unsure of the weight of the paper, but I knew it should be thinner than 18 pt. cover and thicker than 100# text.

Then I asked if the paper she was holding was about the thickness of a paperback book cover. She said yes. I translated this into 10 pt. cover stock (used in many book covers). We settled on 12 pt. cover stock with UV coating or film laminate on both sides to make the pages about 13 pt. in thickness. I then asked her to send me a sample page, but I went ahead and contacted the printer and gave him the specifications to see what the overall price would be.

When the sample page arrived yesterday, I took out my caliper and saw that the actual thickness was 13.5 pt. (my initial guess had been close). However, I saw that the coating had only been applied to one side of the press sheet. Moreover, the colored pages were curling a bit. So I surmised that the coating was a film laminate (rather than a layflat laminate or a UV coating, both of which would have behaved differently). I knew the paper was curling due to moisture's having entered the sheet from the uncoated side.

Now I have enough information to send the printer an updated spec sheet.

What You Can Learn from this Case Study

Here are two things to learn from what just happened to me:

1. Always ask for printed samples. If you're designing something for a department in your office, ask for samples your in-house client likes (both paper and design). Nothing facilitates communication like a physical product both you and your client can look at and touch.

2. If you can't wait, ask your client to compare the paper to common items you both have: an index card, a business card, a paperback book cover. This will at least get you in the ballpark while you await the actual physical sample.

[Steven Waxman is a printing consultant. He teaches corporations how to save money buying printing, brokers printing services, and teaches prepress techniques. Steven has been in the printing industry for thirty-three years working as a writer, editor, print buyer, photographer, graphic designer, art director, and production manager.]