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  • Ren Gudino

Retroreflectivity & High Solvent Latex Inks

If you saw our latest YouTube video, you’ve gotten a speedy overview of the history of the cat’s eye (cataphote) glass beads and retroreflectivity. For the sake of summarization and not boring everyone, I tried to keep the info direct and moving along to the next topic. However, there’s quite a bit more info that I found fascinating but maybe wasn’t the most fitting for a video on sign printing.

When road signs were first put up, the need for reflective signs wasn’t as necessary. Not many people owned automobiles, and even if they did, their speeds weren’t high enough for signs to need to be read from a distance, whether it was dim lighting, raining, or in the dark. However, once speeds started to increase and automobiles became more commonplace, there was a clear need to standardize sign reflectivity. This occurred around 1920, when accessibility to automobiles increased, meaning more people were traveling. After this, metal or plywood signs replaced wooden signs, with the goal of decreasing fatalities by breaking on impact.

Small reflective domed beads, the cat’s eye, were placed along the sides of the road to indicate to drivers where the road was in case of fog, rain, or darkness. These same small glass domes were used within the lettering of road signs for their legibility. Light would hit the spherical glass and bounce off a small mirror on the back. The curve of glass and light reflecting across the mirrored surface are how retroreflectivity occurs.

To efficiently streamline the usage of retroreflectivity, 3M made a tape that mimicked the use of the glass beads so that sign production could run faster while increasing safety on roads by offering a more accessible alternative. This retroreflective tape led to the eventual creation of their “high intensity” retroreflective sheeting. 3M’s newest sheeting used the same concept of the glass beads but utilized “cube corner retroreflection”: reflecting light more efficiently by instead having the light bounce off of three flat surfaces (as though inside of a cube) and back to its source. Most road signs now utilize this type of sheeting.

Why does this matter? Since it’s a specialized material, not any printer can print directly onto it. We use the HP Latex 365 printer which uses “high-solvent latex ink.” Though this was mentioned in the video, there wasn’t time to elaborate on what that means and I actually spent time researching it because I never want to talk about something without understanding how it works. This is what led me down a rabbit hole of inks and this post is already getting way too long, so I’ll find a way to sum it up.

Basically, these signs are weatherproof and UV resistant even though this ink contains a very high water content. Outside of work, I have a little bit of a pen and marker obsession–addiction?--which includes a lot of personal interest in water-based and oil-based inks. Water-based ink is notorious for bleeding–it’s not the kind of ink that you’d want to use for note-taking if you’re going to use it with a highlighter because it’ll definitely smear. You can imagine that learning our printer ink has a high water content and that that’s a part of its durability made zero sense to me–that’s why I had to know how it works. The 65% water content is to suspend pigment and latex particles evenly throughout each ink drop, accompanied with a wetting agent so the ink doesn’t just sit on top of the sheeting but stays in place, and a humectant, which keeps moisture from leaving the mixture too early.

The printer doesn’t work just by laying down the ink. The drying process is a part of the printing process–and this is where that high water content makes more sense. Once the ink is laid onto the surface, radiant heat and forced air work together to evaporate the water. That means that the wetting agent has given the ink something to adhere to within the surface, and the humectant has kept the ink wet so that everything prints evenly before drying. The drying process dries out all of the water leaving JUST pigment and latex particles on the printed surface. I was mind-blown.

Even though it’s not required to laminate them, we still laminate every sign. It only ensures a much more durable weather and UV-ray-resistant surface, so why not? Laminating every sign also means that each print has completely gone through the drying process, otherwise, the ink would smear during lamination. A clean, laminated print from us means that the entire sign printing process was completed in the correct steps–which means the highest quality print produced.

I thought all of this information was fascinating and wanted to give a little more insight into the info that’s in this video here if you’ve missed it!

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