Should I use a solvent adhesive or acrylic? What’s the difference between a removable and a repositionable adhesive? When does a removable adhesive become permanent? If you’ve ever asked yourself one of these questions, You will find the answers here.
This time, we’ll talk about the adhesive compounds used in today’s graphic marking films and examine their strengths, weaknesses, and unique applications. Hopefully you’ll be better able to make choices that result in what I like to call “trouble free stickage”.
Adhesive options in our industry generally come in polar opposites; solvent or acrylic, permanent or removable, clear or pigmented. Which is better? It depends on the application. Most of these choices relate to specific fields like vehicle wraps, wall graphics, and long term outdoor signage. An adhesive that makes a vinyl perfect for wrapping a Ferrari might not work on a humble dirt bike. So what should you use and when? Let’s look at the options.
Solvent Vs. Acrylic Vinyl Adhesive
The first choice you generally have to make regarding adhesives is whether to use a vinyl with a solvent or an acrylic adhesive. This is usually a price issue.
Because it requires compounds that may be flammable and/or emit VOCs, the manufacturing of solvent based adhesives requires stringent controls. Therefore vinyls made with solvent adhesives tend to cost a little more. Acrylic adhesives are generally water-based and are therefore less expensive to manufacture. They’re used on economy or indoor films like LG Hi-Cal 4000 and ORACAL 631.
As with most things in life, you get what you pay for. There are important distinctions between the performance of acrylic and solvent adhesives on applied vinyl graphics. Ironically, the critical difference is in how the adhesives respond to the presence of water and solvents.
Vinyl Film with Acrylic Adhesive: Keep it Dry
Since acrylic adhesives are water-based, they’re naturally more susceptible to moisture and solvents. This affects them in two important aspects of application and durability.
- Application: Lots of sign guys and gals like to use application fluids like RapidTac or SureGlide when applying vinyl graphics. It lubricates the substrate so that you can slide the graphic into place as you apply it. Once it’s properly positioned, you must then squeegee the fluid from under the vinyl and remove the transfer tape. This process puts the application fluid in direct contact with the exposed adhesive of the vinyl. Acrylic adhesives tend to be weakened by this contact resulting in much lower tack. Therefore, it takes considerably longer for the adhesive to cure on the substrate slowing the application process.
- Durability: Once the graphic is installed, it’s exposed to the elements. A vinyl graphic with an acrylic adhesive doesn’t hold up as well “in the wild”. Excessive rain or humidity can weaken the water-based adhesive and shorten its outdoor life. Likewise, if you install a sign in an environment where it will be exposed to chemicals or solvents (even in gaseous forms) an economy vinyl may not reach the expected outdoor life of the face film, which is sure to disappoint your customer. If the environment is dry and solvent free, your graphic should last for the predicted life of the vinyl’s face film.
Speaking of exposure, excess moisture in your shop can be a problem as well. I asked Josh Culverhouse of ORACAL tech support about the possible affects of relative humidity on vinyl with acrylic adhesive. Josh responded “products with water-based adhesives will show signs of slight shrinkage on the liner more so than products with solvent adhesives. This would show signs of occurring when the material is not stored properly or in repeated fluctuations in humidity and temperature.” All vinyl should be stored in relative air humidity between 50% and 60% and temperature between + 64°F and 72°F should be ensured. For more tips on proper vinyl storage, please visit the ORACAL FAQ.
What’s this “Emulsion Adhesive” stuff?
By the way, some manufacturers use water-based adhesives under a different term. Because of the stigma against acrylic, you may see the term “emulsion” instead. Emulsion is simply another term for water-based. However, a vinyl with an emulsion adhesive is not necessarily an inferior product. Molly Waters, Technical Support Representative for Avery Graphics says, “I personally don’t lay a lot of importance on whether it’s solvent or emulsion.” She added that Avery’s MPI 2920, an intermediate vinyl for digital printing, uses an emulsion adhesive. But, it’s not designed for long term outdoor use. Avery UC900 cast vinyl, which is designed for long term outdoor signage uses only solvent adhesives. The key is using it in an application for which it’s suited. So when should you choose a vinyl with an acrylic or emulsion adhesive?
- Appropriate applications: Use vinyls with acrylic adhesives on indoor retail signage, interior décor (aka “wall words”) short term promotion signs, yard signs, political signs, and one-time-use event banners. If it’s going to be outdoors for more than four years, this is not the right product.
Vinyl Film with Solvent Adhesive: Tough and Durable
Solvent adhesives are made of sterner stuff. They’re not easily diluted by moisture and not as easily affected by industrial solvents. This results in vinyl films that can be used in wet applications without drastically affecting cure time. It’s still not good to overdo it though. A light mist should suffice.
Once installed, a vinyl sign on a solvent adhesive laughs at rain and humidity and shrugs off occasional exposure to industrial solvents and VOCs. Making a vinyl film with a solvent adhesive changes it from wimp to warrior in terms of outdoor durability. As noted above, it costs a little more, but for long term outdoor signage, it’s definitely worth it.
- Appropriate applications: Vinyl films with solvent adhesives can be used for all of the above plus long term commercial storefront signage, custom vehicle graphics and wraps, fleet marking, real estate signs, industrial safety signs & labels, traffic and municipal signage, and more.
Vinyl Film: Permanent vs. Removable
Most adhesive backed plotter films are designed for medium to long term outdoor use, so even the acrylic adhesives are generally permanent. But some, like ORACAL 631 and MACtac 8900, have a removable adhesive. It’s a low tack compound designed to come off with relative ease. The ease of removablilty is determined in its resistance to pull force, which is measured in pounds per inch.
- How removable is it? For example, let’s compare ORACAL 631 and 641, both of which have acrylic adhesives. One is rated as removable, the other permanent. ORACAL 631 has an adhesive strength rating of only 1.6 lbs/in2, while ORACAL 641 has a rating of 3.7 lbs/in2. In other words, ORACAL’s permanent acrylic adhesive has 131% more sticking strength than its removable version. Please note that all of these measurements are taken 24 hours after application (typically tested on aluminum or stainless steel which are ideal substrates). The longer a “removable adhesive” vinyl is left in place, the stronger the bond becomes. Eventually, it’s just as hard to remove as a film with a “permanent” adhesive. In other words, all removable adhesives eventually become permanent. Generally after three years, the difference is negligible.
- Residue: Speaking of removal, the other aspect of what constitutes a removable film is adhesive residue. Anyone who’s ever had to replace an old vinyl graphic knows that getting the vinyl off is only half the job. Once the face film is pulled, chipped, or ground off, the adhesive residue must be dealt with. That’s why part of the definition of removability should mean no adhesive residue. Avery Graphics typically defines their removable adhesive vinyls as being able to be removed up to two years later with less than 20% residue.
- Appropriate applications: Plotter or digitally printable vinyls with removable adhesives are generally used for temporary indoor graphics (think trade shows and exhibitions), interior décor, outdoor transit graphics (bus shelters, construction barriers, bus and cab signs) and of course vehicle wraps. Generally speaking, any graphic that’s expected to be replaced within two years should be created on a film with a removable adhesive. Anything expected to be left in place longer than three years calls for a vinyl with a permanent adhesive.
What about Repositionable Vinyl Film?
Changes in technology bring changes in terminology. “Google” used was an obscure mathematical term. As new uses are found for plotter films and printable vinyl, the terms used to define them have also changed. Five years ago, the term “repositionable” referred to a high quality, permanent adhesive such as the one used on ORACAL 651 and LG Hi-Cal 6000. In this context, “repositionable” meant that the film was easy to use in a dry application. These pressure sensitive adhesives allow you to place and reposition the graphic on the substrate as long as you don’t press it. When you hit it with the squeegee, the pressure activates the adhesive. It “wets out” and begins to bond. Once it bonds, it’s considered permanent or well on its way.
These days repositionable means being able to move the entire graphic after it’s been applied; something no one in the sign business even thought about just a few years ago. So unique “wall vinyls” like Avery 2601, ORAJET 3268, and PrismJET WallTEX have a very low tack adhesive that allows you to easily lift the vinyl graphic from one substrate and move it to another without leaving residue and without destroying the ability to move and reapply it again…and again…and again. Ain’t progress grand?
Six of one is not always a half dozen of the other. A removable adhesive is not necessarily repositionable. ORACAL 631 and Avery 2601 are both made to be stuck on walls and removed cleanly. But 631 is not designed to be removed and repositioned. Likewise, ORAJET 3628 is a removable wall vinyl, but it’s not repositionable, while ORAJET 3268 is both removable and repositionable. Admittedly, some of the difference is caused by the face film’s mil spec rather than adhesive characteristics, but it’s important to know the difference. Currently, there are no repositionable plotter films on the market. So if you’re marketing wall words made with ORACAL 631 or MACtac 8900, don’t oversell them as repositionable.
Hopefully, that’s enough to give you a good basic guide for choosing between acrylic or solvent, removable or permanent and removable or repositionable adhesives. Next time, we’ll talk about clear vs. pigmented adhesives and about some of the new developments in high tacks specialty films.