Mottling and what to do about it

Learn what mottling is, what causes it and how to make mottling on vinyl films magically disappear.

By Jim Hingst

Have you ever occasionally noticed a dull, hazy or blotchy appearance on the surface of some vinyl films or overlaminates? This is a condition called mottling.  There’s no reason to get too excited. While this hazy appearance certainly detracts from the aesthetic appeal of your graphics, mottling can easily be remedied, which I will explain all in due time.

Mottling is a dull, hazy or blotchy appearance on the surface of some vinyl films or overlaminates.

Now that you know what you are looking at when you see it, let me explain why mottling occurs. Vinyl films contain plasticizers, which make them soft and pliable. Expensive cast vinyls are especially malleable. The plasticizers that make films soft, also make them very impressionable. So much so that when vinyl films and overlaminates are rolled up on a roll, the films can pick the impression of backside of the release liner.  The impression that is made on the vinyl film is mottling. 

Because vinyls are very impressionable, vinyl manufacturers, such as 3M, Arlon or Avery Dennision, take special care in how they rewind their films.  Rewind pressures should neither too tight, nor too loose.  If a film is wound too tightly, the added pressure squeezes the first surface of the vinyl against the underside of the release liner, exacerbating mottling.  On the other hand, if rewind pressure is too loose, the outer surface of the vinyl film can rub against  the liner, dulling its surface.

Heat and humidity can contribute to the mottling problem.  That’s why more mottling occurs in the summertime.  Here’s what happens.  Most of the pressure-sensitive vinyl films and vinyl overlaminates are manufactured with paper liners.  Paper is a natural material, comprised of plant fibers, which can absorb moisture like a sponge.  When liners absorb moisture they swell and grow, especially at the ends of rolls, which are exposed to outside air.  This is why mottling  sometimes appears running the length on the outside edges of roll, while the inside of the roll of film remains nice and shiny. Heat can also soften the vinyl allowing it to take an impression more easily.

In many cases, vinyl films can leave the manufacturer in perfect condition, either to develop mottling inside the baking heat of an over-the-road trailer, or after it is stored in the heat of a warehouse.  To prevent rolls of film from developing this condition after you receive the material, store the film in a cool part of your shop, away from direct sunlight standing on end to prevent pressure from the weight of the roll creating a flat spot or mottle line.

Not to be confused with mottling, some cold glue overlaminates can exhibit a similar blotchy, “orange peel” pattern.  The difference is that the unappealing appearance is in the adhesive and not in the film.  This similar condition occurs most often with overlaminates manufactured with a paper release liner. 

The “orange peel” effect, which is especially noticeable over the dark colors of a print, results from the adhesive picking up the mirror image of the rough, paper surface of the liner. To correct this defect, manufacturers have made improvements to the smoothness of the release liner. They also have improved the adhesive systems so that after the product is applied, the adhesive will flow and become more clear.

Polyester and other types of plastic release liners are perfectly smooth. The smoothness of the plastic liners makes the adhesive of an overlaminating film perfectly smooth. Hence, overlaminates with polyester liners aren't prone to blotchiness or orange peel. One disadvantage of plastic release liners can be very difficult to remove from an overlaminate. 

Other adhesive issues can contribute to a hazy appearance.  The cleanliness of the adhesive and the consistency of the adhesive coat weight are other factors that weigh on the appearance of the finished product. Coating a perfectly clear adhesive is tricky business. If it was easy, anybody could make a quality overlaminate.  Although we have an easy remedy for making the mottling disappear, problems in the adhesive may be irreparable. For example, entrapped air or impressions made during the lamination,  which can be caused by a damaged roller, are not likely correctable.

Now here are the remedies that I promised. The one first is easy. Do nothing. That’s right, do nothing. Within a few days (possibly longer) after application, the mottled botches should magically disappear. If the vinyl graphic is installed outside in the hot sun, the blotchiness may disappear in a matter of hours.

I told you that this remedy would be easy.  How often do problems correct themselves?  Now try telling that to your customer. Most of them know that if sounds too good to be true, it probably is.  For this reason, expect your explanation to be view with skepticism.

A safer bet is my second remedy, which will require a little extra work, but you won’t have to do any tap dancing in front of your customer. Using your heat gun, apply heat to the mottled surface of the film.  The gloss of the film will reappear with if the mottling is in the film. Post heating a graphic never hurts, because it also helps the adhesive soften and wet out onto the substrate, creating a tighter ultimate bond.

By applying heat to the mottled surface of the film, the gloss of the film will reappear. 

Does heating work 100% of the time? No, but whatever does. Some extreme problems cannot be fixed.  In these cases, or when the problem is in the adhesive coating, contact your sign supply distributor so they can enter a return of material authorization.  After receiving the material in question, the manufacturer will test and evaluate it.  Your feedback on the manufacturer's products is very important to them.  If there is a problem with their product, they need to know about it.  They can’t fix it, if they don’t know it’s broke.

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Vinyl Application Videos

Squeegee Technique. Nothing is more basic in vinyl application than the squeegee. But some squeegees work better than others. And there are right ways and wrong ways to use this simple tool. This video clip reviews squeegee selection, squeegee care and squeegee technique. Click to Link

Wet Applications. Dry applications are typically recommended for most vinyl applications. For those exceptions to the rule, this instructional video explains the right way to perform a wet application. Click to Link

Application of Window Graphics. Installing vinyl graphics on glass can be challenging, because the adhesive aggressively grabs onto this high energy surface. Repositioning graphics on window is generally difficult, if not impossible. This instructional video explains how to dry apply window graphics right the first time. It also describes the necessary steps required for surface preparation. Click to Link

Transferring Frosted Window Graphics Films.  Because frosted window films are highly textured, transferring cut vinyl graphics can be problematic. This video provides direction in selection of the right application tape and how to apply these films quickly, easily and without problems. Click to Link

3-Step Surface Prep. This instructional video describes how to properly clean the surface of a vehicle before applying pressure sensitive vinyl graphics to a trailer or doing a full wrap of a car or van. This three step surface prep involves detergent washing, solvent cleaning and a final wipe down with IPA. Click to Link

Vinyl Application Over Rivets. Applying vinyl graphics on vehicle surfaces with rivets is challenging for most sign makers. Vinyl failures to these surfaces are all too common. This video demonstrates some tips and procedures, used by professional decal installers, which will make these demanding applications easier and more trouble-free.  Click to Link

Vinyl Application to Corrugations. Learn how to apply vinyl graphics to corrugations in a relaxed state. Forcing films into the valleys of corrugations puts too much mechanical stress on the film. Sooner or later, the vinyl will lift or tent in valleys. Click to Link

Applying Air Egress Vinyls. Vinyl films with air egress release liners have almost eliminated bubbles and wrinkles from applied graphics. Air egress release liners with their highly textured surface structure are problematic. Not much will stick to these liners other than the vinyl film. At RTape our best premask solution for air egress liners is a special Conform® tape called 4761RLA. Click to Link

About Jim Hingst: After fourteen years as Business Development Manager at RTape, Jim Hingst retired. He was involved in many facets of the company’s business, including marketing, sales, product development and technical service.

Hingst began his career 42 years ago in the graphic arts field creating and producing advertising and promotional materials for a large test equipment manufacturer.  Working for offset printers, large format screen printers, vinyl film manufacturers, and application tape companies, his experience included estimating, production planning, purchasing and production art, as well as sales and marketing. In his capacity as a salesman, Hingst was recognized with numerous sales achievement awards.

Drawing on his experience in production and as graphics installation subcontractor, Hingst provided the industry with practical advice, publishing more than 150 articles for  publications, such as  Signs Canada, SignCraft,  Signs of the Times, Screen Printing, Sign and Digital Graphics and  Sign Builder Illustrated. He also posted more than 325 stories on his blog (hingstssignpost.blogspot.com). In 2007 Hingst’s book, Vinyl Sign Techniques, was published.  Vinyl Sign Techniques is available at sign supply distributors and at Amazon. 

© 2016 Jim Hingst