Avoiding Vinyl Failure Part 2: Identifying your Application Surface
By Denise Nathan
Many vinyl failures are caused due to a mishandling of, or failure to identify the application surface. The previous tips and tricks looked at the impact of surface contamination and how this impacts on vinyl and adhesive performance. The next thing to consider to ensure graphic performance is the surface composition and how some popular substrates require special consideration and preparation before application.
Plastics
Not all plastics are the same. Some are easy to apply to and some are not so knowing the composition of the plastic will assist you in which method to apply. Acrylics, polycarbonates and fibre glass usually contain a trapped moisture layer close to the surface. It is critical to pre-dry the substrate or the moisture will remain under the layer of vinyl. As the environmental temperature rises the moisture is released and causes bubbles to appear under the film. This is known as out-gassing.
Polyethylene and polypropylene are not recommended surfaces unless a special adhesive is used or the surface is flame treated. Flame treatment alters the molecular structure of the substrate for a short period of time allowing the adhesive to form a better initial bond.
Soft PVCs (banner) contain plasticisers that can migrate to the surface of the banner. This can cause adhesion issues or tunneling of the vinyl as the plasticisers migrate into the film. Only self adhesive products designed for this type of application should be used.
Painted surfaces:
If the surface is pre-painted, the first thing to check is that the paint has formed a good bond to the substrate and that the paint has fully cured. Drying is different to curing. Paints may feel dry to the touch hours after painting but solvents may continue to evaporate for days. Some automotive paint specialists even recommend waiting up to 3 weeks to apply graphics on a newly painted vehicle.
Urethane Paint Systems are often used in marine and automotive applications. These paint systems use a chemical cure which results in out-gassing. Therefore, it is crucial to observe paint manufacturers’ recommendations. If you are unsure you can test for out-gassing prior to application simply by applying a piece of vinyl to the surface and waiting 24 hours. Polyester is the best film to use for this test because it is not porous and will not allow any of the gas to escape. If bubbles appear within that time the paint is not suitable for application. You must wait until the cure process is finished and bubbles no longer appear under the test film. Alkyd primers or paints should be avoided as they are very slow drying taking months to reach a level that is acceptable for good adhesion. Other painted surfaces to avoid are paints that chalk or bleed such as paints with dye-based tints and paints that include ingredients that migrate to the surface such as waxes, silicones or anti fungal agents.
Rubber:
Not recommended. Rubber has a very low surface energy. The lower the surface energy the harder it is for success with long term adhesion. Special adhesives are available for this application but generally not in the signage and digital markets.
Unpainted wood:
Wood generally needs to be primed and/or painted to achieve adhesion. Wood contains a certain amount of natural moisture and will also absorb moisture from the atmosphere if not properly sealed, leading to out-gassing or substrate bleeding. Woods with a heavy natural resin or oil content (e.g. pine) should be avoided.
Unpainted metals:
Aluminum- Only use etched and degreased or anodised aluminum for best results.
Steel- Unpainted -Do not apply graphics to unpainted steel. Steel must be primed and painted. If the steel is already painted, check for oxidation. If oxidation is evident then the steel must be completely refinished.
Phosphate-coated or galvanised- must be thoroughly cleaned to remove zinc oxide salts from the surface.
Electronically galvanised or base steel- Must be degreased and coated with a good phosphate coating before priming and painting.
If you have any doubts about the surface you are applying to there are a few tests you can perform. Adhesives require the surface to have good “wet out” properties to form a good bond. To test a surface you suspect has a wax or other anti –adherent coating, a good rule of thumb is to place drops of water on the surface. If the water forms into small beads there is a coating on the surface that will affect adhesion. This coating will have to be removed for a successful application. This is also a good test for surface energy levels. The lower the surface energy of a surface (e.g. Silicon, Teflon) the more likely it will repel water and therefore adhesion will be difficult. The higher the surface energy (e.g. Glass) the more the water droplets will flow and is a good indication of an adhesive friendly surface.
Adhesives usually take 24-48 hours to cure (longer if using the wet method and in cold temperatures). Clean and prepare the test substrate for application. Apply a piece of the film you intend to use and wait 24-48 hours. If the film has not formed a good bond to the surface in this time period chances are it never will and is an application that should be avoided.
Vinyl and adhesive technology is forever changing and today a wider range of applications are possible. There is greater confidence and the perception that self adhesive vinyl can be applied to just about anything. While this is almost true, it can not compensate for poor surface preparation and evaluation. Taking the time to evaluate your surface prior to application can save you a lot of time and
money and is a worthwhile investment.
Denise Nathan is Marketing Manager - MACtac in Oceania
denise@mactac.co.nz
www.mactac-europe.com
