Cleaning, wetting, and surface activation is necessary to guarantee robust and reliable adhesive bonding of plastic and composite materials.
In a previous post, We Have a Water Problem, liquid cleaning was shown to be an inferior choice due to consumable costs, process control issues, and energy required to clean and dry the parts or components. The old adage of, “You are only as clean as your last rinse,” is really true.
For bonding preparation of low-surface-energy plastics, adhesion promoters and primers are well known and have been a common choice for decades. The adhesive providers have done a good job in making these primers work for a wide variety of materials and applications. There are many approaches and chemistries offered, including aggressive acid or alkali etching and some aqueous systems.
However, the most common priming systems for plastics contain high percentages of solvents, such as toluene, acetone or methanol, with the addition of highly profitable “Pixie Dust” chemistry additives. These liquid solvents typically attack (solvate) the plastic surface leaving the “Pixie Dust” chemistry on the surface.
Keep in mind that when you purchase a consumable primer, you are mostly buying solvents, with their associated hazards and process inefficiencies. You own that chemical for its entire life cycle, from the receiving dock to emissions and hazardous waste streams. Again and again.
Other undesirable attributes of a wet priming process are application issues such as mixing and masking, and energy costs to apply and cure the primer.
Time to apply and cure the primer may be the worst deficiency of wet primers. I have detailed some of these issues directly from the MSDS and Data sheets of typical and popular liquid primers for plastics.
TEN REASONS TO AVOID LIQUID PRIMING
- HANDLING AND STORAGE – Store in cool, dark place preferably between 60-75 degrees, away from sparks, flames and sources of ignition. Storage conditions can adversely affect properties.
- HEALTH HAZARDS – EYES: Can cause severe irritation, redness and tearing.
- HEALTH HAZARDS – SKIN: Prolonged contact can cause severe irritation and rash.
- HEALTH HAZARDS – INHALATION: Can cause nasal and respiratory irritation dizziness, weakness, fatigue and nausea. Also can causes kidney damage, liver damage in lab animals with chronic expos.
- FIRE/EXPLOSION HAZARDS: Vapors are heavier than air & may travel along ground and be ignited by pilot lights, other flames or sparks.
- SPILLS: Eliminate all possible sources of ignition such as pilot lights and flames. Absorb liquid. Stop spill at source.
- STABILITY/MATERIALS TO AVOID: Avoid contact with strong oxidizing agents. May form toxic materials such as carbon monoxide, various hydrogens and nitrogen compounds.
- WASTE DISPOSAL: Destroy by liquid incineration or dispose in approved landfill in accordance with local, state, and federal regulations.
- TIME: Apply and cure per instructions. Wait and watch it dry. Do you really have the time to prime?
- THERE IS A BETTER WAY: Plasmatreat’s Openair® Atmospheric Plasma cleaning and activation can replace wet primers. Using only compressed air and electricity, Openair® priming activation is fast, touchless and dry.