Surface treatments have been used to improve the adhesion of flexographic inks to films and papers for many years. Water-borne and solvent-borne inks' partial absorbency into the substrate is critical for paper adhesion. However, partial vaporization and absorbency cannot be relied on when printing water-based inks on a non-porous film or foil.
Shelf Life Of Treated Surfaces
Pre-treated products have a shelf life ranging from hours to years, depending on the plastic, its formulation, how it was treated, and whether it was exposed to high temperatures during treatment.
The most critical aspect is material purity. Antiblock agents, mold release, and antistatics are all low molecular weight components that reduce shelf life. These components eventually migrate to the surface of clean polymers. As a result, printing or bonding to the substance soon after treatment is recommended. The bond becomes permanent until the treated surface is interfaced with a coating, ink, adhesive, or another substance.
Tips And Tricks For Easier Surface Treatment
Almost all surfaces must be prepared to define minimum adhesion criteria. Pretreatment and posttreatment and the ink layer's receptivity are terms used to describe this process. Here are some pointers for making printing and inking easier on the surface.
1. Using Flame Treatment To Prevent Ink Adhesion
A mixture of low-pressure air and gas is aimed at the surface to be decorated while flaming. Since too much flame will harm the surface, the process requires extra skill. A lack of flame, on the other hand, can prevent ink adhesion.
Materials such as biaxially focused polypropylene, polyethylene terephthalate, polyethylene, terephthalate, coextruded films, metal foils, paperboard, and foams are commonly treated with flame.
Flaming often burns away rough surface fibers, resulting in a smooth, flat surface that's ideal for coating. Flame treatment is a more delicate and risky method than a corona discharge, but it can still be very successful when used correctly.
2. Improve Adhesive Bonding With Plasma Treatment
Most manufacturers use in-line atmospheric plasma treatment to strengthen adhesive bonding on plastics, metals, composites, and glass surfaces. Plasma pretreatment removes chemicals from surfaces, making them cleaner. Air plasma's ability to functionalize surfaces activates their receptiveness to adhering with all forms of glues, and the process often etches surfaces, producing more bonding sites to facilitate stronger bonds.
Cold glue, hot-melt, pressure-sensitive, and UV curable adhesives may all benefit from plasma treatment. They can be constructed as part of a new work cell or incorporated into existing production lines. Plasma treaters are often paired with adhesive dispensing equipment in the same process. While certain products will retain the benefits of treatment for hours or days, it's best to treat the surface right before applying the adhesive or glue.
3. Using Corona Treaters
Corona treatment results in a decrease in carbon proportion and an increase in oxygen, and an increase in the O/C ratio. The growth of oxygen and O/C contribution is caused by the rise in VA proportion in EVA.
Activators are devices that professionals at ahlbrandt.com use to treat corona. They are made up of a generator, a transformer, and a series of electrodes that include a high-voltage electrode and a grounded electrode. Polyesters, ceramic, vulcanized synthetic rubber, epoxy coating, hardened polyester resin composition, and glass fiber cover the grounded electrode.
This treatment method works wonders for increasing the surface tension of almost every object. For plastic films/fabrics with a normal surface tension that isn't high enough to allow for good wetting, surface treatment is needed.
4. Treatment With Atmospheric Plasma
By grafting functional species that can mimic the reactive groups found in primers, atmospheric plasma treatments enable users to modify the surface composition of most materials selectively. Plasma treatments have the advantage of not requiring solvents or drying steps, resulting in a substantial reduction in the process's environmental effects and lower operating costs.
Plasma treatments in the atmosphere have been heralded as a game-changing technique that would revolutionize surface care. However, due to various reasons, they are still rarely used on a large scale in the industry. Atmospheric plasmas have most likely been oversold. The treatment's chemistry must be tailored to the specific procedure.
The chemistry used to improve adhesion during PEEK metallization differs from improving adhesion between a PP film and an epoxy. Atmospheric plasmas can be difficult to monitor due to a lack of knowledge of the chemical and physical processes. Finally, they are often misunderstood as a substitute for corona.
As you've seen, industrial users commonly use surface treatment tips to prepare low surface energy substrates for bonding. Although much time can be spent discussing the discrepancies between the approaches described, the ultimate question is still, "How successful was it?"