GENERAL ANTI-TACK INFO
We must first distinguish between internal anti-tacking additives and external anti-tack coatings. Internal anti-tacking additives are compounded into a given material to create inherent non-stick characteristics, but compounding additives
may not eliminate tackiness entirely. This page will discuss external anti-tack coatings in greater detail for those applications where compounding ingredients are not sufficient.
Anti-tack coatings are applied externally to reduce the adhesive condition (stickiness) of a given material, usually an uncured natural or synthetic elastomer. Anti-tack coatings differ from lubricants in that they are designed to reduce inherent tackiness while lubricants are designed to reduce friction between any two surfaces. A McLube Technical Representative can help you determine if your application calls for an anti-tack coating or lubricating formula.
TYPES OF ANTI-TACK COATINGS
AND WHAT THEY'RE USED FOR
In order to determine what type of anti-tack is right for your operation, you must first consider how and for what type of process the rubber will be used. Pigmented anti-tack coatings are ideal for operations that include a remilling or finishing step before molding or other use of the rubber compound. Without proper milling before use, fillers (clay, talc, mica) used
in a pigmented anti-tack can negatively affect the physical properties of the rubber when molded or prevent rubber-metal bonding. Unpigmented (or nonpigmented) anti-tack coatings do not contain fillers and harmlessly melt into the rubber during molding. If an extra remilling step is not possible or undesirable, then unpigmented, unfilled anti-tack coatings are the best option.
THERE ARE THREE MAIN TYPES OF EXTERNAL ANTI-TACK COATINGS:
1. Stearates and Powder Coatings
Stearates are unpigmented and may or may not be dispersible in water. Zinc stearates are effective anti-tack coatings that
will solubilize into rubbers without causing physical abnormalities, but their use is highly regulated by the Environmental Protection Agency (USA) because they kill bacteria necessary for the decomposition of organic matter in waste treatment processes. Calcium stearates do not threaten waste treatment but require longer molding times to solubilize into rubbers. Stearates may be dusted onto the rubber or added to a dip tank or slurry. While the hydrophobic qualities of most stearates have advantages for water-cooled rubber processes, the inability of stearates to emulsify in a water tank requires extra equipment, care, costs, etc. to keep the stearates dispersed.
Powders such as talc and mica may also be dusted onto rubbers or added into dip tanks but, while inexpensive, these anti-tack coatings cause endless housekeeping and safety concerns similar to dusted stearates.
Stearates and powders tend to clump and streak on rubber surfaces when dusted, or poorly dispersed or floated in dip tanks. Uneven coating of the rubber surface will result in poorer anti-stick performance and may also cause physical or aesthetic defects in the rubber during molding. Stearates and powders can also have difficulty wetting out on low temperature rubber surfaces with further impact on anti-stick performance. See below for more information about wetting and why
it is important.
2. Pigmented Slurries
Use of pigmented slurries will require finishing or remilling of the rubber before it can be used in compression or transfer molding operations. Slurries are also associated with increased transportation costs when compared to stearates or dilutable liquid coatings. Dry powder pigments are starting to replace slurries because they are cheaper to ship, but these coatings may not be effective on low temperature surfaces unless used to a costly degree. Plant managers wishing to use one anti-tack coating for multiple applications will find that pigmented slurries provide little versatility when compared to some stearates and liquid coatings.
3. Liquid Coatings
Liquid anti-tack coatings contain fatty acid soaps or other ingredients that deliver anti-sticking properties directly to the rubber material. These coatings generally absorb or melt into the rubber without issue and do not require an extra milling step. Some liquid anti-tack coatings do contain mica and are used in the tire industry to release tires from a curing bladder. Liquid coatings are a cleaner and safer alternative to powders and stearates containing heavy metals and generally require less machinery to agitate (mix) and apply. Drawbacks to using liquid coatings include foaming and the risk of excessive lubricity.
McLube anti-tack formulas eliminate the safety and housekeeping concerns of powders and stearates and improve upon the drawbacks of slurries and competing liquid coatings. See below for information about the advantages of McLube’s powder-free line of liquid anti-tack coatings.
WETTING: WHAT IT IS
AND WHY IT MATTERS
Success or failure of an anti-tack coating depends on its ability to “wet” the tacky surface on which the coating is applied. Wetting refers to a compound’s ability to spread out and adhere to a given substrate (surface). Adherence to the substrate ensures the coating will be durable, long-lasting, and effective. The most crucial factor impacting wetting characteristics
is temperature; hotter rubber surfaces in excess of 150°F (66°C) wet out much easier, but if you are cooling your rubber
to prevent scorching, or working with cold flow compounds, then you will require an anti-tack coating with enhanced surfactant technology.
Wetting of certain rubbers can also be further complicated by specific chemical compositions and storage methods. One particular elastomer, ethylene propylene diene monomers (EPDM), can be particularly difficult for anti-tack coatings to wet out. McLube offers specialty anti-tack coatings that are tailored to particular types of rubber compounds to ensure ideal wetting characteristics are achieved.
THE IMPORTANCE OF SELECTING
THE RIGHT ANTI-TACK FOR YOU
Process aids like anti-tack coatings are often considered less impactful than compounding ingredients because they do not (and should not) chemically alter the process material. Too many manufacturers overlook the importance of selecting an appropriate external anti-tack with varying consequences, including:
• Production cost increases due to fouling, downtime, and extra cleaning steps
• Poor quality products due to material contamination
• Environmental hazards and decreases in plant safety
• Slabs falling from pallets and equipment
Most anti-tack coatings will fail under factory conditions unless they are properly selected and tested outside the lab.
McLube Technical Representatives can assist with selecting the ideal anti-tack for your operation as well as provide additional process and application assistance during the testing phase.
OUR POWDER-FREE APPROACH
McLube’s line of powder-free anti-tack coatings includes many specialized formulas designed to improve upon the shortcomings of stearates, slurries, and competing liquid coatings. Our liquid coatings solve the safety and housekeeping concerns associated with powder coatings by delivering anti-tacking ingredients directly to the rubber without the risk of migration.
Our liquid coatings settle out from dip tanks much slower than stearates and slurry fillers because the active ingredients are less hydrophobic and easily emulsified into a liquid base. Slower settling means our products eliminate the need for some of the extra agitation equipment required to keep powder-based coatings like stearates and slurries dispersed. McLube also offers colloidal anti-tack coatings that require little or no agitation, providing an opportunity for process engineers to eliminate costly, maintenance-heavy equipment from their processes entirely. Emulsions and colloidal dispersions provide far superior anti-stick characteristics when compared to stearates and slurries because they create a more uniform coating of active ingredients on the rubber surface that will not clump, streak, or cause physical defects during molding. All of McLube’s liquid anti-tack coatings are unpigmented and melt harmlessly into rubbers during molding without affecting physical properties or preventing rubber-metal bonding.
The shortcomings of competing liquid coatings include undue foaming and excessive lubricity. McLube has developed several non-foaming liquid anti-tack coatings and McLube Technical Representatives can also help rubber processors incorporate our soap-based formulas into their process to prevent foaming. McLube’s line of anti-tack coatings includes many specialized formulas with tailored slip coefficients to prevent excessive lubricity. Our Formulation Chemists may also alter an existing formula or engineer a custom formulation for unique or challenging applications. McLube also offers concentrations of our most popular anti-tack formulations that are easily diluted inhouse to save on transportation costs. Diluting also gives process engineers more control over their process aids and the opportunity to apply the same coating across multiple processes at different concentrations.
Contact McLube to learn more about our powder-free approach to anti-tack or visit our product pages by clicking below.
McLube's anti-tack coatings are tailor-made for your manufacturing needs.
Get in touch with a MvLube expert to discuss your process challenges here.
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