LOCTITE Instant Bonding Adhesives - FAQs
What is blooming?
Blooming or frosting is a phenomenon that occurs when cyanoacrylate monomer vapourises and reacts with moisture in the surrounding environment and falls back down on the part, leaving a white powdery residue behind. (Interesting fact: it is actually used by detectives to find finger prints at crime scenes.) There are several ways to prevent blooming such as sufficient ventilation over the assembly area, applying less adhesive and/or curing the adhesive faster. The other option is to simply use a LOCTITE Low Odour / Low Bloom instant adhesives which is less volatile and thus less likely to bloom.
What does surface insensitive mean?
Instant adhesives are acid stabilised and require a weak base (i.e. moisture) to react. Thus acidic substrates (e.g. paper and zinc dichromated steel) or residue (e.g. vinegar) on a part can slow or even inhibit instant adhesives from curing. Surface insensitive cyanoacrylate (CA) adhesives on the other hand are formulated to react much faster than traditional CAs on inactive and active surfaces as well as dry climates for a more consistent reliable bond.
How are CA adhesives toughened?
There are several methods to toughen CA adhesives, but the most popular ways are using rubber or anhydride toughening agents. The toughening agents are designed to absorb and distribute impact and stress applied to the adhesive bondline, resulting in a tougher bond.
What is a thermoplastic plastic?
A thermoplastic plastic, as opposed to a thermoset plastic, is a solid polymer that can be reshaped or moulded with pressure or temperature. Hotmelts and cyanoacrylates are the most common types of thermoplastic adhesive.
How do I separate my rapidly bonded fingers?
CA adhesives bond skin very rapidly because of its high moisture content. An easy way to separate bonded fingers and skin is to apply a peel force to the bond line by simply rolling a pen or pencil through the bond joint. You could also try warm water and soap.
How should I store my cyanoacrylate?
For the best shelf life results it is recommended to store unopened bottles of cyanoacrylate in a refrigerator. Once the bottle is opened it is best to store it at room temperature as storing in the refrigerator will cause any moisture contamination to condense and prematurely cure the adhesive.
What’s the difference between “fixture time” and “cure time”?
An adhesive has “fixtured” when the bond is strong enough that the assembly can be handled without compromising the long-term strength of the adhesive. On a lab scale, fixture time is equivalent to the time required for 25mm wide lap shears bonded with a 12mm overlap to support a 3kg weight in shear mode for at least 5 seconds. For CAs this time is usually seconds. Full cure is achieved when the adhesive has reached its highest bond strength. For CAs this is typically 24 hours.
What types of solvents/chemicals attack CAs?
In general, cyanoacrylate adhesives resist non-polar solvents (e.g. motor oil, ether, and toluene) very well but demonstrate poor resistance to strong polar solvents (e.g. caustic, acetic acid, acetone, etc.). Consult the product’s TDS for more specific chemical resistance data.
For excellent results with any LOCTITE instant adhesive, please ensure that the surfaces are clean and grease-free. LOCTITE 770 is especially recommended for polyolefin plastics, such as polypropylene (PP), polyethylene (PE). Where working with a combination of materials, the primer should only be applied to the plastic substrate.
When should I use a CA primer?
CA primers are solvent-based products that are pre-applied to promote adhesion (not cure speed) to "inactive" surfaces so that they can be bonded with cyanoacrylate adhesives. Time must be allowed for the solvent carrier to flash off the substrate (typically < 1 min) prior to applying the adhesive. Primers may not be recommended for use on all substrates so it is suggested to consult the product’s TDS or the LOCTITE Plastic Bonding Guide for more detailed data.
When should I use a CA activator?
CA activator are solvent-based products that are pre-applied or post-applied to increase the cure speed and/or increase the gap-filling capabilities of cyanoacrylate adhesives. They can also be post-applied to cure exposed cyanoacrylate resin that has squeezed out of a bond joint or to tack something into place, such as a wire. They are especially useful in the winter months when the environment is very cold and dry.
What is stress cracking and what causes it?
Leaving uncured liquid CA remaining on some plastic substrate (such as polycarbonate, acrylic, and polysulphone) in a stressed condition may cause the formation of cracks in the plastic. Some remedies for avoiding/minimizing stress cracking are closing the bond joint quickly, using reinforced grades of plastic, annealing parts, or speed curing the CA with activator or light (for light cure products only).
Why aren’t CAs recommended on glass?
When using CA to bond glass, the strength is initially high but degrades dramatically over time. The cure speed is extremely fast due to the basic nature of glass and this is likely to generate high stresses in the bond line immediately adjacent to the glass at a molecular level. This high stress makes the cured polymer around the bondline susceptible to chemical and physical degradation as a response over time to contraction and expansion of the joint with changes in temperature, or hydrolytic attack by moisture, etc. A permanent bonded in joint cannot be achieved when bonding substrates involving glass.
How does a Cyanoacrylate Adhesive cure?
Traditional cyanoacrylates are acid-stabilized, single-component adhesives that react rapidly at room temperature when contacted with moisture (a weak base) between tight bond lines. Henkel also offers Light Cure Instant Adhesives which have the traditional CA adhesive cure mechanism but also contain photoinitiators that polymerise rapidly upon exposure to the correct wavelength of light. Two-component static-mix instant adhesives are also available for applications with large gaps.