Cyanoacrylate (CA), otherwise known as instant or "super" glue, is one of the strongest and quickest bonding adhesives available. Modern formulations have added flexibility, toughness and surface insensitivity, allowing broader usage across industries. The growing market for micro speakers, including ear buds, hearing aids and most other electronic devices, has necessitated new advances and methods of application. Because of CA's strength and quick bonding to many surfaces, along with other factors, it has been the adhesive of choice for many aspects of loudspeaker construction for years.
"For dressing lead wires, UV CAs offer the quickest curing option, and can also fill gaps."
There are a number of different bonding applications in loudspeaker construction, including wiring, cones, gaskets, dust caps, surrounds, spider assemblies, voice coils, magnets and mounting top plates. Specific CA adhesives are ideal fits for bonding each of these parts in their respective places. In bonding top plates to frames, CA glues can actually eliminate the need for a gasket by forming a seal and strengthening the joint at the same time. When bonding the spider assembly to the frame, cyanoacrylate can be a quick and simple option for both low- and high-powered speaker. Speakers expected to endure large spider movement and vibration can be adhered with a rubber-toughened formulation to handle the additional stresses. Voice coil bonding can also be achieved with CA adhesives, though special technique may be necessary when using a low-surface energy cone like polypropylene. Temperature-resistant formulations are available that can withstand extended periods of high temperature. Bonding the surround to the cone or frame encompasses one of the largest bonding areas in speaker construction. CAs can make a cleaner bondline and decrease volume of adhesive needed for this process. Gasket to surround bonding is an excellent place for CA adhesive for the same reasons.
A Place For UV Light Cured CAs
Cyanoacrylates can also be made in UV-curing formulations. This allows them to be applied and then cured instantly when exposed to UV light. This is a particularly useful property in dust cap and lead wire assembly. In dust caps, UV-curing CAs are used because of their extremely quick cure time and ability to bond low-surface energy materials. Likewise, for dressing lead wires, UV CAs offer the quickest curing option, and can also fill gaps. They are also frequently used in micro-speaker manufacturing, where concerns about precise cure-profiles and throughput speeds are paramount.
Activator and Primers
While cyanoacrylate glues can often be used on their own to achieve excellent results, the use of an activator can further enhance bonding strength and/or speed. Primers can be used to prepare surfaces and allow adhesion on difficult-to-bond surfaces like polypropylene. Activators and primers are often either sprayed or wiped on before application, and activators can sometimes be added after adhering to speed bonding. Use of an activator often decreases fixturing time to under five seconds.
"Because of the quick, strong bonds formed with CA glue, testing and packaging directly after assembly is possible."
Distinct Advantages and Dispensing Options
Cyanoacrylate adhesives offer some distinct advantages that can't be matched by other glues. Their ease of use, either with direct application or the use of a primer or activator, makes adaptation to high-speed assembly simple. Because of the quick, strong bonds formed with CA glue, testing and packaging directly after assembly is possible, which may not be the case with epoxies or other adhesives. Because extremely small amounts of adhesive provide excellent bonding without the need for clamping or long cure-times they make a perfect fit for the micro speaker industry. Fully or semi-automatic dispensing systems are available that can be tailored to individual systems and dispense in dots, beads or sprays with precision. Manual dispensers for one or two-part formulations with meter-mix cartridges and pneumatic dispensers are available as well. Equipment is available to work with large quantities in barrels, or smaller bottles in pressure reservoirs. Care must be taken to avoid contact with moisture, so dry pressurized air is needed to provide pressure and polyethylene pins help to keep equipment free of cured adhesive. Light curing systems for separate or in-line assembly can be used with UV cyanoacrylates.