Instant Adhesives

Blooming is the whitish discoloration at the bondline that occurs when volatile components of the cyanoacrylate monomer outgas, react with the moisture in the environment, and deposit as a white, powdery material on the part. (Did you know: This phenomenon is used in forensic science to reveal fingerprints at a crime scene.) There are several methods to prevent blooming, e.g. B. ensure sufficient ventilation over the workplace, apply less adhesive or harden the adhesive more quickly. The other option is to simply use a low-bloom, low-odor LOCTITE^® instant adhesive that is less volatile and therefore less prone to blooming.

Instant adhesives are acid stabilized and require contact with a weak base (i.e. moisture) to react. So acidic surfaces (e.g. paper and zinc dichromate coated steel) or residues (e.g. vinegar) on a part can slow down or even prevent the curing of instant adhesives. Surface tolerant instant adhesives react much faster than traditional instant adhesives on passive and active surfaces and in dry environments, resulting in more consistent and reliable bonds.

There are several methods of impact modifying instant adhesives, the most common being elastomeric or anhydride impact modifiers. These impact modifiers can absorb and distribute shock loads and stresses applied to the bond line, providing a bond with higher impact strength.

A thermoplastic - as opposed to a thermoset - is a polymeric material that can be deformed or heated by the action of pressure or temperature. Hot melt adhesives and instant adhesives are the most common types of thermoplastic adhesives.

Due to its high level of moisture, skin can be bonded very quickly by instant adhesives. A simple way to separate patches of skin and fingers that have been stuck together is to roll a pen or pencil through the adhesive layer, thereby peeling the adhesive apart. You can also try warm water and soap.

In addition to their unique shape, the patented 20 g (1 oz) LOCTITE^® . Instant glue bottles have a thinner and more even wall thickness. This reduces the force required to compress by more than 30% and the improved moisture barrier achieves a longer shelf life. The nozzle has been designed to accept most standard dispensing needles. It is protected by an easy-to-use twist-on/off cap with click closure.

In order to achieve optimal shelf life, it is recommended to store the unopened instant adhesive bottles in the refrigerator. Once opened, the bottle is best stored at room temperature, otherwise any moisture that may have gotten into the bottle could condense during refrigeration and cause the adhesive to set prematurely.

An adhesive is "hand-tight" when the bond has achieved sufficient strength so that the joined parts can be handled without affecting the long-term strength of the adhesive. On a laboratory scale, the time to reach handling strength is the time it takes for a 25mm wide lap shear specimen bonded with a 12mm overlap to withstand a shear load from a 3kg weight for at least 5 seconds. For instant adhesives, this period is usually just seconds. Complete curing is achieved when the adhesive has reached its maximum adhesion. For instant adhesives, this is typically 24 hours.

In general, instant adhesives have very good resistance to non-polar solvents (e.g. motor oil, ether and toluene), while resistance to strongly polar solvents (e.g. caustics, acetic acid, acetone, etc.) is poor. More detailed information on chemical resistance can be found in the technical data sheet for the respective product.

Instant Adhesive Primers are solvent-based products that are applied prior to bonding to increase bond strength (not cure speed) to &quot;passive&quot; Raise surfaces so that they can be glued with cyanoacrylate adhesives. After application of the primer, a waiting time must be observed to allow the carrier solvent to flash off the surface before applying the adhesive (<1 min is typical). Primers may not be recommended for all surfaces, therefore reference should be made to the relevant Technical Data Sheet or the LOCTITE^® Plastic Bonding Guide for further details.

Instant adhesive accelerators are solvent-based products that are applied before or after the bonding process to increase the cure speed and/or gap filling capacity of instant adhesives. They can also be post applied to cure excess adhesive squeezed out of a bond line or to cure exposed beads of instant adhesive used to secure and fasten wires or similar. They are particularly useful during the winter months when ambient conditions are very cold and dry.

With some plastics under mechanical stress (e.g. polycarbonate, acrylic and polysulfone) uncured instant adhesives in the liquid state can crack the plastic with prolonged exposure. Possible measures to avoid/reduce stress cracks are e.g. B. to join the bonds quickly, to use reinforced types of plastic, to temper the plastic parts or to accelerate the curing of the instant adhesive with an accelerator or with light (only light-curing Flashcure products).

When instant adhesives are used to bond glass, the strength is initially high but then degrades dramatically over time. Due to the basic properties of glass, the curing speed is extremely fast; this can result in high stresses in the adhesive joint at the molecular level in the boundary layer on the glass. These high stresses leave the cured polymer at the bond line susceptible to physical and chemical degradation over time, due to expansion and contraction of the bond due to temperature changes, hydrolytic attack from moisture, etc. When gluing connections with glass, a permanent bond can therefore not be achieved.

Traditional instant adhesives are acid-stabilized, one-part adhesives that react rapidly at room temperature when placed between two closely fitting surfaces under the influence of moisture (a weak base). Henkel also offers light-curing ("flashcure") instant adhesives, which, in addition to the conventional CA curing mechanism, contain photoinitiators that cause rapid polymerization when exposed to light of the appropriate wavelength. For applications with large gap widths or tolerances, 2-component instant adhesives are also available for application with a static mixer.