Types of adhesives

WET ADHESIVES

Wet adhesives are only applied to a single part which is then immediately affixed to a second one. The parts must be clamped together, as adhesion only occurs when the solvents have evaporated. Water is the carrier substance in so-called "solvent-free" adhesives. Wet adhesives dry best on materials with open pores.

Adhesives with solvents are needed for many bonding applications, particularly when trying to avoid paper curling, gluing non-porous materials or when a fast application speed is important. These adhesives consist of resins or rubbers suspended in conventional liquid solvents, e.g. alcohol, acetone or methyl acetate. The adhesive hardens when the solvent evaporates. The solvent must therefore be able to escape through the material, which is the case with wood, cardboard and leather. But with impermeable, dense materials, such as metal, porcelain or hard plastic, the adhesive surface must be as narrow and elongated as possible so that the solvent can escape laterally. What's more, when bonding plastics, you should always pay attention to the corresponding package instructions as many plastics can be damaged or even dissolved by solvent adhesives.

CONTACT ADHESIVES

Contact adhesives are applied to both parts to be bonded. After the flash-off time, which can vary depending on the solvent, the parts are joined together with high contact pressure. The parts adhere immediately and the workpiece can bear loads shortly after.

UHU contact adhesives, such as UHU All Purpose Adhesive Power or UHU greenit, are applied using the two-sided contact bonding process. They are particularly suitable for bonding dense materials that are impermeable to solvents. Contact adhesives deliver immediate adhesion that achieves high strength in a short time. They remain elastic even after drying, so are ideal for materials that need to remain flexible at the bonding point (e.g. shoe soles, leather belts). Contact adhesives are also widely used for large area jobs (e.g. applying veneer to tables). Solvent-free UHU contact adhesives are also available. 

What is "contact bonding"?

Contact bonding is a process in which the sides of both parts to be bonded are thinly and evenly coated with adhesive. The parts are not assembled immediately but are left exposed (so the solvent can evaporate) until the adhesive surfaces feel "touch-dry". Once this happens, the parts are gently placed on top of each other, aligned and pressed together briefly but vigorously. Here, the force of the pressure is important, not its duration. If contact bonding is successful, the parts can no longer be adjusted. 

REACTIVE ADHESIVES

Reactive adhesives harden and set through chemical, physical or catalytic reaction. Depending on their reactive behaviour, they can have one or two components.

One-component reactive adhesives
One-component adhesives either react to humidity, UV light or oxygen in the atmosphere (aerobic adhesives) or to metal ions when oxygen is not present (anaerobic adhesives). One-component adhesives are applied to one of the sides to be bonded. The reaction starts immediately thanks to the second reactive component present in the environment or on the adhesive surface.

Two-component reactive adhesives
Two-component adhesives consist of liquid, paste or powder components, which usually have to be mixed precisely to the exact ratio. They have a limited processing time (pot life) as curing starts immediately. The bond must be clamped until it has completely hardened. Curing times depend on the type of adhesive used and the ambient temperature.

High-performance bonding with reactive adhesives
(fast, strong and versatile)

Reactive adhesives harden and set through chemical, physical or catalytic reaction. They are usually used when maximum strength is required. These reactive adhesives usually have two components (a binder and a hardener). Binders and hardeners are always packaged separately. If both components come into contact with each other, a reaction begins that hardens the adhesive material and allows it to achieve its final strength.

One-component reactive adhesives contain a non-active hardener which is inactive in the packaging under normal conditions. The reaction starts when the hardener comes into contact with the second reactive component. Depending on the type of adhesive, the reaction is triggered by humidity, UV light or oxygen in the atmosphere (aerobic adhesives).

ONE-COMPONENT REACTIVE ADHESIVES

One-component adhesives either react to humidity, UV light or oxygen in the atmosphere (aerobic adhesives) or to metal ions when oxygen is not present (anaerobic adhesives). One-component adhesives are applied to one of the sides to be bonded. The reaction starts immediately thanks to the second reactive component present in the environment or on the adhesive surface.

High-performance bonding with reactive adhesives
(fast, strong and versatile)

One-component reactive adhesives contain a non-active hardener which is inactive in the packaging under normal conditions. The reaction starts when the hardener comes into contact with the second reactive component. Depending on the type of adhesive, the reaction is triggered by humidity, UV light or oxygen in the atmosphere (aerobic adhesives).

HERE'S HOW THEY WORK:

For one-component adhesives, the adhesive is applied to one side of the item to be bonded. The reaction starts immediately if the second reactive component is present in the environment or on the adhesive surface. The second component must actually be present.

TWO-COMPONENT REACTIVE ADHESIVES

Two-component adhesives consist of liquid, paste or powder components, which usually have to be mixed precisely to the exact ratio. They have a limited processing time (pot life) as curing starts immediately. The bond must be clamped until it has completely hardened. Curing times depend on the type of adhesive used and the ambient temperature.

High-performance bonding with reactive adhesives
(fast, strong and versatile)

Reactive adhesives harden and set through chemical, physical or catalytic reaction. They are usually used when maximum strength is required. These reactive adhesives usually have two components (a binder and a hardener). Binders and hardeners are always packaged separately. If both components come into contact with each other, a reaction begins that hardens the adhesive material and allows it to achieve its final strength.

HERE'S HOW THEY WORK:

For two-component adhesives, the binder and hardener are mixed thoroughly to the specified ratio and applied within the curing time (between one hour and several hours, depending on the type of adhesive). A temperature of approx. 20°C is ideal for bonding.

HOT MELT ADHESIVES

Hot melt adhesives are available as cartridges, pens, powders, granules, nets or foils. They are solvent-free and usually need no mixing or dosing.
Hot melt adhesives liquify when heated. This is done either directly on the adhesive bond (e.g. by ironing on edging) or by using an adhesive gun which applies the hot glue to the parts to be bonded. Hot melt adhesives melt at temperatures between 110°C (UHU Gun Low Melt 110) and over 220°C in other products in the range.

PRESSURE-SENSITIVE ADHESIVES

Pressure-sensitive adhesives are products that stay perpetually sticky. They are used when a bond should not be permanent as parts have to be separated in the future. Pressure-sensitive adhesives are mainly used for adhesive films and tapes, double-sided sticky tape and pads, as well as sticky notes, self-adhesive labels and films.