An adhesive is a type of substance that holds two or more materials together with cohesive forces and surface attachment in a practical way. Adhesives can be made from and be composed of a variety of substances such as tree sap, bee wax, cement, and epoxy.Ideally, there are two broad adhesive categories, natural and synthetic adhesives. Most commercially found adhesives are synthetic adhesives as they provide better consistency, bond strength, and adaptability compared to natural adhesives. Synthetic adhesives are further classified as consumer adhesives and Industrial adhesives based on their application.
An adhesive’s chemical composition determines its application methods, usage, and bonding strength. Therefore, adhesive manufacturers need to custom-engineer modern synthetic based on the needs of different industries and applications.
Adhesive Applications In Various Industries
1. Bonding:
Bonding is a process in which two surfaces are practically joined together with the help of a suitable adhesive, such as epoxy adhesives. Adhesives are used for bonding materials in various industries, such as electronics, medical, food, optical, chemical and oil and gas industries to bond a range of metals, ceramics, glass, plastics, rubbers and composites.
2. Sealing:
Unlike bonding which sees two surfaces fused together, sealants are ideal for closing gaps and cavities to block fluids, dust, and dirt from either entering or getting out. Sealants are widely used in aerospace, oil and gas, chemical, electronic, optical, automotive and specialty OEM industries.
3. Coating:
Coatings are predominantly used in aerospace, electronic conformal coating, along with some other uses in OEM and oil & chemical industries. Industrial adhesive coatings can provide superior protection against chemicals, dust and moisture, reduce friction, improve abrasion resistance and provide EMI/RFI shielding.
4. Potting:
Potting is an encapsulation method used in the electronics industry to cover small or large electrical components placed inside a housing with a suitable potting material that can withstand high temperatures, protect the circuits from moisture, dirt, dust and other harsh conditions. Potting and encapsulation are used for electronic and microelectronic components, such as sensors, motors, coils, transformers, capacitors, switches, connectors, power supplies, and cable harnesses.
5. Impregnation:
Impregnation is a method used to wet various fibres, such as glass, carbon, kevlar, aramid among others. Once the fibres are completely saturated with the resin, the resin is allowed to fully cure in place forming a composite substrate. Such impregnated composite surfaces are widely used in the aerospace, windmill and electronics and electrical industries.
How Do Adhesives Work?
The working of adhesive depends on the types of bonding process used to attach the surfaces to each other. Mechanical adhesion and chemical adhesion are two types of bondings that can be used to stick one surface to another with adhesives.
Usually, surfaces that need to be attached with the help of adhesives, have a lot of micropores. These pores when filled with adhesives act as grips to keep another surface attached to them. This is called mechanical adhesion. With mechanical adhesion, the adhesives are in liquid form. The liquid adhesives will gradually penetrate the pores during the drying and curing process. You should also keep in mind that mechanical bonding is dependent on the surface roughness and surface energy of the substrates to be bonded. The higher the surface energy and roughness of a substance, the stronger is the bond.
On the other hand, chemical bonding is completely different which sees the surface of a material completely bond with another material on a molecular level. It is a complex process but very effective at the same time. Chemical bonding is further categorised into two types; adsorption and chemisorption depending on the type of bond between the adhesive’s molecules and the surface. Although chemical adhesives are easily available, they are not a common form of adhesive used in Industries.
Types of Adhesives
1. Hot Melt:
Hot melt is a type of thermoplastic polymer adhesive. Thermoplastic polymer adhesives are in a solid state at room temperature. During the application process , they are liquified by heating to be applied as an adhesive. Hot melt adhesives are used for manufacturing and packaging purposes in a wide array of industries due to their superior bonding strength, versatility and setting time. They are also eco-friendly, safe and have a longer shelf life.
Different hot melt adhesives might have different softening points and hardening times as per their applications. Some of the common types of hot melt adhesives are polyurethane, metallocene, EVA hot melt, and polyethene hot melt adhesives.
Let’s talk about reactive hot melt adhesives, which are different from hot melt adhesives. Reactive hot melt adhesives, once applied to a surface and cured, will not be able to melt again as they generate additional chemical bonds during the curing process. This makes reactive hot melt adhesives a better choice than simple hot melt adhesives as they have stronger adherence. Reactive hot melt or RHM are high-quality adhesives also known for their heightened resistance to moisture, and other chemicals with higher thermal stability.
2. Thermosetting:
Thermosetting adhesives are materials which cannot be re-melted after they have cured. Thermosetting adhesives are usually made of two parts, namely, the resin and hardener. However one-part forms can also be found.
There are various types of thermosetting grades such as:
- Phenolics
- Epoxies
- Polyesters
- Polyurethanes
- Silicones
Out of these, epoxy thermosetting resins are the most commonly used in various industries such as electronics and electrical, oil and chemical, automotive, aerospace, optical etc. This is due to their excellent resistance to heat and harsh chemicals and superior mechanical bonding properties.
3. Pressure Sensitive:
Pressure-sensitive adhesives are low-modulus elastomers which means they can be easily taken apart, but are the best choice for light usage. Pressure-sensitive adhesives can be easily found in tapes, bandages, sticky notes, etc. Pressure sensitive adhesives are non-structural adhesives which are not suitable for high-pressure industrial applications. However, they can be used for lighter and thinner material surfaces for which strong adhesives are not suitable. Pressure sensitive adhesives are also cheaper as compared to other adhesive materials and can be found more easily.
4. Contact Adhesive:
Contact adhesives are generally used to create strong mechanical bonds by applying adhesive to both surfaces that are supposed to be bonded together. Contact adhesives are also elastomeric which means the polymers used in the adhesives have rubber-like properties which helps them stay in shape. This gives contact adhesives excellent flexibility and mechanical strength. These adhesives are commonly used in the automotive industry, construction, aerospace and OEM for sealing and coating. They can also be found in rubber cement or countertop laminates. Contact adhesives are ideal for applications which require stability and durability.
Adhesive Application Methods
1. Manual:
As the name suggests, in this method, the applicator uses handheld devices and tools to apply adhesives to the surfaces. Manual adhesive application methods can include spraying, web coating, using a brush and a roller, curtain coating etc. Manual application is cost-effective and is recommended for smaller applications.
2. Glue Applicator:
Glue applicators are handheld devices that assist you to apply adhesives uniformly and at a faster rate than manually. These applicators contain a gun fitted with a cartridge containing the adhesive. A mixing tip is attached to the front of the cartridge to eliminate the need for any manual mixing. These semi-automatic devices enable higher speed, precision and efficiency. Glue applicators are ideal for medium to large-scale applications and are commonly used in the aerospace, electronics and optical industry to fuse small and detailed pieces of equipment.
3. Automatic Dispensing:
Automatic dispensing is ideal for fast-paced and high-volume environments where consistency and quality finish is crucial. This method is more costly as compared to the above two, however, automatic dispensing can increase efficiency, reduce waste and complete the task at a large scale. Metre-mix-dispense systems are used for two component adhesives and robotic dispensing is used for single component adhesives.
Conclusion
Adhesives are used in almost every manufacturing and packaging industry and are an important part of their process. As we have seen, there are different types of adhesives with varying properties suitable for numerous industries.
You can get custom-engineered adhesives from a professional adhesive manufacturer in India. These adhesives are specifically designed and crafted for your unique business needs. If you are currently looking for custom-made high-quality adhesives, feel free to contact us!
