What are Hot Melt Adhesives?
Hot melt adhesives are thermoplastic polymer adhesives that are solid at room temperature but liquefy when heated above their softening point.
Due to their low softening temperature, hot melt adhesives are capable of being used in a wide variety of sectors. The liquid state of hot melt adhesives allows them to bond to various surfaces.
In their solid state, hot melt adhesives can take a variety of forms, including beads, blocks, pellets, chips, pillows, or glue sticks. Depending on the application, the hot melt adhesive can be sprayed, rolled, or extruded.
Hot Melt Adhesive Raw Materials
There are many types of additives that can be used in a hot melt, and the quality of the additives will determine a hot melt’s functionality, function, and cost. Generally, a hot melt is composed of polymers and many types of additives.
Among these additives are antioxidants, resins, plasticizers, waxes, and other chemicals.
Resins in Hot Melt Adhesives
A hot melt’s tack is determined by its resins. Tack is defined as the amount of adhesive stickiness. It is usually defined as the amount of time the adhesive remains intact after application. Additionally, resins control how an adhesive wets. During the contact between hot melt and surface substrate, resins control how long it remains liquid.
Hot melt resins play a significant role in the nature of the product. Selecting a resin depends on a variety of factors, including its softening point, compatibility with the main polymer, and adhesion characteristics. Generally, hot melts use rosin, hydrogenated rosin, rosin ester, Hydrogenated hydrocarbons, terpene phenolics, C5 and C9.
In some melts, aromatic monomers are also used. More resin means a hot melt with a lesser tack and a faster drying time. Less resin implies a hot melt that is tougher and more aggressive.
Adhesives made from polymers
Polymers are considered to be the basic constituents of hot melts. These are long chains of specific molecules with different properties. Polymers are responsible for most of the hot melt’s physical properties.
In addition to heat resistance, flexibility, strength, shear resistance, and impact resistance, hot melts are also heat resistant, flexible, strong, and shear-resistant because of polymers. Hot melts with a high polymer content will have high viscosity. Viscosity is defined as the thickness of the liquid. An increased polymer content will also result in greater flexibility and toughness.
Antioxidants in Hot Melt Adhesives
A hot melt’s main purpose is to keep the material from degrading over time. Antioxidants used in hot melts include aromatic amines, phenols, BHT, phosphites, and phosphates, all of which are added together with stabilizers in very small quantities. They do not affect the hot melt’s physical properties. Antioxidants provide protection to the hot melt when it is molten, when it is applied, and when it is compounded.
Waxes in Hot Melt Adhesives
Open time and set speed in hot melts are mainly controlled by wax in a hot melt. Open time is defined as the time it takes for a bond to form. When using pressure sensitive hot melts, the time can range from a short period of time to a long period of time. In order to determine how quickly the hot melt can form a bond of acceptable strength, the set speed is used.
In addition to the heat resistance and sub-ambient adhesion of the hot melt, wax should also be in perfect harmony with the parameters used in the production line. Synthetic waxes, microcrystalline waxes, and natural waxes are usually used in hot melts. A wax’s characteristics are determined by its molecular weight, crystallinity, and melting point.
Hot melts with a lower wax content will be more flexible and more aggressive when bonding. When wax content is lower, the hot melt will be more flexible, lower viscosity, and set much faster.