First, let's know about what is hot melt adhesives
Hot melt adhesive is a thermoplastic adhesive that is melted by heating to bond. It is solid at room temperature, but when heated to a certain temperature, it changes from solid to molten state, and can be applied to the object to be bonded by coating or spraying equipment. After the hot melt adhesive cools, it will re-solidify for easy storage, and the next time it is used, it can be reheated. The melting temperature of hot melt adhesive is 65℃~180℃. Since it is 100% solid and does not contain any solvents, it meets the most stringent air pollution prevention and control regulations. Meanwhile, it has almost no risk of fire or explosion.
What Are types of hot melt adhesives
Classified according to the main resin raw materials used
Polyolefin hot melt adhesives
Including polyethylene hot melt adhesives and polypropylene hot melt adhesives. Polyethylene hot melt adhesives are odorless, non-toxic, low-temperature resistant, chemical resistant, low water absorption, low price and easy to bond to porous surfaces. Polypropylene hot melt adhesive has a slightly slower curing speed and low heat resistance. It is often mixed with low molecular polyethylene or crystalline polypropylene to improve performance. It is mainly used for paper packaging, carpet backing, paper lamination, etc.
Ethylene and its copolymer hot melt adhesive
Mainly includes ethylene-vinyl acetate copolymer (EVA) hot melt adhesive. EVA hot melt adhesive has excellent adhesion, softness, heating fluidity and cold resistance. It is suitable for book binding, wood processing, plywood production, packaging, shoe automation operation, construction industry and other fields. However, its strength is low, it is not heat-resistant and fatty oil-resistant, and is usually used in occasions with low strength.
Polyester hot melt adhesive
It has excellent electrical insulation and good bonding strength, and has good impact resistance, water resistance, heat resistance, cold resistance, medium resistance and elasticity. It is suitable for clothing, electrical appliances, shoemaking, construction and other industries. Due to its high melt viscosity, manual operation is more troublesome, and amorphous polyolefins are often added to reduce viscosity.
Polyamide hot melt adhesive
It is divided into high molecular weight and low molecular weight. High molecular weight polyamide hot melt adhesive has good fluidity and high bonding strength, and is suitable for the clothing and textile industries. Low molecular weight polyamide hot melt adhesive has good strength and toughness, and is suitable for the bonding of leather, fabric, plastic, metal and other materials. It is widely used in industries such as footwear, automobiles, civil engineering and furniture.
Polyurethane hot melt adhesive
Including thermoplastic polyurethane hot melt adhesive and reactive polyurethane hot melt adhesive. The former has high strength and good elasticity, and is suitable for high-speed automatic production lines. The latter combines the advantages of hot melt adhesive, reactive adhesive and polyurethane adhesive,. It is suitable for bonding fabrics, metals, glass and other materials.
Styrene and its block copolymer hot melt adhesive, such as SBS and SIS
It has good solubility and compatibility, and is suitable for the preparation of hot melt pressure-sensitive adhesives.
What are the forms of hot melt adhesives?
Hot melt adhesive particles
This is one of the basic forms of hot melt adhesives, which is often used to make hot melt adhesive products in other forms, and can also be directly melted and coated.
Hot melt adhesive blocks
When used, it needs to be put into a furnace to melt into a liquid state, and then directly coated on the surface of the bonded object by a machine.
Hot melt adhesive powder
Mainly used for clothing lining, compounding lining fabric and fabric together, making the fabric less likely to wrinkle, thus giving the clothing a straight effect.
Hot melt adhesive stick
This is one of the most common forms of hot melt adhesive, often used for handmade DIY and small-scale production, and requires the use of a hot melt glue gun.
Hot melt adhesive film
Mainly used in clothing, footwear, home decoration, automobiles, electronics, packaging and other fields, with or without substrate, can replace traditional adhesives.
Hot melt adhesive net
Mainly used for large-area fabric compounding, widely used in decoration, clothing, footwear and other fields.
Hot melt adhesive line, hot melt adhesive strip, hot melt adhesive sheet
These forms of hot melt adhesive also have some special application scenarios. For example, hot melt adhesive line is often used in specific processes, while hot melt adhesive sheets are used for specific bonding needs.
The most commonly used plastic resin for making hot melt adhesive - EVA
The basic resin of hot melt adhesive is ethylene and vinyl acetate copolymerized under high temperature and high pressure, that is, EVA resin. This resin is the main component of hot melt adhesive. The proportion and quality of the basic resin determine the basic properties of the hot melt adhesive. Generally, the VA content is 18-33 and the melt index (MI) is 6-800. The lower the VA content, the higher the crystallinity and the greater the hardness. Under the same conditions, the higher the VA content, the lower the crystallinity and the greater the elasticity. The selection of EVA melt index is also very important. The smaller the melt index, the worse the fluidity. The greater the strength, the higher the melting temperature, and the poorer the wetting and permeability of the adherend. On the contrary, if the melt index is too large, the melting temperature of the glue is low, the fluidity is better, but the bonding strength is reduced. The selection of its additives should be selected with an appropriate ratio of ethylene to vinyl acetate.