Characteristics of Hot Melt Glue Stick
Initially, Hot Melt Adhesive were primarily developed for industrial use. They have been, and are now, widely used in many application markets such as packaging, bookbinding, woodworking, electronics, lamination, shoemaking, craft gluing, hobby work, cabinet making, florist work, upholstery, product assembly, and many other applications. Hot melt adhesives have also been promoted to home and shop use by providing hot melt glue sticks accompanied by simple and light weight glue guns.
Several different types of hot melt glue sticks are available in the market. Typical characteristics of hot melt stick adhesive include:
Appearance: Water white to dark amber, clear to opaque glue sticks are all available. Normally, the light color and clear glue sticks are more expensive. Some of these look nice aesthetically but often offer insufficient adhesion performance when compared to dark adhesives due to their relatively low surface energy.
Color: Any customer required colors are possible upon specific request. Color is sometimes needed for craft, hobby, and certain artworks. Coloring agents can be organic dyes and inorganic pigments.
Size: Various diameters and lengths are readily available in the glue stick market, such as: 1/4″ dia. (diameter) mini x 4″ long, 7/16″ dia. x 4″ long, 7/16” dia. x 10″ long, 5/8″ dia. x 2″ long, 5/8″ dia. x 10″ long, 1″ dia. x 3″ long, 1-3/4″ dia. x 1-3/4″ long plugs. Technically, glue stick manufacturers are able to provide any diameter and length according to the selected glue guns and specific market needs. Among the above diameters, 7/16” (about 11.2 mm) diameter is the most commonly used size in this market. The consistency of the diameter plays the most important role for glue gun application.
Raw materials: Three thermoplastic elastomers are commonly used for making hot melt glue sticks, these are EVA (Ethylene Vinyl Acetate), APAO (Amorphous Poly Alpha Olefin), and PA (Poly Amides). Various tackifiers are also incorporated in these hot melt glue sticks. They are basically categorized as natural resin such as rosin and terpene derivatives, and synthetic petroleum hydrocarbon resins such as aliphatic, aromatic, and di-cyclo-pentadiene. PA glue stick is a 100% synthetic polymer without modifying any tackifying resins.
Basic Properties: Ring and ball softening point, and melt viscosity are two major physical properties shown on most technical data sheet.
Processibility: Open time, set time, and hot tack of hot melt adhesives are very important properties that will greatly affect the degree of bonding. Since these performances are greatly affected by the applicators, application conditions, and substrates, most data reported on technical data sheet are very subjective and are used for reference only.
Performance: Adhesion performance to various substrates is also very subjective and is greatly dependent upon the cohesive strength and surface energy of bonded substrates. A real world trial is always required before one can select an appropriate hot melt glue stick. Normally, the rosin derivative incorporated hot melt adhesives can offer better adhesion to low surface energy materials. However, the color of these adhesives is normally darker than their counterparts. Application at a higher temperature, like 190C (374F), is also very helpful for bonding onto low surface energy plastic substrates. Because the elevated temperature can melt the surface of plastics and induce more contact surface.
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