"Adhesives" are defined as materials that adhere simply by pressing together the parts of the joint to be bonded. At room temperature, they show a permanent and permanent bond.
Hot melt adhesives are solvent-free adhesives. This means they are solid at temperatures below 180°F (82°C), become low viscosity liquids above 180°F, and quickly harden on cooling. Before the development of hot melt technology, melted wax was used for gluing. When melted wax was no longer an effective solution, thermoplastic systems were introduced. Hotmelt technology emerged from this development. Get more here about this or electronics assembly adhesives.
Adhesive technology now
Today, these adhesives are used in a variety of manufacturing processes, including packaging, bookbinding, and product assembly. There are a number of hot melt adhesives, the most common of which are those used for pressure sensitive hot melt applications:
• Ethylene vinyl acetate (EVA) copolymers compatible with paraffin, the original hot melt
• Styrene Isoprene Styrene (SIS) copolymers
• Styrene Butadiene Styrene (SBS) copolymers
• Ethylene ethyl acrylate copolymers (EEA)
• Polyurethane Reactive (PUR) For the most part, additives such as resins, waxes, antioxidants, plasticizers and other materials are combined with these polymers to allow them to perform at their best.
Some of these adhesives have found acceptance in many manufacturing industries where they can be applied to small joints to eliminate the use of mechanical fasteners such as staples, screws, rivets, staples, snaps, nails or stitching.
Usage & Properties
Today's adhesives are primarily used in packaging, textiles, labels, tapes and other pressure-sensitive applications, disposable products, postage stamps, envelopes, and product assembly processes. Conventional household products such as diapers and disposable pads are made using this technology, along with a significant amount of food packaging.
Hot melt processes
Production is a continuous process. In most cases, a compounder is used to create a homogeneous melt. After plasticizing/masticating and compounding the various rubbers, the resins (solid or liquid) and plasticizers/oils are added downstream. For larger quantities, the liquid can be fed in at several points along the extruder via several kneading and homogenization stages.
Feed rates and ingredients
Typical throughput ranges are 100 - 1000 kg/hr (220 - 2200 lb/hr).
Depending on the recipe and the number of ingredients, typical dosages are:
• Elastomers: 30-50%
• Resins: 20 - 40%
• Plasticizers / oils: 10 - 40%
• Fillers: 1 - 10%
• Color pigments: 0.1 - 3%, stabilizers: 0.1 - 3%
High accuracy requirements
High performance requirements are placed on the various types of hotmelt in terms of the types of use and stress on the connection points, temperature, range, service life, etc. Typically, there is a rather short residence time (from 10 - 20 seconds) in the mixing zone of the extruder. In order to ensure a consistently high quality of the end product, a consistently high dosing accuracy is required for the additive dosing system.
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