Hot Melt Adhesives in Production
Hot Melt Adhesive are defined as materials that adhere simply through pressing together the parts of the joint which requires bonding. At room temperature, they demonstrate a lasting and permanent bonding.
Hot melt adhesives are solvent-free adhesives. This means that they are solid at temperatures below 180°F (82°C), become low viscosity fluids above 180°F, and set rapidly upon cooling. Prior to the development of hot melt adhesive technology, molten wax was used for bonding. When molten wax was no longer an effective solution, thermoplastic systems were introduced. Hot melt technology stemmed from this evolution.
Uses & Properties
Today's adhesives are used primarily for packaging, textiles, labels, tapes, and other pressure sensitive applications, disposable products, stamps, envelopes and product assembly processes. Common household products like diapers and disposable pads are made from 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 produce a homogenous melt. After plasticizing/masticating and compounding the various rubbers, the resins (solid or liquid) and softeners/oils are added downstream. For larger quantities, the liquid can be fed at several locations along the extruder, using multiple kneading and homogenizing stages.
Feedrates and Ingredients
The typical throughput ranges are 100 - 1000 kg/hr, (220 - 2200lb/hr).
Depending on the recipe and number of ingredients, typical feed rates are:
• Elastomers: 30-50%
• Resins: 20 - 40%
• Softeners / Oils: 10 - 40%
• Fillers: 1 - 10%
• Color pigments: 0.1 - 3%, Stabilizers: 0.1 - 3%
High Accuracy Requirements
There are tough performance requirements on the various types of hotmelts with regard to working load and types of stress on the joints, temperature, range, lifetime etc. Typically there is a rather short residence time (as little as 10 - 20 seconds) in the extruder's mixing zone. To ensure constant high quality of the end product, a continuous high feeding accuracy is required for the additive feeders.
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