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Why Solvent Based Adhesives Are Still Being Used?

Gary Avalon

There are 4 basic adhesive technologies used to manufacture Pressure Sensitive Adhesive tapes and labels: Solvent, Emulsion, Hot Melt and Radiation-Cure. Over the years the Industry has continued to work toward improving the performance of the more eco-friendly technologies, trying to move away from Solvents.

Unfortunately, while many applications are now served with emulsion, hot melt product or Rad-Cure adhesives, the current state-of-the-art has not been able to replace all of the solvent products for applications that use low surface energy materials such as PE, PP, Silicone, PTFE, PVA, PS and EVA.

Pressure –Sensitive Adhesives are developed using 3 basic polymer systems: Rubber, Acrylic and Silicone. Each system can be modified using additional ingredients such as tackifying agents, cross-linkers, plasiticizers and fillers depending on the end-use performance requirements and cost.

In solvent-based systems, the adhesive ingredients (polymers, tackifiers, etc.) are dissolved in the solvent solution and applied to a web of material. After coating, the solvent is dried off, leaving the adhesive residue. The solvents are captured during the process and delivered to a Thermal Oxidizer where they are decomposed at very high temperatures prior to being safely released to the atmosphere. Today this process is 95% efficient in treating these effluents.

In emulsion systems, the adhesive ingredients are emulsified in water, applied to a web and then dried. They require higher heat loads to drive off the water in the system than solvents, which evolve more rapidly. However, they do not need to be passed through a Thermal Oxidizer unless they have some toxic additives that may need treatment.

Hot melt adhesives are typically thermoplastic rubber systems that include tackifiers and oils so that they can be coated onto webs while hot (300F) and do not require any solvent or water. The downside of these systems is that they are usually more susceptible to high temperatures and lack the resistance for certain applications.

Radiation-curable (UV) systems typically require the use of heat to deliver them to the web and include acrylic monomers and photo-initiators, which need to be controlled/ ventilated due to their toxicity. They do not require water or solvent.

Performance is a key when deciding which system to pursue for your application. Solvent –based systems are fully dissolved and form one homogenous layer. They can be formulated to provide excellent adhesion and shear resistance for many Low Surface Energy materials (LSE). These substrates are being found in numerous products including automobiles, appliances, packaging and various medical and electronic devices.

Emulsion systems, especially the acrylics, exhibit better outdoor weather-ability and chemical resistance but typically fall short for adhesion to the LSE materials.

Radiation curable systems are gaining ground but have some of their own concerns with controlling monomers and photo-initiators. They also require investments in the radiation process technology, but have the benefit of a smaller footprint (space conservation) and no need for expensive drying ovens.

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