Waterborne adhesives

Waterborne adhesives were conceived as environmentally friendly, healthier alternatives to solvent-based adhesives. They are used in a wide variety of end uses. For non-pressure sensitive adhesive applications, flooring adhesives, and contact adhesives command the largest volumes. For pressure sensitive adhesives (PSA) the largest single-use is for labeling but with rapid growth in a variety of tape applications including office tapes and packaging tapes.

As with other adhesive technologies, waterborne polymer alone usually cannot impart the optimum adhesion to the adhesive. Tackifier resins are required for improving the adhesion to many different substrates. For example, polychloroprene-based adhesives for contact assembly applications are used to bond to a wide variety of substrates including leather, wood, canvas, PVC and more. Solvent borne polychloroprene-based adhesives have been used for many years combining rubber, tackifier, and other ingredients in order to create a system with general adhesion. Changing the vehicle for the adhesive to water does not remove the necessity of formulating the system with the same types and concentrations of modifiers as are used in the solvent borne system.

Tackifier resins are low molecular weight, thermoplastic, non reactive, and water insoluble materials. In water-based and hot melt adhesives the base polymers and resins are easy to combine in a homogeneous system. When the base polymer is an emulsion, the tackifier resins must also be dispersed in water. Since the tackifier resins are by nature hydrophobic, this presents a considerable technical challenge.

The first water dispersions of adhesives used materials dissolved in solvent and then dispersed in water using appropriate emulsifiers. This solvent cut technique works well, but produces dispersions with a considerable concentration of organic solvent. In North America, Europe, and parts of Asia the environmental protection regulations have become more restrictive and solvent cut based adhesives have been banned in many countries. In much of the world, adhesives with less than 10% volatile organic compounds (VOCs) are now required.

Waterborne tackifier resin dispersions are commonly used for PSA label, decal, or tape applications based on acrylic emulsion polymers or various types of natural or synthetic rubber latex. The major uses are general-purpose permanent, removable, deep freeze, wine bottle, and wash-off applications. In order to improve the adhesion, and to make the PSA bond on a variety of substrates, suitable water-based tackifier resins are added.

Waterborne tackifier resin dispersions:
• Improve specific adhesion especially to polyolefinic and paper substrates.
• Improve flow and wetting out properties of the adhesives.
• Provide an optimum balance between tack, adhesion and cohesion.

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