Selecting an Adhesive

When specifying an adhesive tape it is also important to know whether a rubber or acrylic-based adhesive is more appropriate for the application. Note: It is important to recognize that both types of adhesive, while they have different natural adhesion characteristics, can be made to bond to most surfaces through special formulating techniques.

Rubber-Based Adhesives

Rubber-based adhesives are comprised of a rubber structure and a variety of additives that impart special characteristics, such as oxidation resistance, color and stability. Rubberbased adhesives are also very thermoplastic. The addition of heat will soften the adhesive and directly affect its function.

Advantages

  • High initial bond to substrates
  • Adhere to a wide range of materials (polar and non-polar)
  • Generally very economical
  • Resistant to polar chemicals (active oxygen-containing solvents)

Disadvantages

  • Poor cohesive strength at elevated temperatures [150° F (66° C)]
  • Fair to poor resistance to non-polar chemicals
  • Generally poor resistance to ultraviolet light and oxidation
  • Susceptible to plasticizer migration

Acrylic-Based Adhesives

As copolymers, acrylic-based adhesives do not require as many additives as rubber-based adhesives. In fact, the addition of other ingredients tends to detract from their strength. Acrylics are thermoplastic by nature; they soften when exposed to heat and harden when cooled. They are formulated or polymerized to relatively low molecular weights (short chain lengths) so that they are inherently soft at ambient temperatures.

Advantages

  • Good adhesion to polar substrates (metal, glass, polyesters, polycarbonates, etc.)
  • Acrylic adhesives are cross-linkable
  • Deliver good resistance to varying temperature ranges [-50° F (-45.5° C) to 350 °F (176° C)]
  • Good resistance to chemicals (gasoline, petroleum naphthas, etc.)
  • Good adhesion to irregular or rough surfaces
  • Age well in presence of ultraviolet light, corona and oxidation
  • Very color stable
  • Can be easily removed and reinstalled in the application if positioned incorrectly
  • Offer excellent oxidation and plasticizer resistance

Disadvantages

  • Generally have poor adhesion to non-polar surfaces (polyethylene, polypylene, etc.)
  • Tend to be more expensive
  • Initial bond or tack strength is low (it can take 48 to 72 hours to achieve ultimate strength)

Achieving Maximum Adhesion

  1. Surface Preparation. Although the type of bonding surface is important, it should be noted that one of the most critical and overriding factors in adhesion is the condition of the bonding surface. The presence of surface contaminants, such as oils, grease, plasticizers, mold release or dirt in general, can cause adhesive failure regardless of the specific adhesive. Isopropyl alcohol can be used to remove most surface contaminants.
  2. Sufficient Pressure. Sufficient pressure must be applied to get full contact (wet-out) between the substrate and the adhesive to create the best bond.
  3. Proper Storage. Adhesives should be stored in a dry, dust-free environment and at room temperature.

(The preceding information on PSA joining systems was taken from the MACtac Engineered Products OEM and Converter Guide, copyright MACtac 2004, and 3M Brochure 70-07030-7540-0, copyright 3M 1991.)