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Adhesives: Rubber vs. Acrylic |
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Adhesive selection:
Rubber vs. Acrylic
By Bill Jones
Bill Jones is a technical marketing manager for MACtac Technical Products (
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). For more information, call (800) 321-0011 or e-mail
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.
 Pressure sensitive adhesives (PSAs) have evolved from natural rubber/resin formulas to synthetic rubbers, acrylic multi-polymers and specialty chemicals. Despite these developments, it is important to understand the features and benefits of the two predominant types of adhesives ñ rubber/resin and acrylic.
Although both rubber/resin and acrylic adhesives can bond to most surfaces through special formulating techniques, each type has specific adhesion characteristics. Rubber-based types make excellent general-purpose adhesives because they stick well to many non-polar, low energy surfaces. Acrylic adhesives have good adhesion to polar surfaces such as metals, glass, polyesters and polycarbonates.
Rubber-based adhesives and non-crosslinked acrylics generally lose a great deal of their cohesive strength above 66°C. On the other hand, cross-linked acrylics can maintain most of their original strength and perform adequately at 93° to 121°C. Cold temperatures are easier on PSAs ñ most can be bonded as low as 10°C.
The degree of resistance is influenced by the duration of chemical exposure and product construction. Non-polar and rubber/resin adhesives are more resistant to polar chemicals such as active oxygen-containing solvents (esters, ketones, etc.). Polar acrylics are more resistant to hydrocarbon solvents (gasoline, petroleum naphthas, etc.).
 Plasticizers, which are often put into rubber and vinyl products to make them soft and flexible, affect PSAs by migrating into the adhesive and softening it, changing its adhesion properties. Rubber/resin adhesives are very susceptible to this plasticizing action, turning soft and gummy. Cross-linked acrylic adhesives are normally less affected.
Acrylic adhesives have the advantage of being inherently resistant to oxidation and ultraviolet (UV) light degradation. Rubber/resin adhesives have relatively poor resistance to the outdoors and may darken, lose their tack and become brittle if overly exposed, whereas acrylics remain virtually unaffected. Consequently, acrylics are normally selected for outdoor applications or for any use with direct exposure to sunlight.
Acrylic adhesives are known to be relatively expensive. However, with the advent of emulsion adhesives, some acrylics are much more cost effective. Comparing a solvent-based rubber adhesive to the water-based acrylic adhesive may add to the cost confusion. The actual cost of organic solvents and the special handling to make them EPA acceptable has added a significant cost to all solvent-based adhesives.
It is important to match the adhesive with your application needs and product construction to obtain the required performance at the most reasonable cost. MACtac offers both rubber and acrylic-based PSAs.
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