Performance Requirements

Type of Substrates

In most applications, two substrates are involved. One will bond with the unwind adhesive during the converting process and is called the “lamination” substrate. The other will bond with the liner side adhesive and is called the “mounting” substrate. Substrates come in many different forms and substances – however, a few characteristics are key:

Surface Energy

The surface energy of a substrate will affect the adhesive’s ability to ‘wet out’ or spread over the substrate. Low Surface Energy (LSE) materials resist adhesive wet out, making bonding more difficult. However, high surface energy materials allow excellent wet out and provide the best adhesion.

For example, picture an unwaxed car when it rains. The water spreads out (or wets out) on the car creating puddles. In this case, the car’s surface is displaying high surface energy. However, a waxed car will cause water to bead up because the car’s surface is displaying LSE characteristics. Since pressuresensitive adhesives bond well when they can wet out, they bond well to high surface energy materials (the unwaxed car) but not so well to LSE materials (the waxed car).

Rubber based and modified acrylic adhesives typically offer better adhesion to LSE substrates, as they are softer and flow better. Some materials will require corona treating, primers or top coating to promote better adhesion.

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Surface Texture

The texture of a substrate can affect the adhesive bond strength. Textured materials do not allow 100 percent contact of the adhesive to the substrate (less contact + less bonding area = lower bond strength).

Performance improvements to heavily textured materials can be achieved with proper product selection:

  • Heavier adhesive mass allows for more flow into material
  • Softer adhesives have better flow properties
  • A more aggressive adhesive maximizes bond strength at  contact areas
  • A more flexible tape conforms to textured materials
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Surface Contamination

Surface contamination prevents effective bonding. There are many types of surface contamination - some are not visible to the eye, but can be identified analytically. Simply cleaning the surface (washing or flame treating) will ensure an effective bond.

The surface may be contaminated if:

  • The presence of ‘loose’ material on the surface of the substrate is noticed
  • Material feels slippery, greasy and/or slimy
  • All surfaces tested appear to have the same poor bond and the adhesive feels non-tacky after being removed from the substrate


Common contaminants include:

  • Dust, anti-static agents, moisture, plasticizers and mold release  agents
  • Silicone (from other release liners), oils, anti-block coatings and powders

Surface Contour

The contour of the substrate will influence both the adhesive selection and the product selection. For conformability around irregular angles, materials with higher flexibility are recommended. Regardless of the adhesive’s strength, it is virtually impossible for an adhesive to overcome continued stress from a rigid material trying to return to its original form (memory).

  • Consider a conformable tape, such as a transfer tape or a double coated tape with a flexible carrier (tissue or nonwoven)
  • Consider adding stress relief to a converted part (e.g. scores, perforations)

Environmental Conditions

Several environmental factors can affect the performance of a tape:

Temperature During Application

Temperature of the substrate and/or the adhesive when applied or laminated. General minimum temperature recommendations are 50°F.

Temperature During Service

Temperatures to which the adhesive is exposed during the normal service life of the finished product.

General recommended ranges are 0°F to 400°F for acrylic based adhesives, -10°F to 225°F for rubber based adhesives and -50°F to +500°F for silicone based adhesives.

Humidity

Duration and intensity of moisture exposure.

Outdoor Conditions

From indoor to extreme weathering exposure.

Exposure to Chemicals

Including solvents, chemicals or fuels.

UV Exposure

Direct or indirect.

Required Bond Strength


Adhesives have many performance characteristics, which are specified and measured depending on the end application. Three common performance characteristics include adhesion, tack and cohesion. These characteristics and the recommended method of measurement are detailed below.

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Adhesion

Adhesion is the molecular force of attraction or bond between the adhesive and the contact surface. The strength of the attraction or bond is determined by the material’s surface energy and the chemical make-up of the adhesive. A pressure-sensitive adhesive’s measure of performance is expressed in ounces, pounds or the metric equivalents per inch width as the tape is pulled at a 90 or 180 degree angle, 12 inches per minute, usually off a polished stainless steel panel. A 90 degree version of this test is used when testing foam carrier tape adhesion.

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Tack

Tack is the property of a pressure-sensitive adhesive that allows it to adhere to a surface with very light pressure and a minimum contact time (often referred to as “quick stick”). It also refers to the ability of the adhesive to quickly “wet out” on the surface. During testing, no pressure is applied to the tape. Instead a loop of tape is lowered to a stainless steel or glass surface until contact is made. The tape loop is pulled back at 12 or 20 inches per minute.

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Cohesion

Cohesion, or cohesive strength, refers to the internal strength of an adhesive and its ability to resist splitting caused by external shear forces. Cohesion is measured by its resistance to forces parallel to the surface. A standard area of tape is applied to a vertical test panel; a standard weight is suspended on the bottom of the portion of the supported tape. Measurement is given in minutes until failure and/or distance slipped. Shear can also be measured in a Dynamic test (tensile tester-clamp moving 2 mm/min). Failure can be forced by conducting this test in an oven that gradually and consistently rises in temperature. The temperature at which the tape fails is called the Shear Adhesion Failure Temperature (SAFT).