Pressure-sensitive adhesive (PSA), or self-adhesive, is used with many of our composite materials to simplify their application to the surface being treated. PSA is a thin, flexible adhesive coating that adheres to various surfaces.

Even though the technical performance of a material is not directly related to the adhesive, proper PSA application is critical. Many of the field problems we see with composite materials are actually due to adhesive failure.

How to Choose the Right PSA

You need to consider the following elements when selecting an adhesive:

• Surface Cleanliness
• Surface Type and Texture
• Environment
• Temperature & Humidity
• Weight of the Product

PSA comes in a variety of different formulations. Working with a materials supplier allows manufacturers to test conditions and adhesive strength and optimize the adhesive choice before designing it into an application. Below are the most common types of PSA adhesives manufacturers use.

Rubber Adhesive, also called SBR, is a cost-effect solution that provides quick stick capabilities and is easy to modify with antioxidants, oils, and tackifying resins. However, rubber adhesives are not suitable for applications with exposure to elevated temperatures, typically above 175°F.

 

Acrylic Adhesive is created using acrylic polymers and can withstand temperatures up to 250°F and greater. This type of adhesive forms a strong bond that is resistant to solvents and other environmental conditions. Formulations are available for standard and low-energy surfaces, which are more difficult to adhere to.

Silicone Adhesive primarily consists of silicone polymers. This unique formulation allows this adhesive to bond to silicone-based and low-energy surfaces and can withstand higher temperatures than rubber or acrylic adhesive, typically approaching 500°F. However, silicone adhesive tends to come with lower tack properties and higher production costs.

Surface Preparation for PSA

Cleanliness is a critical first step toward applying any adhesive, especially PSA.

If you don’t properly clean your surface before application, the risk of failure increases. For example, say you have a production line with a lot of residual dust in the environment. If you apply PSA to a dusty surface, the particles block the adhesive’s effectiveness, creating a weak bond that is subject to failure.

For manufacturers dealing with light dust, a microfiber or tack cloth works well to clean the surface. If you have to use a solvent to remove more difficult contaminates, choose one that meets your operational guidelines and leaves no residue on the intended surface.

Surface Texture

PSA requires a fairly smooth surface for optimum performance. The adhesive polymer must flow or wet out the surface to achieve its proper adhesion level. A textured surface may need a softer or higher-tack adhesive polymer to wet the surface properly. The more aggressive the texture, the more it may compromise adhesion.

Characteristics of Adhesive Performance

Adhesive performance is characterized by tack, peel, and shear. These factors define the type of bond an adhesive creates between two surfaces or between a material and the application surface.

• Tack is defined by how quickly an adhesive bond is formed when two surfaces are pressed together with light to moderate pressure. The faster the surfaces bond, the higher the tack. Tack is also sensitive to temperature. Subjectively, tack is related to how “sticky” the adhesive appears to be.
• Peel is defined as the measure of force necessary to break the bond between the surface and adhesive perpendicular to the surface. Most suppliers can provide manufacturers with peel testing data.
• Shear is the ability of the adhesive to resist lateral forces, typically parallel to the surface, such as gravity or the weight of the material that causes the adhesive to slide against itself. Shear is measured by the time needed for forces to cause the material to come loose from the surface when pulled parallel to the surface.

Shear, peel, and tack are interrelated. Adhesives with high tack have reasonable peel values but typically have lower shear values. Most high-shear adhesives have low or moderate tack but also high peel values. An adhesive with high shear and peel may not have sufficient tack to hold it onto the surface until the adhesive can wet the surface and gain adhesion.

How to Use PSA with a Composite Material

Here are the general steps when utilizing a PSA to bond a foam or composite insulator.

• Clean The Surface. This means the surface should be dry and free of contaminants like grease, dust, lint, or oil.
• Peel the Release Liner.
• Align the Material with the Surface. A low tack, high-shear adhesive is more forgiving when placing composite materials. It can more easily be repositioned. A very high tack adhesive will not allow for repositioning once applied.
• Apply pressure to the entire surface evenly. This allows the adhesive to wet the surface and form a proper bond. Around 15 PSI of force is needed to create an adequate bond. A roller is preferred, but most installations use hand pressure.

Find the Right Composite for Your Application

Polymer Technologies works with a broad range of material manufacturers and offers one of the widest selections of acoustical and thermal composites for OEM applications. Our technical expertise can deliver composite materials backed with the right PSA for your application. Contact us.