What are Pressure Sensitive Adhesives (PSAs) and how do they work?

Pressure Sensitive Adhesives are pressure sensitive sticking materials, generally delivered on one or two-sided substrate(s), made of plastic, cloth, paper, metal or other flexible materials, that bond two surfaces directly with some amount of pressure required and no need for additional agents such as solvents, water or heat to activate the adhesive. Simply stated, the adhesive systems in PSAs are generally made of polymer chains that are large molecules made of numerous (poly) interlinked and repeating chains of small molecules (monomers). These natural or man-made polymers are both viscoelastic and tacky, depending on their formulation, and can provide a wide range of properties, from elasticity for padding to ultra-thin coatings for medical applications.

The principle for activating a PSA is very simple: the user removes the protective liner, that typically uses a silicone release coating formulation, and applies the substrate, adhesive side exposed, to the surface that requires bonding.  The adhesive is generally made of natural or synthetic rubber, acrylic or silicone. The choice of which material to use is based on the application and performance requirements. For example, rubber-based adhesives are cost-effective, have quick sticking properties but are subject to melting when exposed to heat and cannot be used in all applications. Acrylic adhesives offer stronger bonding properties and are more resistant to solvents or heat but may not bond to all substrates. Silicone adhesives bond with substrates where organic adhesives do not perform well and applications can be as varied as skin, metal, or glass as well as bonding silicone components. They can  withstand higher temperatures than rubber or acrylic but are more costly and must be carefully formulated and used in critical applications. The choice of materials can only be determined by a review of the specifications, an understanding of the application, and the environment where the product will be used. This means that manufacturers of final products and PSA materials providers must work closely to find the right match between manufacturing processes, cost-effectiveness, and performance. 

Comparing Silicone PSAs with Rubber and Acrylic PSAs:

 

 

Silicone

Rubber

Acrylic

Tack

Low

High

Low/High

180° peel

Low/medium

Medium/High

Low/High

Shear

Medium

Low/ High

Low/High

UV resistance

Excellent

Poor

Excellent

Chemical resistance

Excellent

Poor

Good

Plasticizer resistance

Good

Poor

Medium

Bond to low energy surfaces

High

Medium

Low/High

Service temperature

-70°C to -270°C

0°C to -65°C

-40°C to -150°C

Service environment

Indoor / Outdoor

Indoor

Indoor/Outdoor

Cost

High

Low

Medium

 

How do silicone-based Pressure Sensitive Adhesives provide the best performance in a wide range of critical applications?

Let’s have a quick look at a few of many applications where silicone PSAs offer truly valued-added benefits.

Silicone PSAs for tapes, paper labels and protective linings

Silicone pressure sensitive adhesives can be specifically designed and formulated to serve many applications: masking tapes for painting and decorative surfaces that do not damage the existing surfaces, films for transparent screen protection liners that are truly resistant and enable tactile performance, safe and easy-to-install adhesive plastic or mica tapes for electrical and electronic insulation.

Silicone-based PSAs offer a variety of tack and peel adhesion options and are resistant to extreme exposure in all climates and environments. They bond well on low surface energy substrates, stick well on hard-to-wet surfaces, age well, and can be easily removed without leaving any residues.

Let’s take the example of silicone-based adhesive mica tapes that are used for critical electrical insulation in harsh environments. They provide excellent insulation as well as thermal conductivity and heat resistance.  These properties make them particularly valuable in applications such as energy generators, industrial facilities, or electrical vehicles where temperature variations can be extreme.

Silicone PSAs: providing wound care healing solutions for medical staff and patients

Healthcare product makers, like electronics manufacturers, are constantly innovating through the use of silicone-based ingredients and formulations to provide health professionals and their patients with biocompatible, hypoallergenic and non-invasive adhesives for bandages, dressings and surgical tapes. Silicone PSAs can be adapted to different types of injuries and skin types to prevent bacterial growth and keep out unwanted liquids and harmful substances, thus accelerating the healing process. Silicone PSA bandages and dressings enable easy removal and replacement to avoid exacerbating existing wounds and ulcers, thereby providing less pain and discomfort to patients. These medical-grade silicone solutions can also be designed to provide padding and protection to prevent further trauma, in the form of absorbent foam wound dressings, ulcer island dressings, post-operative dressings and multiple contact layers for negative pressure wound therapy (NPWT).

Silicone medical PSAs can be accurately adjusted for optimal tack and adhesion, variable viscosity and cured kinetics.  These properties can be further customized using different coating processes and various substrates in accordance with strict medical protocols.  Additionally, the use of these adhesives can also take into consideration the needs of all parties involved in the healing process: patients, care staff and cost-sensitive managers.

PSAs for Transdermal Drug Delivery Systems (TDDS): a non-invasive method for providing patients with medication

Transdermal Drug Delivery Systems (TDDS) are adhesive patches that carry medication through the skin to deliver specific doses into the body at a defined release rate. They are noninvasive, eliminating the need for injections, and accurately deliver medication into the body painlessly and gradually.

Medical grade silicone pressure sensitive adhesives are widely used to manufacture TDDS they provide distinct advantages over other traditional adhesive technologies, including biocompatibility, adjustable adhesion, and comfortable removal. They can be profiled by leveraging the versatility of silicone network specifications without the use of exogenous tackifiers, stabilizers, antioxidants, plasticizers or other potentially toxic extractable. 

You can learn more about silicone adhesives used in Transdermal Drug Delivery Systems by downloading the e-book: Main challenges to face when considering silicones for your transdermal patch.

Why silicone-based pressure sensitive adhesives are increasingly the materials of choice for key bonding, fastening and release applications

As we have seen above, silicone-based PSAs can be formulated to meet very exacting needs and specifications in very different applications, from electronics to medical applications. This is due to their versatility, their inertness and their performance potential in very different environments. The silicone industry is constantly searching for new and innovative formulations to meet current and future needs. This is why it is essential for manufacturers of high-quality products that require pressure sensitive adhesives to closely examine the advantages and the added value of silicone materials.