Navigating the Complexities of Bonding Plastics with PSA Tapes
Plastic substrates present unique challenges when it comes to bonding. There are many different types of plastic surfaces; the materials are diverse, and each have their own unique chemical composition and physical properties. This requires a specialized approach to successful adhesive bonding. The process of selecting the best pressure-sensitive adhesive (PSA) tapes for bonding plastics involves understanding the specific substrate you are working with, and which types of adhesive tapes will adhere to it. What are the specific challenges, and how can you choose a PSA tape that works well?
Bonding Plastics Presents Numerous Challenges
Plastic materials present a very specific set bonding of challenges:
Material Compatibility
There are hundreds of types of plastics and each of these have many different vendor formulations. The chemical makeup of each one significantly influences its compatibility with different adhesive tapes. It’s important to select the right adhesive tapes that can form a strong bond with the specific plastic material.
Surface Energy
The surface energy of a material refers to the excess energy at the surface compared to its bulk. It's a measure of how well the materials can wet out or adhere to other materials. Plastics can be broadly categorized into low surface energy plastics (LSE) and high surface energy plastics (HSE) materials. As an important note, high surface energy plastics are still more challenging to bond to than high surface energy metallic surfaces.
Low surface energy plastics have weaker cohesive forces at their surface. This means that molecules at the surface are less attracted to each other and to other materials, making it difficult for liquids and adhesives to wet out or spread across these surfaces. LSE plastics, like PFTE, polyethylene, and polypropylene, are notoriously difficult to bond due to their non-polar, chemically inert surfaces. These materials often require surface treatment or special adhesives to improve adhesion.
Plastics with higher surface energy have molecules at their surface that exhibit stronger cohesive forces, meaning they are more strongly attracted to each other. The higher this characteristic the better the wetting properties when in contact with liquids or adhesives, as these materials can more easily spread over the surface of a high surface energy material. HSE plastics, such as PVC and acrylic, present a better surface for adhesive bonding, and adhesives and coatings typically adhere well to these materials without the need for special treatments.
Thermal Expansion
Different plastics exhibit varying degrees of thermal expansion, potentially stressing adhesive joints under temperature fluctuations which can lead to bond failure.
The Application’s Environment
The application environment, including exposure to chemicals, moisture, and UV light, can impact the longevity and effectiveness of the bond. Make sure to choose a PSA tape with appropriate resistance to your application's environmental conditions.
Off-Gassing
Plastic parts are made by combining plastic pellets and colorants at temperature to extrude, pour, or shape the cooling material into its final state. Oftentimes, through this process the plastics material will off-gas for hours, days, and weeks. Off-gassing is the escape of gasses from the cooling, curing plastic. Some plastics and some brands of plastics within one category will off-gas more than others, while some plastics take weeks to finish this process without forced acceleration. If these gases are constrained by a PSA, the result will be adhesion voids occurring within the bond. These voids will dramatically weaken the adhesive bond and likely result in bond failure.
The Best PSA Tapes for Low Surface Energy (LSE) Plastics
Fortunately, PSA tape vendors have long known about the challenges of bonding LSE plastics. Over time, they have continued to deliver innovative solutions to meet this challenge.
Modified Acrylic-Based Adhesives: these adhesives offer long-term durability and are adept at resisting environmental factors such as moisture, UV light, and temperature extremes. They are particularly effective for LSE plastics, providing a robust bond that withstands challenging conditions. These types of tapes are often used in automotive trim attachments, outdoor equipment labeling, and signage for polyethylene surfaces.
Some acrylic PSA tape options include:
Rubber Adhesives: known for their enhanced initial tack, rubber adhesives can form strong bonds quickly with difficult-to-bond LSE plastics, making them ideal for applications requiring immediate adhesion. Their limited environmental and temperature resistance makes them ideal for lighter duty indoor applications. These types of adhesive tapes are often used on polypropylene automotive parts or for fastening components in consumer electronics.
Some rubber PSA tape options include:
Silicone Adhesives: silicone excels when bonding with other silicone-based substrates, offering remarkable performance across extreme temperatures, from very high to low. Typically, their overall bond strengths are lower, and they are more expensive than the acrylic and rubber-based PSA options. These types of adhesive tapes are often used in high temperature sealing applications, or insulation wrapping in electronics.
Some silicone PSA tape options include:
The Best PSA Tapes for High Surface Energy (HSE) Plastics
For HSE plastics, the bonding challenge is significantly reduced, allowing for a broader selection of adhesive tapes. The most important factor to consider is the specific environmental conditions, resistances, and physical stressors that will be applied to your bond. Make sure to choose a PSA tape that can fit your application’s parameters. However, as mentioned above, there are many factors that can still make high surface energy plastics a challenge to bond. While most rubber-based PSA tapes should bond well, if you need an acrylic PSA tape for higher application performance, it is still smart to test your PSA adhesion. Typically, general purpose acrylic tapes are the best place to start.
General Purpose Acrylic PSA tape options include:
Find the Best PSA Tapes for Plastics
At Engineered Materials, we specialize in finding the right bonding solution for any material. We custom fabricate PSA tapes for our clients and can even laminate tapes to fit any substrate in any application. We’re here to help you solve your most challenging bonding issues. Just let us know what materials you are working with and how your tapes need to be used; we’ll help you find the right solution.