Omar Khalid
Low Surface Energy (LSE) plastics are solid materials with low surface energy that present challenges for adhesives to bond with. The surface energy of a material quantifies the disruption of intermolecular bonds and indicates the strength of the affinity between molecules. LSE plastics have molecules on the surface with low energy that cannot easily join with the molecules of adhesives. This results in minimal contact and weak bonds. To address this issue, manufacturers often use primers, surface treatments, or specially formulated adhesives to increase the surface energy and improve adhesion. Examples of LSE plastics include polyethylene, polypropylene, and polytetrafluorethylene (PTFE). These plastics are commonly used in packaging, containers, and various applications where their unique properties are advantageous.
| Characteristics | Values |
|---|---|
| Definition | Plastics with very low surface energy |
| Surface energy | Below 36 dynes/cm |
| Adhesion | Difficult to bond with adhesives |
| Surface wetting | Poor wetting |
| Bonding | Requires special adhesives and surface preparation |
| Surface preparation | Degreasing, abrasion, priming, flame treatment, corona treatment |
| Examples | Polypropylene, polyethylene, TPOs, PTFE, polyolefin plastics |
| Applications | Packaging, containers, bottles, sporting equipment, appliances |
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What You'll Learn
- Low surface energy plastics are difficult to bond with adhesives
- Surface energy is quantified by disruption of intermolecular bonds
- Surface energy can be measured using the Wetting Method
- Priming is a common way to prepare plastics for bonding
- Specialty adhesives can bond LSE plastics without pre-treatment
Low surface energy plastics are difficult to bond with adhesives
Low Surface Energy (LSE) plastics have very low surface energies, making it challenging for adhesives to wet out and bond. The surface energy of a material quantifies the disruption of intermolecular bonds, and a higher value indicates a stronger affinity between molecules. However, the molecules on the surface of LSE plastics have low energy and struggle to join with the molecules of adhesives.
The low surface energy of these plastics prevents adhesives from flowing out across the surface and achieving intimate contact. As a result, conventional adhesives and tapes may not be suitable for bonding LSE plastics, leading to minimal contact and weak bonds. Traditionally, LSE plastics have been primed, flame-treated, or corona-treated to increase surface energy and improve bonding with conventional adhesives.
To address this issue, specialty adhesives have been developed to provide high-strength adhesion to LSE plastics. These adhesives can bond various LSE plastics, including polypropylene, polyethylene, and TPOs, without requiring special surface preparation. For instance, 3M offers a range of double-sided acrylic foam tapes specifically designed for low surface energy substrates, creating strong bonds without the need for primers or promoters.
Additionally, surface preparation techniques can enhance adhesion to LSE plastics. Cleaning the surface with isopropyl alcohol and applying a primer can increase the surface energy and promote better adhesion. Manufacturers can also modify their adhesives by adding tackifiers, softening the adhesive resin, and improving its ability to "wet out" the substrate. These advancements in adhesive technology enable stronger and more efficient bonding of LSE plastics, expanding the possibilities for product design and performance.
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Surface energy is quantified by disruption of intermolecular bonds
Low Surface Energy (LSE) plastics are a type of solid material with low surface energy. The surface energy of a solid is the energy at the surface resulting from incomplete bonding. In solid-state physics, surfaces must have higher energy than the bulk of the material, or else there would be a driving force for surfaces to be created, removing the bulk of the material by sublimation.
The most common way to measure surface energy is through contact angle experiments. This involves measuring the contact angle of the surface with several liquids, usually water and diiodomethane. The contact angle method is simple, quick, and applicable to a wide range of surfaces. The contact angle is the angle at which a liquid contacts a solid surface, and it depends on the surface energy of the solid. A lower surface energy will result in a higher contact angle, as the surface will not want to interact with the liquid.
The surface energy of plastics specifically defines the adhesion strength. LSE plastics are difficult to bond because their surface molecules have low energy and cannot join with the molecules of an adhesive. This presents bonding challenges, as adhesives struggle to "wet out" and bond with LSE plastics.
To improve the surface energy of plastics and make them more amenable to adhesion, methods such as corona, flame, or plasma surface treatment can be used.
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Surface energy can be measured using the Wetting Method
Low Surface Energy (LSE) plastics have very low surface energies, which makes them challenging for adhesives to bond with. The surface energy of plastics quantifies the disruption of intermolecular bonds in the material. A higher value indicates a stronger affinity between molecules, which determines how readily these molecules bond to other substances.
The Wetting Method can be quantified using the Young-Dupré equation, which relates the interactions between the liquid and solid to surface tension and contact angle. The spreading coefficient measures the tendency for a liquid to wet a solid, where wetting occurs for positive values. This can be further broken down into the spreading parameter, S, which distinguishes the two different regimes of wetting. If S is positive, the liquid spreads completely to lower its surface energy. If S is negative, partial wetting occurs.
The contact angle is another important factor in the Wetting Method. This is the angle formed between the liquid and the solid surface. If the contact angle is less than 90 degrees, the liquid is considered "mostly wetting". If the contact angle is greater than 90 degrees, the liquid is considered "mostly non-wetting".
The Wetting Method is a simple and effective way to determine the surface energy of plastics, which can impact their bonding and coating properties.
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Priming is a common way to prepare plastics for bonding
Low Surface Energy (LSE) plastics are solid materials with low surface energy, which makes them difficult to bond with adhesives. The surface energy of a plastic quantifies the disruption of intermolecular bonds in the material. A higher value indicates a stronger affinity between molecules, which makes it easier for the molecules to bond with other substances.
First, the plastic surface needs to be cleaned and degreased with a volatile solvent such as isopropyl alcohol to remove any dirt or contaminants. This step may need to be repeated after abrasion to remove debris. Next, the surface should be abraded or roughened with sandpaper to enlarge the bonding area and improve adhesion. This step may not be possible for all plastics, so caution must be exercised.
After abrasion, the surface can be treated with a flame, plasma, or corona treatment to increase surface energy. Flame treatment involves exposing the surface to a gas flame for a few seconds, which oxidizes the surface and increases surface energy. Plasma treatment involves activating gas plasma under a partial vacuum to produce excited species that react with the plastic substrate, providing better stability. Corona treatment is similar but does not provide the same level of stability.
Finally, the plastic surface is ready for priming. Priming seals the surface and prepares it for bonding with adhesives. This step may not be necessary for all plastics, as some adhesives are designed to bond with LSE plastics without the use of a primer. However, for plastics with very low surface energies, a primer may be required to ensure a strong bond.
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Specialty adhesives can bond LSE plastics without pre-treatment
Low Surface Energy plastics (LSE) are solid materials that have low surface energy due to the molecules on their surface having low energy. This makes them difficult to bond with adhesives as they cannot join with the molecules of the adhesive.
LSE plastics include materials such as polypropylene, polyethylene, polystyrene, acetal, EVA (ethylene vinyl acetate), and powder-coated paints. They are generally soft and have a low melting point, making them easy to process and mold. However, their low surface energy makes them challenging to bond with traditional adhesives.
To bond LSE plastics, various methods can be used, including priming or surface treatment. Primers can create a strong chemical bond with the plastic and form a new layer for the adhesive to adhere to. Surface treatments such as corona, plasma, and flame treatment can alter the chemical structure of the plastic's surface, increasing its surface energy and making it more receptive to adhesives.
However, these traditional methods may add complexity to the manufacturing process and increase production time and costs. In response to these challenges, specialty adhesives have been developed that can bond LSE plastics without the need for pre-treatment. These adhesives can permeate the material's surface and create a strong mechanical and chemical bond without the use of primers or promoters, reducing overall production time.
One example of such an adhesive is the two-part, acrylic-based adhesive offered by 3M, which can bond various low surface energy plastics, including polypropylene, polyethylene, and TPOs, without special surface preparation. This adhesive eliminates the need for mechanical fasteners, primers, or additional surface treatments, simplifying the bonding process and improving efficiency.
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Frequently asked questions
Low Surface Energy (LSE) plastics have very low surface energies, making it challenging for adhesives to bond with them.
The simplest way to identify low surface energy plastics is through the Wetting Method. When water drops are sprinkled on the plastic and they do not spread, it means the plastic has low surface energy.
Examples of low surface energy plastics include Polypropylene, Polyethylene, Polyolefin, and Polytetrafluorethylene (PTFE).
The low surface energy of these plastics makes it difficult for adhesives to bond with them, requiring special adhesives or treatments.
Solutions for bonding LSE plastics include using specialty adhesives, applying a primer, or treating the surface through abrasion, flame, or corona treatment to increase surface energy and improve adhesion.
