Polyimide (Kapton) tape is widely recognized for its ability to withstand both sub-zero and high temperatures; however, how does it actually behave across this broad range? Surprisingly, the answer to this question has little to do with the polyimide base film itself and more to do with the “tape” (i.e., the adhesive used to make it sticky).
As mentioned in an earlier article, “How Polyimide Tapes are Made,” polyimide (Kapton) tapes have two layers: a polyimide base film and an adhesive layer, typically made of either acrylic or silicone.
Polyimide tapes with silicone adhesives have an operating temperature range between –73 °C (–100°F) and 260 °C (500 °F). In contrast, polyimide tapes with acrylic adhesives have a more limited operating temperature, –30 °C (–22 °F) to 175 °C (347 °F).
In this article, we will compare acrylic and silicone adhesives for these tapes, highlighting their respective advantages and discussing their performance at different temperatures.
Acrylic Adhesives for Polyimide Tapes
Acrylics are commonly used in adhesives for polyimide (kapton) tapes for many reasons, including:
- Adhesion to a wide range of materials and plastics in particular
- Very fast curing time
- Temperature range: –30 °C (–22 °F) to 175 °C (347 °F)
- Low outgassing
- High tensile and shear stress properties
- Transparency for aesthetics
- Chemical resistance
To understand the benefits and why we would choose an acrylic-based polyimide tape, we must first understand acrylics.
Acrylic is a synthetic material commonly used in plastics, resins, paints, and textiles. In tapes, the adhesive component is an acrylic polymer, typically made from a blend of acrylic monomers formulated to meet specific performance requirements. The molecular structure of acrylic polymers contributes to their exceptional adhesion strength and tensile/shear properties. The polymer backbone consists of multiple linked carbon atoms, which impart stability and durability. In addition, many formulations incorporate cross-linked polymers, further enhancing their strength.
These characteristics make polyimide tapes with acrylic adhesives suitable for a broad range of applications, including electrical insulation, temporary and permanent bonding, and masking. As a result, they are widely favored in industries such as aerospace, medical, automotive, and manufacturing.
Silicone Adhesives for Polyimide Tapes
Silicones have been used for decades to formulate adhesive products due to their flexibility, temperature cycling resistance, chemical resistance, and wide range of material properties. Silicone adhesives have the following general characteristics:
- High flexibility (low modulus) at sub-ambient temperature
- Consistent performance over the wide temperature range
- High-temperature resistance / great thermal stability
- Temperature range: –73 °C (–100 °F) to 260 °C (500 °F).
- Good resistance to polar solvents
- Excellent electrical resistance
- Good adhesion to many materials including metals, plastics, glass, and ceramics.
- Hydrophobic
Like acrylic, silicone is a synthetic polymer. It is composed of siloxanes, and used in materials such as lubricants, sealants, insulating materials, and cookware. The Si–O bonds in silicones are stronger and more thermally stable than the carbon–carbon bonds in acrylic, allowing silicones to handle higher temperatures than acrylic adhesives.
Silicone adhesives are also highly flexible due to their Si–O backbone, which allows movement of the polymer chains without bond breakage. This flexibility, combined with a low glass transition temperature (Tg = –60 °C), enables silicones to remain soft and flexible even at extremely low temperatures. Another key advantage of silicone adhesives is their resistance to polar solvents, such as water, alcohols, and ketones. Its polarity allows silicone to be inherently water resistant, which comes in handy when working in conditions where moisture is a concern and might affect the adhesive.
Silicone-based polyimide tapes are a popular choice due to their wide temperature range and excellent electrical resistance. Their flexibility and insulating properties make them ideal for bonding and masking electrical components, wafer dicing, die cutting, and high-temperature masking. Like acrylic tapes, they are widely favored in industries such as aerospace, medical, automotive, and manufacturing.
Key Differences between Acrylic and Silicone Adhesives
Silicone-based adhesives are certainly more standard, but sometimes a customer might require an acrylic adhesive because they cannot have silicone in their systems. Another reason might be the need for higher adhesion at mid-range temperatures. Choosing between silicone and acrylic adhesive varies vastly based on the application requirements.
| Material | Acrylic | Silicone |
| Chemistry/Structure | C–C Bonds | Si–O Bonds |
| Operating Temperature | –30 °C (–22 °F) | –73 °C (-100 °F) |
| Operating Temperature | 175 °C (347 °F) | 260 °C (500 °F) |
| Flexibility | ■■■□ Flexible | ■■■■ Very Flexible |
| Chemical Resistance | ■■□□ Moderate | ■■■■ High |
| Electrical Insulation | ■■■□ Good | ■■■■ High |
| Cost | ■■■□ Less expensive | ■■■■ More expensive |
Comparing Performance of Acrylic and Silicone Adhesives across Temperature Extremes
Acrylic adhesives are brittle at lower temperatures, limiting their performance. At extremely low temperatures (below –30°C), the adhesive can crack. On the other hand, exposure to high temperatures (>175°C) can cause acrylics to soften or melt. In polyimide acrylic tapes, the polyimide film itself can withstand a wide temperature range and remain suitable for many high-temperature applications. However, the overall adhesion properties of the tape are limited due to the acrylic adhesive.
Generally, acrylic adhesives offer higher adhesion strength than silicones in mid-range temperatures (0 to 100 °C). In contrast, silicone adhesives provide superior adhesion at both lower temperatures (<0 °C) and higher temperatures (> 100 °C). At low temperatures, silicone adhesives are less prone to cracking than acrylic adhesives due to their chemical composition and flexibility. NOTE: While silicone adhesives can withstand both higher and lower temperatures compared to acrylics, they still have their limits. When exposed to extreme temperatures (>260 °C), the chemical bonds in silicones begin to degrade, resulting in a loss of adhesive properties. As the silicone softens, the adhesive strength weakens.
Just a side note: Now that we have covered how temperature affects adhesion, it is worth mentioning that the adhesive strength of polyimide tape is independent of its thickness (1, 2, or 5 mil) provided the adhesive layer thickness remains constant. As shown in Table 2, the adhesion strength of LINQTAPE PIT1S, PIT2S, and PIT3S to steel remained the same, even though the tapes had different thicknesses, because they all used 1.5 mil-thick silicone adhesives. The same holds true for LINQTAPE PIT1A, PIT2A, and PIT3A. This observation depends on the substrate the tape adheres to, and other variables can affect how the adhesive performs, but this is a good rule of thumb.
| Product | Description | Film Thickness [mil] | Adhesive Thickness [mil] | Adhesion Strength to Steel [oz/in] |
| PIT1S | 1 mil polyimide tape with silicone adhesive | 1 | 1.5 | 25 |
| PIT2S | 2 mil polyimide tape with silicone adhesive | 2 | 1.5 | 25 |
| PIT3S | 3 mil polyimide tape with silicone adhesive | 3 | 1.5 | 25 |
| PIT1A | 1 mil polyimide tape with acrylic adhesive | 1 | 1.5 | 25 |
| PIT2A | 3 mil polyimide tape with acrylic adhesive | 2 | 1.5 | 25 |
Polyimide (Kapton) Tapes with Silicone and Acrylic Adhesives available at CAPLINQ
Choosing the right polyimide (Kapton) tape is critical for improving protection and reliability in many high or low-temperature applications, so an application-specific assessment should be conducted. Contact us and our application engineers and in-house experts will help you out with product selection for your application requirements.
