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Silicone vs. Acrylic Adhesive:
Polyimide tapes are made of two distinct layers, each of which is critical to the properties of the final product. The first layer is the Polyimide film (also known as Kapton® made by DuPont) and the second layer is the adhesive applied to the film. Most of the tapes have Silicon adhesive while some applications require an Acrylic adhesive.
Polyimide film is a kind of a high performance polymer through polycondesation of symbenzene tetracarbonic acid dianhydride and diaminodiphenyl ether, which combines excellent physical, electrical, and mechanical properties at temperatures as low as -452°F (-269°C) and as high as +752°F (+400°C). PI film offers excellent dimensional stability combined with excellent chemical resistance.
Silicone adhesives:
Silicones have been used to formulate adhesive products for decades due to their flexibility, high temperature resistance, chemical resistance, electrical insulation, solvent resistance and radiation protection.
Polyimide tape with Silicone adhesive is made by having a Polyimide film coated it with a heat-resistant silicone adhesive. Silicone offers better elongation at break, and is used for electrical insulation of electrical equipment and high temperature insulation. It offers the highest heat resistance among film adhesive tapes, so it can also be applied for insulation in high-end electronic equipment, motors, and Lithium (Li) batteries. Other applications include the protection of the gold fingers on Printed Circuit Boards (PCBs) during wave soldering, as lead-free solders often require re-flow temperatures up to 5000°F/260°C - leaving no adhesive film once the tape is removed.
Silicone adhesives have the following general characteristics:
- High flexibility at sub-ambient temperature
- Consistent performance over wide temperature range (for Polyimide application)
- Excellent ageing and UV resistance (LED application)
- High temperature resistance
- Good resistance to polar solvent
Acrylic Adhesives:
Acrylic adhesives can either be water-based (emulsion or dispersion) or solvent-based. Water-based are slower drying compared to solvent-based systems but generally solvent-based acrylic systems have better resistance to other solvents, chemicals and water. Comparatively, water-based systems are less expensive than their solvent-based counter parts.
Polyimide Acrylic Tape uses the same process as the silicone process described above, but it cannot withstand the high temperature range of the silicone PSA described above. Acrylics tend to be more brittle, so the lower temperature range is also somewhat more limited as the adhesive can crack at extremely low temperatures. The Polyimide film itself is still able to withstand a wide temperature range and can still be used in many of the same high-temperature applications but the adhesion properties of the film become more limited due to acrylic adhesive and its properties.
Acrylic adhesives share the following characteristics:
- Reasonable adhesion to a wide range of substrates
- Good aging, transmittance and UV resistance (Fiber Optic application)
- Reasonable temperature resistance but below silicone adhesive’s high temperature threshold
Acrylic adhesive has a lower tack (stickyness when dry) and less adhesion on hard-to-bond plastics such as high- and low-density polyethylene (HDPE & LDPE) and polypropylene (PP). Acrylic adhesives are primarily used on tapes whose applications are bonding, sealing or surface protection.
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