Polymide pressure sensitive adhesive (PSA) tape is actually made up of two separate steps. The first is the manufacture of the polyimide film itself, and the second is applying an adhesive backing depending on the intended application.
Polyimide Tape is made up of two separate steps. First is the manufacture of the polyimide film itself and the second is the application of the adhesive backing.
The required carrier or backing material is coated with cohesive adhesive. The correct combination of carrier and adhesive depending on the various quality factors required is very essential for manufacturing good quality PSA tapes. The non-release side of the carrier (after passing it through surface treatments such as priming, release-coating, corona-treatment, and waterproofing etc. if required) is coated with adhesive using different coating methods such as coma-coating, Mayer-bar coating, etc. depending on the coating weight, carrier type.
The carrier along with the coated adhesive is then passed through an oven chamber in which the required temperature is set, depending on the type of adhesive and carrier being used, that is required to cure the adhesive. The PSA tape after passing through the heated chamber is winded on to a jumbo roll which is then stored in a curing room for a minimum of 7 days.
On completion of 7 days of curing, the jumbo roll is then transferred to the rewinding and logging station, during which the jumbo roll undergoes quality check such as any occurrence of adhesive transfer, uneven coating, whether the carrier has developed wrinkles or has been unevenly stretched.
The final process is transferring the good quality jumbos either to warehouse for processing of future orders or to the conversion station where the jumbo roll is converted into log rolls or cut-size rolls depending on the customer specifics.
THE POLYMIDE FILM MANUFACTURING PROCESS
Polyimide film, is synthesized by polymerizing PMDA and ODA in strong polar solvents through the process of forming film and imine treatment at high temperature. This synthesis creates excellent physical, chemical, and electrical properties, as well as atomic radiation resistance, solvent resistance and low & high temperature resistance. It performs well in a wide range of temperatures as low as ‑452°F (-269°C) and as high as +500°F(+260°). Because of these characteristics, it is uniquely suitable for specific for many high temperature applications.
MANUFACTURING POLYMIDE SILICON TAPES
Polyimide Silicone Adhesive Tape is made by first taking polyimide film and coating it with a heat-resistant silicone adhesive. Due to its stable pressure-sensitive macromolecule adhesive layer at high temperature, the tape offers excellent properties of heat resistance, electrical insulation, solvent resistance and radiation protection. Being silicone, it 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 reflow temperatures up to 260°C — an operating temperature for which polyimide tape is uniquely suited — leaving no adhesive film once the tape is removed. Finally (though the true list of applications is nearly endless), it can be used for shielding in high temperature applications.
MANUFACTURING POLYMIDE ACRYLIC TAPES
Polyimide Acrylic Tape is made using the same process as the silicone process described above, but though the acrylic is typically a heat-resistant acrylic, it still cannot withstand the high temperature range of the silicone PSA described above. Also, 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. However, since the polyimide acrylic tape still uses a base of polyimide, the film itself is still able to withstand a wide temperature range and can still be used in many of the same high-temperature applications; it is just that the adhesion properties of the film become more limited with an acrylic adhesive. Acrylic chemistries are typically cheaper materials also, so the final selling price of acrylic-based polyimide tapes are generally lower. Though i-STIX offers both acrylic-based and silicone-based tapes; given the marginal price difference and the wider range of applications, the most popular tapes remain the silicone-based polyimide tapes.
PARAMETERS FOR TESTING PSA TAPES
Thickness of the carrier
Micron: It shows that thickness of the carrier and is mostly used in plastic film based carriers such as polyester, LDPE.
GSM: It stands for grams/1 square-meter and it indicates the weight of the carrier in grams for one square-meter area. This is mostly used in paper or cloth based carriers.
Peel Adhesion
This test parameter measures the approximate force required to peel off the PSA tape from a substrate or its own backing material. It is also commonly known as adhesion to steel as during the test, the PSA tape is applied on a steel plate.
Roll Ball Tack
This test measures the initial stickiness of the adhesive on the PSA tape at the time of application on the intended substrate.
Shear adhesion
The time required for a tape to come loose at a particular attached weight from a vertical panel decides the shear strength of the PSA tape. Internal or cohesive strength of adhesive coated is tested.
Temperature test
Shows the range of operating temperature that a particular PSA tape will withstand determining its temperature resistance and how it will behave in different climate conditions.
Breakdown voltage
It is the maximum voltage stress which a single layer of PSA tape can withstand before dielectric failure occurs. This test basically determines the electric strength of insulating tapes.
Tensile strength
It is a test determining the force that is required to break the PSA tape.
Elongation
It tells how far the PSA tape can stretch before it breaks. Elongation test indicates as how well the tape can handle the continuous stress of being stretched, once it is applied / at the time of application.
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