Solventless Silicone Pressure-Sensitive Adhesives for Electronics
In today’s technology-driven world, the need for high-performing electronics is growing exponentially. With visual displays on many new electronics based products these days, including smartphones, automobiles, appliances, and smart buildings, businesses and consumers are scooping up more complex electronics every day. Because of this, there is a growing need for materials that can effectively support the current iterations of these applications, as well as future ones.
Silicone pressure-sensitive adhesives (PSAs) often play varied roles of vital importance for fast-growing applications in the electronics sector. For example, protective films with ultra-stable peel adhesion and masking tape products with excellent performance in high temperatures and chemicals resistance, are necessary in applications like electronic circuit board masking. There are different types of PSAs, with the most common form being those that have a solvent base. Compared to typical organic-based PSAs, solvent-based silicone PSAs have historically been effective in handling extreme temperatures in high-performance applications like electronics manufacturing.
However, as consumers grow increasingly environmentally conscious and regulatory requirements become more stringent, major organizations are beginning to carefully consider the materials that go into their products to offset their impact on the environment and the health of end-users. These materials of concern often include solvents, especially benzene, toluene, ethylbenzene, xylene (BTEX). To tackle the growing urgency of more sustainable materials and the rapidly changing electronics industry, solventless silicone PSAs have emerged as a promising alternative to traditional solvent-based silicone PSAs.
While solvent-based PSAs have been effective in providing high bond strength in demanding electronics applications such as sensitive electronic circuitry protection, they also require bigger equipment and more of it, including a dilution tank or mixer, evaporation heater, and a solvent recovery system to minimize worker exposure and environmental impact. Solvents also have a complex supply chain with many elements to consider such as their storage method, time for processing, as well as amount of energy to evaporate, condense, and transport them. With this many elements at play, solvent-based PSAs can leave room for error in the development process.
As previously noted, environmental concerns are one of the largest pain points associated with solvents. When pressure-sensitive tape manufacturers work with solvent-based formulations, volatile organic compounds (VOCs) and hazardous air pollutants (HAPs) are contributed to the environment, requiring their emissions to be highly regulated1.
While the PSA category is still growing, efforts have been made to incorporate solvents with less harmful materials like BTEX. For example, benzoyl peroxide (BPO) cure heptane-based silicone PSAs have well-balanced adhesion, tackiness, and outstanding heat-resistance performance (>260°C) for high-temperature masking tape and hot-seal tape application during semiconductor processing. Due to a special technical route to produce heptane-based silicone PSAs, the cyclic content in heptane-based silicone PSAs is extremely low, which offers many benefits during downstream application, especially since the VOC no longer contains BTEX. Aromatic solvents are typically vaporized during the downstream BPO cure process for silicone PSAs where the insufficient solvent recovery system may cause BTEX solvents to be released into the atmosphere. Heptane-based silicone PSAs are formulated from raw materials without BTEX, which solves this issue from the source. Final products are also less likely to retain residual VOC and reduce the generation of dust in the curing oven, as it is easier to control the VOC boil-off. The result is higher production efficiencies, reduced equipment cleaning costs, and less maintenance.
In recent years, the range of solventless silicone PSAs has expanded with a better-balanced performance that addresses the requirements of protective films, specialty tapes, and electronic assembly. There are two main categories solventless silicone PSAs fall within: high adhesion and low adhesion. Through in situ reactions of chain extension and crosslinking, high adhesion solventless PSAs can meet general coaters’ needs for a solvent-free PSA offering that provides comparable performance to solvent-based silicone PSAs. Low-adhesion solventless PSAs are designed for protective film applications in electronics, particularly for displays and screens that can be directly coated onto substrates with a more stable performance in peel adhesion.
Source: Dow Chemicals