Abstract
Acrylic pressure-sensitive adhesives (PSAs) are used as fixatives between layers of a display. PSAs’ function is an important factor that determines the performance of the display. Of the various display types available, the touch screen panel (TSP) of smart devices is firmly related to the relative permittivity of the elementals. Therefore, adjusting the relative permittivity of the PSA is indispensable for driving the TSP. Accordingly, selected acrylic pre-polymers were polymerized and the pre-polymer was blended and cross-linked with monomers with different chemical structure to adjust the relative permittivity. The monomers were hexametyldisiloxane (HMDS), N-vinylcaprolactam (NVC), tert-butyl acrylate (TBA), and isooctadecyl acrylate (ISTA). The gel fraction and transmittance as a function of the monomers show a similar result to the pure acrylic PSA. However, the gel fraction value decreased to about 90% and the transmittance decreased to about 85%, due to the immiscibility between nonpolar HMDS and acrylic PSA. On the other hand, the adhesion properties were improved when NVC was added because of the polarity of the nitrogen group. In addition, the relative permittivity of the PSA decreased regardless of the monomer chosen. There was, however, a difference in the optimal content of each monomer, and NVC decreased from 4 phr content to about 3.4 in reducing relative permittivity. Through the above results, it was confirmed that NVC having a nitrogen group is most advantageous in lowering adhesion properties and relative permittivity, and necessitates further research based on the findings.
Highlights
A study was conducted on the relative permittivity of Pressure-sensitive adhesives (PSAs), which is closely related to the touch
A study was conducted on the relative permittivity of PSA, which is closely related to the touch sensitivity of touch screen panel (TSP)
The gel fraction value and transmittance according to the chemical structure and content of the monomer did not show a significant difference compared with the pristine acrylic PSA
Summary
Pressure-sensitive adhesives (PSAs) are widely used in various industrial fields, such as medical products, aircraft, space shuttles, electrical devices, optical products, and automobiles.In particular, the demand for functional PSAs is rapidly increasing in the display market [1].Displays are composed of a plurality of layer types and PSAs play an important fixative role.The PSA can fix the base material by applying slight pressure and becomes easy to adjust, Polymers 2020, 12, 2633; doi:10.3390/polym12112633 www.mdpi.com/journal/polymersPolymers 2020, 12, x FOR PEER REVIEW base material by applying and easy to adjust,the while the processing rate can while the processing rate slight can bepressure increased [2].becomesRecently, to improve technological development be increased [2].Recently, to improve the technological development of displays, broader properties of displays, broader properties of the PSA function are required including transparency high elongation, ofhigh the recovery, PSA function are required including transparency high elongation, high recovery, and heat and heat dissipation [3]. dissipationOptical clarity means a transmittance of 90% or more in the range of 400 to 800 nm and PSA satisfies clarity means a transmittance of adhesives90% or more in thePSA range of 400rubber, to 800acrylic, nm and PSA this Optical criteria defining the utility of optical clear (OCAs).includes silicone, satisfies this criteria defining utility of optical clearofadhesives includes and urethane, and acrylic. The PSA can fix the base material by applying slight pressure and becomes easy to adjust, Polymers 2020, 12, 2633; doi:10.3390/polym12112633 www.mdpi.com/journal/polymers. Polymers 2020, 12, x FOR PEER REVIEW base material by applying and easy to adjust,the while the processing rate can while the processing rate slight can bepressure increased [2].becomes. To improve technological development be increased [2]. To improve the technological development of displays, broader properties of displays, broader properties of the PSA function are required including transparency high elongation, ofhigh the recovery, PSA function are required including transparency high elongation, high recovery, and heat and heat dissipation [3]. 90% or more in thePSA range of 400rubber, to 800acrylic, nm and PSA this Optical criteria defining the utility of optical clear (OCAs). Includes silicone, satisfies this criteria defining utility of optical clearofadhesives includes and urethane, and acrylic
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