Dong-Hyuk Lim

Preparation of SIS/SBS-based UV-cross-linkable pressure-sensitive adhesives using the thiol-ene reaction

Hot-melt pressure-sensitive adhesives (HMPSAs) usually contain styrene-isoprenestyrene (SIS) or styrene-butadiene-styrene (SBS) block copolymers, tackifier, plasticizer and other additives. However, these PSAs cannot be used in high-temperature applications or where solvent and chemical resistance properties are required. We, therefore, developed UV-cross-linkable HMPSAs by the thiol-ene reaction with the aim to increase adhesion properties at elevated temperature. For effective UV cross-linking, the selection of photoinitiator and photo-cross-linker is very important for thermal stability and fast curing. Adhesion properties, such as probe tack, peel strength and shear adhesion failure temperature (SAFT), were evaluated to measure PSA performance as a function of photoinitiator type.

Effect of grafting of acrylic acid onto PET film surfaces by UV irradiation on the adhesion of PSAs

To improve the peel strength between a pressure-sensitive adhesive (PSA) and its substrate, grafting of acrylic acid (AA) onto the surface of poly(ethylene terephthalate) (PET) film was carried out. After AA was coated onto the surface of PET films using a spin coater, the coated PET films were irradiated by UV. To investigate the surface chemistry and topography of the PET-g-AA films, the grafted surface of the PET films was characterized by FT-IR spectroscopy, X-ray photoelectron spectroscopy (XPS) and scanning probe microscopy (SPM). From these investigations, the effects of grafting of AA at the surface of PET by UV irradiation were discussed. In addition, to determine the effect of grafting on the adhesion between PSA polymer and PET-g-AA films, peel strength was measured after the PSA/PET-g-AA system was cured at various temperatures. As the esterification between PSA polymer and PET-g-AA films occurred in the interfacial region, the peel strength of the PSA/PET-g-AA system generally increased with increasing curing temperature.

Curing Behavior and Adhesion Performance of UV-Curable Styrene–Isoprene–Styrene-Based Pressure-Sensitive Adhesives

This article reports on the curing behavior and adhesion performance of ultraviolet (UV)-curable, polystyrene–polyisoprene–polystyrene (SIS)-based pressure-sensitive adhesives (PSAs) blended with di- or tri-functional monomers and a photoinitiator. The curing reaction was achieved by direct excitation of PSAs by irradiation with a 100 W high-pressure mercury lamp at different UV doses. The curing behavior of the PSAs was studied by gel fraction determination, rigid-body pendulum type physical properties test (RPT) and Fourier transform-infrared–attenuated total reflection (FT-IR–ATR) spectroscopy. The adhesion performance was determined by probe tack, peel strength and shear adhesion failure temperature (SAFT) measurements. The reaction rate and extent of UV curing reaction were found to be strongly dependent on the curing rate for the following five multifunctional monomers studied: three di-functional monomers, ethylene/glycol dimethacrylate (EGDMA), triethylene glycol dimethacrylate (TEGDMA) and poly(ethylene/glycol)(400) dimethacrylate (PEG(400)DMA), and two tri-functional monomers, trimethylolpropane triacrylate (TMPTA) and trimethylolpropane ethoxylated (6) triacrylate (TMPEOTA). In addition, the adhesion performance was affected by the semi-interpenetrating polymer network (IPN) structure formed depending on the curing rate and degree of cross-linking.

A 4.8Gb/s impedance-matched bidirectional multi-drop transceiver for high-capacity memory interface

With the scaling of CMOS transistors and advance in I/O circuitry, the data rate of memory interfaces has recently reached 16Gb/s per channel [1], in which a point-to-point channel is required rather than a multi-drop channel for the high data rate. While point-to-point channels are advantageous in achieving higher data rates because of the absence of undesired reflections that occur at each stub of multi-drop channels, they are not suitable for high-capacity, high-throughput memory systems such as transaction servers or cloud computing nodes due to their prohibitively large PCB routing area connecting the memory chips. FBDIMM [2] and the cascading memory architecture [3] aim to reduce the routing area by the use of daisy-chained configurations, but they suffer from increased latency problems. This is why the recent DDR2/3 memory interface still uses the multi-drop bus architecture called stub series terminated logic (SSTL), and a number of proposals have been made to mitigate the problem of stub reflections in SSTL. For instance, a decision feedback equalizer has been used [4] to cancel the inter-symbol interference (ISI) due to stub reflections; but this requires a large number of filter taps, resulting in a limited speed under 3Gb/s. Another approach to eliminate impedance discontinuity is to use a 2Z0 ohm transmission line [5], but this scheme is only applicable to 2-slot configurations.

A low-noise differential front-end and its controller for capacitive touch screen panels

A low-noise front-end and its controller are proposed for capacitive touch screen panels. The proposed front-end circuit based on a ΔΣ ADC uses differential sensing and integration scheme to maximize the input dynamic range. In addition, supply and internal reference voltage noise are effectively removed in the sensed touch signal. Furthermore, the demodulation process in front of the ΔΣ ADC provides the maximized oversampling ratio (OSR) so that the scan rate can be increased at the targeted resolution. The proposed IC is implemented in a mixed-mode 0.18-μm CMOS process. The measurement is performed on a bar-patterned 4.3-inch touch screen panel with 12 driving lines and 8 sensing channels. The report rate is 100 Hz, and SNR and spatial jitter are 54 dB and 0.11 mm, respectively. The chip area is 3 × 3 mm2 and total power consumption is 2.9 mW with 1.8-V and 3.3-V supply.

A Digital Readout IC with Digital Offset Canceller for Capacitive Sensors

A digital readout IC for capacitive sensors is presented. Digital capacitance readout circuits suffer from static capacitance of sensors, especially single-ended sensors, and require large passive elements to cancel such DC offset signal. For this reason, to maximize a dynamic range with a small die area, the proposed circuit features digital filters having a coarse and fine compensation steps. Moreover, by employing switched-capacitor circuit for the front-end, correlated double sampling (CDS) technique can be adopted to minimize low-frequency device noise. The proposed circuit targeted 8-㎑ signal bandwidth and oversampling ratio (OSR) of 64, thus a 3 rd -order ΔΣ modulator operating at 1 ㎒ was used for pulse-density-modulated (PDM) output. The proposed IC was designed in a 0.18-㎛ CMOS mixed-mode process, and occupied 0.86 × 1.33 ㎟. The measurement results shows suppressed DC power under about -30 ㏈FS with minimized device flicker noise.

Fabrication of optically clear acrylic pressure–sensitive adhesive by photo-polymerization: UV-curing behavior, adhesion performance, and optical properties

Acrylic pressure–sensitive adhesives (PSAs) with 2-phenoxy ethyl acrylate (PEA) were polymerized using UV-curing technology. This study examined the effects of PEA content and UV dose. The photo-polymerization behavior of the pre-polymer was examined by viscosity measurements, real-time Fourier transform infrared spectroscopy, and photo-differential scanning calorimetry. The curing behaviors of the acrylic PSAs were investigated by shrinkage test, a modular advanced rheometer system, and gel content. differential scanning calorimetry and Advanced Rheometric Expansion System were used to characterize the acrylic PSAs. Adhesion performances were measured by probe tack, peel strength, and shear adhesion failure temperature. The optical properties of acrylic PSAs were examined by UV–visible spectroscopy and prism coupler. The PEA content had a larger effect on improving the optical properties, than did the UV dose. The transmittances of the acrylic PSAs with <75% PEA were >95%. The refractive indices of the acrylic PSAs increased with increasing PEA content, due to its high refractive index, >1.5, which affected the overall refractive indices, particularly in the visible region.

Optical properties and adhesion performance of acrylic PSAs; influence of functionalized monomer and curing agent

Acrylic pressure–sensitive adhesives (PSAs) were synthesized by solution polymerization using zirconium carboxyethyl acrylate (ZrCEA) with methyl aziridine derivatives (MAZ) as a curing agent. The acrylic PSAs were characterized by Fourier transform-infrared spectroscopy and gel contents. The viscoelastic properties of the acrylic PSAs were determined using an advanced rheometric expansion system. The adhesion performance of the acrylic PSAs was determined by measuring the probe tack, peel strength, shear adhesion failure temperature, and holding power. The optical properties of the acrylic PSAs were evaluated by the transmittance and refractive index. The results show that the adhesion performance and optical properties of the acrylic PSAs are influenced by the ZrCEA and MAZ content.

Adhesion Properties of Urea-Melamine-Formaldehyde (UMF) Resin with Different Molar Ratios in Bonding High and Low Moisture Content Veneers

ABSTRACT The objective of this research was executed to investigate the effect of molar ratio of formaldehyde to urea and melamine (F/(U+M)) of urea-melamine-formaldehyde (UMF) resin on bonding high and low moisture content veneers. For that purpose, UMF resin types with 5 different F/(U+M) molar ratios (1.45, 1.65, 1.85, 2.05, and 2.25) synthesized were used in present study. First, their curing behavior was eval-uated by differential scanning calorimetry. Second, their adhesion performance in bonding high and low moisture content veneers was evaluated by probe tack and dry and wet shear strength tests. Curing temper-ature and reaction enthalpy decreased with the increase of F/(U+M) molar ratio. And the dry and wet shear strengthsof plywood manufactured from low moisture content veneers were higher than thoseof plywood manufactured from high moisture content veneers. Also, the maximum initial tack force on the low mois-ture content veneer was higher than that on the high moisture content veneer. Keywords : urea-melamine-formaldehyde resin, adhesion performance, moisture content, veneer