• 대한기계학회논문집A
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• 제32권5호
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• pp.419-423
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• 2008

A new polymer replication technology using ultrasonic vibration is proposed and demonstrated. A commercial ultrasonic welder has been used in this experiment. Two different types of nickel molds have been fabricated: pillar type and pore type microstructures. Polymethyl methacrlylate (PMMA) has been used as the replication material and the optimal molding time was 2 sec and 2.5 sec for pillar-type and pore-type micromolds, respectively. Compared with the conventional polymer micromolding techniques, the proposed ultrasonic micromolding technique has the shortest processing time. In addition, only contact area between micromold and polymer substrate is melted so that the thermal shrinkage can be minimized. The fabricated PMMA microstructures have been very accurately replicated without vacuum. The proposed ultrasonic molding technique is a good alternative for high volume production.

• 반도체디스플레이기술학회지
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• 제11권4호
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• pp.7-12
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• 2012

Extrusion is one of the most important operations in the polymer-processing industry. Development of models for extrusion and computer tools offer a route to developing reliable and optimized process designs. The models are based on the analysis of physical phenomena encountered during the process. Balance equations for mass, momentum and energy are fundamental to the problem. A predictive computer model has been developed for the single screw extruders with conventional screws of different geometry. The model takes into account melting zones of the extruder and describes an operation of the extruder system, making it possible to predict mass flow rate of the polymer, pressure and velocity profiles along the extruder screw channel. The simulation parameters are the material and rheological properties of the polymer; the screw pitch, and screw speed.

• Macromolecular Research
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• 제16권7호
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• pp.620-625
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• 2008

A novel nitrogen-phosphorus compound, diphenyl piperazine-1,4-diylbis(methylphosphinate)(DPPMP) was synthesized via a two step reaction and its flame retarding efficiency as a single component additive was investigated. The success of synthesis was confirmed by FTIR and $^1H$ and $^{31}P$ NMR analysis. The product was mixed with polycarbonate (PC), poly(butylene terephtalate) (PBT), ethylene-vinyl-acetate copolymer (EVA), and acrylonitrile-butadiene-styrene copolymer (ABS). The flame-retarding efficiency was evaluated using the limiting oxygen index (LOI) and the UL-94 vertical test methods. The addition of DPPMP enhanced the flame retardancy of the polymers and the V-0 ratings were obtained for the polymers examined in this study at a loading of 7-30 wt%. The gas-phase flame retardancy mode of action was suggested for this material from the thermogrametry experiment results.

• 한국공작기계학회논문집
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• 제18권1호
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• pp.68-75
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• 2009

A major disadvantage of thermal nanoimprint lithography(NIL) is the thermal cycle, that is, heating over glass transition temperature and then cooling below it, which requires a significant amount of processing time and limits the throughput. One of the methods to overcome this disadvantage is to make the processing temperature lower Accordingly, it is necessary to determine the effects on the processing parameters for thermal NIL at reduced temperatures and to optimize the parameters. This starts with a clear understanding of polymer material behavior during the NIL process. In this work, the squeezing and filling of thin polymer films into nanocavities during the low temperature thermal NIL have been investigated based upon a two-dimensional viscoelastic finite element analysis in order to understand how the process conditions affect a pattern quality; Pressure and initial polymer resist thickness dependency of cavity filling behaviors has been investigated.

• Macromolecular Research
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• 제16권4호
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• pp.360-366
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• 2008

Poly(dialkoxyphenylene 1,3,4-oxadiazole)s were conveniently synthesized to compare their material properties of solvent solubility, thermal stability and molecular alignment with respect to alkyl chain length and meta/para-phenylene structure. All prepared polymers exhibited good solubility in co-solvents containing various volume levels of chloroform to trifluoroacetic acid. Meta-polymers showed slightly better solubility than para-polymers. All polymers produced were thermally stable up to $320^{\circ}C$. Photoluminescence of polymer films was observed with blue light emission at around 450 nm. X-ray diffraction patterns of all polymers indicated that they were composed of stacked molecular sheets with the same layer-to-layer distance of $3.4\;{\AA}$. However, side chain-to-side chain and main chain-to-main distances within the layers increased with increasing alkyl chain lengths. The meta-polymer chains were separated more than the para-polymer chains.

• Journal of the Korean Wood Science and Technology
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• 제48권5호
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• pp.755-764
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• 2020

Due to pronounced mechanical performance and being environmental friendly, aqueous polymer isocyanate adhesive (API) has been widely applied in the production of formaldehyde-free wood products. In this study, flame retardant formaldehyde-free plywood was prepared by incorporation of flame retardants into the API adhesive. Partially phosphorylated poly (vinyl alcohol) (PPVA) which was prepared by reacting poly (vinyl alcohol) with phosphoric acid was used to replace PVA in API formula. In addition, Mg-Al layered double hydroxides (LDH) was chosen as additive flame retardant, replacing traditional filler CaCO₃ in API adhesive formula. And then, the flame retardant API adhesive with main agent (PPVA replacing PVA70wt.%, SBR emulsion 30wt.%), curing agent 10wt.% (accounts for of the main agent), and 20wt.% LDHs (accounts of the main agent) was used to prepare flame retardant plywood. The effect of application of PPVA and Mg-Al LDH on bonding strength of plywood was investigated. The flammability characteristics of the plywood were determined by cone calorimeter test (CCT). The results revealed that compared with the plywood prepared with API adhesive, the use of PPVA and LDH enhanced the flame retardancy of plywood without negatively affecting bonding strength. The CCT tests indicated that the heat release and smoke production flame retardant API plywood were lower than those of the ordinary API glued plywood. Promising developments for flame retardant API adhesive were expected in future applications of flame retardant formaldehyde-free plywood.

• 한국터널지하공간학회 논문집
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• 제12권6호
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• pp.451-461
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• 2010

장기 부식 등 일반적인 건설재료의 문제점을 보완할 수 있는 대체재료로서, 섬유강화 복합재료의 활용이 증대되고 있다. 하지만 일반적으로 선형의 섬유강화 복합재료를 아치형인 터널구조물의 부재로서 활용하는 데는 많은 문제점이 대두된다. 따라서, 본 연구에서는 섬유강화 복합부재를 일정곡률로 인발성형 할 수 있는 신개념의 곡면 FRP 부재 성형장비를 개발하고 시제품을 생산하였으며, 시제품에 대한 물리적 특성 시험을 수행하였다. 이어, 곡면 FRP 시제품과 합체되어 제작된 콘크리트 복합부재에 대한 수치해석 검토 및 분석을 통하여 시제품의 터널 구조체로써의 적용성을 평가하였다. 수치해석적 적용성 검토 결과, 곡면 FRP 부재를 터널 구조물로 적용함에 있어서 터널 안정성을 충분히 확보할 수 있는 것으로 파악되었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 하계학술대회 논문집
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• pp.338-338
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• 2009

To date, rubbing has been widely used to align LC molecules uniformly. Although rubbing can be simple, it has fundamental problems such as the generation of defects by dust and static electricity, and difficulty in achieving a uniform LC alignment on a large substrate. Therefore, noncontact alignment has been investigated. Ion beam induced alignment method, which provides controllability, nonstop process, and high resolution display. We investigated the high pretilt angle effects on electro-optical properties of ion beam (IB)-irradiated liquid crystal cells. on a blended polymer surface. High pretilt angle of liquid crystals IB-irradiated on a blended polymer surface including such as 5% and 10% of homeotropic polymer contents can' be achieved. The threshold voltages of IB-irradiated twisted nematic (TN) cells on a blended polymer surface decrease with increasing the pretilt angle. Also, the rising time of IB-irradiated TN cells decreases with increasing the pretilt angle. However the decay time of IB-irradiated TN cells increases with increasing the pretilt angle. Consequently, the electro-optical properties of IB-irradiated TN cells depend strongly on the pretilt angle in a blended polymer surface.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 춘계학술대회 논문집
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• pp.57-58
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• 2009

The dynamics of nano or micro sized-particles in liquid crystal (LC) medium under an external electric field is of theoretical and technological interest. A fullerene of 10 wt% was doped into the LC medium and its electric field induced motion was controlled by both in-plane and vertical electric fields. In the proposed device, pixel electrode I and pixel electrode II were designed consecutively on the bottom substrate and common electrode on the top of the substrate. When the electric field was applied, the fullerenes start to move in direction of applied electric field. The dark, grey and white states in the proposed device can be obtained by suitable combination of the polarity of applied electric field at pixel electrode I, pixel electrode II and common electrode. The dynamical motions of fullerene particles in LC medium suggest that fullerene can be designed for electronic-paper like displays.

• 폴리머
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• 제32권1호
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• pp.90-93
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• 2008

암 치료의 보조요법의 하나로 제시될 수 있는 전자파를 이용한 온열치료법의 기초연구를 수행하였다. 폴리에틸렌, 탈이온수, 그리고 염화나트륨 등으로 구성되는 젤리형의 인체 뇌 팬텀을 제작하고 이들 팬텀 재료의 다양한 구성비에 따른 팬텀의 전기적 특성을 유전율상수와 전도도를 측정하여 평가하였다. 그 결과, 염화나트륨의 양이 증가함에 따라 팬텀의 도전율이 증가하는 것을 제외하고는 팬텀 재조에 사용한 재료의 함량이 증가할수록 팬텀의 전기적 특성 값들은 대체로 감소함을 확인하였다. 또한 시간 경과에 따른 무게비로 측정한 팬텀의 장기안정성은 6개월이 경과한 시점까지도 양호하게 유지됨을 알 수 있었다. 이러한 연구 결과는 향후 각종 인체장기에 대응하는 자성유체가 혼입된 젤리팬텀의 전자기적 특성과 온도 상승을 관찰함으로써 암 치료에 있어서의 새로운 방법론을 제시할 수 있을 것으로 기대된다.