• Journal of the Korean Wood Science and Technology
• /
• v.42 no.3
• /
• pp.339-345
• /
• 2014

For enhancing productivity of glulam, high frequency (HF) curing technique was researched in this study. Heat energy is generated by electromagnetic energy dissipation when HF wave is applied to a dielectric material. Because both lamina and adhesives have dielectric property, internal heat generation would be occurred when HF wave is applied to glulam. Most room temperature setting adhesives such as phenol-resorcinol-formaldehyde (PRF) resin, which is popularly used for manufacturing glulam, can be cured more quickly as temperature of adhesives increases. In this study, dielectric properties of larch wood and PRF adhesives were experimentally evaluated, and the mechanism of HF heating, which induced the fast curing of glue layer in glulam, was theoretically analyzed. Result of our experiments showed relative loss factor of PRF resin, which leads temperature increase, was higher than that of larch wood. Also, it showed density and specific heat of PRF, which are resistance factors of temperature increase, were higher than those of wood. It was expected that the heat generation in PRF resin by HF heating would occur greater than in larch wood, because the ratio of relative loss factor to density and specific heat of PRF resin was greater than that of larch wood. Through theoretical approach with the experimental results, the relative strengths of ISM band HF electric fields to achieve a target heating rate were estimated.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.18 no.6
• /
• pp.263-268
• /
• 2017

A hot forming process is required for Mg alloys to enhance the formability and plastic workability due to the insufficient formability at room temperature. Mg alloy undergoes dynamic recrystallization (DRX) during the hot working process, which is a restoration or softening mechanism that reduces the dislocation density and releases the accumulated energy to facilitate plastic deformation. The flow stress curve shows three stages of complicated strain hardening and softening phenomena. As the strain increases, the stress also increases due to work hardening, and it abruptly decreases work softening by dynamic recrystallization. It then maintains a steady-state region due to the equilibrium between the work hardening and softening. In this paper, an efficient optimization process is proposed for the material model of the dynamic recrystallization to improve the accuracy of the flow curve. A total of 18 variables of the constitutive equation of AZ80 alloy were systematically optimized at an elevated forming temperature($300^{\circ}C$) with various strain rates(0.001, 0.1, 1, 10/sec). The proposed method was validated by applying it to the constitutive equation of AZ61 alloy.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.2 no.4
• /
• pp.23-32
• /
• 1982

In order to obtain the necessary data for the safety maintenance, repair, and reinforcement of steel structures, experiment was carried out to examine the mechanical capacity and toughness variation for steel with service history and without. In this paper, hardening and embrittlement by fatigue accumulation, and the decrease of toughness was examined and weld that was commonly used as the connection method of steel structure was also examined. It was found that hardening and embrittlement have more effect on the decrease of toughness than the increase of strength. Such a tendency was also similary state in case of weld. And it was found that, in the weld of steel with service history and without, embrittlement was observed at normal temperature.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2012.05a
• /
• pp.81.1-81.1
• /
• 2012

나노임프린트 리소그라피(Nano-Imprint Lithography, NIL) 기술은 기판위의 resin을 나노구조물이 각인된 스탬프로 눌러서 나노구조물을 형성하는 기술로, 경제적이고 효과적으로 나노구조물을 제작할 수 있는 기술이다. 그중에서도 UV 기반의 나노임프린트(UV-NIL) 기술은 resin을 투명한 스탬프로 누른뒤 UV로 경화시켜 나노구조물을 형성하는 기술로써 고온, 고압($140{\sim}180^{\circ}C$, 10~30bar)이 필요한 가열식 나노임프린트 기술에 비해 상온, 상압($20^{\circ}C$, 1bar)에서도 구조물 형성이 가능하여 다층구조 형성에 적합하다. 연속적인 임프린팅 공정에 의해 resin이 quarz 스탬프에 잔류하여 패터닝에 결함을 유발하게 되므로 오염물을 제거하기 위한 세정공정이 필요하다. 하지만 UV에 의해 경화된 resin은 cross-linking을 형성하여 화학적인 내성이 증가하게 되므로 제거하기가 어렵다. 현재는 resin 제거를 위한 세정공정으로 SPM($H_2SO_4/H_2O_2$) 세정이 사용되고 있는데 세정시간이 길고 세정 후에 입자 또는 황 잔유물이 남으며 많은 유해용액 사용의 문제점이 있어 효과적으로 resin을 제거할 세정공정이 필요한 상황이다. 본 연구에서는 친환경적인 UV 세정 및 오존수 세정공정을 적용하여 경화된 resin을 제거하는 연구를 진행하였다. 실험샘플은 약 100nm 두께의 resin을 증착한 $1.5cm{\times}1.5cm$ $SiO_2$ 쿠폰 wafer를 사용하였으며, UV 및 오존수의 처리시간을 달리하여 resin 제거효율을 평가하였다. ATR-FTIR 장비를 사용하여 시간에 따른 resin의 두께를 측정한 결과, UV 세정으로 100nm 높이의 resin중에 80nm의 bulk resin이 단시간에 제거가 되었고 나머지 20nm의 resin thin film은 오존수 세정으로 쉽게 제거되는 것을 확인 하였다. 또한 표면에 남은 resin residue와 particle을 제거하기 위해서 SC-1 세정을 진행하였고 contact angle과 optical microscope 장비를 사용하여 resin이 모두 제거된 것을 확인하였다.

• Journal of Adhesion and Interface
• /
• v.16 no.1
• /
• pp.15-21
• /
• 2015

In this study, rheological properties and flow dynamics in roll coating process of basecoat paints have been investigated for automotive precoated metal (PCM) sheet applications. Various rheological properties for basecoats with three colors (black, blue, and silver), such as shear viscosity data at room temperature and elastic/viscous moduli under thermal curing condition, have been measured using a rotational rheometer. It is found that the relative portion of function groups inside basecoats and their viscosity level have greatly affected the formation of crosslinked networks by thermal curing. Also, operability coating windows for basecoats have been established in three-roll coating process system by observing their flow instabilities such as ribbing and cascade. It is confirmed that rheological approaches applied in this study have been usefully applied to develop environmentally-friendly PCM coating technology and optimally control the coating operations for non-Newtonian PCM paints.

• Elastomers and Composites
• /
• v.33 no.4
• /
• pp.267-273
• /
• 1998

Isocyante terminated urethane prepolymers were synthesized by the reaction of 4,4'-dimethyl phenyldiisocyanate(MDI) and ester type polyols such as ethylene glycol/ butanediol adipate(EBA), neopentylglycol/butanediol adipate (NBA) and hexanediol adipate (HA) . All of the NCO-terminated urethane prepolymers are solid at room temperature, but they become mobile enough to be disposed onto a substrate upon heating about $80^{\circ}C$. Subsequently, they are solidified and cured through the reaction with moisture. Tensile behavior of the ore-thane hotmelt exhibits characteristic features depending on the type of polyol. The adhesive strength determined by single lap shear joint is higher in order of HA, NBA and EBA based ore thane hotmelt, which can be correlated with the magnitude of breaking energy of the cured films. The failure mode are cohesive for all cases and the adhesive strength increases as the test is performed faster. This indicates that the strength of the adhesive joint is primarily dependent upon the bulk properties of the adhesives.

• Polymer(Korea)
• /
• v.30 no.3
• /
• pp.230-237
• /
• 2006

Copolymers(HSA-98-20, HSA-98-0, HSA-98+20) which we acrylic resin containing 80% solid content were synthesized by the reaction of monomers, including methyl methacrylate, n-butyl acrylate, and 2-hydroxyethyl acrylate with a functional monomer, acetoacetoxyethyl methacrylate (AAEM), which nay give improvements in cross-linking density and physical properties of films. The physical properties of prepared acrylic resins, containing AAEM, are as follows viscosities, $1420\sim5760cps$ ; number average molecular weight, $2080\sim2300g/mol$; polydispersity index, $2.07\sim2.19$ ; and conversions, $88\sim93%$. In the next step, high-solid coatings (HSA-98-20C, HSA-98-0C, HSA-98+20C) were prepared by the curing reaction between acrylic resins containing 80% solid content and isocyanate at room temperature. Various properties were examined on the film coated with the prepared high-solid coatings. The introduction of AAEM to the coatings enhanced the abrasion resistance and solvent resistance, which indicated the possible use of high- solid coatings for top-coating materials of automobile. Since the curing by viscoelastic measurement occurred in sequence of HSA-98+20C > HSA-98-0C > HSA-98-20C, it was concluded that the curing rates became faster with incresing $T_g$ values.

• Journal of the Korean Society for Railway
• /
• v.18 no.6
• /
• pp.543-551
• /
• 2015

Quick-hardening track (QHT) is a construction method which is used to change from old ballast track to concrete track. Sufficient time for construction is important, as the construction should be done during operational breaks at night. Most of the time is spent on exchanging the ballast layer. If it is possible to apply the ballast non-exchange type of quick-hardening track, it would be more effective to reduce the construction time and costs. In this paper, pouring materials with high permeability are suggested and a construction method involving a layer separation pouring process considering the void condition is introduced in order to develop ballast non-exchange type of QHT. The separate pouring method can secure the required strength because optimized materials are poured into the upper layer and the lower layer for each void ratio condition. To ensure this process, a rheology analysis was conducted on the design of the pouring materials according to aggregate size, the aggregate distribution, the void ratio, the void size, the tortuosity and the permeability. A polymer series was used as the pouring material of the lower layer to secure the void filling capacity and for adhesion to the fine-grained layer. In addition, magnesium-phosphate ceramic (MPC) was used as the pouring material of the upper layer to secure the void-filling capacity and for adhesion of the coarse-grained layer. As a result of a mechanics test of the materials, satisfactory performance corresponding to existing quick-hardening track was noted.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.20 no.4
• /
• pp.503-509
• /
• 2019

The demand for smaller, faster, and multi-functional mobile devices in increasing at a rapidly increasing rate. In response to these trends, Stacked Chip Scale Package (SCSP) is used widely in the assembly industry. A film type adhesive called die attach film (DAF) is used widely for bonding chips in SCSP. The DAF requires high flowability at high die attachment temperatures for bonding chips on organic substrates, where the DAF needs to feel the gap depth, or for bonding the same sized dies, where the DAF needs to penetrate bonding wires. In this study, the mixture design of experiment (DOE) was performed for three raw materials to obtain the optimized DAF recipe for low elastic modulus at high temperature. Three components are acrylic polymer (SG-P3) and two solid epoxy resins (YD011 and YDCN500-1P) with different softening points. According to the DOE results, the elastic modulus at high temperature was influenced greatly by SG-P3. The elastic modulus at $100^{\circ}C$ decreased from 1.0 MPa to 0.2 MPa as the amount of SG-P3 was decreased by 20%. In contrast, the elastic modulus at room temperature was dominated by YD011, an epoxy with a higher softening point. The optimized DAF recipe showed approximately 98.4% pickup performance when a UV dicing tape was used. A DAF crack that occurred in curing was effectively suppressed through optimization of the cure accelerator amount and two-step cure schedule. The imizadole type accelerator showed better performance than the amine type accelerator.

• Journal of Conservation Science
• /
• v.36 no.6
• /
• pp.475-482
• /
• 2020

In this study, we synthesized rosin-based epoxy resin and manufactured two components adhesives and epoxy putty using this epoxy resin. This study manufactured main element of adhesives for enabling it to form epoxide group by letting epichlorohydrin react to maleic anhydride modified rosin, and used room temperature curing type triethylenetetramine for hardener. The ratio between main element and hardener of of manufactured adhesives was 100 : 20, and main element and hardener of filling material were manufactured as clay type by mixing them with filler. Manufactured undiluted adhesives and filling material showed very stable result in the adhesive strength (3.06 MPa) and ultraviolet irradiation, showing outstanding result comparing to existing restoration adhesives. And it is considered a material having reversibility as it was dissolved in organic solvents such as acetone and toluene after being hardened, which showed a result that solved part of possible problems caused by restoration. As a result of use and application of manufactured adhesives and filling material for actual wood crafts, they showed excellent results in workability, stability, removability etc., and this study confirmed that the material can be used for and applied to various fields.