• Elastomers and Composites
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• v.36 no.2
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• pp.111-120
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• 2001

Mechanical properties and their adhesion behavior with zinc- and brass-plated steel cords of natural rubber/acrylonitrile-butadiene blend compounds were investigated as a function of blend ratio. The Mooney viscosity and stress relaxation time were found to be lowered with increasing NBR content. Tensile modulus generally increased with increasing NBR content. Tensile stress at break stayed constant up to about 40 phr and showed minimum at $50{\sim}60 phr$, and thereafter increased with increasing NBR content. Strain at break decreased linearly below 50 phr, and above the level it showed nearly constant value. Based on the abrupt drops in elastic modulus and tan ${\delta}$ peak, the glass transition temperature of NR and NBR were found to be -55 and $-10^{\circ}C$, respectively. In the case of NR/NBR blend compounds, two distinct transition points were observed and each transition position was not affected by NBR level indicating an incompatible nature of NR/NBR blend system. The pullout force and rubber coverage decreased to the level of about 40% to that of pure m compound, when the 50 phr of NR was replaced by NBR. However, the pure NBR compound showed the comparable adhesion performance with NR(${\sim}90%$). The sulfur concentration was found to become lower with the increased NBR content at the adhesion interface based on the Auger spectrometer results, representing a lack of adhesion layer formation, and this was explained for a possible cause of low adhesion performance with adding NBR.

• Elastomers and Composites
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• v.39 no.1
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• pp.12-22
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• 2004

The plasma surface modification of natural rubber vulcanizate was carried out using chlorodifluoromethane in a radio-frequency (13.56 MHz) electrodeless bell type plasma reactor. The modification was qualitatively assessed by Fourier transform infrared spectroscopy. The frictional force of the plasma-treated surface was found to decrease with the time of plasma treatment. An increase in the surface polarity, as evidenced by the decrease in contact angle of a sessile drop of water and ethylene glycol on the natural rubber vulcanizate surface, was noted with the plasma modification. In the case of similar plasma treatment of glass surface, only a reduction in the polarity was observed. The use of geometric and harmonic mean methods was found to be useful to evaluate the London dispersive and specific components of surface free energy. Irrespective of the method used for evaluation, an increasing trend in the surface free energy was noted with increasing plasma treatment time. However, the harmonic mean method yielded comparatively higher values of surface free energy than the geometric mean method. The plasma surface modification was found to vary the frictional coefficient by influencing the interfacial, hysteresis and viscous components of friction in opposing dual manners.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.154-154
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• 2006

Samsung Electro Mechanics ink jet has developed ultra high resolution alignment system. The alignment system has been developed for repeatable printing of conductive ink. The resolution of alignment system is 0.5um and the velocity of printing working plate is 1.5m/s. So far repeated printing results included sintering process have over 30um of drop mislocation data. In order to improve line thickness and conductivity of metal line, we need to develop the higher mechanical accurate align system. On the demand, this developed align system has under $1{\sim}2{\mu}m$ mispositioning performance and can measure of mechanical accuracy of inkjet printer, as well as the straightness of jetted drop from inkjet head. There is no kinds limit of substrate and ink to use SEM alignment system. By using this alignment system, we progress two experiment of reiterate printing drop and making conductive line on the glass and photo paper. Optical microscope and 3D profiler has been used for measurement of printed ink.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.28 no.3
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• pp.257-266
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• 2018

Objectives: The objective of this study was to evaluate asphalt fumes and PAHs exposure among asphalt road paving workers. Methods: Task-based personal air samplings(n=41) were carried out in 3 asphalt road paving construction sites using PTFE (polytetrafluorethylene) filters for asphalt fume and XAD-2 with glass fiber filters for PAHs. The concentration of fumes and PAHs were showed by four different job(paver finisher operator, paving laborer(raker), macadam roller operator and tire roller operator). Results: The geometric mean(GM) concentration of asphalt fumes as benzene soluble aerosol was highest at paving laborers($42.32{\mu}g/m^3$), followed by in order, paver finisher operators($41.57{\mu}g/m^3$), macadam roller operators($31.9{\mu}g/m^3$), and tire roller operators($30.31{\mu}g/m^3$). The GM of total PAHs concentration was highest at paver finisher operators($37.5{\mu}g/m^3$), followed by in order, paving laborers($20.13{\mu}g/m^3$), tire roller operators($8.66{\mu}g/m^3$), and macadam roller operators($6.23{\mu}g/m^3$). The results of the evaluation of 16 compounds of PAHs showed that the concentrations of naphthalene, achenaphthylene, achenaphthene, pyrene, fluorene and benz (a) anthracene was higher than those of other PAHs compounds and as the carcinogenic substances, benzo(a)pyrene, and debenz(a,h) anthracene were detected. The benzo(a)pyrene equivalent concentration(BaPeq) was $2.81{\mu}g/m^3$ at paver finisher operators, $2.07{\mu}g/m^3$ at paving laborers, $0.41{\mu}g/m^3$ at tire roller operators and $0.22{\mu}g/m^3$ at macadam roller operators. Asphalt road paving workers have higher benzo(a)pyrene equivalent(BaPeq) values even though at lower total PAHs concentration than workers in steel pipe coating and tar industry. Conclusions: Asphalt road paving workers were found to have risk of carcinogen exposure due to higher Benzo(a)pyrene equivalent concentration(BaPeq) than other PAHs exposure occupations. This study confirmed the carcinogenic hazards among asphalt paving workers.

• Elastomers and Composites
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• v.19 no.1
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• pp.13-31
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• 1984

The purposes of this dissertation are to demonstrate that DSC theromoanaytical methods of vulcanization can provide useful informations on the vulcanization characteristics of industrial formulations and also provides the potential basis for a rapid and complete method of sulfur and vulcanizing accelerator analysis for quality control. The influences of those factors such as heating rate, scan temperature, vucanizing accelerator's type and concentration upon vulcanization exotherm in NR and NBR compounds in the presence of vulcanizing accelerators such as TMTD,MBTS,DPG,TMTM,CBS, and MBT were evaluated by means of DSC. In order to examine the credibility in the DSC method, the same samples which were used for DSC method were studied to compare the DSC results with the ODR (Oscillating Disk Rheometer) data. The results obtained were as follows 1. In the DSC dynamic experiments, the observed enthalpy results from vulcanization depends upon the heating rate; In the range of 2 to $20^{\circ}C/min$ of heating rate, as the heating rate was increased the enthalpy change was also increased. However, over the heating rate of $30^{\circ}C/min$ it was observed that the enthalpy change was decreased as the heating rate was further increased. Without regard to the change of enthalpy, tremendous instantaneous heat evolving was observed in the range of high heating rates. 2. For the samples which are added with various vulcanizing accelerators, the activation energies of vulcanization were as follows; 3. Regarding to the influences of vulcanizining accelerator's types upon the characteristics of vulcanization exotherm, NR and NBR compounds in the presence of thiuramsulphide compounds type accelerators such as TMTD, TMTM, were exhibited sharper and higher vulclanization exotherm than others. From the resuts of DSC thermograms which was distributed in even shape in the broad temperature range, it was clearly shown that the guanidine compounds type accelerator such as DPG acts as a delayed acting accelerator. 4. In the comparison of DSC and ODR results, the dependency of temperature in the cure rate and the observed conversions show good agreements between two results. 5. In the same curatives, by the comparison of glass transition temperatures, it was possible to predict relative values of maximum torques. Consequently, from the present studies, it is shown that the DSC thermoanalytical method can provide an alternate new method for rapid and complete quality control analysis of rubber industry.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.11
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• pp.105-115
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• 2018

The purpose of this study was to clarify whether or not alcohol drinking patterns are associated with sleep quality. A cross-sectional study was carried out by self-administered questionnaire in May, 2017 among 553 male workers who employed in manufacturing industries in D city. Logistic regression analysis was used to evaluate whether or not alcohol drinking patterns (as measured by frequency, amount of alcohol per day, and amount of alcohol per week) were associated with poor sleep quality (as measured by Pittsburgh Sleep Quality Index). As a result, in comparison with male workers who did not drink, the adjusted odds ratio for poor sleep quality was 0.44 (95% CI=0.232-0.845) for those who drank alcohol once a week or more, 0.31 (95% CI=0.192-0.829) for those who drank less than 1 glass daily, and 0.28 (95% CI=0.167-0.762) for those who drank 1-3 glasses daily. The results of this study suggest that some alcohol drinking patterns may affect sleep quality among male workers.

• Journal of the Korean Geosynthetics Society
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• v.17 no.4
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• pp.169-177
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• 2018

Glass fiber reinforced polyester (GFRP) composites are widely used as structural materials in harsh environment such as underground pipes, tanks and boat hulls, which requires long-term water resistance. Especially, these materials might be damaged due to delamination between gelcoat and composites through an osmotic process when they are immersed in water. In this study, GFRP laminates were prepared by surface treatment of UPE (unsaturated polyester) gelcoat by vacuum infusion process to improve the durability of composite materials used in underground pipes. The composite surface coated with gelcoat was examined for surface defects, cracking, and hardness change characteristics in water-immersion environments (different temperatures of $60^{\circ}C$, $75^{\circ}C$, and $85^{\circ}C$). The penetration depth of cracks was investigated by micro CT imaging according to water immersion temperature. It was confirmed that cracks developed into the composites material at $75^{\circ}C$ and $85^{\circ}C$ causing loss of durability of the materials. The point at which the initial crack initiated was defined as the failure time and the life expectancy at $23^{\circ}C$ was measured using the Arrhenius equation. The results from this study is expected to be applied to reliability evaluation of various industrial fields where gelcoat is applied such as civil engineering, construction, and marine industry.

• Clean Technology
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• v.25 no.1
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• pp.7-13
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• 2019

Recently, attention has been paid to obtaining bio-polyols from renewable resources. Successful use of these natural ingredients successfully produced in the industry for the synthesis of various polyurethanes is a very important task. In this study, a series of dimethylformamide (DMF) based polyurethanes were synthesized from methylene diphenyl diisocyanate (MDI)/1, 4-butanediol and bio-polyol (polytrimethylene ether glycol based on 1, 3-propanediol : B-POL)/polyester polyol (polyadipate diol based on 1,4-butandiol : H-PET). The effect of different ratio of bio-polyol (B-POL)/polyester polyol (H-PET) on the physical properties of polyurethane was investigated. As the B-POL content in B-POL/H-PET mixture increased, the glass transition of soft segment (Tgs) and tensile strength of polyurethane decreased, however, the elongation at break and tear strength increased. On the other hand, artificial leather was produced by wet process using synthesized DMF-based polyurethanes. It was found that there was almost no difference in the effect of the B-POL/H-PET composition on the average size and density (the number of cells per unit volume) of the porous cells formed in artificial leather. These results show that there is no problem in using bio-polyol (B-POL) based polyurethane for artificial leather produced by wet process.

• Korean Journal of Heritage: History & Science
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• v.52 no.3
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• pp.240-251
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• 2019

This study examined the manufacturing technology used for the flat iron axes excavated from Ulsan Hadae. Their microstructures were analyzed using metallurgical methods. In addition, a variety of manufacturing technologies were examined and compared using existing research materials on flat iron axes. As a result of analyzing ten flat iron axes, which were excavated in the order that they were laid out in a row in one of the wooden coffin tombs at Ulsan Hadae, Tomb No. 44, it was possible to classify the flat iron axe manufacturing technology and system into three types: 'pure iron - shape processing', 'pure iron - shape processing - carburizing', and 'pure iron - shape processing - carburizing - decarburizing.' All of the flat iron axes were produced by forging, and most of them were made by beating the pure iron into their shapes. In particular, a number of the flat iron axes were reinforced through a carburizing process after shaping the iron. This appears as steel products forming the basis of the steel industry at the time were commonly used as an intermediary material or currency. On the other hand, it was commonly found in all samples that the hardening was not performed after shaping or carburizing. Since the microstructure of the flat iron axes made of pure iron contained a large number of impure inclusions and the result of analyzing the components of the non-metal inclusions showed characteristics of slag which contains a mixture of glass phase and wustite, it is possible that low-temperature reduction was used in the refining process.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.31 no.3
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• pp.213-225
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• 2021

Objectives: This study identifies the trends in possible and probable occupational disease among chromium workers and reviews the literature on domestic and foreign chromium workers to review the industries, biological exposure levels, and major results. Methods: The results of the Ministry of Employment and Labor's special health-screening program for hazard agents among workers from 2009 to 2019 were used. Also, the industries, biological exposure levels, and major results on chromium workers were reviewed using PubMed and RISS. Results: The average annual proportion of both possible and probable occupational disease for chromium workers has recently increased. The average annual proportion of possible and probable occupational disease that can occur was high for both men and women in their 60s or older by age and 10 to 14 years by work duration. By industry, possible occupational disease showed high in manufacturing. In the literature review, many electroplating-related chromium-workers reported high levels of exposure to blood and urine chromium, as did dental technicians; tannery, tile factory or glass mill workers; cement workers; and sodium bichromate workers. Furthermore, a number of main findings in recent studies have reported that chromium exposure is related to genetic toxicity among workers. Conclusions: In this study, the average annual rate of both possible and probable occupational disease in domestic chromium workers is increasing, and a body of literature shows that chromium exposure is related to genetic toxicity and associated indicators among workers, which requires more systematic study.