• 월간산업보건
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• s.8
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• pp.4-30
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• 1988

Examination of working environments was conducted to get more detailed data about harmful working environments and to make a contribution to more effective management. Study was carried out on 722 factories located in Taegu city and eight counties in Kyungpook Province, Korea, for a period of one year, from February 1 to December 30, 1986. The total number and proportion of workers exposed to harmful material was 37,697, 45.2% among 83,368 workers. The results according to exposed material were as follows: 1. In the case of noise, proportion of exceeding the 8-hour TLV was 59%, Included were nail-cutting in assembly metal manufacturing industry and weaving process in textile. 2. Dust in mill process of coal manufacturing industries exceeded the TLV of second class of dust at all parts and exceeded the TLV at 6% as a whole.: 3. The fields of industry lower than 70 lux of illumination were storage equipment of food, auto-winder of textile, painting of wood wares and coal mixing, and 44% of all cases was lower than standard. 4. As a result of temperature index investigation(WBGT), about 12% of all sujects exceeded limit value. Included parts were rolling machine and reducing room. 5. In the case of organic solvents, TLV was exceeded at about 8%, The parts exceeded TLV according to materials belonged to this category were as follows. 1) Toluene: adhesive work in assembly metal manufacturing 2) Xylene: printing and paint mixing in chemical manufacturing 3) Methyl ethytl ketone: paint mixing in all parts examined and coating machine partially in chemical manufacturing 4) Methyl isobutyl ketone: printing in chemical manufacturing 5) Acetone: vapor polishing in assembly metal manufacturing 6. Among specified chemical materials, the concentration of HC1 in the air in metal assembly manufacturing factory exceeded TLV. in one of three assembly metal manufacturing examined. Others, such as benzene, acetic acid, formic acid, sodium hydroxide, formalin, ammonia, copper, chromate etc. were lower than TLV in its indoor atmospheric concentration. As a whole, the proportion of exceeding TLV was about 0.8% 7. The concentrations of inorganic lead were lower than TLV in all parts examined. The results of this investigation show the fact that current management of working environments is not satisfactory, and so more active management is needed.

• Journal of the Korean Applied Science and Technology
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• v.32 no.2
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• pp.215-225
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• 2015

Recently, the importance of energy saving and alternative energy is significantly increasing due to energy depletion and the phase change material (PCM) research for saving energy is also actively investigating. In this research, the membrane emulsification using SPG membrane was used to make various microencapsulated phase change material (MPCM) particles which were comprised of $Rubitherms^{(R)}$ (RT-21 and RT-24) core and silica coating. We investigated the pressure of the dispersion phase, the concentration of surfactant, and the ratio of $Rubitherm^{(R)}$ and silica to prepare various MPCM particles. The DSC and TGA were used to examine the heat stability and latent heat properties. Also, PSA, SEM, and optical microscopy were used to confirm the size of $Rubitherm^{(R)}$ particles and the thickness of silica shell. The average of particle size was $7-8{\mu}m$. And, FT-IR was also used to enforce the qualitative analysis. Finally, the MPCM particles obtained from membrane emulsification showed monodispersed size distribution and the heat stability and latent heat were kept up to 80% compared to pure $Rubitherm^{(R)}$. So, it can be effectively used for wallpaper, buildings and interior products for energy saving as PCMs.

• The Journal of Korean Academy of Prosthodontics
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• v.34 no.2
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• pp.266-276
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• 1996

Numerous factors are known to affect the accuracy of elastomeric impression materials. Factor often overlooked is the quality of the bond between putty and wash during corrective reline impression technique. The putty-wash bond strength must be strong enough to over-come the local stress at putty-wash interface. It is not always possible to avoid saliva contamination in making corrective wash impres-sion. And putty preliminary impression material con be used as a template for provisional restoration. Human saliva and the residual monomer of autopolymerizing acrylic resin are thought to affect the bond strength and the failure type. This study examined the effect of contaminants like human saliva, and residual resin monomer on the putty-wash bond strength and the effectiveness of treatment. 1. Of the tested three brands of Vinyl Polysiloxane impession meterial, Express Exhibited the greatest bond strength followed by Eamix and Perfect showed the lowest putty-wah bond strength. 2. Coating the putty substrates with human saliva did not produce decreased failure load in all the breands of Vinyl Polysiloxane impression meterail. 3. Of the three brands of VPS impression material that were exposed to methhylmethacry-late resin(Jet), only the putty-wash bond strength of the Perfect group diminished signifi-cantly. Moreover, all the specimens from group C of Perfect exhibited adhesive failure. 4. Exposing the substrates to ethylmethacrylate resin(SNAP. diminished the putty-wash bond strength significantly. With Perfect and Examix, failure occurred cohesively through the light-body, whereas with Express, failure occurred adhesive-cohesively. 5. Removing approximately 1mm thickness of the contaminated putty interface was the most effective treatment in countering the undesirable effect caused by residual resin monomer. The putty-wash bond strength of the groups that were treated with 1mm even putty reduction was not significantly different from those of control groups. With Perfect and Examix, cleaning the specimens with gauze soaked in 70% isopropyl alcohol increased the putty-wash bond strength, but was not as effective as 1mm even reduction of contaminated putty substrates. With Express, 70% isoproryl alcohol treatment exhibi0ted comparable putty-wash bond strength to that of control group.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.18 no.4
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• pp.310-317
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• 2008

The objective of the survey is to define and judge exposure profiles semi-qualitative data in high risk processes using styrene. The survey was conducted on 98 factories out of 229 factories based on data from periodic working environment monitoring for styrene. Styrene is widely utilized as a raw material for PS and co-polymers such as ABS, SAN, SBR, SBL, unsaturated polyester resins(UPR) and others. An approximate breakdown of styrene's markets in Korea is PS 30%, expandable PS 17%, ABS 33%, SAN 5%, SBL 4%, SBR 3%, UPR 1% and other 7%. Although UPR accounts for 1% of total amount of styrene, workers dealing with it are exposed to very high concentrations up to 64 ppm. Especially styrene is widely used in the laminating process of fiberglass reinforced plastics(FRP) manufacturing industry. The Applications using styrene are largely classified into two sections which are applied to styrene monomer(SM) and UPR. SM is utilized for a raw material of resins, surfactant and adhesive. UPR is employed for FRP and non-FRP. For SM control targets are mixing colors and packing in the gelcoat resins manufacturing industry(MI), for UPR control targets out of works using UPR are 1) laminating in the MI of plastics, automobile parts and boats, 2) mixing and packing in the SMC/BMC MI, 3) molding and cutting in the other specific plastics MI, 4) mixing and coating in artificial marble product MI, 5) dipping in the electric motors & transformers MI, 6) molding in the button MI, 7) painting in the musical instrument MI. Findings from the study have given the information for the high risk processes and working practices so that occupational health professionals could focus on targeted workplaces to prevent occupational diseases. It is also useful to develop a control strategies and specific controls for high risk processes and facilities using styrene.

• Analytical Science and Technology
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• v.31 no.2
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• pp.78-87
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• 2018

Asian lacquer has been used as an adhesive and coating material in Asian countries, such as China, Japan, and Korea, and other southeast Asian countries. In this study, the changes in the chemical structure of lacquer with drying was analyzed using pyrolysis/GC/MS (which is useful in analyzing polymeric material) to understand its drying procedures. Upon increasing temperature, the dried lacquer was fully pyrolyzed above the pyrolysis temperature of $500^{\circ}C$. The repeatability was good at the pyrolysis temperature of $500^{\circ}C$ (rsd = 2.6-22.3 %); however, there were differences in the pyrogram patterns when the difference in sample quantity was large. The characteristic peaks of Asian lacquer components, such as those corresponding to 1,2-benzenediol and 3-methyl-1,2-benzenediol, were detected and the compound of each peak was assigned according to the mass library. As the lacquer dried, the composition of pyrolysis products with urushiol derivatives bearing 3 C=C bonds was severely reduced compared with the ones with no C=C bonds, indicating that the polymerization is related to C=C bonds. These results can be applied to confirm the presence of lacquer in excavated relics and to monitor the changes in the composition of raw lacquer with drying.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.2
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• pp.95-101
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• 2017

In this paper, the sizing removal condition for the pretreatment of composite materials is obtained numerically by applying an image processing algorithm and nickel-plated carbon fiber is fabricated by a dry process method to enhance its electromagnetic shielding performance. Sizings that are wrapped in a polymer type material during the manufacturing of carbon fiber should be removed for dry coating. A numerical value, that is the correlation, can be obtained by determining the regular pattern of the carbon fiber in the image taken by a scanning electron microscope (SEM) after the sizing is removed. The application of the proposed numerical method to the SEM image of the fiber after the sizing is removed with solution, compressed air, solution and compressed air (hybrid), showed that this method of eliminating the sizing is superior to the hybrid method. Then, by spreading the carbon fiber roll with the sizing removed, we were able to produce nickel plated carbon fiber by the roll-to-roll sputtering method. The electromagnetic shielding performance of the fabricated 30, 40 and 100 nickel coated carbon fibers was measured. The Korea Advanced Institute of Science and Technology evaluated the electromagnetic shielding performance of the 100 nickel-coated carbon fiber to have a maximum value of 73.2 (dB) and a minimum value of 66.7 (dB). This is similar to the electromagnetic shielding rate of copper and shows that this material can be used as a cable for EV / HEV automobiles.

• International Journal of Highway Engineering
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• v.13 no.4
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• pp.117-122
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• 2011

Asphalt concrete pavement can be widely seen on urban streets, highways, parking lots, and bike trails. Asphalt concrete pavement is relatively temperature sensitive materials due to the viscoelastic behavior, which can be defined as flexible performance in summer and rigid performance in winter. In terms of maintenance, it can be fixed quite easily if damaged. In addition, asphalt concrete pavement is generally found to be black and grey in color. However, several colors can be adopted to change the appearance of plain old boring, black and grey. Generally, there are two types of color systems in hot mix asphalt concrete materials. One system uses colored cementitious material that is applied to pavement surface through coating the surface of the asphalt pavement. The major disadvantage to this system requires a careful skill set to be used on the construction site in order to prevent taking off the cementitious material. The other coloring system colors the asphalt hot mixtures through using color additives. The main advantage to this system is that the asphalt pavement layer is colored using the same techniques that are already used in paving. The disadvantage is that the colors are limited to mainly reds and browns. In this study, a suggested color additive was evaluated, based on rutting, moisture sensitivity, and fatigue cracking performance.

• Korean Journal of Materials Research
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• v.11 no.8
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• pp.690-696
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• 2001

$TiO_2$ coated coal fly ash has been prepared in order to develop the low price $TiO_2$ photocatalyst and spread out its utilizing field. $TiO_2$ particles is coated on the surface of coal fly ash by precipitation method. In this method, $TiCl_4$ aqueous solution was used as a titanium stock solution and $NH_4HCO_3$ was used as a precipitant. The titanium hydroxide precipitated on the surface of coal fly ash in these neutralizing reaction process was oxidized by heat treatment in temperature ranges of $300~700^{\circ}C$. The crystal structure of the generated titanium dioxide showed anatase type. The crystal size of titanium dioxide increased with raising the temperature of heat treatment, but the removal ability of NO gas decreased. When the titanium dioxide was heated at temperature ranges of $300~ 400^{\circ}C$ for 2 hours, the crystal size of titanium dioxide appeared about 9nm, and the removal rate of NO gas showed 85~ 92%. The whiteness of $TiO_2$ coated coal fly ash increased with raising the coating rate of titanium dioxide and the temperature of heat treatment.

• Korean Chemical Engineering Research
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• v.46 no.2
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• pp.402-407
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• 2008

Recent popularity in mobile electronics requires higher standard on the mechanical strength of electronic packaging. Thus, the method of soldering between chip and substrate in electronic packaging process is changing from conventional method using intermetallic compound to a new method using organic solderability preservative (OSP) in order to improve the stability and the reliability of final product. Since current organic solder preservatives have several serious problems like thermo-stability during packaging process, however, it is necessary to develop new OSPs having thermo-stability. The main purpose of this study is to investigate the effect of MeOH/IPA (Isopropyl alcohol) ratio on the fluxing of a new OSP, developed in previous research, andto find out an optimum formulation of flux components for the application of the OSP in current packaging process. As a result of this study, it was revealed that higher MeOH/IPA ratio in flux showed better performance of fluxing a new OSP.

• Journal of the Korea Concrete Institute
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• v.20 no.3
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• pp.283-290
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• 2008

The repair technique using surface impregnation of reactive compound is so effective for deteriorated concrete structures that many researches are recently focused on these works. Particularly, inorganic impregnant is regarded as ecofriendly material because there is no air-pollution during manufacturing process as well as field coating works. Furthermore, The delamination between old concrete and impregnated surface does not occur, resulting from different material characteristics. In order to evaluate the durability performance of surface-impregnated concrete, durability evaluation through the long-term exposure tests is significant, however, experiments are usually limited to the temporary and qualitative laboratorial scope. In this study, durability characteristics for inorganic and organic/inorganic impregnated concrete specimens are evaluated through longterm chloride exposure test. The specimens with 21MPa and 34MPa strength have been prepared and exposed to chloride attack in the atmospheric, tidal, and submerged conditions. Evaluation for compressive strength, chloride penetration, and electrical potential (half cell potential) for steel corrosion are performed for the specimens exposed for 2 years. From the results, no distinct strength gaining is observed but the resistance to chloride penetration and steel corrosion is evaluated to be improved through surface impregnation. The more improved resistance to chloride attack is measured in the inorganic impregnated concrete and the results from atmospheric condition show more improved resistance to chloride attack than those from submerged and tidal condition.