JOURNAL OF KOREA SOCIETY OF PACKAGING SCIENCE & TECHNOLOGY. Vol. 15, No. 1 1~6 (2009) 진동및충격조건에대한완충재별완충성능분석 오재영 한국생활환경시험연구원 Cushioning Performance Analysis of Cushioning Materials for Vibration and Impact Condition Jae Young Oh Korea Environment & Merchandise Testing Institute Abstract The impact absorption materials made of synthetic organic chemical product like Expanded Polystyrene(EPS), Expanded Polyethylene(EPE), Expanded Polyurethane(EPU), etc. have been used with general packaging material until the present. But nowadays, the use of these materials is intended to be decreased and to be recycled in connection with environmental pollution. In addition, it has been tried to substitute these materials with non-pollution materials(natural materials) like pulp mould, paper protectors, etc. At the same time, it is required to evaluate and analyze these cushioning materials for cushioning properties based on impact and vibration, in order to make an efficiency on the overall packaging system because they are generally being used by a random choice regardless of the properties of contents and cushioning materials. Therefore, this study provides analyzed data on cushioning properties of various cushioning materials against impact and vibration, and is intended to provide more efficient model for packaging system by minimizing their using amount through choosing an optimal cushioning material as well as intended to lead to the use of nonpollution materials in case these cushioning materials have same cushioning properties. Keywords Cushioning properties, Cushioning materials for packaging, Impact absorption, Vibration of packages 서 론 생산제품의다양성과더불어이들제품의유통시안전성과관련하여많은포장재료및포장방법들이개발되어져왔으며, 나아가물류비의절감이나물류합리화, 자원절약등의측면에서포장시스템의설계가이루어져왔다. 그러한포장완충재중에서도 EPS( 발포폴리스티렌 ), EPE ( 발포폴리에틸렌 ), EPU( 발포폴리우렌탄 ) 과같은합성유기화학제품들이지배적위치를차지해왔으나환경문제와병행하여포장설계시이러한재료사용의최소화및재활용을지향하고있으며, 최근에는 Corrugated Pad, Honeycomb 과같은지류포장완충재나전분완충재와같은환경친화적포장재료로의대체를시도해오고있다. 이에따라다양한포장완충재료들이등장하고, 실제유 Corresponding Author : Jae Young Oh Korea Environment & Merchandise Testing Institute, 459-28, Gasan-dong, Gumcheon-Ku, Seoul, 153-803 Korea E-mail : <jyoungo@kemti.org> 통상에사용되기도하지만대부분의경우, 그사용에있어서내용물및완충재의특성에관계없이임의의재질을선택하여제품이파손되지않을만큼두께나면적에있어그사용량을늘이는것이일반적이다. 그러나과연그재질이 다른재질의완충재에비해제품의보호에가장적합한가, 사용량은적당한가, 비용은적절한가? 등과같은효율성에대해간과할수없다. 따라서전반적인포장시스템의효율화를위해, 여러재질의완충재들간의충격이나진동에근거한완충성능의비교평가및분석에대한필요성을공감할수있다. 1,2,3,4,5) 이러한포장완충재와관련하여, EPS( 발포폴리스티렌 ) 나 Corrugated Pad와같은몇몇대표적인완충재에대해서는그발포배율이나골심지의골형태등에따른충격완충성능에대한평가및연구가개별적으로이루어져왔으나, 여러완충재들간의충격이나진동, 온습도에따른물리적특성이상호비교분석된자료를찾기가어렵다. 따라서본연구에서는다양한포장완충재들간의충격이나진동에대한물리적완충특성을비교분석한자료를제공함으로써부하에따른최적완충재를선택하고, 그사
2 오재영한국포장학회지 용량을최소화하여재료비를절감시키고, 이에따른포장물의부피축소로부터물류비용을절감시킴과동시에, 동일한완충성능의완충재에대하여환경친화적포장재료의사용을유도하는등포장시스템전반에걸쳐보다효율적인모델을제공하고자한다. (2) 고온다습조건 (Tropical Condition) 온습도변화에민감한지류완충재의완충성능변화를확인하기위해지류완충재를고온다습조건 (38±1 o C, 85±5% RH) 에서 72 hr동안전처리한후 (ISTA Test Procedure 2A, 2007), 충격실험을수행하였다. 재료및방법 1. 실험재료본연구에서공시된재료는 Fig. 1에나타낸바와같이상용완충재료 5종이며, 이들재료의완충성능을상호비교하기위하여두께를 51 mm로통일하였다. Corrugated Pad 완충재는 A골양면골판지 10겹으로구성되었고, Honeycomb 완충재는공극밀도 (Pore density) 가 76 pore/100 cm 2 이며, EPS(Expanded Polystyrene), EPE(Expanded Polyethylene) 및 EPU(Expanded Polyurethane) 완충재의밀도는각각 15 kg/m 3, 20 kg/m 3, 40 kg/m 3 이었다. 2. 완충성능실험방법 2.1. 전처리 (1) 표준대기조건실험재료의온습도의영향을최소화하기위해 KS M ISO 187에규정된표준대기조건 (23 ± 1 o C, 50 ± 3% RH) 에서 72 hr 동안전처리한후 (ISTA Test Procedure 2A, 2007), 진동및충격실험을수행하였다. 2.2. 진동실험 9,10,12) 특정무게를가진 Steel Plate에응답용가속도센서를부착하고, 해당실험재료로써 Steel Plate의상면및하면을고정하여포장상자에넣고, Table 1의진동실험조건 (KS R 1034) 으로진동을가하여완충재의탄성에따른공진진동수및그시점에서발생되는최대가속도를측정하였다 (Fig. 2). Table 1. Conditions for vibration experiments Experiment Factors Weight Atmospheric conditions Vibrational direction Frequency Range Displacement (peak to peak) Acceleration Sweep Rate Conditions 98, 196, 294 N Standard condition (23 ± 1, 50 ± 3% RH, 72 hr) Vertical 1-5 Hz 5-200 Hz 20 mm (1-5 Hz) Not available (5-200 Hz) Not available (1-5 Hz) 9.8 m/s 2 (5-200 Hz) 1.0 octave/min Fig. 1. Cushioning Materials used for the experiments of cushioning properties, 51 mm of thickness : Corrugated Pad type (A) ; Honeycomb type (B) ; EPS type (C) ; EPE type (D) ; EPU type (E).
Vol. 15, No. 1 (2009) 진동및충격조건에대한완충재별완충성능분석 3 Fig. 2. Schematic diagram for performing vibration experiments. 2.3. 충격실험 1,3,7,13,14,15) 특정무게를가진 Steel Plate에가속도센서를부착하고, 특정한높이 (ISTA, 2008) 에서정해진면적과두께를가진완충재 (Test Block) 상에자유낙하시켜충격가속도를계측하였다 (Fig. 3). 실험조건은 Table 2와같으며, 각 Plate에대해 3회씩실험하여계측된데이터의평균값을완충곡선을구하는데에사용하였으며, 매측정시마다새로운실험 재료를사용하였다. 3. 측정장비전처리를위해항온항습기 (PL-4KPH, ESPEC, Japan), 충격실험을위해 Precision Drop Tester(PDT-227, Lansmont, USA), FFT Analyzer(TP3, Lansmont, USA) 및 Accelerometer (353B34/353B18, PCB Piezotronics, USA), 진동실험을위해 Vibration Test System(CV-700, IMV, Japan) 와 Accelerometer (VP-31/VP-02S, IMV, Japan) 가사용되었다. 결과및고찰 1. 진동실험결과 Fig. 4에서 EPU type 완충재를제외한나머지재료들은부하가증가함에따라공진진동수가낮아짐을확인할수있는데, 이는이러한완충재료들이스프링의고유진동수 (w n ) 와강성 (Stiffness, k) 및질량 (m) 의상관관계를나타내는다음의일반식에부합되는탄성거동을따름을실험적으 Fig. 3. Schematic diagram for performing impact experiments. Table 2. Conditions for impact experiments. Experiment Factors Conditions Weight 49, 98, 196, 294 N Drop Height 762 mm Atmospheric conditions Thickness of specimen Size of specimen Standard condition (23 ± 1, 50 ± 3% RH, 72 hr) Tropical condition (38 ± 1, 85 ± 5% RH, 72 hr) 51 mm 250 100 mm Fig. 4. The change of resonance frequency according to the load, measured from vibration experiment after preconditioning at standard atmospheric condition(23±1 o C, 50±3% RH, 72 hr).
4 오재영한국포장학회지 로확인할수있다. Fig. 4 및 Fig. 5의진동실험결과로부터, 포장내용물의무게및운송화물이받는상용진동수범위에따라적합한완충재료를확인할수있다. 즉, Jung 등 5) 이연구한차량에의한국내농산물유통경로의진동특성에서운송화물의주요진동수분포대역이 20~40 Hz이므로, 우선완충재가가지는공진진동수가이진동수범위에있지않는완충재를선택하고 (Fig. 4), 그다음에공진진동수에서의진동가속도값이최저 (Fig. 5) 인완충재가완충성능이가장우수한재료이다. 따라서 Table 3에그결과를나타내었으며, EPS Foam의경우모든하중영역에서우수한완충능력을보여주었다. Fig. 6. The change of accelerations according to the static stress, measured from impact experiment after preconditioning at standard atmospheric condition(23±1 o C, 50±3% RH, 72 hr). 2. 충격실험결과주어진조건에서의충격실험결과를 Fig. 6 및 Fig. 7에나타내었다. EPS Foam의경우진동실험에이어충격실험에서도모든부하에대하여전반적으로양호한완충성능을보여주었다. 반면, CorruPad 완충재의경우에는표준대기조건에서전반적으로충격가속도값이높게측정되어완충성능이좋지않음을확인할수있었다. 이는 CorruPad type 이 Honeycomb이나 EPS 등다른완충재에비해물결모양의조밀한골을가진단단한구조이므로충격흡수시간이비교적짧고상대적으로완충성능이좋지못함을 Fig. 8을통해확인할수있다. 또한 49 N의가벼운하중이작용될때 CorruPad는충격을한번에그대로흡수하고있으나 (Fig 8. Fig. 7. The change of accelerations according to the static stress, measured from impact experiment after preconditioning at tropical atmospheric condition(38±1 o C, 85±5%RH, 72hrs) and it also shows the change of accelerations compared to that of standard atmospheric condition(23±1 o C, 50±3% RH, 72 hr) at the same time. Fig. 5. Maximum accelerations at resonance frequency according to the load. \ Table 3. Excellent cushioning materials according to the loads, measured from vibration experiments. Load (N) 90 196 294 Cushioning materials EPS Foam, Honeycomb, CorruPad EPS Foam, EPU Foam, Honeycomb CorruPad, EPS Foam, EPU Foam A), 196 N의경우는골의붕괴를통해완충작용이이루어지고있으며그만큼충격흡수시간이길어짐을확인할수있었다 (Fig 8. B). 따라서 CorruPad type경우완충성능은우수하지않지만, 제품이단단하고충격시변형이되어서는안되는중량물의포장에는적합할것으로사료된다. 지류완충재들은 Fig. 7에서보여지는바와같이온습도에영향에따라충격흡수성능이민감한차이를보임을확인할수있었다. 즉, 고온고습조건에서는재질이종이류이므로수분을함유함에따라재질이부드러워지고 (Soft), 변형이용이해지므로충격값이낮아지지만, 중량물에대해서는그성능이급격히저하되었다. 2) 진동실험에서얻은 Table 3의결과를바탕으로 Fig. 6의충격실험결과를조합하면, 중량에따라충격완충성능이가장우수하고제품의특성에적합한포장완충재를선택할수있다. 즉, Table 3에서중량별가장우수한완충성능의완충재를선택한후, Fig. 6에서그중량에서의충격가속도값이최저인완충재를선택함으로써진동및충격에대한완충성능을최대화할수있다.
Vol. 15, No. 1 (2009) 진동및충격조건에대한완충재별완충성능분석 5 Fig. 8. Acceleration graph for CorruPad with 49 N (A) and 196 N (B) weight. 따라서, 상기충격및진동실험결과를통해완충재의재질별충격및진동에따른완충성능에대하여다음과같이요약할수있다. 2.1 Corrugated Pad Type 중량이 294 N이상이고, 정적응력이 12 kpa 이상의부하에서충격완충성능이양호하고, 공진진동수에서도저레벨의진동가속도를보이므로, 그러한제품의완충재로적합하다. 단, 충격흡수시간이비교적짧고구조가단단하여제품의유동을허용하지않기때문에무겁고단단한제품의포장에있어서, 고정재겸완충재로써의사용에적합하다. 2.2 Honeycomb Type 중량이 98 N 이상이고, 정적응력이 4kPa 이상의부하에서충격완충성능이양호하고, 공진진동수에서도저레벨의진동가속도를보이므로, 그러한제품의완충재로적합하다. 2.3 EPS(Expanded Polystyrene) Foam Type 다른재질의완충재들과비교하여, 모든정적부하및정적응력의범위에서양호한충격흡수성능및공진진동수에서저레벨의진동가속도를보이므로, 중량에관계없이일반적인제품의포장완충재로적합하다. 2.4 EPE(Expanded Polyethylene) Foam Type 중량이 196 N 이하이고, 정적응력이 4kPa 이하의부하에서충격완충성능이양호하고, 공진진동수에서도저레벨의진동가속도를보이므로, 그러한제품의완충재로적합하다. 단, 중량및정적응력의부하가높아질수록탄성이커지므로변형이불가한제품에대해서는부적합하다. 2.5 EPU(Expanded Polyurethane) Foam Type 중량이 196 N 이상이고, 정적응력이 4kPa 이상의부하에서충격완충성능이양호하고, 공진진동수에서도저레벨의진동가속도를보이므로, 그러한제품의완충재로적합하다. 결론 1) 지류완충재들의완충성능은온습도변화에매우민감하며, 충격후복원성이거의없으므로반복충격에대하여는매우취약하였다. 그러나 CorruPad의경우, 충격흡수시간이비교적짧고구조가단단하여제품의유동을허용하지않기때문에무겁고단단한제품을포장할때, 고정재겸완충재로사용할수있다. 2) 합성유기화학성분의플라스틱완충재들 (EPS, EPE, EPU) 은온습도변화에덜민감하고, 복원성및탄성이우수하므로반복충격에대하여양호한완충성능을유지한다. 특히, EPS Foam 완충재는진동및충격에대한우수한완충성능을보였으며, 일반적인완충재로가장적합한재료임을확인할수있었다. 그러나폐기물로써의환경부하의원인이되는약점이있으므로재활용기술및재활용율증가방안에대한연구가지속적으로이루어져야할것으로사료된다. 3) 결론적으로, 완충재의재질별진동및충격에대한완충특성을비교분석함으로써포장내용물의특성및용도에따라최적의완충성능을발휘하는재료를선택할수있었다. 이에따라제품에따른최적의완충성능을가진완충재를사용함으로써사용량을줄이고, 적재공간을늘여물류비용을절감시킬수있을것이다. 또한동일한비용과성능의완충재라면,
6 오재영한국포장학회지 보다환경친화적인재료를사용하는것이바람직할것으로사료된다. 감사의글 이연구를위해실험재료를제공해주신 ( 주 ) 동진판지, ( 주 ) 제일산업, 화산수출포장, 아이진수출포장, ( 주 ) 실드에어코리아에감사를전합니다. 참고문헌 1. M. S. Kim, H. M. Jung, J. M. Park, Y. H. Lee. 2001. Development of Measuring System for Cushioning Properties of Package Cushioning Materials. Proceeding of Winter Conference of Korean Society of Agricultural Machinery : pp. 280-285. 2. M. S. Kim, H. M. Jung, J. M. Park, Y. H. Lee. 2001. Cushioning Properties of Package Cushioning Materials. Proceeding of Summer Conference of Korean Society of Agricultural Machinery : pp. 167-172. 3. J. M. Park, S. G. Kwon, S. H. Eam, M. S. Kim. 1998. Design of measuring system of cushioning performance for packaging materials. Korean Soc. for Food Eng. 2(2) : pp. 123-128. 4. J. M. Park, M. S. Kim. 1998. Cushioning Properties Analysis for Packaging Materials - corrugated fiberboard. Korean Soc. for Food Eng. 2(2) : pp. 129-136. 5. H. M. Jung, M. S. Kim, G. S. Kim, B. K. Cho, D. Y. Kim. 2006. Analysis for vibration characteristics of the watermelon for optimum packaging design in domestic distribution. J. Korea Soc. Packag. Sci. & Tech. 12(2): pp. 97-102. 6. KS M ISO 187. Paper, board and pulps-standard atmosphere for conditioning and testing and procedure for monitoring the atmosphere and conditioning of samples. 7. KS A 1029. Testing methods of dynamic compression for package cushioning materials. 8. KS A 1030. Testing methods of static compression for package cushioning materials. 9. KS A ISO 8318. Packaging - Complete, filled transport packages and unit loads - Sinusoidal vibration tests using a variable frequency. 10. KS R 1034. Vibration testing methods for automobile parts. 11. Asvanit, P. 1988. On the effect of moisture content on the shock transmissibility properties of honeycomb cushioning. M.S. thesis, School of Packaging, Michigan State Univ., East Lansing, MI, USA. 12. ASTM Standard D 3580. Standard Test Methods for Vibration (Vertical Linear Motion) Test of Product. 13. ASTM Standard D 1596. Standard Test Method for Dynamic Shock Cushioning Characteristics of Packaging Material. 14. Marcondes, J. A. Waldeck, G. Burgess and S. P. Singh. 1990. Application of high-speed motion analysis to measure shock in cushioned drops. Packaging Technology and Science 3 : pp. 51-55. 15. Marcondes, J. A. 1992. Cushioning properties of corrugated fiberboard and the effects of moisture content. Trans. of the ASAE 35(6) : pp. 1949-1953. 16. Test Procedure 2A, International Safe Transit Association(ISTA) Resource Book 2008.