Measuring Total Thermal Resistance, R t :

1. Effect of Screen Printing Ink on the Thermal Performance of Running Shirts Seth Moczydlowski 1.0 INTRODUCTION • Total Evaporative Resistance,Ret • Overall, the ensemble exhibited a negligible increase in evaporative resistance • Focusing solely on the Torso [Zones 13,14,15,16,17,18], however, shows a significant increase in evaporative resistance. There was a 7% increase with the grid pattern, and a full 25% increase in evaporative resistance of the torso area from the block pattern. • Measuring Total Thermal Resistance, Rt: • Thermal resistance is the measure of a garment’s resistance to a heat flow over a temperature gradient. Clothing articles with a higher thermal resistance require less energy to maintain a given temperature gradient. • Total thermal resistance is the thermal resistance of the garment, and the air layer enclosed above the skin. • Testing was conducted according to ASTM F1291-04 “Standard Test Method for Measuring the Thermal Insulation of Clothing Using a Heated Manikin” [4]. • Chamber conditions were held constant at 23°C and 50% relative humidity. Manikin skin temperature was held constant at 35°C. • Manikin was dressed in clothing ensemble to be tested and data measurements were taken using control software every minute until steady state conditions were achieved. • Steady state was defined as a constant reading of manikin skin temperature and power input within ±3% over a period of 30 minutes. • The test was replicated a total of 3 times for each shirt and the results were obtained using an area weighted average to calculate the Total Thermal Resistance. Today’s running enthusiast has a variety of options when selecting athletic garments to purchase. It is common knowledge that lightweight, wicking polyester fabric will keep the wearer drier and more comfortable than a similarly cut cotton garment [1]. Besides a reduction in comfort, excessive moisture can increase the effects and occurrence of chafing and irritation during exercise [2], and make clothing stick to skin, potentially limiting mobility. Running shirts are offered in a variety of styles and colors and marketed with trademarked names to promote the performance qualities of the fabric. These garments also frequently are screen printed with logos and graphics promoting companies or sponsored running events. Commercial screen printing operations generally use a heat-cured plastisol ink consisting of PVC resin and a plasticizing agent. When cured at around 160°C, the resin particles absorb the plasticizer and merge to create a thin, uniform, plastic film [3]. The film is durable and abrasion resistant to remain visible and intact throughout the life of the garment including repeated washing and drying. Unfortunately, this film also acts as a watertight barrier, reducing the amount of surface area available for evaporation and potentially limiting the wicking performance of the garment. • The stomach zone exhibited the highest increase of139% with the block pattern. • The upper chest also showed increases of 10% and 27% for the grid and block patterns , respectively. • Interestingly, the mid-back reduced its evaporative resistance by around 10%. 2.0 OBJECTIVE • Determine the impact of screen printed graphics on the thermal performance of lightweight, wicking polyester running shirts using a thermal manikin. • Provide a set of recommendations that can be used either by apparel companies concerned with the design of high-performance running shirts or by athletes when selecting garments for purchase. • Measuring Total Evaporative Resistance, Ret: • Evaporative resistance is the measure of a garment’s ability to resist the evaporation of water through the piece of clothing. Clothing with a higher evaporative resistance will evaporate less water through the garment given a constant environment. • Total evaporative resistance is the evaporative resistance of the garment, and the air layer enclosed above the skin. • Testing was conducted according to ASTM F2370-05 “Standard Test Method for Measuring the Evaporative Resistance of Clothing Using a Heated Manikin”[5]. • Chamber conditions were held constant at 35°C and 40% relative humidity. Manikin skin temperature was held constant at 35°C. • Manikin skin was applied and wetted to ensure full saturation. Sweat pumps were turned on and set to pre-determined flow-rates. • Manikin was dressed in clothing ensemble to be tested and data measurements were taken using control software every minute until steady state conditions were achieved. • Steady state was defined as a constant reading of manikin skin temperature and power input within ±3% over a period of 30 minutes. • The test was replicated a total of 3 times for each shirt and the results were obtained using an area weighted average to calculate the Total Evaporative Resistance. 3.0 MATERIALS AND METHODS • A survey of store-bought running shirts with screen-printed graphics revealed a range of ink coverage from 2% to 16% of the measured flat-pattern area, with an average of 9% coverage. • Samples: • Three white running shirts made of 100% 4.0 ounce weight polyester wicking fabric. • All shirts were modified with zipper on the left shoulder to enable quick garment change on thermal manikin. • Two shirts were hand-screened with different patterns using glossy black plastisol ink. Ink was cured to 160°C using a heat gun and laser-sighted infrared thermometer. The results clearly show an increase in evaporative resistance of the stomach and upper chest due to the presence of the PVC graphic pattern blocking airflow and reducing surface area available for evaporation. Users wearing this garment would experience a noticeable increase in moisture in the chest and stomach region during athletic activity compared with the rest of the garment. The increase in moisture could lead to chaffing and irritation during vigorous exercise. 5.0 CONCLUSIONS & FUTURE WORK 4.0 RESULTS AND DISCUSSION • Conclusions: • The experiment confirmed that plastisol screen printing ink does have a measurable negative effect on the thermal performance of wicking polyester athletic shirts. While a slight local increase of 10% thermal resistance was recorded, local increases in evaporative resistance were measured as high as 139%. • Recommendations for Design/Use of Screen Printed Graphics on Polyester Athletic Shirts: • For minimal negative effect, keep the coverage area of screen printed designs at or below 5% of the flat-pattern shirt area. • Avoid graphic designs with large solid block ink sections. Use of patterns can help provide a large perceived graphic size, while using minimal amounts ink. • Maintain a consistent ink coverage area throughout product lines or athletic wear wardrobe. Wearing new and/or different clothing articles on “race-day” can negatively affect performance. • Future Work: • Next steps for this work will include design of an athletic shirt product line using the above guidelines. • Thermal Resistance, Rt • Overall, no significant change in thermal resistance was noted. Half - Grid Pattern 9% Coverage Coverage Area: 0.034 m² Full – Block Pattern 18% Coverage Coverage Area: 0.068 m² Blank – No Pattern 0% Coverage Total Shirt Area: 0.371 m² • Locally, a thermal resistance increase of 10% was indicated over the Zone 15, the Stomach. 6.0 REFERENCES Methods: Testing was conducted using a 34-zone Newton model thermal manikin in the form of a 50% human. The manikin accurately simulates metabolic heat output of the human body using a computer controlled system of heating elements and sensors. The system also has the ability to “sweat” via micro-pump-controlled pores positioned throughout the body and a removable skin suit that evenly distributes moisture over the surface . [1] "Chafing." Skin Chafing Causes, Treatments, Prevention. Ed. Varnada Karriem-Norwood. WebMD, 31 Aug. 2012. Web. [2] Greene, Warren. "Proper Attire." Proper Running Attire at Runner's World. Runner's World, 10 Feb. 2004. Web. [3] "Water Based Ink vs Plastisol." OoShirts, 28 Nov. 2012. Web. [4] ASTM Standard F1291-04, "Standard Test Method for Measuring the Thermal Insulation of Clothing Using a Heated Manikin" ASTM International, West Conshohocken, PA, 2004. [5] ASTM Standard F2370-05, "Standard Test Method for Measuring the Evaporative Resistance of Clothing Using a Sweating Manikin" ASTM International, West Conshohocken, PA, 2005. The slight increase in thermal resistance of the Stomach zone indicates that the PVC graphic does provide some insulative value to the fabric. However, when averaged over the entire garment and ensemble, these increases are washed out and show no change in thermal resistance. ACKNOWLEDGMENTS The manikin is housed in a temperature controlled chamber that maintains environmental conditions at a specific temperature from 10 to 40°C and 30 to 70% relative humidity (RH). Philadelphia University Research Center – Laboratory for Engineered Human Protection Professor Janet Brady and Wendy Anderson for advising and screen printing tips. Jennifer James for seamstress skills and moral support.