Soft package hot air drying energy-saving reforming process

Abstract: This paper introduces a new drying and energy-saving system by analyzing the process factors that affect the drying effect, such as drying temperature, air inlet volume, exhaust air volume, and wind speed. It can ultimately achieve energy savings of 50% to 80% in the printing and compounding processes. In the flexible packaging process, the drying system is the largest energy-consuming part of the gravure printing press and the dry laminating machine. The energy consumption of heating and air intake accounts for 70% to 80% of the energy consumption of the entire machine. It is also the place where organic solvents accumulate and are discharged. Most gravure printing machines and dry laminating machines use electric heating or steam-heated ovens, although there are now new energy-saving heating methods such as hot air ovens, solar energy, and heat pumps. These systems quickly evaporate organic solvents, enabling fast drying of ink and adhesive layers. Proper setting of drying parameters is not only crucial for ensuring print quality but also essential for meeting hygiene standards regarding residual solvent levels. Therefore, the drying parameters include temperature, air intake, airflow, and wind speed, which are key elements in the compounding process. First, the current printing and compounding drying principle and technology 1. Drying Temperature The volatilization of a solvent is a physical process in which a liquid changes into a gas. In an open environment, it occurs naturally. In gravure printing and compounding, the equipment runs at high speeds, with printing presses exceeding 300m/min. To adapt to the high-speed operation of plastic film gravure printing machines and laminators, and to ensure that ink dries quickly on the film, enterprises generally increase the oven temperature to accelerate solvent evaporation and reduce drying time. The criteria for setting the drying temperature are that the substrate should not deform under tension and the temperature should remain stable (within a deviation range of ±1°C). The temperature, pressure, and air volume deviations at each air outlet in the same oven should be minimized. Low temperatures result in low solvent volatility, leading to inadequate drying. High temperatures may cause substrates to deform, especially when the ink or adhesive layer is thick, resulting in surface drying while internal drying remains insufficient, thus reducing product quality. Single-layer substrates like OPP, NY, and PE are more prone to stretching, while PVC substrates tend to shrink. It is recommended that the drying temperature does not exceed 65°C, and the machine tension parameter must be matched accordingly. If the drying temperature is unstable, large temperature differences can generate internal stress on the substrate, reducing the flatness and consistency of the final product and affecting its quality. 2. Air Intake, Exhaust, and Wind Speed These three data can be combined into one, known as the circulation amount. Wind speed is determined by the air intake and exhaust volume under constant oven structure conditions. The structure of the oven is known, and the number and size of the air nozzles are fixed. As the air intake and exhaust volumes increase, the wind speed increases. South Korea's BOOSUNG Engineering company's Wen Yongshi director found that there are two forms of oven outlets for intaglio printing machines from various manufacturers worldwide: one is a nozzle structure, and the other is a hole structure. The nozzle structure oven allows wind speed to be monitored as a data point, while the hole structure oven can only serve as a reference for total exhaust air circulation. Adjusting the air intake serves two purposes: first, to adjust the air volume according to the printing area of each printing unit to achieve adequate drying and save energy; second, to create a relative negative pressure inside the oven. When the difference between the air inlet and exhaust volume is set, the oven can be in either positive or negative pressure states. (1) Positive Pressure: Inlet air volume > Exhaust air volume In a positive pressure state, the air entering the oven will cause the ink to skin over when the wind is greater than the exhaust hot air oven spills, increasing heat loss and creating an odor in the workshop. At the same time, since the hot air entering the oven takes away the volatile solvent, the exhaust volume cannot discharge it promptly due to being too small, causing the solvent concentration in the oven to increase and reducing drying efficiency. As shown in the figure above, when the oven temperature is 70°C and the ambient temperature is 20°C, a large amount of 70°C hot air overflows if the positive pressure is too large, wasting energy. (2) Negative Pressure: Inlet air volume < Exhaust air volume Generally, the oven requires a negative pressure state during the printing process so that the exhaust air volume is slightly larger than the intake air volume, allowing hot air containing volatile solvents to be removed from the oven, maintaining a certain solvent concentration inside the oven to create a rapid drying condition. However, if the negative pressure is too high, a large amount of 20°C ambient air is sucked into the oven, neutralizing the required 70°C process temperature, resulting in 20% to 30% of the original oven drying area being below 70°C, decreasing drying efficiency and causing energy waste of about 30%; the same plant dust in the air will enter the oven, contaminating the printed object. Second, New Drying Energy-Saving Technology For currently used drying technology, Shanghai Tepeng Energy Saving Equipment Co., Ltd. has developed a new heat pump energy-saving system. Using clean energy + temperature, air volume data + oven inlet and outlet air volume balance, it achieves scientific management, guarantees a 50%-80% energy-saving rate, and improves equipment utilization efficiency. Heat pump energy-saving system features include: 1. Core elements of hot air ventilation and drying: (heat + wind + balance) data (quantification) To improve this, the following reform measures can be taken: Equipping the air outlet with an accurate measuring instrument (FMS), which measures the air volume accurately (accuracy ±0.3%) on the line and uses the frequency converter to control the air volume in real time, such as 45 cubic meters per minute. Only through the inverter control fan needs to calculate the wind pressure loss rate when the wind passes through the heat exchanger, wind pipe joints, diameter, bending angle, and other places. The final output simulated air volume and actual air volume are very large. Therefore, it is very necessary to install an online measurement instrument. Balance - Pass: The relative balance of the intake air volume and the exhaust air volume has not been taken seriously before. In traditional equipment, simply adjusting the damper in the exhaust pipe to adjust the balance problem. In fact, the balance of intake air volume and exhaust volume close to 1:1 has a considerable impact on the performance of dry residual solvent indicators, energy consumption, and operating environment. We put the plastic film strip on the lower end of the oven and judged the positive and negative pressure with the method of "seeing the film strip being blown or sucked in." When the negative pressure felt the temperature difference between the lower end and the upper end of the oven, only experienced operators could do it well. Retrofit measures: Each set of drying unit is equipped with a digital balance meter and an automatic exhaust air valve. According to the data displayed on the online balance meter, the automatic air damper in the exhaust air is adjusted to adjust the balance of the intake and exhaust air. Third, Summary The drying process of flexible packaging accounts for 70% to 80% of the energy consumption of the whole machine. It is the most promising place for energy saving and greatly reduces production costs. By using clean energy + oven inlet and outlet to control air volume balance, it can make the environment clean and reduce odor. At the same time, through system control such as frequency converter, PLC, thyristor, FMS, automatic exhaust valve, etc., to realize the balance of temperature and air flow, and use digital settings to manage scientifically and ultimately reduce undesirable products. Improve product quality and achieve 50% to 80% energy savings. Shanghai Tepeng special techniques from BOOSUNG Engineering company, BOOSUNG business since 1983, 30 years in development, a variety of hot air drying system equipment supply flexible packaging industry, intaglio printing machine, laminating machine and coater, and after years of efforts, the company launched the energy-saving hot air dryer product (E-SAVER) using the international patent "Heat exchange element with heat recovery device" and became a global hot air drying company. Invention Patent No. 1 (PCT/KR2009/006395). Special Friends of Energy was established in Shanghai in 2013. So far, it has produced more than 200 sets of energy-saving heat pump systems and has served all domestic large and medium-sized packaging companies. The effective energy-saving rate is 50% to 80%. (Shanghai Tepeng Energy Saving Equipment Co., Ltd.)

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