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 an energy saving 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 the organic solvent accumulates and discharges. Most gravure printing machines and dry laminating machines use electrically heated or steam-heated ovens. (There are new energy-saving heating methods, such as hot air ovens, solar energy, and heat pumps.) These systems quickly evaporate organic solvents, allowing the ink and adhesive layers to dry rapidly. Proper setting of drying parameters is not only key to ensuring good print quality but also essential for meeting hygienic standards regarding residual solvents. Therefore, the drying parameters include drying temperature, air intake, air flow, and wind speed, which are crucial parts of the compounding process. First, the current printing compound drying principle and technology 1. Drying Temperature The volatilization of a solvent is a process in which a liquid changes into a gas or vapor, and it is one of its physical properties. In an open environment, the solvent volatilizes naturally. In gravure printing and compounding, the equipment runs fast, and high-speed printing presses have speeds exceeding 300 m/min. To adapt to the high-speed continuous operation of the plastic film gravure printing machine and laminating machine, and to meet the requirement that the ink dries quickly on the film, companies generally use the drying system to increase the temperature in the oven to accelerate solvent evaporation and shorten the time needed to achieve the drying effect. The criteria for setting the drying temperature is that the deformation of the substrate will not occur under tension and the temperature will remain stable (within a deviation range of ±1°C). The temperature, air pressure, and air volume deviation of each air outlet in the same oven should be minimized. Low temperatures will result in low solvent volatilization rates, leading to inadequate drying; high temperatures may cause the substrates to deform (when the ink layer or adhesive layer is thicker, higher temperatures can cause the surface to dry faster while internal drying is insufficient), resulting in decreased product quality. Single-layer substrates such as OPP, NY, and PE are more prone to stretching, while PVC substrates are more likely to shrink. It is recommended that the drying temperature be set to no more than 65°C, and a reasonable machine tension parameter must be matched with the drying temperature. If the drying temperature is unstable and the temperature difference is too large, internal stress will be generated on the substrate, causing a decline in the flatness and consistency of the finished product, which will affect the product quality. 2. Intake, Exhaust, and Wind Speed These three data can be combined into one, called the circulation amount. The wind speed is determined by the amount of air intake and the amount of exhaust air under conditions of constant oven structure. The structure of the oven is known, the number and size of the air nozzles are constant, and the wind speed increases as the air intake volume and air discharge volume increase. South Korea's BOOSUNG Engineering company Wen Yongshi director found in the study of the structure of the intaglio printing machine oven of various printing equipment manufacturing companies in the world. There are two forms of the outlet of the oven of the intaglio printing machine of Fuji in Japan: one is the wind nozzle structure and the other is the wind hole structure. The wind nozzle structure oven can use the wind speed as a data monitor; the air hole structure can only be used as a reference for the total circulation of the exhaust air. And we adjust the amount of air intake, the purpose of the amount of air: on the one hand, according to the printing area of each printing unit to adjust the air volume to achieve adequate drying and save energy; the second is to create a relative negative pressure inside the oven. When the difference between the amount of air inlet and the amount of air in the oven is set, the positive pressure and the negative pressure are in two states. (1) Positive Pressure: Inlet air volume > Exhaust air volume When a positive pressure state, into the dry version will appear with the ink skinning when the wind is greater than the amount of exhaust hot air oven spills, heat loss while increasing the odor workshop environment, and hot air is blown gravure ink tray. At the same time, since the hot air entering the oven takes away the volatile solvent, the exhaust volume cannot be discharged out of the oven in a timely manner because the exhaust volume is too small. As a result, the solvent concentration in the oven increases, and the drying efficiency decreases. As shown in the figure above, the drying temperature in the oven is 70°C, and the ambient temperature is 20°C. When the positive pressure is too large, a large amount of 70°C hot air overflows to waste energy. (2) Negative Pressure: Inlet air volume < Exhaust air volume Generally, in the printing process, the inside of the oven is required to reach a negative pressure state, so that the amount of exhaust air is slightly larger than the intake air amount, and hot air containing volatile solvents is taken out of the oven to maintain a certain solvent concentration in the oven to create a rapid volatile drying condition. However, when the negative pressure is too high, 20°C air in the environment is sucked into the oven in large quantities to neutralize the 70°C process temperature required in the oven, and 20% to 30% of the original oven drying area is lower than 70°C, resulting in a decrease in drying efficiency; excessive exhaust again just entering deg. C hot air oven 70 has not drying i.e. discharge, resulting in waste of energy about 30%; the same plant dust in the air will enter the oven-like object printed contamination. Second, drying energy-saving new technology For the 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, achieve scientific management, guarantee 50% - 80% energy-saving rate, improve equipment use efficiency. Heat pump energy-saving system features include: 1. The core elements of hot air ventilation and drying: (heat + wind + balance) data (quantification) In this regard, the following reform measures can be taken: The air outlet is equipped 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 on-line 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 adjust 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 the 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. The specific parameters may refer to the operation interface of the recycled waste heat hot air drying system produced by Shanghai TePeng Energy Saving Equipment Co., Ltd. using the patented technology of Korea BOOSUNG Engineering Co., Ltd.: Third, the summary The drying process of flexible packaging accounts for 70%~80% of the energy consumption of the whole machine. It is the most promising place for energy saving and greatly reduces the production cost. 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 Engineeting 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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