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 the energy saving of printing and compounding processes by 50%~ 80%.

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 machine and a dry laminating machine, an oven, or heating boilers are generally electrically heated heating steam, etc. (There are new energy-saving heating, such as hot air oven, solar energy, heat pumps, etc.), formed by a hot air wind quickly evaporate Organic solvents quickly dry the ink and adhesive layers. The proper setting of drying parameters is not only the key to ensuring good quality of prints, but also the fundamental guarantee that the amount of residual solvent meets the requirements of the hygienic standards. Therefore, the drying parameters include the drying temperature, air intake, air flow, and wind speed. The most important part of the process in 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 a vapor, and is one of its physical properties. In an open environment, the solvent volatilizes naturally. In gravure printing and compounding, the equipment runs fast and the high speed printing press has a printing speed exceeding 300m/min. In order to adapt to the high-speed continuous operation of the plastic film gravure printing machine and laminating machine, and the process requirements that the ink can be quickly dried on the film , Enterprises 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 are minimized.

Low temperatures will result in low solvent volatilization rates, which will result in inadequate drying; substrates with high temperatures will tend to deform (when the ink layer or adhesive layer is thicker, higher temperatures will cause the surface to dry faster, and internal drying will not be sufficient) , resulting in decreased product quality. . In particular, single-layer substrates such as OPP, NY, and PE are easier to stretch, and PVC substrates are easier to shrink. It is recommended that the drying temperature is set to not exceed 65° C., and a reasonable machine tension parameter must be matched with the drying temperature.

If the drying temperature is unstable, if the temperature difference is too large, internal stress will be generated on the substrate, and the flatness and consistency of the finished product will decline, which will affect the product quality.

2. Intake, exhaust, and wind speed

In fact, these three data can be combined into one, called the circulation amount.

Oven structure diagram

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 adjust 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.:

Heat - Temperature: detected by the temperature probe; need to pay attention to the installation of the temperature probe, try to take the position near the inlet of the oven, so as not to detect the temperature and the temperature error in the oven is too large; good insulation measures.

Wind - Air volume: There is no air flow measurement device in traditional equipment. Manually control the air valve to adjust the air volume. In order to ensure the quality of drying, operators generally use an excessive amount of hot air and need to re-adjust or re-adjust the air volume after changing the printing plate. Generally, they are rarely adjusted, resulting in waste of energy.

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 Peng 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. )