Influence of dry compound process parameters Dry compound is the last checkpoint of the residual state of the solvent. It determines the final solvent residue, and the control of the product with very low solvent residue (if the total amount is less than 5mg/m2), Most of them pay more attention to the control of this stage. I will first discuss the control of dry compound process parameters on this issue.
1 Temperature Gradient and Ventilation Effects Dry-combined oven temperature gradients and venting effects are very important factors affecting the solvent residue. Controlling a good temperature gradient and good ventilation are critical. The so-called standard process parameter three-segment oven temperatures are 60°C, 70°C, and 80°C, respectively, for normal machine speeds (80-120m/min) and ethyl esters as solvents. In general, good ventilation plus such a temperature gradient, the residual solvent is controlled to a lower level (for example, less than 5mg/m2) or the xylene is used in the printing process, or the residual toluene content is more than mg/m2 in the full-bottom printing process. When using a film that swells to absorb ethyl esters, the temperature of the dry compound oven should be increased by 5-10°C. Note that increasing the temperature will increase the migration of the slip agent in the film—migration to the bonding layer. , resulting in an increase in the coefficient of friction and a decrease in the bond strength. For coil products, in particular, attention should be paid to the decrease in the coefficient of friction due to the increase in temperature, which in turn leads to poor adaptability to the customer's flow-through bag making equipment, and to the temperature increase for BOPP. High, ethyl ester volatilization rate and adsorption rate increase who dominate, generally the former under 90 °C dominant, 90 °C above, the latter dominant, and in the adjustment, the first section of the oven temperature as immobile as possible The evidence that ethyl ester and toluene volatilize too quickly will form a denser hard glue layer on the surface of the adhesive. Its presence will seriously affect the evaporation of ethyl ester and toluene in the inner layer adhesive and the ink, resulting in an increase in the residual solvent amount. .
In the second stage, a temperature increase of 5-10°C is preferred, and the ethyl ester and toluene in the inner layer adhesive and the ink are forced to evaporate. In the third stage, the volatilization of ethyl ester and toluene is difficult because the hard rubber on the surface has formed. The remaining small amount of ethyl ester and toluene are difficult to break through the adhesive layer and evaporate. This is why the final stage temperature in the process standard can be increased by 5-15°C, but this data is based on the machine speed in the range of 80-120m/min. As a result of the experiment, if the speed is reduced, the temperature can be adjusted accordingly.
2 Effect of coating amount The greater the coating effect per unit area, the thicker the coating layer, the greater the hindrance of the surface layer hardening during the passage of the oven on the evaporation of deep ethyl esters, and the corresponding increase in solvent residue.
The effect of toluene in a certain solvent mixed with a small amount of high-boiling liquid, the evaporation solvent of the mixed solvent will significantly increase, in other words the difficulty of volatilization of the mixed solvent greatly increased, if using solvent-based ink, there must be residual toluene after printing The residual toluene is not only an important part of the residual solvent, but because of the presence of residual toluene, it will further affect the volatilization of the ethyl ester, so this is why we often emphasize in practice to control the residual amount of toluene in the printing is to control the total The reason for the critical steps of the residual amount of solvent. In practice, I found an interesting data. Generally, the final residue of ethyl ester is always about 1.5-2.0 times that of toluene (according to different equipments, the control parameters are different, and it changes accordingly), so the toluene residue in the printing process is controlled. Bad, it will increase the difficulty of volatilization of the mixed solvent in the compounding process, dry compounding cannot guarantee low solvent residue. Reducing the residual amount of toluene in the printing process, the current methods are mainly used in the following ways: 1 change the operating parameters of the printing press, mainly refers to increase the temperature or reduce the printing speed; 2 the equipment is partially reformed and replaced with double ventilation; 3 the use of new materials combination. Generally in the printing process, the toluene residue is controlled at about 4mg/m2 (meaning full-bottom printing) is relatively normal, if you use more precise and precise control, you can control below 2mg/m2, so after the dry composite process after toluene The remaining amount can be controlled to about 1mg/m2, or even lower, it can fully meet the requirements of international food packaging. Recently, the structure of double-vessel ventilation has been more widely used, especially the recently introduced Japanese equipment. There is a strange problem in the printing process. The color blocks with a small area are printed first. Since the area is small, it is easy to dry, but it passes many The oven, while the much larger full-bottom color blocks were printed last, only through an oven, such a structure is not reasonable from the perspective of solvent residue. Duplex ventilation solves this problem by designing an oven on the last large area color block, which greatly improves the drying effect of full-bottom color blocks, and the toluene residue can be further reduced. In addition, the combination of alcohol-soluble inks and solvent-based adhesives can not only meet the requirements for low solvent residues, but also prevent excessive material costs. It is also a good method to be promoted, which has been obtained by many manufacturers. The success, because the ink does not contain toluene at all, the volatile component does not contain toluene, and there is no problem of the impact on the volatilization rate of ethyl ester in dry compounding. It seems that alcohol-soluble inks have been used successfully for BOPP printing, but the effect on PET is just what the packaging industry is waiting for.
The effect of the film is due to the fact that the process we use is to dilute the ink and adhesive and apply it to the adhesive film. After oven drying, the film is finally compounded. The different adhesive films use the same ink and adhesive agent and the same After the production of the process, the residual solvent is not the same. Why? Because the adsorption and release rates of different solvents on the solvent-borne film are different, the release rate of ethyl ester in the commonly used film is ranked as PET> NY> BOPP (absolutely opposite), under normal drying conditions. The temperature is closer to the melting point of the BOPP film, and its molecular random activity is more intense. The adsorption rate of organic solvents such as ethyl ester and toluene is accelerated, which makes it more difficult to return. Therefore, we discussed the process parameters discussed earlier. BOPP film, it is more difficult to reduce its solvent residue, and it is necessary to consider two factors that increase the solvent release rate and forced volatilization rate. In addition, composite membranes with different barrier properties are composited. According to the above-mentioned detection methods, the results of solvent residues are also different, as in the PET/VMPET, PET/VMBOPP and PET/PE structures, under the same process conditions, The order of solvent residues is as follows (values ​​are ranked from highest to lowest); PET/PE, PET/VMBOPP, PET/VMPET. This is due to the higher barrier properties in the PET/VMPET structure and the more difficult solvent release under the experimental conditions, so the measured residual solvent content is lower. In the production of a three-layer composite film (such as PET/VMPET/PET), the second pass compounding generally uses PET/VMPET as a carrier film without the interference of toluene, so the second pass of solvent residue is relatively easy to control. (To be continued) (China Packaging Newspaper and Printing Weekly)
1 Temperature Gradient and Ventilation Effects Dry-combined oven temperature gradients and venting effects are very important factors affecting the solvent residue. Controlling a good temperature gradient and good ventilation are critical. The so-called standard process parameter three-segment oven temperatures are 60°C, 70°C, and 80°C, respectively, for normal machine speeds (80-120m/min) and ethyl esters as solvents. In general, good ventilation plus such a temperature gradient, the residual solvent is controlled to a lower level (for example, less than 5mg/m2) or the xylene is used in the printing process, or the residual toluene content is more than mg/m2 in the full-bottom printing process. When using a film that swells to absorb ethyl esters, the temperature of the dry compound oven should be increased by 5-10°C. Note that increasing the temperature will increase the migration of the slip agent in the film—migration to the bonding layer. , resulting in an increase in the coefficient of friction and a decrease in the bond strength. For coil products, in particular, attention should be paid to the decrease in the coefficient of friction due to the increase in temperature, which in turn leads to poor adaptability to the customer's flow-through bag making equipment, and to the temperature increase for BOPP. High, ethyl ester volatilization rate and adsorption rate increase who dominate, generally the former under 90 °C dominant, 90 °C above, the latter dominant, and in the adjustment, the first section of the oven temperature as immobile as possible The evidence that ethyl ester and toluene volatilize too quickly will form a denser hard glue layer on the surface of the adhesive. Its presence will seriously affect the evaporation of ethyl ester and toluene in the inner layer adhesive and the ink, resulting in an increase in the residual solvent amount. .
In the second stage, a temperature increase of 5-10°C is preferred, and the ethyl ester and toluene in the inner layer adhesive and the ink are forced to evaporate. In the third stage, the volatilization of ethyl ester and toluene is difficult because the hard rubber on the surface has formed. The remaining small amount of ethyl ester and toluene are difficult to break through the adhesive layer and evaporate. This is why the final stage temperature in the process standard can be increased by 5-15°C, but this data is based on the machine speed in the range of 80-120m/min. As a result of the experiment, if the speed is reduced, the temperature can be adjusted accordingly.
2 Effect of coating amount The greater the coating effect per unit area, the thicker the coating layer, the greater the hindrance of the surface layer hardening during the passage of the oven on the evaporation of deep ethyl esters, and the corresponding increase in solvent residue.
The effect of toluene in a certain solvent mixed with a small amount of high-boiling liquid, the evaporation solvent of the mixed solvent will significantly increase, in other words the difficulty of volatilization of the mixed solvent greatly increased, if using solvent-based ink, there must be residual toluene after printing The residual toluene is not only an important part of the residual solvent, but because of the presence of residual toluene, it will further affect the volatilization of the ethyl ester, so this is why we often emphasize in practice to control the residual amount of toluene in the printing is to control the total The reason for the critical steps of the residual amount of solvent. In practice, I found an interesting data. Generally, the final residue of ethyl ester is always about 1.5-2.0 times that of toluene (according to different equipments, the control parameters are different, and it changes accordingly), so the toluene residue in the printing process is controlled. Bad, it will increase the difficulty of volatilization of the mixed solvent in the compounding process, dry compounding cannot guarantee low solvent residue. Reducing the residual amount of toluene in the printing process, the current methods are mainly used in the following ways: 1 change the operating parameters of the printing press, mainly refers to increase the temperature or reduce the printing speed; 2 the equipment is partially reformed and replaced with double ventilation; 3 the use of new materials combination. Generally in the printing process, the toluene residue is controlled at about 4mg/m2 (meaning full-bottom printing) is relatively normal, if you use more precise and precise control, you can control below 2mg/m2, so after the dry composite process after toluene The remaining amount can be controlled to about 1mg/m2, or even lower, it can fully meet the requirements of international food packaging. Recently, the structure of double-vessel ventilation has been more widely used, especially the recently introduced Japanese equipment. There is a strange problem in the printing process. The color blocks with a small area are printed first. Since the area is small, it is easy to dry, but it passes many The oven, while the much larger full-bottom color blocks were printed last, only through an oven, such a structure is not reasonable from the perspective of solvent residue. Duplex ventilation solves this problem by designing an oven on the last large area color block, which greatly improves the drying effect of full-bottom color blocks, and the toluene residue can be further reduced. In addition, the combination of alcohol-soluble inks and solvent-based adhesives can not only meet the requirements for low solvent residues, but also prevent excessive material costs. It is also a good method to be promoted, which has been obtained by many manufacturers. The success, because the ink does not contain toluene at all, the volatile component does not contain toluene, and there is no problem of the impact on the volatilization rate of ethyl ester in dry compounding. It seems that alcohol-soluble inks have been used successfully for BOPP printing, but the effect on PET is just what the packaging industry is waiting for.
The effect of the film is due to the fact that the process we use is to dilute the ink and adhesive and apply it to the adhesive film. After oven drying, the film is finally compounded. The different adhesive films use the same ink and adhesive agent and the same After the production of the process, the residual solvent is not the same. Why? Because the adsorption and release rates of different solvents on the solvent-borne film are different, the release rate of ethyl ester in the commonly used film is ranked as PET> NY> BOPP (absolutely opposite), under normal drying conditions. The temperature is closer to the melting point of the BOPP film, and its molecular random activity is more intense. The adsorption rate of organic solvents such as ethyl ester and toluene is accelerated, which makes it more difficult to return. Therefore, we discussed the process parameters discussed earlier. BOPP film, it is more difficult to reduce its solvent residue, and it is necessary to consider two factors that increase the solvent release rate and forced volatilization rate. In addition, composite membranes with different barrier properties are composited. According to the above-mentioned detection methods, the results of solvent residues are also different, as in the PET/VMPET, PET/VMBOPP and PET/PE structures, under the same process conditions, The order of solvent residues is as follows (values ​​are ranked from highest to lowest); PET/PE, PET/VMBOPP, PET/VMPET. This is due to the higher barrier properties in the PET/VMPET structure and the more difficult solvent release under the experimental conditions, so the measured residual solvent content is lower. In the production of a three-layer composite film (such as PET/VMPET/PET), the second pass compounding generally uses PET/VMPET as a carrier film without the interference of toluene, so the second pass of solvent residue is relatively easy to control. (To be continued) (China Packaging Newspaper and Printing Weekly)
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