Changing the angle at which the extruded profile is pulled out of the die can change the location of the glue on the die, making it easier to clean. In addition, the die glue can be transferred to the product by artificial methods, and then completely removed. For thin plates, automatic mechanical scrapers can be used to remove the adhesive.

       However, operators often need to pay the expensive price of parking to remove the die glue. After the cleaning is completed, applying a mold release agent or silicone resin to the exit area of the die head can reduce the generation speed of the adhesive and extend the interval between two cleanings. In addition, lowering the running speed of the device can also reduce the die glue, but this will affect the output.

       All of the above methods have a permanent cure, but a better solution is to find the cause of the formation of viscose.

       The die glue is related to the stress at the die outlet. On the inner surface of the die, the flow rate of the molten resin is relatively slow, and then, it suddenly accelerates at the die outlet. This acceleration causes stress inside the melt. Under the effect of stress, the low-molecular-weight polymer component is separated from other components in the melt and deposited at the exit of the die to form a glue. Therefore, the solution to the problem is to reduce the exit stress of the die or reduce the tendency of the melt components to separate from each other. This may involve changes to the process, raw materials, or die. Figure 1 The reason for the thick and soft die glue may be part of the melt foaming, resin compatibility problems, or excessive die stress changes Craftsmanship

       Increasing the temperature of the die and the melt is one of the ways to reduce the pressure at the outlet of the die, but it may cause additional degradation, resulting in an increase in low molecular weight components. Therefore, the temperature of the melt and die must be adjusted separately. However, it should be noted that sometimes, the die temperature is too low, a slow flow resin cold flow layer may be formed on the inner surface of the die, the cold flow layer and the main flow of resin are separated from each other, and eventually lead to the formation of adhesive.

        The simulation of die flow can be used to study the stress change of the resin at the die outlet. This stress will eventually lead to the generation of die glue (picture from Compuplast). To set the die temperature, first determine the true melt Body temperature. Because standard melt thermocouples often produce errors, the melt temperature needs to be measured manually. Although this method is more difficult, it is very necessary to find the cause of the failure. In addition, since the surface temperature at the exit of the die head is much lower than the temperature of the die head itself, surface thermocouples should be used when checking the exit temperature of the die head.

       Blowing the die outlet can reduce and control the formation of viscose, and at the same time can bring various flue gas and condensable gas away from the die. In addition, the blast also helps to cool the die glue, making it less susceptible to oxidation and blackening. N2 can also be used to prevent oxidation. However, it should be noted that do not blow too hard or lower the die temperature too low, so that the extrusion profile is deformed.

       Changing the raw materials will produce different forms of die glue, some are thin and sticky, and some are thick and loose. The thin and viscous viscose is formed by vaporizing at the die outlet and condensing on the die surface, usually generated from low molecular weight components in the raw material. Thick and loose viscose is usually caused by partial foaming inside the melt, compatibility issues, or excessive pressure inside the die. Therefore, when extruding, avoid excessive humidity or degradation of the resin, as well as possible melt fracture or improper venting.

       Some suppliers' resins produce more viscose than resins from other sources, even if these resins have exactly the same technical specifications. When die glue appears, try to use resins of similar grades from other suppliers. If the glue problem improves, then the initial resin may have performance problems.

       Resins from different suppliers may have similar shear viscosities but very different elongation viscosities. If no difference in other properties is found, you can try to detect its elongational viscosity. A resin with a higher elongational viscosity may generate more viscose due to the increased die outlet pressure.

In some cases, resins with larger changes in die expansion will have a higher rate of die glue generation. When the resin has a narrow molecular weight distribution, the die swelling may be lower, but this does not necessarily mean that less viscose is generated. Generally, resins with a narrow molecular weight distribution are difficult to process and may generate low molecular weight components, which ultimately leads to die glue.

       Recycled resins usually contain low-molecular-weight components resulting from thermal degradation during previous processing. For this, an auxiliary agent for inhibiting degradation may be added, or a chain extender that can polymerize the degraded component again may be used. If these do not work, these recycled materials will not be suitable for use.

       Sometimes, adding lubricant helps to reduce the viscose, but too much lubricant may also increase the generation of viscose in the die. The chemical compatibility of different components in the formulation is also one of the important factors affecting the viscose problem. For example, when highly incompatible polymers are melt mixed together, extreme cases of die glue often occur. In this case, the use of compatibilizers will help alleviate the formation of viscose. In addition, the addition of a small amount of fluoropolymer processing aid can also reduce the die outlet stress. Figure 3 The improved die outlet geometry (some have applied for patent protection) can reduce the generation of die glue

       For the type of die adhesive that will quickly oxidize, turn yellow or turn black, antioxidants can be added to the formulation. Although this does not solve the problem of die glue, it can make the glue adhering to the product invisible.

       Change the die to apply fluoropolymer, such as PTFE, on the die surface to prevent the formation of viscose to a certain extent. A more effective method is to use a metal coating to make the fluoropolymer penetrate the inside of the die to reduce the stress at the die outlet.

       On the other hand, die flow simulation has been successfully applied to solve the problem of die adhesive. By simulating the flow state of resin at the die, the cause of the die outlet stress can be studied, and the effect of changing the geometry of the die outlet geometry on the viscose can also be evaluated.

       It is a widely used method to improve the geometry of die outlet to reduce stress. Some die shapes have been applied for patent protection by processors and resin manufacturers. It is said that the improved die outlet that can reduce the generation of die glue includes: sharp square outlet, sharp pointed mouth outlet, rounded outlet, outward stepped outlet, inward stepped outlet, and outward Funnel-shaped exit.

       In addition, by increasing the length of the molding section of the die, thereby reducing the variation range of the resin at the die outlet, it also helps to reduce the die outlet stress.