Adjustable lip slit coating die for improved productivity and accuracy of hot melt coating
In the field of hot melt adhesive coating, the adjustable lip slit coating die has great advantages due to its versatility, accuracy and wide operating capability, especially for those who need to perform small batch production and frequent The material processor of the job change is more valuable.
Numerous material processors are increasingly seeing slot coating die systems as a more efficient and controllable alternative to roll coating and other conventional methods of applying fluids to planar substrates. In the field of hot melt adhesive coating, the adjustable lip slit coating die has great advantages due to its versatility, precision and wide operating capability, and these advantages have also benefited many material processing traders. This is especially valuable for material processors who need to perform small batch productions and frequent job changes.
Several different types of slit coating dies are currently available on the market, including fixed lip and adjustable lip system. One of the reasons for the increasing attractiveness of slot-coated die systems is that the fierce competition in the global marketplace has increased the pressure on companies to maximize economics, productivity and quality assurance. The use of slit coating dies will help meet the needs of these markets because it differs from the roll coating in two key ways:
1. It is a “predicted amount†system that can apply hot melt adhesive to the surface of a flat substrate at a constant speed, and can precisely control the coating amount and distribution on the entire planar substrate; it can reduce waste. Achieve high line speed and high solids coating, which can improve product quality and uniformity;
2. It is a closed system, so it can effectively prevent the pollution of impurities in the air environment.
The function of the slit coating die is to maintain the fluid at the proper temperature suitable for coating, to evenly distribute the fluid to the desired coating width, and to apply the fluid to the planar substrate. The die can be split into an upper die body and a lower die body, and the upper and lower die bodies can be bolted together. A hanger-shaped flow passage (ie, a manifold) is enclosed in the two mold bodies, the flow passage is machined from the upper mold body or the lower mold body portion, and the widest portion thereof is located at the exit slit, and the width is The coating width corresponds. The manifold distributes the coating fluid entering the die to its entire target width, which ensures a uniform and streamlined distribution of the coating stream through the exit slit of the die.
The key to coating control:
Constant coating speed
The slot coating die provides advanced control over the coating process, helping to achieve its constant coating speed. The forward displacement pump feeds the hot melt into the die at a constant rate without pulses, and all fluid entering the die is applied to the planar substrate. In roll coating, only a portion of the coating on the coating roll can actually be transferred to the planar substrate, and the amount of coating varies with factors such as fluid viscosity, substrate travel speed, and roll speed. Another disadvantage of roll coating is the need to recycle the remaining coating liquid, since this coating method can only partially utilize the coating liquid on the coating roll. Impurity contamination can cause damage to product quality and lead to waste of raw materials. The constant coating speed of the slit coating die allows these dies to be coated efficiently at line speeds above the roll coating. Since the roll coating only allows a part of the coating liquid to be transferred from the coating roll, product defects may occur due to cracking of the coating liquid film at the time of high speed coating. In the slit coating process, the proper design of the coating lip can effectively avoid the defects caused by the cracking of the liquid film during coating. The achievable coating speed varies greatly depending on the coating: in hot melt coating, the slit coating die can usually be coated at speeds up to 600 m/min; The corresponding high speed is only 365 m / min.
Versatility and precision of the adjustable lip slit coating die
One of the keys to the versatility of the adjustable lip slit coating die is the ability to change the lip opening clearance (or the applied wet film thickness) on the production line without disassembling the die. In contrast, if you want to change the lip spacing of the fixed lip slit coating die, insert a thin metal strip or spacer between the upper and lower body and then use more spacers at the back of the die to eliminate The resulting lip faces are offset and they are again in the same plane.
In addition, the adjustable lip slit coating die also exhibits extremely high coating accuracy. Nordson Corporation's Ultracoat HM slit coating die maintains uniformity of coating in the range of +/- 1.75-3.50%. There are three reasons for achieving this accuracy:
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