2023 The 16th Ningbo International Plastics & Rubber Industry Exhibition

June 15-17, 2023

Ningbo International Convention And Exhibition Center

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What is the relationship between PVC pipe extrusion precipitation, color difference, paste and other issues and stabilizers?

1. Precipitation problem:

The precipitation problem in the processing of hard products, especially extruded products, also occurs when the lead salt composite stabilizer is used, but the use of environmental protection stabilizers such as calcium and zinc exposes more problems, the reasons are more complicated, and the solution is more difficult. The precipitation problem that occurs when using lead salt composite stabilizer and calcium-zinc environmental protection stabilizer for extrusion mainly occurs on the die and setting sleeve. There are two situations on the die: one is the white or yellow wax (oil) that appears on the die. The reason is obvious, that is, the low melting point lubricant that is poorly compatible with PVC is too much and is freed on the surface of the product , When exiting the die, it leaves the product and forms a white or yellowish brown wax (oil) on the die. The other is the longer and longer "moustache" on the die. The reason is more complicated. The author thinks that the melt strength of the material is insufficient due to the lack of lubrication in the later stage, and the demoulding effect in the later stage is not enough. The precipitation of the setting sleeve is the precipitation that is relatively easy to occur after the calcium-zinc stabilizer is used. The reason is more complicated or everyone has not figured it out, and it is difficult to solve it completely. Whether it is possible to use external lubrication with high efficiency and high melting point as much as possible, and use as little lubricant as possible (including internal and external lubrication) under the premise of meeting processing requirements, and pay attention to melt strength and mold release.

2. Color/color difference problem:

After the stabilizer of rigid PVC products is changed from lead salt to environmental protection stabilizer such as calcium and zinc, the color problem is also a relatively common problem with various forms, and it is relatively difficult to solve. Its manifestations are as follows:

1. Stabilizer replacement leads to changes in product hue. After the stabilizer is changed from lead salt to calcium and zinc, it is easy to find that the hue of the product is often cyan, and it is difficult to realize the hue from cyan to red.

2. The color inside and outside of the product is inconsistent after using the environmentally friendly stabilizer. Usually, the outer color is relatively positive, and the inner part is easy to be green and yellow. This situation is easy to occur in profiles, and it also occurs in pipes.

3. The color drift of the product during processing after using the environmental stabilizer. In the process of using lead salt stabilizer to process products, there will be a certain hue deviation between each machine and the same machine at different time periods, but the fluctuation range is relatively small. With the use of environmentally friendly stabilizers, this fluctuation may become larger, and the effect of small fluctuations in raw materials and processes on hue may be more obvious. I have encountered the situation that when using environmentally friendly stabilizers to produce pipe fittings, the pressure change not only affects the hue of the product, but also affects the performance of the product. This change is much more sensitive than when lead salt stabilizer is used.

4. The color problem of the product during storage, transportation and use after using the environmentally friendly stabilizer. Rigid PVC products using traditional lead salt stabilizers have little color change during storage, transportation and use. After being converted to environmental stabilizers such as calcium and zinc, it may appear yellowish and greenish after standing. When some stabilizers are used in products with high iron ion content in calcium powder, the problem of product redness may occur.

The main reason for the color problem is that the material components of the environmental stabilizer are relatively complex. The thermal stability in the early, middle and late stages is achieved through the coordination of various materials. Each component has a certain influence on the hue of the product. a possibility.

3. Paste problem:

Paste is also a common problem. The paste is mainly due to sticky material in the mold mandrel and some corner positions of the mold design, and then turns into a yellow line or a black line on the surface of the product. More seriously, the paste is blocked and the mold is shut down. The paste is definitely caused by the local thermal decomposition of the material, but the reasons for the decomposition of the material in the actual operation process are relatively complex and cannot be generalized. If the paste is caused by insufficient stability, it can be solved by strengthening the stability of the material. However, if the paste is caused by sticky material due to insufficient lubrication or insufficient lubrication and dispersion in the later stage, it cannot be solved by simply adding a stabilizer, and it is necessary to strengthen lubrication or lubrication. Insufficient dispersion and so on. In addition, insufficient melt strength may cause the material to stick to the wall, which may lead to paste, excessive or uneven mold design corners may cause paste, and impurities or coarse particles in the filler may cause paste and so on.

Of course, the paste is not created by the use of environmentally friendly stabilizers, but has always existed. We have some experience in using traditional lead salt stabilizers to solve the paste. After mastering the essential characteristics of the environmentally friendly stabilizer, it can also be used to solve the problem of environmental protection. The paste problem during the use of the stabilizer.

4. Thermal stability problems under unexpected production conditions:

There are inevitably some unexpected situations in industrial production. The common accidents in the processing of PVC products are sudden power outages or sudden shutdowns caused by some emergencies. Sudden shutdown is more of a test of the static stability of the material. If the static stability of the material is not good, the sudden shutdown of the unexpected situation may cause decomposition and sintering due to the material stagnant in the equipment for too long. Equipment may be damaged. If the material is sintered in the barrel due to sudden shutdown and improper disposal, the final result is that the screw barrel is directly scrapped. Relatively speaking, environmental stabilizers are slightly worse than lead salts in terms of static stability, so preparations for sudden shutdowns also need to be more fully prepared. The following are some suggestions for preparing for sudden shutdown: a. The amount of environmental stabilizer in the production process should be kept as safe as possible to ensure the static stability of the material. b. If possible, try to use the transition of starting and stopping materials as much as possible, and do not let the normal production materials stay in the machine for too long. c. Try to use environmentally friendly stabilizers that consider static stability, rather than blindly pursuing low prices for stabilizers.

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