The transparent PVC tube is made by extruding polyvinyl chloride resin with a certain amount of stabilizer and other additives.
Transparent PVC pipe has the characteristics of transparency and smoothness, light weight, beautiful appearance, and good colorability. It is widely used in construction, chemical industry, and household, for water infusion, and transport of corrosive media.
The formula of transparent PVC tube mainly includes: PVC resin, heat stabilizer, lubricant, plasticizer and colorant, etc. According to the analysis of the above technical indicators, the formula design of transparent PVC tube should meet the requirements of transparency, moderate hardness and high strength.
In order to improve the transparency, when selecting the auxiliary materials for processing, the additives with the same or similar refractive index as the PVC resin refractive index (1.52~1.55) should be selected as much as possible.
Because when raw materials with the same or similar refractive index are processed into a uniform mixture, their refractive index is also similar to that of the raw material.
In this way, the scattering phenomenon in the direction of incident light will not increase, so the turbidity of the product will not increase, and the transparency of the product will not be greatly affected.
1. PVC resin
Since the amount of plasticizer in the formula is relatively large, it is required that the PVC resin has good oil absorption, and a loose resin should be selected. At the same time, a batch of resin with high whiteness, good thermal stability, and fewer impurities and fish eyes is required.
Under the premise of meeting the requirements of mechanical properties, the production of transparent PVC tubes should try to use resins with a slightly lower molecular weight.
Because the commonly used plasticizers DOP and DBP often contain components with relatively low molecular weight, when the processing temperature is higher than 105°C, they will often volatilize and form bubbles, and the temperature can only be controlled at a low temperature.
In this case, the degree of plasticization and melting of the resin with a low relative molecular mass is higher than that of the resin with a large relative molecular mass, which is beneficial to improve the transparency of the product.
In addition, resins with a slightly lower molecular weight are also easy to process. Generally, PVC-SG3, SG4, and SG5 resins are acceptable, and can be selected according to product requirements.
Mainly consider its plasticizing effect, cold resistance, durability and influence on the transparency of transparent PVC tubes. DOP is a comprehensive plasticizer with a refractive index of 1.484, which is close to that of PVC. It is often used as the main plasticizer for transparent PVC pipes.
The refractive index of DBP is 1.492, which is also close to the refractive index of PVC resin. It will not affect the transparency too much, but its plasticizing efficiency is poor and volatile. It is generally used as an auxiliary plasticizer for DOP. In order to improve the cold resistance, DOS can be added as an auxiliary plasticizer, and the amount of plasticizer is generally 40~55 parts.
3. Heat stabilizer
In addition to requiring basic properties such as heat resistance, weather resistance and ease of processing, its transparency should also be considered. Organotin stabilizers are the most ideal and most commonly used heat stabilizers for transparent PVC tubes, but the price is relatively high.
Metal soap stabilizers, such as calcium stearate, barium stearate, zinc stearate, etc., are commonly used heat stabilizers for transparent PVC tubes, and their composite products Ca/ Zn, Ba/ Zn, Ba/ Ca and Ba /Ca/Zn is more ideal.
In order to reduce the amount of organic tin in the actual formula, calcium stearate (calcium soap) and zinc stearate (zinc soap) with good transparency and lubricating effect are selected as auxiliary stabilizers.
It can be divided into two types: internal and external lubricants. In transparent PVC tubes, due to the large amount of plasticizer used, the viscosity of the material is relatively small and the fluidity is good, so the amount of lubricant used is less, and the amount used is 0.1~1.0 parts.
More objectively speaking, it should be a color supplement. Due to the particularity of the molecular structure of PVC, heat and mechanical friction during processing will cause yellowing to a certain extent even if enough stabilizers are added. Adding a little pigment can cover up the yellow color and make the product more beautiful.