Two problems that are easily overlooked in TPE injection molding

  • Time of issue:2021-09-10
  • Views:485

Two problems that are easily overlooked in TPE injection molding

  • Categories:Industry News
  • Author:SPP
  • Time of issue:2021-09-10
  • Views:485

Thermoplastic Rubber (TPR), also known as Thermoplastic Elastomer-TPE, is a material that combines the characteristics of rubber and thermoplastic. Thermoplastic elastomers have a variety of possible structures. The most fundamental one is that at least two mutually dispersed polymer phases are required. Under normal use temperature, one phase is fluid (make the temperature higher than its Tg-glass transition temperature) , The other phase is solid (make the temperature lower than its Tg or equal to Tg), and there is an interaction between the two phases. That is, a polymer material that shows rubber elasticity at room temperature and can be plasticized at high temperature has mechanical properties and use properties similar to rubber, and can be processed and recycled as thermoplastics. It is built up between plastic and rubber. A bridge. Therefore, thermoplastic elastomers can process rubber products as quickly, efficiently and economically as thermoplastics. In terms of processing, it is a kind of plastic; in terms of properties, it is also a kind of rubber. Thermoplastic elastomer has many advantages over thermosetting rubber.

  一.TPR dyeing / color matching

   SBC-based TPE is superior in color to most other TPR materials. Therefore, they only need a small amount of color masterbatch to achieve a certain color effect, and the color produced is purer than other TPR. Generally speaking, the viscosity of the color masterbatch should be lower than that of TPR. This is because the melt index of TPR is higher than that of the color masterbatch, which will facilitate the dispersion process and make the color distribution more uniform.

   For SBS-based TPE, polystyrene-based vehicle is recommended. For TPR based on harder SEBS, polypropylene (PP) vehicle is recommended. For TPR based on softer SEBS, low-density polyethylene or ethylene vinyl acetate copolymer can be used. For softer varieties, PP vehicle is not recommended because the hardness of the composite material will be affected. For some overmolding applications, the use of polyethylene (PE) vehicle may adversely affect the adhesion to the substrate.

  二.TPR drying / drying

  According to the characteristics of the material and the supply situation, the appearance and process performance of the material should be tested before molding. The supplied pellets often contain varying degrees of moisture, flux and other volatile low-molecular-weight substances, especially the moisture content of TPR, which has a tendency to absorb moisture, always exceeds the allowable limit for processing. Therefore, it must be dried before processing and the water content must be measured. At high temperatures, the moisture content of TPR is required to be below 5%, even 2%-3%, so a vacuum drying oven is commonly used for drying at 75°C-90°C for 2-3 hours.

The dried material must be properly sealed and stored to prevent the material from absorbing moisture from the air and losing the drying effect. For this reason, the drying chamber hopper can be used to continuously provide dry hot materials for the injection molding machine, which is useful for simplifying operations, maintaining cleanliness, and improving quality. It is advantageous to increase the injection rate. The filling amount of the drying hopper is generally 2.5 times the hourly consumption of the injection molding machine

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