Overview of the TPU Materials Overmoulding Process

TPU materials encapsulation is actually a secondary molding process of TPU encapsulated hard (or soft) resin, which usually includes body (hard resin, such as PC/ABS, ABS PA PA66 PS hardware parts and metal parts). In the process of mold manufacturing and production, the main mold is usually dominated by hard resin products. Firstly, the main hard resin product is manufactured, and then TPU materials are used for secondary injection coating molding to cool the product.

Methods for TPU materials encapsulation

• Double-colored injection molding - one-time molding with double-colored machine;

• Sleeve injection molding - the machine needs to be packaged with plastic for secondary molding.

Types of TPU materials encapsulation:

• True encapsulation - the compatibility of soft and hard resin (or soft resin) in softening and melting process (compatibility mainly depends on the solubility parameter SP of the material, the closer the solubility parameter is, the better the compatibility between the two materials). An adhesive layer is formed on the contact surface of the two materials, which greatly improves the adhesion between TPU soft and hard resin (or soft resin);

  
  

• False encapsulation - usually does not involve the compatibility of materials. Mainly through mechanical force, mold design and mold surface treatment, and increasing insert fasteners to ensure the adhesion of TPU to other materials.

Common product problems of TPU materials encapsulation

• Coating is not firm;

• There are filling points and gloss on the surface of the product;

• Rough edges;

• Deformation;

• Missing glue and insufficient mold.

Factors affecting the TPU materials encapsulation process:

• Mold design - firstly, the shrinkage rate of TPU materials, the size of hole avoidance and sealing position should be considered. The mold surface should be as far as possible to adopt the frosted surface for easy demolding;

• TPU materials should adopt heat-resistant materials as far as possible (comprehensively considered). According to the product structure design, choose TPU materials with appropriate hardness, viscosity and crystallinity;

• The TPU molding temperature is generally recommended as 30-50℃;

• The molding process is usually slow burning rate at medium and high pressure;

• For products with thicker encapsulation, post-treatment annealing is recommended to eliminate internal stress and improve mechanical properties;

• TPU materials encapsulation is sensitive to the oil stains, release agents and other additives on the mold surface. It is recommended to check the mold surface during the production process and clean it in time.

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