Huizhou TPE manufacturer shares: What factors determine the light transmittance of translucent TPE raw material particles?

The light transmittance of translucent TPE pellets isn't determined by a single factor; rather, it's influenced by a combination of factors, including the raw material formulation, production process, impurity control, and post-processing and storage. These factors alter the propagation of light within the pellets, ultimately determining the quality of light transmittance. Below, Huizhou Zhongsuwang's editors will analyze in detail how each factor influences the light transmittance of translucent TPE pellets, focusing on key factors.

1. Raw Material Formulation

The raw material formulation fundamentally determines the light transmittance of translucent TPE pellets. The selection and proportions of different components directly alter the optical properties of the pellets:

1. Base Elastomer Selection

The base elastomer types used in TPE (such as SEBS, SBS, and TPU) inherently vary in light transmittance. For example, SEBS elastomers exhibit excellent light transmittance when they are of high purity. However, due to the distribution of benzene rings in their molecular structure, SBS elastomers, without special processing, have slightly lower light transmittance than SEBS. TPU elastomers, on the other hand, are significantly affected by the ratio of hard and soft segments. A high proportion of hard segments can easily cause light scattering, thereby weakening the translucency.

2. Plasticizer Compatibility and Dosage

Plasticizers primarily adjust the hardness and flexibility of TPE raw materials, but they also affect light transmittance. If the selected plasticizer is not compatible with the base elastomer, it can precipitate within the particles or form tiny phase regions. Light passing through these regions will refract and scatter, reducing light transmittance. Excessive plasticizer addition can form a film on the particle surface or cause an uneven internal structure, similarly affecting light transmittance uniformity. 3. Impact of Fillers and Modifiers

Some translucent TPE raw material formulas contain fillers (such as calcium carbonate and talc) or modifiers (such as antioxidants and masterbatches). If the filler is an inorganic powder with a large particle size exceeding 1 micron, it will act as an obstacle to light scattering, significantly reducing light transmittance. Even if a nano-scale filler is used, if it is not evenly dispersed, it will form localized high concentration areas, disrupting the uniformity of light transmittance. Light-colored or transparent modifiers have little effect on light transmittance, while dark-colored modifiers directly absorb light, reducing the translucency.

II. Production Process

The control of process parameters during production directly affects the stability of the internal structure of the pellets, which in turn affects light transmittance:

1. Melt-mixing Process Precision

TPE raw material pellets are melt-mixed in an extruder. If the extruder screw speed is too low or the barrel temperature distribution is uneven, the raw materials will not be fully mixed, resulting in residual unmelted elastomer particles within the pellets or the formation of plasticizer aggregates. These areas have a different refractive index than the surrounding matrix, scattering light as it passes through them, giving the pellets a hazy appearance and reducing light transmittance. Conversely, excessively high screw speeds can cause excessive shearing of the raw material, leading to localized overheating and degradation, and the formation of tiny carbonized particles that hinder light penetration.

2. Process Control of Granulation and Cooling

During the granulation process, mismatching the cutter speed with the extrusion speed can result in uneven particle size, burrs, and depressions on the pellet surface. This can cause irregular light reflection on the pellet surface, affecting overall light transmission. During the cooling process, excessively high cooling water temperature or insufficient cooling time can generate internal stress within the pellets, disrupting the molecular chain alignment and forming tiny voids. Light refracts through these voids, reducing light transmission uniformity. Excessively rapid cooling can cause inconsistent shrinkage between the pellet surface and interior, resulting in cracks and further impairing light transmission. III. Impurity Control

Impurities are a significant risk to the light transmittance of translucent TPE raw material pellets. Impurities primarily come from two sources:

1. Impurities in the Raw Materials

If raw materials such as base elastomers and plasticizers contain dust, metal debris, or other contaminants, these impurities can remain within the finished pellets, blocking light. In particular, metal debris can reflect light, creating noticeable bright spots within the pellets and impairing the translucent effect. Improper storage of raw materials, such as moisture absorption or microbial contamination, can also lead to bubbles or mold within the pellets, further impairing light transmittance.

2. Impurities Introduced During the Production Process

Dark raw materials or impurities from previous batches left in the extruder barrel can be mixed into the current batch of pellets. Metal powder from worn cutters in the pelletizing equipment and dust from the workshop air can also enter the raw materials and become impurities. These impurities, regardless of size, will show up in the translucent pellets, affecting light transmittance and potentially causing cosmetic defects in subsequent products. IV. Post-Processing and Storage

Even if translucent TPE raw material pellets with good light transmittance are produced, improper post-processing and storage can lead to reduced light transmittance:

1. Pre-Processing Drying

If translucent TPE pellets absorb moisture before processing, this moisture will evaporate during heating, forming bubbles that are distributed within the product. Light passing through these bubbles will scatter, reducing the product's light transmittance. Therefore, the pellets must be dried before processing. However, excessively high temperatures or prolonged drying times can cause surface oxidation, forming an oxide layer that blocks light penetration.

2. Impact of the Storage Environment

If translucent TPE pellets are stored in high-temperature, high-humidity environments for extended periods, they will absorb moisture from the air or slowly age, leading to plasticizer precipitation and molecular chain degradation. This, in turn, alters the pellets' internal structure and gradually reduces light transmittance. Dust or oil in the storage environment can also cause contaminants to adhere to the pellet surface, blocking light and negatively impacting light transmission. In summary, the light transmittance of translucent TPE granules is the result of the combined effects of the raw material formula, production process, impurity control, and post-processing and storage. Improving the light transmittance of translucent TPE granules requires optimizing the formula, selecting compatible components, and reducing undesirable fillers. Precisely controlling the production process ensures uniform mixing of raw materials and optimizes cooling conditions. Strictly controlling impurities, ensuring thorough raw material screening and a clean production environment, and standardizing post-processing and storage procedures, ensuring proper drying, light protection, and moisture protection, are essential to achieving the desired translucent effect.