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Serum bottles are specialized containers used for storing serum and various culture media. They are typically made of high-transparency PET material through an injection stretch blow molding process. However, in some cases, the bottle body appears dull. What causes this phenomenon?
The dull appearance of serum bottles is primarily due to PET material decomposition and increased crystallinity. PET is transparent in its amorphous state. Within the temperature range of 50-250°C, PET undergoes crystallization, with nucleation occurring at lower temperatures and spherulite growth being more pronounced at higher temperatures, peaking at around 180°C. The crystallization process is also affected by resin viscosity—the lower the viscosity, the lower the resistance to molecular chain rearrangement, making crystallization easier. Additionally, the degree of crystallization is influenced by the residence time within the crystallization temperature range; the longer the time, the higher the crystallinity. In thick-walled preforms, the core area dissipates heat more slowly, making it more prone to crystallization. When the crystallinity exceeds 40%, the bottle's transparency decreases, resulting in a dull appearance.
From a production perspective, both the injection molding of PET preforms and the reheating-stretching-blowing process can contribute to increased crystallinity. This issue is particularly noticeable in hot-fill bottles, which require a heat-setting process. Additionally, the PET resin used for hot-fill bottles generally has lower viscosity, making it more susceptible to reduced light transmittance.
Based on practical experience, lower crystallinity in preforms is beneficial for production control. To achieve this, the cooling capacity of the preform injection mold should be enhanced. Common approaches include increasing the cooling water pressure to above 0.5 MPa and lowering the cooling water temperature to below 10°C. In the reheating process of two-step molding, heating time should be minimized, and heating temperature should be reduced. For hot-fill bottles produced using the two-step method, the heat-setting process helps adjust crystallinity and relax amorphous orientation. Increasing the setting temperature can shorten setting time and improve transparency. Additionally, during material drying, the temperature should be controlled between 150-160°C for 5-6 hours.
The above analysis outlines the causes of serum bottle dulling and corresponding solutions. Strict control of every processing stage is essential to ensuring the production of high-quality bottles.
Note: Some references are sourced from the "China Plastics" journal. Please contact for removal if necessary.
The FAI climbed 5.9 percent year-on-year in the first 11 months of 2018, quickening from the 5.7-percent growth in Jan-Oct, the National Bureau of Statistics (NBS) said Friday in an online statement.
The key indicator of investment, dubbed a major growth driver, hit the bottom in August and has since started to rebound steadily.
In the face of emerging economic challenges home and abroad, China has stepped up efforts to stabilize investment, in particular rolling out measures to motivate private investors and channel funds into infrastructure.
Friday's data showed private investment, accounting for more than 60 percent of the total FAI, expanded by a brisk 8.7 percent.
NBS spokesperson Mao Shengyong said funds into weak economic links registered rapid increases as investment in environmental protection and agriculture jumped 42 percent and 12.5 percent respectively, much faster than the average.
In breakdown, investment in high-tech and equipment manufacturing remained vigorous with 16.1-percent and 11.6-percent increases respectively in the first 11 months. Infrastructure investment gained 3.7 percent, staying flat. Investment in property development rose 9.7 percent, also unchanged.