The foaming ratio of Pearl Cotton is a key factor affecting its performance and quality. Its control requires comprehensive consideration from multiple aspects such as raw materials, process parameters and equipment.
1. Raw material selection and proportioning
Selection of polyethylene resin: Pearl Cotton is mainly made of polyethylene resin. Different types and specifications of polyethylene resin have a significant impact on the foaming ratio. Low-density polyethylene (LDPE) is usually used to produce Pearl Cotton with high expansion ratios because its molecular chains are relatively short and have low crystallinity, making it easier to be expanded by gas during the foaming process. High-density polyethylene (HDPE) has long molecular chains and high crystallinity, so foaming is relatively difficult and the foaming rate is low. In production, the type of polyethylene resin is reasonably selected according to the target foaming ratio, and its dosage is accurately controlled.
Selection and dosage of foaming agent: Foaming agent is the key raw material for Pearl Cotton foaming. Commonly used chemical foaming agents such as azodicarbonamide (AC) decompose when heated to produce gas, causing Pearl Cotton to foam. The decomposition temperature, gas production rate and gas production volume of the foaming agent directly affect the foaming ratio. Choose a blowing agent with a suitable decomposition temperature to match the processing temperature to ensure that gas is generated at the right time. At the same time, the dosage of foaming agent must be precisely controlled. If the dosage is too much, the foaming ratio will be too large, the Pearl Cotton structure will be loose, and the strength will be reduced; if the dosage is too small, the foaming ratio will be insufficient, and the expected buffering and heat insulation properties will not be achieved.
2. Process parameter adjustment
Temperature control: Temperature is an important parameter in the Pearl Cotton foaming process. During the mixing and extrusion processes, appropriate temperatures can fully plasticize the polyethylene resin and create conditions for foaming. In the foaming stage, the temperature needs to be accurately controlled near the decomposition temperature of the foaming agent so that the foaming agent can decompose uniformly and stably to produce gas. For example, when using AC foaming agent, the foaming temperature is generally controlled between 180 and 20°C, and there may be certain adjustments for different equipment and formulas. If the temperature is too high, gas will be generated too quickly, which may cause the Pearl Cotton surface to crack and foam unevenly; if the temperature is too low, the foaming agent will not decompose completely, and the foaming ratio will not meet the requirements.
Pressure adjustment: During the foaming process of Pearl Cotton, pressure also has an important impact on the foaming rate. Appropriate pressure can make the gas evenly dispersed in the resin to form a fine cell structure. In the extruder, the pressure of the material in the barrel is controlled by adjusting the screw speed and head pressure. Generally speaking, a high pressure is maintained before foaming to prevent premature escape of gas. When the material reaches the foaming area, the pressure is quickly reduced to expand the gas to achieve the required foaming ratio.
3. Equipment optimization
Selection and debugging of extruder: Different types and specifications of extruders have different abilities to control the foaming rate of Pearl Cotton. The structure and aspect ratio of the screw will affect the conveying, mixing and plasticizing effects of the material. A screw with a large aspect ratio can make the material stay in the barrel for a longer time and mix more fully, but it also requires more precise temperature and pressure control. At the same time, the heating and cooling systems of the extruder need to be stable and uniform to ensure that the temperature of the material at each stage meets the process requirements. Regular debugging and maintenance of the extruder to ensure its stable performance is crucial for accurately controlling the foaming rate of Pearl Cotton.
