Detailed explanation of parameters for three-layer co extrusion blown film machine? Is thickness control accuracy important

1、 Application scenarios and core advantages of three-layer co extrusion blown film machine

The three-layer co extrusion blown film machine is a key equipment in the modern packaging industry. Through three independent extrusion systems, different performance raw materials (such as LLDPE, EVOH, PA, etc.) are melted and molded into thin films with a multi-layer structure through a composite die. Its core advantage lies in achieving "functional layering": the inner layer is responsible for heat sealing, the middle layer provides oxygen/water vapor barrier properties, and the outer layer ensures mechanical strength and wear resistance. It is widely used in high-end fields such as food vacuum packaging, pharmaceutical aseptic packaging, and daily chemical product packaging. To understand its performance, it is necessary to conduct in-depth analysis from two aspects: key parameters and thickness control accuracy.

2、 Detailed explanation of key parameters of three-layer co extrusion blown film machine

The parameters of the three-layer co extrusion blown film machine determine the quality, efficiency, and cost of the film, and the core parameters can be divided into the following five categories:

1. Extrusion system parameters

Screw diameter (Φ 25~Φ 150mm): corresponding to different production capacities, the larger the diameter, the higher the production capacity. The screw of a three-layer extruder is usually designed with differentiation: the inner screw is adapted to heat sealing materials (such as LLDPE, low shear), the middle screw is adapted to barrier materials (such as EVOH, which needs to be gently plasticized to avoid degradation), and the outer screw is adapted to strength materials (such as HDPE, high shear mixing).

Length to diameter ratio (L/D=28~35): The larger the length to diameter ratio, the more fully plasticized and evenly mixed the raw materials, but it is necessary to balance energy consumption and degradation risk (such as EVOH length to diameter ratio should not exceed 30).

Compression ratio (1.8-3.5): The compression ratio determines the melting efficiency of raw materials. For heat sealing materials, a low compression ratio (1.82.2) is used to reduce shear heat, while for barrier materials, a medium compression ratio (2.53.0) is used to ensure compactness.

Screw speed range (0~150rpm): The speed should match the traction speed. If it is too high, it can easily cause degradation of the raw material, while if it is too low, it will result in insufficient plasticization.

2. Composite die parameters

Mold head structure: The mainstream is the "spiral composite mold head", which achieves uniform stacking of multiple layers of material flow through spiral channels to avoid interlayer mixing; Some high-end models adopt a "stacked die head", which is suitable for precise layering of high barrier materials.

Mold diameter (Φ 50~Φ 600mm): determines the diameter of the membrane bubble and needs to match the width of the film (membrane width ≈ membrane bubble circumference × 0.5).

Mold gap (0.5~3.0mm): The size of the gap affects the initial film thickness and needs to be adjusted according to the target thickness and traction ratio (traction ratio=traction speed/mold discharge speed).

3. Cooling and shaping system parameters

Cooling air ring type: Dual air outlet air ring (outer layer strong cooling, inner layer slow cooling) can improve the stability of film bubbles; High end models are equipped with a "membrane bubble internal cooling system", suitable for thick film or high resistance membranes, with a cooling efficiency increase of over 30%.

Wind volume/pressure adjustment range: The air volume should evenly cover the circumference of the membrane bubble, and the wind pressure fluctuation should be ≤ ± 5Pa, otherwise it may cause membrane bubble shaking and uneven thickness.

4. Parameters of traction winding system

Traction speed (5-150m/min): linked with the screw speed, determines production efficiency; Need to match the film thickness (the higher the speed, the thinner the film).

Roll up diameter (≤ 1500mm): affects the frequency of roll change. Large diameter roll up can reduce downtime and improve continuous production capacity.

Tension control accuracy (± 1N): Uneven tension can cause wrinkling and uneven winding of the film, and closed-loop control needs to be achieved through magnetic powder brakes or servo motors.

5. Automation control parameters

PLC control system: It needs to support multi parameter linkage (such as screw speed, traction speed, and air circulation volume), with a response time of ≤ 0.5s.

Accuracy of online thickness gauge: The accuracy of non-contact thickness gauges (such as beta rays and infrared) needs to reach ± 0.1 μ m in order to achieve real-time thickness feedback and automatic adjustment.

3、 The core value of thickness control accuracy

The precision of thickness control (usually requiring within ± 0.5 μ m) is the "lifeline" of three-layer co extrusion blown film machines, and its importance is reflected in the following four aspects:

1. Product quality stability

Uneven thickness can lead to local differences in the mechanical properties (tensile strength, tear strength) and barrier properties (oxygen permeability) of the film. For example, if the local thickness of food packaging film is only 80% of the target value, the oxygen barrier properties will decrease by more than 50%, resulting in a shortened shelf life of the food; If the local thickness is too thick, it will reduce the heat sealing efficiency and cause packaging leakage.

2. Raw material cost savings

For every 1 μ m deviation in film thickness, the raw material loss rate increases by approximately 10%. Assuming an annual production of 1000 tons of 10 μ m film, if the average thickness exceeds the tolerance by 1 μ m, 100 tons of raw materials will be wasted each year. Calculated at a PE unit price of 12000 yuan/ton, the annual loss will reach 1.2 million yuan. Accurate thickness control can directly reduce raw material costs by 5% to 10%.

3. Production efficiency improvement

Fluctuations in thickness can lead to frequent shutdowns and adjustments, reducing production efficiency. For example, after adopting a thickness measurement system with an accuracy of ± 0.3 μ m, a certain enterprise reduced the number of downtime adjustments from 5 times per day to 1, resulting in a production capacity increase of over 20%.

4. Downstream processing adaptability

Uneven thickness can affect downstream processes: inaccurate overprinting during printing, inconsistent heat sealing strength during bag making, and fluctuations in interlayer peeling force during lamination. For example, if the thickness deviation of pharmaceutical packaging film exceeds ± 0.5 μ m, it will cause the heat sealed edge of the sterile bag to break easily, leading to compliance risks.

The parameter design of the three-layer co extrusion blown film machine needs to revolve around "functional layering+efficient production", and thickness control accuracy is the core link connecting parameters and product value. For enterprises, optimizing parameter settings and improving thickness control accuracy can not only reduce costs and improve efficiency, but also enhance product competitiveness and gain an advantage in the high-end packaging market.