How to avoid the generation of bubbles during the production of ABA blown film machine

1、 Analysis of the causes of bubble formation

During the production process of ABA blown film machine, the generation of bubbles can seriously affect the quality and appearance of the film. To effectively avoid bubbles, it is necessary to first understand the root cause of their formation:

Raw material issue: One of the main reasons for bubble formation is the presence of moisture or volatile substances in the raw materials. When plastic particles contain moisture, it vaporizes and forms bubbles during the high-temperature melting process. In addition, low molecular weight volatiles in the raw materials will also release gases when heated.

Improper processing temperature: Excessive temperature can cause plastic to decompose and produce gas, while low temperature may result in poor fluidity of the melt and difficulty in releasing gas. Especially in the ABA structure, different material layers have different temperature sensitivities and require accurate control.

Unreasonable screw design: Improper parameters such as compression ratio and aspect ratio of the screw can lead to insufficient melting or poor exhaust, causing gas to remain in the melt.

Mold issues: Unreasonable mold head design, uneven lip clearance, or dead corners inside the mold head can all lead to uneven melt flow and gas retention.

Improper setting of process parameters: mismatched parameters such as screw speed, traction speed, and inflation ratio can affect melt flow and gas discharge.

Improper equipment maintenance: Long term uncleaned screws, barrels, or molds may accumulate degradation products, which can release gases at high temperatures.

2、 Raw material processing and selection

Pre drying of raw materials: Materials with strong moisture absorption properties such as PA, PET, etc. must be thoroughly dried. It is generally recommended to dry at 80-120 ℃ for 4-6 hours to reduce the moisture content to below 0.02%. Before use, the actual moisture content of the raw materials should be tested.

Raw material screening: Avoid using materials that are damp, contaminated, or degraded. For recycled materials, the quality and addition ratio should be strictly controlled, and if necessary, re granulation treatment should be carried out.

Additive selection: Adding defoamers or dehumidifiers appropriately can help reduce bubbles. However, attention should be paid to the compatibility between additives and substrates, as excessive addition may affect the performance of the film.

Raw material storage: Raw materials should be stored in a dry and cool environment to avoid moisture absorption. After opening, the raw material bag should be sealed in a timely manner or a hopper protected by dry air should be used.

3、 Optimization of process parameters

Temperature control: ABA blown film machines usually require three temperature settings: A material temperature, B material temperature, and composite temperature. Each temperature segment should be accurately set according to the material characteristics:

The temperature of layer A (outer layer) is usually slightly higher than that of layer B (middle layer)

The melt temperature should be maintained within the recommended range of the material to avoid excessive decomposition

The temperature of the mold head should be uniform, and the temperature difference should be controlled within ± 2 ℃

Screw speed: Excessive speed can cause excessive shear heat, which may lead to material degradation; If the speed is too low, the melting will not be sufficient. Better speed should be found based on equipment specifications and material characteristics.

Back pressure control: Appropriate back pressure helps with melt homogenization and gas discharge, but excessive back pressure can increase energy consumption and melt temperature. Generally controlled at 5-15kg/cm ².

Inflation ratio and traction ratio: These two parameters affect the orientation and thickness uniformity of the film. Unreasonable settings can lead to unstable melt and increase the risk of bubbles. Usually, the inflation ratio is controlled between 2:1 and 4:1.

Cooling system: Good cooling can quickly solidify film bubbles and reduce the chance of bubble expansion. The position, air volume, and wind speed of the wind ring should be optimized and adjusted to ensure the stability of the membrane bubble.

4、 Equipment maintenance and improvement

Screw and barrel maintenance: Regularly check the wear of screws and barrels. Severe wear can lead to uneven melting and decreased mixing efficiency. Repair or replace as necessary.

Mold cleaning and maintenance: The mold should be disassembled and cleaned regularly to remove carbon deposits and degradation products. The gap between the mold lips should be evenly adjusted to ensure balanced flow of the melt.

Exhaust system: For blown film machines with exhaust function, ensure that the exhaust port is unobstructed and the vacuum system is working properly. The temperature of the exhaust section should be appropriately reduced to assist in the condensation and discharge of volatile substances.

Filtering system: Use appropriate mesh filters and replace them regularly. The filter can block impurities and increase the back pressure of the melt, which helps to remove gases.

Equipment upgrade: Consider using barrier type screws, static mixers, or melt pumps to improve melt uniformity and stability.

5、 Production operation specifications

Startup program: Strictly follow the heating curve to increase the temperature and avoid sudden temperature changes. After reaching the set temperature, it should be kept warm for 15-30 minutes to ensure thermal uniformity.

Transition material handling: When changing raw materials or colors, there should be sufficient transition time to avoid compatibility issues between different materials that may cause bubbles.

Production process monitoring: Regularly check the stability of the film bubbles, the appearance of the film, and the uniformity of the thickness. Discover bubbles and adjust process parameters in a timely manner.

Environmental control: Keep the production environment clean and control the temperature and humidity in the workshop. High humidity environments can increase the risk of moisture absorption in raw materials.

Operation records: Detailed records of process parameters, raw material batch numbers, and equipment status for each production, facilitating problem tracing and analysis.

6、 Quality Inspection and Problem Solving

Online detection: Use online thickness detectors, infrared thermometers and other equipment to monitor the production process in real time and detect abnormalities in a timely manner.

Sample testing: Regularly take samples to test the physical properties and airtightness of the film, and evaluate the impact of bubbles on its performance.

Bubble analysis: Conduct morphological analysis on the generated bubbles to determine their source:

Small and uniform bubbles usually originate from the moisture content of the raw material

Large and irregular bubbles may be a problem with melt flow

The concentrated occurrence of local bubbles may be related to mold or screw problems

Corrective measures: Take targeted measures based on the type of bubbles, such as adjusting temperature, increasing back pressure, extending drying time, or cleaning equipment.

To avoid bubble problems in ABA blown film machine production, it is necessary to comprehensively consider multiple factors such as raw materials, processes, equipment, and operations. Establish a systematic quality control system to strictly control every step from raw material entry to finished product delivery, in order to continuously produce high-quality film products. Regular training of operators to improve their understanding of the process and problem-solving skills is also key to reducing bubble generation. Through continuous optimization and improvement, bubble defects can be minimized to the greatest extent possible, improving production efficiency and product qualification rate.