Moisture content control of brucite powder: key points for preventing bubble defects in aluminum-plastic panels
Bubble defects have always been one of the important factors affecting product quality in the production process of aluminum-plastic composite panels. Especially in high-temperature composite processes, if the moisture in the filler is not effectively controlled, bubbles can easily form inside or on the surface of the board, resulting in poor product appearance, decreased mechanical properties, and even scrap.
As a new type of environmentally friendly functional filler, brucite powder is increasingly widely used in aluminum-plastic panels. It not only has good flame retardancy and thermal stability, but also improves the processing performance and finished product quality of the board. However, due to its natural mineral properties, brucite powder is prone to absorbing moisture from the air during processing, storage, and use, resulting in a high moisture content. If not strictly controlled, it will directly cause bubble defects in aluminum-plastic panels.
Therefore, the reasonable control of the moisture content of brucite powder has become one of the key links in preventing bubble defects in aluminum-plastic panels.
1、 Why is brucite powder prone to moisture absorption?
Magnesite (Mg (OH) ₂) is a layered hydroxide mineral with a crystal structure containing a large number of hydroxyl groups (- OH), which have strong adsorption capacity for water molecules. In addition, brucite powder generates a larger specific surface area during the crushing and grinding process, further enhancing its hygroscopicity.
When stored or transported in humid environments, brucite powder is prone to absorbing moisture from the air, leading to an increase in moisture content. If the moisture enters the subsequent composite process without sufficient drying, it will rapidly vaporize at high temperatures, forming a large amount of gas, which will produce defects such as bubbles and micropores in the board.
2、 Hazard and Cause Analysis of Bubble Defects
In the production of aluminum-plastic panels, bubble defects not only affect the appearance quality of the product, but may also bring the following problems:
Decreased mechanical strength: The presence of bubbles weakens the density of the material, reducing its bending and impact resistance.
Deterioration of weather resistance: Bubble areas are prone to become channels for water vapor infiltration, which may cause delamination and bulging of the board during long-term use.
Damaged fire resistance: Although brucite itself has good flame retardant properties, the non-volatile water may actually generate steam pressure at high temperatures, exacerbating the formation of bubbles and affecting the flame retardant effect.
Reduced processing efficiency: After bubbles appear, rework or downgrading is required, which increases costs and affects delivery cycles.
The main causes of bubble defects include:
The moisture content of the filler is too high
Inadequate drying process
Improper composite temperature control
Poor exhaust of resin system
Among them, controlling the moisture content of fillers, especially brucite powder, is the focus of source control.
3、 How to effectively control the moisture content of brucite powder?
In order to ensure the stable quality of aluminum-plastic panel products, it is necessary to control the moisture content of brucite powder from the following aspects:
1. Optimize the drying process
Before leaving the factory, high-efficiency and energy-saving drying equipment should be used for deep dehydration treatment of brucite powder. Common drying methods include:
Airflow drying: suitable for low viscosity powders, with fast drying speed.
Hot air circulation drying: suitable for continuous production, with high temperature control accuracy.
Microwave drying: It can achieve synchronous heating inside and outside, resulting in more thorough dehydration.
It is recommended to control the drying temperature between 100~150 ℃, and adjust the time according to the amount of material. Generally, it is advisable to control it within 1-2 hours. The moisture content of the dried powder should be controlled below 0.3%.
2. Reasonable packaging and storage
The dried brucite powder should be packaged with moisture-proof materials, such as woven bags lined with PE film or vacuum packaging, and stored in a ventilated and dry warehouse with humidity below 60%. Avoid mixing with other materials that are highly hygroscopic.
3. Production site management
Before feeding into the aluminum-plastic panel production line, the moisture content of brucite powder should be retested. If necessary, an online drying device can be added before mixing to ensure that the powder remains dry before entering the mixing stage.
4. Matching of process parameters
During the composite process, the temperature curve and pressure system should be adjusted according to the type of filler. Appropriately extending the insulation and pressure holding time helps to fully discharge gas and reduce residual bubbles.
4、 Testing methods and standards
In order to scientifically evaluate the moisture content level of brucite powder, production enterprises should establish a standardized testing process. Common detection methods include:
Drying weight loss method: Place the sample in a constant temperature oven at 105 ℃ to dry to a constant weight, and calculate the weight loss percentage.
Karl Fischer method for moisture determination: suitable for detecting trace amounts of moisture with higher accuracy.
Infrared rapid moisture analyzer: suitable for on-site rapid detection, easy to operate.
It is recommended that enterprises control the factory moisture content of brucite powder to ≤ 0.3% to meet the production process requirements of aluminum-plastic panels.
5、 Reference for practical application cases
During the initial stage of introducing brucite powder as a substitute filler, a large aluminum-plastic panel enterprise experienced multiple occurrences of foam formation in the panels. After investigation, it was found that the main reason is the high moisture content of brucite powder (over 0.8%) and insufficient efficiency of the drying system.
The company subsequently upgraded its drying equipment, added a cooling and sealing packaging process, and installed dehumidification devices in the workshop. After improvement, the moisture content of brucite powder remained stable within 0.2%, and the bubble defect rate of aluminum-plastic panels decreased from 8% to below 1%, significantly improving the product qualification rate and customer satisfaction.
With the deepening promotion of the concept of green building materials, the application prospects of brucite powder as an environmentally friendly functional filler in the aluminum-plastic panel industry are broad. However, in order to truly leverage its advantages, it is necessary to pay attention to the key aspect of controlling its moisture content.
By optimizing the drying process, strengthening warehouse management, and improving production site control, enterprises can effectively prevent the occurrence of bubble defects, improve product quality, and enhance market competitiveness. In the future, with the continuous advancement of technology, the application of brucite powder will become more mature, helping the aluminum-plastic panel industry move towards a new stage of high-quality and sustainable development.