Aluminum plastic panel bending whitening: solution for coarse particle size of brucite powder
Bending whitening is a common quality defect in the production process of aluminum-plastic panels. Especially when using brucite powder as a flame retardant filler, this problem becomes more prominent. Many companies have found in practical applications that when aluminum-plastic panels with added brucite powder are bent, there will be obvious white marks on the bent parts, which seriously affects the appearance quality and market acceptance of the products.
One of the main reasons for this phenomenon is that the particle size of the brucite powder used is too coarse. So how to solve the problem of "excessive particle size of brucite powder causing bending and whitening of aluminum-plastic panels"? We can study and propose practical solutions to help enterprises improve product quality and process level.
1、 The phenomenon and causes of whitening in aluminum-plastic panel bending
The so-called "bending whitening" refers to the phenomenon of white or misty spots appearing at the corners of aluminum-plastic panels after bending processing. This phenomenon not only affects the appearance, but also may reduce the durability and anti-aging performance of materials.
From a material perspective, the fundamental reason for bending whitening is that the internal structure of the plastic core material is damaged during the deformation process under stress, especially the interface bonding between the filler and the matrix resin is weakened, resulting in stress concentration and changes in light refraction, thus forming a visual "whitening".
As an inorganic filler, brucite powder plays a dual role: on the one hand, it can enhance the flame retardant properties of the material; On the other hand, if its particle size is not properly controlled, it can easily become a key factor causing bending whitening.
Specifically:
Coarse particle size: Large particles of brucite powder are difficult to evenly disperse in the plastic matrix, which can easily form stress concentration points. During the bending process, these areas are more prone to microcracks or debonding.
Insufficient surface treatment: The compatibility between brucite powder and resin without effective activation treatment is poor, further exacerbating the risk of interface separation.
Excessive filling ratio: Blindly pursuing flame retardant performance and increasing the amount of filler added will also increase the probability of bending and whitening.
2、 The influence mechanism of particle size of brucite powder on bending performance
The particle size of brucite powder directly affects its dispersion state in plastic systems and its bonding strength with resins. The finer the particle size, the larger the specific surface area, which theoretically is more conducive to enhancing the interaction with the resin and improving the overall performance of the composite material.
Experiments have shown that using brucite powder with an average particle size in the range of 1-2 μ m, combined with appropriate coupling agents, can significantly improve its dispersibility in the resin, reduce stress concentration effects during bending, and effectively alleviate whitening problems.
On the contrary, if products with a coarse particle size of 3 μ m or more, or even 5 μ m or more, are used, it is not only difficult to achieve good dispersion effect, but also form "hard spots" inside the material, resulting in local fractures during the bending process, ultimately manifested as whitening or cracking at the bending site.
3、 Specific solution for solving bending whitening
In response to the problem of bending and whitening of aluminum-plastic panels caused by coarse particle size of brucite powder, systematic solutions can be taken from the following aspects:
1. Choose products with appropriate particle size
It is recommended to prioritize the selection of ultrafine brucite powder with an average particle size between 1.5 and 2.0 μ m. This type of product undergoes fine grinding and grading treatment, with good particle size distribution and high whiteness, which can better integrate into the resin system and reduce physical interference.
2. Strengthen surface modification treatment
In order to improve the interfacial bonding ability between brucite powder and resin, effective surface activation treatment should be carried out. Common processing methods include:
Coating with silane or titanium ester coupling agents;
Add an appropriate amount of lubricant (such as polyethylene wax) to improve fluidity and dispersibility;
Control the processing temperature and time to ensure that the surface treatment agent is fully adhered without decomposition.
Modified brucite powder can significantly improve its compatibility in resin, thereby reducing the risk of stress concentration during bending process.
3. Optimize formula design and filling ratio
Reasonable control of the addition ratio of brucite powder is crucial. Generally speaking, it is recommended to control the addition amount within 40%, and it can be used in combination with other functional fillers (such as talcum powder, calcium carbonate, etc.) to ensure flame retardancy without sacrificing the flexibility and processing performance of the material excessively.
In addition, introducing toughening agents or compatibilizers appropriately can also help improve the impact resistance and bending stability of materials.
4. Improve production process parameters
During the extrusion and compounding process, process parameters should be adjusted according to the characteristics of brucite powder, such as:
Raise the mixing temperature to fully integrate the filler and resin;
Extend the mixing time to ensure even mixing of materials;
Control the cooling rate to avoid residual internal stress caused by excessive temperature differences.
These measures help to improve the overall density and uniformity of the material, fundamentally reducing the possibility of bending and whitening.
Although the whitening of aluminum-plastic panel bending is a common issue, with the application of new materials and the upgrading of market demand, the technical details behind it have become increasingly complex. As an environmentally friendly flame retardant filler, brucite powder has many advantages. However, if key steps such as particle size control and surface treatment are ignored, it will actually affect the quality of the finished product.
Therefore, in the process of material selection and production, enterprises should pay more attention to the refined management of raw materials and the systematic optimization of processes. Only in this way can the value of brucite powder in aluminum-plastic panels be truly realized, and the industry be continuously developed towards high-quality and green direction.