PVC board, also known as decorative film or adhesive film, is a PVC-based vacuum plastic absorbing film with a honeycomb mesh cross section. Its versatile applications extend to various industries such as building materials, packaging, and medicine. However, in some cases, PVC sheets may experience issues such as embrittlement and delamination. To determine the cause of these problems, it is necessary to delve deeper into the potential factors behind these phenomena.
One issue to address is the insufficient hot pressing time. It is crucial to extend this time appropriately. When the hot pressing time is not enough, the temperature required for bonding between the sheets cannot be reached. Although the sheets are somewhat bonded together under high pressure, they become prone to separation when exposed to external forces such as shearing or sawing. To avoid this, it is necessary to adjust the hot pressing time and ensure that the bonding temperature is adequately achieved. By doing so, the sheets will be securely bonded and less susceptible to stratification.
One of the main causes of brittle and reddish flakes in PVC sheets during the lamination process is the excessively high forming temperature or prolonged heating time. Even if the pressing temperature is appropriately reduced during lamination, if the sheet was formed abnormally in the previous process, this cannot prevent delamination and may lead to the failure of the bonding temperature of the sheet. Increasing the plasticizing temperature of the sheet and corresponding pressing temperature to prevent delamination may worsen brittleness and reddish surface of the sheet. Therefore, the processing conditions of PVC sheets should be under strict control, the forming temperature should be lowered, and the heating time shortened to ensure high-quality lamination.
To ensure proper bonding and prevent layer stratification during the pressing process, it is essential to maintain a clean production environment and promptly remove any dust or debris from the surface of the material sheet. Even with controlled pressing conditions, failure to address surface cleanliness can result in poor bonding and stratification. When hot pressing a PVC sheet, temperature and pressure control should be implemented in three stages. Firstly, the low-temperature preheating stage prepares the sheet for further processing. Secondly, the medium-temperature pressure holding stage ensures proper bonding. To expedite heat transfer, the middle layer's temperature should reach 120 degrees after a period of low-temperature heating, indicating the transition to the next stage. It is crucial to manage any outward sheet expansion by properly adjusting the pressure to prevent excessive bulging. By adhering to these guidelines, optimal results can be achieved in the hot pressing process.
During the high temperature pressing stage, when the middle layer of the sheet reaches the bonding temperature, the sheet undergoes a state of melting flow, resulting in bonding between the layers. It is crucial to control the temperature in the high temperature stage within the range of 170 to 175 degrees. However, it is important to avoid excessively long heating time. Additionally, the pressure should be maintained between 0.8 to 1 MPa initially. These specific conditions necessitate a prompt and efficient response to ensure successful bonding.