How to solve the problem of bubbles or holes appear on the surface of WPC door panel?
Many wood-plastic composite (WPC) door manufacturers face the issue of bubbles or holes appearing on the surface of WPC door panels. This not only affects the appearance of the doors but also reduces their strength and quality. This problem can be caused by various factors, including production techniques, material properties, or environmental conditions. How can this issue be solved? Here, the Sure professional technical team analyzes the potential causes of this problem and proposes corresponding solutions.
· Inhomogeneous mixing of raw materials: wood-plastic materials are made up of wood fibers, plastics and additives. If the mixing is not uniform, the local plastic is not fully melted or the gas is not completely discharged, bubbles will be formed.
· Improper processing temperature:
· High temperature: the plastic decomposes at high temperature and produces gas (such as HCl gas produced by PVC decomposition), forming bubbles.
· Low temperature: the plastic is not fully plasticized, and the combination with wood fiber is not close, and the shrinkage forms holes after cooling.
· Insufficient extrusion pressure: insufficient pressure during extrusion, unable to compact the material, internal gas can not be discharged, resulting in surface bubbles or internal cavities.
· Mold design defects: the mold runner is not smooth or the exhaust hole is set improperly, the gas is retained in the material, and bubbles remain after molding.
· High moisture content: the moisture content of wood fiber exceeds the standard, and the water evaporates to produce steam during high temperature processing, forming bubbles (especially the natural wood powder that is not dried).
· Improper additive selection:
· Excessive amount of foaming agent or mismatch between decomposition temperature and processing temperature lead to loss of control of foaming.
· Excessive lubricant will reduce the melt viscosity of the material, and gas is easy to escape to form holes.
· High proportion of recycled materials: too much recycled plastic (containing impurities or degradation products) is used, which releases gas at high temperature and increases the risk of bubbles.
· Moisture after installation: the wood-plastic door is in a humid environment for a long time (such as the toilet), the material absorbs water and expands, and the surface coating or substrate cracks to form holes.
· External impact: the surface is impacted or scratched by a sharp object, resulting in local damage, coating peeling off, and exposing internal holes (especially for inferior products with loose internal structure).
· Optimize raw material processing:
· The moisture content of wood fiber should be strictly controlled (it is recommended to be less than 5%), and it should be fully dried before processing.
· Select plastic raw materials with high purity and good stability (such as HDPE, PVC), and reduce the proportion of recycled materials (especially inferior recycled materials).
· Adjust processing parameters:
· Precise control of extrusion temperature (e.g. PVC wood plastic processing temperature is about 160-190℃, which needs to be fine-tuned according to the formula) to avoid overheating decomposition or insufficient plasticization.
· Increase the extrusion pressure (usually 10-20MPa) to ensure that the material is compacted, and optimize the mold exhaust structure (increase the exhaust hole or open the exhaust groove).
· Modified formula design:
· Reasonable use of foaming agent (such as AC foaming agent should match the processing temperature), control the amount to avoid excessive foaming.
· Add an appropriate amount of coupling agent (such as silane coupling agent) to enhance the interfacial bonding force between wood fiber and plastic and reduce gas retention.
· Bubble treatment:
· If the bubble does not burst, you can use a fine needle to puncture the edge of the bubble, squeeze out the gas and fill it with the same color wood plastic repair paste (or atomic ash), dry it and sand it smooth with sandpaper, and finally spray the top coat.
· If the bubble has burst to form a hole, clean the impurities in the hole, fill it with a special wood-plastic filler (a mixture of resin and wood powder), polish and paint after curing.
· Coating renewal: if the surface coating is bubbling or peeling in large areas, the old coating can be removed by sanding and re-spraying UV paint or water-based paint to enhance the surface sealing.
· Avoid damp environment: although wood-plastic doors are water-resistant, long-term soaking may lead to expansion. It is recommended to use them in dry areas. In humid environments such as bathrooms, products with better waterproof performance (such as PVC base wood-plastic doors) should be selected and ventilation should be maintained.
· Regular inspection and maintenance: clean the surface with soft cloth, avoid using strong acid and alkali cleaning agents; repair small bubbles or cracks in time to prevent problems from expanding.
· Choose quality products: when buying, give priority to well-known brands and check the product test report (such as density, water absorption rate, surface hardness and other indicators), inferior products are more likely to appear bubbles and holes.
· Production process: establish a strict quality control system, and monitor the raw material inspection, process parameters, finished product appearance (such as bubble rate, surface roughness) throughout the whole process.
· Design optimization: streamline runner and efficient exhaust structure are adopted in mold development to reduce gas retention; for thick wall products, multi-stage extrusion or increased holding time can be used.
· User purchase tips: When accepting, carefully observe the surface of the door, touch it with your hands to check the flatness, and tap it to listen to the sound to judge whether the interior is hollow or loose (the clear sound may be a hole).
Through the above methods, the generation of bubbles and holes on the surface of wood-plastic doors can be effectively reduced, and the product quality and service life can be improved.
