TPR material, due to its unique elasticity and flexibility, is widely used in the stress relief toy industry, and "Bull Demon King" shaped stress relief toys are popular with consumers for their fun and practicality. However, insufficient adhesion during TPR surface spraying often leads to problems such as paint peeling and cracking, affecting the product's appearance and lifespan. To ensure the adhesion of the TPR material surface spraying on Bull Demon King stress relief toys, a comprehensive approach is needed, considering material characteristics, surface pretreatment, paint selection, process optimization, and curing control.
TPR material is an elastomer. When stretched or deformed, if the sprayed paint lacks elasticity, it is prone to cracking or peeling due to its inability to deform synchronously. Therefore, choosing paint with good compatibility with TPR material is crucial. Specialized elastomer paints usually contain flexible resin components that can form a physical or chemical bond with the TPR molecular chains, improving adhesion. In addition, the toughness of the paint must match the elasticity of the TPR to avoid coating cracking due to stretching.
Surface pretreatment is a key step in improving adhesion. TPR material surfaces may contain residual oil, mold release agents, or oxide layers. These impurities can hinder the bonding between paint and the substrate. Pretreatment methods include: wiping the surface with a weakly polar solvent (such as isopropanol) to remove oil and mold release agents; introducing polar groups into the surface through plasma treatment or corona treatment to enhance wettability; for TPR products with higher hardness, light sanding or sandblasting can be used to increase surface roughness and improve mechanical adhesion. After pretreatment, timely painting is necessary to avoid surface activity degradation.
The choice of paint must balance adhesion and elasticity. Ordinary paints are difficult to form a strong bond with TPR materials, easily resulting in pseudo-adhesion (only surface adhesion). Special TPR treatment agents can activate the substrate surface and improve the intermolecular bonding force between the paint and the substrate. When using, the substrate surface should be cleaned first, then a 3-5μm thick layer of treatment agent should be sprayed, baked at 60-70℃ for 3-5 minutes, and then a primer (such as rubber paint or PU paint) should be sprayed. In addition, the dilution ratio of the paint must be strictly controlled to avoid burning or degreasing due to solvent accumulation.
Process optimization must be matched to the characteristics of TPR material. During spraying, the material level should be designed as a flat surface to reduce solvent accumulation; if the design is limited, the paint needs to be diluted to reduce the risk of burning. Controlling the injection temperature and mold temperature is equally important. The TPR melt temperature is recommended to be controlled between 160-200℃ to avoid material decomposition due to excessively high temperatures or reduced fluidity due to excessively low temperatures. Furthermore, the addition ratio of sprue (recycled material) should be controlled below 30% to prevent decreased adhesion due to uneven material distribution.
The curing process is the last line of defense to ensure coating adhesion. The curing temperature and time need to be adjusted according to the paint type and product requirements to ensure that the adhesive or coating is fully cured. If curing is incomplete, the coating is prone to peeling due to internal stress. For elastomeric paints, a tensile test should be performed after curing to verify that the coating can deform synchronously with the TPR without cracking. In addition, TPR materials containing PP or PE should be avoided, as these components reduce paint adhesion. Also, prolonged exposure to humid or high-temperature environments should be avoided after spraying to prevent coating aging. For complex-shaped Bull Demon King toys, a reasonable product structure needs to be designed, such as pre-installed snaps or grooves, to enhance coating stability through mechanical bonding.
Improving the adhesion of TPR material coatings on Bull Demon King stress relief toys requires a coordinated effort across multiple stages, including material selection, pretreatment, paint matching, process optimization, and curing control. Through scientific methods and strict process management, paint peeling issues can be effectively resolved, ensuring a dual improvement in product appearance and performance.
