In the production of silicone two-color watch straps, the precision control of the two-color dividing line is a core factor determining the product's appearance quality. Its achievement relies on the systematic coordination of mold design, material compatibility, process parameter optimization, and equipment precision. Mold design is the physical basis for dividing line precision, requiring precision machining to ensure accurate positioning during two-color injection molding. For example, when using a rotary positioning mold, the mold's rotation axis must be strictly perpendicular to the parting line, and the rotational positioning accuracy must be controlled within a very small range to avoid dividing line misalignment due to mold offset. Simultaneously, the mold parting surface must be designed with micron-level flatness, coupled with a high-precision guide post and guide sleeve system, to ensure complete mold fit during the two injections, preventing excess glue or blurred dividing lines.
Material compatibility directly affects the fusion effect of the two-color interface. If the vulcanization speed, shrinkage rate, or surface energy of the two silicone materials differ too much, it will lead to weak interface bonding or insufficient dividing line clarity. Therefore, it is necessary to select silicone materials of the same system or those that have undergone compatibility testing, such as liquid silicone (LSR) of the same brand and series, which have similar molecular structures and high vulcanization kinetic matching, enabling molecular-level fusion. If different materials are used, surface treatment techniques such as plasma etching or chemical primers are needed to enhance interfacial activity and improve adhesion between the two materials, preventing delamination or bleeding at the boundary.
Optimizing process parameters is the dynamic guarantee of boundary accuracy. Injection speed, temperature, and pressure parameters need to be finely adjusted according to material characteristics and mold structure. For example, during the first injection, the injection speed must be controlled to avoid high-speed impact causing air retention in the mold cavity, forming bubbles or flow marks. During the second injection, a "low-pressure, slow-speed" mode should be used to ensure the second material slowly fills the surface of the first molded part, preventing deformation of the first material or boundary misalignment due to excessive pressure. Furthermore, the mold temperature must be uniform and stable. A dual-loop mold temperature controller should be used to control the temperature difference within a minimal range to prevent inconsistent material shrinkage due to temperature differences, which would affect boundary accuracy.
Equipment precision is the hardware support for boundary control. High-precision injection molding machines need to be equipped with a closed-loop control system to monitor and adjust injection volume, pressure, and speed in real time, ensuring repeatability of each injection. For example, closed-loop control of the screw position can keep the injection volume accuracy within a very small error range, ensuring that the dimensional tolerances of key components such as the silicone two-color watch strap buckle strictly meet design requirements. Simultaneously, the robotic arm's pick-and-place accuracy must reach the micrometer level to avoid secondary positioning deviations caused by minute displacements during semi-finished product transfer. For complex molds using vertical or rotary injection molding, a high-rigidity clamping mechanism is required to ensure uniform distribution of clamping force and prevent mold deformation from affecting the parting line quality.
The detection and correction of parting line accuracy are equally critical. During production, a machine vision system must be used to detect the parting line in real time. A high-resolution camera captures the width, straightness, and edge sharpness of the parting line and compares it with the design drawings, automatically identifying defective products with deviations exceeding standards. For detected defective products, the causes must be analyzed, such as mold wear, parameter drift, or material contamination, and targeted adjustments to the process or replacement of mold components are necessary. Furthermore, regular mold maintenance, such as cleaning residual material from the parting surface and calibrating worn locating pins, can ensure long-term stable parting line accuracy.
Environmental control is an implicit guarantee of the precision of the dividing line. The production workshop must maintain constant temperature and humidity conditions to avoid temperature fluctuations that could cause changes in material shrinkage or mold thermal expansion and contraction. Simultaneously, the cleanliness of the workshop must meet specific standards to prevent dust or oil contamination of the mold cavity or semi-finished product surface, affecting the bonding quality of the two-color interface. For example, the production of medical-grade silicone two-color watch straps must be completed in a Class 10,000 cleanroom to eliminate interference from microorganisms or particles on the precision of the dividing line.
The precision control of the two-color dividing line of silicone two-color watch straps requires a multi-dimensional approach, including mold design, material selection, process optimization, equipment precision, detection and correction, and environmental control. Through the physical positioning of precision molds, molecular fusion of compatible materials, precise matching of dynamic process parameters, stable operation of high-precision equipment, intelligent correction through real-time detection, and the implicit guarantee of a clean environment, millimeter-level or even micrometer-level precision of the two-color dividing line can be achieved, ultimately presenting a silicone two-color watch strap with a natural color transition and sharp, clear edges.
