To optimize the silicone formula to reduce the risk of mold sticking, it is necessary to start from the viscosity, curing characteristics, additive selection and compatibility with other materials of silicone. The following are specific optimization strategies:
1. Adjust the viscosity and fluidity of silicone
Reduce viscosity:
By reducing the entanglement of polymer segments or adding low molecular weight diluents, silicone can flow more easily in the mold and reduce the contact resistance with the mold surface. For example, adding an appropriate amount of silicone oil or low viscosity siloxane to the formula can effectively reduce the overall viscosity.
Enhance fluidity:
Adjust the thixotropy of silicone (i.e. the property of viscosity reduction when subjected to shear force) to make it easier to fill complex structures when injected into the mold and maintain shape stability after curing.
2. Optimize curing characteristics
Control curing speed:
Slow down the initial curing speed: By reducing the amount of catalyst or using a delayed curing catalyst, avoid premature solidification of silicone on the mold surface, thereby reducing mold sticking.
Adjust curing temperature and time: Ensure that the silicone is uniformly cured in the mold to avoid local overheating or overcooling that causes mold sticking.
Improve curing uniformity:
When using two-component silicone, ensure that components A and B are mixed evenly to avoid surface stickiness due to incomplete curing.
3. Choose the right additives
Inner release agent addition:
Add a small amount of inner release agent (such as stearate, fluorosilicone polymer) to the silicone formula to migrate to the surface during the curing process to form an isolation layer and reduce adhesion to the mold.
Anti-adhesion additives:
Add nano-scale fillers (such as silica, alumina) or modified polymers to improve the surface properties of silicone and reduce the tendency to stick to the mold.
4. Enhance compatibility with mold materials
Surface energy matching:
Adjust the surface energy of silicone to make it similar to the surface energy of mold materials (such as metal, plastic) to reduce interfacial adhesion. For example, surface treatment of metal molds (such as chrome plating, Teflon coating) can reduce their surface energy.
Chemical inertness:
Ensure that the ingredients in the silicone formula do not chemically react with the mold material to avoid sticking due to chemical bonding.
V. Testing and Verification
Laboratory testing:
After optimizing the formula, a small-scale trial was conducted to test the demoulding performance, curing time and physical properties (such as hardness and tensile strength) of the silicone.
On-site verification:
Verification was carried out in the actual production environment, the performance of the silicone in the mold was observed, and the formula was further adjusted based on the feedback.
VI. Case description
Case 1: Reducing viscosity
When a silicone product factory was producing concave and convex embossed products, it was found that the high viscosity of the silicone made demoulding difficult. By adding 5% silicone oil to the formula, the viscosity was reduced by 30%, the demoulding efficiency was increased by 50%, and the surface quality of the product did not change significantly.
Case 2: Application of internal mold release agent
During the silicone encapsulation process, a certain electronic component factory had a decrease in the yield rate due to mold sticking. By adding 0.5% of fluorosilicone polymer internal mold release agent to the silicone, the mold sticking phenomenon was reduced by 90%, and the production efficiency was significantly improved.
VII. Precautions
Additive dosage control:
Excessive addition may cause the physical properties of the silicone to decrease (such as reduced strength and poor temperature resistance), and a balance must be achieved between demoulding performance and product performance.
Environmental impact:
Some additives may be harmful to the environment or human body, so materials that meet environmental and safety standards must be selected.
Cost considerations:
Optimizing the formula may increase the cost of raw materials, so a comprehensive assessment of costs and benefits is required.