In the formula of natural curing silicone, adding a retarder can effectively extend the curing time of silicone, thus providing more time for operation. The following are the specific mechanisms and principles of how retarders affect curing time:
1. The working principle of retarders
Retarders delay the crosslinking (Curing) process by adjusting the curing reaction speed of silicone, mainly through the following ways:
Inhibiting catalyst activity:
The curing of natural curing silicone is usually a chemical reaction initiated by a catalyst (such as a platinum catalyst or a tin catalyst). Retarders slow down the curing speed by reacting with the catalyst, reducing its activity.
For example, some retarders form inactive complexes with the catalyst, thereby temporarily preventing the catalyst from reacting with the components in the silicone.
Changing reaction conditions:
Retarders can change the reaction conditions of the crosslinking reaction in the silicone (such as lowering the reaction temperature or delaying the initiation of the crosslinking reaction), thereby extending the curing time.
Dilute the concentration of reactants in silicone:
Retarders are usually chemically inert solvents or diluents (such as certain silicone compounds or organic solvents). They reduce the chance of reactants coming into contact by diluting the cross-linking components in silicone, thereby slowing down the curing speed.
2. The specific effect of retarder on curing time
Extend the operation time:
After adding retarder, the operation time (Pot Life) of silicone will be significantly extended. For example, silicone with an original curing time of 30 minutes may be extended to 1 hour or more after adding retarder.
Delay surface drying and complete curing time:
Both the surface drying time (the time when the surface of silicone is no longer sticky) and the complete curing time will be extended. For example, the surface drying time may be extended from 2 hours to 4 hours, while the complete curing time may be extended from 24 hours to 48 hours.
3. Common ingredients of retarder
Common retarder ingredients include:
Siloxane compounds:
Low molecular weight silicone oils (such as dimethylsiloxane) can dilute the silicone system and delay the curing speed.
Organic complexes:
Certain organic compounds (such as nitrogen-containing complexes) can bind to metal catalysts and reduce their activity.
Solvent-based slow-drying agents:
Certain organic solvents (such as toluene and xylene) can temporarily dilute the cross-linking components in silicone and slow down the reaction rate.
4. How to use slow-drying agents
Addition ratio:
The addition ratio of slow-drying agents is usually 1%-5% of the total amount of silicone. The specific ratio needs to be adjusted according to the silicone formula and the required delay time.
Mix evenly:
The slow-drying agent needs to be fully mixed with the silicone main agent and curing agent to ensure uniform delay of the reaction.
Pay attention to balancing reaction time and performance:
Adding too much slow-drying agent may cause the curing time to be too long, affecting production efficiency; at the same time, if the slow-drying agent affects the activity of the catalyst too much, it may cause the final performance of the silicone (such as strength or elasticity) to decrease.
5. Advantages and limitations of slow-drying agents
Advantages:
Extended operation time:
Suitable for scenes with complex patterns or large-area coatings that require more time for adjustment or printing.
Avoid premature curing:
In high temperature or high humidity environments, slow-drying agents can prevent silicone from prematurely curing.
Limitations:
Extended production cycle:
Extended curing time will reduce production efficiency and may not be applicable for fast production needs.
May affect the final performance:
Excessive use of slow-drying agent may reduce the mechanical properties or adhesion of silicone.
6. Application scenarios
Slow-drying agent is usually used in the following situations:
Complex process:
For example, when multi-layer silk-screen silicone needs to gradually superimpose patterns, more operation time is required.
High temperature environment:
In a high temperature environment, silicone may cure quickly, and adding slow-drying agent can avoid accidental premature curing.
Large area printing:
Large area printing requires longer time to complete the operation, and adding slow-drying agent is very important.
Summary
Slow-drying agent significantly prolongs the curing time of naturally curing silicone by inhibiting catalyst activity, diluting reactant concentration or changing reaction conditions. Although slow-drying agent can provide more operation time, its addition amount needs to be carefully controlled to avoid excessive delay in curing or affecting the performance of silicone.