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Silicones from Dow Corning
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Basics of Processing

Dow Corning ® brand silicone encapsulants are easily applied by a variety of methods. A general overview of these processes is given below. For more specifics, please refer to the Gels and Encapsulants Processing Tutorial.

Many of the encapsulants contain fillers for added strength or improved physical properties, like thermal conductivity. The high density of some of these fillers means that filler separation can occur. How quickly the filler settles depends on the viscosity, filler type, and specific gravity. With some products it can occur in hours, while for others any settling may take months. If filler settling is detected or suspected, the products should be remixed either in the original container or in a separate reservoir before being used. This can be done by hand stirring in pails or by using mechanical mixing equipment. Drum or can rollers can also be used to blend the material in their original containers before use. Remixing may be required periodically or can be done continuously in the dispense reservoirs to maintain a homogeneous mix. Filler settling does not adversely affect material performance once re-homogenized.

Most of the encapsulants are supplied as two-parts products that are either mixed in a 1:1 ratio (Part A & Part B) or a 10:1 ratio (Base & Curing Agent). They can be applied by hand mixing and manual dispensing, by using hand-held manual or powered mixing devices, or by using automated meter-mix equipment. Automated meter-mix is normally used for high volume processes. In low volume, manual weighing and simple hand mixing may be used. 

For assistance in designing a process tailored to the needs of your application, visit our Total Solutions for Electronics Section.

The two components are added in the proper ratio to a clean container and then hand stirred gently but thoroughly.Many of the products have color coding for the two parts to help judge adequate mixing.If air entrapment is a problem, it may be necessary to deair the material after mixing to ensure that the cured material is bubble free.  
The mixed material is then poured into the unit to be encapsulated. The filled unit can also be vacuum de-aired before curing to remove any last air. Take care during any de-airing process since foaming and significant expansion of the mixed material can occur .  

Automated Meter-Mix

Automated meter-mix equipment is typically used for higher volume production processes. These systems consist of a separate feed reservoir and pump for each component. The systems are set to achieve the desired ratio of the two components. The materials are then fed through a dispense head attached to a static mixer which is used to achieve a uniform mix. The dispense head is used to control the amount of material that is dispensed into the part. Static mixer tubes may need to replaced or cleaned when the process is shut down for long periods to avoid having the encapsulant cure in the mix tube. If air entrapment in the cured material is a problem, it may be necessary to deair the material in the feed reservoirs or in extreme cases, deair the material in the parts. Mixing in the reservoirs may also be needed to keep the filler distributed uniformly in some products. 

Manual Mixing and Dispense 

Manual dispense units have separate chambers for each component which connect to a common static mixer tube. Applying pressure to the plungers on the chambers pushes the material through the static mixer. This can be done manually by squeezing a hand trigger or can be gas powered. Static mixers are typically disposable one-time use units and may need to replaced or cleaned when not being used for long periods to avoid having the encapsulant cure in the mix tube. These units can be supplied pre-filled and ready to use or can be loaded with mixed and de-aired material immediately before use.

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< back to Lighting Solutions Home Page  
  1. Encapsulants Tutorial

  2. Solutions for Encapsulants

  3. Key Characteristics - Encapsulants tutorial

  4. Potential Applications - Encapsulants tutorial

  5. Thermal Conductivity - Encapsulants Tutorial

  6. Specialty Encapsulants

  7. Specifications and Other Qualifications

  8. Basics of Processing

  9. Packaging and Storage Considerations

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