BYK-1730

BYK-1730 is a VOC-free, silicone-based defoamer manufactured by BYK Additives. 
BYK-1730 is specifically formulated to eliminate and prevent foam formation in water-based (aqueous) chemical systems without releasing volatile organic compounds (VOCs).
A mixture of foam-destroying polysiloxanes.

BYK-1730 does not have a single CAS number because BYK-1730 is a proprietary chemical mixture rather than a pure chemical substance.

If you are looking for safety, customs, or regulatory registration purposes (such as REACH or TSCA), you must look at the specific Safety Data Sheet (SDS) provided by the manufacturer for your region. 
The individual components within the mixture that are typically tracked include:
Polyglycol (carrier medium): Often falls under general polymer CAS classifications such as 25322-68-3 (Polyethylene glycol) or 25322-69-4 (Polypropylene glycol), depending on the exact molecular structure.
Polysiloxanes (silicone defoamer base): Broadly classified under silicone polymers like 63148-62-9 (Polydimethylsiloxane).

Hydrophobic Solids: Commonly treated silica or similar particulate matrices.
BYK-1730 is a mixture of foam destroying polysiloxanes and hydrophobic solids in polyglycol. 
BYK-1730 is especially suited for pigmented emulsion systems based on styrene/acrylics, acrylics or acrylic/polyurethanes with PVC‘s of 18-25%. 
BYK-1730 can also be used in amine-neutralized systems and is very efficient against microfoam. 
The additive is VOC-free.

Uses
The additive is heavily utilized across the coatings and polymer industries, including:
Architectural Coatings: Ideal for water-based emulsion paints and wall coatings.
Pigment Concentrates: Prevents air entrapment during high-shear millbase grinding and dispersion.
Printing Inks: Ensures smooth application and surface consistency in aqueous printing processes.
Construction Chemicals: Frequently added to waterproofing systems and building materials.
Marine Coatings: Used to stabilize industrial protective layers.