Nowadays, many SMC suppliers are trying to make low-density material. This SMC formulation will be allowed you to get the ability to design with a low specific gravity material without mechanical properties, surface qualities, etc.
Traditional SMC materials used in Class A applications have a density of 1.8 g/cm2 to 1.9 g/cm2 — around 30% less than aluminum and 75% less than steel, but relatively high for plastic material. Because SMC parts must be thicker than steel or aluminum, actual weight savings are smaller than these figures would indicate. The classic method for reducing density in SMC is to add hollow glass microspheres, and formulations are in production for unexposed, lightly loaded components with densities as low as 1.3 g/cm2.
What are the common types of SMC formulations?
- Basic formulations.
- Formulation according to production process and product performance.
- Formulation specially for a particular product.
Depending on the range of products, requirements and the specific conditions of each unit, the components and dosage ratios in the table can be changed in different ways.
SMC Formulation
| Recipe | General/Serving | Corrosion Resistant/Part | Low shrinkage portion |
| Polyester resin | Phthalate 100 | Isophthalic Acid 100 | Phthalate 100 |
| Initiator | Tt-Butyl Benzoyl Peroxide 1 | / | / |
| Low shrinkage additives | Thermoplastic Polymers 0 – 10 | Thermoplastic Polymer 25 – 40 | / |
| filler | Calcium Carbonate 70 – 120 | Barium Sulfate 60 – 80 | Calcium Carbonate 120 – 180 |
| Internal release agent | Zinc stearate 1~2 | Zinc stearate 1~2 | Zinc stearate 3~4 |
| Thickeners | MgO or Mg(OH)2, Ca(OH)2, 1-2 | MgO or Mg(OH)2,Ca(OH)2,0.5-1 | MgO or Mg(OH)2, Ca(OH)2, 1-2 |
| Stabilizer | Appropriate amount | Appropriate amount | Appropriate amount |
| Fiberglass | 25% ~ 35% | / | / |
How to choose unsaturated polyester resin for smc?
The selection of unsaturated polyester should meet the following requirements:
- Low viscosity or solid powder, convenient for glass fiber impregnation or mixing.
- Easy to react with thickener to meet thickening requirements.
- It can cure quickly and improve production efficiency.
- It has high thermal rigidity to ensure that the part will not be damaged when it is demolded.
- It has sufficient toughness and does not crack when the workpiece is deformed.
MDC Mould, as a leading SMC mold maker in china, has developed such compression mold using low density SMC material, and finally testing was successful. Due to this, MDC Mould has been officially qualified by OEMS such as Daimler and Audi.