Specification of Glass Fiber Content in SMC Moulding Process

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The SMC moulding process is the most widely used in the United States. It is mainly used for housings, chassis, bumpers, spoilers in the automotive industry, high-voltage switch cabinets in the electrical industry, building water tank boards, farmland irrigation, and construction accessories.

In the SMC moulding process, the glass fiber content can reach 30%, and the performance requirements of SMC are as follows:

1. Excellent clustering and low solubility, proper permeability. It requires excellent yarn bundling and low solubility. In this way, it can be ensured during the SMC moulding process that the resin paste with high viscosity can penetrate vertically through the thick chopped glass fiber accumulation layer. This requires that the insoluble content of the main film-forming agent of the sizing agent is greater than 90%, the yarn has no tendency to monofilament and is easy to shape.

2. The stiffness is high, preferably greater than 160 mm. This requires high hardness and strength of the sizing agent film, and high solid content of the sizing agent, sometimes up to 13%, to ensure that the yarn oil content LOU is above 1.5%.

3. Excellent cutting performance, good yarn rigidity, low static electricity, and low ribbon formation. Under the premise of ensuring the uniform force of each strand of yarn, each strand of yarn can be dispersed and arranged in parallel. This ensures that it is easy to disperse on the unit and is evenly dispersed after settlement. To further improve the cutting and bundling properties of the yarn, 0.2-1% polyurethane emulsion can also be added to the formulation.

During film formation, a macromolecular network structure is formed due to the action of the crosslinking agent, which improves the rigidity and strength of the film, and at the same time makes it insoluble in styrene. The compound coupling agent used in the formula is also to improve the stiffness of the yarn. When drying the SMC yarn precursor tube, the temperature should be high, generally up to 135°C, and the time should be more than 10 hours to ensure the full progress of the crosslinking reaction of the film-forming agent.