FR-PP Foam Sheet is an alveolar 100% PP sheet with the surface covered with non-woven- Suzhou Shincell New Material Co., Ltd.

FR-PP Foam Sheet is an alveolar 100% PP sheet with the surface covered with non-woven, which combines great versatility and high performances: it’s 100% recyclable, non-toxic, resistant to mechanical stress and chemical agents, thermoformable, printable, and weighs only 1250 gr/sqm or 1500 gr/sqm. FR-PP Foam Sheet is also highly durable and acoustic, while providing good insulation and lightness.

Typical non-nucleated polypropylene foam sheets are difficult to thermoform and have a rough, uneven surface and a poor cell structure. The present invention provides a novel foaming process that produces a foam sheet with a smooth, acceptable surface and a uniform cell structure that can be thermoformed into shaped articles.

The method for producing the foam sheet of the present invention includes adding to the polypropylene melt a physical blowing agent, which is selected from the group consisting of hydrocarbons, chlorinated hydrocarbons, chlorofluorocarbons, nitrogen, and carbon dioxide, or a nucleating agent which is selected from the group consisting of isopentane, citric acid-sodium bicarbonate mixture, talc and titanium dioxide. The physical blowing agent is added to the polypropylene melt at a temperature above the crystallization point of the polypropylene, which is above its melting point and below its glass transition temperature.

Alternatively, the physical blowing agent can be added to the polypropylene melt in the presence of other liquids that are capable of providing a suitable amount of gas to the melt to provide a desired level of cell structure formation. The method also includes measuring the equilibrium compliance Jeo (a measure of melt elasticity) and/or the recoverable shear strain per unit stress Sr/S (a measurement of viscosity). The polypropylene resins which are effective in the preparation of the foam sheet of the invention have an equilibrium compliance Jeo above (12 x 10-5 cm2/dyne) 1.2 x 10-3 m2/N. Resins having a Jeo value below this value yield unacceptable foam sheets with non-uniform cell structures and uneven surfaces.

The polypropylene resins that are useful in the practice of the invention may be blended with other polymers such as linear polypropylene and/or polyethylene resins, provided that they have the required molecular and rheological characteristics. Blends of linear polypropylene and branched polyethylene are also useful.

In addition to the above-mentioned advantages, a further advantage of the present invention is that it enables the production of sandwich laminates which have improved fire behavior compared to those with non-FR PET cores and epoxy face sheets. This improvement is due to the positive interactions between the FR in the foam core and the FR in the epoxy face sheet, especially influencing the initial burning phase by lowering the pHRR. This is the first time that such interaction between different FRs has been demonstrated in a polymer system.