Effect Of Foaming Environment On Cell Quality And Surface Quality Of Polyolefin Foaming Materials

Microcellular materials have been widely used in the fields of automobiles and home appliances for reducing the using of material and maintaining the excellent mechanical properties of products.At present,microcellular injection molding is promising.Microcellular injection foaming is divided into the physical foaming and chemical foaming method according to the way of gas generation.The former requires the transformation of the injection molding machine whose cost is high,while the later needs the conventional injection molding machine.The release pressure molding and the owe injection molding are main methods in microcellular injection molding.Although the release pressure molding products have advantages such as small cell size,high cell density and good cell regularity.it can not produce the complex products,which is bad for application in industry.The owe injection molding has a good prospect in industrial application for producing the complex products.Although the application prospect of the owe injection molding is good,there are some disadvantages such as the deformation of cells and the surface defects of products,which have a bad effect on the application.Therefore,the formation mechanism of cell and surface defects is required to be revealed.And how to get the good cell quality and surface quality is the main problem to be solved in the owe injection molding.By analyzing the influencing factors of the foaming environment of owe injection molding and release pressure molding,and changing the foaming environment of owe injection molding,the paper analyzed the effect of foaming environment on cell deformation and surface defects.At the same time,by introducing gas counter pressure(GCP)and changing the temperature of the mold,the changes of cell quality and surface quality of polypropylene(PP)foams were studied,and the mechanism of improving cell quality and surface quality was revealed.The main research results of the thesis are as follows:(1)It is shown that the diameter of cells of the release pressure molding is small,the size of cells is uniform.When the weight loss of PP foams is 10.5%,the cell diameter is 36.84?m.For the owe injection molding,the cells are easily deformed,and the larger the short size is,the greater deformation the cells are,when the weight loss of PP foams is 11.7%,The cell diameter is 50.33?m.(2)The main factors affecting the cell quality are the melt pressure and the flow distance of the melt by analyzing the difference of foaming environment in the release pressure and the owe injection molding.In the release pressure molding,cells show up after releasing pressure for the high melt pressure before releasing pressure,and the flow distance of the melt is so short that it has no effect on the morphology of the cells,so the quality of the cells is good;In the owe injection molding,the pressure in the melt is so small that the cells are already generated when the melt enters the cavity.The longer distance the melt flows,the greater the cell deformation is,and the worse the cell quality is.By introducing GCP to change the environment of owe injection molding.The experiment results prove that the GCP can improve the cells morphology.The less the injection quantity is,the worse the cell morphology is,and the greater GCP required to suppress the cell deformation is.When the weight loss of the foams is 11.7%,the GCP required to suppress the cell deformation is 0.3MPa.When the weight loss is 14.9%,the required GCP is 0.4MPa.When the weight loss is 20.2%,the GCP of 0.6MPa is still not be able to suppress the cell deformation.(3)The GCP can suppress the nucleation and growth of the cells in the front of the melt to reduce the number of cells so that it can improve the surface quality.The greater the GCP is,the better the surface quality of the foams is.The surface gloss of the PP foams increases by 28% from 12.64 to 16.18 when the GCP increases from 0MPa to 0.6MPa.The surface pits are made by the introduction of GCP.The pits could be eliminated by increasing the mold temperature and the temperature of the gas.The pits on the surface of the acrylonitrile-butadiene-styrene copolymer(ABS)foams are eliminated when the mold temperature is 100 °C,while the temperature of the gas is 200 °C,the pits on the surface of the PP foams could be obviously suppressed.