Abstract: A plasticating screw having a mixing section comprised of two flow channels separated by barrier flights having axially spaced undercut sections and areas of compression and decompression in each channel. Inhomogeneities in the material being plasticated are distributed in both the forward and back directions by means of pressure driven cross-flows caused when the material encounters a section of a channel having a decreasing depth adjacent an undercut section of the barrier flight.

Abstract: An injection molding machine is utilized to develop PVT constants for a given material by pressurizing the material in the barrel against the blocked outlet nozzle, measuring the volume during pressurization, and then weighing the pressurized shot after it is purged from the barrel in order to calculate the specific volume of the material. Plotting specific volume against a variety of pressure and temperature values produces a plot of PVT relationships from which the constants can be derived.

Abstract: A method for controlling certain parameters of an injection molding cycle applying PVT optimization wherein the injection pressure and injection velocity of the melt are utilized to calculate an average viscosity for the melt during injection in a qualifying cycle of the machine as well as subsequent production cycles. A ratio of the average viscosity in a given cycle relative to the viscosity in either the qualifying cycle or a preceding cycle is utilized to adjust the holding time and cooling time, thereby achieving PVT optimization. In a second aspect, an injection molding machine is utilized to develop PVT constants for a given material by pressurizing the material in the barrel against the blocked outlet nozzle, measuring the volume during pressurization, and then weighing the pressurized shot after it is purged from the barrel in order to calculate the specific volume of the material.

Abstract: A method and apparatus for the injection molding of plastics material wherein the forward portion of the screw is designed such that mixing and shear of the material is minimized. This is advantageous when processing materials having diverse colorations so as to produce a mottled product, and also for processing glass reinforced materials wherein high shear processing would break the fibers thereby resulting in a lower quality product. Low shear processing of the material in the forward portion of the barrel is accomplished by providing a screw having a fully flighted rear portion, but a forward portion which is flightless so that a generally unobstructed, annular flow passage is formed between the cylindrical outer periphery of the flighted portion and the inner wall of the barrel. In a mottling application of the apparatus, materials of diverse coloration are softened by the flighted rear portion of the screw but not yet fully mixed so that distinct color patterns are present.

Abstract: A method for the injection molding of plastics material wherein the forward portion of the screw is designed such that mixing and shear of the material is minimized. This is advantageous when processing materials having diverse colorations so as to produce a mottled product, and also for processing glass reinforced materials wherein high shear processing would break the fibers thereby resulting in a lower quality product. Low shear processing of the material in the forward portion of the barrel is accomplished by providing a screw having a fully flighted rear portion, but a forward portion which is flightless so that a generally unobstructed, annular flow passage is formed between the cylindrical outer periphery of the flighted portion and the inner wall of the barrel. In a mottling application of the apparatus, materials of diverse coloration are softened by the flighted rear portion of the screw but not yet fully mixed so that distinct color patterns are present.

Abstract: Styrene is copolymerized with maleic anhydride by mixing maleic anhydride with styrene under mass polymerization conditions in a ratio of styrene to maleic anhydride of at least 5:1, continuing to add maleic anhydride throughout a mass polymerization stage until about 25% to about 40% of the styrene monomer is reacted to produce a reaction mass in which the polymerized maleic anhydride is about 1% to about 10% of the total reaction mass. The polymerization is then completed in a pH-adjusted free-radical initiated suspension stage, which generates homopolymer of styrene. During the suspension stage about 10% to about 20% of the bound maleic anhydride is hydrolyzed. The acid component of the bound maleic acid may be converted back to the anhydride through the use of a vented extruder.