The occurrence of weld-lines is one of the most undesirable phenomena in injection molding because the molded product's appearance is damaged, and its strenght is reduced in the area around the welded portion. It is difficult to prevent and limit the generation of these lines, thus studies have focused on their elimination or reduction.
A Glass-Inserted Mold has been developed to observe the behavior of molten plastic flow inside an injection mold. In this study the weld-line generation process has been visually analyzed using this mold. The main results obtained are summarized as follows.
(1) Weld-line disappear after the meeting angle of two fronts becomes a particular vanishing angle within the range of 120°-150°, and the range particular to the material does not depend on the molding conditions and cavity shapes.
(2) The above vanishing angle depends on the pressure near the melt front because it faces the hot skin layer against the cavity wall after the front makes contact.
(3) Weld-lines are thought to be caused when a 3-D curved surface of two flow fronts swirls back towards a flat cavity wall at their meeting point due to fountain flow, thus folding the surplus area which is generated.
In future research the vanishing angle will be introduced into numerical simulations, thus allowing a perdiction for when the weld-lines disapper.

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PMMA was reacted with PDMS (α, ω-diamino polydimethylsiloxane) in the presence of FeCl₃ in a twin screw extruder at 230°C. The reaction products were analyzed by ¹H NMR: The signal from methyl proton of PDMS was ascribed at 0ppm, indicating the introduction of PDMS onto PMMA. The conversion monotonically increased with time and reached almost 100% after 30min. It was found that CO₂ gas flowing in the twin screw extruder promoted the reaction. The surface tension of the product film cast from dichloromethane was 23.0dyn/cm, which was smaller than that of PMMA film, 41.2dyn/cm. The surface concentration of PDMS of the product was 42.4% when the overall concentration of PDMS was 2%.

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A method for biaxial orientation of synthetic resin under compressive force by pressing was studied. One key factor affecting press oientation is the uniformity of the flow of synthetic resin especially due to plug flow that occurs between the press dies. Uniformity is improved if the die surface is coated with an appropriate lubricant, the die surface has a surface roughness of about 1S, lubricating resin films are present, there is an adequate temperature difference between the surface and core layers of the synthetic resin being processed, and the pressing proceeds at an adequate rate. Efficient press orientation needs efficient die surface heating and cooling. This requirement is met by the stack press orientation method, air gap method, and fixed-die-temperature method.

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