Volume 4, Issue 3

Polycarbonate (PC) is considered to be a proper resin for optical memory disk, however PC resin shows high birefringence. It is very important to reduce birefringence of PC optical memory disk. This research is to obtain the relationship between birefringence and process conditions and to get the optimum condition for the production of low birefringence substrate of PC optical memory disk. The birefringence distribution of PC optical memory disk was theoretically predicted by the calculations of both the stress distribution caused by molecular orientation during the filling stage and the thermal stress caused by temperature difference during the cooling stage. The relationship between birefringence distribution and the process conditions such as rheological properties of PC resin, injection temperature, mold temperature, mold design and annealing condition is possible to be predicted theoretically by calculating shear stress during the injection process and thermal stress during the cooling process. The predicted results of birefringence distribution qualitatively agree with the experimental ones.

The transient flow of a compressible polymer melt in an injection system consisting of a ram, a runner, and a shutoff valve is studied. Experimentally, the exit flow rate is found to have an initial value determined mainly by the precompression level and a steady state determined mainly by the ram speed. This flow rate can fall before it rises again, or it can overshoot its steady state. Such complex behavior is predicted qualitatively by a simplified mathematical model, which neglects elasticity but accounts for the finite compressibility and bulk viscosity. Four dimensionless parameters governing system dynamics are identified and their effects investigated by computation.

Finite element methods offer the potential to greatly refine mold filling analysis. As a consequence, there is strong pressure to apply this technology on a routine basis in industry. Unfortunately, traditional finite element techniques are not adequate to design a viable model of the flow of molten plastic into a mold. This paper explains the mathematical problems that must be solved. It describes why the widely used classical matrix techniques give erratic results, and demonstrates that it is mandatory to apply a total dynamic analysis to obtain a reliable mold filling simulation. A new technique is introduced to solve the problems caused by non-linear material properties and moving boundaries.

By the determination of birefringence and elongation at break as functions of the distance from the surface detailed informations are obtained about the states of orientation of the molecules in injection molded polypropylene plates. Both, the birefringence profile and the profile of elongation at break in the cross-section of the plates, exhibit the skin/core structure typically for injection molded polypropylene articles. An analysis of the results of two polypropylene grades molded at different processing conditions shows a good agreement of both methods.

An experimental study of the rotational molding of polyethylene parts is presented. Specific attention is given to heating and cooling of the molding cycle and to the micro structuring and bulk characteristics. Experimental measurements of the heatup of the oven at the startup of the process is presented. The heatup of different molds in the oven is then measured and interpreted in terms of heat conduction theory and the Fourier number αt/L 2 . In the experiments, thick aluminium molds heated up more slowly than thinner steel molds. The cooling characteristics of mold subject to different quenching conditions were compared with water showers inducing the most rapid cooling followed by fan blowing and the slowest being in quiescent air. The order of cooling of the different molds studied followed the same order as their rates of heating as would be expected from the theory of heat conduction. Polyethylene parts formed in the molds were found to be crystalline, without orientation and to possess large spherulites. The size of the spherulites and the level of the crystallinity was highest where the cooling rate was the lowest. Uniformity of part thickness and warpage were measured. Warp age correlated with rapidity of cooling rate. This suggested a mechanism of thermal quench stresses.

The process of extrusion blow molding was considered in an attempt to obtain biaxial orientation and properties in two thermotropic copply esters: hydroxybenzoic acid/polyethylene terephthalate (HBA/PET) and hydroxybenzoic acid/6-hydroxy-2-naphthoic acid (HBA/HNA). Some degree of biaxial properties and orientation was obtained in blow molded samples in which the die temperature was maintained below the melting temperature. However, the biaxial orientation was present as a layered structure in which the orientation and texture varied from the outside to the inside surface of the blow molded article. Tensile and flexural properties, as well as the morphology and orientation as determined by scanning electron microscopy (SEM) and x-ray diffraction (WAXS), attested to the resulting structure in the blown parison. The orientation and properties were strongly dependent on the thermal and deformation histories during the process. For liquid crystal polymers with relatively slow crystallization kinetics, blow molding in the supercooled state represents a possible processing method to obtain multidimensional properties.

A model is presented which can be used to explain the friction condition on the interface between the composites and the mold during sheet-like parts compression molding of fibre-reinforced thermoplastics. The composites is treated as an incompressible isotropic fluid. Circular hollow disk is compressed in order to derive the position of the neutral surface which can explain the interfacial friction from consideration of minimum energy dissipation. From the theory and the experiment, it is clear that there is slip on the mold surface. By using the nondimensional parameter which measures the ratio ofvicous to frictional resistance, the phenomenon of the friction can be well explained.

The need for nanometer-sized features in integrated circuits calls for the use of dry-etching techniques using glow-discharge plasmas. The reactive ion etching (RIE) mode in which there is a large difference in potential between the gas phase and the solid surface yields particularly desirable, straight-walled etched structures. The design of processes and materials for RIE requires a knowledge of the effects of operating variables on various parameters. In the present work, the parameter emphasized is the etch rate. A novel aspect of the apparatus used incorporates a laser interferometer for in situ measurements of etch rate. Some observations on operating variables are: i. Chamber pressure is more critical when a fluoride-oxygen plasma is used than when oxygen alone is used. This is due to polymer deposition that occurs with the former along with etching. 2. The etch rate in the oxygen/RIE mode is almost the arithmetic sum of the oxygen/plasma mode together with the nitrogen/RIE mode except at low incident power levels where etch rate with oxygen/RIE is much greater than the sum of the other two. 3. Aromatic polymers etch more slowly than aliphatic polymers. 4. The oxygen/RIE rate of polyvinylchloride, PVC, decreases on addition of a compatible organotin compound. A 1:1 mixture of PVC with a tin compound etches at i/10 the rate of PVC alone.

For the fabrication of microstructures with minimum lateral dimensions in the micrometer range and structural heights of up to several hundred micrometers a new microfabrication technique has been developed by the Karlsruhe Nuclear Research Center. The so-called LIGA method is based on a combination of deep-etch X-ray-lithography, electroforming and plastic molding. High-quality micromold inserts can be prepared by deep-etch X-ray lithography and electroforming allowing an arbitrary choice of cross section of the microstructures. By optimization of the process parameters of the reaction injection molding process using casting resins on a methyl methacrylate base it has been shown that a yield of 100% can be achieved. For molding microstructures without any flaws, the mold material has to be degassed, the cavity of the mold must be evacuated and the shrinkage due to polymerization has to be compensated by applying a holding pressure. With an internal mold release agent which is a special salt of an organic acid, cycle times of about 12 min have been achieved in the micromolding process step which are very much shorter than the exposure and development times in the direct lithographic production of microstructures. Such plastic structures can represent the final product or, if microstructures are to be made of metal, they are used as templates in a subsequent electroforming process. Depending on the geometrical configuration of the microstructures, either a metallic gate plate or an electrically conducting plastic layer are used as the electrode for electroforming.

The dynamic and physical properties of neat and glass fiber filled nylon 6 systems were examined. The dynamic viscosity of neat nylon 6 melt was well fitted to: (I)η′=a/(1+b ω)c For the glass fiber filled nylon 6 composite systems, however, a modification of Eq. (1) was required to accommodate the viscosity data. Various types of rheological models are examined to describe the effect of glass fiber on the suspension viscosity, and respective constants of models were determined by a curve fitting. A silane coupling agent had a profound influence on the rheological and physical properties. It increased the dynamic viscosity of composite and yield value, but slightly decreased the activation energy of flow, particularly at high frequency range. Further, it increased the loss factor over the frequency range examined. Plot of storage modulus against loss modulus instead of frequency eliminated the effects of temperature and coupling agent. From the tensile fractured surface of coupling agent treated system, a fibrillar structure was observed.