The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
The most common commercial processes for manufacturing pre-pregs for electronic boards use solvent-based resin systems. Solvents are environmentally unfriendly and contribute to voids in the pre-preg and laminate. The resin impregnation process is done in an open resin bath. This low-pressure impregnation is conducent to voids in the prepregs. Voids cause product variability, which is a major source of scrap in board shops. To eliminate the above mentioned drawbacks, a solventless process, based on the concept of injection pultrusion, is developed. The impregnation is done in a die under pressure to minimize voids.In previous work, chemo-rheological and kinetic measurements were used to identify a potential epoxy-based resin system. In addition, flow visualization using model fluids was used to establish the basic flow mechanism. Here, we use the previous results to develop a mathematical model for the B-staging process. Based on the mathematical model, three potential alternatives to produce prepreg are developed and analyzed. A prototype B-staging die is built and used to verify the mathematical model. The result shows that the model agrees well with the experimental data for low pulling speed and slightly under predicts the high pulling speed runs.
Electron beam curing of a 4,4’-Bismaleimidodiphenyl-methane (BMPM) / BMI-1,3-tolyl / o,o’-diallylbisphenol A (DABPA) based BMI system, and the mixture of the above BMI resin with N-vinylpyrrolidone (NVP) is investigated to build the relationship of temperature rise, dosage and dosage rate and corresponding cure extents. The cure kinetics and effect of initiator on cure reactions are also carried out. Low intensity E-beam exposure cannot initiate BMI polymerization but high intensity E-beam exposure gives high reaction yield due to high temperature rise, which induced thermal curing. However, BMI/NVP systems can be initiated easily by low intensity E-beam exposure without thermal curing being induced. According to FT-IR measurements, 70% reaction conversion of BMI/NVP can be achieved by 200 kGy dosage exposure at 10 kGy per pass with the temperature rise no more than 50°C. The product having a Tg of 180°C can be obtained.
A numerical simulation of the pultrusion process was developed. The material properties were determined experimentally and fitt to a numerical diffusion controlled curing model. The DiBenedetto equation was used to calculate the instantaneous glass transition temperature during the curing process. The simulation determines the expected temperatures and degrees of cure throughout the part, in response to varied processing conditions. The primary application of the simulation is the pultrusion process and part design as well as testing the effect of new unsaturated polyester resins during processing.
A general concept of time-temperature-transformation (TTT) diagrams was numerically established to portray the effects of processing conditions during the curing of unsaturated polyester resins. The isothermal curing curves and the vitrification line were constructed based on a numerical procedure to model the curing of an unsaturated polyester resin. Isothermal and dynamic DSC modes were used to obtain the experimental data. A non-linear least squares Levenberg-Marquardt algorithm was used to fit the reaction rates with an autocatalytic kinetic model with diffusion effects. The DiBenedetto equation (1987) was utilized to correlate the degree of curing and glass transition temperature to model the diffusion-limited part of the reaction. The fitted model shows a good agreement between the experimental DSC scans and the predicted reaction rates. The numerical TTT diagram can be utilized during process design and optimization, since most of the curing behavior is represented in the diagram.
SBM, PolyStyrene-block-1,4-polyButadiene-block-polyMethylMethacrylate, is a new family of block copolymers offering an original way to modify polymer materials performances. Blended with a polymer compatible with one block, SBM disperses readily and imposes a structuration to the host matrix. This organization imparts unique combinations of properties, such as impact strength, high rigidity and transparency. This stands both for thermoplastics and thermosets. Here nanostructured thermosets are presented. These supramolecular architectures yield significant toughness improvements while preserving the optical transparency of the material.
The effect of controlled water addition to the development of random aggregates of alkonium ion substituted montmorillonite clay in epoxy was studied based on changes to the hardener mix ratio, clay composition, and ultrasonic treatment before cure. The effects on the glass transition temperature and microhardness were determined. The introduction of water before ultrasonic mixing altered the apparent size of the treated clay aggregates observed in these mixtures after cure. The clay aggregates also appeared to change the location and the distribution of water-induced microcracks in the cured nanocomposites. This information was used to develop a technique to remove aggregates without causing microcracks.
Complex blow molded parts afford not only a variation of the thickness of the parison in axial direction but also in circumference direction to end up in the desired optimal thickness distribution in the final part. Integrating a partial multi-walled Flex Ring into a blow molding die allows to alter the local flow channel geometry. While deforming the Flex Ring its geometry alters gradually, so no dead spots are created. As additionally the deformation of the Flex Ring keeps within its linear elastic range the deformation can be repeated for every cycle. The principle of the technology will be explained and potential solutions of the new technology will be discussed.
Non-linear finite element simulations of the blow molding and thermoforming processes have been used to provide accurate predictions of the material thinning. However, this powerful simulation tool has provided limited assistance to the design and optimization of the wall thickness distribution of preforms used in injection blow molding. Trial-and-error methods are often used in design. This paper presents a technique that converts finite element analysis of the injection blow molding process into a design/optimization tool. A systematic optimization technique for preform design that uses an iterative series of non-linear finite element simulations will be described. The series of simulations converges on a preform wall thickness distribution that will result in a specified thickness distribution in the blow molded product. This design technique is especially effective for non-circular or irregular shaped products.
Extrusion Blow Molding process is one of the only ways to produce hollow parts. This process is particularly difficult to control due to the parison swelling in the air without mould, contrary to the Injection Blow Molding in which all the different steps of the process take place in mould.There are four stages in this process. First of all the plasticising, followed to the extrusion through the die head. The next stage consists of the parison’s forming, then the transfer in the mould. The third stage is the blowing of the hollow part and finally there is the deflashing so that to obtain the final product.The purpose of this study is to show the importance of the cooling on the final quality of the product. The study has particularly been concentrated on two parameters of the forming of the hollow part. These two parameters are the blowing time and the blowing pressure. We have studied the different shapes obtained with the adjustment of these parameters and we tried to find a correlation between shape and quality of the labeling.
The aim of our study is to show that we can readily obtain a first estimate of the behavior of a tube in blow molding only using free software. From a numerical model of biaxial stretching and blowing of a parison with specific boundary conditions and thanks to a mathematical package freely available on internet : « Octave », we have studied some rheological laws of plastic materials in order to find the evolution of the radius and of the height of the tube during the blowing process. Finally, to prove that our method can be right, we check our analytical results against a complete Finite Elements simulation performed with « Polyflow ».
This paper presents a technique for describing more accurately mechanical behaviors of a PET stretch blow molded bottle by using distributions of modulus and thickness over the bottle surface. The values of modulus and thickness at each point of surface of the bottle were predicted from deformation histories of the material during the blowing process, which were obtained in numerical simulation of the blowing process. It also needed experimental measurements and estimation of mechanical properties of a stretched material up to stretch conditions in the blowing process in order to find out dependency of the properties on stretch conditions.
When a hot runner mold manifold transfers a melt “shot size” into the mold cavity, the hot runner system reduces the shot size, but it also adds a second heat history to the melt.Since temperature has a dynamic impact on the molding process, a melt sensor was developed to measure Volumetric-Pressure-Temperature change and, consequently, confirm the consistency of the thermal state.This sensor was installed into a machine nozzle, and the injected melt fill-and-pack “density” was profiled for consecutive cycles. The sensor application for a hot runner mold and resulting profiles are presented.
Rapid tooling (RT) pushed tool making into new areas. In the 1990s, rapid tooling using SLA, SLS, lasers, and other rapid prototyping (RP) technologies were the new wave. The promise of the processes threatened traditional machining methods, and mold-making shops pondered investment in exotic furnaces, raw materials and dedicated RP technicians.Looking at 2003, trends have changed. Rapid tooling is a reality, but the tooling is made using tied and true methods combined with better communication, verification of design and better machining. Rapid tooling changed the market. Now the question is what is the next step for RP and RT.
Stereolithography is a rapid prototyping technique that is also capable to producing rapid molds with high accuracy in a short time. The mold's life expectancy is strongly dependent on the part geometry. This factor could induce weak regions in the mold that are more susceptible to collapse, like sharp corners and thin features. An alternative that could be used is to conceive the mold as a puzzle where slides are manually placed inside a main slot and drawn during the ejection. This work describes a comparison between two puzzle molds that had been made with and without aluminum inserts.
The direct use of moulds produced by stereolithography (SL) provides a rapid tooling technique, which allows low volume production by plastic injection moulding. The process’ greatest advantage is that it provides parts that are the same as those that would be produced by the conventional hard tooling in a fraction of the time and cost. However, work by the author demonstrates that the parts possess different characteristics to those produced by conventional tooling methods. These revelations defy the greatest advantages of the SL injection moulding tooling process - the moulded parts do not replicate parts that would be produced by conventional hard tooling. This work investigates the mechanisms in SL tooling that induce these different part properties and describes different approaches to modifying the process which allow the moulded parts to demonstrate characteristics closer to those produced by conventional means. The work also indicates control methods that may be unique to SL tooling.
Mold conceptual design is the most important phase of mold design. The decisions made during this phase are of high level and have a direct influence on performance of the mold and development costs. The main task for mold conceptual design is the in-principle determination of each mold element type (design scheme). Because of its non-algorithmic nature, technologies and methodologies such as knowledge-based system (KBS), case-based reasoning (CBR) has been used to do the work. In this paper, a novel approach was proposed to map mold element design requirements onto the corresponding design scheme by using fuzzy logic. The proposed methodology follows three steps: (1) Design requirements for mold element is extracted and generalized. (2) Possible design schemes are presented. (3) The fuzzy mapping relationship between mold element design requirements and design scheme is established based on fuzzy composition and fuzzy relation transition matrices that are assigned by domain experts. A gate type selection example was presented to illustrate the feasibility of the proposed methodology.
Every molder that has tried to maintain squareness in the corners of a plastic part has come to appreciate the unique cooling problems inherent to the five sided box. It has long been understood that corners where two sidewalls meet the top or bottom of a product provide substantially increased heat load to the core of the mold. This increased heat load yields differential cooling, thus corners tend to develop stress, causing the sidewall to warp in. This investigation studied the effect of various core materials to and their effect on the warpage of the sidewalls of a five-sided box. The relative cycle time required to achieve maximum squareness for a given core material was also investigated.
At the design phase the injection mold maker should endeavor to ensure a maximum reliability of the mold to avoid additional costs for subsequent modifications. It is astonishing that today the mechanical design of injection moulds is predominantly done in a conventional and crude way. Finite element analysis has the potential to improve that practice. Hence an approach has been developed to couple iteratively the structural analysis of the injection mold with the filling simulation of the plastics part. That approach for an automatically coupled simulation has resulted in the first prototype version and has shown good results. This paper seeks to present the theoretical and experimental data for review.
The gelation of hydroxypropyl cellulose (HPC) solutions with an anionic surfactant was investigated. First the influence of HPC concentration (1-8%) on viscosity of water was examined. This indicated a change from Newtonian to Non-Newtonian and the development of a biphasic system. A 2 and 8% solution mixed with an anionic surfactant, sodium dodecylsulfate (SDS), was then investigated. At concentrations below the critical micelle concentration of the SDS, a peak in viscosity-concentration was observed. The concentration corresponding to the peak was found to be frequency dependent. The introduction of the SDS into HPC eliminated the biphasic structure of HPC.
The microstructure evolution and corresponding transient rheological behavior of a thermotropic liquid crystalline polymer (TLCP), Vectran V400P, is reported. The structure was characterized by using a Linkam CSS- 450 shearing/hot-stage mounting on a polarized microscope. Rheological characterization in the transient mode revealed that the transient shear stress exhibited two overshoots. We believe that the domain and defect rearrangement leads to the first shear stress overshoot. The relative magnitude of the second shear stress overshoot increases with increasing shear rate and with decreasing temperature.
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