Ever since, and even a little before, their addition to the REACH annex XVII restricted substances list in 2018, low molecular weight cyclic siloxanes have on the minds of those in the silicones business whose market is global in scope.  Low molecular weight cyclic siloxanes, particularly octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and Dodecamethylcyclohexasiloxane (D6) have drawn regulators attention and now, these molecules must be characterized and reported (if certain threshold limits are exceeded.  Methods for characterization these molecules as well as toxicity concerns surrounding D4 will be among the topics of discussion.

In this presentation the possibilities and limits of finite elements method (FEM) simulation of silicone rubber parts under high strain applications are shown. Functional components are often realized by elastomeric materials. Their job is to seal, to pressurize or to pass fluids. In the medical industry especially silicone rubbers are used as elastomers, due to their good physiological properties and high processability. Since the stress-strain behavior of silicones depends on many different effects like the raw material, process parameters or different load cases of the later part, the design phase of silicone components and molds take several iteration loops. These loops are very expensive regarding time effort. 

The simulation of the so called hyperelastic material properties can help to safe much time and money in the early development phase of silicone parts. The FEM Simulation’s result depends highly on the quality of the used database and a realistic estimation of the applied loads towards the later part. The problem is, that silicone rubbers were categorized by their hardness, but not by their stress-strain behavior, which is important for high strain applications. Therefore an own database is created for different realistic load cases.

In this study a spherical thin silicone membrane is simulated. The scenario has got a membrane with a small initial diameter increasing by filling in fluid. The initial diameter was chosen to reach high strain values. This hyperelastic material behavior is typically solved using non-linear material models. Since the membrane must be filled with a defined fluid volume a stress-strain characterization is necessary to make sure, that the membrane will not break before the target volume is reached. In the next step the Mullin’s effect needs to be considered, since the membrane will be filled several times when used. In a third material characterization test the stress relaxation of the material at its highest strain will be measured about a defined time. This material data required for the software is to be evaluated for three different high consistency rubber (HCR) silicone materials.

The specimens for the mechanical tests have been cut out from a sheet manufactured in a compression mold process. This study shows that physical quantities of silicone parts can be predicted using FEM simulation.

The presentation compares different surface treatments to improve adhesion between Polymers and LSR like Pyrosil®, VUV, Primer and Plasma. The advantages (and disadvantages) of Variotherm processes as well as the influence of injection parameters for the product quality and the adhesion strength are presented. Special focus lies on the different behaviour and therefore also different required treatments for material combinations including for example PC, PMMA, PBT, PA66, PA66GF35, ABS, PP, PSU, PEEK, COC etc. as well as the influence of the partnering LSR so there is no “one size fits all” solution. Side effects of treatment and potential overtreatment like yellowing, matting or implementation of internal stress in the parts are demonstrated, which e.g. makes Pyrosil® not suitable for optical surfaces. 

The Technology for Molding parts made of LSR became almost state of the art during the last two decades. Since there is a shift to the next stage down the S-curve of the Technology-lifetime, the number of suppliers for the LSR molding technology is increasing and the Molding Technology becomes more and more transparent from an engineering standpoint.

The key points nowadays are high and low number of cavities, small size parts with a light shot-weight or large, heavyweight components and easy or complex geometries. Molding such variations of parts with the single shot LSR technology, fit to the particular application has nearly reached the level of state of the art.

In order to avoid a patchwork of machine technologies within the production-floor, the focus is on an advanced single shot mold technology and automation on rather standard machines with low waste and increasing quality standards.

During this presentation, the LSR single shot mold technology will be highlighted and how a kind of standards can be followed for a highly challenging production environment.

Production efficiency is critical to making a profit in LSR molding.  Efficiency can be achieved in many areas of LSR molding: through material selection, process optimization, automation, etc. Innovative material science gives Optical LSRs that cure faster and more completely, minimizing process time and cleaning. Furthermore, well developed injection molding equipment and processes can increase productivity. In this discussion, industry leaders Dow SILASTIC and Elmet, will share how collaborative efforts using a new Optical LSR and world class equipment and process knowledge led to an efficient solution for manufacturing complex optical LSR Parts.     

The presentation will provide a detailed overview of the advanced developments in silicone rubber (LSR+HCR) processing and how it creates opportunities for new applications and higher production efficiency. Topics covered will range from ELAST to LSR and compression to injection molding applications. Further topics will discuss the connectivity and industry 4.0 opportunities which are covered by the Engel iQ product line, which leads to smart machines. Lastly, we will show how these combinations lead to higher efficiency and productivity.

Topics to be discussed:

• Advantages in converting HCR compression to injection molding
• ENGEL Smart Machine iQ applications
• How the applications discussed create higher production efficiency

When a customer requires secondary processes for their LSR/LSR 2-shot molded components, for example slitting/punching, pad printing, laser engraving, single packing, assembly, surface texturing, etc., they must typically work with several vendors. Using multiple vendors for a single project can present several challenges such as significant logistics costs, tracking quality issues, accurate and consistent part positioning in the equipment, floor space needed for equipment at the customer’s or contract manufacturer’s location, etc.. 

Two case studies will be presented that will detail the project challenges and the custom solutions SIMTEC Silicone Parts and the RICO Group implemented that proved advantageous to the overall project. We will dive into the technical details of how these solutions improved overall costs, quality and output, and the total-systems, technology-driven approach that was utilized. 

Silicone elastomers are being used in many different industries. They have a unique combination of properties which includes high heat resistance, physiological inertness, and excellent electrical properties. They are typically cured by peroxide initiated free radical polymerization of methylvinyl polysiloxanes, and alternatively, by hydrosilyzation using silicon hybrid cross linking agents. The curing mechanisms require elevated temperatures to obtain an effective degree of cure of a silicone elastomer. The project I would like to present combines 3 different LSR matals.The part consists of three different parts which are manufactured fully automatically in one tool. The use of three LSR types and the overmolding of the single parts to a complete work is a technically high challenge and shows on the one hand how flexible LSR is and on the other hand how high the technical level of the manufacturer is to realize such a solution.

Parts for the Silicone industry are getting smaller and smaller. Challenges are put on mold technologies, molding technologies as well as Automation approaches.

We review the machine technology used for Micro Molding. Discuss ways to handle the challenges of material compressibility as well as runner waste. 

Since Automation is and will be an essential part of Micro LSR, we review the automation approaches and the advantages and disadvantages. 

Finish off with some application examples.

• The importance of precision dosing and mixing of the material for micro-molding
• Precise control of the injection machine; plasticizing and control of the injection profile as well precise clamp force control
• Tooling for micro-molding, including: valve gated cold runner system and cavity design and monitoring of the process. 

Processing LSR can be a challenge. Unfortunately, there aren’t any textbooks to read or study. Most processors had to learn by “on the job” training. Fortunately, we have found that some of the molding principles developed for the thermoplastics industry can be used for Silicone. In this presentation we will examine a case study where a mold is “transferred” from another company. The part presents several challenges from geometry to gating issues. Each panelist will describe their approach to developing a process for this mold. Sample parts will be provided to the audience to show the issues the panelists discovered. Two different brands of silicone with the same durometer will be used to further demonstrate variations a processor is faced with each day.

Moderator: Rick Finnie, President, M.R. Mold & Engineering

Panelists:

Craig Lustek, Applications Engineer, RD Abbott.

Umberto Carchia, Sales Manager, SIMTEC Silicone

Juergen Giesow, Director of Technology, Arburg.

Jeff Hazen, Technical Manager, GW Silicones.

Robert Jovingo, LIMS Process Engineer, Shin-Etsu Silicones. 

To produce 2-component parts from silicone and thermoplastics, special machine technology is required. 

However, when it comes to micro precision molded parts in the mg-range (milligram), conventional machine and mold technology can no longer be used. 

Special machine and tool technology adapted to these micro shot weights is used. 

The presentation will compare the different systems for 2C parts from small to large.

Two component (2K) molding with liquid silicone rubber (LSR) and thermoplastic substrates can provide additional challenges to product development professionals, tool designers and process engineers. This is particularly true when working with polycarbonate thermoplastics and self-bonding LSR. The thermal properties of polycarbonate in combination with the processing conditions required to obtain good adhesion of LSR make the window for success extremely narrow for these parts. As a result, material selection and testing at the early stages of a project becomes critical to the success of the serial production cell in high volume applications where automation is employed. Starlim will present a real world example where design optimization was required to identify the root cause of adhesion deficiencies in a 2K part (already being produced within the market) and the solutions employed to allow fully automated high volume production successfully.

LSR fabricators often ask us at R.D. Abbott “How do I know the demolded part is fully cured?” This is a “How To” discussion that applies to molding of any LSR part. Both predictive and analytical methods to determine the state of cure will be explained and methods outlined as follows:

• A predictive method using a calculator that estimates the state of cure using 3-point MDR rheology as inputs. The calculator (Excel based software free for the asking) uses thermal transfer and cure kinetics equations to determine state of cure in layered finite-element analysis. It can be used to establish LIM process settings and estimating cycle time (TCT) for quoting molded parts.  
• An analytical method called dynamic differential scanning calorimetry (DSC) can determine the state of cure from a sample of few milligrams cut from a demolded part. The procedure and method will be fully explained. Interpretation of DSC results in conjunction with Akron Rubber Development Laboratories will be given as a working example of “how to”. The results can be used as verification that the chosen LIM process settings produce properly cured parts.

Many silicone applications require a post-curing step to eliminate volatile organic compounds (VOC’s). In specific in the food and medical sector there is high demand for “healthy” products. In addition, also mechanical properties are positively affected. A typical process is tempering in an industrial convection oven for 4h at 200°C. E.g., siloxanes are separated at about 150°C. There are different possibilities for a suitable oven concept in the production lines depending on sample sizes and charge amounts. Ovens designs vary from batch chambers and drum turning devices to continuous conveyor systems for one-piece flow. A specific focus is on flammable substances and requires safety strategies to ensure person and product safety.

LSR Optics has a wide range of applications because of the optical brilliance, the possibility to produce undercut geometries and the competitive pricing. In addition it is possible by overmolding of LED circuit boards to seal the electronics and implement the optics in one single step. However the sticky surface which is almost not cleanable makes the LSR parts sensitive to dust and other sorts of pollutions. This hinders the usage of the technology for unsealed applications. Furthermore it requires special treatment during production and installation to avoid waste parts and ensure a stable process.

To overcome these limitations Wilhelm Weber together with the Fraunhofer institute IFAM in Bremen have started a state-funded ZIM project to investigate a suitable chemical-free surface modification. Wilhelm Weber has pioneered in the field of optical silicon applications for almost 15 years while the complex LSR optics of different LED matrix headlights are a recent product highlight.

For standard silicon parts it is already proven and patented that such a surface modification can be generated by the radiation with very short-wavelength UV photons. For optical LSR parts however the influence onto the optical and geometrical properties is unknown.

In the process the surface is irradiated with UV radiation with a wavelength < 200 nm, typically 185 nm or 172 nm. The photons have enough energy to crack the silicon molecules on the very surface layer. By bonding oxygen radicals from the surrounding atmosphere to the silicon molecule fragments a glass-like molecule structure can be created. The thickness of the layer in the range of micrometres can be adapted by the radiation dose as well as the applied wavelength. The whole process can be applied under the normal atmosphere and no additional chemicals are needed.

The newly created “glass-like” surface is significantly less sensitive to dust any more. In addition, also overmolding and gluing is possible onto it.

First experiments have shown that standard polyamide test fibres dust can be shaken off or blown away by compressed air easily while untreated parts are not cleanable. In addition, initial tests of the optical properties like spectral transmission have not shown any difference to the untreated material. However on the surface small microcracks appear which could be a potential source of property changes.

In the presentation the overall principle of the process as well as the latest results on change in refraction index, reflection and transmittance and the effect of the microcracks will be shown. In addition, the geometric effects of the treatment like potential warpage, the long-term behaviour of the treatment as well as the influence of tempering onto the process are reported. The application potentials and the limitations both concerning part design as well as production processes are presented and representative parts are displayed.”

We will explore the molding principles used in scientific molding that can have an affect on silicone processing. Some of the tests apply to LSR and some do not. Actual data will be presented showing the results of using the Scientific Molding process on silicone.

We will discuss how to optimize product design, tooling and process through ‘Autonomous Optimization’ to ensure maximum profitability and efficiency for your LSR and elastomer molding operations. ‘Autonomous Optimization’ eliminates the tedious and costly molding trials and errors on the production floor by running a sequence of multiple experimental designs, ingeniously learning from the previous design and moving towards the optimum solution. We will demonstrate these capabilities using case studies and prove how success is achieved, even with the most challenging products. Case studies will cover different processing areas including:

• LSR mold design
• HCR compression molding 
• Simulation of LSR dosing systems

The impact of silicone waste on the environment and the lack of recycling within the industry has become a major area of concern. Increasing disposal costs, raw material waste, and government regulations addressing a lack of sustainability have all become pressures on the industry.  This presentation will discuss silicone recycling process. It is a necessary step for sustainability, but comes with its own concerns, including increasing the knowledge of the availability of the process.  By providing this information, sustainability in silicone manufacturing can be achieved through minimal waste, circular manufacturing, and eco-conscious recycling processes.

Your registration for LSR 2022 includes a tour to Arburg’s Technical Center to view silicone processing on September 15, as well as a “Silicone Best Practices” workshop. Workshop Instructors include:

Bob Pelletier, Elmet; Topic: Novel Pump

Rick Finnie, M.R. Mold & Engineering; Topic: Silicone Mold Design

Rich Ziebell, R.D. Abbott; Topic: Advanced  Materials

Juergen Giesow, ARBURG;  Topic: Injection Molding Machines.

Lunch will be served after the workshop.