Low Pressure Molding Materials

Low-pressure molding is a superior method of encapsulating sensitive components. The different types of plastics used in low pressure molding are very important because they affect not only the strength but also the durability and thickness of the final product. PA is the material commonly used now in low pressure molding system. The reason is that the PA has higher mechanical properties and melting points. When you&#;re making a decision about your low pressure molding materials for your overmolding electronic design needs, you may find yourself facing a bewildering array of choices. Well, let us be your guide as we go through some basics for choosing a material for your electronics.

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Overview of Low Pressure Molding

Low pressure molding is a process where plastic is injected into a mold under low pressure by low pressure molding machines. The injected plastic forms an overmold around the electronic component, protecting it from damage and providing strain relief. Because it requires less force to push the plastic into the mold, it's also more efficient than conventional overmolding methods.

Read Also : 5 Basic Guide of Low Pressure Molding System
Watch More : Low Pressure Molding Process

Common Materials for Low Pressure Molding

The plastic that is used for this process should have characteristics such as, strength, strong fluidity, thermal stability and resistance to corrosion. The polymerization of the resin will take place in the molding machine where it is at a temperature of between 180°C and 240°C. The plastic must be able to flow around an object without blocking up any of the channels which are necessary for removing air from the mold during injection.

There are many different types of plastics that can be used for low pressure molding. Most commonly, the plastics PA is the polyamide synthetic polymer used in low pressure molding. The reason for this is that PA and PA alloy have higher mechanical properties and melting points. At the same time, a non-polar methylene structure is embedded between the amide groups of the PA molecular chain, and its structure can coexist in crystalline or amorphous regions, polar and non-polar structures, making PA macroscopically tough. In particular, the wire rod that uses PA material, with good friction and wear resistance, self-lubrication and fatigue resistance, has become one of the important reasons for its wide use as an engineering plastic.

The main PA material used for Low pressure plastic injection machine include :

• KY88** series (Kane New Material)
• Model BOSTIK (Bostik Findlay) TRL S.A. series
• TECHNOMELT (Henkel)® PA 668PA
• And more

Bio-based Polyamide (Biopolyamides) is another material that is available for our low-pressure injection molding machines. It is a new class of bioplastics that are derived from renewable resources such as natural fats and oils.

All these low pressure molding materials are suitable for electronics related product applications for UV light resistance, thermal stability, solvent resistance and chemical resistance.

Tips to Select the Right Low Pressure Molding Materials

Low pressure materials can withstand higher temperatures than regular silicone rubber (SIL), so this makes them particularly useful for making electrical components such as heat sinks or connectors. They&#;re also ideal for making flexible parts like cables or wires because they don't require any post-curing time at elevated temperatures that would damage sensitive circuitry inside the device! Here are some tips for you to select the right materials for different applications.

• Automotive electronic parts

  : Because the ambient temperature is high, it is recommended that you choose high temperature resistant materials.

• Outdoor electronics

  : These applications include wearable devices, bicycle components, devices for underwater use, or some sensors, which may require higher viscosity materials.

Versatile Low Pressure Injection Molding Machines

Most of the PA materials are suitable for King's low-pressure injection molding machines, especially modified PA materials or PA alloy materials, which are with improved strength, modulus, hardness, stiffness, and wear resistance. To meet the requirements of electronic devices, King&#;s Solution Corp put in tremendous efforts in R&D on low pressure molding injection machines. We continue to improve and enhance several functionalities in component sealing, moist-proof, water-proof, and dust-proof based on different characteristics of resins.

Read also : C Type Shuttle Table Low Pressure Molding Machine

Critical Steps in Understanding How to Process Them Correctly for Low Pressure Overmolding

In order to understand the characteristics of plastics, simple physical property inspections are generally performed before processing in factories, such as impact resistance, MI melting, softening point Ts, deflection temperature or thermal deformation temperature, tensile strain, and Young's Modulus etc.

In mechanical processing, there is especially a need to use screw shear mixing L/D ratio to inject, extrude, and mix color compounds, considering material applicability, matching mold design, and peripheral mold temperature machine temperature control.

In low-pressure plastic professional models with plastic flow characteristics, King&#;s technical team chose non-screw design and reflow, and back pressure controller.

The PA material is a polyamide synthetic polymer. The presence of the amide group shows water absorption. The amide in the amide is bonded, and the polymer is easy to crystallize. The higher crystallized polymers are, the lower the water absorption is. Therefore, dimensional stability and mold fit should be considered when using highly crystallized polymers. Consequently, it is very important to remove related and affective factors. Usually, lowering the moisture content is required. It is recommended to dry at 80°C for more than 4 hours. For products with higher softened temperature, then using a higher temperature and a longer drying time will help avoiding air bubbles or poor shape after forming.

For more information, please visit Overmolding Services.

Low Pressure Molding Machine Manufacturer

We hope that this article has helped you understand what materials are used in low pressure molding. Remember that it is important to choose the right type of material for your electronic overmolding project because they have different characteristics. The type of material will also determine how well it can withstand wear and tear over time, which affects its performance as well as longevity of use.

For more information about injection molding machines, please refer to Low Pressure Injection Molding Turn-Key Solution or contact us today.

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Low pressure molding (LPM) with polyamide and polyolefin (hot-melt) materials is a process typically used to encapsulate and environmentally protect electronic components (such as circuit boards). The purpose is to protect electronics against moisture, dust dirt and vibration. Low pressure molding is also used for sealing connectors and molding grommets and strain reliefs.

Process

Key to this process are the raw materials and specialized molding equipment. Dimer acid based polyamide materials, better known as hot-melts, are used as molding compounds. They are thermoplastics i.e. the material, when heated, becomes less viscous and is able to be reshaped, then hardens to keep the desired form upon cooling down. These polyamide materials differ from other thermoplastics in two main areas:

1. Viscosity: at processing temperature 210 °C (410 °F) the viscosity is very low, typically around 3,000 centipoise (similar to pancake syrup). Low viscosity materials require low injection pressure in order to inject into a cavity. In fact it is normal to use a simple gear pump to inject the polyamide material. Low injection pressure is paramount, when over-molding relatively fragile electronic component.
2. Adhesion: polyamide materials are basically high performance hot-melt adhesives. The adhesive properties of polyamide is what seals a chosen substrate. The type of adhesion is purely mechanical i.e. no chemical reaction takes place.

The mainly used amorphous thermoplastic polyamides combine a favourable viscosity spectrum with a wide application temperature range from 50 to 150 °C or 122 to 302 °F. The material is heated until liquid (typically at 180 to 240 °C or 356 to 464 °F) and then injected at very low pressure, typically 3.5 to 14 bars (51 to 203 psi) into a relative cold mold-set. The low viscosity polyamide material flows gently into the mold-set cavity and around the electronics to be encapsulated. It also starts cooling down as soon as it touches the mold-set cavity and the electronics. A mold-set cavity is typically filled in a few seconds but a typical full molding cycle is 20 to 45 seconds. As the polyamide material starts to cool down it also starts to shrink. Continuous injection pressure is therefore applied to the cavity, even after its initial fill. This is done in order to compensate for the shrinkage that naturally occurs when the polyamide material goes from liquid to solid (i.e. hot to cold). The polyamide temperature is not too hot for the electronics and does not re-melt or re-flow the solder. This is simply because the relative cold mold-set will absorb the brunt of the heat, thereby reducing the temperature that a circuit board may see. Millions of circuit boards are successfully over-molded without causing any harm in the process. A low injection pressure does not stress a fragile solder joint.

Use

The low pressure molding process was initially used in Europe in the s to seal connectors and create strain reliefs for wires. The first commercial use of the low pressure molding process was in the automotive industry. The driving force was to replace toxic and cumbersome potting processes, faster cycle times, lighter parts and environmentally safe components and for some applications to replace heat shrink tubings.

Since then low pressure molding has spread out to other areas such as industrial products, medical, consumer products, military, wire harness and any unique product that needs to be sealed and protected against the environment, like Automotive sensors in-cabin and even under hood, USB thumb drives, RFID tags, moisture sensors, motor control boards, consumer products. In essence the process acts as a middle ground between plastic injection molding which subjects components to high pressure and temperatures that can often damage them and potting with resin a process that involves waste and lengthy curing times.

Advantages

1. &#;Protection: Provides excellent protection against environmental factors such as moisture, dust, and mechanical stress.
2. &#;Speed: The process is faster compared to traditional potting methods, reducing cycle times and increasing productivity.
3. &#;Cleanliness: LPM is a cleaner process as it minimizes waste and does not involve the use of harmful chemicals.
4. &#;Cost-Effective: Lower material and processing costs compared to traditional potting methods.
5. &#;Environmental Impact:&#;LPM is considered an eco-friendly process as it uses less material, generates less waste, and eliminates the need for harmful potting compounds.&#;The process contributes to a lower carbon footprint, aligning with Environmental, Social, and Governance (ESG) goals.

See also

References

• Verlag Moderne Industrie, Die Bibliothek der Technik, "Hotmelt Molding"; Olaf Mündelein; ; Süddeutscher Verlag onpact GmbH; ISBN 978-3--94-8, English