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LCP for Injection Molding Applications

Liquid Crystal Polymers, ideal for thin walled components

Miniaturization has been a common theme in manufacturing over the years. As many products become smaller, the technologies and parts that build those products must become smaller and manufacturers must adapt to this trend. Thin wall designs have been a challenge to injection molders in the past, until they perfect trifecta was formed. The ideal raw material, plus the right mold design and tooling, and a machine with the processing power to get the job done.

We will explore how the right material, coupled with the right machine, will get the job done right.

Many of today’s most common products require thin wall designs, such as iPads, cell phones, computers/circuit boards, microwave ovens, and even some aerospace and automotive engine components. Finding a suitable material that can withstand the requirements of these types of products has posed a challenge in the past. However, more and more injection molders are turning to Liquid Crystal Polymers (LCP) to get the job done.

So, you may be wondering, what are these Liquid Crystal Polymers (LCPs)?

LCP is a very unique material, it is a tough insulator with high fluidity during molding, features excellent electrical properties, and dimensional stability. The material can also withstand reflow soldering without distorting, melting, or blistering.

LCPs have a high mechanical strength at high temperatures, flame retardency, good weatherability, exceptional chemical resistance, and have a high Z-axis coefficient of thermal expansion. LCPs are inert and resist stress cracking when subject to chemicals (such as, aromatic or halogenated hydrocarbons, strong acids, bases, ketones) at elevated temperatures.

LCPs come in melted or solid forms. The chemical structure consists of linearly substituted aromatic rings linked by amide groups. They are unique in that they can form regions of highly ordered structure while in the liquid phase.

Injection molding LCPs can cause the chained molecules to orient in the flow direction near the mold wall. It is important to consider flow patterns and anisotropy in the cavities when designing the mold. Since LCP components are manufactured by high-speed injection machines, it is essential to design adequate air-venting in the cavity to ensure all gas remaining in the mold discharges quickly and effectively. Proper air venting eliminates the problem of short shots resulting from welds in thin walls or at the ends of the flow.

LCP combined with a plunger type of injection molding machine is an ideal combination. Especially for molding thin walled components, a molding machine that features a quick response to the initial injection is ideal. This is necessary because the material sets rapidly and its shear rate is highly dependent on melt viscosity. Better results come from molding machines that are capable of continuously metering one-third to three-quarters of the total injection capacity. Insufficient metering results in excess resin, which causes molding defects.

While any of Sodick Plustech’s equipment is set up well for LCP because of the inherent acceleration the machines get from the linear motor driven plunger, the LP Series of injection molding machines are ideal for LCP applications, because the LP model is developed with a second linear valve which increases the acceleration even further (2-5 milliseconds) and wllows for LCP applications which often have fill times under 0.1 seconds. LCP does not produce a lot of flash during production because it has low-melt viscosity and sets rapidly. However, during the molding of ultra thin walled components (<0.2 mm), resin can set in the walls, hindering flow. An accumulator on the machine, such that on Sodick machines, remedies this situation.

Sodick injection molding machines are efficient and precise for applications that require LCPs.

Special thanks to Sumitomo Chemical for the content within this blog.

Owing to their high thermal and mechanical performance, inherent UL* 94 V-0 flame retardancy, excellent electrical properties even at high frequencies (25 Hz), stress-crack resistance, and chemical inertness, SumikaSuper® liquid crystal polymers (LCPs) continue to be a preferred material for injection molding a variety of high-performance, high-precision components.

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ABOUT SODICK

As a leading precision injection mold machine manufacturer, Sodick continues to pave the way in providing premier injection quality and repeatability. Our proprietary technology relies on a continuous plasticizing heat profile, constant material viscosity, as well as steady filling volume and holding pressure.

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