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Plastic Optics Looking Good For Our Industry

July 30, 2018

It’s no optical illusion:  increasingly, plastic lenses for optical applications are seen as a superior choice to traditional glass.
There are many reasons but it comes down to this:  polymers enable optical surfaces to join with other features of the product, chiefly mounting features, are lighter in weight, can be molded into an infinite variety of shapes, and cost less than glass. That’s a competitive advantage that has the plastic injection injection molding industry seeing dollar signs in the years ahead.
But, like any other manufacturing process, the unique characteristics of thermoplastics and the injection molding process demands a team approach during all phases of manufacturing,  from initial design through prototyping and ultimately to production.
What can plastics do for optical products?
What can’t they do?  Really, any application that calls for an optical component, whether for imaging, light detection or simple illumination, is a possibility for using a plastic optic. The list of potential applications is large and growing.  They include:

  • supermarket bar-code scanners
  • bio-metric security systems
  • medical devices
  • document scanners
  • spectrometers
  • clean room particle counters
  • telecommunication products
  • LED lighting
  • PC peripherals, such as webcams
  • microscopes
  • smart phone

Most common types of optical thermoplastics

The most common optical molding plastics are:

  • Acrylic,
  • Styrene
  • Polycarbonate
  • Cyclic-olefin polymers & co-polymers

The polymer manufacturers provide data related to their mechanical and optical properties. Optical designers should study how these materials behave under a wide range of conditions so that they can arrive at appropriate solutions.

The optical plastic injection molding process

There are two main components to the process:

  1. the mold
  2. the injection molding machine

The mold

There three main aspects of the mold used to manufacture polymer optics:

1. the cavity specs

2. the optical inserts

3. the housing that holds the cavities and inserts

As noted above, one key advantage of using polymer optics is the ability to marry optical and mechanical features into one platform.

During the molding process, all thermoplastics shrink as they cool. Generally speaking,  the shrinkage is around a half percent. It is critical that the shrinkage be factored in when determining the final dimensions of the mold.

The molding machine

The optical injection-molding machine, aka a press, is comprised of a moving and a fixed platen, a clamping unit and an injection unit. Plastic pellets are introduced into the injection unit where they are melted and and injected into a mold.  As the plastic cools and solidifies in the mold, the material conforms to the shape of the insert and cavity details, producing the final optic.  After cooling, the mold opens and ejects the finished optic product.

Choice of competent optical molder crucial

Optical designers should only partner with an optical molder who thoroughly comprehends the engineering challenges. Ideally, the molder has been working with the designers from the start.

Designers should visit the plastic injection molding facility as soon as possible in the process to determine its capabilities. After all,  the optical parts produced will be no better than the machinery in which they are molded.

To sum up, manufacturing precision polymer optics is a highly-specialized discipline requiring a thorough knowledge of optical design, mold construction techniques, state-of-the-art mold processing capability and optical expertise.


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