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Photochemistry: An Introduction

Photo etching  is one of the many services we offer here at Qualitetch, and it is a process we specialise in as industry leaders.

Whilst many people get the general gist of popular sheet metal processes like stamping (using stamp tools or power presses) and laser cutting (using laser technology), it can take a little longer to get to grips with the various stages of  chemical etching  because of how much is involved.

Photo etching really is an invaluable development in manufacturing, and second to none for components in need of absolute precision and the highest quality finish. However, there is so much more at play than a single machine or a simple design-to-doorstep process.

The photo chemical etching process requires infallible digital design skills, keen attention to detail and a remarkable level of knowledge and experience in the principles of both photography and chemistry – or more accurately, photochemistry.

What is Photochemistry?

Photochemistry is an interesting and fundamental discipline in science and various other fields, concentrating on light and its chemical effects.

Though this predominantly relates to photosynthesis in the natural world, along with vision and the production of vitamin D, there are far more photochemical reactions to consider.

The Basics

“Photo-” means light and “-Chemistry” is the science around elements in the matter, their composition, properties and reactions. So “Photochemistry” is the study of how light reacts with these elements to create new substances.

Photochemistry is destructive (where irreparable damage is done, and the process cannot be reversed), and offers a wider scope than thermal reactions. Photochemical reactions can be caused by the absorption and processing of visible, infrared or ultraviolet light.

There are  two laws  of photochemistry; the Grotthuss-Draper and the Stark-Einstein. The first refers to how light must be absorbed for a reaction, the second to the ratio of light photons to molecules needed for a reaction to occur.

The Types

Three well-known types of photochemical reactions are:

  • Photosynthesis – the conversion of solar energy (sunlight) to carbon dioxide and water to oxygen and glucose in plants
  • Bioluminescence  – a naturally occurring enzyme in living organisms that reacts to produce light, responsible for how fireflies, jellyfish and  bioluminescent algae  glow
  • Photodegradation – one of the least popular reactions, this is the process where light and air alter materials, often destroying their quality (especially with faded photographs, paintings and glassware)

Photoresist and Photo Etching

Another very useful type of photochemical reaction is photoresist – this is one of the most crucial steps in the photo etching process, allowing us to put even the most intricate designs on larger volumes of sheet metal, ready to be processed in the perfectly balance chemical baths.

Photoresist is employed in a number of industrial manufacturing methods, utilising light-sensitive materials to ensure only certain areas of a design are reacted with (whether or not those areas are the exposed or unexposed ones depends on if you use a positive or negative resist).

In our case, the sheet metal and photographic film (displaying the component profile) is laminated with the photoresist, and set in place under a UV light and vacuum. The photoresist is then washed away; the plate developed and the design left in place for the etchant to work away at.

Effectively, the photoresist controls how much of the UV light it is exposed to is absorbed, therefore controlling the rate and extent to which the reaction takes place. This is why we can harden the etching lines of a profile at varying degrees and intricacies, affording more flexibility than many other processes.

So, how important is photochemistry when it comes to photo etching? Very. Without it, we couldn’t control the chemical reaction, protect the crucial parts of the sheet metal, or get the precise and controlled results we need.

A little bit of light (and a lot of chemistry) goes a long way.