Laser slitting
Some scientists doing a survey of technologies available for cutting spotted a trend. This same trend was seen in a variety of different industries. All started off with mechanical cutting using metal blades. The trend was that as the technology improved they moved from metal blades to technologies such as high pressure water jet, plasma torches eventually ending up with laser cutting. This has happened in such different industries such as cutting fabrics through to cutting steel.
So the question I ask is why do we still cut polymers with metal blades?
The answer I have always received is that it is too expensive. Whilst this might have been true some 20 years ago the costs of lasers has fallen considerably and I would challenge that this is no longer the case. The other component of this cost was that lasers were regarded as unreliable and not suitably robust for production.
So if we now disregard the cost and reliability as red herrings and just misinformation put out by those who do not want to consider the option what are we left with? Well polymers are transparent and to get the laser to cut the light needs to be absorbed by the material. As many polymers have absorption bands in the Infra Red (IR) it simply dictates the type of laser required is one that works in the IR so that it is best suited to coupling into the polymer.
I have seen dyed and metallized polymers that have been diced into 25 micron or 50 micron squares but did not get the details of the laser used and it was not clear if the metal layer or dye helped the process or not.
If we go back to the issue of cost, yes lasers can be expensive as a capital cost but the running cost is low by comparison to metal blades that need to be removed and re-sharpened periodically. When was the last time you heard of a laser needing sharpening? For those who are slitting large mill rolls down to customer required widths there will be plenty of down time spent removing blades and changing the spacing of blades to produce different width rolls. Think how much easier this would be with lasers that may change width at the touch of a button. Using mirrors to control the position it is possible to very rapidly change the cutting pattern. This also represents a considerable improvement in productivity of the slitting machine and makes for a reduced running cost.
One of the major problems in slitting with blades is the quality of the cut edge. The edge can be good when the blades are sharp and well set but if the setting is wrong or the blade worn the slit edges can become poor with raised edges, hairs or even tears that can cause winding problems. The raised edges may not be much of a problem winding at atmospheric pressure where air can be entrained between the polymer layers but when in vacuum there is no entrained air and the rolls are much harder and so the raised edges becomes much more of a problem. It can push the film to one side or even in a very high edge fold over the polymer making the rewinding even worse. Laser slitting can leave a clean edge and because the laser does not blunt it will be as good throughout the lifetime of the laser.
A second problem that can come from slitting and that is the generation of debris that as the polymer can generate an electrostatic charge is often attracted onto the web and so poor slitting can lead to more pinholes. Laser slitting vaporises the polymer and so although the process is not without debris the size is much finer and is more easily pumped away using vacuum extract.
Hence I would be interested to see some work done on improving the cleanliness of the polymer film also include laser slitting. As history has shown, as mentioned above, other industries have moved from blade slitting and all have eventually ended up with laser cutting. Thus why go through all the intermediate steps, save all the development time and costs and go straight to laser slitting.
I look forward to someone taking this up and I am convinced that whoever is first to do this will have a considerable advantage because of the more consistent edge quality and better cleanliness leading to fewer pinholes in metallized film.
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