Transfer Printing: Recognising And Resolving Problems

For years, the market of digital transfer printing has been growing and this has been partly at the expense of the traditional screen printing transfer. However, this also opens new possibilities and markets. The entry hurdle is low, because with just a small investment in a plotter and heat press you can start your business. The potential problems, however, remain the same, and new functional fabrics are creating new ones. In a multi-part series of articles I would like to help users to recognise potential problems and to develop solutions. Patent remedies are not available for every problem; however by understanding the backgrounds it is possible to deduce recommendations that help working more quickly, more cost-effectively and preventing complaints. In this first part, I want to explain the process of cutting and weeding.

Part 1 – cutting and weeding

You will probably ask yourself what news I have to offer, and basically you are right, normally it causes no problems. However, there are two problems that are well worth considering: on the one hand there are the thick films, such as flock film and on the other hand there are the thin, elastic flex films.

The problem with thick films is that the knife gets trapped within the material and cannot turn or not turn easily. This results in creased corners and makes it difficult or even impossible to cut smaller motifs. The solution for this is a knife with a sharper angle at the tip. These are usually called flock knives. With 500 μ, flock is indeed a quite thick material.

This is certainly a simple solution for resolving the problem with flock. This is also why the name flock knife became established. However, this is not the best solution any longer. And this arises from the actions of Greenpeace. In their campaign against organostannic compounds in ship coatings, Greenpeace discovered that these organostannic compounds are also used as a catalyst in hot-melt films. Since these catalysts are no longer used, the hot-melt films of flock are now less brittle and a bit more elastic. Therefore, the films, which are a kind of swimming on top of the flock fibres, are more difficult to cut with an obtuse-angled blade. It is easy to cut a carrot with a knife with an obtuse angle, but not a ripe tomato!

But do we have to cut through the entire 500 μ of the flock film? Rather not. Only the hot-melt film and the flock adhesive must be cut.

They are insignificantly thicker than a normal flex film. Because of that, the best solution is to adjust the depth of the knife so that only what is really necessary will be cut. This also allows the cutting of flock films with a high flock density, such as VelCut Evo, more easily with a 45 degree standard knife than with a flock knife.

Thin, elastic films

The thinner and more elastic a flex film is, the more comfortable is the decorated garment to wear. However, it is also more difficult to cut the film. The film will tend to escape instead of being cut. Also here, you should use a rather flat knife.

The measurement in degrees is not always clear; for most knives the free angle α is indicated, but for some knives it is also the cutting angle β. If the cutting angle β is specified, then a 60 degree knife is a flat knife.

Depth of the knife

The adjustment of the knife depth is also important for thin and elastic films, such as FlexCut Advance. This is not only for the result but also for the durability of the plotter parts: knife holder and cutting bar.

If the knife stands out more than necessary from the knife holder, then the lever force that impacts on the bearing at the end of the knife is considerably higher. The bearing is worn out more quickly and will exhibit axial play.

Knife holder

When the knife holder has too much axial play, the knife will bend at every change of direction towards the side, instead of turning. This is the cause of typically fine and uncut areas at the corners, which will complicate the process of weeding or make it impossible. With brittle, thick films, this is not so noticeable, especially not when the carrier has a high adhesion. However, with thin and elastic films it is very noticeable. This is not a problem of the film but a problem of the knife holder. Some drops of oil in the bearing can help to reduce the axial play. Sometimes, however, it is necessary to invest in a new knife holder in order to make the weeding simpler and quicker.

Overcut

A further feature that helps prevent problems during the weeding process is to use the OverCut function of the plotter. If your older plotter does not have this function, an investment in a new plotter may pay for itself quickly. The better the cut, the quicker is the weeding.

Cutting speed

Many users tend to reduce the cutting speed continually lower, when finding out the correct cutting speed. This is certainly the correct approach with thicker and harder materials – craftspeople know: the thicker the board, the lower the sawing speed is. However, with thin and elastic films the contrary is the case. Just as with a ripe tomato, it is easier to cut them with higher speeds.

Weeding

Also for weeding, there are tricks to work more quickly. These may be self-evident, but for a beginner they can be helpful:
• Set a weeding frame around every text line so you can weed line by line.
• First remove first the inner parts of the letters so parts that may fall down will not stick on the polyester film.
• Weed from left to right; most of the letters are open to this side.

Summary:

• Set a weeding frame.
• 45 degree knife as standard knife for everything.
• Possibly a 30 degree knife for thin, elastic films.
• Check and adjust knife depth before starting a new print job.
• Pressure as low as possible; as high as is necessary.
• Lubricate knife holder, possibly replace.
• Use OverCut.

This article appears in the Sign Africa Journal.

Holger Beck Area Manager, SEF Textile | Responsible for sales in Europe and Africa at SEF Textiles.