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Films provide a popular alternative to direct liquid emulsions in the stencil-making process. Technically, they span the range of screenprinting jobs from printing a simple sign to reproducing the intricacies of a printed circuit board. Films pretty much remain the medium of choice throughout the electronics industry, hailed for their superior edge definition, controlled ink deposits and ease of use. Films can offer something for almost every screenprinter, even a newcomer who can’t quite scrape up the investment for an exposure unit.

There are really only four different kinds of film used in making screen stencils and they all work in slightly different ways. What they all have in common is that they are basically two-part systems, some sort of emulsion layer or plastic material lightly bonded to a layer of clear polyester. The clear layer's sole function is to serve as the support for the top layer.

There are four types of film:

1. Handcut masking films.
2. Handcut stencil films.
3. Direct photosensitive films.
4. Indirect photosensitive films.

HANDCUT MASKING FILM
Photo-opaque masking films are used in conjunction with a screen that has been coated with a direct emulsion or another film, a photosensitive one. A design is cut into the photo-opaque layer of the masking film and all non-printing areas are then peeled away to reveal the clear polyester support underneath. The resulting positive is then taped directly to the screen, or photosensitive film, and exposed to UV light. When the exposure unit has been switched off, the masking film’s job is done. It can be rolled up and put away. On the screen or film, areas of the photosensitive emulsion that have been shielded from the light by the mask remain soft and can be washed away by a stream of water. (Some photosensitive films will also require the application of a developer.)

All masking films belong to the category of handcut films. The term handcut has become somewhat misleading because, while some patient souls still cut these films with a swivel knife, today most are done on a computer-controlled plotter -- read vinyl cutter. The one drawback with masking films is that you still need to apply them to a photosensitive material and you still need to expose that material. You need an exposure unit.

HANDCUT STENCIL FILM
A really exciting possibility opens up with handcut stencil films. Every vinyl sign shop has a plotter that can cut these stencil films as perfectly as it can cut vinyl, and the resulting image can be easily transferred to your screen without any need for photosensitive emulsions, exposure units or safelights.

You cut handcut stencil films with a knife blade in exactly the same way you cut your design into masking film. But instead of plastic, the top layer of a handcut stencil film consists of a non-photosensitive emulsion that will adhere to the fabric of a screen. After weeding, this film can be applied directly to your screen. It actually becomes the stencil you print with.

The next thing you need to do is transfer that design into your screen. You place the weeded film, emulsion-side up, on a flat hard surface of about the same size as the film. On top of that, place a clean, degreased screen with an inside dimension a bit larger than the film. The next step is to adhere the stencil using either water or a manufacturer’s recommended solvent. Then, all you need to do is fill in around your stencil with screen filler and you are ready to print. You have created a perfect screen stencil without an exposure unit!

The only real difference between preparing a handcut masking film and a handcut stencil film comes at the weeding stage. With a stencil film you weed out the areas you do want to print!

Some screenprinters scoff at handcut film because it can’t hope to compete with some of the complex artwork that can be reproduced by a photosensitive emulsion. A lot of handcut’s detractors, however, are thinking back to a time when handcut meant exactly that, before the computer-controlled plotter gave all types of handcut film a new lease on life. For signmakers, handcut film offers a way to create screenprinted artwork every bit as good as the vinyl signs they produce. There is just one serious drawback to handcut stencils films: mess up in the adhering process and you have to cut the whole thing all over again right from scratch. This does, however, provide some excellent motivation to get it right every time.

Almost all problems with stencil films come from a poorly bonded stencil pulling away from the mesh. The root of such a problem usually lies with insufficient degreasing of the screen. Even degreased screens that have been sitting around for a while should be redone. You can eliminate most of these difficulties by starting with a perfectly clean screen and taking a little extra time to make sure the film has been properly adhered before you begin to print.

PHOTOGRAPHIC FILMS
Today, only a small portion of stencil films fall into the handcut category. Photographic films have become the far more prominent members of the family. But the photographic film clan is split into two camps: direct and indirect films. Here’s how to tell them apart. Direct films go into the screen before being exposed, indirect films are exposed first and adhered to the screen later.

All photographic stencil films do, however, have one thing in common: they consist of a layer of photosensitve emulsion lightly bonded to a layer of clear polyester.

There is one more difference to keep in mind: The entire stencil film family is divided into two types. Some family members create stencils impervious to solvent-based inks; others have been designed to resist water-based inks. Both handcut and photographic films have members in both camps. So, apart from your choice to either handcut or photographically reproduce your artwork, the film you select for any particular job will be determined by the kind of ink you’ll be printing with. If films have an Achilles’ heel it is in the area of solvent resistance. Even die-hard film buffs become cautious when printing with inks containing more aggressive solvents.

Photosensitive stencil films offer a number of advantages over direct emulsions, especially in their ability to reproduce sharp detail. Because they transfer a uniform layer of pre-sensitized material to a screen, direct films excel at applications where printers need to lay down a consistent ink deposit. This ability has made them the medium of choice for reproducing printed circuit boards.

Indirect films, on the other hand, offer almost identical features and may have a key advantage for a signmaker just getting into exposing his or her own screens. Indirect films are exposed before being adhered to the screen so you can get by with a much smaller exposure unit than one capable of accepting an entire screen.

Direct films, on the other hand, require an exposure unit comparable to those used to expose direct emulsions, and they are more expensive. The temptation to just go with direct emulsion is strong, because direct liquid emulsions stand up better to strong solvent inks like vinyl inks, for example. Direct emulsions also boast a good reputation for durability, especially when print runs number in the thousands rather than the hundreds.

RECLAIMING
As far as ease of use is concerned, both film and direct emulsions have their advocates, but when it comes time to reclaim your screens, film scores a clear victory. Film is much easier to reclaim. Usually, a high-pressure spray of water is all that’s required. To make the process dead easy, brush on a dab of stencil remover and the film will readily dissolve. Easy stencil removal translates into far less wear and tear on the mesh in your screens.

IS THERE A FILM CAREER IN YOUR FUTURE?
Films add a great deal of flexibility to the stencil-making process, and as you can see, offer a great opportunity to signmakers interested in creating stencils in house. For someone just getting into screenprinting, handcut film offers a low-cost, entry-level method of getting artwork into screens and even for the experienced screenprinter, it can offer an ideal way of adding inexpensive spot color to jobs. There are no expensive exposure units to buy, no tubs of sensitized photo emulsion or sheets of photosensitive film sitting around waiting to go bad, and you don't even need a wash tank until you start thinking about reclaiming your screens.

Although most screenprinters prefer to stick with either film or direct emulsion, both methods offer clear advantages on certain jobs. Even a die-hard direct emulsion printer can find it profitable to experiment with film. The easy reclaims and razor-sharp imprints can prove highly seductive.

So, is there a film career in your future? Well, there just might be.