Production of steel and polymer clichés

Portable cliché film developer

This portable, cliché developer is easy to use and suitable for both large and small series production. It is the best solution for the direct production of cheap clichés and provides pad printing with complete autonomy, speeding up the time required from getting a job, through making a conceptual drawing and cliché, to the beginning of the decision to print.

Making drawings and making a movie

Since the quality of the original drawing and the creation of a film positively from it directly affects the quality of the recorded cliché, improvements in the design and generation of the film are the best place to start the discussion.

Since digital files are now the norm, it is important to have a good graphics program that can import different formats without having to significantly change the file. You need a degree of flexibility depending on the type of customers you serve and the industry they represent, as different industries favor certain file formats.

In most cases, you will be well equipped if you keep the current editions of popular graphics programs, such as Adobe Illustrator, CorelDRAW !, and Macromedia Freehand. I'm not a software guru, but I know from experience that programs like these are powerful and versatile, offering wide compatibility for importing and exporting files. In addition, for those who process color images or often work with scanned images and photos, raster image editing software, such as Adobe Photoshop, can also be very useful.

If your clients tend to be engineering-oriented rather than graphic art, you may occasionally encounter files created using a design program such as CAD. However, such files are usually unsuitable for creating clichés. Images saved as CAD files do not offer smooth curves, evenly filled surfaces, and the raster capabilities you expect from a design, nor do you usually import into another graphics program with good results.

Preparation of drawings

Once you have received the design file and opened or imported it into your graphics program, you can begin customizing and splitting the image to meet the requirements of your pad printing process. The following example of a color separation preparation procedure provides a general description that is customizable whether you use the PC or Mac platform. This is based on the preparation of printing in two colors and is supposed to be done on a desktop laser printer.

• Draw a pattern of the actual cliché you will use. The sample for measuring the tampon, in this case, is a cliché of 70 x 150 mm.
• Place the two-color composite design in the desired location, using the guidelines as guides. The image should be centered in the area of ​​the ceramic paint container (Figure 2B). When finished, group all the elements of the image (template and graphic design).
• Duplicate the entire template and graphic image (Figure 2C). This ensures that your separation will match in size and position and that the cliché image for each color will be accurately re-registered relative to each other when you're done.
• Next, you can selectively delete design elements from each of the clichés so that only a design of the same color appears on each cliché. To do this, regroup each of the duplicate images and delete the unwanted elements.
• Replace the colors from each remaining element on each of these two clichés with black. This ensures that when you do color separation, the design elements are printed as dark as possible (some light colors are represented as percentages of black when exiting a black-and-white laser printer). Also delete markers that appear near the image (if any) to reduce the chance that they will be printed with the image.

To avoid confusion, you may want to specify which color is printed on which cliché when the job goes to print. A simple place for a descriptive comment somewhere outside the drop of the tampon so that the comment is not part of the design (Figure 2D). Some printers also include a job number or file name on the help cliché corner.

• In most pad printing applications, the cliches are exposed on the emulsion side with a positive (or the toner side, in the case of printing from a laser printer on a positive) to establish contact with the surface of the cliche. Thus, to get the right reading image when looking at an object, the design elements for each separation must be orchestrated (in a mirror) to produce a positive of the film being printed (Figure 2E).

Separation printing

Your digital design film production options vary depending on the type of output device and the material available to you. At the low price of the spectrum is a conventional laser printer that prints the image directly on a strip or foil. The following are thermal illuminators designed specifically to develop films without a chemical process. And finally, at the high price are laser illuminators with a resolution that far exceeds what a typical pad printing job requires.
For applications such as the job description we have described so far, where the design involves simply overlapping two-color lines, we recommend using a laser printer to make the film. For best results at the lowest cost, you should use a minimum resolution of 600 dpi.

You should also use a media designer specifically to produce a positive film for a laser printer (typically, the most stable materials are polyester-based). Definitely avoid using standard cotton wool or transparent foil, which can cause problems.

If you think that the density of the toner produced by your laser printer will not be high enough to effectively block the light in the drawing area during exposure, you can buy various spray products to improve this density. Your tampon supply vendor should be able to recommend appropriate products to you.

Photopolymer clichés

Improvements in photopolymer materials have led to cost-effective clichés that support high-resolution images, have a long lifespan, and are easy to process at home. Photopolymer cliché consists of a resistant layer of photographic material glued with solid glue to a steel plate. The steel stand allows the cliché to fit easily on the magnetic cliché holders that can be found on most buffer machines.

The photosensitive surface comes covered with a protective foil, and the entire cliché is generally packed in a bag that protects the cliché from exposure to UV rays. The packaging and protective foil should not be removed until you are ready to expose, and then they should be removed in special light conditions, which means that the lighting is filtered so that there is no UV wavelength. You don't have to work in red light and darkroom conditions, but you do have to protect the clichés from the sun and the full range of wavelengths produced by standard fluorescent bulbs.

Price, durability, and image resolution can vary significantly from one type of polymer cliché to another. Some photopolymer clichés develop in water and some in alcohol. In general, water clichés last less than those developed in alcohol, so this article will focus on alcohol clichés. Even within one classification you will find numerous differences between the clichés on offer. The thickness of the base material and the adhesive layer and the type and thickness of the photopolymer may vary.

The thickness of the base material can be of great importance depending on the method used to mount the photopolymer cliches on the buffer machine base. Magnetic cliché holders provide the most consistent way to install, align and remove. Adhesive sprays, double-sided tapes, and screws are other methods for mounting clichés, but with these options, it's hard to get other clichés to fit in the same place if you're printing in two colors. Alignment can become a guessing game, and when tape or spray is used nicely, even a careful operator can bend the cliché while removing it from the stand on a rearrangement or cleaning.

In my experience, clichés with a precise base of clichés to match magnetic holders are the best choice, because they provide secure grip and because they promote quick alignment. If you use a machine with magnetic holders, the cliché material can be of any thickness. But on presses where the cliché is tied with tape or glue, you will need a thicker, heavier base to make sure that the cliché stays flat and does not slip out of position. Thicker, heavier bases are also recommended where clichés will be attached for printing with screws, which can deform clichés on a thin layer of the base when tightened.

The specific types of polymer materials used and the thickness of the material have the greatest impact on the durability and image resolution of the final cliché. Polymeric materials have different molecular structures. When these materials are exposed to UV radiation during exposure, the molecules join in chains through a process called polymerization. The length of the resulting chain determines how deep or hard the finished cliché is.

High-quality polymer materials can withstand more than 100,000 prints, with an image resolution that satisfies or exceeds corroded steel clichés. But lower quality materials can last only a few hundred to a few thousand prints and provide lower quality resolution. Generally speaking, higher quality and thicker material are better.

For example, if your supplier offers three variations of alcohol clichés, photopolymer basins can be 30, 40 and 50 microns thick, respectively. The 30 micron thinner cliché is typical for general purposes, requiring only one exposure before printing. Such a material has a high degree of exposure and produces a fairly consistent depth of etching.

Two thicker materials (40 and 50 microns) require two exposures: the first with a positive film drawing, and the second with a raster. This second exposition has several purposes. First, it controls the depth of the cliché etching. Second, it forms a dot pattern in the image that supports the paint stripping mechanism on both indoor and outdoor systems. In particular, the raster prevents the knife or ceramic dish from removing excess paint from larger areas of the image in the cliché. Third, the raster pattern helps prevent ink spills when the pad is in the position of taking an image from the surface of the cliché, which reduces the chances of the color being "squeezed" above the edges of the image on the cliché and destroying the print definition.

While clichés that are once exposed may be easier to prepare, they have limited use due to the fact that the engraved areas cannot be prevented from excessive peeling. In short, a once-exposed cliché works well for thin images, but not for bold text, images with a large open surface, or images with a combination of thin and bold areas.

Clichés that support double exposure are much more diverse. With different raster film lines, you can control not only the image resolution but also the depth of biting control. In most applications, 120 lines/cm with 90% points is recommended for use, but this number of lines can be changed up or down as it also changes the depth of etching - more lines, less etching.

What type of polymer is right for your application? In nine out of ten cases, you will use the highest quality materials that support the second raster exposure. The combination of high durability, good resolution, and controlled depth of etching makes high-quality clichés seem like a logical choice.

Exposition and making clichés

What do you need for proper production and display of photopolymer cliches? First, you need a UV illuminator. Most pad printing equipment manufacturers offer some type of display (developing) equipment. The cost of exposure is directly proportional to the size of the cliché you make. Here is a list of things to look for when shopping:

• Vacuum is a big plus because it provides good contact between the cliché and the film during the exhibition. Insufficient or uneven contact can lead to uneven biting depth, poor image resolution, or both.
• A light source with a UV wavelength of 350-400 nanometers (nm) is ideal. The closer the light output, which goes up to 350 nm, the better, since the material in photopolymer clichés is generally tuned to polymerize most efficiently and completely at this wavelength.
• Accurate timer is important. Having accurate, integrated timers that will ensure that your exposure is in line with the wavelength. If the digital timer is integrated, you can set it to provide a certain degree of exposure and automatically adjust the exposure time corresponding to the current lamp. This means you can leave the unit unattended during exposure.

Exposure instructions

If you supply your UV illuminator and clichés from the same people, they should give you explicit instructions for exposure and development. If not, you will need to determine the correct exposure yourself. Start by asking for both clichés and UV illuminator recommendations for their instruction. They should be able to give you at least a good idea of ​​where to start.

Depending on the specific cliché material and display equipment you use, your presentation may look like the following procedure:

• Remove the protective foil from the surface of the cliche. Check the surface for clichés and remove any visible surface or debris. Place the film in the positive (emulsion to be down towards the black side of the film) in the desired location. Rub gently due to the air bubbles that are located between the cliché and the film with the pad on the thumb.
• Place the cliches in the UV illuminator and turn on the vacuum. Make sure the drawing is good on the vacuum. The presentation lasts 4 minutes.
• (For clichés that are only exposed twice. Otherwise, go to step 4). Remove the positive film from the cliché and replace it with raster film as shown in Figure 4. The film should be placed on the cliché side where the emulsion is facing down. By including a vacuum, you make sure that there is a good drawing again. The presentation lasts 4 minutes.
• Remove the raster film and place in a development tray (container). Make sure there is enough fluid to completely cover the surface of the cliché. Using a very soft brush, gently shake the surface of the cliché (Figure 5). Do not scrub. Just use the weight of the brush and gently wipe over the surface of the cliché to remove the unlit material from the image area. Do this for 2 minutes.

Your container should be large enough to accommodate clichés so that there is enough space on the side, and it should have a lid to hide fumes to a minimum.

• Remove the clichés from the bowl. Wipe the surface gently with a soft cloth to remove excess liquid. Do not rinse with water.
• Place the clichés back in the UV illuminator (without using film or vacuum) and do the post-treatment for 20 minutes. The heat generated during the post process should be sufficient to dry the cliché. If very little heat is generated by your display equipment then place it in the oven at 120c or blow dry it.

When the cliché dries well, it is ready for use.