1. Paper Grain

Paper traveling through a digital press may be turned in different directions and started and stopped at various intervals. These unusual movements through the press can cause paper jams and registration problems if the incorrect paper is used. The direction of the paper grain is critical to help ensure smooth operation. The grain of the paper also affects some finishing processes, so it must be a consideration for the entire production process.

2. Toner Adhesion

The temperature and moisture content of the paper are critical for the paper to receive the correct electrostatic charge during the digital printing process, which will ensure proper image transfer and toner adhesion. Many digital printing companies have special areas containing the optimum temperature and humidity for both the warehousing of digital paper and for production of the print applications. Any paper used in digital presses, printers, and copiers must be properly acclimated to provide the best results.

3. High Heat During Print Production

Digital papers must be able to withstand the high heat created during the process of image fusion. Many digital printing systems use electrophotographic processes and dry toners, which use heat to fuse toner to the substrate. Some papers may not be able to withstand the high temperature required. The faster a digital press operates, the more heat is generated. This can cause paper jams, curling, and the paper may lose some of its quality, so choosing the correct paper designed specifically for digital printing equipment is very important.

• Besides toner based printing, ink-jet technology is used with many types of digital printing equipment. The resulting print has more gloss than dry toners so using a glossier paper would not be as distracting. Uncoated paper also works well with ink-jet presses.
  
  
• Direct imaging presses have different requirements than fully digital presses. Most of the direct imaging presses utilize waterless offset printing technology. Although the presses run conventional offset stocks, problems can arise with paper fibers adhering to the image carrier (picking) because of the waterless technology. Fibers can then be transferred to the printed areas, producing poor quality. Paper manufacturers are constantly developing paper stocks that are stronger and cleaner to help eliminate the picking problem that can occur with waterless technology. The illustration below shows the results of a digital application printed with substandard paper stock using waterless plates.

• Paper whiteness should always be a consideration for digitally printed applications and the whiteness should be appropriate for the colors of the graphics and images of the particular print project. True white paper varieties are often used for applications containing a high proportion of graphics and images. Blue white varieties are used for this purpose also, but the overall appearance of the printed document often appears cooler. Cream white papers, which provide a slightly yellow tone, are popular for digital book publishing.
  
  
• You may decide that a test run or proof may be the best way to determine if the paper that is to be used is the best choice for the application. Your application may require high contrast between the glossiness of the print and the glossiness of the paper or special effects may be required that can only be accomplished with the use of certain types of stock. An advantage with digital equipment is that a proof or small test run is much less expensive than with traditional equipment. There is very little make-ready involved with digital equipment and the cost per sheet is the same regardless of the quantity, so testing various paper samples for your print project is an easy task. If your application has never been printed with digital equipment, it is probably a good idea to ask for a proof or test run before going ahead with the job, and in many cases, your print provider may require it.
  
  
• Choosing paper is a subjective process so there are no absolute rules when selecting paper or any other type of substrate for your project; however it isn't wise to assume that a paper that has been used for an application printed with conventional equipment will automatically be suitable for digital printing. Make sure you choose a paper that has been tested and approved for digital printing; otherwise you may encounter poor results. Your print provider will be able to recommended paper stocks and other substrates that will help make the selection process easier.