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Computer-To-Screen & Film Technologies for Screen Printing

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Computer-To-Screen & Film Technologies for Screen Printing MANAGEM ENT Computer-to-Screen & Film Technolo- gies for Screen Printing Research and development in new technologies is growing as screen printing continues to compete with alternative imaging technologies. There are several technology choices Higher D-max measurements indicate Another important metric to consider for generating film positives or imaging greater opacity to light. So, a D-max of when choosing a device is its resolution, stencils for screen printing, but choosing 4.50 has a greater ability to block light than usually expressed as dots per inch (dpi). New Products! New Pricing! which to use can be an overwhelming task. a D-max of 4.00. The minimum D-max This standard of measurement indicates the Presented here are the major technologies value recommended for screen printing addressable resolution of an output device When image quality matters, sign on to 3M ©3M 2007. AllRights Reserved©3M 2007. currently used, how they operate and purposes is 3.5 D. However, lower values or printer. It properly refers to the spots of Promotional Products. additional specifications. may provide suitable results for non-critical light or energy used by imagesetters and Research and development in new work or short production runs. If the D- digital-direct exposure systems; or dots Whether your need is for general sign, floor or window technologies is growing as screen printing max value falls below 3.0 D, light will of ink or toner used by an inkjet or laser continues to compete with alternative pass through and prematurely expose the printer, to output your text and graphics. graphic, banner, or bus, the 3M Promotional Products imaging technologies. As the technologies emulsion in areas that were not intended. So, a 600-dpi-by-600-dpi device is capable line has a quality solution at the right price. continue to advance and payback times Some technologies used to generate films, of imaging 600 dots horizontally and 600 become shorter, many screen printers are such as film imagesetters, can achieve a D- dots vertically in one square inch. The For more information, go to www.3Mgraphics.com. integrating some type of digital device to max of 6.0 D. (See Figure 1, page 14) ability to reproduce fine detail diminishes generate films and image screens. The D-min value tells us how well the as dpi values become smaller. Additionally film allows light to pass through the clear for many devices, imaging speeds fall Film Positives areas, and is dependent on the base film as resolution increases. The importance Before discussing film positives, there material, processing procedures and the of a focused inkjet dot or light spot is a are a few metrics and terms you should technology used. Acceptable D-min values considerable factor in producing a stencil be familiar with before shopping for a for screen printing are usually below .05 image with a crisp edge. This is especially solution. To allow for optimum exposure, D. Higher values will ultimately block light true with newer technologies that use light film positives must have enough density in clear areas of the film and may cause to image a screen. to block light in the image area that will premature stencil breakdown, pinholes A raster image processor (RIP) is be printed. However, they must be clear and other related problems associated another consideration when shopping for enough in non-image areas to allow light with underexposed stencils. The difference a technology solution. A RIP is a software to pass and fully expose the emulsion. between the D-min and D-max values application that is used to convert the The terms used for these metrics are is referred to as the dynamic range of information contained in called D-max and D-min, respectively, the positive. Good film positives have your image to the format and are obtained using a transmission high dynamic range values, with a low required by the optical or densitometer, which measures the amount number for transparency (D-min) and a print engine in a device. of light passing through the film. high number for opacity (D-max). Not all devices require ▲ By Johnny Shell, Vice President, Technical Services, SGIA ■ Visit SGIA at SGIA.org SGIA Journal Fourth Quarter 2007 13 j_vol11q4_final.indd 13 11/19/07 3:36:41 PM While advancements in digital technology seem to make film positives an antiquated choice, many screen printers still find comfort andvalue in using films. a RIP, and actually can print halftones to drum. The dry toner is fused to the paper some degree. However, if you regularly as it passes through a pair of heated rollers, print halftone or fine-detailed images, a essentially melting the toner powder and RIP is almost a must. They provide the fusing it to the media. Heat can change the necessary features and controls in order to physical dimension of the material being achieve optimum results. printed, which can be a problem for tight registration on multi-color work. Polyester Film Positive Technology Choices films impart better dimensional stability Film positives are a popular, economical but also cost slightly more. and proven choice for the screen printer In order to print halftones with a laser that offers the largest equipment range printer, you’ll need a RIP or a PostScript — from economical to high-end. While driver supplied by the manufacturer. The advancements in digital technology seem to PostScript driver will simulate the halftone Figure 1: As litho continues converting make film positives an antiquated choice, settings from your graphics application. to Computer to Plate (CtP), look for imagesetter availability to increase making them an attractive many screen printers still find comfort and However, if you have stringent requirements option for many screen printers requiring the finest value in using films. Printer prices have for halftone work this may not be the best fallen to a level that is both economical approach. and inviting. However, consumable costs Laser printers have a maximum for film, ink, toner, necessary chemicals and resolution of 2400 dpi and can produce RIP software are factors when considering a standard page size in a very short time. film as a choice. (See Figure 3) Laser system advantages The first masking film introduced to the include its relatively inexpensive costs for graphic arts industry was called Rubylith® consumables (vellum and toner) compared and invented by Ulano Corp. Masking with alternative choices, and the fact that film is a knife-cut film (usually red or no chemicals are required to produce the yellow) that is coated onto a clear, polyester film. Unfortunately, they produce a D-max backing material. It can be hand-cut but is value of roughly 3.5 D, which is considered now more commonly cut by a computer by some as inadequate for proper stencil Figure 2: The Xante Screen-Writer 4 plotter device. While hand-cut stencils were making. is a popular choice among laser printers. replaced with digital pre-press, computer Often, if there is heavy coverage, regions plotters can still quickly and easily cut text of the page can be “starved” of toner, and solid color areas. rendering them lighter than they should Unfortunately, masking films do not be. This can be improved by using aerosol allow for the reproduction of fine halftones, sprays — available from many screen and the additional cost to remove the excess suppliers — that enhance the quality of material (weeding) can be labor intensive, toner-generated positives by moderately time consuming and costly. Masking films increasing the density. Another drawback cost about $2.40 per square meter (24 to laser is the relatively high D-min values cents per square foot), making them the (>1.0 D) caused by the foggy nature of the most economical choice among the family film material in non-image areas. of films. Cutting can be done with a plotter A new laser printer can be purchased device, which is commonly used for cutting for $2,000 to $4,000, but used printers Figure 3: A close-up of a 65 lpi, 50% dot imaged with a PostScript laser printer. vinyl letters in the sign industry. These can be found for much less. If you print are also economical devices with prices halftone images, be sure the printer is for a 66-cm (26-inch) wide plotter at PostScript compatible. Laser printers do approximately $2,600. offer a solution if your customers are Laser printers are an entry-level, more concerned with price than superb economical choice for generating film prints. However, if you intend to print positives. Current models allow for up photorealistic or fine-halftone images to 33-cm-by-89-cm (13-inch-by-35-inch) greater than 85 lines per inch (lpi), laser output onto paper vellum or polyester printing often won’t provide the necessary film. (See Figure 2) A laser printer uses detail, registration accuracy or film static electricity to generate a printed characteristics. image. It effectively writes the image to a Inkjet printing’s popularity has soared photoconductive drum by neutralizing the as a choice to generate film positives. It is Figure 4: A close-up of a 65 lpi, 50% dot static charge in certain areas. Dry toner an attractive technology choice because printed with an Epson 4800 inkjet printer. then sticks to the charged areas of the of its low start-up costs, lack of chemical 14 SGIA Journal ■ Fourth Quarter 2007 Visit SGIA at SGIA.org j_vol11q4_final.indd 14 11/19/07 3:36:43 PM processing and user-friendly software. known for their extreme quality and Inkjet printing provides acceptable acutance, which are unmatched compared resolution for the garment decorator or with other discussed technologies.
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