PLATE MAKING 

The creation of intermediate image carriers is usually the next step in the printing process.  The image is transferred to some type of ?plate? that will be used in the actual printing process.

For Lithographic Printing

Lithographic plates have ink receptive areas for the image and water receptive non-image areas. 

• Replace plate making processes that involve metal etching or electroplating with those that do not.  This will help to minimize concerns about treating dissolved metals in wastewaters. 

• Use waste reduction procedures for metal fabrication, including any metal etching or electroplating processes.  Contact the Pollution Prevention Program for more information. 

• Photomechanical surface plates are currently the most common image carrier and continuing to grow in use.  These are made from a thin aluminum plate that has been coated with a photoreactive material.  Common plate coatings are diazo compounds or photopolymer resins. 

• Electrostatic plates are non-metallic plates (usually paper) that are coated with a photoconductor that is ionized by an electrophotographic camera.  The charged paper is exposed to light reflected from the image.  Areas exposed to reflected light dissipate their charge.  A liquid toner is then applied to the plate and is attracted to the areas that are still charged. This forms the image on the plate.  This toner now will attract  ink and the rest of the paper will attract water.  The process is very similar to what occurs inside a photocopier.

For Screen Printing

Porous mesh screens are coated to prevent the passage of ink through non-image areas, but still allow ink to pass freely through image areas. 

• Evaluate the use of mechanical methods for attaching screens to a frame, instead of adhesives. 

• Evaluate the use of water based adhesives, instead of solvent  based ones, for attaching the screens to a frame.  These adhesives allow clean-up with water before they set. 

• Use the appropriate screen size in relation to the image tominimize the use of screen block out. 

• New coatings based on diazo compounds and photopolymeric resins are available to replace bichromated coatings.  These avoid toxicity problems associated with the use of chrome and its disposal.

MAKE-READY/PRINTING

The principle wastes generated during the make-ready/printing stages are losses due to rejects during set-up and alignment of equipment.  These rejects result in wasted time, inks, and especially paper.  Below are some suggestions to help reduce these wastes.  Investments in equipment upgrades would have to be evaluated against the potential cost and time savings.

For Lithographic Printing 

• Automated plate benders can minimize problems such asplate cracking, non-straight plate bending, curvature mismatches, etc.

• Automated plate scanners for determining the relative density of the image across the plates surface can be useful in setting the ink fountain keys. 

• Automated ink key setting systems can improve print quality and reduce the number of rejects.  These systems use information from plate scanners and ink density sensors to automatically adjust the ink profile for each ink slide position. 

• Sensors that measure the ratio of ink-to-water can be used to ensure that the proper ratio is maintained.  Adjustments can then be made manually or automatically. 

• Automated registration systems that match registration marks and adjust accordingly can help to reduce waste. 

• The use of a standard ink sequence for jobs can help to reduce waste ink and solvents generated from the cleaning of fountains 
  prior to a change in the ink sequence. 

• For web printers, the use of web break detection devices that automatically shut down the system can minimize damage to equipment and also reduce waste. 

• The use of an automated system for maintaining the optimum level of ink in the fountain can help to ensure consistent product quality throughout a run. 

• Alternative fountain solutions that contain little or no VOCs are available.  These contain substitutes such as surfactants, glycols, and glycol ethers in place of isopropyl alcohol.  Adjustments will have to be made for the new wetting characteristics, but they have been used quite successfully. 

• Collect and recycle any wasted paper. 

For Screen Printing

Screen printers can use many of the principles described above for lithographic printing.  This includes the use of sensors and automation for ensuring proper alignment, registration, and ensuring proper ink density, the use of standard ink sequences, etc.

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