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NSPS Attendance policy. NSPS Fundraising policy. Forms Our school zone Our school zone is available on findmyschool. Information book for Foundation Information book for Almost all rotogravure printing is done on webbed substrate.
Rotogravure presses have printing stations that are connected in-line with each other. As with in-line flexographic printing, each rotogravure station has its own impression cylinder. Although only four printing stations are required to print each side of the web, publication rotogravure presses in the United States can have up to 16 stations.
As with flexographic packaging processes, publication and product rotogravure are typically a relatively small part of the overall manufacturing process. Letterpress printing is one of the oldest forms of printing.
In its most basic form, it involves pressing inked blocks onto paper. Raised images and type, on blocks of metal, wood, or linoleum, are locked in place and covered with ink by a roller also called a dauber. The ink-covered blocks are then pressed onto paper, producing the printed images and type. Since the images and type that are covered with ink are raised, letterpress printing is a form of relief printing. Screen printing involves using a squeegee to force ink or dye through a porous screen mesh.
An image is formed because the stencil, which is added to the screen, blocks out certain areas on the mesh. Screen printing of textiles may be performed with either flat-bed or rotary screen presses. Flat bed screen presses are used to print on garments or fabric pieces. Flat bed presses may be either manual or automatic automatic movement from one color station to the next.
Automatic presses also typically have automatic operation of both the squeegee and flood bar which redistributes ink on the screen, after the squeegee has been used. Rotary screen presses use metal cylindrical screens to print on rolls of fabric. Coating thicknesses in screen printing are typically much thicker than in other forms of printing. In screen printing coating thicknesses range from microns, whereas coating thicknesses in other forms of printing range from 1 micron offset lithography to 6 microns ultraviolet flexography.
These steps include, but are not limited to, cutting, folding, trimming, die cutting, embossing, foil stamping, drilling, saddle stitching, sewing, perfect binding, vacuum forming, and gluing. The gluing steps range from the application of a hot melt adhesive to the back of a book or magazine, to laying of a laminate to the printed substrate. Adhesives used fall into three broad categories: hot melts, water-based, and solvent-based.
Most hot melt and water-based adhesives have little or no VOC content. Emissions from printing operations result primarily from evaporation of organic solvents contained in the inks. Most of the solvent contained in the ink evaporates during the process, although some solvent may remain with the printed product leaving the facility.
Some inks may be water-based and do not produce emissions. In general, the emissions points from a printing line operation include the: 1 ink fountain, 2 the press, 3 the drier, and 4 the chill rolls [actual emissions points vary by the type of printing operation].
Typically, a large fraction of the emissions are associated with exhausts from ink in the drying units drier. Driers typically use natural gas or electricity to heat air.
The warmed air passes over the substrate in the drier, causing the volatile compounds in the ink on the substrate to evaporate. The drier exhaust air containing the volatilized solvents is contained in a duct and the air stream is vented to the atmosphere; the air stream may be directed to an air pollution control device APCD prior to venting to the atmosphere. Emissions that are not collected and routed to a duct or stack are called fugitive emissions. Fugitive emissions can come from several sources in a printing operation, such as ink feeding systems and the chill rolls.
Vapor capture systems e. The printing equipment may include vapor capture systems as part of the design and operation of the equipment. Other sources of fugitive emissions include ancillary operations such as press washing cleaning and ink mixing operations. Air emissions from imaging include potential volatile components in the developer e.
Adhesives used in finishing operations such as laminating also may contain VOC and HAP and are a potential source of emissions. Printing industry pollution is predominantly released into the air. In , the printing industry released 99 percent of its total Toxic Release Inventory TRI poundage to the air, while the remaining one percent of releases were split between water and land disposal. The four top toxic chemicals released, toluene, methyl ethyl ketone, xylene, and 1,1,1-trichloroethane, are all solvents of high volatility.
Toluene is used heavily in the gravure printing process as an ink solvent, but is also used throughout printing for cleaning purposes.
For a more detailed and specific discussion of emissions points from the different printing operations refer to one of the following documents:. The following two general approaches to emissions control are used in the industry: 1 compliant inks and coatings, and 2 capture and control systems. A combination of these techniques is also sometimes used. The use of compliant coatings involves employing inks and coatings formulated to contain no or low concentrations of pollutants VOC or HAP ; pollution is prevented at the source.
Capture and control involves capturing the emissions from the source and directing the emissions to an add-on control system air pollution control device. Below are several links to detailed information on air pollution control technologies typically used in printing operations. Specific control technologies may be used in certain types of printing, but not others. The following paragraphs briefly discuss control technologies and pollution prevention techniques applicable to various sectors of the printing industry.
Control system options for driers in heatset web lithographic printing include thermal oxidizers, catalytic oxidizers, condenser filters with activated carbon and condenser filters without activated carbon.
Fountain solutions for lithography are typically refrigerated to reduce volatilization during the printing process. In flexography, emissions are most commonly controlled with catalytic oxidation or thermal oxidation. In some cases, add-on air pollution control devices can be avoided completely by using compliant coatings, i.
Large publication rotogravure plants typically use carbon adsorption. These presses use a single water-immiscible solvent toluene or a simple mixture toluene-xylene-naptha that can be recovered in approximately the proportions used in the ink.
Recovery is typically performed by flushing with steam, and then subsequently condensing and separating the condensed water from the solvents. At present, only solvent-borne inks are used on a large scale for publication rotogravure printing.
Waterborne inks are still in research and development phases, but some are now being used in limited cases. Some smaller rotogravure operations, such as those that print and coat packaging materials, use complex solvent mixtures in which many of the solvents are water soluble.
Thermal or catalytic oxidation is usually the most feasible control for such operations. In addition to thermal and catalytic oxidizers, pebble bed oxidizers are also available. Pebble bed oxidizers combine the functions of a heat exchanger and a combustion device and can achieve a heat recovery efficiency of 85 percent.
Letterpress publication printing uses a variety of papers and inks that lead to emissions control problems. Losses can be reduced by thermal or catalytic oxidation, either of which may be coupled with heat recovery.
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