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Lithographic Troubles

( Originally Published 1963 )[an error occurred while processing this directive]

Greasing or scumming. This condition occurs when the nonprinting area begins printing to a greater or lesser degree. Ink specks, streaks, or a general dirtiness may appear in the background areas of the print. Often a thickening of the printed characters or a filling of halftones takes place. This results in uneven quality of line work and poor detail in halftone areas. There are a number of causes for this situation which have nothing to do with the ink. For example, in a poorly made plate, the nonprinting area may not have been properly desensitized. The dampening rollers may be dirty. They may not be carrying the fountain solution properly and evenly to the plate. The fountain solution may be too weak or too strong. A weak solution may not be strong enough to maintain a proper desensitized condition in the nonprinting area. A fountain solution which is too strong may attack the metal in the nonprinting area and prevent proper maintenance of desensitized areas which will eventually lead to scum on filled-in halftones. The amount of fountain solution and ink carried to the plate by the respective rollers must be properly balanced. If the ink is too greasy, a fountain solution of excessive strength may be necessary to keep the ink from transferring to the nonprinting area. On the other hand, if the ink is not sufficiently water hydrophobic, it may take up too much fountain solution and become waterlogged or emulsify and transfer to the nonprinted area.

Tinting. This is a much more uniform discoloration of the non-printed area than a condition of scum. It is quite definitely an ink and fountain solution condition. This indicates, of course, that the offending pigment is too water soluble. It may also be due to an actual transfer of pigment from an oil-soluble material to a water-soluble material. The color then is transferred to the nonprinting area by the fountain solution. Fresh ink is more likely to tint than aged ink. As ink ages, the pigment particles become wetted with the vehicle more thoroughly and are therefore protected from water penetration.

Stripping. This condition occurs if portions of ink rollers do not transfer ink from the ink fountain or other inking rollers. Metal rollers are usually affected more than composition rollers. The cause is usually a condition which permits the fountain solution to preferentially wet the rollers and displace the ink. This may be due to an excessive amount of fountain solution or to the inability of the ink to properly emulsify the fountain solution carried to the inking system. The difficulty is most easily remedied by decreasing the amount of fountain solution or by the addition of materials such as Lakatine which have good emulsifying properties to the ink. Replacing the steel rollers with copper or copperplated rollers also is a good remedy for stripping.

Printing too sharp. During production the image area may become progressively weak. This image condition is considered as printing too sharp. An ink with too high a tack may be the cause and if the condition continues, the image may be lost entirely. A pH value of the solution which is too low may tend to etch the printing image from the plate. This causes the image to be more water receptive and more ink repellent. The remedies are (1) to reduce the tack of the ink by the addition of a less viscous varnish and (2) to reduce the attack of the fountain solution on the printing area by changing the pH value to a less acid condition.

Piling. The pigment-carrying properties of the vehicle may be destroyed by the fountain solution which becomes emulsified with the ink. This destruction of the original flow and pigment-carrying properties of the ink makes the ink short and pasty in the fountain and gives it a dead look on the rollers, leading to poor distribution and piling. The cause may be the use of poor protective vehicles or by the use of pigments which are not sufficiently hydrophobic and require greater protection from the fountain solution. Improper balance between the volume of ink fed to the image and fountain solution fed to the plate will often cause piling.

Drying. Drying problems sometimes are aggravated with litho-graphic inks because of the fountain solution. It is well known that papers which contain a high percentage of moisture, or which have a low pH, interfere with proper drying. The use of too much fountain solution, particularly a highly acid one, also interferes with proper drying. From the discussion above, lithographic printing requires a high degree of craftsmanship. Great care must be taken to see that the press, plates, rollers, ink, and fountain solution are clean and in correct condition for production. Care must be taken to see that ink and fountain solutions are checked frequently to be certain that correct pH values are maintained. The pressman must be aware at all times as to the exact condition of inking and dampening systems as well as the mechanical systems of feeding, printing, and delivery of printed work. The high-quality work of which this method of printing is capable cannot otherwise be realized.



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