Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41N—PRINTING PLATES OR FOILS; MATERIALS FOR SURFACES USED IN PRINTING MACHINES FOR PRINTING, INKING, DAMPING, OR THE LIKE; PREPARING SUCH SURFACES FOR USE AND CONSERVING THEM
  • B41N3/00—Preparing for use and conserving printing surfaces
  • B41N3/03—Chemical or electrical pretreatment
  • B41N3/038—Treatment with a chromium compound, a silicon compound, a phophorus compound or a compound of a metal of group IVB; Hydrophilic coatings obtained by hydrolysis of organometallic compounds

Definitions

• This invention relates to lithographic printing plates, and more particularly to a desensitized metal plate and method of producing the same.
• a light-sensitive colloid such as bichromatized albumin
• this coating process being termed sensitizing.
• sensitizing When the sensitizer used is given an exposure through a transparency, it is differentially hardened, and by washing out the exposed plate with water and a desensitizing solution, the non-hardened portions of the sensitizer are washed away, but the lighthardened portions are unaffected thereby and cling to the metal surface to define the printing areas thereof.
• the plates so treated still exhibit a marked tendency toward scumming, probably due to the fact that such desensitizing procedures are mostly acid in nature; in fact, the scum is so tenacious at times as to require the plate to be remade. Also, when working with imaged zinc and aluminum plates, the art has experienced a major problem in the tendency for these plates to corrode during storage.
• Still a further object of this invention is to provide a novel method of treating lithographic printing plates prior to their being sensitized, said' method being characterized by a desensitizing treatment in which the solution used is alkaline in nature in contradistinction to the acidified desensitizing solutions heretofore employed in the art.
• Yet a further object of the present invention is to provide a new and improved pitted and grained zinc or aluminum foil for use in lithographic printing methods.
• Still a further object of the invention is to provide a plate that exhibits substantially no tendency to corrode during prolonged periods of storage.
• the plate of the present invention is characterized, broadly speaking, by a tough, extremely tenacious and difiicult-to-remove, insoluble silicate film immediately overlying and in contact with the pitted and grained surface of zinc and aluminum plates or foils.
• a plate having the type of surface mentioned is simply dipped in, or wiped with, a solution similar to those hereinafter to be disclosed, rinsed in water and allowed to dry. The solution can be applied hot or cold.
• the plate is then ready for a coating of sensitizer, no deoxidizing treatment being required, and following exposure, the non-hardened sensitizer is readily and completely removed with a simple water treatment. Plates so treated exhibit no tendency to scum, due to the completely effective removal of the unhardened albumin or equivalent sensitizer, and observations during printing runs have shown that toning tendency is substantially reduced.
• the practice of the present invention can be used with both zinc and aluminum plates with equally good results, and it is not limited by the specific manner of pitting and graining the metal surface; While I prefer to use albumin as the sensitizer, experimentation has shown that the type of sensitizer used makes no difference asfar as prevention of scumming and toning is concerned.
• the plate of the present invention is equally capable of producing similar results with light-sensitized gela tine, fish glue, and the like.
• Sensitizers as a class are well known in the art, and since the present invention is not confined to any particular one, no further explanation in this respect is deemed necessary, other than to add that they are generally recognized as light-sensitizable hydrophilic colloids. It is also to be understood that the foregoing examples are illustrative only, viscosity, proportions and equivalents being adjusted and selected for the particular need and balance as desired.
• the film on the surface of the plate is the result of'the metal in the plate combining with the soluble, alkali silicate to form an insoluble silicate.
• the film is something more than a mere silica coating, for it is water insoluble,
• the present invention provides a plate that is pre-desensitized in nature, requiring no deoxidizing and-only a simple water treatment for removal of the unexposed sensitizer, and one which undergoes no corrosion-during storage.
• the presenceof the silicate film displacesthe need for. conventional desensitizing solutions, counter-etching; and deoxidizing procedures heretofore found necessary, and in addition provides a plate which does not scum.
• the plate' of. thepresent invention is characterized by a conventionalpitted and grained aluminum or zinc lithographic surface whichlsurface has tenaciously adherent thereto a thin film of silicate.
• a method for preparing lithographic printing plates selected from the group consisting of zinc and aluminum having a pitted and grained obverseside comprising, treating the entire area of such side of the plate with a water solution of an alkali silicate selected from the group consisting of sodium and potassium to establish on the plate a thin adherent and water-insoluble film which is the water-insoluble reaction. product of the metal in the plate and said alkali silicate, the amount of silicate in said solution being within the range of from 0.1% to 5% by weight, and then rinsing in water the plate thus treated and allowing the same to dry.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Printing Plates And Materials Therefor (AREA)

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Publications (1)

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Cited By (5)

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Citations (10)

• 0
  • NL NL79670D patent/NL79670C/xx active
  • US US2732796D patent/US2732796A/en not_active Expired - Lifetime
  • BE BE511084D patent/BE511084A/xx unknown
• 1952
  • 1952-03-28 GB GB7986/52A patent/GB709978A/en not_active Expired
  • 1952-04-16 FR FR1059954D patent/FR1059954A/fr not_active Expired
  • 1952-05-06 CH CH305436D patent/CH305436A/fr unknown

Patent Citations (10)

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