Metal treatment – Process of modifying or maintaining internal physical... – With casting or solidifying from melt
Patent
1991-01-07
1993-02-16
Dean, R.
Metal treatment
Process of modifying or maintaining internal physical...
With casting or solidifying from melt
148691, 148692, 148439, 148440, 430302, 205214, 205325, C22F 104
Patent
active
051867672
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a method for making an aluminum lithographic plate which is more commonly identified as lithoplate. More particularly, it relates to an improvement in the method of making a workpiece from which an improved lithoplate is made.
Lithography is defined as the process of printing from a plane surface such as a stone or metal plate on which the image to be printed is ink-receptive and the blank area ink-repellant. .The stone or metal plate is referred to as lithoplate, but for purposes of discussing this invention and its background, lithoplate will always refer to metal, or more particularly, an aluminum alloy.
The ink-receptive and ink-repellant areas on lithoplate are developed by subjecting the plate to contact with water in the printing press The image area is hydrophobic or water-repellant, and the non-image area is hydrophilic or water-retentive. The inks used for printing are such that they will not stick or adhere to wet surfaces and, thus, when the lithoplate is contacted with an ink-laden roller, ink is transferred only to the image area.
It is evident that the quality or suitability of a lithoplate for printing is directly related to the hydrophobic and hydrophilic characteristics of the image and non-image areas. It has long been known that uniform roughening of the surface by a process known as graining is advantageous in developing both the hydrophobic and hydrophilic areas. To make the image area, a lithoplate workpiece is coated with a hydrophobic light-sensitive material. This material also is resistant to attack or dissolution from acids until it is exposed to light and is commonly called a resist. After the workpiece has been coated with the resist, a negative having the desired image thereon is overlaid on the resist-coated workpiece and exposed to light. In the non-image area, the light causes a reaction in the resist which makes it soluble in acid and, thus, after exposure to light, the plate is contacted with acid to remove the resist in the non-image area. Hydrophobic resist material remains, therefore, only in the image area, and the underlying grained metal surface is advantageous in bonding the resist to it. In the non-image area, with the resist removed, the grained surface is advantageous in enhancing the water retention character of the surface.
Originally, graining of the workpiece was accomplished mechanically by ball graining or brushing. In ball graining, a slurry of steel balls and abrasive material is agitated on the workpiece with the extent of roughening controlled by such things as the type of abrasive, number of balls, speed of agitation, etc. In brush graining, brushes are rotated or oscillated over the surface covered with an abrasive slurry. Mechanical graining usually requires cleaning the plate to make it suitable for further processing. Typically, cleaning is accomplished by immersion in a commercial caustic type solution. It is evident that uniformity and quality of the roughened surface is difficult to control with such methods. In addition, mechanical graining may be relatively slow and costly.
Because of difficulties in mechanical graining, the constant growth of lithographic printing, higher operating speeds of modern printing presses, need for longer lithoplate life, etc., increasing attention has been given to chemical and electrochemical methods of graining. By these methods, the grain is produced by a controlled etching of the surface by the use of chemicals alone or the combination of passing current through a chemical solution. U.S. Pat. Nos. 4,301,229, 4,377,447 and 4,600,482 are cited as examples of many that are directed to electrochemically graining. Whether mechanically grained or electrochemically grained, lithoplate workpieces have certain requirements in common. Lithoplate is used in light gauges, such as 0.008 or 0.012 inch, for example, and by the nature of its use, it must be relatively flat. The surface should be free of imperfections such as deep gouges, scratches and marks which would i
REFERENCES:
patent: 3266900 (1966-08-01), Zelley
patent: 4168167 (1979-09-01), Takenaka et al.
patent: 4377447 (1983-03-01), Bednarz
patent: 4818300 (1989-04-01), Rooy et al.
patent: 5028276 (1991-07-01), Byrne et al.
Granger Douglas A.
Petrey Gerald R.
Reravis, Jr. H. Gray
Richter Raymond T.
Rooy Elwin L.
Aluminum Company of America
Dean R.
Koehler Robert R.
Mueller Douglas P.
LandOfFree
Lithoplate and method for making same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Lithoplate and method for making same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Lithoplate and method for making same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2145775