Coating processes – Nonuniform coating – Deforming the base or coating or removing a portion of the...
Reexamination Certificate
2000-10-03
2002-02-26
Bareford, Katherine A. (Department: 1762)
Coating processes
Nonuniform coating
Deforming the base or coating or removing a portion of the...
C427S425000, C118S321000, C101S401100, C430S307000
Reexamination Certificate
active
06350490
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of manufacturing a rotogravure printing medium and more particularly, to a method of applying a plastic printing medium to a printing roll or cylinder which is employed in rotogravure printing.
The present invention is related to commonly assigned U.S. patent application Ser. No. 514,595, filed Apr. 26, 1990, abandoned, and to commonly assigned, co-pending U.S. patent application Ser. No. 691,693 filed Apr. 24, 1991, abandoned, both of which are incorporated by reference hereinto. The subject matter of these applications later matured into U.S. Pat. No. 5,694,852 which is based on a continuation in part application of Ser. No. 08/525,880 filed Sep. 8, 1995, abandoned, which is a continuation in part of Ser. No. 991,499 filed Dec. 17, 1992, abandoned, which is a continuation of Ser. No. 691,693 noted above.
Rotogravure printing is a generally conventional method of printing on a sheet, web, or other substrate. The substrate may be a coated, uncoated, or metallized paper; glassine; plastic films and sheets made from vinyl, cellulose, acetate, polyester and polyethylene; plastic shrink films; paperboard; aluminum foil; fabrics; and similar materials. Rotogravure printing is capable of reproducing both subtle shades of color and black and white, and is particularly well suited for printing great numbers of copies precisely and rapidly. Typical end products for the printed substrates include labels, cartons, paper and plastic cups, trading stamps, wrapping paper, and sheet vinyl flooring.
Rotogravure printing is the only commercial printing process which can control both ink thickness and the area of ink coverage. This is achieved by etching or engraving recessed microscopic wells, frequently referred to as “cells,” of varying depth and area in a printing medium or image carrier surface. In controlling the size and depth of the cells, the amount of ink available for placement on the substrate is controlled to generate an image composed of an arrangement of large and small dots. Other types of printing, such as flexographic printing, are generally similar to rotogravure printing, but are specifically different, e.g., as to thickness of the printing medium and the character and formation of ink-transferring surfaces.
In typical rotogravure printing, the printing medium or image carrier is a copper film electro-deposited from a chemical bath on a specially prepared steel cylinder. Prior to the engraving of the recessed wells, the copper is mechanically ground and polished. After engraving, the cylinder requires the addition of plated, hard chromium for durability and wear resistance. During the printing process the cylinder is rotated in a bath of ink. Excess ink is wiped away by a doctor blade and the ink remaining in the engraved cells is then transferred to a substrate as discrete dots, while the substrate passes between the engraved, inked cylinder and a soft pressure roller. Rotogravure printing using non-copper printing media is similarly effected.
The recommended modem process to prepare a copper image carrier requires the use of electrolytic deposition from an acid/copper bath. A steel cylinder of the required diameter is partly immersed in a chemical copper solution and rotated at a regulated speed. An electrical current running through the cylinder and the solution gradually deposits a coating of copper on the rotating cylinder until the approximate required thickness is achieved. The copper plated cylinder is washed and then polished to final dimensions with a smooth, mirror-like surface finish.
The copper coating is then engraved, either chemically or electronically. In the chemical engraving process, cells are formed by acid etching of the copper coating. The cells are formed by a screen which prevents the acid from reaching selected portions of the copper surface. The resulting acid-etched wells are round in shape and slightly smaller at the bottom than at the top.
The process of forming the copper coating for the printing cylinder and of chemically engraving the copper coating may result in the formation of waste products which are environmentally hazardous, requiring costly disposal. Further, the prior art techniques are costly and time-consuming.
An object of the present invention is a method of manufacturing a rotogravure printing medium which is inexpensive and expedient to produce and which avoids other shortcomings attending the use of copper (or other metallic) printing media.
SUMMARY OF THE INVENTION
In accordance with an aspect of the present invention, there is provided a method of manufacturing a printing medium for application to a printing apparatus (e.g., a rotogravure printing drum or cylinder). The terms “printing” and “rotogravure printing”, as used herein, include any apparatus, device or method which involves the transfer of an inked image. The printing medium comprises a plastic composition which may be applied to a flat plate or a cylinder to form a plastic-coated printing plate, roll or cylinder, the plastic coating being etched, engraved or otherwise selectively removed to form the printing cells.
The plastic composition is any flowable, self-levelling, curable material capable of being deposited on a flat surface or on a printing cylinder or roll according to the method hereof to form a continuous coating, following curing of which, the composition may be etched, engraved or otherwise selectively removed to produce a printing surface. Preferred plastic compositions are those self-levelling, flowable materials set forth in the commonly assigned '595 and '693 applications.
The plastic composition may be applied to the printing substrate by various means well known in the art. The method of the present invention is particularly applicable to the application of the plastic composition in a flowable form to a printing roll or cylinder which is employed in a rotogravure printing process. The printing roll or cylinder may be made of a metal, such as aluminum, or steel, and may, contrary to the prior art, also be made of a non-metal, such as a plastic.
Prior to the application of the plastic composition to the printing roll or cylinder, the printing roll or cylinder may be pretreated by means of a plasma or corona pretreatment to clean and/or alter the surface (i.e., lower the surface tension) of the cylinder or roll for improved film or coating wetting and bonding strength.
When a corona pretreatment of the surface of the printing roll or cylinder is employed, the surface thereof may be treated with an accurately-directed electrical bombardment of the surface to clean and/or alter the surface of the printing roll or cylinder.
When an aluminum printing cylinder is employed, the surface may be pretreated so as to provide an anodized surface. When a steel cylinder is employed, the cylinder may be treated with an oxide such as black oxide.
Methods of applying the plastic composition include spraying the composition onto the surface of the printing substrate such as the printing roll or cylinder. Such spraying may be accomplished through the use of a nozzle through techniques known in the art. Other methods which may be employed include dip coating, spin coating, and ring coating. The coating, upon application by any method to the surface of the printing substrate intended for use in rotogravure printing, preferably has a thickness of from about 0.003″ to about 0.015″. Where the printing substrate is to be used for other types of printing, such as flexographic printing, thickness up to about 0.040″ or more.
The preferred method of applying a selected plastic composition to the printing roll or cylinder is that described in detail below. Any of the compositions disclosed in the above-noted '693 application, as well as other curable, flowable, self-levelling plastic compositions may be applied to the printing roll or cylinder. Included are compositions in which printing images are “developed” following selective exposure to light or other radiation.
The selected pl
Bressler David E.
Caligaro Daniel
Chesnut W. Richard
Bain John N.
Bareford Katherine A.
Carella Byrne Bain Gilfillan Cecchi et al
Squire William
W. R. Chesnut Engineering, Inc.
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