US2841083A - Method of making cylindrically curved printing plates - Google Patents

Description

July 1, 1958 KIRKPATRICK ETAL 2,341,083

METHOD OF MAK YLINDRICALLY CURVED PRINTING PLATES F1196 Aug- 2, 1954 2 Sheets-Sheet 1 FIG.4.

JAMES $.KIRKPATRICK BY PETER ZYLSTRA JR. M.

A? ATTORNEYS United States Patent METHOD OF MAKING CYLINDRICALLY CURVED PRINTING PLATES James 'S. Kirkpatrick, Detroit, and Peter Zylstra, Jl'., Plymouth, Mich., assignors to Brooks & Perkins, Inc., Detroit, Mich., a corporation of Delaware Application August 2, 1954, Serial No. 447,142 13 Claims. (Cl. 101-4011 The present invention relates to a method of making cylindrically curved printing plates.

It is an object ,of the present invention to provide a method for forming printing plates of magnesium which comprises bending a fiat magnesium printing plate into cylindrical configuration with the printing surface on the convex side thereof by heating the plate to a temperature above 300 degrees Fahrenheit, compressing the plate with its printing side outermost against a cylindrical rigid forming member, covering the printing surface of the plate with a thin covering of aluminum, applying the forming pressure to the plate through a yieldable material, trapping the yieldable material against the printing surface of the plate, applying an essentially hydraulic pressure through the trapped yieldable material of an amount dependent on plate temperature, and finally removing the aluminum from the cylindrically curved magnesium printing plate by treatment in a caustic bath.

Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings, wherein:

Figure l is a perspective view of a cylindrically curved printing plate constructed in accordance with the present invention.

Figure 2 is afragmentary enlarged sectional view of a portion of the printing plate shown in Figure 1.

Figure 3 is a fragmentary sectional view of a portion of theprinting plate upon removal from the press showing the printing surface covered with a covering or coating of aluminum.

Figure 4 is a diagrammaticsectional view showing the printing plate in the forming press.

Figure 5 is a chart showing permissible temperature and pressure limits in forming the curved plate.

In accordance with the present invention printing plates formed of magnesium or an alloy composed mainly of magnesium are produced byconventional practices in the form of a flat plate. Thereafter, the flat plate 1is curved to a true cylindrical configuration with the printing surface of the plate exposed at the convex side thereof.

. Printing plates formed of magnesium offer many advantages over plates previously used in theprinting industry. One of the important advantages of magnesium printing plates is the extreme lightness of such plates as compared to materials previously employed. Modern high speed presses produce relatively large centrifugal forces which of course are dependent upon the weight of the printing plates. Obviously, the use of extremely light magnesium printing plates reduces the centrifugal forces and will accordingly permit faster press operation.

In order to successfully employ magnesium printing plates as disclosed above, it is essential that the plates in their final form have a substantially true cylindrical curvature extending from edge to edge thereof. Previous methods of bending flat plates to generally cylindrical configuration have in general proved unsatisfactory. It has been found however, that when flat magnesium printing plates are curved to cylindrical configuration against a rigid cylindrical forming member while heated to temperatures above 300' degrees Fahrenheit by the application of essentially hydraulic pressure dependent upon plate temprinting surface.

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perature, but preferably of at least 1000 pounds per square inch, magnesium plates retain the exact cylindrical curvature imparted thereto without spring back and accordingly, such plates may be used in their entirety in rotary presses.

It has been found that the magnesium printing plates may be curved from their initial flat shape to the true cylindrical configuration required throughout a substantial range of pressures and temperatures. Figure 5 is a chart illustrating these ranges. It will be observed that the minimum temperature under which the fiat plates may be curved to cylindrical configuration is 300 degrees Fahrenheit since below this temperature the plates have a tendency to crack. The maximum temperature is shown as slightly in excess of 800 degrees since above this temperature the plate becomes so soft that the forming operation results in damage to the printing characters on the plate.

Within these temperature limits the necessary pressure to produce the permanent deformation of the plate to true cylindrical configuration without dimensional distortion or distortion of the printing characters may be varied substantially. Thus for example, at 300 degrees pressure between 3,000 and 18,000 pounds per square inch may be employed. .As the temperature increases the maximum pressure which may be applied to the plate falls off rather rapidly, approaching zero as the plate temperature exceeds 800 degrees Fahrenheit. 7 The actual pressure and temperature of course will normally depend upon equipment available and where means for providing extremely high pressures is not available, the operation will of course be carried out at higher temperatures.

It is pointed out that not only must the temperature and pressure be related as to minimum values, but also as to maximum values so as to prevent growth of the plate during the forming operation, with resultant lack of registration in the printing operation and also to avoid modification of the printing characters on the plate.

In practice, excellent results have been obtained when the plates have been formed at temperatures between 450 and 650 degrees Fahrenheit and at pressures in excess of 1,000 pounds per square inch.

.In order toapply the hydraulic pressure required to cause the plates to retain the shape imparted to them in the press, a yieldable substantially incompressible material such for example as a suitable rubber compound is trapped against the printing surface of the plate. Inasmuch as this rubber material is substantially incompressible the forces developed in the press are essentially hydraulic in character.

It has been found however, that the pressures required in this operation, in conjunction with the relatively high temperatures cause deterioration of the rubber with the result that particles of rubber become separated from the yieldable material and remain in concave portions of the Even when the rubber compound is new, relatively fine crevices or depressions in the printing surface have the rubber compound embedded therein after the pressing operation.

Accordingly, to make the operation as above described commercially practicable, it has been found that the trapping or adherence of particles of rubber to the printing surface of the plate may be avoided by providing a thin covering of aluminum between the printing surface and the rubber compound prior to the application of pressure through the yieldable material. The application of pressure of course causes the thin covering of aluminum to conform to the configuration of the printing surface and in some cases, particles of rubber may adhere or become trapped in concave elements of the aluminum covered surface. Following the pressing opperation however, the cylindrically curved magnesium printing plate is immersed in a caustic bath and the aluminum effectively removed thereby without affecting the magnesium.

In Figure 1 there is shown a cyliudrically curved printing plate having a convex cylindrical surface 12 provided with a printing surface, such surface being diagrammatically indicated at 14. i

In Figure 2 there is shown an enlarged section of the printing plate and the relatively raised and depressed portions 16 and 18 of the printing surface are indicated.

In Figure 4 there is illustrated a press useful in carrying out the method of the present invention.

The press includes a bed plate 20 on which is mounted a lower platen 22 which carries the cylindrically shaped forming block 24. The press includes a downwardly movable upper ram plate 26 having a convex rubber retainer 28 secured thereto provided with a downwardly open recess 30. Preferably, the recess is rectangular in shape for the purpose of applying pressure to a printing plate in a particular manner. Within the recess 30 is provided a plurality of rubber slabs indicated generally at 32. The slabs 32 are of a suitable rubber compound adapted to resist deterioration when subjected to the temperatures employed in the process.

In carrying out this operation a fiat printing plate 10 formed of magnesium and having its upper surface a printing surface and covered by thin aluminum is placed on the block 24. Thereafter, the upper ram plate 26 is lowered, bending the printing plate to conform to the upper cylindrically convex surface of the block 24. At some point in its downward movement the lower edge of the recess 30 passes over the edges of the platen 22, thereby effectively trapping the rubber slabs within the recess 30. Further downward movement of the upper ram plate 26 results in the development of essentially hydraulic pressure within the rubber material so that every element of the magnesium plate is subjected to the relatively high pressure referred to above. It has been found that excessive pressure tends to elongate the printing plate and may in some instances tend to reduce the sharpness or otherwise modify the printing characters on the plate.

Referring now to Figure 3 there is illustrated a section of the curved printing plate after its removal from the press. As illustrated in this figure the printing surface thereof is covered with a thin covering of aluminum indicated at 40.

Preferably, the rubber slabs 32 are so shaped that after the plate is bent to the configuration illustrated in Figure 4, further downward movement of the ram plate 26 results in building up of pressure from the central portion of the printing plate progressively outwardly from the center of the plate toward the ends, as seen in this figure.

The aluminum covering, which protects the magnesium surface from adherence or trapping of rubber particles, may be applied in any one of several ways. In the first place, the aluminum coating may conveniently be applied in the form of a thin aluminum foil which is merely placed over the printing surface before the application of pressure through the rubber slabs 32. The thickness of the aluminum foil may be between .0005 inch and .010 inch. In practice, the thinner foil may. be employed when the rubber is in new condition, and thicker foil may be employed as the rubber ages and is subject to some deterioration. Above .010 inch it is found that the foil does not conform sufficiently easily to the elements of the printing surface.

Alternatively, the aluminum covering may be applied as a spray of aluminum powder, or as a variation, the aluminum covering may be applied as an atomized melted spray.

In any case, following the operation the aluminum covering together with any particles of rubber adhered or trapped thereon, is removed by treatment of the formed printing plate in a caustic solution. Excellent results have been obtained by immersing the curved printing plate in a caustic bath including 10 percent by weight ofsodium hydroxide. However, the exact strength of the caustic solution is not particularly critical and the caustic bath may contain from 1 to 20% by weight of caustic. The strength of the caustic results primarily in a difference in timerequired in the treatment to remove the aluminum covering. Instead of sodium hydroxide, any suitable caustic'efiective to dissolve or partly dissolve and remove the aluminum covering is used.

To facilitate removal of the aluminum covering and any particles of rubber adhered thereby or embedded therein, the printing plate may be givena light brush treatment to accelerate cleaning of the magnesium printing surface. 7

When the method as outlined herein is followed, it is found that the printing plate retains its exact cylindrical configuration after removal from the press, and it is found further that the aluminum covering over the previously produced printing surface protects this surface from contamination by particles of rubber and at the same time avoids any appreciable effect on theaccuracy and detail of the printing surface.

While the printing plate herein is referred to as a magnesium plate, it will be understood that the present invention includes within its scope magnesium alloys including relatively high percentages of magnesium such for example as 95% magnesium as a minimum. It is specifically meant to include plates which may contain a relatively minor percent of other materials, such for example as zinc. The fact that the plate is essentially composed of magnesium however, gives rise to the possibility of producing accurately formed cylindrical plates without spring-back which retain the exact cylindrical form imparted thereto in the press. Moreover, the use of the aluminum covering over the printing surface permits the application to the hot plate of pressure through yieldable rubber materials.

The drawings and the foregoing specification constitute a description of the improved method'of making cylindrlcally curved printing plates in such full, clear, concise and exact terms as to enable any person skilled in the art to practice the invention, the scope of which is indicated by the appended claims. 1

' What we claim as our invention is:

1. The method of making cylindrically curved printing plates which comprises providing a flat magnesium plate with a printing surface at one side thereof, engaging the other side of the plate with a rigid convex cylindrical forming member, pressing a yieldablerubber material against the printing surface of the plate to cause the plate to conform to the forming member, maintaining the'plate at a temperature of between 300 and 800 degrees Fahrenheit during the application of pressure, and trapping the rubber material while increasing the applied pressure and thus applying an essentially hydraulic pressure through the rubber material, the pressure being selected in accordance with the temperature of the plate and having limits in accordance with the following table:

2. The method of making cylindrically curved printing plates which comprises providing a flat magnesium plate with a printing surface at one side thereof, engaging the other side of the plate with a rigid convex cylindrical forming member, pressing a yieldable rubber material against the printing surface of the plate to cause the plate to conform to the forming member, maintaining the plate at selected temperatures during the application of pressure, and trapping the rubber material while increasing the applied pressure and thus applying an essentially hydraulic pressure through the rubber material, the pressure being selected in accordance with the temperature of the plate and having limits falling within the shaded area of the chart of Figure 5.

3. The method of making cylindrically .curved printing plates which comprises providing a flat magnesium plate with a printing surface at one side thereof, engaging the other side of the plate with a rigid convex cylindrical forming member, covering the printing surface with a thin covering of alumium, pressing a yieldable substantially incompressible rubber material against the aluminum covered printing surface to cause the plate to conform to the forming member, maintaining the plate at a temperature of between 300 and 800 degrees Fahrenheit during the application of pressure, trapping the yieldable material against the aluminum covered printing face of the plate and applying an essentially hydraulic pressure through the yieldable material, and finally, removing the aluminum covering from the printing surface by treatment with a caustic bath.

4. The method of claim 3 in which the aluminum covering is between .0005 and .010 inch in thickness.

5. The method of claim 4 in which the aluminum covering is in the form of a foil interposed between the plate and yieldable material.

6. The method of claim 4 in which the aluminum covering is in the form of comminuted particles interposed between the plate and yieldable material.

7. The method of claim 4 in which the aluminum covering is applied in the'form of a powder spray interposed between the plate and yieldable material.

8. The method of claim 4 in which the aluminum covering is applied in the form of atomized melted spray interposed between the plate and yieldable material.

9. The method of claim 3 in which the step of treatment in a caustic bath comprises immersion in a caustic solution of sodium hydroxide between 1% and 20% by weight of the caustic.

10. The method of claim 3 in which the step of treatment in a caustic bath comprises immersion in a caustic solution of sodium hydroxide of about by weight of the caustic.

11. The method of claim 9 which comprises brushing the printing surface of the plate to facilitate removal of aluminum and rubber particles.

12. The method of making cylindrically curved printing plates which comprises providing a flat magnesium plate with a printing surface at one side thereof, engaging the other side of the plate with a rigid convex cylindrical forming member, covering the printing surface with a thin covering of aluminum, pressing a yieldable substantially incompressible rubber material against the aluminum covered printing surface to cause the plate to conform to the forming member, maintaining the plate at a temperature of between 450 and 650 degrees Fahrenheit during the application of pressure, trapping the yieldable material against the aluminum covered printing face of the plate and applying a pressure whose value is within the area determined by a pressure of between 1450 and 9700 pounds per square inch when the temperature is 450 degrees Fahrenheit, and between 300 .and 3750 pounds per square inch when the temperature is 650 degrees Fahrenheit, and finally removing the aluminum covering from the printing surface by treatment with a caustic bath.

13. The method of making cylindrically curved printing plates which comprises providing a fiat magnesium plate with a printing surface at one side thereof, engaging the other side of the plate with a rigid convex cylindrical forming member, covering the printing surface with a thin covering of aluminum, pressing a yieldable substantially incompressible rubber material against the aluminum covered printing surface to cause the plate to conform to the forming member, maintaining the plate at a temperature of between 300 and 800 degrees Fahrenheit during the application of pressure, trapping the yieldable material against the aluminum covered printing face of the plate and applying an essentially hydraulic pressure through the rubber material, the pressure being selected in accordance with the temperature of the plate and having limits of between 3200 and 18,500 pounds per square inch when the plate has a temperature of 300 degrees Fahrenheit, the pressure limits decreasing toward zero as the temperature of the plate exceeds 800 degrees Fahrenheit, and finally removing the aluminum covering from the printing surface by treatment with a caustic bath.

References Cited in the file of this patent UNITED STATES PATENTS 1,276,532 Hubbard Aug. 20, 1918 1,688,648 Novotny Oct. 23, 1928 2,486,130 Dietrich et al Oct. 25, 1949 OTHER REFERENCES Gray: Forming magnesium alloy, pub. in April 21, 1947, issue of Steel, pages 91 and 126 to 134.

Harvey et al.: Magnesium sheet easily formed pub. in May 25, 1944, issue of American Machinist, pages -108.

Ashburn: How to work magnesium alloys, pub. in November 7, 1946, issue of American Machinist, pages 117-132.

Flader et al.: Modern Photoengraving, pub. 1948, Modern Photoengraving Publishers, Chicago, Cincinnati. Page 185.

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