US2212234A

US2212234A - Method of coating printing cylinders

Info

Publication number: US2212234A
Application number: US239968A
Authority: US
Inventors: Charles L Henderson
Original assignee: Paper Patents Co
Current assignee: Paper Patents Co
Priority date: 1937-05-17
Filing date: 1938-11-12
Publication date: 1940-08-20
Anticipated expiration: 1957-08-20
Also published as: US2212233A; GB502662A; CH198975A

Description

2%, 1946. c. L HENDERSON r 2,212,234

METHOD OF COATING PRINTING CYLINDERS Original Filed. May 17. 1937 4 Shee ts-She et l Aug. 20, 1940. c, HENDERSON 2,212,234

METHOD OF COATING PRINTING CYLINDERS Original Filed May 17, 1937 4 SheetsSh'eet 2 20, 0- c. L. HENDERSON 2,212,234

METHOD OF COATING PRINTING CYLINDERS Original Filed May 17, 1937 4 Sheets-Sheet 3 3 9 i949- c. 1... HENDERSON 2,212,234

METHOD OF COATING PRINTING CYLINDERS Original Filed May 17, 193'? 4 Sheets-Sheet 4 Patented Aug. 20, 1940 UNITED STATES PATENT OFFICE METHOD OF Cosmo PRINTING CYLINDERS Charles L Henderson, Appleton, Wis., assignor to Paper Patents Company, Neenah, Wis., a corporation of Wisconsin Original application May 17, 1937, Serial No.

142,999. Divided and this application November 12, 1938, Serial No. 239,968

1 Claim.

transparency or other reproduction of the design or pattern to be printed is photographically transferred to a sheet of specially treated, sensitized material, which sheet is then wrapped around the surface of a smooth finished, un-

etched cylinder so as to form a covering or coating therefor. This sheet material has the property that the portions thereof which have been exposed to light become relatively insoluble in developing solutions and in etching solutions.

Hence, when the exposed sheet wrapping is developed, i. e., when it is treated, as by washing, so as to remove the soluble portions thereof, the exposed portions of the sheet remain in place on the cylinder, and during the subsequent etching operation form what is termed a "resist" which prevents or limits the etching of the exposed areas so as to assure proper reproduction of the pattern or design to -be printed on the surface of the printing plate.

These sheet coverings are very difficult to handle, and there has long been a need in the art for procedures whereby resist coatings can be applied directly to the surface of an unetched printing cylinder. as by the use of a liquid coating material, so as to make possible the direct photographic transfer to the printing cylinder of the pattern or design to bereproduced. In the past, attempts have been made to coat printing cylinders by the use of various types of liquid coat- 4 ing materials, but, so far as I am aware, prior to the discovery of the apparatus and processes set forth in my United States Patent No. 2,084,642 and .in my co-pending application Serial No 139,706, flled'April 29, 1937, the attainment of uniform, even coatings by the direct application of liquid coating materials to printing cylinders has never been successfully accomplished. Extensive tests and experimentation have established that the apparatus and methods disclosed in the above identified patent andapplication constitute a satisfactory solution of the problem with reference to the coating of small and medium size printing cylinders by the direct application thereto of liquid coating materials. However, while it is probably possible to coat large diameter cylinders such as are used in newspaper work by the methods and apparatus disclosed in these applications, considerable difileulty has been encountered.

The principal object of the present invention, 5 therefore, is to provide methods and procedures whereby printing cylinders, particularly cylinders of large diameters, may be coated by direct application thereto of liquid coating materials. It

is also an object of my invention to provide coat- 1o ing methods and procedures of this general type which shall make possible the obtaining of even coatings of readily controllable thickness.

The present application is a division of my copending application Serial No. 142,999, filed May l5 17, 1937, and in its more general aspects is a continuation in part of my Patent No. 2,084,642 and my co-pending application Serial No. 139,706.

The coating method disclosed in my prior Patent No. 2,084,642 and application Serial No. 20 139,706 is based upon the discovery that an even, uniform resist coating can be formed on a printing cylinder by applying a suitable liquid coating material to the printing cylinder and then rotating the cylinder about its own longitudinal axis 5 and also about a central vertical axis generally perpendicular to its longitudinal axis during at least a portion of the period when the liquid coating material so applied is being spread and dried.

As stated previously, while this method is satis- 30 factory for small printing cylinders, I have found that large printing cylinders can be coated satisfactorily only by following certain definite variations or extensions of this general method, which procedures will be set forth in considerable detail 35 hereinafter. In particular, it is necessary that the cylinder being coated shall be rotated at independently controllable speeds about its longitudinal axis and about the central axis perpendicular to the longitudinal axis during the spread- 40 ing and drying operations. Also, it is necessary that the relative speeds of rotation about these axes shall be varied during the spreading and drying operations at independently controllable and often very different rates. 4 In carrying out these procedures of the present invention, the liquid coating material ordinarily will be applied to the printing cylinder when such cylinder is being rotated about its longitudinal axis at a slow speed, although the coating mate- 50 rial may be applied when the cylinder is being rotated at slow speed about both its longitudinal axis and about the axis perpendicular to the iongitudinal axis. After the coating has been so applied the cylinder will be rotated about its longi- 55 tudinal axis at a moderate speed, and about the central axis which is perpendicular to its longitudinal axis at a very slow speed, this slow speed being continued for a short space of time to spread the coating evenly over the surface of the cylinder. Thereafter, it is usually desirable to greatly increase the speed of rotation of the cylinder at least about the central axis perpendicular to the longitudinal axis of the cylinder, which increased speed is continued throughout at least the greater portion of the drying operation. Under certain circumstances, it may also be desirable to independently increase the speed of rotation of the cylinder about its longitudinal axis during the drying operation, as will be here inafter made more apparent.

Other objects and advantages of my invention will be made more apparent by reference to the accompanying drawings and the following description of one preferred embodiment thereof. In the drawings- Figure l is a perspective view of an apparatus designed particularly for carrying out the coating methods of the present invention. The covers and other closures of the apparatus have been illustrated as opened up or cut away to make clear the several structural features;

Figure 2 is a sectional view of the coating apparatus illustrated generally in Figure l. The view is taken on the general line 2-2 of Figure 3;

Figure 3 is a sectional view on the general line 3-3 of Figure 2;

Figure 4 is a sectional view on the general line 4- 4 of Figure 3. A printing cylinder is also shown in place in this figure;

Figure 5 is a reduced plan view of the apparatus showing the relation of the various covers; and

Figure 6 is a perspective view of the mechanism utilized for applying the coating solution to the roll.

Referring to the drawings, l0 designates a hollow, cast iron base upon which is mounted a fixed vertical post I I. Rotatably mounted on the post Ii by upper and lower anti-friction bearings 12 and I3 (Figure 4) is the central hub l4 of areinforced circular table 15. A pair of pedestals 16 are rigidly mounted on opposite sides of the table and are provided at their upper ends with open bearings. l1 which receive and journal the ends of the supporting shaft 18 for the cylinder to be coated.

During the coating operation it is highly desirable that the cylinder to be coated shall be protected from dust and air currents, and to this end the table 15 is provided with a generally cylindrically shaped housing 19 for enclosing the cylinder during the coating operation. The housing 19 is of. split construction, and the upper section 20 thereof may be swung back on suitable pivots 2| to permit the cylinder to be placed within or removed from the housing. Re-

leasable clamp members 22 are provided for holding the upper and lower sections of the housing l9 together during the coating operation. The upper housing section 20 is provided with a circular opening 23 normally tightly closed by a removable cover 25 and a fine mesh screen 26, the purposes of which will hereinafter appear. If desired, the end portions of the housing 19 which engage the cylinder-supporting shaft may be provided with felt sealing rings 21 or the like for assuring a tight connection between the hous are .used, an airtight, dust proof housing for the cylinder is made possible.

The table 15 is rotated about its vertical axis by a variable speed, electric motor 29 mounted at one end of the stationary structure of the coating apparatus. The shaft of this motor 29 carries a pulley 30 which drives a belt 3| trained over two idler guide pulleys 32 and adapted to encircle a suitable ring member 33 supported at the periphery of the table 15. The cylinder is revolved about its longitudinal axis by a variable speed motor 34 adjustably supported upon the table l5, as illustrated particularly in Figures 1 and 2. For convenience in operation, the cylinder motor 34 drives an intermediate pulley 35 which is connected to the cylinder being coated through a suitable belt 33. Collector rings 31 supported upon the bottom of the table 15 are arranged to cooperate with brushes 38 for bringing power to the cylinder motor 34.

The revolvable table structure is enclosed within an outer housing 39 which is generally cylindrical in form and is preferably constructed of sheet metal, reinforced with angle iron. The outer housing 39 is completely covered at its top by a sheet metal cover 40 which includes two oppositely arranged, hinged sections 41 and 42, as illustrated particularly in Figures 3 and 5. The hinged sections 41 and 42 are provided primarily for permitting convenient access to the interior of the outer housing and to permit the cylinder to be coated to be readily located upon or removed from the table l5.

The central hinge section 42 is provided with a circular opening 43 which is normally partially closed by a hollow, open ended, hinged cover 44 of special design. The walls of this hollow cover 44 are insulated, and a plurality of electrical heater elements 45 are located in the spacetherebetween. The opposite ends of the hollow cover are open, as illustrated in Figure 4. The circular opening 43 in the central cover section 42 aligns with the opening 23 in the inner housing 19, as is illustrated in Figures 3 and 4, the purpose of the

openings

23 and 43 and the heater units 45 being to permit the introduction of heated air into the inner housing 19 during the drying of the coating. When the cover 25 for the inner housing I9 is in place no air will be admitted through the

openings

23 and 43, and when the cover 25 is removed to permit air to flow into the inner housing, the screen 26 serves as a filter.

The coating solution is preferably applied simultaneously along the entire length of the cylinder being coated by means of an elongated, shallow tray 41 supported upon the table 15 near the bottom of the inner housing l9. A lifting mechanism which includes two lifting levers 48 and an operating handle 49, as illustrated particularly in Figures 3 and 6, is provided for raising and lowering the tray 41 during the coating operation. The lifting mechanism assures that the.

coating material shall be brought into contact with the cylinder only at the proper time. The tray 41 is also used to hold water or alcohol or other suitable liquid for washing the cylinder preparatory to the coating operation, as will hereinafter appear.

The inner housing I9 is maintained closed and substantially airtight during at least the initial portions of the coating applying operation. The upper section of the housing I9 is, however, provided with a pair of vent openings which may be opened if desired through the actuation of autoing and the cylinder. When such seal rings; 53???? 1 31 91165. These vent Openings are. illustrated at 5| in Figures 3 and 4 and are normally closed by pivoted cover members 53. The covet members 53 are biased to the open position by centrifugal force when the table l5 rotates and are held in the closed position by pivoted latches 54. The latches 54 may be readily tripped from without the inner closure l9 during the coating operation when it is desired to open the vents.

The preferred method of accomplishing the coating of a printing cylinder in accordance with my invention is substantially as follows: The cylinder to be coated is placed in the apparatus, as illustrated in Figures 1 and 4, and is connected to the cylinder motor 34 by the belt 36. The inner housing I9 is then closed, the vent covers 53 are latched in place, and the central opening 23 in the upper section of the inner housing is closed by the tight cover 25. Distilled water or alcohol or other suitable liquid has previously been placed in the tray 41, and it is assumed, of course, that the surface of the cylinder to be coated has previously been carefully polished and prepared in the proper manner.

The cylinder motor 34 is then operated to rotate the cylinder about its longitudinal axis at a relatively high speed. The tray 41 containing the distilled water or alcohol is thereupon raised by operation of the handle 49, and the cylinder is washed by the water or alcoholin the tray 41. This washing operation effectively removes all dust particles or the like from the surface of the cylinder, and is of great value in assuring an even coating free from imperfections.

After washing, and while the rotation of the cylinder about its longitudinal axis continues, the table I5 is rotated about its vertical axis by operation of the motor 29. This rotation of the table l5 causes the water or alcohol in the tray 41 to flow out of the ends of the tray into the inner housing l9. Suitable spouts 55 located at the ends of the housing I9 serve to carry the water or alcohol into catch buckets 51 releasably attached to the bottom of the table. After a few minutes the tight cover 25 for the opening 23 in the inner housing 'is removed and the vent latches 54 are tripped to release the vent covers 53 and open the vents 5|. Air, filtered by the screen 26, then circulates through the inner housing l9 and out the vents 5| as a result of the centrifugal action produced by the rotation of the table l5.

When the roll is dry the machine is stopped. The vents 5| are closed and the tight cover 25 is put in place. The cylinder is then ready for coating with the sensitized resist solution. The

distilled water or alcohol or other liquid is re- 1 moved from the catch buckets 51, and the buckets are replaced in position at the bottom of the table; sections of the outer housing 39 may be opened to permit access to these buckets. A proper amount of coating solution is then poured in the tray 41 by means of a long stemmed funnel which passes through a tube guide 59 suitably located in the upper section 20 of the inner housing Hi. This guide is normally closed, as by a cork. A fine mesh screen 58 located at one end of the tray 41 serves to prevent the formation of bubbles as the coating solution is poured into the tray. The funnel is removed and the guide tube 59 closed.

Next, the table motor 34 is energized to revolve the cylinder about its longitudinal axis, preferably at a relatively slow speed (about 20 to 40 R. P. M.). The tray 41 containing the coating solution is raised by operation of the handle 49, and the surface of the cylinder picks up the coating solution. After two or three revolutions of the cylinder, the tray should be lowered.

of rotation about the vertical axis is gradually increased to several times its original value. At the same time, the speed of rotation of the cylinder about its longitudinal axis may likewise be increased.

The high speed rotation about both axes is continued for a sumcient time to permit the coating to begin to set; the actual time necessary to accomplish this will, of course, be determined by experiment. At this point the vent latches 54 are tripped to open the vents 5| and the cover 25 is removed, preferably without slowing down the apparatus. This permits free circulation of air through the inner housing, and in a short time the drying of the coating will be accomplished. Excess coating solution thrown off the cylinder and out of the tray 41 runs through the spouts and into the catch buckets 51 and can be reused. In certain instances it will be desirable to heat the air admitted to the interior of the housing during'the drying operation; this may readily be accomplished by energizing the heater units 45.

.Briefly summarizing the operation, the cylinder to be coated is supported upon the table l5 within the housing I9. This housing is tightly closed, and the cylinder is washed in situ with distilled water, alcohol, or other suitable liquid and dried. Then, without opening the cylinder housing 9, the coating solution is introduced into thetray 41 which is located within the housing. Following this, the cylinder is rotated slowly about its own longitudinal axis, and the coating material is applied simultaneously along its entire length by raising the tray 41. Immediately following the application of the coating material, the tray 41 is lowered, and the rotation of the cylinder about the axis extending at right angles to its own longitudinal axis, i. e., the vertical axis of the apparatus, is commenced.

The rotation of the cylinder about both axes is carried out at a slow speed for a period of a few minutes. Then both speeds of rotation are individually increased at uniform but independently controllablerates, the speed of rotation about the axis which extends at right angles to the longitudinal axis of the cylinder being increased in the order of about 15 to 20 times its initial value, and the speed of rotation of the cylinder about its own longitudinal axis being increased inthe order of about 1 to 2 times its initial value. This high speed rotation serves to thin the film'of coating material uniformly over the cylinder and is preferably continued unchanged until the coating material begins to set. At such time filtered air is admitted to the interior of the housing l9 within which the cylinder is contained to speed up the drying of the coating and, if desired, this air may be heated. The speeds of rotation about the longitudinal axis and about the other axes are ordinarily continued unchanged during the final portions of the drying operation. When the coating is dry, the ma- 7 chine is stopped and the cylinder removed thereoperation whereby the design to be printed is photographicaliy transferred to the coating thereon.

In one commercial embodiment of the invention when coating a cylinder about 14 inches in diameter, the coating solution is applied at a time when the speed of rotation of the cylinder about its own longitudinal axis is approximately 20 R. P. M. Immediately following the application of the coating material, the cylinder is rotated about the vertical axis of the apparatus at a speed of about or 6 R. P. M., and these speeds are maintained for a period of approximately two to three minutes. Then the speed of rotation about the longitudinal axis of the cylinder is increased to about 40 R. P. M., or possibly less, and the speed of rotation about the vertical axis is gradually increased to a value within the range of about 60 to 100 R. P. M. These speeds are maintained for a period of approximately 10 minutes, during which time the coating sets or begins to set. The drying of the coating-after the setting period does not usually require more than 10 or minutes, and in this embodiment of the invention no change in the speeds of rotation is ordinarily made during the final drying period. It will be understood, of course, that the proper speeds during each period will vary, dependent upon the coating material used and upon the thickness desired in the finished coating. The speeds given in the foregoing are for a coating material sold under the trade name "Cold Top, which material comprises an aqueous solution of shellac containing an ammonium dichromate sensitizer. Other coating materials may well require different timing and different speeds. The exact figures can, of course, be determined by test.

In the example given in the foregoing, the cylinder is rotated both about its longitudinal axis and about the vertical axis, which is perpendicular to its longitudinal axis, during the entire period when the coating is being distributed over the surface of the cylinder and is being dried. Tests indicate that the rotation about both axes must, in most instances, be carried on during the entire period, and it is certain that the speeds of rotation must be independently controllable if satisfactory results areto be obtained.

There are a number of separate, although more or less related, features which are believed responsible for the improved coating which is made possible by the apparatus of the present invention. Of particular importance in this connec tion is the rotation of the cylinder about its longitudinal axis and about an axis generally at right angles to the longitudinal axis during the drying and setting of the coating. Also, the arrangement whereby the cylinder is completely enclosed within an airtight housing which is not much larger than the cylinder and which rotates with the table support for the cylinder is thought to be of importance in accomplishing the objects of the invention, This housing apparently prevents the generation of air currents which might tend to set the coating locally before it has spread thinly and evenly over the entire cylinder.

It also appears to be important that the speed of rotation of the cylinder about the axis extending at right angles to the longitudinal axis of the cylinder (the vertical axis of the apparatus) shall be relatively low at the early stages of the coating operation. This slow speed which is gradually increased as the coating sets and bedust or other contamination between the washing', drying, and coating operations, and the vent arrangement, in combination with the filter opening through which air enters the cylinder housing during the final stages of the drying operation, permits increased speed of drying without danger of dust contamination.

The arrangement of the tray ,for applying the coating solution to the roll is also an important feature of the invention, for the reason that unless the coating material is applied to the cylinder at the proper instant great difllculty will be experienced in the attainment of satisfactory distribution of that material. The screen for preventing bubbles from reaching the central portions of the tray where they might cause spots in the finished coating is another feature of importance.

The particular apparatus and methods disclosed in the foregoing are especially suitable for coating cylinders having a diameter in excess of '7 or 8 inches and a length in excess of about 30 inches. Tests indicate that substantially all cylinders of this size can be satisfactorily accommodated if the table motion shall have a speed range of approximately to 1, and if the driving motor for rotating the cylinder about its longitudinal axis shall have a speed range of approximately 3 to 1. Independent control of the speed of rotation about both axes is, of course, essential to the carrying out of the method of my invention.

In accordance with the patent statutes, I have herein shown and described a form of apparatus which has been found by extensive tests to permit the satisfactory carrying out of the coating methods of the present invention. It will be understood, however, that the structural details of this apparatus and the exact sequence and timing of the steps of the method may be varied or changed in particular instances. Accordingly, it is my desire that the accompanying claim shall be accorded the broadest possible construction consistent with the language appearing therein and the prior art.

I claim the following as my invention:

The method of coating a printing cylinder with a sensitized resist which consists in applying liquid coating material to the cylinder, then rotating the cylinder about its own longitudinal axis and about a central axis extending at right angles to said longitudinal axis at independently controlled, differing speeds of rotation to spread said coating material evenly over the surface of said cylinder, and then drying the spread coating material, the cylinder being independently rotated about its own longitudinal axis and about said central axis at predetermined, independently controlled, differing speeds during at least a portion of the period when the coating material is being dried, and said cylinder being totally enclosed within a close fitting enclosure during the spreading and drying operation so as to prevent air currents which might result from the rotation of said cylinder about said central axis from causing unevenness in the applied resist.

CHARLES L. HENDERSON.