US2036835A

US2036835A - Transfer method and means

Info

Publication number: US2036835A
Application number: US701412A
Authority: US
Inventors: Benjamin L Sites
Original assignee: Miehle Printing Press and Manufacturing Co
Current assignee: Miehle Printing Press and Manufacturing Co
Priority date: 1933-12-08
Filing date: 1933-12-08
Publication date: 1936-04-07
Anticipated expiration: 1953-04-07
Also published as: DE625327C

Description

s E w s L B TRANSFER METHOD AND MEANS H ling m y n [I al pro '7, 1936 man ,AT E N T l 2,0dhb35 TRANSFER Benia 1L. Sites, @hieago, designer to The Miehle Printing ess and ltdanufactng @opany, iflhicago, Hill, a corporation of ois Application December 0, i933, Serial lilo. 701,412 llll dam, (oi. rot-ire) purpose of transferring a printing image without made of rubber, gelatin, or other compositions.

Mechanisms of this nature would include inking mechanism of printing presses which embo'dy series of ink distributing rollers, some of which are of steel and others of a flexible substance, some of the latter rollers being in contact with the steel rollers in order to distribute the ink, while others are arranged to contact with a printing form for the purpose of applying a film of ink thereto.

A particularly advantageous application of my invention would be in connection with a pianographic offset printing press in which a rubber blanket is used to transfer an impression from a planographic printing plate to the paper, that is to say, instead of effecting an impression direct from the printing plate onto the material to be printed, an impression is, first transferred from the inked plate to the rubber blanket, which then applies the impression to the print receiving material.

- While the usefulness of the invention may be extended to any type of offset press it is more advantageously applied in connection with the rotary type of planographic offset press, the printing units of which include a form cylinder having a hard surface, a transfer or blanket cylinder having a resilient surface, and an impression cylinder having a hard surface.

Accordingly I have elected to describe and illustrate my invention as embodied in a planegraphic press of the latter class.

Heretofore, in preparing presses of this class for printing, it has been common practice to so dimension said cylinders by packing or otherwise, that their peripheral i. e. gear pitch line diameters were identical.

It is also a well established procedure in presses of this class to'pack one or the other, or both of the complementary cylinders several thousandths of an inch above their bearers, i. e. above their gear pitch lines, in order to attain the squeeze necessary for eflecting an impression. For instance, in making rotary offset presses ready for printing, it has been known to pack the plate cylinder .001 inch, the blanket cylinder .002 inch to .003 inch, and the impression cylinder .002 inch above their bearers. Other proportional thicknesses of packings have been resorted to, which thicknesses varied depending on the prevailing conditions, such as the gauge and structure of the stock to be printed, the quality of the ofiset blanket to be used, etc. The motive of all the packing methods heretofore used, however, is the same, namely that of attaining the necessary impression for printing.

1 have ascertained that when, under any of the above conditions, the impression is effected from a resilient surface, as is the case in ofiset printing, the subject very often prints long, that is to say, the length of the printed matter or desimi is in excess of that of the design on the form or plate, and the dots of halftone printing show a slight elongation. Such conditions are exceedingly undesirable, particularly so inmulticolor work where accurate register of the successive impressions is essential, or in printing articles such as scales and other measuring implements where a variation in the divisions is not permissible.

In order to definethe cause of this variation with a view to eliminating the inherent defects, I have made very careful observations and have analyzed the prevailing conditions as follows:

In rotary printing presses, where two or more cylinders are in rolling contact with each other for the purpose of effecting impressions on paper or other material, it is desirable to establish true rolling between the cylinder surfaces in order to obtain satisfactory printing results. In the case where the contacting cylinder surfaces are made of non-resilient material, it is not difilcult to maintain true rolling. However, when the surface of one of the contacting cylinders is made of hard i. e. non-resilient material, and the surface of the complementary cylinder is of a resilient substance, such as rubber, then the problem of attaining true rolling becomes a difficult one.

I- have found that when the normal diameter of two cooperating cylinders, one of which has a hard surface and the other a resilient surface, are the same, then the effective diameter of the cylinder with the resilient surface, when in rolling contact with the other cylinder and when under the two contacting cylinders, also to some degree on the nature of the material which constitutes the resilient surface.

This fact I have proven by the following simple experiment:

A roller with a coating of composition having a thickness of inch and the roller having a total diameter of 0.8 inch, was rolled over a flat surface and by suitably marking the roller periphery, it was ascertained that when the composition was not compressed during the rolling of the roller over said surface, the roller traveled 2.5 inches per revolution; however, when during rolling, the composition coating was compressed to half its normal thickness, then the roller traveled 2.75 inches. In other words, compressing of the composition coating to half its normal thickness added about 10 per cent to the diameter of the roller at its point of contact with a solid or non resilient surface.

It will be readily understood therefore, that if a similar condition prevails in an offset press, the quality of printing will be seriously impaired, the main cause for this being that due to the increase of the effective or working diameter of the blanket cylinder at the printing zone, a certain amount of slippage takes place when the material to be printed passes between the blanket cylinder and the impression cylinder, which latter, due to its hard surface, of course retains its normal diameter. slippage of this nature, besides the fact that it will cause the subject to print long, is probably also responsible for such printing defects as smudging, gear streaks, inaccurate register and others.

As indicated above, the fundamental elements of an offset press are three cylinders, namely a plate cylinder which carries the printing plate or form, a blanket cylinder which is provided with a resilient blanket to receive an impression from the form, and an impression cylinder, the surface of which latter might be bare metal or if desired, might be covered with a suitable non-resilient packing. All of these cylinders are provided with bearers and intermeshing gears which are essential elements in printing presses of this class, the bearers of the plate cylinder under normal conditions being in rolling contact with the bearers of the blanket cylinder, and the bearers of the latter in turn being in rolling contact with the bearers of the impression cylinder.

These bearers necessarily are of equal diameters, which correspond with the pitch line diameters of the respective gears arranged on each cylinder for driving them. Assuming that there is no back lash between the intermeshing gears, namely between the gears of the plate, blanket and impression cylinders, then no slippage will be possible between the bearers on the respective cylinders. In other words, there will be a true rolling condition between the bearers, and consequently the surface speed of all cylinders will be equal, because, as stated herein, according to common practice, the plate, blanket and impression cylinders are so dimensioned that their peripheral i. e. gear pitch line diameters are identical. Theoretically, therefore, there should be no slippage of the material to be printed and the dimension of the impression thereon should be identical with that of the design or subject on the printing plate.

However, as explained above, in order to effect a printing impression, it is essential that pressure, .commonly termed in the trade -squeeze", be applied at the printing zone, that is to say, at the aoaaaes point of contact between the cooperating members of a printing unit, which, in case of an offset press, would be between the blanket cylinder and the impression cylinder, as well as between the blanket cylinder and the plate cylinder. Therefore, due to the compression and consequent displacement of the resilient material, namely the rubber blanket on the blanket cylinder, the efiective diameter of the latter, as proven by the example given above, will increase and consequently the impression transferred from the plate cylinder to the blanket cylinder and then from the blanket to the material to be printed, will print long.

With a view to eliminating this condition, which among other defects causes a variation in the dimensions of the printed subject, I have carried out extensive experiments which proved the necessity of avoiding any slippage of the material at the printing zone and of establishing a true rolling condition between the surfaces of the cooperating printing members at the printing zone in order that it may be possible to obtain true impressions, the size of which coincide exactly with the image on the printing plate or form. Furthermore, I found that the difficultics heretofore experienced with smudging, etc. will be effectively overcome when true rolling between the printing members is maintained.

In view of the fact that the surface speed of the blanket cylinder at its printing zone, that is to say, at its points of contact with the plate and impression cylinders, increases due to the conditions explained above and as proven by my tests, it is evident that in order to avoid any distortion of the printing image and any slippage of the material during printing, the surface speed of the impression cylinder as well as of the plate cylinder should be correspondingly increased. This I propose to accomplish by making the diameters of the latter two cylinders appreciably larger than the diameter of the blanket cylinder, while preferably I under pack the blanket cylinder so that the printing surface of the blanket will be below the bearers of the blanket cylinder. The proportions of the respective diameters being such that under non-printing conditions the surface speed of the plate and impression cylinders will be greater than that of the blanket cylinder, while under printing conditions the surface speed at the printing zone of these cylinders will be identical.

I realize, however, that an increase in the surface speed of said cylinders could be made possible by other methods, and therefore I do not wish to limit myself to the specific feature of increasing the diameters of the cylinders for the purpose of correspondingly increasing their surface speed.

In order to more clearly disclose the objects of my invention, I have illustrated the above referred to conditions in the accompanying drawing, in which:

Figure 1 shows the general arrangement of an offset press in connection with which my invention may be applied to advantage;

Figure 2 shows the distortion of the resilient material on a'printing roller when rolled under pressure over a non-resilient flat surface;

Figure 3 indicates to an exaggerated extent the condition which arises in an ofiset press when pressure is applied at the printing zone between the respective printing cylinders;

Figure 4 gives an enlarged view of the distorted portion shown in Figure 3 of a printing blanket at the point of contact between the blanket cylinder nuances and the impression cylinder of a printing press; and

Figure 5 illustrates diagrammatically a formcylinder, blanket cylinder and an impression cylinder with their bearers and associated gears.

Referring now more specifically to Figure l,

which shows in diagrammatic elevation the prin-' cipal elements of a single color ofiset press, in

which, for the purpose of illustration, the sheet" it is shown as having been fed down over the feed board ii to grippers if of the impression cylinder it. In the vicinity of the plate cylinder i i, and in operative relation therewith, the press is equipped with the conventional dampening mechanism it and inking mechanism it, the former of which mechanism serves for applying a film of ink repelling substance to the non-design portions of the plate ll before the form rollers of the inking mechanism are brought into contact with the plate in order to ink its design portions.

The peripheries of the bearers on the impression cylinder it, plate cylinder it and blanket cylinder it are denoted by reference numerals it, i l and iii respectively. These peripheries also correspond with the pitch lines of the gears which, as indicated'above, are provided on each one of said cylinders.

As indicated above, instead of applying the printing impression from the plate direct onto the material to be printed, in offset printing the impression from the inked plate is first applied onto a blanket it or other resilient surface provided on the transfer or blanket cylinder it, and then transferred from said blanket to the printreceiving material. It will therefore be seen that the sheet iii receives its impression during its passage between the impression cylinder lt and the blanket cylinder ill. After receiving its impres-' sion, the printed sheet will be released by the grippers if of the impression cylinder and taken over by any suitable delivery mechanism, not forming part of this invention and therefore not shown. in order to convey it to sheet receiving means such as a delivery table. r

In order to illustrate the above referred to condition that is set up at the printing zone i. e. at the point of contactbetween a hard impression surface and a soft surfaced printing member when under pressure, I have shown in Figure 2' how the soft material on the printing member becomes displaced and thereby increases the effective radius of said member in the printing zone.

In this figure the radius R represents the normal overall radius of the roller D. Assuming that the roller D is rotated in a clockwise direction, as viewed in Figure 2, and rolled under pressure over a hard surface A, then therubber coating B at the zone of contact with the hard surface A will undergo a deformation and the displaced rubber will become deflected to the right. Therefore it will be seen that due to the displacement of rubber, the normal radius R has become increased to assume a dimension R.

It is evident, therefore, that as a result of the displaced rubber, the effective radius of the roller- A similar condition develops when two or more rollers, traveling at the same surface speed, but one having a resilient surface, are rolled together under pressure. This example I have illustrated in Figure 3, in which an impression cylinder it and a plate cylinder it are in simultaneous rolling contact under pressure with a blanket cylinder it. These cylinders, the overall diameters of a which are equal, and the bearers of which arein rolling contact, rotate in the direction of the arrows and are geared together, as indicated in Figure 5, so that their respective surface speeds are the same, a measure which is common practice in conventional offset presses heretofore built.

In order to obtain an impression from the plate cylinder it onto the blanket cylinder it and then from the latter onto the material which passes between the blanket cylinder and impression cyl-' inder, it is necessary to apply a certain amount of squeeze between the cooperating pairs of cylinders. Thereforaunder printing conditions, the rubber blanket it on the cylinder is undergoes a transformation at the zones of contact with the cylinders it and Ni so that at the printing points of the cylinders the effective radius of the blanket cylinder it will be R and consequently the surface speed of that cylinder at the printing zone is greater than the surface speed of the cylinders it? and it. Inasmuch as all of these cylinders are geared together in a manner to prevent backlash as is well known in the art, and are driven positively at a 1 to 1 ratio, it is obvious that due to the increased effective radius of the blanket cylinder it, there must be slippage between the cooperating cylinders at their respective zones of contact.

In order to explain the effect of such slippage on the printing condition, I will deal separately with each rolling pair of cylinders. The first pair to be considered is the plate cylinder it and the lanket cylinder it, the surfaces of which during printing are in direct rolling contact, because the blanket on the cylinder it is to receive an im pression direct from the inked plate on the cylinder i l. Planographic plates such as are commonly used in direct as well as in offset lithog raphy have a grained surface which carries a design or image usually produced by means of a halftone screen so that'the design is made up of equally spaced infinitesimal dots varying in area according to the depth of the tone to be printed.

It will be understood, therefore, that the slightest slippage between the plate, i. e. these dots, and the surface to which the design made up by these dots is to be transferred, causes an elongation of the printeddot as well as other undesirable defects, such as for example smudging of the design to be printed, premature wear of said dots on the plate. as well as of the grained non-design portionof the plate, distortion of the image, i. e. change in the dimensional proportions of the original design, loss of register, etc.

The condition prevailing between the second rolling pair of cylinders, see particularly Figure 4, namely the impression cylinder i3 and the blanket cylinder iii, while similar in principle, adds another factor to these applying in connection with the first rolling pair discussed above.

The difference involved is due to the fact that the second rolling pair functions to transfer the impression from the blanket It to the print receiving material during the latters passage between the blanket cylinder and the impression cylinder. Assuming that, due to the increase of the radius at the printing zone of the blanket cylinder ill, the eflective periphery of that cylinder has increased 5 per cent, as compared with its normal periphery, which latter is equal to that of the cooperating plate and impression cylinders, then a slippage of 5 per cent of the material to be printed will occur during each revolution. This slippage of the material may all take place with relation to either one of the two cylinders, or it may be divided between them, that is to say, the material may to some extent slip on the blanket and to some extent on the impression cylinder. If there is any slippage between the material and the blanket, then during the transferring of the impression to the material, further smudging of the design will result, but in the opposite direction, so that possibly the impression on the material will print short as compared with the impression on the blanket, which was previously transferred thereto from the plate cylinder.

On the other hand, however, if the material follows the blanket and thereby assumes the increased surface speed developed at the printing zone, as explained above, then all the slippage of ie material will be confined to the impression cylinder surface, and as a result there will be less smudging, but the impression will print long on the material.

In Figure 4 I have also indicated how the internal structure of the rubber blanket is distorted under printing conditions. At position a, the radius R is undisturbed, at position b the rubber undergoes a slight distortion and due to the displaced rubber accumulated at that point, the effective radius increases, while at position 0 the rubber is almost fully compressed. This condition brings about a conflict between the natural speed of rolling and the normal surface speed of 'the rolling cylinders as imparted by the gear drive. As a result, slippage occurs and thus a volume of rubber will build up on the entering side of the cylinders in rolling contact.

In order to establish a definite range of packing thicknesses for the cylinders of different sized presses, I have developed and applied in practice a formula which gives the correct thickness of packings for all sizes of the cylinders.

This formula shows that for instance in an offset press in which the diameter of the cylinder bearers is 20 inches, the plate cylinder diameter should be increased .010 inch over the bearer diameter, the blanket cylinder diameter .006 inch under its bearer, and the impression cylinder diameter .010 inch over the bearer diameter of the cylinder, allowing for a squeeze of .004 inch.

For a smaller size press in which the cylinder bearer diameter is 8 inches, the packing dimensions are as follows: plate cylinder .005 inch over the bearer, blanket cylinder .001 inch under the bearer, and impression cylinder .005 inch over the bearer.

At first these dimensions seem extremely excessive and quite contradictory to any packing methods heretofore used on offset presses, particularly so because, according to my formula, the modified diameter over-all of the blanket cylinder is appreciably less than the diameter of the blanket cylinder bearer. However, the congruity and accuracy of this formula has been fully substantiated by numerous tests which were run under actual commercial printing conditions, and which have proven beyond any doubt that by my method of packing the cylinders, an absolutely true rolling contact is established and maintained at the printing zone of complementary cylinders. It is therefore evident thatmy method is based on actual facts developed during a period of long experimentaton, and that by means of my formula I can definitely ascertain the accurate packing dimensions for offset presses of any size.

It is also of importance to note that by dimensioning the cylinders as taught by mymethod, the bearers of all the complementary cylinders will remain in rolling contact under printing conditions. Heretofore it has been quite common that during printing, the complementary cylinders would not ride on their respective bearers, a condition evidently due to incorrect packing methods.

I also wish it to be understood that the formula by means of which I have obtained the above figures is based on commercially standard qualities of rubber blankets, and that these figures may vary slightly when either softer or harder quality blankets are used.

While the conditions set forth herein could be substantiated in more detail by elaborate discussions of the theoretical points involved, I believe that the illustrations given and the facts pointed out above furnish sufficient proof in support of the contention that in order to establish true rolling conditions between the cooperating printing members, it is essential that under printing conditions, the surface speed of all said members at the printing zone be identical.

It will also be understood that while I prefer to accomplish the desired result by suitably dimensioning the diameters of the respective rolling pairs of printing members, the same effect could be obtained by any other method whereby the surface speed at the printing zone between such members can be equalized and maintained the same during printing conditions.

Furthermore, it will be evident that while I have illustrated and described my method of printing as applied in connection with a planographic printing press, it could be equally well used in connection with any other type of printing press where similar conditions are set up between the printing couples when the press is in operation.

I claim:

1. In a printing press, the combination of cooperating form and blanket cylinders having relatively hard and soft operating surfaces whereby a printing impression is conveyed from one to the other, each of said cylinders having engaging bearers, said blanket cylinder having its impression receiving surface below its bearers and the form cylinder having its active surface above its bearers whereby said surfaces at the printing zone travel at the same speed to transfer a true image undistorted.

2. In a printing press, the combination of cooperating form, blanket and impression cylinders having relatively hard and soft operating surfaces whereby a printing impression is conveyed from said form cylinder to said blanket cylinder and from the latter to material passed between said blanket and impression cylinders, each of said cylinders having engaging bearers, said blanket cylinder having its impression receiving surface below its bearers, and said form and impression cylinders having their active surfacesv above their bearers, whereby all of said surfaces at the printing zone travel at the same speed to transfer a true image undistorted.

3. In a printing press, the combination of cooperating blanket and impression cylinders having relatively hard and soft operating surfaces whereby a printing impression is conveyed from said blanket cylinder to material passed between the latter and said impression cylinder, each of absence said cylinders having engaging bearers, said blanket cylinder having its impression receiving surface below its bearers and said impression cylinder having its active surface above its bearers whereby said surfaces at the printing zone travel at the same speed to transfer a true image undistorted.

4.-. In a printing press, the combination of cooperating form, blanket and impression cylinders having relatively hard and soft operating surfaces whereby a printing impression is conveyed from said form cylinder to said blanket cylinder and from the latter onto material passed between it and said impression cylinder, said form and impression cylinders being so ,dimensioned that their surface speeds will be greater than the peripheral speed of their corresponding bearers, while said blanket cylinder is so dimensioned that its surface speed will be less than the peripheral speed of its bearers.

5. In an offset press, a plate cylinder in which the printing surface is raised between .004 inch and .040 inch above the normal pitch line of its gear, a blanket cylinder in which the surface of the resilient blanket is depressed between .004

inch and .036 inch below the pitch line of the I blanket cylinder gear, and an impression cylinder in which the impression surface is arranged so that the surface of the material receiving the impression is from .004 inch to .040 inch above the normal pitch line of the impression cylinder gear.

6. The method of printing with a press having a plurality of cooperating, relatively hard and soft surfaced printing members, having bearers associated therewith, consisting in so dimensioning the soft surfaced one of said members that its operating surface will be below its bearers, dimensioning the hard surfaced cooperating member or members so that the operating surface of each will be above the bearers, and applying printing pressure to said members to thereby establish true rolling condition between said printing members.

member having its active surface above its bearers, the proportionate dimensioning of said members being such that under printing condition said surfaces at the printing zone travel at the same speed to transfer a true image undistorted.

8. In a printing press, the combination of operating form and blanket cylinders having relatively hard and soft operating surfaces whereby a printing impression is conveyed from one to the other, each of said cylinders having engaging bearers of equal diameters to thereby produce true rolling contact between said bearers, said blanket cylinder having its impression receiving surface below its bearers and said form cylinder having its active surface above its bearers, the

diameters of said cylinders being so dimensioned 1 impression receiving surface below its bearers and said form cylinder having its active surface above its bearers, the diameters of said cylinders being so dimensioned that under printing condition said surfaces at the printing zone travel at the same speed to transfer a true image undistorted.

10. In a printing press, the combination of co- 7 operating form and blanket cylinders having relatively hard and soft operating surfaces whereby a printing impression is conveyed from one to the other, said cylinders being geared together and having engaging bearers, the diameters of said bearers being equal to the pitch line diameters of the gears associated with said cylinders, said blanket cylinder having its impression receiving surface below its bearers and said form cylinder having its active surface above its bearers, the diameters of said cylinders being so dimensioned that under printing condition said surfaces at the printing zone travel at the same speed to transfer a true image undistorted.

11. In a printing press,'the combination of cooperating form, blanket and impression cylinders having relatively hard and soft operating surfaces whereby a printing impression is conveyed from one to the other, said cylinders being geared together and having engaging bearers, the diameters of said bearers being equal to the pitch line diameters of the gears associated with said cylinders, said blanket cylinder having its impression receiving surface below its bearers and said form and impression cylinders having their active surfaces above their bearers, the diameters of said cylinders being so dimensioned that under printing condition said surfaces at the printing zone travel at the same speed to transfer a true image undistorted.

BENJ.

1 L. SITES.