US3431846A - Offset image transfer process - Google Patents

Description

March 11, 1969 R. H. BECK OFFSET IMAGE TRANSFER PROCESS Filed July 28, 1966 Sheet of4 INVENTOR ROBERT HAUN BECK ATTORNEY March 11, 1969 R. H. BECK 3,431,846

OFFSET IMAGE TRANSFER PROCESS Filed Ju1y28. 1966 Sheet 2 of 4 Fl 6. a ,5

INVENTOR ROBERT HAUN BECK ATTORNEY Marchll, 1969 R. H. BECK OFFSET IMAGE TRANSFER PROCESS Sheet Filed July 28, 1966 ROBERT HAUN BECK ATTORNEY March 11, 1969 BECK OFFSET IMAGE TRANSFER PROCESS Fild July 28. 1966 FIG. 6

Sheet hVACUUM PUMP \J hwwuuu PUMP 9 VARIABLE SPEED W MOTOR CLUTCH COIL I I l ROBERT HAUN BECK United States Patent 3,431,846 OFFSET IMAGE TRANSFER PROCESS Robert Haun Beck, Fair Haven, N..I., assignor to E. I.

du Pont de Nemours and Company, Wilmington, Del.,

a corporation of Delaware Filed July 28, 1966, Ser. No. 568,663

US. Cl. 101426 Int. Cl. B410 3/00; B41f 3/12; B41m 1/06 ABSTRACT OF THE DISCLOSURE An offset image transfer process and apparatus comprising a frame, two coating rolls carried by the frame, one roll being one-half the diameter of the other, means for rotating the rolls in synchronism and in surface contact, and for disengaging the surfaces; and securing means on the larger roll to hold a matrix image-bearing sheet and an image receptor sheet 180 apart while in a fixed position on the larger roll. This process is useful in color proofing where images in various colors are transferred in superimposed registrations onto a receptor sheet.

This invention relates to an offset printing machine and more particularly to dry offset image transfer for color proofing from shear sensitive photopolymer coatings.

The offset method of ink transfer from a planographic printing plate to paper is old. The offset method of transfer is used in machines which are now commercially available, for example, A. B. Dick Model 320 duplicator. Generally in these machines more than 2 rolls are needed and fountain solutions are necessary. The transfer is done wet while only one pass completes the transfer. Since only one pass is needed no precise method of hold down or registration of matrix and receptor is needed or available. In a typical offset printing press there exists end play in the rolls and backlash between the gears coupling the rolls. Furthermore, the prior art equipment is not economically useful in color proofing such as for four color half-tone transfer. This results because separation halftones are proofed by first making an offset test plate and then making short runs under actual printing conditions.

The offset image transfer machine of this invention is designed to provide a novel apparatus to make color proofing copies with a minimum of time, effort and cost while eliminating the need of a wet system. This apparatus comprises two cylindrical rolls of different diameters, the largest being twice the diameter of the other; drive means to rotate the rolls; synchronizing means causing the smaller roll to rotate twice per rotation of said larger roll; actuating means to engage and disengage the surface of the rolls with each other; and securing means on the larger roll to hold a matrix and image receptor on the roll in a fixed position.

A practical offset dry image transfer machine of this invention will now be described with reference to the following drawings.

FIGURE 1 is an isometric view of the assembled machine.

FIGURE 2 is a front view of the essential parts of the machine.

FIGURE 3 is an end view showing the relationship of the rolls to each other and to the drive motor.

FIGURE 4 is a sectional view of the engage-disengage pivot mechanism taken from See. 4-4 of FIGURE 2.

FIGURE 5 is a view of the system which moves the engage-disengage pivot arm in the transverse direction.

FIGURE 6 is a schematic view showing the electrical circuits and certain parts of the system controlling the machine.

FIGURE 7 is an isometric view of the proofing cylinder and a schematic view of the vacuum hold-down system.

2 Claims 3,431,846 Patented Mar. 11, 1969 FIGURE 8 shows the shaft mountings at one end with the position of the preloaded ball bearings and the drag brake.

Referring now to the drawings wherein similar parts have similar reference numerals throughout the several figures, the machines of this invention may have a suitable base frame 1, pressed metal casing 2 and a control box 3.

With particular reference to FIGURES l and 2 a proofing cylinder roll 4 is journalled in bearing supports 5 and carried by the base frame. On the outer surface of the proofing cylinder are imbedded registration pins 6 to accommodate the matrix and receptor papers as they are to be positioned out of phase on cylinder 4. Vacuum for paper hold-down is applied through two sets of open air channels 7 set in the proofing cylinder 4 (only one set shown). The channels are separated so that vacuum holddown for matrix and receptor paper may be separately controlled.

Immediately behind the proofing cylinder is the offset transfer cylinder roll 8. In size the offset transfer cylinder is one half the diameter of the proofing cylinder. It is mounted on an eccentric shaft and journalled into suitable bearing supports carried by the base frame. In space relationship, it is mounted on an eccentric shaft to that in the disengaged position the center of a cross section of the offset roll lies below a line connecting the centers of the two rolls in the engaged position, see FIGURE 3. The center of the offset transfer cylinder 8 in the engaged position is marked by numeral 50, and in the disengaged position by numeral 51. Rotation of the offset cylinder from the disengage to the engage position, that is from reference center point 51 to reference center point 50, is a clockwise rotation as viewed in FIGURE .3. The outer surface of the offset cylinder 8 is covered by a standard offset printing blanket consisting of rubber facing on a rubber impregnated fabric base.

An electric motor 9 is attached to the shaft of the proofing cylinder through a pulley arrangement 10. In turn, the drive system of the proofing cylinder 4 is geared to the offset cylinder on a 1 to 2 ratio through gear box 11.

The proofing cylinder is mounted on a fixed center while the offset cylinder may assume either of two positionsengage with the proofing cylinder or disengage from the proofing cylinder. The engage-disengage system works as follows. (See FIGURES 4 and 5.) Axially mounted on the proofing cylinder shaft is the engage cam 12 and the disengage cam 13. Axially mounted on the offset cylinder shaft is pivot arm 14. Attached to the upper end of pivot arm 14 is the cam follower 15 which when engaged with cam 13 causes the top of the pivot arm 14 to rock forward disengaging the offset cylinder 8 from the proofing cylinder 4. When cam follower 16 is caused to engage cam 12, the top of the pivot arm rocks backward engaging the rolls.

The cams 12 and 13 utilized in the preferred apparatus as herein described have part of their internal section removed so that each cam resembles a container such as a round pan. The internal diameter contains the actual cam riser 54 (shown only for cam 12) surface. The cam followers 15 and 16' are arranged to extend into the interior of the cams when transversely moved and thereby contact the cam riser. The cam risers merely act to trip the cam followers to begin or end a printing cycle. Once tripped, the cam followers are locked into place just out of reach of the cam risers by the action of holding magnets 36 or 37. As the drums rotate during a printing cycle there is no action between the cam followers and cam risers.

Shaft 17 upon which the offset cylinder 8 and pivot arm 14- are mounted is eccentrically constructed and 0perates in a manner similar to a crank shaft in that the rotational effect caused by the rocking of the pivot arm 14 will cause the offset cylinder to engage and disengage.

In order that pivot arm 14 may cause cam followers 15 or 16 to engage one cam or the other, the pivot arm is made to slide along shaft 17 by the sliding mechanism 18 which is positioned by a mechanical yoke 19 and controlled by solenoids 20 and 21. Solenoid 20 positions the cam follower 15 to ride on cam 13 and disengage the offset cylinder, while solenoid 21 causes cam follower 16 to ride on cam 12 and engage the oifset cylinder. The sliding mechanism 18 is keyed to the shaft by a sliding key 48.

End play or transverse motion of the drums is eliminated by the use of holding means such as preloaded ball bearings commercially obtainable, i.e., New Departure Ball Bearing Type 20,000, shown in FIGURE 8 and labelled numeral 40. The bearings which have an angular contact design are loaded by adjusting means 41, a hearing locknut with a complementing bearing lock washer 42.

Backlash between the teeth of gear system 11 is contained by the use of a spring loaded friction disc engaged as a drag brake. This drag brake is also commercially obtainable. Referring to FIGURE 8, the braking means is located on shaft 17 adjacent cylinder 8 and is composed of a friction disc 43, a retaining ring 44, a spring washer 45 and a compression adjusting nut 46. The compression adjusting nut 46, the spring washer 45 and the retaining ring 44 are stationary parts. By turning compression adjusting nut 46, the drag created by friction disc 43 can be controlled to prevent backlash between the proofing cylinder 4 and the offset transfer cylinder 8.

The vacuum used for locking the matrix and receptor paper on the printing cylinder is created by pumps 22 and 23, see FIGURE 7. A vacuum is supplied to the surface of the proofing cylinder in the following manner. The outer surface of the proofing cylinder contains two sets of open air channels 7. These channels are in operative contact with vacuum ports 38 and 39. One system of interconnected channels leads into vacuum port 38 and vacuum port 38 is connected by tubing to rotary joint 27 and continues on to vacuum pump 23. This system services the matrix side of the proofing cylinder. Vacuum port 39 with its related channel system is connected to rotary joint 26 and vacuum is supplied through pump 22. This system services the receptor side of the proofing cylinder. Gages 24 and 25 are vacuum gages mounted in the control box 3. Rotary joints 26 and 27 are mounted on the ends of the proofing cylinder shaft.

The preparations necessary prior to machine opera tion are as follows. The matrix coated with a polymerizable photosensitive layer is shear sensitive in the unexposed areas. Such element is described in a patent application by Chambers, entitled Polymerization Processes and Elements Therefor filed July 7, 1966, Ser. No. 6 8,- 367. Exposure of the matrix is through the back of the positive which produces a right reading image on the matrix. After exposure to a half-tone positive under ultraviolet light, the cover sheet is carefully stripped off and the matrix is mounted in register on the proofing cylinder. The paper receptor is also mounted on the proofing cylinder 180 away from the matrix. Vacuum pumps 23 and 24 are turned on by manual switches 50 and 51 to assist in hold down. Following this, the machine is ready for operation.

Looking to FIGURE 6 will aid in defining the machine step sequence. The motor controller is an S47 Silicon Controller Rectifier made by Gerald K. Heller Co., of Las Vegas, Nev.

Motor '9 is energized by manual switch 52. Through pulley system 10, the rolls 4 and 8 begin to rotate. The gears coupling the two rolls are always engaged; there- Lfore, synchronized rotation begins when motor 9 is turned on. Variable speed potentiometer 28 is used to adjusting the motor speed until the proofing cylinder 4 is rotating at the desired rpm.

Single pole, momentary contact push button 29 is depressed and held. To prevent a collision of parts, i.e., to keep cam follower 16 in its transverse motion from landing on the side of cam riser 54, the clutch 30 will not be activated until counting switch 31 is activated by its camming surface 47, indicating the mechanical parts are in a compatible space relationship to engage each other. With push button 29 depressed and counting switch 31 activated, power is fed through the clutch coil 30 into the offset roll-engage solenoid '21. Contact 53 closes completing the power circuit. At the same time, contact 35 closes to maintain a completed circuit to service the clutch coil when push button 29 is released, while contact 32 opens keeping solenoid 20 from being activated.

Contacts 32, 35 and '53 are all contained in one component and are in a fixed relationship to each other. That is 32 is normally closed while 35 and 53 are open. Conversely when 32 is open 35 and 53 are closed.

Mechanically, looking to FIGURES 4 and 5, once the offset roll-engage solenoid 21 is activated, it pulls the mechanical yoke 19 causing the transverse sliding mechanism 18 to move pivot arm 14 towards cam 12 where cam follower 16 will engage cam 12. Once the follower 16 hits the raised portion of cam 12, this will cause the top of pivot arm 14 to rock back moving the bottom of pivot arm 14 to engage switch 33 which activates the counter 34. After the initial pivot arm action resulting from cam 12, the arm 14 is held in the engaged position by magnetic stop 36 for the duration of the printing cycle. In like manner, magnetic stop 37 will hold pivot arm 14 in the disengaged position.

When counter 34 counts out its preset number of revolutions, it de-energizes the clutch coil 30 by opening contact 35, and goes on to de-energize solenoid 21 by opening contact 53 while contact 32 closes. Switch 49 is closed when not engaged by arm 14 and contact 32 is opened. When contact 32 closes a power circuit is completed through solenoid 20 which is now activated and acts to shift the slide mechanism causing the rocker arm 14 to disengage the rolls. To prevent solenoid 20 from burning out, switch 49 will open by the action of arm 14 after contact 32 is closed and solenoid 20 has pulled the rocker arm 14 back to the disengaged position. The pivot arm 14 will be held in this disengaged position by magnetic stop 37.

As the disengage solenoid 20 is activated, it pulls the mechanical yoke 19 towards it which causes the transverse slide mechanism 18 to move pivot arm 14 towards cam 13 where cam follower 15 will engage cam wheel 13. This will cause the top of pivot arm 14 to rock forward and the bottom backwards so that the bottom engages micro switch 49 opening this switch and de-energizing solenoid 20. The offset roller is disengaged from the printing roll due to this rotation of the pivot arm and the printing cycle is completed.

Transfer of the image occurs by the matrix mounted on the printing drum leaving an image on the offset roll and this image is then transferred back to the printing drum but onto the receptor paper which is exactly opposite the matrix. This is accomplished by the fact that the printing cylinder is twice as large as the offset roll in diameter and the offset cylinder is geared to the proofing cylinder on a 2 to 1 ratio.

When the two rolls engage, the printing roll, being made of a harder material than the offset roll, causes the offset roll to be depressed. When the matrix appears in this depressed area, shear forces are set up and these shear forces cause the unexposed and therefore the unpolymerized image areas of the matrix to become fluid due to the pseudoplastic nature of the coating and transfer from the matrix to the offset cylinder occurs. Thin layers of image are transferred first from the matrix on the printing cylinder to the rubber blanket of the offset roll and then to the receptor paper on the printing cylinder with each revolution. Multiple revolutions are generally necessary for color transfer of the same image, therefore the need for proper registration. In addition, when four color half-tone positives are to be proofed, each color is transferred separately to the same receptor and proper matrix registration is essential. For example, a yellow matrix may be used first and take 15 revolutions for proper transfer. The yellow matrix is then removed by first turning the vacuum to the matrix side of the roll off, removing the yellow matrix and replacing it with a cyan matrix, for example. The cyan matrix would be placed in registration, vacuum applied and the machine run for the desired number of revolutions. This is then repeated for any other color to be transferred. Since the transfer is by offset, the right reading matrix image transfers first to the offset cylinder as a wrong reading image then to the receptor paper as a right reading image.

The machine described above can be modified in various ways, for example, the rolls can be activated by one or more motors linked to the different rolls by means of gears, belts or chains and provided with a suitable clutch. The various parts of the machine can be made from conventional materials of construction. The frame and covers can be made of metal such as steel, steel alloys, aluminum, aluminum alloys, copper, brass, etc. or even plastic materials. They may be painted or covered with protective surfaces. The design of the rolls may be modified in size so long as the matrix, transfer image, and receptor paper are kept in phase to effectuate transfer from matrix to receptor.

The machines of this invention are useful for transferring a nearly dry to the touch image from a matrix coated basically with a polymerizable monomer and a thixotropic agent as described in the above-identified Chambers application Ser. No. 563,367.

The matrices of the Chambers application comprise a support, usually a flexible sheet, having coated thereon a photopolymerziable stratum, said photopolymerizable stratum comprising a uniform admixture of (a) an inorganic thixotropic binder (b) a non-gaseous ethylenically unsaturated compound containing at least one terminal ethylenic group and being capable of forming a high polymer by free radical initiated chain propagating, addition polymerization, and having a plasticizing action on (a).

Constituents (a) and (b) being present in from 0.2 to 12 parts by weight and 1 to 30 parts by weight, respectively.

Generally, the photopolymerizable composition is coated from a dispersion in 38 to 90 parts by weight of water, alcohol, or mixtures thereof. The photopolymerizable coating composition preferably contains 4 to 5 parts by weight of constituent (a) and from 1.4 to 1.9 parts by weight of constituent (b). Preferably the photopolymerizable compositions also contain a free radical generating addition polymerization initiator in amounts ranging from 0.05 to 2 parts by weight. A pigment and pigment dispersant may be added and are generally present in 0.4 to 25 and 0.05 to 2 parts by weight, respectively. Also, small amounts of thermoplastic organic polymers as described in Plambeck 2,760,863 may be present as diluents in amounts up to 5% of the thixotropic binder.

Preferred thixotropic agents that range in size from 5 to 500 millimicrons are boehmite alumina crystals having a length to diameter ratio of 20:1, clay mixtures of silicate oxides, e.g., bentonites and gels containing 99.5% SiO with 0.5% of mixed metallic oxides having a surface area of 250-350 square meters/ g.

A preferred unsaturated compound is the triacrylate ester of the reaction product of trimethylol propane and ethylene oxide. This and other unsaturated compounds, photopolymerization initiators and other components are listed in the Chambers application and the references listed in said application.

Some advantages of the machine are as follows. No particular skill is required to operate the machine. It is self-contained, dependable and durable. A nearly dry to the touch image is transferred which would not be obtained by standard offset printing. The machine is comprised of only two rolls which eleminates the extra gear means between the three rolls of the standard offset printing press. Vacuum hold-down is provided which is mechanically difficult in a conventional offset press. The machine is suitable for making single color transfers in addition to multiple color transfer. The image being transferred by a multiplicity of revolutions allows one to control density.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.

1. A process for printing an image of essentially dry pressure-transferable material by offset printing which comprises (a) fastening (1) a printing member having printing areas comprising a radiation-sensitive addition polymerizable monomer and a thixotropic agent and coplanar complementary hardened areas embodying a polymer of said monomer, and said thixotropic agent, and (2) a receptor sheet on opposite segments of the same printing roller; rotating in surface contact and in synchronism (i) said printing member and roller and (ii) an offset roller that is one-half the diameter of the printing roller so that the offset roller rotates at twice the speed of the printing roller; and

(c) containing the rotation of said rollers a plurality of times for the printing of each image, portions of monomer and thixotropic agent in the printing areas being successively transferred on each rotation from the printing member, first to the offset roller, thence to the receptor sheet to form a printed image of the desired density of monomer and thixotropic agent by plural transfers to the same receptor sheet.

2. A process as defined in claim 1, where said printing material is one of at least two different colored materials of the same subject and after image transfer from said material, it is removed and a second material of the same subject but of different color is locked in register and the image of said second material is transferred to said receptor.

References Cited UNITED STATES PATENTS 958,484 5/1910 Evans et al. 101137 2,060,082 11/1936 Johnson et al. 101382. XR 2,280,799 12/1945 Davidson 10l-217 2,417,496 3/1947 Huebner 101-382 XR 2,427,904 9/1947 Davidson 101217 2,759,416 8/1956 George et al 101-217 2,937,593 5/1960 Ritzerfeld et al. l014l5.1 2,909,117 10/1959 Crissy 101-137 EDGAR S. BURR, Primary Examiner.

US. 01. X.R. 101 45o, 137

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