Apparatus For Post-exposure Treatment Of Lithographic Plates

Abstract

Apparatus for post-exposure treatment of lithographic plates comprising a horizontal endless belt for transporting a lithographic plate successively to, through and past a series of operating stations. The apparatus includes a carriage at one of the stations mounted above the belt for reciprocating movement transverse to the belt, rubbing members rotatably carried by the carriage for rubbing developing composition onto the lithographic plate as it is transported on the belt, and a mechanism movable with the carriage for rotating the rubbing members as the carriage is reciprocated.

Parent Case Text

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of our copending application Ser. No. 745,736, filed July 18, 1968, now abandoned.

Description

The invention relates to process and apparatus for post-exposure treatment of lithographic plates to press-ready condition by the "additive process," and the apparatus aspect thereof represents a compact, simplified, and within limits, more economically operatable improvement upon the apparatus disclosed in the copending application of Harrell, Essmueller and Bax, Ser. No. 729,040, filed May 14, 1968, now U.S. Pat. No. 3,608,464.

One object of the invention is to expedite the post-exposure treatment of lithographic plates, and to minimize the consumption of chemicals utilized in such treatment.

Another object of the invention is to provide an apparatus for performing automatically the post-exposure treatments of such plates, and to reduce the consumption of materials employed in such treatments.

A further object is to provide an apparatus which is more economical to manufacture and to operate than that disclosed in the aforesaid application of Harrell et al.

These and other objects of the invention, which will become apparent to the skilled in the art as the description proceeds, are accomplished by providing a process and machine wherein the exposed lithographic plate is moved continuously to, through and beyond, stations at each of which one of the steps of the process is performed. Such steps include: (1) depositing metered quantities of developer composition upon the active surface of the plate; (2) spreading the developer composition over the active surface of the plate and rubbing it with a compound motion which involves both circular and rectilinear components, each in plural directions, while the volatile components of the developer composition are being evaporated; (3) washing away with water all of the developer which has not adhered to the light-struck areas on the active surface of the plate; (4) at least partially drying the active surface of the plate; (5) depositing measured quantities of a preservative composition upon the plate and (6) spreading the preservative composition over, and rubbing it on, the plate.

Such continuous movement of the plate undergoing treatment is conveniently accomplished by transporting the plate on an endless belt. The endless belt is preferably smooth enough and held flat enough that when a thin flexible sheet of metal, such as a common lithographic plate, is laid upon it, air is excluded from the interface, and the two "stick" together so long as substantially flat coincidence is maintained, an action which is facilitated if either contacting face is damp with a liquid which, at least to some extent, wets both. Accordingly, the belt is preferably made of a material which is, at least to some extend, phillic to liquids which are phillic to the reverse (non-active) surface of the plate, and the belt is preferably of a material, for example neoprene, which may be vulcanized into endless condition in situ, i.e., while trained around one or more drive-, or guide-, rollers. While such a belt should be kept damp, care should be exercised to have it substantially devoid of unsorbed or flowable liquid at the time it receives a plate.

A salient feature of the invention is the provision of mechanism which both spreads the developer on a plate and rubs it. This is accomplished, in accordance with the present invention, by providing a continuously circulating pressurized system for supplying the developer liquid in metered quantities to a plate, and immediately thereafter to subject the plate to the action of a plurality of rotating rubbing heads which are translated, transversely of the direction of plate movement, while whirling about their own axes, at a speed sufficient to induce air circulation of a character to accelerate the evaporation of at least part of the liquid components of the developer from adjacent increments of the plate's active surface. Each head is equipped with a rubbing member which is essentially porous, non-abrasive and possessed of at least enough resiliency to compress, albeit slightly without permanent deformation. The rubbing members may have some, but preferably little, absorptivity toward the viscous developer. Any natural or synthetic sponge may be used as a rubbing member, but it is preferable that it be one whose average pore size is large, such as the so-called "coarse grain" cellulose sponge of commerce. The "coarse grain" sponge is characterized by the fact that many of its pores are a quarter inch or more in diameter, the average pore size being greater than three-thirty-seconds of an inch with relatively few as small as one-thirty-second inch, as distinguished from "fine grain" sponges whose pores are predominantly on the order of one-thirty-second inch in diameter, and, according to commercial practice, must be no greater than three-thirty-seconds of an inch.

The several rubbing members are preferably mounted in a cluster so that their respective axes of rotation are parallel and spaced apart a distance approximating the diameter (or diagonal) of the individual rubbing members. Preferably, the rubbing members are arranged in pairs with the individual members of a pair rotating in opposite senses so that, at the bight where their respective peripheries closely approach each other, both are moving in the same general direction which may be either parallel with, or transversely of, the direction of movement of the endless belt. A cluster of two pairs of rubbing members is desirable, so that one pair (herein termed the "leading pair") has its bight motion addressed in the direction of plate and belt movement, while another pair (herein termed the "trailing pair") addressed counter to the direction of plate and belt movement. The invention contemplates that the developer be deposited upon a plate on the moving belt at a position ahead, and preferably immediately ahead, of the leading pair of rubbing members. Preferably, the developer is deposited by dropping it in metered quantities from an outlet substantially aligned, in the direction of plate movement, with the bight between the leading pair of rubbing members, and as close as practical thereto.

In accordance with the present invention, the respective rubbing members are maintained, during operation, under slight, but substantially uniform, compression, e.g., enough to compress a coarse grain cellulose sponge normally one inch thick to a thickness of about seven-eighths inch. While under such compression, and with an exposed lithographic plate moving thereunder, the respective rubbing members are moved with a compound motion, in rotation about their own axes, and in translation crosswise of the endless belt, and at right angles to the direction of belt movement. Hence, the relative movement between a pair of rubbing members and a plate undergoing movement involves not only relative rotation in opposite senses, but also relative translation in two rectilinear directions.

The rectilinear translation crosswise of the belt is achieved by mounting the cluster of rubbing members upon a carriage which is reciprocated in the crosswise direction with a stroke whose amplitude preferably exceeds the width of the belt, so that at least part of each rubbing member will overhang the edge of the endless belt at one end or the other of the reciprocatory stroke. Thus, the edge of the belt acts as a scraper blade to remove excess developer from that or those rubbing members which will be trailing, in the reciprocatory respect, on the impending stroke. In spite of the fact that such imposes a practical limit upon the widthwise (of the belt) dimension of a plate being treated, it is preferred that the frequency of reciprocation of the rubbing carriage be so coordinated with the speed of the endless belt, that the plate move longitudinally no more than about a diameter (or diagonal) of a rubbing member while the rubbing carriage is making a complete cycle of reciprocation transversely of the direction of plate movement in the belt. Hence, the lineal speed of the rubbing carriage must be substantially greater than the lineal speed of the belt.

In order to minimize the time consumed in reversing the carriage stroke (twice during each complete cycle of reciprocation) and to minimize the mechanical shock involved in such reversals, the invention contemplates a carriage drive mechanism which, during operation, moves continuously in the same direction and remains constantly in engagement with the carriage. The latter is accomplished by an endless chain and sprocket drive in which one chain-link or -pin is so connected in force-transmitting relationship to the carriage that, at each end of a reciprocatory stroke, the carriage's rate of deceleration to zero velocity, and its rate of acceleration from zero to the chordal velocity of the chain, is the same as that undergone by any chosen point on the chain as it reverses direction in moving about a sprocket at an end loop, to wit, but for mechanical looseness, like the trigonometric function "versine" decreases from a maximum to zero, and then increases to the maximum as a radius moves from one end of a diameter to the other end of that diameter.

To transmit motive force from the chain to the carriage, the chosen chain-link or -pin is connected to the carriage by means which accommodates relative motion (between the chosen link or pin and the carriage) in the direction perpendicular to a plane which includes the fixed axes of both sprockets. Thus, when the axes of the sprockets are horizontal, the aforesaid relative motion is vertical; and, when the axes of the sprockets are vertical, the relative motion is horizontal. One of the chain and carriage may have an affixed raceway, while the other has an affixed follower caged in the raceway; and the raceway preferably has a length sufficient to accommodate movement of the follower between opposite extremities of the sprockets' pitch circle diameter. The latter, while not imperative, reduces mechanical strain on the follower.

The same reciprocatory drive may also motivate a reciprocating rubbing member at the preservative station of the apparatus, and, if desired, may, through a rack and pinion, impart rotary motion to one or more such rubbing members.

After an increment of a plate moving with the endless belt has departed from the region of operation by the developer rubbing members, the active surface of the plate is subjected to a spray of water which erodes and washes from the plate passing therebeneath all of the loose material, solid and liquid, of the developer which has not, during the preceding treatments, become adhered to the light-reacted areas of the plate. Beyond the water spray station, a wiping member of the squeegee type makes water-sealing engagement against the active surface of the plate. Such a squeegee may be either a roller or a blade, in either event having a contacting part of rubber, or other relatively soft material, which makes a substantially water-tight seal with the plate traveling therebeneath. Thus unsorbed and flowable water on the active surface of the plate is wiped off as the belt moves the plate under the squeegee, and such water is drained sidewise off the belt, as by tilting the belt at that region; and any tendency for such water to flow, counter to the belt movement, back into the developer station may be overcome by tilting the apparatus, or at least that region of the belt, so that gravity prevents such counterflow.

Beyond the last-mentioned squeegee, the plate passes to a preservative station under another rubbing member, which may be of like character to those previously mentioned, but not necessarily so because the preservative composition usually requires less rubbing then does the developer composition. Prior to passing under the preservative rubbing member, there is dropped upon the dewatered moving plate metered quantities of the preservative composition. As at the developer station, one, or a series of spaced metering devices is arranged so as to drop the requisite quantity (usually less than that of the developer) of the preservative composition upon the subjacent plate. The preservative composition then undergoes rubbing of like character to, but lesser degree than, that which the developer previously underwent. Upon emerging from the preservative rubbing member, the plate is squeegeed to remove excess "preservative" (including entrained water and organic solvent). This completes the post-exposure treatment in situations where the treated plates are transported individually from the apparatus to the press, as the time consumed in such transportation and in mounting the plates on the press is sufficient to permit natural evaporation of such water and organic solvent as may remain entrained in the residual preservative after the last-mentioned squeegeeing. On the other hand, where it is desired to accumulate plates emerging from the apparatus by stacking them one upon the other, it is advisable to expedite the evaporation of water and organic solvent as by passing the plates individually through any suitable dryer before they are stacked.

The series of post-exposure treatment operations requires an elapsed time which is but a small fraction of that required when the operations are carried out by hand, and the drying aspect of the development operation, as well as that of the preservative application, is expedited by the air circulation induced by the motion of the several rubbing members.

One form of apparatus embodying the inventions is disclosed in the accompanying drawings, in which:

FIG. 1 is a perspective view taken from above the plate input end of the apparatus, and looking toward the discharge end thereof;

FIG. 2 is a sectional view taken along line 2--2 of FIG. 1;

FIG. 3 is a sectional view corresponding to FIG. 2, but taken along line 3--3 of FIG. 1, and showing a relationship of parts not shown in FIG. 2, as well as omitting certain other parts;

FIG. 4 is a sectional view taken along line 4--4 of FIG. 1, showing the rubbing carriage for the developer station on enlarged scale, and with portions broken away to reveal the relationship of driving parts;

FIG. 5 is a sectional view taken along line 5--5 of FIG. 4, and showing the gear system for driving the cluster of rubbing members in rotation;

FIG. 6 is a perspective view showing the bottom or plate-engaging surface of one of the rubbing members shown in FIG. 4;

FIG. 7 is a perspective view showing the same rubbing member illustrated in FIG. 6 from the upper or mechanically connecting surface thereof;

FIG. 8 is a detail view in side elevation, showing the link of the drive chain for the rubbing carriage which is equipped with the means for transmitting reciprocatory force to the rubbing carriage;

FIG. 9 is a perspective view showing the storage and distribution systems for the developer composition and the preservative composition;

FIG. 10 is a top plan view of the apparatus shown in FIG. 1, with the rubbing carriage in a different position; and

FIG. 11 is a sectional view taken along line 11--11 of FIG. 10.

FIG. 12 is a sectional view of the preservative station of FIG. 2 with a rotatable rubbing member.

The embodiment illustrated in the drawings includes an endless belt 1, the front loop of which is trained about a roller 2, and the rear loop of which is trained about a roller 3. An adjustable tension roller (not shown) can be provided on the lower reach of the belt.

An exposed lithographic plate to be treated is fed into the apparatus adjacent roller 2, and transported on the upper reach of belt 1 toward roller 3. The roller 3 is, in the embodiment shown, a drive roll, while the roller 2 is an idler roll, so that the upper reach of the belt moves from the roller 2 toward the roller 3, and is constantly tensioned in the direction of its movement to, through, and beyond, a superimposed idler roll 4, a developing station 5, a washing station 6, a preservative station 7, and a squeegee roll 8, all as indicated in FIG. 1.

At the developing station 5, there is provided a carriage 9, which is driven in reciprocation to translate transversely of the direction of the movement of the upper reach of belt 1. The carriage is mounted upon spaced trunnions 10 and 11, which guide it during the aforesaid reciprocatory translation; and the carriage is driven in such reciprocatory translation by an endless chain 12 threaded about an idler sprocket 13 and a driven sprocket 14. The sprockets 13 and 14 are mounted for rotation about shafts supported by cross-bar 15, from which there projects radially a bracket 16 for mounting a motor 17. The motor 17 drives shaft 18 (and sprocket 14 fixedly mounted on that shaft) in rotation which may be either clockwise or counterclockwise, but is always in the same direction.

THe trunnion 10 has its opposite ends mounted respectively in links 19 and 20, while the opposite ends of said links are hinged on trunnion 11, which is permanently mounted to opposite pedestals 21 and 22, which are in turn securely mounted upon the side frames of a table 23 which subtends the developing station portion of the upper reach of belt 1. A comparable pair of pedestals 24 and 25 support the front ends of links 19 and 20, and may be provided with any suitable means 124 and 125 for releasably latching or detenting such front ends, and the intervening trunnion 10, in the operating position shown in FIG. 1. The hinging of the parts for limited rotation about trunnion 11 serves no function in the operation of the apparatus, but does facilitate the removal and replacement of expendable parts of a rubbing assembly mounted upon and movable with carriage 9, later to be described. Since motor 17 is a part of the thus hingedly mounted assembly, the motor is preferably equipped with a mercury switch, or other tilt-sensitive device, to automatically disconnect the source when the hingedly mounted assembly is moved out of the position shown in FIG. 1 and toward the position shown in dotted lines in FIG. 3.

An electric motor 26, having a drive shaft 27 projecting axially downward, is mounted upon carriage 9, and its shaft 27 is equipped with a pinion 28 which engages a gear 29 and drives the same in rotation. Gear 29 is one of a cluster of four identical gears 29, 30, 31 and 32, which intermesh with each other, as shown in fig. 5, so that alternate ones of the cluster rotate in opposite directions about their respective shafts.

The lower end of each gear shaft projects beneath carriage 9, and has removably mounted thereon a rubbing member 33 of which there are four in the embodiment shown. As clearly shown in FIGS. 6 and 7, each rubbing member is preferably composed of a slab 34 of coarse grain cellulose sponge, or other comparable material, secured to a metal plate 35. The obverse and reverse faces of the rubbing members are shown in FIGS. 6 and 7, respectively; the obverse face being the one which makes rubbing engagement with a plate undergoing treatment; and the metal plate being the reverse face. In the form shown, the rubbing members are of circular periphery, but other curvilinear or polygonal shapes may be employed. The obverse face of each such rubbing member has a central aperture 36 which is preferably acircular, and shown as rectangular. Such a central aperture accomplishes a dual function: first, it accommodates parts which project downwardly from discs 37 (one of which is fixedly mounted on each of the shafts for gears 29-32) through keyways 38 in mounting plate 35 for snap-on connection with the respective rubbing members 33, and provides access to retaining screws therefor; and second, if acircular, it tends to keep in motion any developer composition which may accumulate therein and thereby minimize caking thereof with resultant short-radius streaking of a lithographic plate undergoing treatment.

The reciprocatory traversing movement of carriage 9 and its adjunct parts transversely of the motion of belt 1 (and transversely of a lithographic plate moving with the belt) is accomplished without reversing the direction of rotation of drive sprocket 14, or the direction of movement of chain 12 about its orbit by means now to be described. The drive chain 12 is a common link and roller, or link and block, endless chain. In such a chain, opposite links 39 are connected by a common pin 40 either to preceding and succeeding links, or to adjacent blocks. The invention contemplates that one such pin in the chain be equipped with a round-ended cylindrical projection or follower 41 at one side of the chain, and with a ball bearing projection or follower 42 at the other side of the chain. The follower members 41 and 42 project sidewardly from the chain in opposite directions, as shown in FIG. 8. The parts 41 and 42 are thus free to rotate about the axis of pin 40, and may, if desired, be separated from links 39 by nylon washers 43 and 44. The driving force for carriage 9 is transmitted from chain 12 through the single pin 40 of the chain which has bearing members 41 and 42 associated with it. The transverse components of the motion of pin 40 are transmitted to the carriage through a C-shaped yoke 45, shown in FIG. 4. The yoke 45 is permanently affixed to carriage 9, and moves with it in translatory reciprocation horizontally at right angles to the direction of movement of the belt 1. For confining, yet accommodating vertical movement of, bearing member 41 at the end loops of chain 12, the yoke 45 is provided with a raceway 46 in the continuous side of the C-shaped yoke, and likewise the bearing member 42 is movably confined in opposite discontinuous, but vertically aligned, raceways 47 and 48 in the discontinuous side of the yoke. These raceways are cross-sectionally contoured to be substantially contrageneric with the cross-sections of bearing members 41 and 42, respectively, and to accommodate said bearing members for free running vertical movement while held captive therein, as pin 40 of the chain changes direction at either sprocket, 13 or 14, from the upper chord of chain 12 to the lower chord thereof, or vice versa. To facilitate the installation and caging of the ball extensions 41 and 42 in the raceways, the yoke 45 may have a separable part 145 which constitutes both the top bar of the C shape and the upper dependent in which raceway 47 is located.

Upon the carriage 9, there is also mounted a metering device 49 for delivering measured quantities of developer composition, and depositing it, either as a continuous stream or drop by drop at spaced intervals, on a subjacent lithographic plate 50 at a position immediately ahead of the rubbing members. While economy of developer composition may be effected by the drop-by-drop technique, the continuous stream technique is preferred for assurance of quality. In any event, the developer composition is preferably deposited on a subjacent plate at a position which will cause each increment to be caught in the bight between the leading pair of rubbing members 33 and 33', as seen in FIG. 10. At this position, each member of the leading pair of rubbing members 33 and 33' (when rotating as shown in FIG. 10) has its increments adjacent the bight moving toward each other and generally rearward, i.e., in the direction of movement of the belt 1. Accordingly, such increments of so-deposited developer, as are not smeared on the plate by the leading pair of rubbing members, are cast toward the trailing pair of rubbing members and are either smeared on the plate by them, or cast back toward the leading pair.

The metering device 49 is supplied with developer from a tank 51 which can be arranged at any convenient place about the apparatus, but, for clarity of illustration, is shown mounted upon a stationary part of the apparatus over the washing station, but it will be understood that the tank can be mounted upon, and movable with, carriage 9, if desired. The tank 51 has a discharge line 52 extending to a pump 53 which discharges through a line 54 to a T 55, one side of which leads to a T 56, one branch 57 of which returns to tank 51 and terminates with a fixed restrictive orifice located within the tank; and the other branch 58 of which extends to a flexible tube 59 leading to the developer metering device 49, as shown in FIG. 1. In order to prevent the flexible tube 59 from becoming entangled with adjacent parts during the translatory reciprocation of carriage 9, the flexible tube 59, which conducts developer composition to metering device 49, and the electrical conductors 60, which control operation of the metering device 49, are each mounted upon a spring strip 61 pivotally secured at one end 62 to channel 15, and pivotally secured at the other end 63 to carriage 9. The spring strip 61 may be formed of stainless steel having a thickness (e.g., 0.020 inch) such that it is readily bowed in the thickness direction without exceeding its elastic limit, a width sufficient (such as 1 inch or more) to make it relatively stiff and resistant to bending in the widthwise direction under the load which it is required to sustain, and of a length sufficient to reach from the pivotal connection 62 to pivotal connection 63 when the carriage 9 is at either extreme of its stroke, but when the carriage is intermediate the ends of its stroke, the strip 61 bows as shown in FIG. 1. The tube 59, as well as electrical conductors 60, are anchored to the spring strip 61 not only at the ends of the latter, but at at least one intermediate position, and the security of such anchorage is preferably such as to prevent creepage of either tube 59 or conductors 60 relative to the spring strip during repeated bowing and straightening of the strip.

In the embodiment shown, the metering device 49 is controlled electrically to open and close a valve therein at predetermined intervals, as, for example, the time interval required for the carriage to move 4 to 6 inches. While the tank 51 may be covered, in the arrangement shown, it is open to the atmosphere, and in order to assure the existence of necessary pressure on the developer composition in flexible tube 59 as and when the valve in metering device 49 opens, means is provided for causing the liquid developer in pipe 56 to preferentially flow through branch 58 and tube 59. Such means may comprise a constriction in branch 57, or making the entire branch 57 of smaller bore than branch 58 and tube 59, or providing a valve in branch 57 which automatically closes when the valve in metering device 49 opens. Alternatively, especially when the developer is thixotropic, the branch 57 may be replaced by a return line from metering device 49 to tank 51, so that there is a continuous flow of developer past the inlet orifice for metering device 49. In either event, the continuous movement of developer from tank 51 through pump 53 and back to tank 51 maintains the developer liquid in well-agitated condition, but when thixotropic developer is employed, the aforesaid alternative prevents such increase in its viscosity that supply to metering device 49 is impeded.

For the purpose of ready removal of residual developer composition from tank 51, as at shut-down of the apparatus at the end of a day, T 55 is also connected to a line 64 controlled by a valve 65, which leads to a flexible tube 66 whose open end is situated at a convenient place for capturing the developer discharged therethrough. Under operating conditions, however, valve 65 is closed.

For convenience in removing and replacing the rubbing members 33 which are expendable, the entire carriage 9 and its associated parts, including trunnion 10, chain 12, sprockets 13 and 14, motor 17, and the spring strip 61, is mounted for hinging about trunnion 11 (as shown in broken lines in FIG. 3) to an extent sufficient to enable the rubbing members 33 to be readily accessible.

At the washing station 6, there is provided an inverted trough 67 within which there is housed a water header having a series of transversely spaced nozzles 68 for spraying water downwardly and away from the developing station, upon subjacent increments of plate 50 as they pass beneath the trough 67. Such rinses away the hydrophilic components of the developer which have not become adhered to the now-hardened lacquer-forming components of the developer. While normally the volume of water so sprayed is insufficient, particularly when the belt is moving to tend to flow backward toward the developing station, the entire apparatus may be tilted slightly to eliminate any such tendency. As shown, however, the table 23 terminates short of the washing station so that there is no supporting member in contact with the lower side of the upper reach of belt within the washing station. This has the two-fold effect of reducing the mechanical drag on the belt, and of facilitating the elimination of washing water without back-flow into the developing station.

At the rear end of the washing station, there is provided a squeegee which, in the form shown, is a rubber lip 69 biased into contiguity with the upper reach of belt 1, and consequently when a plate, such as 50, moves therebeneath on the belt, the rubber lip 69 flexes slightly to wipe all flowable water from a plate as it passes. The thus removed water flows over the edges of belt 1 and is caught by sink 85, shown in FIG. 2. Preferably, the squeegee 69 engages the upper surface of belt 1 at a position where the belt is supported as by table 230 which also sustains the load of rubbing under pressure at the preservative station 7.

The preservative station 7 is immediately behind the squeegee device just mentioned. At station 7, there is provided one or more metering devices 70 for depositing metered increments of a preservative composition upon a subjacent plate. While, in the embodiment shown, the metering device 70 is stationary, it will be understood that, if desired, it can be reciprocated in a manner comparable to the reciprocation of metering device 49, but otherwise, it suffices to provide metering devices 70 permanently located in spaced relation 8 to 10 inches apart transversely (widthwise) of the belt 1.

Metering device 70 is supplied with preservative composition from a tank 71 which, as shown in FIG. 9, is equipped with a pump 72, which discharges into a tee 73, one leg of which extends to tube 74 leading to metering devices 70. As in the case with metering device 49, metering devices 70 are electrically controlled to regulate the time interval between successive discharges, and they may, if desired, have a master control which deactivates all of them save when a plate is present therebeneath. The other leg of T 73 is connected to a pipe 75 having a valve 76, which is closed during normal operation of the apparatus, but, as in the case of the developer, may be opened to drain tank 71 at shut-down. While the nature of the preservative composition is usually not such as to require continuous agitation during operation, where the preservative composition does require it, line 74 may be provided with a branch leading back to tank 71, as in the case of the developer system.

At the preservative station 7, and immediately behind the metering device 70, there is also provided means for rubbing the preservative composition and spreading it throughout the length and breadth of a subjacent plate. Such a device may, if desired, be in the form of a reciprocating carriage comparable to carriage 9, and in such case, the metering device 70 may be mounted upon, and movable with, such a carriage, but need not embody a gang of rubbing members, as one will suffice. However, in the embodiment shown in the drawings, the rubbing means is mounted upon an arm 78 having a boss 79 encircling trunnion 11 (for both sliding movement axially of, and rotational movement about, trunnion 11), and restrained against movement relative to the carriage 9 in the direction of the latter's reciprocation. Thus, the bar 78 reciprocates with the carriage 9, but may be hinged relative to the carriage 9 about trunnion 11 as an axis when the carriage and adjunct structure are tilted to the position shown in dotted lines in FIG. 3, or the arm 78 may be independently tilted in the counterclockwise direction from the position shown in FIG. 2. As clearly shown in FIGS. 2 and 10, the arm 78 projects rearwardly from trunnion 11 over the washing station 6 and into the preservative station 7, so that its free end can support a rubbing member for operation upon a lithographic plate at the preservative station. Two forms of rubbing member are illustrated in the drawings. In the form illustrated in FIGS. 2 and 10, a single rubbing member 77, of the same material as rubbing members 33, but of length (widthwise of the belt) approximately equal to twice the diameter of a rubbing member 33, is fixedly mounted upon the rearward extremity of arm 78. Hence, the rubbing member 77 is reciprocated in translation concurrently with carriage 9, and the rubbing member is so disposed that its stroke (widthwise of the belt) in such reciprocation is equal to that of the leading pair of rubbing members 33 and 33' on carriage 9. Thus, the rubbing member 77 operates upon a subjacent plate with compound relative motion consisting of the component which is moving the plate lengthwise of the belt 1, and the component which is moving the rubbing member 77 in reciprocation widthwise of the belt. Under circumstances depending upon the materials employed, where it is desirable to impart a rotational motion to the rubbing member at the preservative station, the rubbing member 77 may be replaced by a rotatable one 770 as shown in FIG. 12. The rotatable rubbing member 770 is preferably formed of the same material as rubbing members 77 and 33, and is preferably circular in external periphery, but due to space limitations at the preservative station, is somewhat smaller in diameter than the rubbing members 33. The rotatably rubbing member 770 is mounted on the lower end of a shaft 771, retained in a bearing block 772, which is secured to the free end of arm 78. Shaft 771 has affixed to it a pinion 773 which engages a fixed rack 774 extending transversely of the apparatus, and mounted upon a stationary bar 90, as shown in FIG. 3.

Immediately after emerging from the ambit of rubbing member 77, the leading edge of a plate, such as 50, enters the nip between idler roll 8 and belt 1, and as the belt 1 makes the turn about drive roll 3, the plate which has been operated upon is peeled from the belt and delivered to a discharge apron 80. While the roll 8 may be spring biased toward the belt, such is likely to permanently deform the surface of roll 8 when the apparatus is idle, as over a long weekend, unless some means is provided to automatically release the bias when the apparatus is idle. A simpler safeguard against such deformation is to mount one end of roll 8 with a fixed nip as shown in FIG. 1, while the other end is provided with a suitable quick-release mechanism 108 as shown in FIGS. 2 and 3.

A receiving apron 81 is arranged at the front end of the apparatus to guide a plate to be treated into the nip between idler roll 4 and belt 1, and apron 81 is equipped with a plate sensor 82 which is the operator of an electric switch, and so disposed that the switch is normally open, but when a plate passes thereunder, the switch is closed to initiate, in predetermined sequence, the energization of a plurality of electrical circuits which respectively control motors 17, 26, and pumps 53 and 72, as well as metering devices 49 and 70; movement of the belt 1 being similarly controlled and so interlocked with the plate sensor 82 that the latter will not initiate the energization of any circuit unless the belt is running.

Since relative movement, between the belt 1 and a lithographic plate being transported by it, is restrained only by surface tension which requires substantial exclusion of air from the belt-plate interface, it is important that the belt 1 be sufficiently wet with liquid to assure such exclusion of air from the interface that the plate adheres to the belt with sufficient tenacity to prevent its movement relative to the belt while being operated upon by the rubbing members. Hence, means for wetting the belt prior to reaching its loop about idler roll 2 is provided. In the embodiment shown, such a means comprises a water spray head 83 situated below the lower reach of belt 1, and disposed to direct a spray of water upwardly onto the lower surface of the lower reach of belt 1 for the full width thereof. In order to assure that there is no flowable liquid on the belt as it passes under idler roll 4, a squeegee device 84, shown in the form of a wiping blade in FIGS. 2 and 3, is provided for surface engagement with the belt as it makes the turn about idler roll 2. Thus, when an increment of belt 1 comes into contact with the inactive surface of a lithographic plate being fed through the nip between idler roll 4 and belt 1, the belt is damp at least to the extent that whatever pores may be in the belt are filled with liquid, and there is at least a monomolecular film of liquid on the surface of the belt, but there is substantially no flowable or unsorbed water on the surface of the belt. This precaution has a two-fold effect: first, it minimizes the transfer of water from belt 1 to idler roll 4 when idler roll 4 is running in contact with the belt, i.e., with no plate intervening; and second, it minimizes the likelihood that liquid will be squirted out of the interface between a plate and the belt at the developing station when the plate is being squeezed between rubbing members 33 and the belt. While, in the embodiment shown, the belt is pre-wet with water, it will be understood that other liquids can be used for this purpose. With the arrangement shown, water is discharged above the belt at station 6 and drains into collector sink 85, which also receives the drippings from the lower reach of belt 1, as well as the excess discharged by spray head 83 and the drippings from squeegee member 84.

In situations where it is desired to stack the processed lithographic plates one upon the other immediately as they emerge on to discharge apron 80, it is desirable to completely dry them before they are stacked one upon the other, and accordingly the discharge apron 80 may be equipped with any suitable drying apparatus, such as one which directs a stream of warm, dry air against the emerging plate, and before it is stacked. Since, in accordance with the present invention, a plate, such as 50, being processed in the apparatus is held fast on the belt 1 by virtue of moisture at the interface, it is of particular importance to dry the lower surface of any such plate which is to be stacked upon another because the moisture on the inactive surface of a plate is more detrimental to the active surface of the plate next below it in the stack than is residual moisture in the active surface of the lower plate. Accordingly, the invention contemplates the provision of a warm air duct 86 for conducting a stream of warm, dry air from a suitable source, and directing it through a series of louvers 87 in discharge apron 80, so as to impinge the warm air against the inactive surface (which has been in contact with belt 1) of a processed lithographic plate as it passes over the louvers 87.

For features of the apparatus which are not specifically described herein such as the character and speed of the belt 1, the mode of securing the lithographic plate against movement relative to the belt, automatic control of discharges, and the material of which the rubbing members may be formed, reference may be had to the aforesaid application of Harrel et al.

In the operation of the device, it is preferred that movement of the belt and release of water from spray head 83 be initiated first to pre-condition the belt for the reception of a plate. After the belt has moved for a distance sufficient to bring the leading increment, wet by spray head 83, to the nip between idler roll 4 and the belt, an exposed lithographic plate is moved across apron 81 into contact with sensor 82, whereupon the motors 17 and 26 and developer pump 53 begin to operate. Thereafter, within an increment of time no greater than that sufficient to bring the leading edge of the plate into position between the belt and the leading pair of rubbing members 33 and 33', metering device 49 is energized to release a charge of developer composition near the leading edge of the incoming plate; within an increment of time no greater than that sufficient to enable the leading edge of the plate to reach washing station 6, the supply of water to header 68 is opened; and within no greater than the increment of time required for the leading edge of the plate to reach preservative station 7, pump 72 and metering device 70 are energized. In the embodiment shown, all these devices remain energized, at least periodically, until movement of belt 1 is stopped, but it will be understood that appropriate devices sensing the presence or absence of a plate on the belt, subjacent the devices operating thereon at the successive stations 5, 6 and 7, may be provided for discontinuing the operation of such devices sequentially when there is no plate to be operated upon by them respectively. Absent such plate-present sensors in the respective stations, means which is adjustable in accordance with the dimension (in the direction of movement of the belt) of the plate may be provided for automatically discontinuing the operation of the devices at the respective stations.

At developer station 5, increments of developer are dropped on a subjacent plate throughout the reciprocatory stroke of carriage 9 in both directions, and concurrently rubbed over and into the active surface of the plate. Preferably, the speed of reciprocation of the carriage 9 is so coordinated with the speed of belt 1 that any given increment of plate is operated upon by at least two of the rubbing members 33 during each half-cycle of reciprocation, but where speed of the operation is more important than quality of the development, it is sufficient that each increment of the plate be operated upon by at least one of the rubbing members during a whole cycle of reciprocation. In either event, during a full cycle of reciprocation of the carriage 9, the path of a given rubbing member on a lithographic plate undergoing treatment on the moving belt is "V" shaped, or half "W" shaped, depending upon the position chosen for the beginning of the cycle; and to achieve optimum results with the form of apparatus shown, the speed of belt 1 is so coordinated with the speed of the carriage's reciprocation that the belt moves no more than a radius of a rubbing member 33 during a complete cycle of reciprocation; but to decrease the time required for the entire operation, more rubbing members may be added to the cluster thereof on the carriage 9, and the speed of the belt increased accordingly. Where, as shown in FIG. 10, the width (i.e., parallel with trunnions 10 and 11) of the belt 1 is sufficiently less than the length (i.e., parallel with trunnions 10 and 11) of the stroke of carriage 9 is such that at least half the surface of the lefthand pair of rubbing members (33' and the one behind it) overreach the lefthand edge of the belt at the lefthand extremity of the reciprocatory stroke, and conversely at least half the area of the righthand pair of rubbing members (33 and the one behind it) overreach the right edge of belt 1 at the right extremity of the reciprocatory stroke. Since the rubbing members are resilient and, when in contact with a plate or the belt, are under some compression, the increments thereof which overhang the edge of the belt at the respective ends of the reciprocatory stroke momentarily expend as they leave the belt, but are recompressed when, no more than 180.degree. of rotation later, the re-encounter the edge of the belt. Hence, the edge of the belt serves as a squeegee member to remove any excess of developer as the momentarily expended increments of the rubbing member are re-compressed upon emerging from a zone at which their compression was released into a zone wherein their compression is resumed. This, together with the feature of discharging the developer composition from the reciprocatory carriage, at spaced intervals during its strokes, effects improved utilization of the developer composition, and spreads it uniformly thin so that evaporation of its volatile components is accelerated -- which latter is further induced by the air turbulence induced by the rotating, counter-rotating, rubbing members.

Because of the compound rubbing motion involved, the construction and mode of operation of the cluster of rubbing members on carriage 9 is ideal for the post-exposure treatment of lithographic plates, not only with developer composition, but also with preservative. The compound relative motion between a lithographic plate undergoing treatment and the cluster of rubbing members involves a number of components; longitudinal rectilinear motion in the direction of the single-headed straight arrow in FIG. 10; transverse rectilinear motion back and forth in the directions indicated by the double-headed straight arrow in FIG. 10; curvilinear motion in the clockwise direction by half the rubbing members in the cluster; and curvilinear motion in the counterclockwise direction by the other half of the rubbing members in the cluster. A given increment of a lithographic plate undergoing treatment is subjected to at least three of those motions concurrently; and within a given half-cycle (indeed, within a fractional part of each stroke, which amounts to a maximum of slightly more than the diameter of a rubbing member 33) of the carriage's reciprocation, such increment of the plate is subjected to all four of those motions. Not only is the character of the relative motion variegated, but the speed thereof is variegated insofar as concerns the rotation of the rubbing members because the relative speed between a point on a lithographic plate momentarily situated near the periphery of a rubbing member 33 is greater than the relative speed at that same point on the plate when it assumes a location nearer the center of rotation of a given rubbing member.

In contrast with the variegated rubbing action which takes place at the developing station, that which takes place at the preservative station is not necessarily variegated to the same degree. While, in the form shown in FIG. 2, the rubbing action at the preservative station involves only a compounding of longitudinal and transverse rectilinear motions, there are certain preservative compositions which perform better if rubbed in a manner comparable with, but not necessarily in the degree of, the rubbing action which takes place at the developing station; and accordingly it is contemplated that where such is necessary, the rectilinearly reciprocating rubbing member 77 at the preservative station be replaced with one, of the character shown in FIG. 12, which rotates while reciprocating, clockwise in one-half cycle of reciprocation and counterclockwise in the other half-cycle of reciprocation. Whether the rubbing member at the preservative station is or is not rotating, the mounting of it with freedom for vertical movement enables its own weight to impose pressure on the plate being rubbed, and such pressure can be varied by adding to or subtracting from the dead weight of the rubbing assembly.

While one complete embodiment of the invention has been illustrated in the accompanying drawings, and has been described hereinbefore, save with respect to some details which are common to the disclosure of the aforesaid application of Harrell et al; and while certain modifications and variations in the apparatus shown in the drawings have been hereinbefore indicated, it is not to be understood that the invention is limited to the specifics of the foregoing disclosure. From the foregoing description, those skilled in the art will readily understand the structure, function and mode of operation of the invention, and realize that it accomplishes its objectives efficiently, expeditiously, and economically.

Claims

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

1. Apparatus for developing lithographic plates comprising a moving endless belt having a substantially horizontal upper reach, said upper reach supporting and transporting an exposed lithographic plate to, through and beyond a succession of operating stations located along said reach, a carriage mounted for reciprocation above said upper reach transversely with respect to said upper reach from adjacent one side thereof to the other, at least one rubbing member mounted on said carriage for reciprocation therewith back and forth across said upper reach, said rubbing member having an active surface disposed for engagement with a subjacent lithographic plate traveling on said upper reach, means mounting said rubbing member for rotation relative to the carriage about an axis substantially perpendicular to said upper reach, means for driving said carriage in reciprocation back and forth transversely across said upper reach, and means for rotating said rubbing member on its said axis as the carriage reciprocates back and forth.

2. The combination of claim 1 in which there is a cluster of rubbing members rotatably mounted on said carriage, and said last-mentioned means rotates different members of said cluster in opposite senses.

3. The combination of claim 1 in which said means for driving said carriage is an endless chain, a pair of spaced sprockets engaging said endless chain to confine the path thereof to spaced chords between the sprockets and end loops at the sprockets, and force-transmitting means interconnecting said chain with said carriage to reciprocate the latter while the chain moves continuously in the same sense about its path.

4. The combination of claim 1 having metering means on the carriage for dropping measured charges of developer composition on a lithographic plate being transported by said upper reach before the plate reaches said rubbing member.

5. The combination of claim 4 having a stationary developer supply tank, means connecting said supply tank with said metering means including a flexible tube for conducting developer fluid to said metering means, and means relatively flexible in the horizontal direction but relatively stiff in the vertical direction for supporting said flexible tube adjacent the carriage and following movement of the carriage during reciprocation.

6. Apparatus for developing lithographic plates comprising a moving endless belt having a substantially horizontal upper reach, said upper reach supporting and transporting an exposed lithographic plate to, through and beyond a succession of operating stations located along said reach, a carriage mounted for reciprocation above said upper reach, a rubbing member rotatably mounted on said carriage, said rubbing member having an active surface disposed for engagement with a subjacent lithographic plate traveling on said upper reach, means for driving said carriage in reciprocation in directions transverse to the movement of said upper reach, and means for imparting arcuate motion to said rubbing member, said means for driving the carriage comprising an endless chain, a pair of spaced sprockets engaging said endless chain to confine the path thereof to spaced chords between the sprockets and end loops at the sprockets, and force-transmitting means interconnecting said chain with said carriage to reciprocate the latter while the chain moves continuously in the same sense about its path, wherein said force-transmitting means includes: a follower mounted on and projecting from one of said carriage and said chain; and raceway means on the other of said carriage and said chain, said raceway means accommodating said follower and transmitting force therebetween throughout the path of said chain.

7. The combination of claim 6 wherein: the follower is affixed to the chain and has a rotatable bearing member disposed outwardly of the chain on at least one side thereof; and said raceway is affixed to the carriage, extends in the direction parallel with the interspace between said chain chords, and is contoured to be substantially contrageneric, but have a free-running fit, with said bearing member as the latter moves about the loops of said path.

8. Apparatus for developing lithographic plates comprising a moving endless belt having a substantially horizontal upper reach, said upper reach supporting and transporting an exposed lithographic plate to, through and beyond a succession of operating stations located along said reach, a carriage mounted for reciprocation above said upper reach, a rubbing member rotatably mounted on said carriage, said rubbing member having an active surface disposed for engagement with a subjacent lithographic plate traveling on said upper reach, means for driving said carriage in reciprocation in directions transverse to the movement of said upper reach, and means for imparting arcuate motion to said rubbing member, metering means on the carriage for dropping measured charges of developer composition on a lithographic plate being transported by said upper reach before the plate reaches said rubbing member, a stationary developer supply tank, means connecting said supply tank with said metering means including a flexible tube for conducting developer fluid to said metering means, and means relatively flexible in the horizontal direction but relatively stiff in the vertical direction for supporting said flexible tube adjacent the carriage and following movement of the carriage during reciprocation, wherein said last-named means is a strip of material having:

a. resiliency sufficient to withstand repeated bowing about an arc whose radii are substantially parallel with the thickness of said strip; and

b. stiffness sufficient to resist bowing about an arc whose radii are substantially parallel with the width of said strip;

said strip being substantially wider than it is thick, and substantially longer than it is wide, means connecting one end of said strip to a stationary member, hinge means connecting the other end of said strip to said carriage, and the length of said strip being at least about half the reciprocating stroke of said hinge means.

9. Apparatus for developing lithographic plates comprising a moving endless belt having a substantially horizontal upper reach, said upper reach supporting and transporting an exposed lithographic plate to, through and beyond a succession of operating stations located along said reach, a carriage mounted for reciprocation above said upper reach, a rubbing member rotatably mounted on said carriage, said rubbing member having an active surface disposed for engagement with a subjacent lithographic plate traveling on said upper reach, means for driving said carriage in reciprocation in directions transverse to the movement of said upper reach, and means for imparting arcuate motion to said rubbing member, said carriage being entrapped on and movable along parallel spaced guide rails, means connecting said guide rails together at each of their ends, means permanently mounting and holding captive both ends of one of said guide rails, means releasably mounting both ends of the other guide rail, and said first-mentioned guide rail providing an axis about which said other guide rail and said carriage may be hinged to make said rubbing member accessible for replacement.

10. Apparatus for developing lithographic plates comprising means for continuously conveying an exposed lithographic plate along a predetermined path with the exposed face of the plate facing up, means for applying a developer to said face, a carriage mounted for reciprocation above said path and transversely with respect to said path, at least one rubbing member for said developer mounted on said carriage for reciprocation therewith back and forth across said path, said rubbing member having an active surface disposed for engagement with a subjacent lithographic plate traveling in said path, means mounting said rubbing member for rotation relative to the carriage about an axis substantially perpendicular to said path, means for driving said carriage in reciprocation back and forth transversely across said path, and means for rotating said rubbing member on its said axis as the carriage reciprocates back and forth.

11. Apparatus as set forth in claim 10 having a plurality of rubbing members each mounted on the carriage for rotation relative to the carriage on an axis substantially perpendicular to said path, said rubbing member rotating means being carried by the carriage and including means for rotating different rubbing members in opposite directions.

12. Apparatus as set forth in claim 10 wherein said means for driving the carriage comprises an endless chain drive including an endless chain having a reach traveling in one direction transversely across said path and another reach traveling in the opposite direction transversely across said path, and means for interconnecting the carriage and said one reach at one end of said chain drive for moving the carriage in said one direction across said path and for interconnecting the carriage and said other reach at the other end of said chain drive for moving the carriage in the opposite direction across said path.

13. Apparatus as set forth in claim 10 having support means extending in downstream direction from said carriage reciprocable with the carriage, metering means for dropping measured charges of preservative composition on a lithographic plate moving in said path downstream from said carriage, and rubbing means carried by said support means for distributing said preservative over said lithographic plate.

14. Apparatus as set forth in claim 13 wherein said preservative rubbing means comprises at least one preservative rubbing member rotatably mounted on said support means, and means for rotatably driving said preservative rubbing member.

15. Apparatus as set forth in claim 14 wherein said preservative rubbing member driving means comprises a stationary rack extending transversely relative to said path and a pinion carried by said preservative rubbing member in mesh with said rack for rotatably driving said preservative rubbing member as it is reciprocated transversely of said path by the carriage.

16. Apparatus as set forth in claim 10 wherein said carriage driving means drives the carriage back and forth across said path at a speed substantially greater than the speed of travel of each plate along said path so that said rubbing member contacts substantially the entire area of said face of each plate as it travels below said rubbing member along said path.

17. Apparatus for developing lithographic plates comprising means for continuously conveying an exposed lithographic plate along a predetermined path with the exposed face of the plate facing up, means at a first location along said path for applying a developer for the plate on to the said exposed upper face of the plate, and means at a second location along said path for rubbing the developer over the upper face of the plate, said rubbing means comprising a head extending transversely with respect to said path across said apparatus above said path, sponge means carried by said head for rubbing movement relative to the head and engageable with the upper face of the plate to rub in the developer, means carried by said head for driving said sponge means to effect said rubbing movement of the sponge means relative to said head, means for detachably connecting said sponge means to said driving means for removal and replacement of said sponge means, and means mounting said head for swinging movement between an operative position with the sponge means facing downward for engagement with a plate being conveyed along said path and a raised position for facilitating removal and replacement of the sponge means.

18. Apparatus as set forth in claim 17 wherein the said mounting means for the head supports the head for swinging movement about an axis extending across said apparatus above said path.