Apparatus for developing offset printing plates

Abstract

Planographic offset printing plates are prepared by a plate processor apparatus comprising three sections: a developing section in which a developer solution is applied to the exposed plate surfaces, a rinsing section in which a rinse solution is applied to the plate surfaces, and a gumming section for treating the plate with a gumming agent. The plate is delivered by a chain-driven roller system through the developing section where an appropriate solution is discharged against the plate surfaces, and one or more pairs of rotatable applicator brushes operate to scrub the developer over the plate surfaces as the plate is passed between the brushes. Each pair of applicator brushes includes an upper and a lower brush comprising a tufted bristle material, such as polyolefin, arranged in a spiral pattern on the outside surface of the brush roller. A spiral channel is formed between the rows of tufted bristle material which provides both a reservoir and dwell time for the residue of the developer. In operation, the applicator brush provides a screw thread action of the bristle which uniformly spreads fresh developer over the plate. In addition to transporting the plate through the apparatus, the rollers located between the separate sections are used to squeegee excess solution from the plate. Following the gumming step, as the plate leaves the apparatus it is dried by forced air and ready for the press.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to plate making apparatus and more particularly to the automatic processing of undeveloped sensitized printing plates.

2. Description of the Prior Art

There is presently known in the art apparatus for preparing planographic offset printing plates used in the lithographic printing process. One such apparatus is described in U.S. Pat. No. 3,732,808, issued on May 16, 1973 to Robert C. Graham. In this patent there is disclosed a developer apparatus which has a receiving station therein for receiving an exposed printing plate comprising a single plate with two surfaces to be developed or two, one surface plates placed back to back with the exposed surfaces facing outwardly. A partially enclosed developer dispensing station is also provided where developer solution is introduced and dispensed evenly over the complete surface of both exposed surfaces of the plate under pressure and for a period of time sufficient to cause proper soaking of the coatings without the use of spray nozzles. A scrubbing station is positioned after the developer station where scrubbing material, properly suited for processing the plate and assisting the chemical action of the developing solution, contacts both surfaces of the plate. After the scrubbing station the plate is passed through a second developer station similar to the first to remove all traces of unwanted coating from the two sides of the plate, and the plate is discharged from a discharge station. At the scrubbing station there is disclosed the use of upper and lower cylindrical brush rollers mounted for both rotation and reciprocation and spaced so as to provide for intimate contact of the brush bristles with the opposed surfaces of the plate passing therebetween.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide automatic processing of offset printing plates in a uniform and time saving manner.

This as well as other objects are achieved by the present invention which provides an apparatus for developing offset printing plates including a developing section in which a developer solution is applied to the exposed plate surfaces, a rinsing section in which a rinse solution is applied to the plate surfaces, and a gumming section for applying a gumming agent onto the plate. The plate is delivered by a chain-driven roller system through the developing section where an appropriate solution is discharged against the plate surfaces, and one or more pairs of rotatable applicator brushes operate to scrub the developer over the plate surfaces as the plate is passed between the brushes. Each pair of applicator brushes includes an upper and a lower brush adapted to receive the plate therebetween. Each brush comprises a tufted bristle material, such as polyolefin, arranged in a spiral pattern on the outside surface of the brush roller. The bristle material forms a spiral channel between the rows of such bristle material which provides both a reservoir and dwell time for the residue of the developer. In operation, the applicator brush provides a screw thread action of the bristle which uniformly spreads fresh developer over the plate. The plate is transported from the developing section through the respective rinsing and gumming sections by the driven rollers which also act to squeegee excess solution from the plate. Following the gumming step, as the plate leaves the apparatus it is dried by forced air and ready for the press.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic sectional view of an apparatus constructed according to the present invention;

FIG. 2 shows a pair of rotatable brushes for spreading the developer solution onto the printing plates;

FIG. 3 is a perspective view of the apparatus of the present invention employing an anti-foam baffle in the developing section;

FIG. 4 is a perspective view of the output end of the apparatus, including the drying chamber and plate delivery mechanism;

FIG. 5 is a side view of the plate delivery mechanism;

FIG. 6A through 6D are views of hold-down clamps for the drive rollers shown in various positions; and

FIG. 7 is a cross-sectional view of plate guides mounted behind each pair of brushes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, there is shown a diagrammatic sectional side view of an apparatus constructed according to the present invention. The apparatus includes a developing section 2 at the receiving end where a planographic printing plate P is received and a developing solution is applied on to the upper and lower surfaces of the plate P, a rinsing section 4 where water or other suitable rinse solution is applied to the surface of the plate P, a gumming section 6 for dispensing a gumming solution for protecting the non-printing area of the plate during storage, and a drying section 8 for drying the plate prior to its removal from the apparatus.

The apparatus is housed in a structure indicated by numeral 10 which may include a supporting shelf 12 at its input end on which the plate P is supported at the entry station. The plate P is a previously exposed but undeveloped sensitized printing plate, particularly a lithographic plate, which is received between a first set of input rollers 14 A and B which guide and support the plate P through a dispensing chamber formed between upper and lower parallel walls 16 and 18, respectively. A plurality of orifices 20 and 22 are located in the upper and lower walls 16 and 18, respectively, and directed to discharge a developing solution received from delivery lines 24 and 26 from a displacement pump 28. Pump 28 has its input line 30 connected at the bottom of the main reservoir 32 of the developing section 2 so that any fluid located in the reservoir 32 is pumped through the orifices 20 and 22 against the surfaces of plate P. Flexible membranes 34 and 36 are secured at the upper and lower walls 16 and 18 so that they extend inwardly towards each other and form a dam to retain the developing solution in the dispensing chamber formed between the walls 16 and 18. At the same time, the flexible membranes 34 and 36 provide the flexibility for allowing the plate P to pass therebetween and into the dispensing chamber. The flexible membranes 34 and 36 are of a type described in the above-mentioned U.S. Pat. No. 3,732,808 issued to Graham.

As the plate P passes through the dispensing chamber of the developing section 2, it is fed between two sets of brushes 38A, B and 40A, B which spread and scrub the developer solution on the plates. Each pair of brushes 38A, B and 40A, B includes an upper and lower rotating brush having a tufted bristle material, shown as 42 and 44, arranged in a spiral pattern on the outside of the brush rollers. The spiral arrangement of the tufted bristle material 42 and 44 forms a spiral channel between rows of tufted material as will be described in more detail hereinafter.

As shown in FIG. 2, the tufted bristle material 42 used on the upper and lower rollers of a given pair, such as pair 38A, B is arranged in a spiral pattern around the hard core 46 of each brush, with a spiral channel 48 being formed between the tufted material 42. The spiral channel 48 provides both a reservoir and dwell time for the residue of the developer solution. As the plate passes between an upper and lower rotating brush 38A and 38B, the spirally formed tufted bristle material 42 provides a screw thread action of the bristle and constantly feeds fresh developer onto the plate P. The tufted material 42 on the upper and lower rotating brushes can be arranged in a spiral pattern which moves either in the same or opposite direction relative to each other. In both arrangements, the spiral groove 48 and spiral tufted bristle material 42 act to both apply the developer solution onto the plate P as well as driving such solution off of the plate in a spiral-drive fashion.

The tufted material 42 may be comprised of bristles which essentially contact the exposed plate at right angles to the exposed plate surface. The material 42 contains bristles of suitable stiffness, length and density to form the brush so that the ends of the bristle when forced against the exposed ends of the plate P remain in contact with the plate and the bristles do not bend substantially as to cause contact of the sides of the bristles with the plate rather than the end portions of the bristle. The spiral brush arrangement has been found to be effective in applying the developer and scrubbing the plate so as to loosen and remove the non-image areas, and also in cleaning out the background of the plate down to the base material in such cases where the lithographic plate has a base material.

Although the bristles in the tufted material 42 might be in the form of a brush, i.e., tufts of bristles or fibers set into holes spaced apart in the applicator backing, it is preferred that the applicator surface be in the form of a pile fabric with either a woven or knitted backing to which the pile is attached. It is possible to use such a fabric alone as the applicator of this invention, but it is preferred that it be attached to a relatively regular and rigid surface, either flat or curved, so that it will be possible to apply the developer with more uniform pressure to the surface of the exposed plate. Tufted material 42 may suitably include a polyolefin pile or polypropylene plush meterial arranged in the spiral pattern shown in FIG. 2.

After passing through the two sets of rollers 38A, B and 40A, B having the spirally arranged tufted material thereon, the plate P is passed through a second set of rollers 50A, B at the downstream end of the developer 2. Rollers 50A, B act to deliver the plate to the next section as well as providing a squeegee to remove the excess developer from the plate. It is to be noted that one or more pairs of brushes 38 may be provided, such as the two sets 38A, B and 40A, B shown in FIG. 1 in accordance with the needs of the system.

Referring again to FIG. 1, the large reservoir 32 for holding the developing solution is located at the bottom of the developing section 2. According to one embodiment, a shallow tray 52 is located under the brushes 38A, B and 40A, B and the rollers 50A, B in the developing section 2 and maintains the rollers in contact with the developing solution so that the main reservoir 32 at the bottom of the developing section need not be constantly filled in order to keep the brushes and rollers 50A, B wet. A vertical wall 54 on the wetting tray 52 acts as a dam for keeping the developing fluid from being splashed into the rinsing section 4. Also, weep holes 56 are provided in the wetting tray 52 to provide a slow drainage path for the developer solution into the main reservoir 32. Thus, the wetting tray 52 not only saves in the amount of developer solution required in the reservoir, but also maintains moisture in the rollers thereby preventing scale or precipitate build up.

At the upstream end of the dispensing chamber in front of the lower wall 18, there is provided a dry guard 58 located behind the front rollers 14 of the developing section 2. The dry guard 58 comprises a gutter formed at the front end of the lower wall 18 of the dispensing chamber for catching any drip-off from such chamber, thereby preventing the developing solution from rolling off the walls on to the front rollers 14A, B. The dry guard 58, by maintaining the front rollers dry, prevents slippage and unequal wetting of the plate P.

In another embodiment of the developer section shown in perspective view in FIG. 3, an anti-foam baffle 60 is located on the downstream side of the dispensing chamber of the developer section 2 and constitutes an inclined wall for causing the developer to flow down to the reservoir 32 along an inclined ramp rather than free-falling and splashing into such reservoir. the anti-foam baffle thereby acts to prevent any tendency, when using a sudsing-prone liquid, to cause foaming. It is noted that when the above-described wetting tray 52 shown in FIG. 1 is employed, the anti-foam baffle 60 is not needed since the developer drops into the wetting tray 60 rather than falling into the reservoir 32.

As shown in FIG. 2, each of the rotating upper and lower brushes 38A and 38B has its roller 46 rotatably mounted on a shaft 62 and is fixed against relatively transverse movement along the shaft 62 by an end cap 64 secured to the shaft 62. It is noted that identical numerals are used to indicate the identical portions of brushes 38A and 38B. A roller bearing 66 permits relative rotative movement of the brush shaft 62 which is also supported on the supporting structure 10 of the apparatus. The brush shaft 62 is driven by a conventional drive means, such as the motor 68 driving a chain 70 connected between pulleys or sprockets 72 and 74. As mentioned previously, each of the rollers of the system can be driven by a chain linkage arrangement operated from a single motor, such as the motor 68 shown in FIG. 2. The brushes 38A, B are driven at a speed sufficient to provide a scrubbing action on the plate surface. Thus, the linear velocity of the brushes must be greater than the rate of passage of the plate. Preferably, the linear velocity of the brushes should be two to five times the velocity of the plate.

In the same fashion, one or both of each of the rollers 14A, B; 50A, B; 90A, B or 104A, B are motor driven by a chain linkage arrangement. All of these rollers are interconnected by chain linkages, the details of which are not provided herein since such arrangements are well known in the art.

After the plate passes through the second set of rollers 50A, B in the developing section 2, it enters into the rinsing section 4 where water or other suitable rinsing agent is dispensed through jet orifices 82 and 84 on to the plate P in a chamber formed by a pair of horizontal, spaced apart upper and lower walls 86 and 88. The downstream end of the rinsing section 4 includes a pair of rollers 90A, B for delivering the plate P to the gumming section 6. It is noted that a vertical wall 92 separates the developing section 2 from the rinsing section 4 and, similarly, a vertical wall 94 separates the rinsing section 4 from the gumming section 6. A gumming agent is dispensed between the gumming chamber formed by a pair of spaced apart upper and lower walls 96 and 98. The gumming agent acts to protect the non-printing area of the plate during storage, prior to going to press. Displacement pumps 100 and 102, respectively, provide recirculation of the rinsing and gumming agents from their reservoirs to the jet orifices at the dispensing chambers. After the plate is gummed, it is passed between a pair of output rollers 104A, B and then through the drying section 8 where it is removed from the machine.

Referring to FIGS. 1 and 4, the drying chamber comprises a pair of spaced apart upper and lower walls 106 and 108 which diverge outwardly towards the downstream portion of the chamber. The walls extend the width of the machine and are closed at the end portions thereby enclosing the chamber except for the receiving end and the exit end. A strip 110 of a tufted bristle material, such as the black polyolefin material used on the brushes, is secured across the lower and/or upper walls of the drying chamber and acts to create turbulence as warm air is forced through one or both ends of the drying chamber, by means of heating device 112 supplying hot air through hoses 114 and 116. A passage 118 is shown in FIG. 4 at the end of hose 114. Because of the diverging cross section of the drying chamber, the drying air is caused to seek the path of least resistance and thereby flows outward from the machine causing a blanket of air to envelop the plate, even after leaving the machine. By causing the air to flow outward from the machine rather than circulating into the machine, the air is prevented from drying out the gumming agent or other chemicals used in the prior machine stages. Also, the black, high pile polyolefin material 110, in addition to providing a turbulent flow, serves as a heat sink when using a warm air in the chamber which tends to retain a higher than ambient temperature in the drying chamber.

Referring to FIGS. 4 and 5, at the output of the machine there is a plate delivery mechanism comprising a motor driven shaft 120 which extends across the width of the machine and has a plurality of rollers 122 spaced apart along the shaft 120. The center of the delivery shaft is maintained at a height which is higher than the two ends of the shaft by means of a center support 124 fixed to the machine structure 10 at the desired height. This provides a plate delivery crown at the center of the shaft which causes the plate being ejected from the machine to be controlled more readily during delivery. This delivery shaft 120 is a hollow cylindrical member having a low modulus of bending with the center bearing support 124 forcing the center of the roller shaft upwards from its normal straight configuration. A drive motor and pulley combination 126 is located at one end of the shaft 120 and bearings 128 are located at each end of the shaft. Alternately, the shaft 120 may be driven by a suitable belt or chain connected to the roller 104B.

Referring to FIGS. 6A-6D there is shown a plurality of hold-down clamps employed in the plate processor apparatus. Each hold-down clamp is mounted at the end of the respective axis of each of the upper rollers 14A, 50A, 90A and 104A for the purpose of placing a downward pressure on the roller shaft 131 which is transmitted through the shaft bearings. As shown in FIGS 6A, 6B and 6C, each clamp includes a metal bar 130 having a generally U-shaped metal retainer bracket 132 welded or attached at one end 133 to the back of the bar 130 while the other end of the bracket 132 is bent at a right angle around one end of the clamp bar 130. A keeper bolt 134 passes through one end of the ring formed by the metal bar 130 and the bracket 132 and holds the clamp in place. A pressure screw 136 is passed through a nut 140 in a locking nut arrangement 138 mounted on the apparatus support structure 10 and applies a downward pressure against one end of the bar 130. As shown in FIG. 6D the roller shaft 131 is mounted in a retainer collar 140 secured by a set screw 142. Shaft 131 also passes through a retainer ring 144 having a groove 146 in the side and bottom portions which receives the edge wall portions of the support structure 10. In this fashion, the retainer ring 144 is slidably mounted on the structure 10 by the groove 146 and will not rotate since the groove 146 does not form a complete circle. The retainer ring 144 can slide in a vertical movement relative to the support structure 10 in response to the pressure exerted by the clamp bar 130 thereon. Bar 130 is thereby pressed downward against the roller shaft 131 via the clamp bar 130 by the action of the fixed keeper screw 134 at one end and the pressure screw 136 at the other end. As shown in FIG. 6C, an operator can rapidly release the roller by momentarily pressing down on the roller, shown by the direction of arrow 149, to relieve the pressure on the hold-down clamp while simultaneously sliding the clamp out from under the pressure screw and the keeper screw, as shown by the direction of arrow 148.

Referring to FIG. 7, there is shown a plate guide arrangement for preventing flipping and/or bending of the tail edge of the plate (P) as it leaves each set of brushes. The plate guide arrangement includes a T-shaped metal or plastic guide 150A and 150B spaced apart to form a chamber which permits plate passage therethrough while being sufficiently close to prevent plate flipping and/or bending. Guides 150A and 150B are located at the downstream side of the brushes 38A and B. Similarly, a second set of guides 152A and 152B are mounted at the downstream edge of the brushes 40A and 40B. Each of the T-shaped guides is tapered or shaped at its edges 154 and 156 to conform with the periphery of the adjacent brush.

Although the above description is directed to the preferred embodiments of the invention, it is noted that other variations and modifications will be apparent to those skilled in the art, and therefore, may be made without departing from the spirit and scope of the present disclosure.

Claims

What is claimed is:

1. Apparatus for developing offset printing plates, comprising:

means for supplying a developer solution for application to the exposed surface of said plates;

means for discharging said developer solution against the exposed surfaces of said plates; and

at least one pair of cylindrical, axially rotatable applicator brushes adapted to receive said plate between each pair of said brushes, each of said brushes including a tufted bristle material arranged in a spiral pattern on the outside surface of the brush, said spiral pattern of the bristle material forming a spiral channel between the adjacent rows of bristle material which provides both a reservoir and dwell time for the residue of the developer; whereby said applicator brush provides a screw thread action of the bristle on said plate and feeds the developer solution on to the plate.

2. Apparatus as recited in claim 1, wherein the tufted bristle material on each of said rotatable applicator brushes is comprised of a polyolefin.

3. Apparatus as recited in claim 1, wherein said tufted bristle material on each of said rotatable applicator brushes is comprised of polypropylene.

4. Apparatus as recited in claim 1, further comprising means for rotating said applicator brushes at a speed such that the tufted bristle material moves across said plate surface at a speed which is greater than the speed of movement of said plate through said apparatus, thereby providing a scrubbing action of said applicator brushes on said plate surfaces.

5. Apparatus as recited in claim 1, further comprising roller means for transporting said plates through a developing section of said apparatus where said developer solution is discharged against the surfaces of said plates.

6. Apparatus as recited in claim 1, further comprising a developing section including an upper wall and a lower wall which are spaced apart in parallel relation to form a chamber therebetween where said developer solution is applied to the exposed surfaces of said plates by said discharging means for said developer solution.

7. Apparatus as recited in claim 6, further comprising a rinsing section including an upper wall and a lower wall which are spaced apart in parallel relation to form a rinsing chamber therebetween, and means for applying a rinse solution to the surfaces of said plate as said plate is transported through said rinsing chamber, said rinsing section being located adjacent to and downstream of said developing section.

8. Apparatus as recited in claim 7, further comprising a gumming section including an upper wall and a lower wall which are spaced apart in parallel relation to form a gumming chamber therebetween, and means for applying a gumming agent to the surfaces of said plate as it passes through said chamber, said gumming section being located adjacent to and downstream of said rinsing section.

9. Apparatus as recited in claim 6, further comprising a main reservoir located at the bottom of the developing section for storing developing solution, means for pumping said developing solution from said main reservoir to orifices located in said upper and lower walls forming said developing chamber, said pump means and said orifice means constituting said discharging means, and an auxiliary reservoir located under said rotatable applicator brushes for receiving any excess developing solution dripping from said brushes, said auxiliary reservoir being adapted for maintaining a height of developer solution which is above the bottom portion of the roller applicator brush thereby maintaining said applicator brush in contact with said developer solution.

10. Apparatus as recited in claim 9, wherein said auxiliary reservoir further comprises means for draining developing solution from said auxiliary reservoir into said main reservoir.

11. Apparatus as recited in claim 6, further comprising a trough located at the upstream end of said lower wall of the developing section for catching any drip-off of developing solution from rolling off said lower wall and into the front drive rollers of said drive apparatus which transport said plate into and through said developing section.

12. Apparatus as recited in claim 6, further comprising an anti-foam baffle located on the downstream side of the lower wall of said developing section, said anti-foam baffle comprising a downwardly inclined wall for causing said developer solution to flow from said lower wall down along said inclined wall into said main reservoir.

13. Apparatus as recited in claim 8, further comprising a drying section located downstream of said gumming section, said drying section comprising a drying chamber formed by an upper wall and a lower wall which are spaced apart and diverging outwardly from each other in the downstream direction such that said drying chamber diverges outwardly in the downstream direction, and means for blowing warm air in said drying chamber, whereby the surface of said plate is dried as the plate is passed through said drying chamber.

14. Apparatus as recited in claim 13, further comprising means for producing a turbulent flow of air in said drying chamber.

15. Apparatus as recited in claim 14, wherein said means for producing a turbulent flow of air includes one or more strips of high pile material secured to a portion of the walls of said drying chamber.

16. Apparatus as recited in claim 1, further comprising plate delivery means at the output end of said apparatus, said plate delivery means including a driven shaft which extends substantially across the width of the apparatus for receiving said plate thereon, said shaft having a plurality of rollers spaced apart along the length of the shaft, and a center support crown for maintaining the middle portion of said shaft at a vertical height which is slightly higher than the height of the opposite ends of the shaft, whereby said plate is controlled during delivery from the output of said apparatus by said plate delivery means.

17. Apparatus as recited in claim 1, further comprising a plurality of pairs of rollers for transporting said plate through said apparatus, each pair including an upper roller and a lower roller which are spaced apart to receive said plate therebetween and transport said plate in the space formed between said rollers, and a hold-down clamp mounted at the end of the shaft of each of said rollers and secured to the housing of said apparatus, said hold-down clamp including a clamp bar which provides a force acting against the end of said roller shaft in a direction perpendicular to the axis of said roller shaft.

18. Apparatus as recited in claim 17 wherein said hold-down clamp comprises pressure screw means for exerting a downward pressure against one end of said clamp bar, a keeper screw means for maintaining the other end of said clamp bar in fixed position, and a retainer means for maintaining said clamp bar on said keeper screw, said clamp bar being pressed against a portion of said roller shaft through the action of said keeper screw and said pressure screw.

19. Apparatus as recited in claim 17, further comprising a retaining collar mounted around one end of said roller shaft at a position where said clamp bar is pressed against said retainer ring and thereby provides a pressure against said roller shaft.

20. Apparatus as recited in claim 19, wherein said retainer ring includes a groove cut along the central portion of each outer side of said retainer ring, said groove being adapted to receive a horizontal wall portion of the support structure for said apparatus, whereby said retainer ring is mounted for slideable vertical movement.

21. Apparatus as recited in claim 1, further comprising plate guide means located adjacent said rotatable applicator brushes for guiding said plate upon its passage between said brushes, said plate guide means including a pair of substantially parallel wall portions which are spaced apart to form a chamber which permits plate passage therethrough while being sufficiently close to guide said plate and prevent flipping and/or bending of said plate as it passes between said brushes and said wall portions.

22. Apparatus for developing offset printing plates, comprising:

at least one pair of cylindrical, axially rotatable applicator brushes located in a developing area where developer solution is applied to said plates, said brushes adapted to receive said plates between each pair of brushes, each of said brushes including a tufted bristle material arranged in a spiral pattern on the outside surface of the brush, said spiral pattern of the bristle material forming a spiral channel between the adjacent rows of bristle material which provides both a reservoir and dwell time for the residue of developer solution; and

plate guide means located adjacent said rotatable applicator brushes for guiding said plate upon its passage between said brushes, said plate guide means including a pair of substantially parallel wall portions which are spaced apart to form a chamber which permits plate passage therethrough while being sufficiently close to guide said plate and prevent flipping and/or bending of said plate as it passes between said brushes and said wall portions;

whereby said applicator brushes provide a screw thread action of the bristle on said plate and feed the developer solution on to the plate.