JPH02220060A - Developer scum removing device for waterless planographic plate - Google Patents

Abstract

PURPOSE:To facilitate cleaning inside a developer collecting tank by scavenging developer scum floating in the developer collecting tank to an overflow tank and removing it with the aid of a filter. CONSTITUTION:Developer 18 in the developer collecting tank 22 gets over a lower partition 22A and flows in the overflow tank 52. The developer scum floating in the surface part of the developer 18 flows in the overflow tank 62 and is accumulated there. Meanwhile, the developer 18 in the overflow tank 62 is sucked from a branch pipe 58 and guided into the pipe 58 by actuating a circulating pump 44. The developer 18 containing much developer scum, which is sucked into the branch pipe 58, passes the filter 46, so that the developer scum in the developer is removed and the developer is fed to spray pipes 34, 40 and 42 again through a pipe 38.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is used in a waterless lithographic printing plate development processing apparatus that develops a waterless lithographic printing plate while circulating a developing solution. The present invention relates to a developer scum removing device for a waterless planographic printing plate for removing developer scum from a developer solution.

[Prior art] Waterless PS plates using a silicone layer as an ink repellent layer are disclosed in Japanese Patent Publication No. 44-23042 and Japanese Patent Publication No. 46-160.
44, a waterless PS in which a commercially solubilizable or photoinsolubilizable photosensitive layer and a silicone rubber layer are laminated on a substrate.
Edition, JP-A-48-94504, JP-A-50-501
No. 02, a waterless PS plate has been proposed in which a photoadhesive photosensitive layer and a silicone rubber layer are laminated on a substrate.

These can print tens of thousands of sheets without using dampening water.

The above-mentioned waterless PS plate has a photosensitive tank and a silicone rubber layer laminated on a support such as aluminum, and a protective film is laminated on the upper surface of these to protect the surface. When an image is printed on this waterless PS plate, the photosensitive layer corresponding to exposed areas, that is, non-image areas, hardens and becomes more adhesive to the support, while the photosensitive layer corresponding to unexposed areas, ie, image areas, does not harden. In this state, when a developer is applied to the surface, the unexposed portions of the photosensitive layer swell and peel off from the support together with the silicone rubber layer. The peeled residues of the photosensitive layer and silicone rubber layer are collected together with the excess developer into a developer recovery tank.

The developer is again applied to the waterless lithographic printing plate by the circulation pump. A filter is placed in the middle of this circulation to filter out dust and the like in the developer.

[Problems to be Solved by the Invention] However, since the developer residue collected in the developer recovery tank along with the excess developer floats in the developer, it does not circulate together with the developer and A problem arises in that the developer adheres to the developer and contaminates the inside of the developer recovery tank. Therefore, the inside of the developer recovery tank must be cleaned periodically, making maintenance of the developer recovery tank complicated.

The present invention has been made in consideration of the above-mentioned facts, and an object of the present invention is to provide a development scum removal device for a waterless planographic printing plate that can remove development scum from a developer in a developer recovery tank.

[Means and effects for solving the problem] The present invention is used in a waterless lithographic printing plate development processing apparatus that develops a waterless lithographic printing plate while circulating the developer using a circulation pump. A developer scum removing device for a waterless lithographic printing plate for removing floating developer scum from a developer, wherein the surface layer of the developer in a developer storage tank containing the developer flows into the developer. It is characterized by having a collecting means for collecting floating developer scum, and a filter for removing the collected developer scum from the circulating developer.

Thereby, the developer residue in the developer recovery tank is collected by the collecting means and then removed from the developer by the filter.

[Embodiment] FIG. 1 shows an embodiment of a waterless lithographic printing plate developing device 10 to which the present invention is applied. This waterless lithographic printing plate developing device 10 consists of a developing section 14 and a dyeing fls 16,
This is an apparatus that performs a dyeing process to facilitate plate inspection work after developing the waterless 23rd plate 12.

The waterless 23rd edition 12 used here is a patent application published in 1986-86.
177, in which a primer layer, a photosensitive layer, a silicone rubber layer, and a protective film are sequentially laminated on a substrate is used.

Further, the developer 18 used in the developing section 14 is
317843, an aqueous developer containing an organic solvent proposed in Japanese Patent Application No. 63-86177 is used. The staining solution 17 used in the staining section 16 includes a staining solution 1 containing crystal violet, astrazone red, etc.
7 is used.

The developer tank body 20 of the developer section 14 opens upward,
The bottom is formed in an inverted mountain shape, and a developer recovery tank 22 is formed in the center of the bottom. A developer 18 is accommodated in the developer collection side 22 .

Pairs of transport rollers 24, 26, and 28 are arranged at the top of the developer tank body 20 in order from the waterless PS plate 120 entry side. The pair of transport rollers 24, 26, and 28 are supported by a rack side plate (not shown), are rotated by the driving force of a driving means (not shown), and are configured to nip and transport the waterless 23 plate 12 in the direction of the arrow in FIG. It has become. The transport roller pair 28 is disposed at the last end of the transport path for the waterless 23rd plate 12 in the developing section 14 and has the role of a squeeze roller that squeezes out the developer from the waterless 23rd plate 12.

A brush roller 30 is arranged between the transport roller pair 26 and the transport roller pair 28. This brush roller 30 is for scraping off the photosensitive layer and silicone layer corresponding to the image area on the plate surface by rubbing the plate surface of the waterless 23 plate 12 being conveyed. The brush roller 30 is also supported by a side plate (not shown) in the same way as the transport roller pair 24, 26, 28, and the driving force of a driving means (not shown) is transmitted to the brush roller 30 in the same direction as the rotation direction of the transport roller pair 24, 26, 28 (first direction). 1
Figure) In other words, it rotates counterclockwise.

Also, in some cases, the brush roller 30 in FIG. 1 may rotate clockwise.

The brush roller 30 is formed by planting a brush material on a roll made of plastic or metal, and rotates in the forward direction (FIG. 1), that is, clockwise, with respect to the conveying direction of the waterless 28 plate 12. The surface of the plate 12 is rubbed. The number of rotations of this brush roller 30 is 100
The speed is set at ~500 rpm (preferably 200-400 rpm). Further, in order to prevent vignetting in the waterless PS version, it is preferable to install a vignetting prevention bar 31.

Further, by rotating the brush roller 30 and reciprocating it in the axial direction, the effect of scraping off the photosensitive layer and silicone layer on the surface of the waterless 23rd plate 120 is further improved.

A support stand 32 made of a relatively flexible material such as plastic, such as high-density polyethylene, is disposed below the brush roller 30. When the waterless 28 plate 12 passes, the surface is rubbed by the brush roller 30 while the waterless 28 plate 12 is supported on the stand 32, ensuring that the photosensitive layer and silicone layer corresponding to the image area are completely covered. It is designed to be scraped off. The lower support of the brush roller 30 is a stand 32
A roller may be used instead.

A spray pipe 34 is arranged above the transport roller pair 24. This spray pipe 34 is provided with discharge ports 34A at appropriate intervals along the axial direction, facing the upper roller of the pair of transport rollers 24. This spray pipe 34 is communicated with a developer supply device, which will be described later, through a conduit 38 via a valve 36. As a result, the developer 18 is sent to the spray pipe 34, and the conveying roller pair 2
Discharge the developing solution to the upper roller of 4 to create a waterless 28 plate 1.
2, the developer is applied onto the surface.

Spray pipes 40 and 42 are also arranged between the transport roller pair 26 and the transport roller pair 28. The spray pipe 40 is arranged between the brush roller 30 and the transport roller pair 26, and has a discharge port 40A formed opposite to the brush roller 30, similarly to the spray pipe 34. Like the spray pipe 34, this spray pipe 40 is also connected to a developer supply device, which will be described later, via a valve 36 through a pipe line branching from the pipe line 38. As a result, the developer is fed into the spray pipe 40, and the developer is discharged and supplied to the brush roller 30.

Further, the spray pipe 42 has a discharge port 42A formed opposite to the upper roller of the pair of transport rollers 28. This spray pipe 42 also communicates with a developer supply device, which will be described later, through a pipe line branching from the pipe line 38 via a valve 36. As a result, the developer is fed into the spray pipe 40, and is discharged to the upper roller of the transport roller pair 28.

A cover 39 having a substantially U-shaped cross section is disposed to extend from the conveying roller pair 26 to the upper part of the brush roller 30.

This cover 39 prevents the developer 18 from being scattered by the brush roller 30 to other areas.

The developer supply device includes a circulation pump 44, a filter 46,
Pipe line 4 communicating circulation pump 44 and developer recovery tank 22
It consists of 8.

The circulation pump 44 is a variable flow rate pump, and the control device 52
and its discharge flow rate is controlled. A pipe line 38 is connected to the discharge port side of the circulation pump 44, and one end of the pipe line 48 is connected to the suction port side. The other end of the pipe 48 is communicated with the bottom of the developer recovery tank 22 via a valve 55 in the middle.

By the operation of this circulation pump 44, the developer recovery tank 22
The developer in the pipes 34, 40, 40.
42.

A flow rate sensor 50 is disposed in the middle of the conduit 38,
The flow rate of the developer passing through the pipe line 38 is detected. This flow rate sensor 50 is connected to a control device 52, and is adapted to transmit the detection result of the flow rate of the developer. Although a general flow meter can be used as the flow rate sensor 50, a rotary type is preferable in order to downsize the device.

A filter 46 is disposed in the middle of the conduit 48, and a filter 46 is provided in the middle of the conduit 48 to remove a small amount of water from the developer passing through the conduit 48.
It is designed to filter out development residue from the photosensitive layer and silicone layer that have been scraped off the surface.

Further, a notification device 56 is connected to the control device 52,
When the flow rate of the developer 18 passing through the pipe line 38 becomes less than a predetermined amount, a notification is given that it is time to replace the filter 46. This allows the filter to be replaced. The mesh size of this filter is 10μ to 500μ (preferably 100μ
~300μ) are used. Further, a valve 56 is disposed in the middle of the conduit 40 to open and close the conduit 48.

A branch pipe line 58 branches off from the middle of the pipe line 48, and communicates with an overflow tank 62, which is a collection means, via a valve 60. The overflow tank 62 is disposed on the side of the developer recovery tank 22 , is provided on a partition wall of the developer recovery tank 22 , and is communicated with the developer recovery tank 22 through a long hole 64 that runs along the surface of the developer 18 . ing. As a result, the surface layer of the developer in the developer recovery tank 22 is removed from the developer recovery tank 22.
The liquid flows over the upper end of the lower partition wall 22A and into the overflow tank 62. Overflow [
The overflow flow rate of the developer into the developer 62 is set to 1/3 to 1 (preferably 1/2 or more) of the total circulation amount.

Further, the upper partition wall 22B prevents the developer particles once collected in the overflow tank 62 from spreading into the developer recovery tank 22 when the developer circulation pump 44 is stopped.

As shown in FIG. 1, the overflow tank 62 is opened at the top to form an opening, which can be opened and closed with a lid 66, and can be removed from the opening when performing maintenance on the overflow tank 62. ing. The upper part of the side wall 68 of the overflow tank 62 is inclined to form an inclined wall 68.
A is formed. A branch pipe line 58 is communicated through the lower part of the side wall 68, and the developer 18 in the overflow tank 62 is sucked by the operation of the circulation pump 44. Due to this suction, the inclined wall 68A
A flow of the developer 18 is formed in the direction of arrow B along. In addition, the developer recovery tank 22 is
The surface layer of the developer 18 inside flows into the overflow tank 62, and the developer particles floating in the developer in the developer recovery tank 22 flow into the overflow tank 62, where the developer particles are collected and collected by the inclined wall 68A. Conduit 5 by flow
It is designed to be sent into 8. When replacing the developer, connect the drain valve 93 through the drain pipe 88.
The developer can be drained and a new developer can be added.

Further, a heater 88 is arranged at the bottom of the developer recovery tank 22 . This heater 88 is connected to a power source (not shown) to heat the developer. This heater 8
8, the temperature of the developer is set at 15° to 45° (preferably 25° to 30°).

In addition, the development time is set to 10 seconds to 3 minutes (preferably 30 seconds to 2 minutes) with this device, and the staining time is set to 5 minutes.
It is set to 1 second to 1 minute (preferably 10 seconds to 30 seconds).

Next, the dyeing section 16 will be explained.

The dye tank main body 90 of the dyeing section 16 opens upward like the developer tank main body 20, has an inverted mountain-shaped bottom, and has a dye solution recovery tank 92 formed in the center of the bottom. The staining liquid 17 is accommodated in the staining liquid recovery tank 92 .

At the top of the dyeing tank main body 90, pairs of transport rollers 94 and 96 are arranged sequentially along the transport direction of the waterless 23rd printing plate 12 from the entrance side of the waterless 23rd printing plate 12 into the dyeing tank main body 90.

The pair of transport rollers 94 and 96 are supported by a rack side plate (not shown), are rotated by the driving force of a driving means (not shown), and are designed to nip and transport the waterless 23 plates 12. These conveyor roller pairs 94 and 96 are made of common rubber (
That is, the material is made of silicone, EPTSNBR, etc.) so as not to damage the surface of the waterless 23 plate 12 being transported.

A pair of conveying rollers 98 is disposed on the downstream side of the dyeing tank main body 90 in the conveying direction of the waterless 23 plate 12.

The transport roller pair 98 is made of NBR rubber (nitrile butadiene rubber) or the like, and has improved wipeability of the dye solution.

A brush roller 100 is arranged between the transport roller pair 94 and the transport roller pair 96. The brush roller 100 is also supported by a side plate (not shown) like the transport roller pair 94.96, and the driving force of a drive means (not shown) is transmitted to the brush roller 100, so that the brush roller 100 rotates in the opposite direction to the rotation direction of the transport roller pair 94.960 (clockwise in FIG. 1). It is designed to rotate to . This brush roller 1
00 is formed by planting a brush material on a plastic or metal roll, and the waterless PS plate 12 is rotated in a direction that resists the transport direction of the waterless PS plate 12 (clockwise in Figure 1). It is designed to rub 12 surfaces. Further, depending on the case, it may be rotated in the forward direction with respect to the transport direction of the waterless PS plate 12. The rotation speed of the brush roller 100 is 100 to 500 rpm (preferably 200 to 40 rpm).
0 rpm). Furthermore, it is preferable to install a vignetting prevention bar 31 to prevent waterless vignetting.

A support stand 102 made of a relatively flexible material such as plastic, for example high-density polyethylene, is arranged below the brush roller 100.

Further, a rubber roller may be arranged instead of the pedestal 102. Therefore, when the waterless PS plate 12 passes, the receiver is
While the waterless PS plate 12 is being guided on the surface of the PS plate 12, the staining liquid 17 is applied to the surface by a brush roller 100.

A spray pipe 104 is installed above the brush roller 100.
is installed. This spray pipe 104 is surrounded by a substantially U-shaped rectifying plate 106.

A suitable number of discharge ports 104A are formed in the spray pipe 104 along the axial direction, facing the current plate 106.

This spray pipe 104 is connected via a valve 108 to a dye solution supply device to be described later through a conduit 110. As a result, the dyeing solution 17 is fed into the spray pipe 1 [ ) 4 and is discharged toward the current plate 106 .
6 and supplied to the brush roller 100. At this time, the staining liquid 17 spreads while flowing down on the rectifying plate 106 and is uniformly supplied onto the brush roller 100.

A spray pipe 112 is also arranged between the brush roller 100 and the conveying roller pair 96 on the conveying roller pair 96 side. This spray pipe 112 is also the spray pipe 104.
Similarly, it is surrounded by a substantially U-shaped rectifying plate 106. This spray pipe 112 has a discharge port 112A connected to the rectifier plate 10.
6 are provided in an appropriate number along the axial direction. The spray pipe 112, like the spray pipe 104, is communicated with a dye solution supply device to be described later through a conduit 110 via a valve 108. With this, the spray pipe 11
A dyeing liquid 17 is fed into the roller 2 , and is discharged and guided toward the rectifying plate 106 so that the dyeing liquid 17 is supplied to the upper roller of the pair of transport rollers 96 . At this time, the dyeing liquid 17 spreads while flowing down on the rectifying plate 106 and is uniformly supplied to the pair of conveying rollers 96.

A cover 107 having a substantially U-shaped cross section is arranged above the brush roller 100 and the conveying roller pair 96. This cover 107 prevents the staining liquid 17 from being scattered elsewhere by the brush roller 10 ports.

The dye solution supply device includes a circulation pump 114 and a filter 116.
and a conduit 118 that communicates the circulation pump 114 and the dye solution recovery tank 92. A pipe line 110 is connected to the discharge port side of the circulation pump 114, and a pipe line 1 is connected to the suction port side.
One end of 18 is connected. The other end of the pipe line 118 is communicated with the bottom of the dyeing solution recovery tank 92. By the operation of this circulation pump 114, the dye 't in the dye solution recovery tank 92 is
i, 17 is sucked into the circulation pump 114 through line 118 and into the spray pipe 104 through line 110.
112.

A filter 116 is disposed in the middle of the conduit 118,
It is designed to remove dust (mainly dust from the photosensitive layer and silicone layer scraped from the surface of the waterless PS plate 120 brought in from the developing section) in the dyeing solution passing through the pipe 118.

When replacing the staining solution, the staining solution can be discharged through the drain pipe 91 using the citrine valve 95, and a new developer can be introduced.

A heater 88 is disposed at the bottom of the dyeing solution recovery tank 92, and is connected to a power source (not shown) to heat the dyeing solution. The temperature of this staining liquid 17 is 15 to 45°C.
(preferably 20 to 30°C).

Next, the operation of this embodiment will be explained.

The waterless 23rd plate 12 on which the image has been printed is inserted into the developing section 14 after passing above the aluminum detector 86 using an image printing apparatus (not shown). The portion of the photosensitive layer of the waterless 23 plate 12 inserted into the developing section 14 that is irradiated with light, that is, the exposed portion, hardens and adheres to the primer layer, and the unexposed portion is in a state where it can be swollen or eluted by the developer 18. It becomes.

From this state, after peeling off the protective film laminated to protect the surface of the waterless 23rd plate 12, the waterless 23rd plate 12 is inserted into the developing section 14, and is conveyed while being held between the pair of conveying rollers 24 of the developing section 14. The developer 18 is applied to the surface while being applied. As a result, the photosensitive layer in the unexposed area (image area) of the waterless 23 plate 12 swells and becomes easily peeled off from the primer layer.

Further, the waterless 23rd plate 12 is pinched and conveyed by a pair of conveying rollers 26, and a brush roller 30 and a receiver are inserted between a table 32. The brush roller 30 rotates in the forward direction (FIG. 1), that is, counterclockwise, with respect to the conveyance direction of the waterless 23rd plate 12, and the receiver rubs the upper surface of the waterless 23rd plate 12 passing over the table 32. The developer 18 is also supplied to this brush roller 30, and while the waterless 23rd plate 12 is coated with the developer 18, the surface is rubbed by the brush roller 30, and the developer 18 is rubbed by the brush roller 30.
8, the swollen photosensitive layer and silicone rubber layer are scraped off. As a result, a photosensitive layer and a silicone layer corresponding to exposed areas (non-image areas) remain on the waterless 23rd plate 12, and a positive image is formed.

The surplus developer 18 after the developer 18 applied to the surface of the waterless 23 plate 12 falls into the developer recovery layer 22 and is collected.

Furthermore, the water-less 23 in which the unexposed portion (image portion) of the photosensitive layer and the silicone layer are scraped off by the brush roller 30
The plate 12 is conveyed while being held between a pair of conveying rollers 28, and the developer 18 is once again applied to the plate 12, and the developer 18 is squeezed out from the waterless plate 12.

The waterless 23rd plate 12 in this state is inserted between the pair of transport rollers 94 in the dyeing section 16. The waterless 23rd plate 12 is conveyed by the pair of conveying rollers 94 by the brush roller 10.
0 and the receiver are inserted between the base 1020. This brush roller 100 rotates in a direction (clockwise in FIG. 1) against the conveyance direction of the waterless 23rd plate 12, and the dyeing solution 17 supplied while being guided by the current plate 104 is directed onto the upper surface of the waterless 23rd plate 12. Apply.

Further, depending on the case, the brush roll 100 may rotate in the forward direction with respect to the conveyance direction. As a result, the staining liquid 17 adheres to the primer layer, that is, the unexposed area (image area) and is dyed.

Further, the waterless 23rd plate 12 is inserted between the pair of conveying rollers 96 1, and the rectifying plate 10 is transferred to the upper roller of the pair of conveying rollers 96.
The dyeing liquid 17 guided and supplied by the dyeing liquid 6 is applied to the surface, and the dyeing liquid 17 is squeezed out. This staining is a process to make it easier to distinguish between the image area and the non-image area, as the surfaces of the image area and non-image area of the waterless 23 plate 12 after development are the same color, making plate inspection work easier. This is a process carried out to achieve

After the waterless 23 plate 12 with the image area dyed is sent out from the dyeing section 16, it is inserted between the pair of transport rollers 98, and the staining solution 17 remaining on the surface is squeezed out. Since the pair of transport rollers 98 is made of NBR rubber, the ability to wipe off the staining liquid 17 is improved. In particular, if the dyeing solution 17 remains in the non-image area, the ink repellency of the silicone rubber layer will decrease, making it impossible to obtain a good image during printing. Since it is wiped off, a good image can be obtained.

Next, the circulation of the developer 18 in the developing section 14, removal of residue, and replenishment of the developer 18 will be explained.

Circulation> As shown in FIG. 1, the developer 18 in the developer recovery tank 22 is sent to the spray vibrator 34, 40, 42 by the operation of the circulation pump 44, and the developer 18 is transported through the developer section 14 without water. It is applied to the PS plate 12. Excess developer 18 after coating the waterless PS plate 12 falls and is collected into a developer recovery tank 22.

There is no water in the developer collected into the developer recovery tank 22.
Dust is mixed with development scum from the photosensitive layer, silicone rubber layer, etc. that has peeled off from the surface of the S plate 120. These development scum has a lighter specific gravity than water, so it floats on the surface layer of the developer in the developer recovery tank 22. are doing.

Dust Removal> In this state, the developer 18 in the developer recovery tank 22 flows into the overflow tank 62 over the lower partition wall 22A. As a result, the developer residue floating on the surface layer of the developer solution 18 flows into the overflow tank 62 and is accumulated therein.

On the other hand, the developer 18 in the overflow tank 62 is sucked in from the branch pipe 58 by the operation of the circulation pump 44, and this suction forms a flow along the inclined wall 68A in the overflow tank 62 (not shown). direction of arrow B). As a result, the developer particles collected in the overflow tank 62 are guided into the branch pipe 58 along this flow. The developer 18 containing a large amount of developer residue sucked into this branch pipe 58 passes through the filter 46 to remove the developer residue from the developer, and
is sent again to the spray vibrator 34.40.42. This prevents developer residue from accumulating in the developer recovery tank 22, making it easier to clean the developer recovery tank 22.

When the operation of the circulation pump 44 is stopped and the circulation of the developer 18 is stopped, the liquid level of the developer 18 in the developer recovery tank 22 rises. Along with this, the developer 1 in the overflow tank 62
The liquid level at 8 also rises and rises from the elongated hole 64. At this time, the upper partition wall 22B serves as a weir to prevent the developer residue accumulated in the overflow tank 62 from spreading into the developer recovery tank.

When the filter 46 becomes clogged with developer residue, the circulating flow rate of the developer 18 passing through the pipe 38 decreases. The flow rate sensor 50 detects this and transmits the detection result to the control device 52. The control device 52 operates the notification device 56 to notify that the filter 46 is clogged. This allows the operator to know when to replace the filter 46 with a new one.

In this way, in this embodiment, there are two circulation paths for the developer 18, the branch pipe 58 and the pipe 48, and the developer 18
Developer residue can be removed from the developer collection tank 2.
2. Development debris does not accumulate in the circulation pump 44, which facilitates maintenance thereof.

[Effects of the Invention] In the present invention having the above-described configuration, the developer residues floating in the developer recovery tank are collected in the overflow tank, and the developer in the overflow tank is circulated by the circulation pump. Since the developer residue in the developer can be removed by the filter, an excellent effect can be obtained in which cleaning of the developer recovery tank is not necessary.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of a waterless lithographic printing plate developing apparatus according to the present invention. lO... waterless planographic printing plate developing device, 12... waterless planographic printing plate (PS plate), 14... developing section, 16... staining section, 18... developer, 44...・Circulation pump, 46...Filter, 62...Overflow tank, 89...Developer solution discharge pipe, 91...Staining solution discharge pipe, 93...Developer solution discharge valve, 95...Staining Valve for liquid discharge.

Claims (1)

[Claims] (1) Used in a waterless lithographic printing plate development processing device that develops a waterless lithographic printing plate while circulating the developer using a circulation pump, water is used to remove developer debris floating in the developer from the developer. None A developer scum removal device for a lithographic printing plate, comprising a collecting means for collecting developer scum floating in the developer into which the surface layer of the developer flows into a developer storage tank in which the developer is stored. and a filter for removing the collected developer residue from the circulating developer.