JP2001051559A - Sheet cleaning device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To excellently swell an already printed sheet and to excellently remove printing material by detecting the surface tension of swelling liquid by a surface tension detection means and adjusting the surface tension of the swelling liquid based on the measured result. SOLUTION: By bringing a rotating brush roller 31 into contact with the sheet 2 whose swelling layer is swollen, the printing material is scraped from the sheet 2 in a printing material removing part 7. The swelling liquid 6 is sprayed from a nozzle 32 so as to wash away the scraped printing material from the sheet 2. The printing material is removed from the washed liquid 6 by a filtering device 38, and the liquid 6 is cleaned and recovered to a swelling liquid reservoir tank 25. The sheet 2 from which the printing material is removed is carried to a heating part 8 by carrying rollers 17 to 19, and heated by a heater 41 and ejected to a paper ejection part 9 in a dried state. A surface tension adjusting mechanism 5 adjusts the surface tension of the liquid 6 to a specified value by supplying surfactant 61 or water 64 after measuring the surface tension of the liquid 6 reservoired in the tank 25.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet cleaning apparatus for removing a printing material by swelling the surface of a printed sheet with a swelling liquid.

[0002]

2. Description of the Related Art Conventionally, the surface of a sheet having a swelling layer formed on its surface has been wetted with a swelling liquid obtained by adding a surfactant to water to swell the swelling layer. A sheet cleaning device for removing a printing material printed on a swelling layer (the surface of a sheet) has been proposed.

To wet a sheet with a swelling liquid, the sheet is immersed in a swelling tank in which the swelling liquid is stored, or the sheet is sprayed with the swelling liquid.

In a sheet cleaning apparatus that swells a sheet by immersing it in a swelling liquid stored in a swelling tank, the swelling liquid is reduced by adhering to the sheet when the immersed sheet is carried out of the swelling tank. In addition, water evaporates over time. As described above, the conventional cleaning apparatus has a problem that the swelling layer of the sheet does not swell properly due to a decrease in the swelling liquid and an increase in the concentration of the surfactant due to evaporation of the water in the swelling liquid.

Further, a sheet cleaning device has been proposed which compensates for the shortage of the swelling liquid by replenishing water. In the sheet cleaning device, even when the swelling liquid decreases, water is contained in the swelling liquid. As replenished, the concentration of surfactant in the swelling solution decreases. As described above, when the concentration of the surfactant is reduced, there is a problem that the speed at which the swelling liquid permeates the sheet is reduced and the swelled layer of the sheet does not swell properly.

Further, when the replenishment of water is not sufficient in the sheet cleaning device and the concentration of the surfactant is high, bubbles are generated in the swelling liquid, and the bubbles are scattered to contaminate the inside of the sheet cleaning device. There is a problem.

When a sheet is immersed in a swelling tank in which a swelling liquid is stored to cause swelling, a transport roller is provided inside the swelling tank to carry out the sheet from the swelling tank.
When the concentration of the surfactant is high, the friction between the transport roller and the sheet is reduced, and a slip occurs between the transport roller and the sheet, and the sheet cannot be carried out of the swelling tank. was there.

Similarly, in a sheet cleaning apparatus for injecting a swelling liquid onto a sheet, the swelling liquid ejected onto the sheet adheres to the sheet, so that all the swelling liquid is reduced without being collected. In addition, the concentration of the surfactant increases due to the evaporation of the water in the swelling liquid. As a result, there is a problem that the swelling layer of the sheet does not swell well even in the sheet cleaning device that sprays the swelling liquid onto the sheet.

In order to solve the above problems, Japanese Patent Application Laid-Open No. 10-9 / 1998
No. 7164 proposes a recording material reproducing apparatus (sheet cleaning apparatus). In the above-mentioned reproducing apparatus, the concentration of the image removal accelerating liquid (swelling liquid) is determined by measuring the conductivity of the image removal accelerating liquid (swelling liquid). Adjustment).

[0010] However, the value of the electric conductivity required as a substitute for the concentration largely changes according to the type of the surfactant and the temperature change, and thus lacks reliability. Thus, in the above-mentioned reproducing apparatus, the image removal accelerating liquid (swelling liquid)
However, it was not possible to obtain an accurate concentration of the swelling solution, and it was not possible to accurately prepare an image accelerating solution (adjust the concentration of the swelling solution).

In the method for regenerating an image-bearing support described in JP-A-10-91046, the concentration of a surfactant is determined by measuring the transmittance of a diluting liquid (swelling liquid), and the obtained value is used as the value. It is used for adjusting the diluent (swelling liquid).

However, the value of the transmittance, which is obtained as a substitute for the concentration, changes greatly depending on the type of the surfactant and the temperature change, so that it lacks reliability. As a result, in the above-mentioned regenerating method, there was a problem that an accurate concentration of the diluent (swelling liquid) could not be obtained, and the concentration of the diluent could not be adjusted accurately.

[0013]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. According to the first aspect of the present invention, there is provided a printing method for removing a printing material of a printed sheet swollen with a swelling liquid. It is characterized by comprising material removing means, surface tension detecting means for detecting the surface tension of the swelling liquid, and surface tension adjusting means for adjusting the surface tension of the swelling liquid.

According to a second aspect of the present invention, in the sheet cleaning apparatus according to the fourth aspect, the swelling liquid is obtained by adding a surfactant to water, and the surface tension adjusting means includes adding water to the swelling liquid. Alternatively, the surface tension of the swelling liquid is adjusted by supplementing a surfactant.

According to a third aspect of the present invention, in the sheet cleaning device according to the first or second aspect, the surface tension detecting means includes a capillary and a liquid level detecting means for detecting a liquid level of the capillary. It is characterized by becoming.

According to a fourth aspect of the present invention, there is provided a printing material removing means for removing a printing material of a printed sheet swollen with a swelling liquid; a surface tension detecting means for detecting a surface tension of the swelling liquid; Concentration adjusting means for adjusting the concentration of the swelling liquid based on the measurement result of the tension detecting means.

According to a fifth aspect of the present invention, in the sheet cleaning apparatus according to the fourth aspect, the swelling liquid is obtained by adding a surfactant to water, and the concentration adjusting means includes adding water or water to the swelling liquid. It is characterized in that the concentration of the swelling liquid is adjusted by supplementing a surfactant.

According to a sixth aspect of the present invention, in the sheet cleaning apparatus according to the fourth or fifth aspect, the surface tension detecting means includes a capillary and a liquid level detecting means for detecting a liquid level of the capillary. It is characterized by becoming.

[0019]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a sheet cleaning apparatus 1 according to the present invention. The sheet 2 from which the printing material such as toner is removed by the sheet cleaning device 1 is a so-called reusable sheet or a reusable OHP sheet, and a swelling layer made of a water-swellable resin is formed on the surface thereof. By swelling the swelling layer, the printing material printed on the sheet 2 can be removed.

The sheet cleaning apparatus 1 includes a sheet supply unit 3 for supplying a printed sheet 2 into the main body. The surface of the sheet 2 supplied into the main body by the sheet supply unit 3 is wetted by the swelling unit 4 in which the swelling liquid 6 whose surface tension (concentration) is adjusted to be constant by the surface tension adjusting mechanism 5 is jetted. Swell. The sheet 2 in which the swelling layer has swollen is conveyed to the printing material removing section 7 where the printing material is removed, and then conveyed to the sheet heating section 8 where it is discharged to the sheet discharging section 9 while being heated and dried.

Hereinafter, the configuration and operation of each part of the sheet cleaning apparatus 1 will be described in detail. The sheet supply unit 3 includes a tray 10 on which the printed sheets 2 are placed. The tray 10 is urged upward by a spring 11, and the uppermost sheet 2 placed on the tray 10 is in contact with a supply roller 12 provided above the sheet supply unit 3. The sheet 2 is fed into the sheet conveying path 13 by being driven to rotate.

The sheet transport path 13 is provided for transporting the sheet 2 from the sheet supply unit 3 to the sheet heating unit 8, and includes a guide plate 14 for supporting the sheet 2 and a sheet 2
And a plurality of transport rollers 15, 16, 17, 18, and 19 arranged on the guide plate 14 along the transport direction of the transport roller.

A housing 22 forming the swelling portion 4 and a housing 33 forming the printing material removing portion 7 are attached to the guide plate 14 of the sheet conveying path 13. The swelling part 4 is a sheet 2 that passes through the sheet conveying path 13.
The housing 22 includes a nozzle 21 for injecting a swelling liquid into the nozzle 21 and a swelling liquid supply unit 23 for supplying a swelling liquid to the nozzle 21. The swelling liquid supply unit 23 includes a swelling liquid supply pipe 24 and a swelling liquid storage tank 2 in which the swelling liquid 6 is stored.
And 5. One end 26 of the swelling liquid supply pipe 24 is inserted into the swelling liquid storage tank 25 and the other end 2
7 is connected to the nozzle 21. A pump 28 for pumping the swelling liquid 6 and an electromagnetic valve 29 for adjusting the flow rate of the swelling liquid 6 are connected to an intermediate portion of the swelling liquid supply pipe 24.

The printing material removing section 7 includes the housing section 33 having the nozzle 32 for spraying the swelling liquid 6 onto the sheet 2 conveyed while the printing material is removed, and the conveying roller 16.
And 17, and a swelling liquid collecting section 34 for collecting the swelling liquid 6 injected from the nozzle 32. The nozzle 32 is connected to a swelling liquid supply pipe 35 connected to the other end 27 of the swelling liquid supply pipe 24 so that the swelling liquid 6 can be ejected from the nozzle 32.

The swelling liquid recovery section 34 is constituted by a swelling liquid discharge pipe 36 having one end connected to the bottom surface of the housing section 33 and the other end connected to the top plate of the swelling liquid storage tank 25. The swelling liquid discharge pipe 36 is connected to an electromagnetic valve 37 for adjusting the discharge amount of the swelling liquid, and a filtration device 38 having a filter for removing a printing material contained in the swelling liquid. The swelling liquid 6 accumulated on the bottom surface is cleaned and collected in the swelling liquid storage tank 25.

The sheet heating section 8 is composed of a pair of heaters 41 sandwiching the sheet 2 from above and below. The sheet 2 sent out from the conveying roller 19 provided at the end of the sheet conveying path 13 is heated by the heater 41. It is heated and dried by passing through the space. A transport roller 42 is provided at the downstream end of the heater 41 in the transport direction, and the dried sheet 2 is transported to the sheet discharge unit 9. The sheet discharge section 9 includes a tray 43 on which the sheet 2 from which the printing material has been removed is placed.

Next, the surface tension adjusting mechanism 5 which is a feature of the present invention will be described. The inventor of the present invention has found that since the surface tension and the concentration of the swelling liquid 6 are correlated with each other, the concentration of the swelling liquid 6 can be obtained by measuring the surface tension of the swelling liquid 6. ing.

The surface tension adjusting mechanism 5 includes a swelling liquid storage tank 25.
A surface tension detecting device 46 for measuring the surface tension of the swelling liquid 6 stored in the swelling liquid, a surfactant replenishing device 47 for replenishing the swelling liquid storage tank 25 with a surfactant, and replenishing water to the swelling liquid storage tank 25. And a water replenishing device 48. Also,
The surfactant replenishing device 47 and the water replenishing device 48 are controlled by a control device 49 based on the measurement result of the surface tension detecting device 46.
It is controlled by.

As shown in FIG. 2, the surface tension detecting device 46 has a detecting tank 51 in which the swelling liquid 6 is stored. The top plate of the detection tank 51 and the bottom surface of the swelling liquid storage tank 35 are connected by a swelling liquid inflow pipe 53 having an electromagnetic valve 52. The electromagnetic valve 52 is controlled by a control device 49, and the swelling liquid 6 stored in the swelling liquid storage tank 35 flows into the detection tank 51 by opening the electromagnetic valve 52.

A swelling liquid discharge pipe 54 is connected to the bottom of the detection tank 51. The other end of the swelling liquid discharge pipe 54 is disposed inside the swelling liquid storage tank 35, and by driving a drainage pump 55 connected to the swelling liquid discharge pipe 54,
The swelling liquid 6 stored in the detection tank 51 can be discharged to the swelling liquid storage tank 35.

A photoelectric sensor 56 for detecting the level of the swelling liquid 6 stored in the detection tank 51 is provided inside the top plate of the detection tank 51. Further, inside the detection tank 51, a capillary tube 57 and a photoelectric sensor 58 are provided. Photoelectric sensor 5
Numeral 8 is composed of a light receiving portion and a light projecting portion, which are provided so as to sandwich the capillary 57, so that the height of the swelling liquid 6 that has entered the capillary 57, that is, the surface tension of the swelling liquid 6, can be measured. It has become. The photoelectric sensor 58 and the photoelectric sensor 56 are connected to a control device 49, and the measurement results are output to the control device 49.

The surfactant replenishing device 47 includes a tank 62 in which a high-concentration surfactant 61 is stored, and a known tube pump 63 for feeding the surfactant 61 in the tank 62 to the swelling liquid storage tank 35. Have been. The tube pump 63 is connected to the control device 49.
A predetermined amount of the surfactant 61 can be sent to the swelling liquid storage tank 35 based on the control signal of (1).
As the surfactant 61, anionic, cationic, nonionic, amphoteric and the like are used.

The water replenishing device 48 includes a water storage tank 65 for storing water 64 and a water storage tank 25 for storing the water in the tank 65.
And a water supply pipe 66 for supplying the water. A pump 67 is connected to the water supply pipe 66. The pump 67 is connected to the control device 49,
Based on the control signal of No. 9, the water stored in the water storage tank 65 can be supplied to the swelling liquid storage tank 25.

Next, the operation of the sheet cleaning apparatus 1 having the above configuration will be described. The sheet 2 placed on the top of the tray 10 of the sheet supply unit 3 is sent to the sheet conveyance path 13 by the rotation of the conveyance roller 12. The swelling liquid 6 is ejected from the nozzle 21 in the housing portion 22 of the swelling portion 4 of the sheet 2 to which the conveying force is applied by the conveying roller 15, and the swelling layer swells.
Since the swelling liquid 6 is adjusted to a predetermined concentration by the surface tension adjusting mechanism 5, the swelling layer of the sheet 2 swells well. The swelling liquid 6 swelling the sheet 2 in the swelling section 4 flows along the guide plate 14 into the housing 33 of the printing material removing section 7, where the printing material is removed by the filtering device 38, and the swelling liquid is cleaned. It is collected in the storage tank 25.

The printing material is scraped off from the sheet 2 having the swollen layer swollen by the rotating brush roller 31 in the printing material removing section 7. Further, the swelling liquid 6 is jetted from the nozzle 32, and the scraped printing material is washed away from the sheet 2. The printing material is removed from the swelling liquid 6 washed off from the sheet 2 by the filtration device 38, and is cleaned and collected in the swelling liquid storage tank 25.

The sheet 2 from which the printing material has been removed is conveyed to the heating section 8 by conveying rollers 17, 18 and 19. The sheet 2 conveyed to the heating unit 8 is discharged to the sheet discharging unit 9 in a state of being heated and dried by the heater 41.

The surface tension adjusting mechanism 5 includes a swelling liquid storage tank 25.
After the surface tension of the swelling liquid 6 stored in the swelling liquid 6 is measured, the surface tension (concentration) of the swelling liquid 6 is adjusted to a predetermined value by adding a surfactant 61 or water 64.

Here, the relationship between the surface tension and the concentration of the swelling liquid 6 will be described. As shown in FIG. 3, the surface tension (height above the liquid surface of the swelling liquid 6 stored in the detection tank 51) and the concentration measured by the capillary tube 57 (0.2 cm in diameter) are the value of the surface tension. Has a correlation in a range 70 of 30 to 71 dyne / cm, and it can be seen that the value of the surface tension in the range 70 reflects an accurate concentration. In the surface tension adjusting mechanism 5, when the measured value of the surface tension of the swelling liquid 6 is a value within the above range 70 and deviates from the set value,
Adjust the value of the surface tension as described below (for example,
The concentration of the surfactant contained in the swelling liquid 6 is 0.0005 to
When it is set to 0.005%, the level of the swelling liquid 6 entering the capillary 57 is 0.84 to 0.64 cm, and the surface tension is 41.2 to 31.4 dyne / cm. )

Next, measurement of the surface tension of the swelling liquid 6, replenishment of the surfactant, and replenishment of water in the surface tension adjusting mechanism 5 will be described in detail.

The surface tension of the swelling liquid 6 is measured by flowing a predetermined amount of the swelling liquid 6 into the detection tank 51 so that the swelling liquid 6 can enter the capillary 57. Regarding the operation, FIG.
This will be described with reference to the flowchart shown in FIG. Control device 4
9, the photoelectric switch 56 provided in the detection tank 51 is energized to make the level of the swelling liquid 6 stored in the detection tank 51 detectable (step S).
1).

The swelling liquid 6 stored in the swelling liquid storage tank 25 is caused to flow into the detection tank 51 by opening the solenoid valve 52 (step S2). The control device 49 determines whether the level of the swelling liquid 6 stored in the detection tank 51 is at a predetermined height (step S3). When the liquid level of the swelling liquid 6 has reached a predetermined height, the control device 49 closes the solenoid valve 52 and stops the swelling liquid 6 from flowing into the detection tank 51 (step S4).

The level of the swelling liquid 6 stored in the detection tank 51 is adjusted to a predetermined height because the value of the surface tension of the swelling liquid 6 adjusted to the set concentration is a predetermined value in the capillary 57. This is to ensure that the height is the same. That is, it is to prevent the level of the swelling liquid 6 that has entered the capillary 57 from changing according to the level of the swelling liquid 6 stored in the detection tank 51. This is also to make the value of the surface tension of No. 6 fall within the detection range of the photoelectric sensor 58.

Next, measurement of the surface tension of the swelling liquid 6, replenishment of the surfactant 61, and replenishment of the water 64 will be described with reference to the flowchart shown in FIG. When a predetermined number of sheets 2 have been cleaned, the control device 49 energizes the photoelectric switch 58 to cause the swelling liquid 6 having entered the capillary 57 to pass through.
The value of the surface tension (liquid level height) is detected, and the controller 49 determines whether this value is the surface tension corresponding to the set concentration (steps S10 and S11).

It is determined whether the detected value of the surface tension is equal to or less than the set value (step S12). If the value is equal to or less than the set value, the water storage pump 67 is driven to activate the value of the surface tension of the swelling liquid 6. A predetermined amount of water 64 is replenished to the swelling liquid 6 stored in the swelling liquid storage tank 25 so that the swelling liquid becomes the set value (Step S13). After refilling the water 64, the water storage pump 67 is stopped (step S14).

On the other hand, if it is determined in step S12 that the value of the detected surface tension exceeds the set value, the tube pump 63 is driven so that the surface tension of the swelling liquid 6 becomes the set value. A predetermined amount of the surfactant 61 is replenished to the swelling liquid 6 stored in the swelling liquid storage tank 25 (Step S15). After replenishing the surfactant, the tube pump 63 is stopped (step S16).

The operation of adjusting the surface tension of the swelling liquid 6 stored in the swelling liquid storage tank 25 as described above, that is, the operation when the concentration adjustment is completed, will be described with reference to the flowchart shown in FIG. The control device 49 controls the drain pump 5
5 is driven to discharge the swelling liquid 6 stored in the detection tank 51 to the swelling liquid storage tank 25 (Step S30). Detection tank 51
Is determined to be empty (step S31),
The drain pump 55 is stopped (Step S32).

As described above, each time the value of the surface tension of the swelling liquid 6 stored in the swelling liquid storage tank 25 is adjusted, the detection tank 51 is adjusted.
Since the swelling liquid 6 stored in the swelling liquid storage tank 25 is replaced, the accurate surface tension of the swelling liquid 6 stored in the swelling liquid storage tank 25 can be measured.

The configuration for measuring the surface tension of the swelling liquid 6 stored in the swelling liquid storage tank 25 is not limited to the capillary 57 and the photoelectric switch 58, but may be a dropping method, a suspension ring method, or the like.
Although an apparatus to which a method such as a maximum bubble pressure method, a vibrating droplet method, and a surface wave method can be used, the configuration including the capillary tube 57 and the photoelectric switch 58 is the cheapest and has the highest reliability.

In the surface tension adjusting mechanism 5, water 64 or surfactant 6 is used based on the measured surface tension value.
1 is added to the swelling liquid 6 to adjust the surface tension of the swelling liquid 6 to a predetermined value. In order to secure the amount of the swelling liquid 6, a predetermined amount of water 64 is added to the swelling liquid 6. Thereafter, the surface tension may be measured, and the surface tension may be adjusted by replenishing the water 64 or the surfactant 61.

Further, the swelling liquid 6 stored in the swelling liquid storage tank 25 is provided so as to be maintained at a constant amount by adjusting the pumping amount of the pump 28, for example.
7 and the photoelectric sensor 58 may be provided in the swelling liquid storage tank 25 to measure the value of the surface tension of the swelling liquid 6 stored in the swelling liquid storage tank 25. In this configuration, since it is not necessary to provide the detection tank 51 and the like, the manufacturing cost of the sheet cleaning device 1 can be reduced.

In the sheet cleaning device 1, the surface tension detecting device 46 is used instead of the surface tension adjusting mechanism 5.
And the surfactant replenishing device 47 and the water replenishing device 4
8 may be provided (not shown). In the concentration adjusting mechanism, the measured swelling liquid 6
Is converted into a concentration, and water 64 or a surfactant 61 is added to the swelling liquid 6 to adjust the concentration of the swelling liquid 6 to a predetermined value to maintain the swelling property of the sheet 2 in good condition. Can be.

[0052]

As is clear from the above description, in the present invention, the surface tension of the swelling liquid is detected by the surface tension detecting means, and based on the measurement result, the surface tension detecting means detects the surface tension of the swelling liquid. Or the concentration adjusting means adjusts the concentration of the swelling liquid. The measured value of the surface tension of the swelling liquid is accurate and stable compared to the measured values of the electric conductivity and the transmittance, and since there is a correlation between the surface tension and the concentration, The density can be adjusted to a predetermined value. Therefore, the printed sheet can be swelled satisfactorily, and the printing material can be satisfactorily removed.

Further, by forming the surface tension detecting means with a capillary and a liquid level detecting means for detecting the liquid level of the capillary, an inexpensive and accurate sheet cleaning apparatus can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a sheet cleaning device according to the present invention.

FIG. 2 is a schematic explanatory view of a surfactant replenishing device.

FIG. 3 is a chart showing the relationship between surface tension and concentration.

FIG. 4 is a flowchart showing an operation of storing a swelling liquid in a detection tank.

FIG. 5 is a flowchart showing an operation of adjusting the concentration of the swelling liquid.

FIG. 6 is a flowchart showing an operation of discharging a swelling liquid from a detection tank.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Sheet cleaning device, 2 ... Sheet 5, 5 ... Surface tension adjustment mechanism, 6 ... Swelling liquid, 25 ... Swelling tank, 47 ... Surfactant replenishing device, 48 ... Water replenishing device, 49 ... Control device, 6
1 ... surfactant, 64 ... water.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C061 AS13 GG03 GG07 GG13 GG22 GG33 2H034 FA00 3B116 AA04 AB16 AB42 BA02 BA15 BB01 BB22 BB33 BB62 CA01 CD22 CD42 CD43 3B201 AA04 AB16 AB42 BA02 BA15 BB01 BB22 BB33

Claims (6)

[Claims] 1. A printing material removing means for removing a printing material of a printed sheet swollen with a swelling liquid, a surface tension detecting means for detecting a surface tension of the swelling liquid, and adjusting a surface tension of the swelling liquid. A sheet cleaning device comprising: a surface tension adjusting unit. 2. The swelling liquid is obtained by adding a surfactant to water, and the surface tension adjusting means reduces the surface tension of the swelling liquid by replenishing the swelling liquid with water or a surfactant. The sheet cleaning apparatus according to claim 1, wherein the adjustment is performed. 3. The sheet cleaning apparatus according to claim 1, wherein said surface tension detecting means comprises a capillary and a liquid level detecting means for detecting a liquid level of the capillary. 4. A printing material removing means for removing a printing material of a printed sheet swollen with a swelling liquid, a surface tension detecting means for detecting a surface tension of the swelling liquid, and a measurement method based on a measurement result of the surface tension detecting means. And a concentration adjusting means for adjusting the concentration of the swelling liquid. 5. The swelling liquid is obtained by adding a surfactant to water, and the concentration adjusting means adjusts the concentration of the swelling liquid by replenishing the swelling liquid with water or a surfactant. The sheet cleaning device according to claim 4, wherein: 6. A sheet cleaning apparatus according to claim 4, wherein said surface tension detecting means comprises a capillary and a liquid level detecting means for detecting a liquid level of the capillary.