EP0041198B1 - Device for the removal of developing liquid from a recording material - Google Patents

Description

The invention relates to a device for removing developer liquid from a recording material in an electrophotographic copier, in which the recording material is charged, exposed with an image of an original and the latent charge image is developed by applying the developer liquid to a visible image with one moving in the opposite direction Recording medium rotating roller, which forms a gap to the surface of the recording material of less than 0.05 mm.

Such a device is described in DE-B-2 361 833, in which a wiping roller for the developer layer rotates in a collecting container and wipes developer liquid from the photoconductor layer. The smaller the gap between the photoconductor layer and the counter-rotating roller, the greater the wiping effect. In the known device, the column width is 0.01 mm to 1 mm. In this device, the roller is electrically insulated from the copier and a pretension is applied to it. To ensure the gap, lateral support rollers are provided, over which the roller rolls.

A doctor blade arrangement held in fixed contact with the roller serves to wipe off the excess developer liquid from the roller and to clean it. The developer liquid stripped from the doctor blade arrangement is collected in the collecting container.

Wiping off the excess developer liquid is necessary in order to leave only a precisely defined remaining thickness of developer liquid on the photoconductor layer and in order to be able to easily clean the photoconductor layer before starting a new copying cycle. Decreasing the developer liquid layer on the photoconductor layer prior to transferring the developed charge image improves the quality of the transferred charge image and facilitates drying of the copies.

In the device known from DE-A-1 937 019 ^; A squeeze roller is held under pressure against the surface of the recording material to squeeze off excess developer liquid therefrom, but there is a risk that the toner image may be damaged.

In the device known from US-A-3 596 635, too, a roller rests on the surface of the recording material in order to wipe off excess developer liquid from the surface. The problem with these known devices is that the pressure between the stripper roller and the surface of the recording material can be different, since it is known that it is very difficult to produce rollers with very smooth and uniformly curved peripheral surfaces. For example, photoconductor drums, on the circumferential surfaces of which the recording material is attached, are generally either bulbous or barrel-shaped, deviations from an ideal cylinder surface of up to 0.02 mm can occur, which in rare individual cases can even be higher. The diameter of the scraper rollers is also subject to certain manufacturing fluctuations due to the post-treatment of the surfaces, so that when the squeeze roller is in direct contact with a photoconductor drum, different pressures between the two rollers must always be expected, which can lead to the toner images being unevenly removed from the photoconductor drum the image receiving material is transmitted.

The stripper rollers used in electrophotographic copiers generally have an aluminum surface which is provided with an anodized layer. It is shown that fine grooves can be ground in such anodized layers due to dust that adheres to the squeegee, with prolonged use, which can impair the wiping off of the excess developer liquid squeezed off by the photoconductor drum using the squeegee.

It is therefore desirable to keep the gap between the photoconductor drum or the recording material and the roller for removing the excess developer liquid as small as possible, but such a gap reduction can only be achieved by changing the diameter of the support rollers on which the squeeze roller runs or by Changing the diameter of the squeeze roller because of the aforementioned manufacturing tolerances of the curvature of the cylinder surface is not readily feasible if the aim is always to maintain a gap between the recording material and the squeeze roller.

The object of the invention is to improve a device for removing the developer liquid of the type described in the introduction in such a way that the developer liquid transferred from the recording material to the image-receiving material is reduced to an amount sufficient for proper image development compared to known removal devices, and at the same time the environmental pollution caused by vaporized hydrocarbon is reduced is reduced from the dispersant of the developer liquid.

This object is achieved in that the roller carries a surface layer made of a material with greater lubricity and a lower degree of hardness than the recording material and that the surface layer is applied to the roller by shrinking or spraying.

The width of the gap between the roller and the recording material is preferably in the range from 0.025 to 0.03 mm. The surface layer of the roller consists of a material that is softer than the recording material. To achieve this, the surface layer of the roller consists of silicone resins, polymers or a shrink film made of organic material.

In a further embodiment of the invention, the surface layer of the roller is formed by shrinking on two shrink films. The shrink films preferably have the form of polyester shrink sleeves, which shrink on the roller due to the action of hot water or hot air while reducing the diameter.

The further development of the invention results from the features of claims 7 to 12.

With the invention in particular the advantages are achieved that the surface layer of the stripping roller can be replaced in a simple manner and that manufacturing tolerances of the cylindrical surface of the stripping roller and also the photoconductor drum surface can be compensated for by adapting the thickness of the surface layer of the stripping roller to the different diameters.

Exemplary embodiments of the invention are described below with reference to the drawings.

• Fig. 1 eine schematische Schnittansicht einer Anordnung aus Fotoleitertrommel und eine Ausführungsform der Abstreifwalze;
• Fig. 2 eine schematische Schnittansicht einer Anordnung aus einer Fotoleitertrommel mit ungleichmäßigem Durchmesser über die Trommellänge und der mit ihrem Durchmesser daran angepaßten Abstreifwalze;
• Fig. 3 eine schematische Schnittansicht einer Anordnung aus Fotoleitertrommel und einer weiteren Ausführungsform der Abstreifwalze;
• Fig. 4 eine schematische Schnittansicht einer Anordnung aus einer Fotoleitertrommel mit ungleichmäßigem Durchmesser und der daran angepaßten Ausführungsform der Abstreifwalze nach Fig. 3;
• Fig. eine schematische Schnittansicht, ähnlich derjenigen nach Fig. 3, mit zwei Schrumpffolien auf der Abstreifwalze.

It shows

• Figure 1 is a schematic sectional view of an arrangement of photoconductor drum and an embodiment of the stripping roller.
• Figure 2 is a schematic sectional view of an arrangement of a photoconductor drum with an uneven diameter over the drum length and the stripping roller with its diameter adapted to it.
• 3 shows a schematic sectional view of an arrangement comprising a photoconductor drum and a further embodiment of the stripping roller;
• FIG. 4 shows a schematic sectional view of an arrangement of a photoconductor drum with an uneven diameter and the embodiment of the stripping roller according to FIG. 3 adapted to it;
• Fig. A schematic sectional view, similar to that of FIG. 3, with two shrink films on the stripping roller.

The schematic sectional view according to FIG. 1 shows an arrangement of a photoconductor drum 1 and a stripping roller 2 arranged at a distance therefrom. Instead of a photoconductor drum 1, the circumference of which is covered with the photoconductor 12, a photoconductor belt guided around a roller can also be used. As is known, in electrophotographic copiers, the photoconductor layer which is applied to the photoconductor drum or the photoconductor tape as the recording material is electrostatically charged, imagewise exposed, and the charge image obtained with developer liquid from liquid hydrocarbons as the dispersing liquid and the electrostatically charged pigments dispersed therein is developed into a pigment image which the image carrier material, for example paper, is transferred. The photoconductor layer is cleaned of residual electrostatic charges and pigments for each copying cycle.

In order to improve the quality of the pigment image transferred and to facilitate the drying of the copies, the thickness of the film of developer liquid on the photoconductor layer is reduced before the transfer to the image carrier material. The electrical corona charging device, exposure station, development station, image transfer station and a cleaning device arranged around the photoconductor drum 1 are not shown.

The stripping roller 2 consists of a roller core 10 and a surface layer 4. Between the stripping roller 2 and the photoconductor drum 1 there is a gap d which is less than 0.05 mm and in particular in the range from 0.025 to 0.03 mm.

On the shaft of the stripping roller 2 there are 8 support rollers 3 at a short distance from the end faces, which rest against the photoconductor drum 1 and roll on the latter during the rotation of the stripping roller 2 and the photoconductor drum 1.

The surface layer 4 consists of a material with greater lubricity than the recording material or the photoconductor on the photoconductor drum 1. The size of the gap d is determined by the thickness of the surface layer 4. If the gap is made ever smaller, there is a risk that the photoconductor layer and the circumferential surface of the stripping roller 2 touch in an undesirable manner. In the case of a conventional scraper roller, which generally has a hard anodized surface, this would lead to an irreparable result. Scratching the photoconductor layer. Because of the surface layer 4 made of a material with greater lubricity than that of the photoconductor layer, if the photoconductor drum 1 and the stripping roller 2 are not touched during operation, the mutual abrasion effect between the photoconductor drum and the stripping roller is negligible and no damage occurs since the surface layer 4 softer, in the sense of a lower degree of hardness than the photoconductor layer. Silicone resins, polymers or organic foils are used as the material for the surface layer 4.

The lubricity of these materials is important for operation, since with gap widths of less than 0.05 mm, only the direct copying attempt can ultimately provide information as to whether the surface layer 4 can be further reinforced, i.e. the gap d can be further reduced or whether the photoconductor drum 1 and the surface layer 4 of the stripping roller 2 are already touching. The latter case will as a result that the copies show wiping flags at appropriate locations.

The arrangement according to FIG. 2 shows a schematic sectional view of a photoconductor drum 1 with an uneven diameter over the drum length and a stripping roller 2 with its diameter adapted to the photoconductor drum. The bulge of the photoconductor drum 1 is exaggerated in FIG. 2. The roller core 10 of the stripping roller 2 is connected to a voltage source 9, which supplies either a fixed voltage or a variable voltage.

The stripper roller 2 of this arrangement is formed, for example, with a surface layer 4 by spray application of a solution of poly-N-vinyl carbazole, dissolved in tetrahyrofuran. The spray application offers the possibility of building up the thickness of the surface layer 4 in several stages, by reinstalling the stripping roller 2 in the copying machine after each spray application and checking whether wiping flags occur. The polymer specified above is a material that is also used as a photoconductor. In the present case, however, use is not made of photoconductivity, but only of the property that poly-N-vinyl carbazole does not dissolve in the dispersing liquid for the toner pigments. This dispersing liquid is an aliphatic hydrocarbon.

When applying the surface layer 4 by spraying, it turns out that the individual adaptation of the surface of the stripping roller 2 to the surface profile of the photoconductor drum 1 can be done without great difficulty, since the spraying does not result in a uniform reinforcement of the surface layer 4 over the entire length of the Scraper roller 2 must lead. To compensate for or to compensate for the bulge or convex or concave curvatures over the length of the photoconductor drum 1, it is possible to reduce or increase the thickness of the sprayed surface layer compared to the curvatures of the photoconductor drum 1, so that the gap d over the entire Length of stripper roller 2 and photoconductor drum 1 has a uniform width.

For the service life of the surface layer 4 for a few tens of thousands of copies, surface layers made of materials in the form of organic foils, such as shrink foils or shrink sleeves, have proven particularly useful. FIG. 3 shows a stripping roller 2 which has a shrink film 5 made of an organic material as the surface layer. It is preferably a polyester shrink tube that is shrunk onto the stripper roller 2 by the action of hot air or hot water at a temperature greater than 100 ° C. For example, such a polyester shrink tube has a diameter of 32 mm and is shrunk onto a stripper roller 2 with a 28 mm diameter. In order to avoid wrinkles occurring in the shrink tube during operation, a heat seal layer 6 of 5 to 10 μm thick is applied to the inside of the shrink film 5 or to the circumferential surface of the roller core 10 of the stripping roller 2 before shrinking on. The heat seal layer 6 can be a conventional hot melt adhesive which is not or only very slightly soluble in the dispersing liquid of the developer liquid. Suitable hot melt adhesives consist, for example, of polystyrene or wax-resin mixtures and soften at temperatures of up to 80 ° C.

The shrink film 5 is provided with end pieces 5a which laterally protrude beyond the end faces 8 of the stripping roller 2 before being shrunk on. The end pieces 5a contract more during the shrinking than the parts of the shrink film 5 which shrink directly onto the roll core 10 and thereby lie laterally on the end faces, thereby tearing the shrink film 5 and penetration of dispersing liquid between the shrink film 5 and the surface of the roller core 10 of the stripping roller 2 is prevented.

The roller core 10 of the stripping roller 2 is connected to a voltage source 9 and, for example, a voltage of +500 volts is applied to the stripping roller 2.

With a stripping roller 2 prepared with a tubular film 5 of 0.02 mm thickness, investigations into the discharge of dispersing liquid were carried out in a conventional copying machine, the heating for switching off the copies being switched off. The copies were weighed before and after copying. A discharge of dispersing liquid of 0.069 g / A4 copy was calculated from the difference in weight. With the shrink-free stripping roller 2 and a nominal gap d between the stripping roller 2 and the photoconductor drum 1 of 0.05 mm, the discharge of dispersing liquid was 0.108 g / A4 copy. Similar values were obtained with different dispersing liquids, such as Isopar G, Isopar H, Isopar L and Isopar M, which are all aliphatic hydrocarbons. In these investigations, the gap d between the stripping roller 2 provided with a tubular film 5 and the photoconductor drum 1 was 0.03 mm.

In the case of a double-shrunk stripper roller 2 with an effective thickness of the tubular film of 0.04 mm, the discharge of dispersing liquid was only 0.02 g / A4 copy, but the copies showed wipers, so that a gap d of 0 for practical use , 01 mm between the stripping roller 2 and the photoconductor drum 1 is not possible. Practical tests showed that the width of the gap d was 0.025 mm.

It is obvious that with in the thickness graduated heat shrink tubing of, for example, 0.020 mm, 0.025 mm, 0.030 mm and 0.035 mm, a quick and individual adjustment of the gap d between the stripping roller 2 and the photoconductor drum 1 of a removal device for excess developer liquid can be carried out in copiers.

4 shows an arrangement of a photoconductor drum 1 with a non-uniform diameter over the photoconductor length and a further embodiment of the stripping roller 2 adapted to it. In this stripping roller 2, a molded layer 7, for example a polymer, is applied by spraying onto the peripheral surface of the roller core 10. The bulky nature of the photoconductor drum 1 is again exaggerated in FIG. 4. The molded layer 7 is adapted to the surface profile of the photoconductor drum 1 in such a way that the gap d has a constant width over the entire length of the photoconductor drum. As soon as the molding layer 7 has hardened, a tubular film 5, which is provided on the inside with a heat-sealing layer 6, is shrunk onto the stripping roller 2 in the manner described above.

5 shows an arrangement of stripping roller 2 and photoconductor drum 1, which is constructed similarly to the arrangement according to FIG. 3, with the difference that instead of a single tubular film 5, two tubular films 5 and 11 are shrunk onto the roller core 10 of the stripping roller 2 .

The tubular films or polyester shrink sleeves are very stable and, for example, no signs of wear can be seen after 15,000 copies. With the above-described or equipped with shrink-wrapped tubular films, the advantages are achieved that the discharge of dispersing liquid is considerably reduced compared to conventional removal devices for excess developer liquid and that a renewal of the surface layer of the stripping rolls is possible without great effort. To renew the surface, for example, the tubular film is cut on one side and pulled off the stripper roller, which is cleaned of residual hot melt adhesive with a solvent. A new tubular film is then shrunk onto the stripper roller.

A renewal of the surface layer, which was formed by spray application of a polymer, is possible in a similarly simple manner. These sprayed-on surface layers are removed by washing with suitable solvents and can then be reapplied.

Claims (12)

1. A device for removing devr toper liquid from a recording material present in an electrophotographic copying machine in which the recording material is charged, exposed to an optical image of an original, and the latent charge image obtained is developed into a visible image by applying developer liquid, for which purpose a roller rotating in the direction opposite to the direction of movement of the recording material is used, said roller being arranged in a way such that a gap (d) (smaller than 0.05 mm) is formed between the roller and the recording material, characterized in that the roller (2) is provided with a surface layer (4) of a material having better sliding properties and a smaller degree of hardness than the recording material (12), and in that said surface layer (4) is surfaced onto the roller (2) by shrink fitting or spraying .

2. A device as claimed in claim 1, characterized in that the width of the gap (d) between the roller (2) and the recording material (12) is in a range from 0.025 mm to 0.030 mm.

3. A device as claimed in claim 1, characterized in that the surface layer (4) of the roller (2) is made of silicone resins or of polymers.

4. A device as claimed in claim 1, characterized in that the surface layer (4) of the roller (2) is made of a shrink film (5) of an organic material.

5. A device as claimed in claim 4, characterized in that the surface layer (4) of the roller (2) is formed by shrinking on two shrink films (5, 11).

6. A device as claimed in claims 4 and 5, characterized in that the shrink films (5, 11) have the form of polyester shrink tubes which by the action of hot water or hot air shrink onto the roller (2), whereby their diameter is reduced.

7. A device as claimed in one of the claims 4 to 6, characterized in that a hot seal layer (6) is present on the inside of the shrink films (5, 11), said layer having a thickness of 5-10ftm.

8. A device as claimed in claim 7, characterized in that the hot seal layer (6) is insoluble in the dispersing liquid of the developer liquid.

9. A device as claimed in claim 3, characterized in that the surface layer (4) of the roller (2) is formed by spraying on a solution of poly-N-vinyl carbazole, dissolved in tetrahydrofurane.

10. A device as claimed in claim 9, characterized in that the spray application of the surface layer is carried out in accordance with the surface of the roller (2), such that all irregularities, concave or convex bulgings of the latter over its length are compensated for in a way such that the gap (d) has a uniform width over the whole length of the roller (2) and of the recording material (12).

11. A device as claimed in one of the claims 4 to 7, characterized in that each front surface (8, 8) of the roller (2) is overlapped by an end piece (5a) of each shrink film (5, 11) and in that the two end pieces (5a, 5a) are shrunk to such a high degree that they are adjacent to the front surfaces (8, 8) of the roller (2) and seal the latter so that no developer liquid can penetrate under the shrink films (5, 11).

12. A device as claimed in claim 7, characterized in that a shapeable layer (7) is applied onto the roller core (10), which layer is adjusted to the circumferential surface of the photoconductor drum (1) serving as the recording material.

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