EP0754985B1 - Inking device for developing drum - Google Patents

Description

The present invention relates to a device for inking a drum development and concerns the development of latent images in a non-impact printer with high printing speed, i.e. for speeds greater than 10 m / min.

In this type of printer, a latent image is generated on a medium and is then developed by ink made up of particles solids (toner). This toner is then transferred to the print medium (paper, plastic, labels, ...) and finally fixed on this support.

• la magnétographie : l'image latente est générée sur une couche d'enregistrement (médium) par des têtes d'écriture magnétique,
• l'électrophotographie ou xérographie : le médium est une couche photosensible qui est sensibilisée par rayon lumineux (généré par laser ou par une rangée de diodes),
• l'électrographie ou ionographie : le médium est une couche diélectrique sur laquelle les têtes d'écriture déposent des charges électriques.

The printers concerned by this invention are based on the following technologies:

• magnetography: the latent image is generated on a recording layer (medium) by magnetic writing heads,
• electrophotography or xerography: the medium is a photosensitive layer which is sensitized by light ray (generated by laser or by a row of diodes),
• electrography or ionography: the medium is a dielectric layer on which the writing heads deposit electrical charges.

The toners concerned are of the mono-component type: the particles ink contain magnetic pigments.

The inking devices known to date consist in putting the toner in contact with the medium in order to develop the latent image which is present on its surface. On the other hand, in non-pictured areas, it should not not stay toner.

• sur une image latente, les forces de développement (attraction magnétique du toner par les dots) sont supérieures aux forces antagonistes et il y a encrage,
• dans les zones ne devant pas être encrées, les forces antagonistes doivent être supérieures aux différentes forces qui tendent à fixer les particules d'encre sur le médium (forces d'adhésion, forces électrostatiques,...).

A good inking device must therefore bring into play opposing forces, which will act on the ink particles in the following manner:

• on a latent image, the development forces (magnetic attraction of the toner by the dots) are greater than the opposing forces and there is inking,
• in the areas not to be inked, the opposing forces must be greater than the various forces which tend to fix the ink particles on the medium (adhesion forces, electrostatic forces, ...).

Such a device must make it possible to obtain good darkness with a minimum background (residual toner in non-inked areas).

In most devices used in other technologies, the opposing forces are magnetic and the forces of development are electrostatic. These magnetic forces are created by magnets arranged inside a tube. This device is called a magnetic brush. It is limited in writing speed and cannot be used with our technology because the magnets disturb the latent image which is itself magnetic. On the other hand, the presence of a magnetic shunt under the layer recording, due to magnetography in the case of a writing perpendicular to the surface of the medium, to allow writing perpendicular to the surface of the medium, makes the forces ineffective antagonistic, because equivalent but opposite "image" forces are generated through this shunt, and cause an increase important from the bottom.

Another technique taught by EP patent applications 086683 and FR 2530044 has been developed. It consists of putting ink pressure on the medium. The ink is taken to the drum by by means of a magnetic conveyor consisting, for example, of a tube coated with magnetic rubber attracting toner particles. This tube is scraped by a metallic "wedge" located very close to the drum, which allows the ink to come into contact with it, and to compact it in the development area.

The opposing forces are then mainly forces of inter-particle cohesion.

a) dans la zone de développement, le toner en contact avec le tambour est entraíné par celui-ci, mais il existe une vitesse relative entre ce toner, et le tambour :

• à basse vitesse d'impression, cette vitesse relative devient très faible car le toner est facilement entraíné par le tambour, ce qui génère un fond important mais avec une forte noirceur de l'écriture,
• à haute vitesse d'impression, la vitesse relative devient importante, et il est alors difficile d'entraíner les particules de toner sur le tambour. Le niveau de fond devient très bas mais avec une noirceur plus faible, particulièrement sur les traits horizontaux ;

   ce système convient donc pour une vitesse d'impression de l'ordre de 15 m/mn et on observe à grande vitesse (> 40 m/mn) des difficultés à développer des horizontales de faible épaisseur.

b) d'autre part, la distance entre le coin d'encrage et le tambour étant petite (de l'ordre de 1 mm), des traces blanches dans l'impression dues à des agglomérats de toner restant bloqués entre le coin et le tambour, peuvent apparaítre dans certaines conditions.

However, prior devices using a covered tube scraped by a metal wedge have the following limitations:

a) in the development zone, the toner in contact with the drum is driven by it, but there is a relative speed between this toner, and the drum:

• at low printing speed, this relative speed becomes very low because the toner is easily entrained by the drum, which generates a significant background but with a strong blackness of the writing,
• at high printing speed, the relative speed becomes important, and it is then difficult to entrain the toner particles on the drum. The background level becomes very low but with a lower blackness, particularly on the horizontal lines;

this system is therefore suitable for a printing speed of the order of 15 m / min and we observe at high speed (> 40 m / min) difficulties in developing thin horizontal lines.

b) on the other hand, the distance between the inking corner and the drum being small (of the order of 1 mm), white marks in the printing due to toner agglomerates remaining blocked between the corner and the drum, may appear under certain conditions.

Furthermore, such devices require for operation correct the presence of a touch-up device such as that taught by the European patent application EP 0142446. Such retouching devices thus made it possible to obtain printing speeds of the order of a few tens of cm / s, i.e. around 15 to 20 m / min. These devices retouch consisted of a rotating cylinder inside which a fixed magnet is placed inside the rotary cylinder, the assembly being disposed near the development drum downstream of the device solid particle applicator with respect to the direction of rotation of the drum.

The object of the invention is therefore to overcome the drawbacks of the art prior.

This object is achieved by the fact that the device for inking a drum development including a function in an inking box drum inking, magnetic retouching function, pneumatic touch-up and a sealing device for the inking box characterized in that the printing medium drum is inking by a wave of solid particles containing a powdery pigment magnetic contained in the inking box raised by means of anchoring device, said wave moving in opposite direction to the displacement of the surface of the print drum.

According to another particular feature, the means of the inking device have a magnetic conveyor drum associated with a deflector inclined relative to the horizontal by a determined angle, said drum conveyor rotating in opposite direction of the medium printing drum at a determined speed, said deflector being arranged downstream of the direction of Junction of the conveyor drum and printing drum centers on the one hand at a first adjustable distance from this direction and on the other hand at a second adjustable distance from the printing medium drum.

According to another particularity, the determined speed is understood between 85 rpm and 180 rpm for a printing speed of 20 to 60 m / min.

According to another particular feature, the determined angle of inclination is around 50 °.

According to another particular feature, the first adjustable distance is from 0 to 5 mm, and the second adjustable distance is from 4 to 5 mm.

According to another particularity, a device for calibrating the thickness of the ink layer of the inking device consists of a second lower conveyor drum arranged below the first conveyor drum, a scraper being arranged in contact with the second conveyor and providing space with the first conveyor drum and on the other hand a pressure plate placed at a distance of the order of 3 mm from the first conveyor drum and at an angle of about 56 ° per compared to the horizontal.

According to another feature, the scraper is arranged at a distance of the first conveyor drum of the order of 2.6 mm.

According to another particular feature, the device comprises a mixer toner and a sensor to determine the transfer of new amount of toner from a reserve box to the ink box.

According to another particular feature, the magnetic retouching device comprises a third magnetic conveyor drum arranged at a adjustable distance and rotating at high speed in reverse direction of the drum printing medium and associated with a cleaning squeegee of this third drum, said third drum being arranged downstream of the first drum printing medium in relation to the direction of rotation of the medium drum printing.

According to another particular feature, the adjustable distance is between 1 and 3 mm.

According to another particular feature, the pneumatic retouching device has a suction nozzle arranged perpendicular to the drum printing medium for vacuuming toner particles entrained in the wake of other particles.

According to another particular feature, the sealing device comprises a closing plate of the inking box disposed downstream relative to the direction of rotation of the printing medium drum, said sheet having a square shape with one side parallel to the drum and very close of it, a fan is disposed outside of the inking box to generate an overpressure near the sheet between the nozzle and the box.

Other features and advantages of the present invention will appear more clearly on reading the description below made in reference to the single appended figure which represents the block diagram of the device according to the invention.

The device includes an inking function (15) of the drum (1), a magnetic retouching function, a pneumatic touch-up and a function ensuring the tightness of the box inking. The ink drum printing function is performed by the projection of ink or toner, formed of solid particles of a pigment pulverulent with magnetic properties on the drum (1) printing medium.

This projection is provided by an upper conveyor drum (2) on which the ink layer present on its surface is scraped by a deflector (3). The rotation speed of the conveyor drum is such that the deflector generates a "wave" of ink or toner into which the printing drum in the opposite direction to the wave.

To calibrate the thickness of the ink layer of the conveyor drum upper (2), a conveyor / wedge device is used. The toner transported by the lower conveyor drum (6), is scraped by the wedge (7), and is put in contact with the upper conveyor drum (2). The choice of distance (E) between the corner (7) and the upper conveyor drum (2) will adjust the thickness of this layer. In addition, the toner is kept pressed on this upper conveyor drum (2) by the pressure plate (8) arranged at a distance (D) from the upper conveyor drum (2).

The toner present in the bottom of the inking box, remains "fluid" through the use of a mixer (9), and its level is precisely regulated by a sensor (10) which controls the transfer of the toner, from a reserve (not shown) to the box (15), as soon as the toner / sensor distance becomes too important.

The magnetic retouching function which consists in removing the excess toner the inked areas is done by the touch-up device magnetic. Unlike the prior art device composed of a fixed magnet inside a rotating metal cylinder, the invention uses here a third conveyor drum (4), similar to the previous ones, rotating at high speed in reverse direction of the print drum (1) and cleaned by a squeegee (5). The latent image being, in this new printer, formed of alternating magnetic dots, each of the dots will be subjected to the alternating magnetic fields of the magnets of the retouching drum (4). The speed of retouching should be high enough to avoid modulations of blackness in writing, and in particular in gray.

Adjusting the distance (C) between the third conveyor drum (4) and the printing drum (1) allows to take into account the type of magnetic coating used for the conveyor drum and level desired retouch.

Pneumatic touch-up device includes a nozzle suction (11) arranged perpendicular to the medium drum (1) printing. This device improves the straightness of the edges of the lines, removing by suction all the toner particles which are entrained in the wake of others and which deteriorate the sharpness of these traits.

The vacuum inside the suction nozzle (11) can be adjusted to have the best compromise between the darkness of the writing and the sharpness of the edges of lines.

A sealing device (12) of the inking box ensures sealing for high writing speeds> 50 m / min and prevents toner particles can be entrained by the drum the outside of the inking box and thus generate tasks in the impression.

To avoid these problems, a sheet (13) for closing the box anchor (15), has a square shape, one of the faces of which is parallel to the printing drum (1) and whose positioning is adjusted very close to this one. In addition, a fan (14) generates an overpressure between the device pneumatic touch-up and the sheet (13) outlet of the inking box.

The different conveyor drums are coated with rubber magnetic with straight poles, 2.54 mm pitch, and 1 mm thick.

The rotation speed of the first conveyor drum (2) is between 95 rpm and 180 rpm for a varying printing speed between 20 and 60 m / min.

The deflector (3) has a width of 6 mm, and its active face inclined by the order of 50 ° relative to the horizontal and the edge (30) of the deflector (3) located near the conveyor drum (2) is arranged at an adjustable distance (B) between 0 and 5 mm, while the upper edge of the deflector arranged at proximity to the printing drum (1) is arranged at a distance (A) adjustable between 4 and 5 mm. The space (E) available between the lower corner (7) and the conveyor drum (2) is of the order of 2.6 mm.

The pressure plate (8) located between the beater drum (9) and the lower conveyor drum (6) has an inclination relative to the horizontal of the order of 56 °. The upper end of the sheet (8) is located at distance (D) of the order of 3 mm from the upper conveyor drum (2).

The magnetic retouching conveyor drum (4) is arranged at a distance (C) adjustable from 1 to 3 mm from the printing drum (1). The speed of rotation of the magnetic retouching drum (4) is included between 85 and 160 rpm for a writing speed varying from 20 to 60 m / min.

The closing plate (13) is arranged at an adjustable distance of from 0.15 to 0.25 mm from the printing drum (1).

So in this new inking device, a conveyor drum magnetic (2) is covered with a layer of toner, due to the attraction magnetic between the toner and this conveyor drum (2). This layer, enough compact, is separated from the conveyor by the action of a deflector (3).

Given the speed of the conveyor drum (2), there is formation a wave of toner that separates frankly from the conveyor drum and from the upper edge of the deflector before returning to fix it again or fall back into the inking box (15). The printing drum (1) penetrates slightly in this wave, and moves in the opposite direction, training a little toner with him. The toner particles are therefore projected against the drum, and there is a differential speed between that of the particles of toner in contact with the drum and the linear speed of the surface of the drum.

Indeed the thickness of the toner layer driven by the drum conveyor between the latter and the squeegee (7) is limited by the dimension E to worth 2.6 mm. Furthermore the distance between the upper edge (30) of the deflector (3) and the printing medium drum (1) is greater than the value of the thickness of the toner layer driven by the conveyor drum (2). If there was no detachment and creation of a wave, the toner would not come not in contact with the printing medium drum (1).

For particles to attach to the drum, the forces must magnetic due to the latent image be able to retain these particles on its surface. In unwritten areas, parasitic forces (forces adhesion, electrostatic forces ...) are too weak to retain toner, and the background level is then very low.

In the ink area, the toner is not compacted and the ink particles are projected against the drum. In addition, the device allows an increase in the speed of the conveyor drum and the printing drum speed, which gives a correct ink for high write speeds, such as 60 m / min, especially in the case of fine horizontal lines. On the other hand, the distance between the medium drum printing (1) and the deflector (3) which is of the order of 5 mm, allows avoid the presence of agglomerates in this area, and the generation of white marks in the writing.

Claims (12)

1. Inking device of a development drum comprising in an inking container (15) an inking function of the drum, a magnetic retouching function (4), a pneumatic retouching device (11) and a sealing device (12, 13) of the inking container (15) characterized in that the inking of the printing medium drum (1) is carried out by a wave of solid particles containing a magnetic pulverulent pigment contained in the inking container (15) raised by means (2, 3) of the inking device, the said wave displacing in the opposite direction to the displacement of the surface of the printing medium drum (1).
2. Inking device of a development drum according to Claim 1, characterized in that the means of the inking device comprise a magnetic conveyor drum (2) associated with a deflector (3) inclined with respect to the horizontal by a given angle, the said conveyor drum (2) turning in the opposite direction to the printing medium drum (1) at a given speed, the said deflector (3) being disposed downstream of the direction of junction of the centres of the conveyor drum (2) and of the printing drum on the one hand at a first adjustable distance (B) from this direction and on the other hand at a second adjustable distance (A) from the printing medium drum (1).
3. Inking device of a development drum according to Claim 2, characterized in that the given speed is between 85 rpm and 180 rpm inclusive at a printing speed of 20 to 60 m/mn.
4. Inking device of a development drum according to Claim 2 or 3, characterized in that the given angle of inclination is of the order of 50°.
5. Inking device of a development drum according to one of Claims 2, 3 or 4, characterized in that the first adjustable distance (B) is of the order of 0 to 5 mm, and the second adjustable distance (A) is of the order of 4 to 5 mm.
6. Inking device of a development drum according to one of Claims 2 to 5, characterized in that a calibration device of the thickness of the layer of ink of the inking device is constituted by a second lower conveyor drum (6) disposed below the first conveyor drum (2), a scraper (7) being disposed in contact with the second conveyor drum (6) and contriving a space with the first conveyor drum (2) and on the other hand a pressure sheet (8) disposed at a distance of the order of 3 mm from the first conveyor drum (2) and according to an angle of the order of 56° with respect to the horizontal.
7. Inking device of a development drum according to Claim 6, characterized in that the scraper (7) is disposed at a distance from the first conveyor drum (2) of the order of 2.6 mn.
8. Inking device of a development drum according to one of the preceding Claims, characterized in that the device comprises a toner mixer (9) and a pick-off (10) to determine the transfer of anew quantity of toner from a reserve container towards the inking container (15).
9. Inking device of a development drum according to one of the preceding Claims, characterized in that the magnetic retouching device comprises a third magnetic conveyor drum (4) disposed at an adjustable distance and turning at high speed in the opposite direction to the printing medium drum (1) and associated with a scraper (5) for cleaning this third drum (4), the said third drum (4) being disposed downstream of the first printing medium drum (1) with respect to the direction of rotation of the printing medium drum (1).
10. Inking device of a development drum according to Claim 9, characterized in that the adjustable distance is between 1 and 3 mm inclusive.
11. Inking device of a development drum according to one of the preceding Claims, characterized in that the pneumatic retouching device (11) comprises a suction nozzle disposed perpendicular to the printing medium drum (1) to remove by suction the particles of toner entrained in the wake of the other particles.
12. Inking device of a development drum according to one of the preceding Claims, characterized in that the sealing device comprises a closure sheet (13) of the inking container disposed downstream with respect to the direction of rotation of the printing medium drum (1), the said sheet having a square shape, one of the faces of which is parallel to the drum and very close thereto, a fan (14) is disposed outside the inking container (15) to generate an overpressure in proximity to the sheet between the suction nozzle and the container.

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