Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1998-09-11
2001-07-17
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06260955
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a printing apparatus of the type which is used in various types or printers, in copying machines, in telefax machines etc., and which operates using a dry toner (colour powder) which is by an electrical process applied to the object to be printed, for instance the paper, and which is fixed to the paper, generally by a heat treatment.
BACKGROUND OF THE INVENTION
The invention is more particularly directed to a printing apparatus of said type, which is named a “toner-jet” printing apparatus, and in which a dry colour powder, generally named “toner”, is, by a direct method, transferred from a rotating toner feeder roll, through apertures of a fixed matrix in the form of a flexible printing circuit and to the object to be printed, for instance the paper, which is moved over a support roll, and in which the toner received on the paper is finally fixed on the paper by a heat treatment.
The principle of said process is that there are created two electric fields for transferring the toner from the feeder roll to the paper, a first electric field between the toner feeder roll and the toner matrix, which field can be brought to invert its polarity, and a second electric field, preferably a constantly downwards directed positive electric field between the matrix and the support roll over which the paper is conveyed.
The toner matrix is formed with a large number of very narrow, through apertures having a diameter of for instance 100-300 &mgr;m, and around each such aperture an electrically conducting ring of a suitable metal, for instance copper, in the following referred to as “copper ring”. Each copper ring is arranged so that a positive potential, for instance +300 V, can be impressed thereto, which potential is higher than the potential of the feeder roll, which can be for instance between +5 and +100 V, preferably about +50 V, but which is lower than the potential of the support roll for the paper, which can be for instance +1500 V. The electrically conducting ring, when impressed with a voltage, makes the belonging matrix aperture become “opened” for letting through toner. If, on the contrary, the matrix aperture is given a potential which is substantially less than the potential of the toner feeder roll, for instance if it is connected to earth the belonging matrix aperture becomes “closed” thereby preventing toner from passing down through said aperture.
The function is as follows:
the colour powder (toner) gets a negative potential in that the toner particles are rubbed against each other;
the toner is supplied to the toner feeder roll, which has a positive charging of a predetermined potential, often a potential which can be varied between +0 and +100 V, and the toner is spread in an even, suitably thick layer on the feeder roll by means of a doctor blade;
each aperture of the matrix which corresponds to a desired toner point is opened in that the matrix aperture ring is impressed by a positive potential which is higher that the potential of the feeder roll, for instance +300 V; apertures corresponding to non-toner-carrying portions remain connected to earth, which means that said apertures are to be considered as “closed” and that they thereby make it impossible for toner to pass said apertures; the combination of opened matrix apertures create a sign to be imaged;
depending on the difference in potential, for instance +50 V to +300 V=+250 V between the feeder roll and the toner matrix the negatively charged toner particles are sucked down from the feeder roll to the matrix, and depending on the difference in potential between the toner matrix and the support roll mounted underneath same, for instance +300 V to +1500 V=+1200 V toner particles are moved from the matrix and deposit on the paper conveyed over the support roll;
the paper having toner deposited thereon is finally moved through a heat treatment apparatus in which the toner is fixed to the paper.
There is an almost linear relationship between the current density and the traction force that the electric field exerts on the toner particles. The greatest density of the field is located very close above the copper rings and the density decreases in the direction towards the centre of the aperture. By reducing the potential of the feeder roll and thereby increasing the difference in potential between the feeder roll and the matrix it is possible to increase the amount of toner which is allowed to pass same; an increase of the potential of the feeder roll provides a corresponding reduction of the amount of toner which is let through.
By connecting a copper ring of the matrix to earth the direction of potential is inverted between the feeder roll from having been +250 V in the direction downwards to be +50 V in the direction upwards, and this makes negatively charged toner particles stick to the feeder roll, or makes such particles become sucked back thereto, respectively.
In a particular embodiment of a printing apparatus the distance between the feeder roll and the matrix was adjusted to about 0.1 mm, and the distance between the matrix and the support roll to about 0.6 mm. For the above mentioned potentials, which are given as examples, this gives a field strength of 2.5 V/&mgr;m, which is higher that the insulation property of air, which is about 1 V/&mgr;m. For eliminating the risque of flash-over between the feeder roll and the copper ring of the matrix and between the copper ring and the support roll it is therefore necessary that the matrix aperture ring be insulated.
In printing apparatus of toner-jet type, so far known, the copper rings have been insulated by being “baked into” (embedded in) the matrix material, and therefore the inner diameter of the copper ring of the matrix aperture has been made greater than the diameter of the matrix aperture, and an insulation material has been applied so as to cover all sides of the matrix. For a matrix aperture having a diameter of for instance 190 &mgr;m the inner diameter of the copper ring was made 250 &mgr;m. This means that the matrix aperture for letting toner down has a surface which is only 57.8% of the surface inside the copper ring, and the aperture for letting toner through is located some distance radially inside the inner diameter of the copper ring, where the field density is highest and should have given maximum force for sucking toner down. As a consequence there is a highly restricted degree of toner supply.
SUMMARY OF THE INVENTION
The object of the invention therefore is to solve the problem of providing a printing apparatus of toner-jet type having a substantially increased capacity of letting toner down than what is possible with the above discussed previously known printing apparatus.
This problem is solved in that the diameter of the toner aperture is made at least nearly as wide as the inner diameter of the charged copper ring, whereby the copper ring might be used to a maximum for moving toner from the feeder roll, through the matrix and down to the paper. The copper rings preferably are mounted directly on top of the matrix base in which the matrix apertures are drilled, and the matrix apertures thereby get the same diameter as the inner diameter of the copper rings. As mentioned above it is necessary, however, that the copper rings always are insulated, and according to the invention the charged copper rings are fixed mounted on top of the matrix base so that the matrix apertures and the copper rings extend edge to edge, and that the entire matrix is coated for instance by an evaporation method, with an insulation material which covers all free surfaces and the edges of the matrix, the matrix apertures and the copper rings. A available method is the method named the Parylene® method (Union Carbide) according to which a polymeric insulation material, poly-para-xylene, is applied to the matrix in a vacuum apparatus in layers having a well controlled thickness. The material has an electrical
Array Printers AB
Barlow John
Gordon Raquel Yvette
Knobbe Martens Olson & Bear LLP
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