US 3133833 A
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y 1954 E". c. ammo, JR
POWDER CLOUD GENERATING APPARATUS Filed June 1. 1961 INVEN 49mm 6 644m #1 lfrrwr/ United States Patent Orifice 3,133,833 Patented May 19, 1964 3,133,833 POWDER CLOUD GENERATING APPARATUS Edward C. Giaimo, Jr., Princeton, N.J., assignor to Radio Corporation of America, a corporation of Delaware Filed June 1, 1961, Ser. No. 114,186 3 Claims. (Cl. 118637) This invention relates generally to the art of electrostatic printing, and more particularly to improved apparatus for generating a cloud of toner powder. The novel apparatus of the present invention is particularly useful for developing latent electrostatic images on recording elements in an electrostatic printing process.
In electrostatic printing processes wherein a latent electrostatic image is developed by dusting it with an electroscopic powder, the electric charge of the latent image attracts powder of an opposite electric charge, resulting in a visible powder image. If all the toner particles are not of the same polarity and of substantially uniform charge, the developed image may have a dirty appearance. This results from a deposition of particles of toner powder in areas where they were not required. To obtain good, clean prints, it is necessary to develop the latent electrostatic image with a toner powder whose particles have a uniform electric charge of one polarity only. Since many developer mixtures comprise a carrier material and a toner powder whose particles may contain, for example, shellac, rosin, and pigmented coloring material, the particles may vary in composition and the electric charge they attain, by the triboelectric effect, may vary in amplitude and polarity.
Accordingly, it is an object of the present invention to provide improved apparatus for separating particles of toner powder of predominantly one polarity of electric charge from a developer mixture of a carrier and a toner powder.
Another object of the present invention is to provide improved apparatus for generating a cloud of toner powder of predominantly one electric charge from a developer mixture.
A further object of the present invention is to provide improved apparatus for separating particles of toner powder of predominantly one polarity of electric charge from a developer mixture at one location and for generating a powder cloud of the separated particles at another location.
Still another object of the present invention is to provide cloud generating apparatus of the type described that is relatively simple in structure, easy to operate, and highly efiicient in use. i
In accordance with the present invention, the improved apparatus comprises means for separating particles of toner powder of predominantly one polarity of electric charge from a developer mixture of magnetic particles and toner powder. The developer mixture exhibits a triboelectric effect, that is, the magnetic particles and the particles of toner powder acquire opposite electric charges when they are separated from each other. The developer mixture is disposed in coincident magnetic and electrostatic fields and in contact with one surface of a web of insulating material that is moved through the fields. Particles of toner powder of predominantly one polarity are attracted to the moving web under the influence of the electrostatic field. The magnetic particles remain in the magnetic field. Thus, the toner particles of predominantly one polarity on the moving web are moved out of the developer mixture and to a location where they can be removed from the moving web.
The novel features of the present invention, as well as additional objects and advantages thereof, will be described in greater detail by reference to the accompanying drawing, the single figure of which is a perspective view, in cross-section, of the improved apparatus of the present invention.
Referring now to the drawing, there is shown cloud generating apparatus 10 comprising a hopper 12 for a developer mixture 14 to be used in an electrostatic printing process. The developer mixture 14 comprises a carrier of magnetic particles and a pigmented toner powder for dusting a latent electrostatic image to develop it. Examples of suitable developer mixtures are given in US. Patent No. 2,854,947, for Electrostatic Printing, issued to the instant inventor on October 7, 1958. The developer mixture 14 exhibits a triboelectric effect in that the particles of toner powder develop an electric charge that is opposite to a charge on the magnetic particles when the toner particles and magnetic particles are separated from each other. Depending upon the composition of the toner particles, the charge on the toner particles may be positive or negative, with respect to the charge on the magnetic particles. The charge of the toner particles is de-v termined by the relative position of the toner particle materials with respect to the magnetic particles (iron filings) in the triboelectric series.
The hopper 12 comprises side walls and a cover lid 16. One side wall is formed by a portion of an insulating endless web 18 that is disposed against the side opening of the hopper 12. It will now be understood that the developer mixture 14 is held in the hopper 12 by the proximity of portions of the endless web 18 along the side opening of the hopper. A smaller hopper 20 communicates with the interior of the hopper 12, through the lid 16, for replenishing the supply of toner powder in the de veloper mixture 14 in the hopper. A vibrator 22 is mechanically connected to the hopper 20 to cause the toner powder to flow easily.
The endless web 18 is supported for rotation in a boxlike structure 24 by two upper, horizontally disposed rollers 26 and 28 and two lower, horizontally disposed rollers 30 and 32. One of the rollers, such as the roller 30, is coupled to a motor 33 to cause the endless belt to move in the direction indicated by the arrows. The direction of rotation of the endless belt is such that portions of the belt 18 forming the fourth side wall of the hopper 12 move upwardly. The hopper 12 is fixed to a side wall 34 of the box-like structure 24. The lid 16 is also hinged to the wall 34.
Means are provided to produce coincident electrostatic and magnetic fields in a transverse direction to the direction of travel of portions of the endless belt 18 that form the side wall of the hopper 12. To this end, a shaft 38 of magnetic material is disposed in a horizontal position in the hopper 12. The shaft 38 is coupled to a motor 40 for rotation in the direction indicated by the arrow 42. A plurality of disks 44 are aligned in substantially parallel relationship on the shaft 38 and inclined with respect to the shaft 38 in a manner whereby the disks have a wobble I motion as the shaft rotates. Thus, it will be understood that, as the shaft 38 rotates, the disks 44 will stir the developer mixture 14.
The shaft 38 and the disks 44 thereon are made of magnetic material and form one pole in a magnetic circuit cooperating with another pole 46 of magnetic material disposed within the loop defined by the endless belt 18 and opposite to the shaft 38. The magnetic field thus defined is substantially perpendicular to the direction of travel of the endless belt 18 through it.
An electrostatic field is also provided that is substantially coincident with the magnetic field. To this end, the shaft 38 is connected to one movable arm of a reversible, double-pole double-throw switch 48. A non-magnetic electrode 50, positioned in the magnetic field and inside the loop defined by the endlessbelt 18, is connected to the other movable arm of the switch 48. A unidirectional power supply 52 is connected to one pair of fixed contacts of the reversible switch 48. By throwing the switch in one direction or in the other, an electrostatic field of desired direction is produced transversely to the path of travel of the endless belt 18. Depending upon the capacity of the apparatus, the output voltage of the power supply 52 should be sufficient, say, about 600 volts, to attract particles ofone polarity to the endless belt 18.
A nozzle or chute 54 isfixed to the top of the box-like structure 24 and is formed with a restricted opening 56 adjacent to the top horizontal portion of the endless belt 18. Any particles on the belt 18 can thus be blown off the belt by means of a gas, such as air, forced, for example, under compression through the chute 54. A chamber 58 communicates with the restricted opening 56 to receive the cloud 60 of particles that are blown from the belt 18.
In operation, the endless belt is moved in the direction indicated by the arrows by means of the motor 33. The shaft 38 is rotated by the motor 40 to stir the contents of the developer mixture 14. The switch 48 is closed so that the chargeon the shaft 38 is positive and the charge on the electrode 50 is negative, thereby producing an electrostatic field between the electrode 50 and the shaft 38 with its inclined disks 44. As portions of the endless belt 18 move past the developer mixture 14, the positively charged particles of toner powder move toward the negatively charged electrode 50. These positively charged particles are deposited-on the moving belt and move out of the developer mixture 14 with the moving belt 18. Negatively charged particles tend to move toward the positively chargedshaft 38. -The magnetic particles remain within the magnetic field between the pole piece 46 and the shaft 38 with the disks 44. This field resists the tendency of any magnetic particles to adhere to the belt 18.
Thus, toner particles of predominantly positive electric charge adhere to the belt 18 and move out of the developer mixture 14 and into the blast of gas coming through the restricted opening 56 in the chute 54. The belt 18 may be roughened to cause the toner particles to adhere to it easily. The blast of gas blows the charged particles into the cloud chamber 58 to form the cloud 60 of particles of predominantly the same electric charge. In an electrostatic printing process, a recording element (not shown) bearing a latent electrostatic image will be placed in the cloud 60 so that the latent image can be dusted with the toner particles to develop the image.
In some electrostatic printing processes, it is desired to develop a latent image with a cloud of negative particles. A cloud of negatively charged particles can be produced by employing a suitable developer mixture and by revcrsing the polarity of the electric field by means of the reversing switch 48 so that the electrode 50 becomes the positive electrode. Under these conditions, negatively charged particles will be attracted to the moving belt 18 and moved to the location where they can be blown into the cloud chamber 58 to form the cloud 60 of desired polarity.
1. Apparatus for generating a developer cloud of toner powder of predominantly one polarity of electric charge from a developer mixture of magnetic particles and toner powder, said particles and said powder exhibiting a tribeelectric effect, said apparatus comprising an endless web of insulating material, means providing a magnetic field,
means providingan electrostatic field substantially coincident with said magnetic field, means to move said web of insulating material through said fields substantially perpendicular thereto, means to support said developer mixture within said fields and in contact with one surface of said web, and means adjacent to said web to blow toner powder adhering to portions of said web to form said developer cloud after said portions have passed through said developer mixture.
2. In an apparatus for developing an electrostatic image on a recording element with a cloud of toner particles of predominantly one polarity of electric charge from a de- .veloper mixture of magnetic particles and toner powder,
said magnetic particles and'said particles of toner powder exhibiting a triboelectric efiect; the improvement comprising: magnetic pole means providing a magnetic field, means including positive and negative electrodes cooperating with said first named means to provide an electrostatic field coincident with said magnetic field, one of said electrodes comprising at least part of said magnetic pole means; an endless web of insulating material, means to move said endless web of insulating material substantially perpendicular to said fields with one surface of said web in contact with a quantity of said developer mixture supported in said fields between said surface and said one of said electrodes; blower means adjacent to said web to blow particles of said toner powder adhering to portions of said web to form a cloud after said portions have passed through said fields; and, a chamber communicating with on a recording element comprising in combination: a substantially vertical wall; a hopper for a developer mixture of magnetic particles and particles of toner powder fixed to said wall, said wall and said hopper being formed with a common opening; an endless web of insulating material, means to dispose a portion of said endless web in said opening so that it forms a side wall of said hopper; means to rotate said endless web so that said portion moves upwardly from said opening; a pair of magnetic poles, one of said poles being rotatably mounted in said hopper to stir developer mixture contained in said hopper and carry it into contact with one surface of said portion of said web, the other of said poles being juxtaposed adjacent the opposite surface of said portion of said web to create a magnetic field transverse to said portion; means including at least one of said poles providing an electrostatic field coincident with said magnetic field, said developer mixture carried into contact with said one surface of said portion of said web exhibiting a triboelectric effect whereby particles of toner powder in said mixture acquire an electric charge and are attracted to said portion of said web in said fields; and, means to direct a blast of gas onto said portion of said web after it has moved upwardly from said opening to remove toner powder particles from said web and develop said electrostatic image therewith.
References Cited in the file of this patent UNITED STATES PATENTS 2,815,449 Giaimo Dec. 3, 1957 2,843,295 Ricker July 15, 1958 2,857,290 Bolton Oct. 21, 1958 2,890,968 Giaimo June 16, 1959 2,914,403 Sugarman Nov. 24, 1959 i l l