AU596766B2 - Process and device for applying a layer of toner - Google Patents

Description

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AUSTRALIA

PATENTS ACT 1952 COMPLETE SPECIFICATIO 596766 Form

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(ORIGINAL)

FOR OFFICE USE Short Title: Int. Cl: Application Number: Lodged: Complete Specification-Lodged: Accepted: Lapsed: Published: lir Priority: Related Art: a TO BE COMPLETED BY APPLICANT Name of Applicant: Address of Applicant: E. I. DU PONT DE NEMOURS AND COMPANY 1007 MARKET STREET

WILMINGTON

DELAWARE, 19898

U.S.A.

Z?4 Actual Inventor: Address for Service: GRIFFITH HACK CO., 601 St. Kilda Road, Melbourne, Victoria 3004, Australia.

Complete Specification for the invention entitled: PROCESS AND DEVICE FOR APPLYING A LAYER OF TONER.

The following statement is a full description of this invention including the best method of performing it known to me:- GP-1005 PROCESS AND DEVICE FOR APPLYING A LAYER OF TONER

DESCRIPTION

TECHNICAL FIELD This invention relates to a process for applying a layer of toner from an intermediate support to the surface of a permanent support with imagewise modified 0 flp tacky areas. This invention also relates to a device ao 10 for performing said process.

0 .lo BACKGROUND OF THE INVENTION In a known process as described in U.S. Patent 0 3,060,025, the surface of a support consisting of a photopolymerizable material is modified imagewise by exposure. At room temperature or at a raised temperature tacky areas are formed to which a toner B0 000consisting of, dyes, inks, pigments, color formers, metals, etc., adheres, and nonsticky areas from which the toner can be subsequently removed. This support surface is then brought into intimate temporary contact with a layer containing the finely distributed o0 separate toner particles, and is then wiped off, so that the desired image is formed by means of coloration of uoar the tacky areas. The toner layer is first applied to a roller or to another intermediate support, in the form of a pigment dispersion, a dye coating, or the Slike. Alternatively the toner can also be applied I mechanically to the tacky support surface, with a cotton pad or with a rotating brush.

In all instances, certain variations in the application of the toner must be expected to occur.

This leads to differences in the strength of the coloration of the tacky areas. However, for many

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i 1 I ii~ I~l i I- I 2 applications, in the production of the color printing proofs by means of the Cromalin® photopolymer proofing process of E. I. du Pont de Nemours and Company, Wilmington, Delaware, the highest possible uniformity is desired.

From electrostatic photocopy devices it is known to uniformly electrostatically charge the surface of a drum consisting of a semiconductor coating or of a so-called o °master and to subsequently imagewise modify this charge 1 by means of an exposure. The charge flows away in the At 00 0 exposed areas, so that a toner made of an electrostatically chargeable powder will, after it is CIOapplied, adhere either to the exposed or the unexposed areas, depending on its polarity. Subsequently, the resulting image is transferred to a sheet of paper or film and is then fixed to this sheet by heating.

o0 In addition, a reproduction process is known from Sloan et al. U.S. Patent 3,762,944 in which exposure of a photopolymerizable and electrostatically chargeable resin with heat radiation causes areas to be formed which are both sticky and whose electrical charge has o0 been modified. Subsequently a toner is applied, which osOo o0a adheres both by adhesion and by means of electrostatic forces. In this instance, however, the toner is applied directly to the support.

In all these processes the toned areas are not as uniform as desired. It is therefore desired to develop a process wherein it is possible to apply to a temporary support a very uniform toner coating which is capable of being transferred to the surface of a permanent support.

SUMMARY OF THE INVENTION In accordance with this invention there is provided a process for applying a layer of toner from the surface 2 3 of an intermediate support to the surface of a permanent support having imagewise modified tacky areas, the improvement wherein uniformly charging electrostatically the surface of the intermediate support with a positive or negative polarity, bringing into contact with said surface of the intermediate support a layer of toner particles electrostatically charged to a polarity opposite to that of said surface, bringing into contact 0 with the electrostatically toned layer the surface of 1 0 said permanent support and separating said surfaces o0 04 o whereby toner is transferred to the tacky areas of the 0 permanent support.

0t CO In accordance with a preferred apparatus embodiment of this invention there is provided a device for applying a layer of toner from the surface of an 0 intermediate support to the surface of a permanent 0 601 oo support having imagewise modified tacky areas, the improvement wherein the intermediate support is provided S0 with an electrostatically chargeable surface capable of being transported over a first transport path on which, in the forward direction, there is an electrostatic charging means having a corona discharge unit where a uniform charge is applied, a toner supply means having a rotatable, permanent magnetic roller which applies toner uniformly across the width of the uniformly charged intermediate support surface, and a transfer station having a second corona discharge unit which attracts the electrostatic toner particles to the permanent support surface, and a second transport path which meets the first transport path at the transfer station, is provided for the permanent support.

3I 4 BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood by reference to the following description taken in conjunction with the accompanying drawings, in which: FIG. 1 depicts a schematic representation of a device according to this invention; and FIG. 2. depicts a magnified partial section of a modified embodiment of this invention.

DETAILED DESCRIPTION OF THE INVENTION 1 0 The invention utilizes a toner made of an electrostatically chargeable powder, by uniformly electrostatically charging the surface of the intermediate ;uptwiha given polarity and bringing it into contact with electrostatically charged toner 1 5 particles which carry a charge of the opposite polarity, L Q~;so that a toner coating is formed on the surface of the intermediate support, and by transferring this toner coating to at least the tacky areas of the permanent S support.

The uniformly charged state of the intermediate support surface, which is also present when the toner is applied, also causes the toner layer to have a very uniform thickness. This is because the charge on the surface of the intermediate support is progressively neutralized by the impinging toner particles until, finally, the force becomes insufficient to attract additional toner particles. A uniform layer is achieved if the usual precautions to ensure a uniform toner supply are met; however, even if the toner supply is not uniform, but is sufficient, a uniform layer is achieved.

In comparison with the known processes for applying toner to the tacky areas of a support surface, this process has the additional advantage of great

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cleanliness. This is because the electrostatic field largely prevents escape of the toner particles into the

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environment. It is therefore possible to also utilize a toner in fine powder form and thus to achieve high image resolution.

In many instances, it is sufficient to bring the permanent support surface into contact with the 9ointermediate support surface, because the tacky areas o i then accept the toner coating due to adhesion. It is, 9999 1 0 however, particularly advantageous if the transfer o 4o occurs with the aid of an electrostatic field which 9 4 2 attracts the toner particles to the permanent support surface. By means of this electrostatic field the toner powder is transferred to the permanent support with its full thickness and with certainty.

A particularly preferred process is obtained if the 0 intermediate support is transported along a path where it is sequentially charged, supplied with the toner and o 9°°o brought into contact with the permanent support surface.

All three of these process steps can be performed rapidly in sequence and repeated.

According to this invention as set out above, an improved device for performing the process is provided 90*090 wherein the intermediate support is provided with an electrostatically chargeable surface capable of being transported over a first transport path on which, in the forward direction, there is a charging station, B where a uniform charge is applied, a toner supply station, which applies toner uniformly across the width of the uniformly charged intermediate support surface, and a transfer station, and that a second transport path which meets the first transport path at the transfer station, is provided for the permanent support.

r A 6 The intermediate support can, for instance, be provided with an electrostatically chargeable layer lying on a drum, that is circular. An alternative embodiment consists of an intermediate support to being a sheet which rests on a drum and is provided with an electrostatically chargeable surface. The drum also defines the first transport path (A) The charging station appropriately contains a 0* corona discharge unit. By means of the corona discharge S 10 it is possible to achieve very uniform charging.

oo o o 0 0 In addition, it is advantageous for the toner 0 000 supply station to contain a permanent magnet roller and 0 a for the toner to be mixed with magnetizable particles.

By means of this "magnetic brush", known to the art, a 1 5 sufficient amount of toner is supplied to the charged *c intermediate support surface, while excess toner, e.g., 0 00 0°.0 in the form of powder, is allowed to be led away.

Advantageously, the transfer station is equipped with a second corona discharge unit which attracts the electrostatically charged toner particles to the permanent support surface. This second unit is operated S,9o such that it produces an electrostatic field which counteracts the electrostatic adhesive force (attracting toner to the intermediate support). By this means it is assured that the entire thickness of the toner layer is transferred.

Advantageously, the first transport path is I equipped with a cleaning station which rids the intermediate support surface of any toner present thereon. This provides the intermediate support with a clean surface for the next operating cycle.

It is also possible to equip the second transport path with a cleaning station behind the transfer 7 station, whereby toner adhering to nontacky areas of the permanent support is removed. The imagewise developed permanent supports then leave the device with clean surfaces.

As illustrated in FIG. 1, a toner application device contains a drum consisting of a dielectric material which can be rotated in the direction indicated by the arrow. It forms an intermediate support with an electrostatically o° 10 chargeable surface This surface moves along the first transport path a circular path.

The surface then traverses a charging station (4) The latter consists of a corona discharge unit which has a wire extending across the width of the drum This wire is connected to a negative DC potential .O ,of several kV. By this means the surface is OO uniformly charged with a negative charge. A wire (6a) is connected in front of the corona discharge unit.

o" This wire lies at a high AC potential and serves to erase any charge which may still be present on the surface before it enters the charging 0 station.

o Behind this, in the circular transport direction, there is a toner supply station The toner supply station contains a toner supply vessel with an exit opening (10) whose size can be adjusted by means of a slide The toner powder drops onto two mixing rollers (11 and 12) which lead the material toward a socalled "magnetic brush" The latter consists of a permanent magnet roller. The toner is mixed with a magnetizable material, iron filings or shavings, etc. These magnetizable materials position themselves radially on the roller such that the toner 7 r- .I r i r rr l, 8 particles migrate to the outer tips of these magnetic particles. They are charged positively with respect to the charge carried by the surface charge of the drum This is achieved by the fact that the housing of the corona discharge unit and the magnetic roller are grounded. It is therefore generally unnecessary to take special precautions to assure that the toner particles are charged. A stripping knife (14) provides for a uniform coverage of the periphery of the magnetic brush 10 (13) with the toner powder.

41 II As soon as the surface of the drum (2) approaches the magnetic brush (13) the positively charged toner particles are attracted to the negatively charged surface This produces a highly uniform 1 5 toner layer (15) on the surface (3) r A second transport path is shown as a dashed line. It leads from an inlet slit (16) past the pair of a 4 4 transport rollers (17 and 18) to the transfer station 4 o where it encounters the first transport path It continues over a conveyor belt (20) to an exit slit At the transfer station (19) there is a second g. 441 So corona discharge unit whose wire (23) also has an applied negative DC potential of several kV. The polarity is thus selected such that the resulting force applied to the toner particles in the toner layer attracts the toner particles toward the second transport path (B) Along transport path permanent supports (24) are transported which have a tacky surface which is modified imagewise. Suitable tacky surfaces are, for example, those disclosed in Chu, et al., U.S. Patent 3,649,269 and Brazzel, U.S. Patent 4,356,253 for positive imaging and Cohen and Fan, U.S. Patents i 4,174,216, 4,247,619, 4,282,308 and 4,304,839 for negative imaging of a photopolymerizable or photohardenable surface coating. The disclosures of these patents are incorporated herein by reference. The course of the support (24) is synchronized with the rotation of the drum When the support (24) traverses the transfer station the toner layer is transferred to the support The toner particles then adhere strongly to the tacky areas.

A cleaning station (25) contains a rotating brush in particular a fiber brush, which works against the surface of the drum The surface is thus r cleaned for the next cycle. A filter box (27) takes up the toner which is brushed off, into a dust bag.

1 5 A suction fan (28) attached on the side provides for *removal of the dust from the brush (26) A second cleaning station (29) also contains a 0 0 rotating brush in particular a fiber brush. It o oI removes toner located outside of the tacky areas (nontacky areas) from the permanent support surface Here too the excess toner is collected in the 0O filter box The permanent support (24) thus reaches the exit slit (21) with a clean image.

In Fig. 2 the drum (32) is merely a means for transporting the intermediate support consisting of a sheet (34) with a coating (35) made of an electrically non-conducting or poorly conducting material. The minus signs indicate that the surface (36) of the intermediate support (33) carries a negative electrical charge. The toner particles (37) which are released by the magnetic brush (13) are, on the other hand, positively charged, as indicated by the plus I: _C signs. Consequently, the uniform toner layer (15) is formed behind the toner supply station (7) The drum can consist of any dielectric or semiconducting material. It is also sufficient if only the surface layer consists of such a material. For instance, a selenium drum such as that used in electrostatic photocopying can be considered. E, if an intermediate support (34) which is separate from the a drum is utilized, it is possible to select known o 10 materials, a sheet (34) with a ZnO layer Since, in contrast with electrostatic copying, it is not necessary to expose the electrostatically chargeable So surface, it is not necessary to consider only light o sensitive semiconductors, but one may also consider 1 5 other non-conductors or semiconductors, such as glass or t synthetic organic materials, such as polytetrafluoroethylene, polyvinyl chloride, polystyrene, as well as mixtures of pigments with :1 ,resins, whereby a given resistance can be achieved by a design.

The toners need not necessarily be thermoplastic, osince they adhere sufficiently well to the tacky areas on the support surface without requiring fixing by means of a heat treatment. Suitable pigmented plastic particles made of a linear or a crosslinked polymer, polymethylmethacrylate, cellulose acetate, polystyrene, polycarbonate, or polyethylene, etc. can be used. It is understood by one having ordinary skill in the art that all toners applicable for electrostatic photocopying or electrostatic copying processes are also suitable. An average particle diameter of 1-4 gm is preferred, so as to make full use of the high resolution in the tacky areas.

j i c Two component toners, in which the second component consists of a magnetic or an electrostatically chargeable material with a grain size of 100 gm, are preferred. In particular, these can be iron filings or shavings or ferrites.

The strength of the charge on the intermediate support and therewith the thickness of the toner layer can be controlled by adjusting the potential applied to t the corona discharge unit or the slit between the corona discharge unit and the surface.

If one compares the present device with the usual f electrostatic copying device, then the exposure system i and the fixing heater are found to be absent. The corona discharge unit slit must, if necessary, be adjusted to a smaller size, so that the desired layer thickness is obtained. In addition, the adjustment for toner supply should be made to provide the maximum supply of toner, because the entire surface is to be Z +covered.

It is understood by one having ordinary skill in the art that the toner particles may also be charged at their own electrode. It is also possible to set the corona discharge units to a positive potential and to thus apply a positive charge to the intermediate support surface. However, a negative charge is preferred.

Example The following example illustrates, but does not limit, the invention.

An electrophotographic developer consisting of an iron carrier with 0.8% black toner (commercially available from the APECO Co., D-6072 Dreieich, West Germany, was first coated via a magnetic brush on a zinc oxide/binder film charged to -500 V. The coating which 12 was uniformly covered with powder was brought into contact with an imagewise exposed photopolymerizable i film, of the type sold commercially as Positive Cromalin®, E. I. du Pont de Nemours and Company, Inc.

coated on paper, and the toner was transferred to the I Cromalin® film with application of a corona transfer potential (-600 The toning step was repeaved four times and subsequently the toned image was cleaned with a rotating fiber brush (or with a soft cloth). An image of excellent quality is obtained (resolution of 11 pm lines, tone range 3-96% with a screen ruling of 4 i 1 I2 Li

Claims (18)

1. A process for applying a layer nf toner from the surface of an intermediate support to the surface of a permanent support having imagewise modified tacky r areas, t-e .im.r.rnm nt auniformly charging electrostatically the surface of the intermediate support with a positive or negative polarity, bringing into contact with said surface of the intermediate support a layer of toner particles electrostatically 1 0 charged to a polarity opposite to that of said surface, Sbringing into contact with the electrostatically toned layer the surface of said permanent support and i'rt separating said surfaces whereby toner is transferred to the tacky areas of the permanent support.

2. A process according to Claim 1 wherein the o transfer occurs with the aid of an electrostatic field o* which attracts the toner particles to the surface of the permanent support.

3. A process according to Claim 1 wherein the intermediate support is transferred along a path along which it is sequentially charged, furnished with toner Sand brought into contact with the permanent support ,o surface.

4. A process according to Claim 2 wherein the intermediate support is transferred along a path along which it is sequentially charged, furnished with toner and brought into contact with the permanent support surface.

A process according to claim 3 wherein the intermediate support transport path is defined by a ci::cular drum, the surface of which is electrostatically chargeable. 13

6. A process according to claim 3 wherein the intermediate support transport path is defined by a circular drum, the surface of which is provided with a sheet having an electrostatically chargeable surface.

7. A device for applying a layer of toner from the surface of an intermediate support to the surface of a permanent support having imagewise modiried tacky areas according to claim 1, the imr mn wherein the intermediate support is provided with an (1 0 electrostatically chargeable surface capable of being transported over a first transport path on which, in the forward direction, there is an electrostatic charging means, where a uniform charge is applied, a toner supply means, which applies toner uniformly across the width of the uniformly charged intermediate support traI surface, and a transfer station, and a second transport 6lr path which meets the first transport path at the transfer station, is provided for the permanent support.

8. A device according to claim 7 wherein the intermediate support provided with an electrostatically chargeable surface is in the form of a circular drum. S° a

9. A device according to claim 7, wherein the intermediate support is formed of a sheet equipped with an electrostatically chargeable surface which rests on a S325 drum.

A device according to claim 7 wherein the electrostatic charging means contains a corona discharge unit.

11. A device according to claim 7 wherein the toner supply means comprises a rotatable, permanent magnetic roller and that the toner is mixed with magnetic particles. 14 15

12. A device according to claim 7 wherein the transfer station is equipped with a second corona discharge unit which attracts the electrostatic toner particles to the permanent support surface.

13. A device according to claim 7 wherein behind the transfer station, the first transport path is provided with a cleaning station which rids the intermediate support surface of toner.

14. A device according to claim 7 wherein behind the transfer station, the second transport path is provided with a cleaning station which rids the Spermanent support surface of toner from the nontacky areas.

A device for applying a layer of toner from the surface of an intermediate support to the surface of a permanent support having imagewise modified tacky areas, wherein the intermediate support is provided with an electrostatically chargeable surface capable of being transported over a first transport path on which, in the forward direction, there is an electrostatic charging means having a corona discharge unit where a Suniform charge is applied, a charged toner supply means t t having a rotatable, permanent magnetic roller which applies toner uniformly across the width of the uniformly charged intermediate support surface, and a transfer station having a second corona discharge unit which attracts the electrostatically charged toner particles to the permanent support surface, and a second transport path which meets the first transport path at the transfer station, is provided for the permanent support.

16. A device according to claim 15 wherein the intermediate support provided with an electrostatically A chargeable surface is in the form of a circular drum. 1 16

17. A device according to claim 15 wherein the intermediate support is formed of a sheet equipped with an electrostatically chargeable surface which rests on a circular drum.

18. A device according to claim 15 wherein benind the transfer station, the first transport path is provided with a cleaning station which rids the intermediate support surface of toner. o 20. A device according to claim 18 wherein behind B" 10 the transfer station, the second transport path is a aprovided with a cleaning station which rids the o0 o permanent support surface of toner from the nontacky °o areas. 0a 0 o a DATED this 16th day of MARCH 1989. 2 xE.I.DU PONT DE NEMOURS AND COMPANY S 4tt By its Patent Attorneys: 1GRIFFITH HACK CO. Fellows Institute of Patent Attorneys of Australia. 1a 16