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United States Patent 3,658,518
Baltazzi April 25, 1972

THREE-LAYERED REFLEX ELECTROPHOTOGRAPHIC RECORDING ELEMENT

Abstract

A three layer photoelectrostatic recording member comprising a first insulating base support layer which is a polymeric film, a second layer of a conductive polymeric material, bonded to said base support layer and a third layer of an organic photoconductive material bonded to said second conductive layer.


Inventors: Baltazzi; Evan S. (Brookfield, IL)
Assignee: Addressograph-Multigraph Corporation (Mt. Prospect, IL)
Appl. No.: 04/813,418
Filed: April 4, 1969


Current U.S. Class: 430/123.4 ; 428/337; 428/340; 430/395; 430/62
Current International Class: G03G 15/00 (20060101); G03G 5/07 (20060101); G03G 15/22 (20060101); G03G 5/10 (20060101); G03g 001/00 (); G03g 005/00 ()
Field of Search: 96/1.5 252/500 117/17.5,201

References Cited

U.S. Patent Documents
3272626 September 1966 Shinn
3011918 December 1961 Silvernail et al.
3232755 February 1966 Hoegl et al.
3316087 April 1967 Munder et al.
3485624 December 1969 Thiebaut et al.
Primary Examiner: Lesmes; George F.
Assistant Examiner: Wittenberg; M. B.

Claims



What is claimed is:

1. The method of making an electrostatic reproduction by a reflex technique using a reusable photoelectrostatic recording element having a base layer, a second conductive polymeric layer, and a third photoconductive layer comprising the steps of:

applying a blanket electrostatic charge to the photoconductive layer of said member,

contacting the photoconductive layer with a graphic original,

directing a source of radiant energy against the base layer of said recording element to produce an electrostatic latent image thereon, said base layer consisting of an insulating polymeric polyester film material, said second layer consisting essentially of a conductive polymeric material having a surface resistivity of less than 10.sup.10 ohms per square bonded to said base layer, said conductive polymeric material selected from the group consisting of poly (N, N-dimethyl- 3,5 - methylene piperidinium chloride), dipotassium salt of a styrenemaleic anhydride copolymer and a polymeric vinyl benzyl quaternary ammonium compound, and said photoconductive layer comprising an organic photoconductive material, selected from the group consisting of poly(N-vinylcarbazole) and poly(N-vinylbenzocarbazole), said photoelectrostatic recording element having an average light transmittance greater than 1% of the incident radiant energy emitted from said radiant energy source and less than 10 percent differential in light transmittance through said member between two given areas on the photoconductive surface of said element;

developing the latent electrostatic image; and

transferring the developed image to a receiving sheet.

2. A method as claimed in claim 1 wherein said conductive polymeric material consists of poly (N,N-dimethyl-3, 5-methylene piperidinium chloride).

3. A photoelectrostatic recording element as claimed in claim 1 wherein said conductive polymer comprises a vinylbenzl quaternary ammonium compound having the following general formula:

where R, R' and R" each represent a monovalent radical selected from the group consisting of CH.sub.2 OHCH.sub.2 --, CH.sub.3 CHOHCH.sub.2 --, CH.sub.2 OHCHOHCH.sub.2 --, and alkyl, aryl, cycloalkyl and aralkyl hydrocarbon radicals; collectively, the R, R' and R" representing the trivalent radical of the formula:

wherein the three valences are attached to the nitrogen atom; the R groups containing a total of not more than 12 carbon atoms in the sum of the constituent radicals and the Y is an anion.

4. A photoelectrostatic recording element as claimed in claim 5 wherein said vinylbenzl quaternary ammonium compound consists of a homopolymer of vinylbenzl trimethyl ammonium chloride.

5. A photoelectrostatic recording element as claimed in claim 1 wherein said conductive polymer comprises a dipotassium salt of styrene maleic anhydride.

6. A photoelectrostatic recording element as claimed in claim 1 wherein said base layer has a thickness from 1 - 25 mils.

7. A photoelectrostatic recording element as claimed in claim 1 and 6 wherein the weight of 3000 - 3300 square feet of said recording element subsequent to being coated with said conductive polymer and prior to the overcoating thereof with said photoconductive layer, falls within a range of 0.5 - 2.5 lbs.
Description



BACKGROUND OF THE INVENTION

This invention relates generally to photoelectrostatic recording elements and more particularly to photoelectrostatic recording elements of the type including an organic photoconductive layer disposed on a base or support member.

The making of copies of a graphic original electrostatically involves the application of a uniform electrostatic charge in the dark to the photoconductive surface of a photoelectrostatic recording element, selectively discharging the surface of the element by exposure to a pattern of light and shadow in accordance with the original being copied to provide a latent electrostatic image and rendering the image visible by applying finely divided electroscopic particles thereto.

In order for the photoconductive surface of the recording element to accept a charge during the charging step, the surface requires a conductive backing or the like.

In the case of a recording element using a paper base or support member, the paper base serves as the required conductor. On the other hand, in the case of a recording element including an organic photoconductive surface, the photoconductive surface is conventionally disposed on an insulating base or support member which is a polymeric film material. Such support may be, for example, cellulose acetate, cellulose nitrate, cellulose acetate butyrate, cellulose acetate propionate, polyvinylidene chloride, polyvinyl chloride, polyurethane, polystyrene, polymethyl methacrylate ("Plexiglas"), acrylonitrile-butadienestyrene, phenol-formaldehyde, melamine laminate ("Formica"), polyester, polycarbonate, and terephthalic acid-ethylene glycol polyester ("Mylar"), and the like. Because the polymeric film is highly insulative, an attempt to charge a photoconductive layer disposed thereon will result in failure. Consequently, it becomes necessary to provide a conductive layer between the base support and the photoconductive layer.

Conductive layers of the metallic type, such as for example, aluminum, have been used with some success between the photoconductive layer and the base member. These materials, however, suffer from certain drawbacks which make them less desirable. In the first place, it is difficult to lay down on the base member a uniform layer of aluminum or the like. Furthermore, in the event the photoconductive layer laid down on the aluminum layer includes pinholes or gaps, there is a chance that when using a biased magnetic brush developer, (i.e. a magnet brush developer to which there has been applied an electrical potential for the purpose of enhancing the development of a copy sheet) a short circuit will occur between the brush developer and the aluminum which is exposed through the gap in the photoconductive layer, causing shorting streaks in the final copies. Consequently, recording elements using metallic conductive layers are not entirely satisfactory for use in reflex or "shoot through" copying techniques.

SUMMARY OF THE INVENTION

Accordingly, it is a primary object of the present invention to provide a new and improved recording element of the above described type which overcomes the aforementioned disadvantages.

It is another object of the present invention to provide a recording element of the above type which is equally well-suited for all copying techniques, including reflex copying.

It is a more specific object of the present invention to provide a new and improved recording element comprising three layers, including a conductive layer sandwiched between an insulative base member and an organic photoconductive layer.

It is yet another object of the present invention to provide a three layer recording element of the above described type wherein the conductive layer comprises polymeric materials.

Briefly, a recording element according to the invention includes a base layer of an insulative, flexible, dimensionally stable, durable plastic, such as an insulating polymeric film. A layer of conductive polymeric material is provided over the base layer and is bonded thereto, enabling the photoconductive layer of the recording element which in turn is bonded to the conductive layer, to accept a charge during the charging step of the electrostatic process. In a preferred embodiment, the photoconductive layer is of an organic photoconductive material comprising a polyvinylcarbazole or polyvinylbenzocarbazole, and is coated over the polymeric conductive layer.

Each of the layers has a translucent quality, thus the recording element is ideal for use in reflex copying wherein during the exposure step, radiant energy is directed through the recording element onto the original, whereby the radiant energy is absorbed in the image areas and reflected back to the photoconductive layer of the recording element in the background areas, to produce a latent image on the photoconductive layer. The recording element likewise may be used in projection or contact copy making techniques with equal success.

In addition, in the event a gap or pinhole is present in the organic photoconductive layer and the conductivity of the conductive polymeric layer is less than 1 .times. 10.sup.-.sup.7 mhos, the conductive polymeric material will not cause a short circuit upon being contacted by a biased magnetic developing brush and thus no shorting streaks will appear along the final copy.

DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention and its organization and construction may be had by referring to the description below in connection with the accompanying drawings wherein:

FIG. 1 is an enlarged fragmentary view of a photoelectrostatic recording element according to the invention; and

FIG. 2 is a schematic cross sectional view of an electrophotographic copying machine using a recording element in the form of an endless belt member, according to the invention.

DETAILED DESCRIPTION

The recording element, illustrated in FIGS. 1 and 2 of the drawings and designated generally by the numeral 10, comprises three layers 12, 14 and 16. The three layers are bonded together and are each light transmitting, being either transparent or translucent.

The base layer 12 of the recording element is flexible, dimensionally stable and durable, and is preferably made of a polyester plastic film, such as, for example, mylar; however, other polymeric insulating film base supports may be used if desired, as described heretofore. As will be shown when describing FIG. 2, the polyester base material is easily formed into an endless belt member for use in a copying machine, such as described in co-pending patent application, Ser. No. 792,617, inventors Loren E. Shelffo, et al, filed Jan. 21, 1969, and assigned to the same assignee. The base layer 12 is usually chosen to be from 1 to 25 mils in thickness, and is mattibrated for better holding of layer 14 thereto.

A conductive layer 14, sandwiched between and bonded to the base layer 12 and the photoconductive layer 16, is preferably comprised of a conductive polymeric material. Metals, such as aluminum, also may be used as the conductive layer for a recording element but the metals suffer from the drawbacks described heretofore.

Suitable conductive polymeric materials which may be used in the recording element according to the invention are as follows:

1. A polycationic water soluble organic polymer such as, for example, poly (N,N-dimethyl-3, 5 -methylene piperidinium chloride) ##SPC1## known as polymer 261 and produced by the Calgon Corporation. Further information regarding the above chemical compound can be found in Vol. 51, No. 12, 1968, December, Tappi Publication, pages 552 - 554.

2. A vinyl benzyl quaternary ammonium compound which may be a homopolymer or a co-polymer; the homopolymers being prepared using different vinylbenzyl ammonium compounds or co-polymerizing the vinylbenzyl ammonium compounds with a non-acidic compound such as acrylamide or divinylbenzene. The vinylbenzyl ammonium compound is always present in a predominant amount.

The preferred vinylbenzyl quaternary ammonium compounds have the following general formula:

in which R, R' and R" represent a monovalent radical selected from the group consisting of CH.sub.2 OHCH.sub.2 --, CH.sub.3 CHOHCH.sub.2 --, CH.sub.2 OHCHOHCH.sub.2 , and alkyl, aryl cycloalkyl, and aralkyl hydrocarbon radicals. Collectively, the R, R' and R" represent the trivalent radical of the formula:

wherein the three valences are attached to the nitrogen atom. The R groups contain a total of not more than 12 carbon atoms in the sum of the constituent radicals, and the Y is an anion, as for example, sulfate, chloride, nitrate, or a hydroxyl ion.

Vinylbenzyl quaternary ammonium compounds are especially preferred wherein R represents an alkyl radical containing from one to four carbon atoms, and the R' and R" each represent a radical from the group consisting of CH.sub.2 OHCH.sub.2 --, CH.sub.3 CHOHCH.sub.2 --, CH.sub.2 OHCHOHCH.sub.2 --, and lower alkyl radicals containing from one to four carbon atoms.

One preferred co-polymer contains at least 65 percent by weight of any one or more of the preferred vinylbenzyl quaternary ammonium compounds and not more than 35 percent by weight of acrylamide. Another preferred co-polymer contains, in the polymer molecule, residues corresponding to from 95.0 to 99.99, preferably from 99.0 to 99.99, percent by weight of any one or more of such vinylbenzyl quaternary ammonium compounds and from 5.0 to 0.01, preferably from 1.0 to 0.01, percent by weight of divinylbenzene. Mixtures of any two or more homopolymers or co-polymers may also be used.

Specifically a preferred embodiment of the above described general formula is a homopolymer of vinylbenzyl trimethyl ammonium chloride having the formula:

The above-described vinylbenzyl quaternary ammonium compound is described in U.S. Pat. No. 3,011,918.

3. Dipotassium salt of styrene maleic anhydride, a conductive polymer available from Dow Chemical Company, and identified as polymer 4700.

It has been found that unless the surface resistivity of layer 14 is less than 10.sup.10 ohms per square, this layer does not maintain adequate electrical contact with the photoconductive layer 16 and the element 10 will be unable to accept a uniform charge, which it must in order to faithfully reproduce an original.

The surface resistivity as described was measured using a sample 12 inches long and 1 inch wide. Two leads from a suitable ohm-meter were placed in contact with the conductive layer, with a spacing of 10 inches between the two points of contact. To minimize contact resistance errors with the ohm-meter lead, the leads are soldered to a copper block (1 inch .times. 1 inch .times. 1 inch) which is polished flat on the base. The use of the blocks minimizes damage to the conductive layer and also provides a more accurate measurement. The resistance measured across the 10 inch strip is equivalent to the resistance of 10 1 -inch squares connected in series. To determine the resistance in ohms per square, the total resistance is divided by ten (the number of units squared).

The amount of conductive material and the manner in which it is applied to the base is carefully controlled so that the conductive layer 14 has the correct surface resistivity and the element 10 has the correct optical properties. A solution of the conductive polymers is mixed with a suitable solvent and applied to the polyester base. With different conductive materials, different solids will be required in order to achieve the required properties. The weight of a ream or 3000 - 3300 square feet of material after being coated with the conductive polymer should be within a range of from 0.5 - 2.5 lbs. This measurement is made in lieu of measuring the thickness of the conductive layer, since the layer thickness is difficult to determine and is not uniform throughout.

Application of the conductive polymeric materials to the polyester base support and of the photoconductive coating to the conductive polymeric layer is accomplished by well-known coating methods, such as, for example, band coating wherein the polyester base support is fashioned into an endless belt and is rotated about a plurality of roller members, with one portion thereof being passed through the meniscus of a solution of conductive polymer.

The photoconductive layer 16 is made preferably of an organic photoconductive donor material which does not light fatigue. Other well-known photoconductive materials may be used, but in order for the element 10 to be useful as a belt in an electrophotographic copying machine, such as shown in FIG. 2, these materials should not light fatigue. Furthermore, the element 10 to be used for reflex copying, as in FIG. 2, should have an average light transmittance which is greater than 1 percent and a percent differential in light transmittance between any two given areas on the surface of the element less than 10 percent. A recording element having a photoconductive layer 16 of the type described can be rapidly and repeatedly reimaged without undergoing any significant change in photoconductive response. The preferred organic photoconductive donor material is a polymer such as polyvinylcarbazole or polyvinylbenzocarbazole. The preparation of the polyvinylbenzocarbazole is disclosed in detail in the co-pending application of Baltazzi, et al, Ser. No. 698,420, filed Jan. 17, 1968. Other organic non-polymeric photoconductive materials dispersed in a resin binder may also be used.

The donor material is usually mixed with an acceptor material such as trinitrofluoranylidene malonodinitrile. Other suitable acceptors are disclosed in the co-pending application of Baltazzi, Ser. No. 679,246, filed on Oct. 30, 1967. The donor and acceptor materials are dissolved in a suitable solvent and applied to a base 12 using conventional coating equipment. The solvent is evaporated by forced-air drying, and the solution is applied at a rate such that, when dried, a photoconductive layer 14 is provided having a thickness in the range from about 0.10 to 1.0 mil. The preferred thickness of the photoconductive layer is about 0.6 mil.

During charging and exposing operations, the conductive layer 14 must be connected to a suitable reference potential, as for example, ground. To facilitate this, the photoconductive layer 16 is applied so that it does not completely cover the conductive layer 14. This provides a marginal conductive edge 14a. This edge 14a engages a conductor member 11 which electrically couples the layer 14 to a reference potential. The conductor member 11 may be a metal roller connected to ground. Thus, as the element 10 moves, the roller rides along the marginal edge 14a. Alternate constructions for the member 11 are disclosed in the co-pending application of Shelffo, et al, Ser. No. 702,917, filed Feb. 5, 1968.

Examples of the coatings applied to the base layer to form specific embodiments of a three layer recording element according to the invention are as follows:

EXAMPLE I

17.9 grams of vinylbenzl trimethyl ammonium chloride solution having from 30 - 35 percent total non-volatile solids was mixed with a solvent including approximately 21 grams of denatured ethanol and 61.1 grams of water. A coating solution was formed having the proper viscosity. The conductive polymeric solution was meniscus coated on a strip of polyester film of approximately 5 mils in thickness. The conductive layer was dried by the application of forced air at a temperature of from 100.degree. - 130.degree. F. The weight per 3000 square feet of the finished, dried material was 0.54 lbs. and the resistivity measured at 50 percent relative humidity was 1.5 .times. 10.sup.8 ohms per square. A layer of polyvinylbenzocarbazole was meniscus coated over the polymeric layer and dried in the same manner. The last-mentioned coating was applied to within one-quarter inch of the edge of the polyester material, leaving an uncoated strip running along each edge, exposing the conductive layer therebeneath.

EXAMPLE II

8.9 grams of vinylbenzl trimethyl ammonium chloride having from 30 - 35 percent total non-volatile solids was mixed with a solvent including substantially 21 grams of denatured ethanol and 70.1 grams of water. A coating solution was thereby formed having a suitable viscosity. The conductive coating solution was meniscus coated on a strip of polyester material sold under the tradename of "Permatrace." The strip comes prepared with one surface thereof having been physically abbrated for better adhesion. The layer was dried by the application of forced air as in Example I. The weight per 3000 square feet of the finished, dried material was 0.42 lbs. and the resistivity measured at 50 percent relative humidity was 3.4 .times. 10.sup.9 ohms per square. A layer of polyvinylcarbazole was applied thereover. The last-mentioned layer was applied to within one-half inch of the edge of the strip, thereby exposing the conductive polymeric layer.

EXAMPLE III

7.5 grams of polymer 261 having approximately 40 - 45 percent total non-volatile solids was mixed with a solvent comprising 21 grams of denatured ethanol and 71.5 grams of water. A coating solution formed therefrom, was meniscus coated on a strip of polyester material of approximately 5 mils in thickness. The layer was dried in the above-described manner. The weight per 3300 square feet of finished dried material was 0.98 lbs. and the resistivity measured at approximately 50 percent relative humidity was 3.4 .times. 10.sup.7 ohms per square. An overcoat of a layer of polyvinylbenzocarbazole was applied in similar fashion. The last-mentioned coating was applied to within one-quarter inch of the edge of the strip to expose the conductive layer.

EXAMPLE IV

10 grams of polymer 261 of the variety used in Example III with a solvent comprising approximately 69 grams of water and 21 grams of alcohol. The resulting coating solution was coated onto a 5 mil thick strip of polyester material and was dried. The weight per 3300 square feet of finished, dried material was 1.69 lbs. and the resistivity measured at approximately 50 percent relative humidity was 1.4 .times. 10.sup.7 ohms per square. The conductive layer was overcoated with a coating of polyvinylcarbazole photoconductive material in the same manner as in Example III.

EXAMPLE V

The steps of Example I were repeated using like quantities of solvent and a sample of dipotassium salt of styrene maleic anhydride as the conductive polymer. The resulting weight per 3000 square feet of finished, dried conductive polymer was slightly above 2.0 lbs. and the resistivity measured at 50 percent relative humidity was 3.8 .times. 10.sup.7 ohms per square. The conductive polymeric layer was overcoated as in Example I also.

EXAMPLE VI

The steps of Example II were repeated using like quantities of solvent and a second sample of dipotassium salt of styrene maleic anhydride as the conductive polymer. The resulting weight per 3000 square feet of conductive polymeric material (dried) was 1.9 lbs. and the resistivity measured at 50 percent relative humidity was approximately 1.5 .times. 10.sup.8 ohms per square. An overcoating of polyvinylcarbazole was applied as in Example II.

Turning now to FIG. 2, there is illustrated therein an electrophotographic copying machine 18 using the recording element 10 in an endless belt form. The machine uses the reflex exposure technique and is shown merely for illustrative purposes since the belt member 10 which is translucent may also be used in machines utilizing contact or projection exposure techniques. Three driven rollers, 20, 22 and 24 move the belt 10 through a closed looped path, and the conductor member 11 shown in FIG. 1 connects the conductive layer 14 to ground. The belt 10, as it moves through its looped path, first passes a charging station 26, then advances to an exposing station 28, onto a developing station 30, then to a transferring station 32 and lastly to a fixing or fusing station 76.

At the charging station 26, a corona electrode 34 applies a uniform electrostatic charge of approximately 200 - 800 volts to the photoconductive layer 16. As mentioned before, the grounded conductive layer 14 enables the photoconductive layer 16 to accept a uniform charge.

At the exposing station 28, a graphic original feed roller 36 mounted outside the looped path moves the original 38, fed into the machine at opening 40, into optical contact with the belt 10. A tubular fluorescent lamp 42, mounted inside the looped path opposite roller 36 and partially surrounded by a reflector 44, reflex exposes the belt 10, and a latent image 46 corresponding to the original 20 is formed on the belt. The reflector 44 focuses light on the belt 10 so that the light lies along a line which is transverse to the direction of movement of the original 20. Generally, the incident light rays from the lamp 42 strike the surface of the original 20 at right angles.

At the developing station 30, a magnetic brush developing apparatus 48, such as disclosed in U. S. Pat. No. 3,003,462, applies toner to the latent image 28, converting it into a visible image 50. The rotating cylinder portion 52 of the developing apparatus 48 picks up iron and toner particles contained in a trough 54 and forms them into a magnetic brush 56. As described in detail of the co-pending application of Baltazzi, et al, Ser. No. 675,463, filed Oct. 16, 1967, the magnetic brush 56 is electrically biased. As a result, the surface of the belt 10 which corresponds to non-image areas of the original 20 remains free of toner. The bias is provided by connecting the cylinder 52 to a DC power supply 58 which applies to the brush 56 a potential in the range of about 0 - 1000 volts, preferably 50 - 200 volts.

At the transfer station 32, a semi-conductive rubber roller transfer member 60 having an inner conductive core 62 connected to a 500 - 3000 volt DC power supply 64 removes the material image 50 from the belt 10. The pressure between the photoconductive layer 16 and the transfer member 60 is carefully controlled so that the material image 50 is removed without disturbing the latent image 46.

From a stack 66 of receiving sheets mounted on a tray 68 inside the machine 18, a roller 70 feeds a receiving sheet 72 to the transfer station 32 in timed relationship with the moving belt 10. The transfer member 60 transfers the material image 50 to the receiving sheet 72, and forwards the sheet over a guide plate 74 to a fixing station 76. The fixing station 76 comprises, for example, a pair of driven rolls 78 and 80 which by the application of pressure, fuse the developed image 50 to the copy sheet 72. Other known fixing devices, such as, for example, infrared lamps, may also be used.

In operation, an operator merely feeds the original 38 into an infeed station 40 of the machine 18 and the original feed roller 36 brings the image bearing surface of the original into intimate contact with the belt 10. The lamp 42 reflex exposes the belt 10 and the latent image 46 corresponding to the original 38 is formed thereon. A series of rollers 82 with the aid of a guide 84 then feeds the original 38 out an exit opening 86 of the machine 18. The developing station 30 converts the latent image 46 on the recording element into the developed or material image 50 which is then transferred to the copy or receiving sheet 72. The latent image 46 remains intact and, if multiple copies are to be made, the corona electrode 26 and lamp 42 are turned off and the belt 10 recycles the latent image past the developing station 30 for redevelopment. The pressure rollers 78 and 80 feed the receiving sheet 72 out exit opening 88 in the lower portion of the machine. When a copy of another original is to be made, the charging station 34 and lamp 42 are again turned on. The corona electrode, by depositing a uniform electrostatic charge on the surface of the belt 10, erases or masks any previously formed latent image 46 remaining on the surface of the belt.

The particular copying machine 18 illustrated herein can process originals at a rate in excess of 15 ft/min. Since the belt 10 is reflex exposed using an inexpensive fluorescent lamp 50, the design of the exposing station 28 is greatly simplified. Such a lamp 42 does not consume much electrical energy, nor does it generate much heat energy. Therefore, the power supply for the lamp 42 is inexpensive, and since the material image 46 is not subjected to heat while on the belt 10, it does not tend to adhere to the belt and can be readily removed.

While a particular embodiment of the photoelectrostatic recording element has been shown and described, it should be understood that the invention is not limited thereto since many modifications may be made. It is therefore contemplated to cover by the present application any and all such modifications as fall within the true spirit and scope of the appended claims.

In addition to the above, while the recording element has been described as being used in a particular type of copying machine, as illustrated, it likewise should be understood that its use is not limited thereto.

* * * * *

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