WO1996034319A1

WO1996034319A1 - Printing on floor tiles and the like

Info

Publication number: WO1996034319A1
Application number: PCT/NL1995/000190
Authority: WO
Inventors: Benzion Landa; Ishaiau Lior
Original assignee: Indigo N.V.
Priority date: 1995-04-26
Filing date: 1995-06-06
Publication date: 1996-10-31
Also published as: IL113507A0; AU2578695A

Abstract

A printing process for forming images or designs on a floor tile, comprising: (a) providing a protectively coated toner image or design on a floor tile base material; and (b) laminating the coating and image to the base material.

Description

PRINTING ON FLOOR TILES AND THE LIKE FIELD OF THE INVENTION The present invention relates to an improved electrostatic method for printing or coating on floor tiles and the like with toner and toner inks. BACKGROUND OF THE INVENTION Coating floor tiles and especially vinyl floor tiles and producing designs and images thereon is generally performed by printing the designs on a vinyl film and laminating the film and image to a vinyl tile. Alternatively, the images may be printed onto a transfer sheet, transferred to the tile and covered with a clear vinyl sheet which is laminated to the image and tile. Preferably, a white or other solid coating is applied to the tiles before application of the images, since the virgin vinyl surface is not white or of even color. While the tiles can be produced individually, the general procedure prints the images onto a web and then transfers them onto a web of floor tile material. The printed web is then cut-up to produce the tiles. Such printing, in common with many printing processes, requires a long set-up time and substantial tooling for each design to be printed. It thus becomes economic to produce floor tiles, and especially vinyl floor tiles only in large quantities of the same tile. SUMMARY OF THE INVENTION In one aspect of the present invention a toner image, preferably a liquid toner image, is first provided on a flexible transfer substrate and then transferred to a floor tile or the like from the transfer substrate. The image is covered with a protective sheet of polymer and the sheet and the fmage are laminated to the tile. For this embodiment of the invention, the transfer substrate is preferably a polyester substrate or a polyester coated substrate and the transfer to the tile is preferably aided by heat and pressure. In another aspect of the invention the image together with the transfer substrate is laminated to the tile. Preferably, a white layer is provided over the image on the transfer substrate such that it underlies the image when the image is on the tile. Alternatively, the tile is coated with a white coating before the image is transferred thereto. There is thus provided, in accordance with a preferred embodiment of the invention, a printing method for forming images or designs on a floor tile, comprising: (a) providing a protectively coated toner image or design, preferably a liquid toner image or design, on a floor tile base material, preferably a vinyl tile material; and (b) laminating the coating and image to the base material. In one preferred embodiment of the invention (a) comprises: transferring a toner image or design to the base material; and covering the transferred image with a transparent polymer sheet . In a preferred embodiment of the invention the toner image is transferred to the surface from an intermediate transfer member by heat and pressure . In one embodiment of the invention , the intermediate trans fer member has a polyester image transfer surface; in another embodiment the intermediate transfer member has a silicone image transfer surface. In a second preferred embodiment (b) comprises: forming an image on a polymer sheet, preferably a vinyl sheet; and placing the polymer sheet on the surface, with the image facing the floor tile base material, wherein the polymer sheet forms the protective coating. Preferably, the method includes coating the floor tile material with a vinyl coating prior to (a). Alternatively, the image comprises a layer of white toner facing the floor tile base material. Preferably, the toner image is produced by an electrostatic printing method, preferably, an electrophotographic method. There is further provided, in accordance with a preferred embodiment of the invention a printing method comprising: (a) forming an image, preferably a toner image and more preferably a liquid toner image; (b) transferring the image to a polyester surface; (c) transferring the image from the polyester surface to a final surface. Preferably, (b) comprises transferring the image by an electrically aided transfer method. Preferably, (c) comprises: transferring the image by heat and pressure. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more clearly understood from the following description of preferred embodiments thereof in conjunction with the following drawings which: Fig. 1 is a simplified sectional illustration of electrostatic imaging apparatus constructed and operative in accordance with a preferred embodiment of the present invention for printing a design on an intermediate sheet for later transfer to a floor tile; Fig. 2 is a simplified enlarged sectional illustration of the apparatus of Fig. 1; and Fig. 3 is a simplified diagram of an apparatus, in accordance with a preferred embodiment of the invention, for transferring an image from an intermediate sheet to a floor tile. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Reference is now made to Figs. 1 and 2 which illustrate a multi color electrostatic imaging system constructed and operative in accordance with a preferred embodiment of the present invention. As seen in Figs. 1 and 2 there is provided an imaging sheet, preferably an organic photoreceptor 12, typically mounted on a rotating drum 10. Drum 10 is rotated about its axis by a motor or the like (not shown), in the direction of arrow 18, past charging apparatus 14, preferably a corotron, scorotron or roller charger or other suitable charging apparatus as are known in the art and which is adapted to charge the surface of sheet photoreceptor 12. The image to be reproduced is focused by an imager 16 upon the charged surface 12 at least partially discharging the photoconductor in the areas struck by light, thereby forming an electrostatic latent image. Thus, the latent image normally includes image areas at a first electrical potential and background areas at another electrical potential. A preferred photoreceptor sheet and preferred methods of mounting it on drum 10 are described in a co-pending application of Belinkov et al. , IMAGING APPARATUS AND PHOTORECEPTOR THEREFOR, filed September 7, 1994 assigned serial number 08/301,775 and coresponding applications in other countries, the disclosures of which are incorporated herein by reference. Alternatively, photoreceptor 12 may be deposited on the drum 10 and may form a continuous surface. Furthermore, photoreceptor 12 may be a non-organic type photoconductor based, for example, on a compound of selenium and may be of endless (seamless) construction. Also associated with drum 10 and photoreceptor sheet 12, in a preferred embodiment of the invention, are a multicolor liquid developer spray assembly 20, a developing assembly 22, color specific cleaning blade assemblies 34, a background cleaning station 24, an electrified squeegee 26, a background discharge device 28, an intermediate transfer member 30 , cleaning apparatus 32 , and , opt ional ly , a neutrali zing lamp assembly 36 . Developing assembly 22 preferably includes a development roller 38 . Development roller 38 is preferably spaced f rom photoreceptor 12 thereby forming a gap therebetween of typically 40 to 150 micrometers and i s charged to an electrical potential intermediate that of the image and background areas of the image . Development rol ler 38 i s thus operat ive , when maintained at a suitable voltage, to apply an electric field to aid development of the latent electrostatic image . Development roller 38 typically rotates in the same sense as drum 10 as indicated by arrow 40. This rotation provides for the surface of sheet 12 and development roller 38 to have opposite velocities at the gap between them. In accordance with a preferred embodiment of the invention , images in dif ferent colors are individually developed on the photoreceptor surface and sequentially trans f erred in al ignment with previous images onto intermediate transfer member 30 , which is heated so that each color forms a cohesive non-diffused layer . The images are heated to a temperature that causes the colored toner particles in the presence of carrier liquid in each layer to at least partially coalesce, preferably into a cohesive film, i . e . , the toner pigment is fixed in the layer in which it was deposited so that mixing of different color pigments in various layers is prevented . In a preferred embodiment of the invention , an opaque , preferably white , background layer is developed last on the photoreceptor surface and transferred to intermediate transfer member 30, covering the image . It should be noted that in the preferred embodiment of the invention, each of the layers is a viscous liquid and that while heating does cause the layers to coalesce, the balance between viscosity and surface tension of the layers is apparently such that the individual layers have only minimal mixing. When all of the desired images have been transferred to intermediate transfer member 30, the complete multi-color image is transferred therefrom to an intermediate substrate 72. Impression roller 71 only produces operative engagement between intermediate transfer member 30 and substrate 72 when transfer of the composite image to substrate 72 takes place, preferably with heat and pressure. Substrate 72 which is preferably a transparent flexible polymer film and most preferably is a polyester film or polymer coated film, is fed from a feeder roller 77 and is taken up by take up roller 78. The printing process when carried out as described produces a high contrast high quality colored image. Preferably, the motion of the polymer film is halted during the accumulation of the layers on the intermediate transfer member. Just prior to the transfer, the film is accelerated to a velocity substantially equal to the surface velocity of the intermediate transfer member, such that there is substantially zero relative motion between them at the time of contact. Furthermore, between transfers, the film is preferably partially rewound so that, after the acceleration, only a minimal blank space is left unprinted. Multicolor liquid developer spray assembly 20, whose operation and structure is described in detail in U.S. Patent 5,117,263, the disclosure of which is incorporated herein by reference, may be mounted on axis 42 to allow assembly 20 to be pivoted in such a manner that a spray of liquid toner containing electrically charged pigmented toner particles can be directed either onto a portion of the development roller 38, a portion of the photoreceptor 12 or directly into a development region 44 between photoreceptor 12 and development roller 38. Alternatively, assembly 20 may be fixed. Preferably, the spray is directed onto a portion of the development roller 38. Color specific cleaning blade assemblies 34 are operatively associated with developer roller 38 for separate removal of residual amounts of each colored toner remaining thereon after development. Each of blade assemblies 34 is selectably brought into operative association with developer roller 38 only when toner of a color corresponding thereto is supplied to development region 44 by spray assembly 20. The construction and operation of cleaning blade assemblies is described in PCT Publication WO 90/14619 and in US patent 5,289,238, the disclosures of which are incorporated herein by reference. Each cleaning blade assembly 34 includes a toner directing member 52 which serves to direct the toner removed by the cleaning blade assemblies 34 from the developer roller 38 to separate collection containers 54, 56, 58, 60, and 68 and for each color to prevent contamination of the various developers by mixing of the colors. The toner collected by the collection containers is recycled to a corresponding toner reservoir (55, 57, 59 ,61 and 63). A final toner directing member 62 always engages the developer roller 38 and the toner collected thereat is supplied into collection container 64 and thereafter to reservoir 65 via a separator 66 which is operative to separate relatively clean carrier liquid from the various colored toner particles. Separator 66 may be typically of the type described in U.S. Patent 4,985,732, the disclosure of which is incorporated herein by reference. In a preferred embodiment of the invention, as described in PCT Publication WO 92/13297, the disclosure of which is incorporated herein by reference, where the imaging speed is very high, a background cleaning station 24 typically including a reverse roller 46 and a wetting roller 48 are provided. Reverse roller 46 which rotates in a direction indicated by arrow 50 is preferably electrically biased to a potential intermediate that of the image and background areas of photoconductive drum 10, but different from that of the development roller. Reverse roller 46 is preferably spaced apart from photoreceptor sheet 12 thereby forming a gap therebetween which is typically 40 to 150 micrometers. Wetting roller 48 is preferably partly immersed in a f luid bath 47 , which preferably contains carrier liquid received from carrier liquid reservoir 65 via conduit 88. Wetting roller 48 , which preferably rotates in the same sense as that of drum 10 and reverse roller 46 , operates to wet photoreceptor sheet 12 with non-pigmented carrier liquid upstream o f reverse rol ler 46 . The l iquid suppl ied by wetting roller 48 replaces the liquid removed from drum 10 by development assembly 22 , thus allowing the reverse roller 46 to remove charged pigmented toner particles by electrophoresis f rom the background areas of the latent image . Excess fluid is removed from reverse roller 46 by a l iquid directing member 70 which cont inuously engages reverse roller 46 to collect excess liquid containing toner particles of various colors which is in turn supplied to reservoir 65 via collection container 64 and separator 66. Wetting roller 48 is preferably electrically biased to a potential intermediate that of the image and background areas of photoreceptor surface 12 , but different from that of the development roller . This biasing of wetting roller 48 assists in removing toner particles from the background areas of photoreceptor sheet 12 . Wetting rol ler 48 i s preferably spaced apart from photoreceptor sheet 12 thereby forming a gap therebetween which is typically 40 to 200 micrometers. The apparatus embodied in reference numerals 46, 47, 48 and 70 is generally not required for low speed systems, but is preferably included in high speed systems. Preferably, an electrically biased squeegee roller 26 is urged against the surface of sheet 12 and is operative to remove liquid carrier from the background regions and to compact the image and remove liquid carrier therefrom in the image regions. Squeegee roller 26 is preferably formed of resilient slightly conductive polymeric material as is well known in the art, and is preferably charged to a potential of several hundred to a few thousand volts with the same polarity as the polarity of the charge on the toner particles. Discharge device 28 is operative to flood sheet 12 with light which discharges the voltage remaining on sheet 12, mainly to reduce electrical breakdown and improve transfer of the image to intermediate transfer member 30. Operation of such a device in a write black system is described in U.S. Patent 5,280,326, the disclosure of which is incorporated herein by reference. Figs. 1 and 2 further show that multicolor toner spray assembly 20 receives separate supplies of colored toner typically from five different reservoirs 55, 57, 59, 61 and 63. Figure 1 shows five different colored toner reservoirs 55, 57, 59, 61 and 63, typically containing the colors Yellow, Magenta, Cyan, black and white, respectively. In addition, reservoir 65 contains relatively clean carrier liquid whose operation was described. Pumps 90, 92, 94, 96 and 108, may be provided along respective supply conduits 98, 101, 103, 105, and 107, for providing a desired amount of pressure to feed the colored toner to multicolor spray assembly 20. Alternatively, multicolor toner spray assembly 20, which is preferably a three level spray assembly, receives supplies of colored toner from up to six different reservoirs (a sixth reservoir marked S is shown) which allows for custom colored toners in addition to the standard process colors, black and the optional white toner. Cleaning apparatus 32 is operative to scrub clean the surface of photoreceptor 12 and preferably includes a cleaning roller 74, a sprayer 76 to spray a non- polar cleaning liquid to assist in the scrubbing process and a wiper blade 78 to complete the cleaning of the photoconductive surface. Cleaning roller 74, which may be formed of any synthetic resin known in the art, for this purpose is driven in the same sense as drum 10 as indicated by arrow 80, such that the surface of the roller scrubs the surface of the photoreceptor. Any residual charge left on the surface of photoreceptor sheet 12 may be removed by flooding the photoconductive surface with light from optional neutralizing lamp assembly 36, which may not be required in practice. Fig. 3 is a simplified diagram of an apparatus for transferring an image from an intermediate transfer substrate to a floor tile, such as a vinyl tile. Intermediate transfer substrate 72, preferably of polyester or a polyester coated film, on which an image 103 has been formed, as described above, is brought into contact with a floor tile 100 on a belt 102 which is moving in the same direction as substrate 72. An impression roller 104, which is preferably formed with an elastomer layer and which is preferably heated, presses the image side of substrate 72 against the floor tile and transfers the composite image from substrate 72 to the floor tile. Preferably, the belt is backed with a backing member 106 to provide counter-pressure against the impression roller. Furthermore, a heater 109, such as a halogen lamp is preferably provided to preheat the tile to aid in transfer of the image thereto. It has been found that under heat and pressure, toner images, especially those produced according to preferred embodiments of the invention, transfer cleanly and easily from polyester and polyester coated substrates to tiles and to other substrates. If this method of image formation on the tiles is used, then the image is overcoated with a polymer protective film which is laminated to the floor tile, preferably by heat and pressure. Fig. 3 shows printing on individual tiles. However, the transfer of the images to the tiles may take place prior to cutting of the tile material, wherein the tile material is in a web form. It should be understood that while the web is continuous, the printing process using toner allows for each succeeding tile to be different. Thus both web and individual transfer of images to the tile material allow for custom printing of tiles and custom printing of tile sets to order. Alternatively, when substrate 72 is transparent, a portion of substrate 72, with the image facing the tile, is laminated, to the tile, thus providing a protected design on the vinyl tile. Where a white layer is not printed onto the image, then, preferably, the tile is coated with a white vinyl coating for improved color purity and uniformity. While it is to be understood that when a vinyl overcoat is used, the lamination of the tile can be carried out using a standard laminating process for tiles, it may be advisable to use a hot melt adhesive (such as Macromelt 6239) or a basic adhesion promoter such as polyvinylpiridine homopolymer or its copolymer with styrene between the image and the tile and/or between the image and the film covering the image. Toners that can be used with the present invention are described in Example 1 of U.S. Patent 4,794,651, the disclosure of which is incorporated herein by reference or variants thereof as are well known in the art. For colored liquid developers, carbon black is replaced by color pigments as is well known in the art. Other toners may alternatively be employed, including liquid toners and, for some aspects of the invention, including powder toners. Other toners for use in the invention can be prepared using the following method: 1) Solubilizing 1400 grams of Nucrel 925 ( ethylene copolymer by Dupont ) and 1400 g of Isopar L (Exxon) are thoroughly mixed in an oil heated Ross Double Planetary Mixer at least 24 RPM for 1.5 hours, with the oil temperature at 130° C. 1200 g of preheated Isopar L is added and mixing is continued for an additional hour. The mixture is cooled to 45° C, while stirring is continued over a period of several hours, to form a viscous material. 2) Milling and Grinding 762 grams of the result of the Solubilizing step are ground in a IS attritor (Union Process Inc. Akron Ohio), charged with 3/16" carbon steel balls at 250 RPM, together with 66.7 grams of Mogul L carbon black (Cabot), 6.7 grams of BT 583D (blue pigment produced by Cookson), 5 grams of aluminum stearate (Riedel Dehaen) and an additional 1459.6 grams of Isopar L for eight hours at 30° C. 3) Continuation of Grinding 34.5 grams of ACumist A-12 (a micronised polyethylene wax produced by Allied Signal) is added and grinding is continued for an additional 4 hours. The resulting particles are fibrous particles have a measured diameter in the range of 1-3 micrometers. The resulting material is diluted with additional Isopar L and Marcol 82 to give a working developer in which the dry solids portion is about 1.7% and in which the overall ratio of Isopar L to Marcol is between about 50:1 and 500:1, more preferably between about 100:1 and 200:1. Charge director as described in US patent application 07/915,291 (utilizing lecithin, BBP and ICIG3300B) and in WO 94/02887, in an amount approximately equal to 40 mg/gm of solids in the final dispersion, is added to charge the toner particles. Other charge directors and additional additives as are known in the art may also be used. The above described process produces a black toner. Cyan, magenta and yellow toners can be produced by using a different mix of materials for step 2). For Cyan toner, 822g of the solubilized material, 21.33 grams each of BT 583D and BT 788D pigments (Cookson), 1.73 grams of D1355DD pigment (BASF), 7.59 grams of aluminum stearate and 1426 grams of Isopar L are used in step 2. For Magenta toner, 810 grams of solubilized material, 48.3 grams of Finess Red F2B, 6.81 grams of aluminum stearate and 1434.2 grams of Isopar L are used in step 2. For yellow toner 810 grams of solubilized material, 49.1 grams of D1355DD pigment, 6.9 grams of aluminum stearate and 1423 grams of Isopar L are used in step 2. Other preferred liquid toners for use in the present invention are prepared as follows: 300 grams of a chargeable low molecular weight ionomer Aclyn 293A (made by Allied Signal) were solubilized in 1500 grams of Isopar - L with heating to 110°- 120^βC while stirring. To form inks, dispersed pigments or color particles are added to and mixed with the hot solubilized polymer. The composition is allowed to cool while stirring. These toners may include large percentages of pigment, when extremely vivid colors are desired. The following white liquid toner ink is prepared in this way: Ti0₂ BASED OPAQUE WHITE TONER INK A preferred opaque white ink in accordance with the present invention is prepared by adding 200 grams of finely divided Ti02 pigment, having an average diameter of about 0.5 micrometers to the solubilized polymer while stirring. The mixture is allowed to cool and settle with continuous stirring. Charge director, as described above or other charged directors as known in the art, and additional Isopar L and MARCOL 82 carrier liquid are added to form a liquid toner. The opaque white liquid toner so obtained is used, as previously mentioned, to enhance the quality of color images when it serves as a back layer for color contrast. The median pigmented toner particle size in the toner is 4.81 micrometers. An alternative preferred method for producing white toner ink concentrate, in accordance with a preferred embodiment of the invention comprises the steps of ( 1 ) plasticizing 35% Nucrel 699 (ethylene-metacrylic acid copolymer by DuPont) in Isopar L (EXXON) by heating the materials in a Ross double planetary mixer to 150°C while mixing the materials and allowing the mixture to cool while mixing continues until the mixture is fully mixed and homogeneous; (2) mixing 3071 grams of the mixture produced by step (1) with 1075 grams of KRONOS 2310 titanium dioxide (NL Chemicals) and 4454 grams of Isopar L in a Ross type LAB ME high shear mixer until the new mixture is completely homogeneous; and (3) grinding the mixture at about 56^βC (the temperature of the mixture without cooling) for 16 hours in a SWEECO M18 Vibratory Mill charged with 3/8" zirconia media. The resultant toner has a median diameter of about 3 microns. The material is charged and diluted as described above. Intermediate transfer member 30 may be any suitable intermediate transfer member having a multilayered transfer portion such as those described below or in US Patents 5,089,856 or 5,047,808 or in U.S. Patent application 08/371,117, filed January 11, 1995 and entitled IMAGING APPARATUS AND INTERMEDIATE TRANSFER BLANKET THEREFOR and coresponding applications filed in other countries, the disclosures of which are incorporated herein by reference. Member 30 is maintained at a suitable voltage and temperature for electrostatic transfer of the image thereto from the image bearing surface. Intermediate transfer member 30 is preferably associated with a pressure roller 71 for transfer of the image onto substrate 72, preferably by heat and pressure. Additionally, pressure roller 71 may be electrified to overcome the voltage on the intermediate transfer member or to provide an additional electric field to aid transfer of the electrified toner to the substrate. In addition to the details of the printing processes given above, additional details of printing processes and operations, including other preferred liquid toners suitable for the invention, are given in the patents , patent applications and publications incorporated herein by reference. Alternatively, the intermediate transfer member may be of seamless (endless) construction. It should be understood that, while a preferred printing process has been described, other printing processes such as direct printing of toner from the intermediate transfer member to the tile (with subsequent overcoating by a transparent protective film) and separate printing of a white background on the tile prior to transfer of the image thereto are also possible in accordance with alternate embodiments of some aspects of the invention. It should be understood that the invention is not limited to the specific type of image forming system used and the present invention is also useful with any suitable imaging system which forms a toner image on an image forming surface and, the specific details given above for the image forming system are included as part of a best mode of carrying out the invention, however, many aspects of the invention are applicable to a wide range of systems as known in the art for toner printing and copying. Especially suitable printing apparatus for printing toner images on sheets or on webs of polymer include the E- Print 1000 and Indigo Omnius printing presses available from Indigo N.V., The Netherlands. It will be appreciated by persons skilled in the art that the present invention is not limited by the description and example provided hereinabove. Rather, the scope of this invention is defined only by the claims which follow:

Claims

CLAIMS 1. A printing method for forming images or designs on a floor tile, comprising : ( a ) providing a protectively coated toner image or design on a floor tile base material; and ( b ) laminating the coating and image to the base material .

2. A printing method according to claim 1 wherein (a) comprises: transferring a toner image or design to the base material; and covering the transferred image with a transparent polymer sheet.

3. A printing method according to claim 2 wherein the toner image is transferred to the base material from an intermediate transfer member by heat and pressure.

4. A printing method according to claim 3 wherein the intermediate transfer member has a polyester image transfer surface.

5. A printing method according to claim 3 wherein the intermediate transfer member has a silicone image transfer surface.

6. A printing method for forming images or designs on floor tiles according to claim 1 wherein (a) comprises: forming an image on a polymer sheet; and placing the polymer sheet on the floor tile base material, with the image facing the base material.

7. A printing method according to claim 6, wherein the polymer sheet comprises a vinyl film. ,

8. A printing method according to any of the preceding claims and including coating the floor tile material with a vinyl coating prior to (a) .

9. A printing method according to any of claims 1-6 wherein the image comprises a layer of white toner facing the floor tile base material.

10. A printing method according to any of the preceding claims wherein the floor tile is a vinyl floor tile.

11. A printing method according to any of the preceding claims wherein the toner image or design is a liquid toner image or design.

12. A printing method according to any of the preceding claims wherein the toner image is produced by an electrostatic printing method.

13. A printing method according to claim 12 wherein the electrostatic printing method is an electrophotographic method.

14. A printing method comprising : ( a ) forming an image; ( b ) transferring the image to a polyester surface; ( c ) transferring the image from the polyester surface to a final surface .

15. A printing method according to claim 14 wherein ( b ) comprises : transferring the image by an electrically aided transfer method.

16. A printing method according to claim 14 or claim 15 wherein (c) comprises: 1 transferring the image by heat and pressure. 2

3 17. A printing method according to any of claims 14-16

4 wherein the image is a toner image. 5

6 18. A printing method according to claim 17 wherein the

7 image is a liquid toner image. 8

9 19. A printing method according to any of claims 14-18 10 wherein the image is formed by an electrostatic method. 11

12 20. A printing method according to claim 19 wherein the

13 image is formed by an electrophotographic method. 14

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