US3921527A - Reusable printing master and method of making same - Google Patents

Abstract

A reusable master is produced by blanket charging an insulating carrier surface, which is intended to include a dark adapted photoconductor, toning, imagewise charging the toner, and separating the released toner from the retained toner to produce a pattern. This process makes litho masters and electrostatic masters. The toner pattern may be produced on a surface which has a very low surface attraction for grease lithographic ink, and therefore only the pattern will pick up and transfer ink. The master is reusable by dissolving away the image after use. Also, a master sheet which will not hold an electrostatic charge can be imaged, the image pattern charged and toned, and the toner thereafter transferred to plain paper. The master may be a photoconductor, which if charged in a lighted area, or flooded with light after charging, will discharge all but the toned image.

Description

United States Patent 1191 Raschke et a1.

1451 Nov. 25, 1975 1 1 REUSABLE PRINTING MASTER AND METHOD OF MAKING SAME ['15] Inventors: Curt R. Raschke, Warrensville Heights; Ival L. Toepke, Newbury, both of Ohio [73] Assignee: Addressograph Multigraph Corporation, Cleveland, Ohio 1221 Filed: Dec.20,1974

211 Appl.No.:534,729

[52] US. Cl. 101/463; lOl/DIG. 13; 101/425;

427/14; 427/22; 427/24 [51] Int. C1. 841M 5/00; G030 13/22 [58] Field of Search 427/14, 22, 24; 96/1 R,

96/1 SD, 114; 118/637; lOl/DIG. 13,453. 463, 473', 355/17 [56] References Cited UNITED STATES PATENTS 3,071,645 H1963 McNaney 355/17 3,405,682 10/1968 King et al. 118/637 3,443,517 5/1969 Gundlach..... 101/219 3,515,584 6/1970 Yang 101/395 3,589,290 6/1971 Walkup et a1. 101/426 3,632,375 1/1972 Gipe 101/450 Clark 101/DlG, l3 Rittler et a1 1 18/637 Primary Examiner-Michael Sofocleous Attorney, Agent, or Firm-Ray S. Pyle [57] ABSTRACT A reusable master is produced by blanket charging an insulating carrier surface, which is intended to include a dark adapted photoconductor, toning, imagewise charging the toner, and separating the released toner from the retained toner to produce a pattern. This process makes Iitho masters and electrostatic masters.

The toner pattern may be produced on a surface which has a very low surface attraction for grease lithographic ink, and therefore only the pattern will pick up and transfer ink. The master is reusable by dissolving away the image after use. Also, a master sheet which will not hold an electrostatic charge can be imaged, the image pattern charged and toned, and the toner thereafter transferred to plain paper.

The master may be a photoconductor, which if charged in a lighted area, or flooded with light after charging,- will discharge all but the toned image.

9 Claims, 4 Drawing Figures US. Patent Nov. 25, 1975 3,921,527

"III":

whether the surface be insulating, conducting, photo- REUSABLE PRINTING MASTER AND METHOD OF conducting.

MAKING SAME It is a further object of the invention to provide a re- BACKGROUND OF THE INVENTION Lithographic printing has developed rapidly from the original stone masters to modern disposable planographic masters.

A stride in the simplification of master material, not requiring skilled craftsmen to produce, was the provision of a coating of clay on paper which can be prepared by typewriter and used on an offset press. A typed master will accept water and reject greasetype lithographic ink, except in the image area.

The master is first wet with water and then a roller having an ink surface is applied to .the master. The image alone will pick up the ink. The inked master is then rolled against a rubber mat to produce an offset reverse image. Thereafter, the rubber mat is rolled against a plain paper sheet to produce the final printed copy.

Typing such a master greatly facilitated the printing art by making quality printing available to much lower skilled personnel. Nevertheless, the direct image master has limitations. Hence, as electrostatic copy techniques became well developed, means were developed to chemically convert a developed copy sheet into a lithographic master.

Electrostatic copy sheets made of zinc oxide are oleophilic. After being developed and an image fused to the surface, the zinc oxide may be converted to an oleophobic condition by chemical reaction with a conversion solution. The image will not be converted because it is an inert material. It will accept grease ink, but the background will reject grease ink when wet.

Masters which must be converted usually are quite high in printing quality. However, the preparation of a photoconducting coating is an exacting process and sometimes not successful. The reason for failure is not always easy to identify. Usually, the failure is evidenced by a general gray toning of the area which should be free of ink.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration of apparatus suitable to carry out the method of this invention;

FIG. 2 is a section taken along line 2-2 of FIG. 1; FIG. 3 is a section through a representative suitable master sheet; and

FIG. 4 is an illustration of an alternative adaptation of the struture in FIG. 1.

SUMMARY OF THE INVENTION This invention and the development by other prior inventors is based upon the premise that a surface which is naturally oleophobic will not be subject to the incorporeal influences which plague the conversion step in conventional master technique.

The problem is to provide such a surface with an ink accepting image, or an image which may be electrostatically charged and toned.

Therefore, an object of this invention is to provide a commercially acceptable image-producing process for imaging a stable oleophobic, hydrophilic master sheet surface.

A further object of this invention is to provide a reproducible master image on substantially any surface,

usable master in order that the costs of the master sheet may be applied to several or many printing cycles of different context. In this respect, it is the object to reduce the cost of master use and the consequent reduction of solid waste material.

It is further an object of this invention to provide a master suitable for duplicating electrostatic copies as described in U.S. Pat. Nos. 3,271,146 and 3,795,442. If a master is prepared with a fused image of insulating toner on a conducting or semi-conducting surface (such as metal or zinc oxide), the fused image can be charged, toned, and the unfused toner transferred to paper many times to serve as a duplicator.

DESCRIPTION OF THE PREFERRED EMBODIMENT The original stone lithography is a direct image process that is highly successful, but requires a very expensive master in that each stone must be laboriously processed and is useful for one original image only. Such a lithographic process employs a type of stone which when wet has a very low adhesion for ink, and the engraved image to be reproduced actually holds ink in the recess of the engraved image and will transfer some of that ink to a carrier sheet pressed against the surface of the stone.

Because such a stone is a slow and wasteful mastermaking process, the many well-known techniques were developed for planographic printing wherein such easily obtainable materials on aluminum and zinc are used as a master sheet with various means converting that sheet into areas which reject grease ink and those areas which accept the grease ink, thereby making possible a differential to produce an ink image. The ink is then carried in image form by such a master.

Later, direct image masters, which are essentially clay compositions held by synthetic resin binders, replaced the more expensive metal masters. These clay I masters are typed in a conventional typewriter using a ribbon of grease type release ink in order to type an adherent grease image on the master sheet. Then, when the master sheet is wet with starter fluid, the background will not accept grease ink, but the type image will. Thus, by repeating an application of moisture and thereafter an application of ink to the surface of this master, the image will pick up and transfer the grease type ink to an image-receiving surface. If the image is applied to a blanket and then to a receiving sheet, the image will be reversed on the blanket and then right reading on the final receiving sheet. Such masters are relatively inexpensive but are discarded after each use and also subject to the sometimes unexplainable vagrancies which upset the system and fail to produce good results. Such failures are rare but do exist.

Inventors have long made an effort to provide a lithography system that would produce an easily made master but would not require a delicate balance of moisture and ink. Two such patents are illustrated by U.S. Pat. Nos. 3,677,178 and 3,511,178.

These prior references have approached the basic problem of eliminating the need for conversion and moisture by taking advantage of the natural ink-rejecting characteristics of silicone rubber. By selecting an ink and polysiloxane combination of related characteristics, a master sheet coated with a thin layer of polysiloxane will not accept an ink of sufficient surface tension. A grease type ink will usually provide the low adhesive attraction for polysiloxane surfaces.

Curtain US. Pat. No. 3,511,178 provided the image by causing image areas of a non-ink receptive surface to wash away, exposing a highly ink receptive surface in image configuration to be exposed in a background which is ink-rejecting. Gipe US. Pat. No. 3,677,178 improved somewhat on the means to produce such image cavities in a polysiloxane field.

Sorkin US. Pat. No. 3,775,1 provided a means for producing an electrostatic image under the polysiloxane surface, and thereby set up a field effect to hold a toner on the polysiloxane surface until fused. This development elimated the need for processing the polysiloxane surface to wash away an image portion thereof, but does require an undercoating of photoresponsive material for each master. The toned image will carry ink for impressing on a receptive carrier.

The present invention employs an ink-rejecting surface master sheet and establishes an image in an improved manner over these prior art teachings. One very suitable surface is a polysiloxane materiial, which has a very low adhesion for grease type printing ink. The patentee of US. Pat. No. 3,511,178 characterizes such a surface as being adhesive. Other suitable surfaces are Teflon and polyethylene.

FIG. 3 of the drawing is representative of the cross section of a master sheet according to this invention. A dimensionally stable base sheet A may be of a selected one of many suitable materials, such as aluminum, paper, or dimensionally stable man-made plastic material. A coating B of polysiloxane of the type amply disclosed and discussed by Curtain US. Pat. No. 3,51 1,178, which is expressly incorporated herein by reference, will provide the adhesive coating.

The apparatus and method for making a reusable master according to this invention is illustrataed schematically in FIG. I. The actual apparatus is sufficiently similar to electrostatic copying and duplicating machines that this schematic illustration will be sufficient for those skilled in the art.

A belt 10 is made of a conducting backing 12. The backing is preferably metal. The backing 12 is coated with a dielectric surface 14. The selected dielectric will accept a static electric charge on the surface thereof and not lose that charge over an extended period of time. The Dupont Corporation is a source of several such materials. Teflon is one such material which is satisfactory, and this is the trademark of the Dupont Corporation for a product known chemically as polytetrafluoroethylene. Mylar is a Dupont trademark for polyester film.

The belt 10 is shown as a horizontal endless belt reaved around two rollers 16.

The method to be carried out to produce a temporary image for transfer to the polysiloxane, Teflon, or polyethylene master surface is accomplished by flooding the surface 14 with a uniform charge by means of a corona device 20. A corona device is well-known in the photocopy art and consists usually of a wire or braid of wire behind a reflector and connected to a source of high voltage.

After the dielectric surface 14 is flooded with a charge, whether negative or positive it does not matter, the charge is uniformly toned by means of any conventional toning device, using a toner compatible with the sign of the charge, illustrated as being a magnetic brush 22. Cascading and other types of toning systems are optional. An example of a brush toner may be seen in U.S. Pat. No. 3,387,586. The brush 22 operates to pick up and supply toner from a toner supply source illustrated diagrammatically by a container 24.

The belt can be toned directly without a corona precharge, if a biased magnetic brush is used. In this case the brush is biased relative to the back of the insulating belt in a manner to force the charged toner particles onto the insulation. (Positive, relative to the belt, if positive toner used, and negative if negative toner used.)

The next step in the method is to release toner from the uniformly toned dielectric surface 14 in an image configuration which is to be copied or reproduced. A stencil screen 30 is illustrated as an ion modulating device to filter out a stream of ions produced by a corona device 32. The stencil screen 30 is illustrated as a reusable photoconductor screen but may literally take the form of a metal stencil with the image pattern cut in the metal. The ion discharge produced by the corona device 32 is then permitted to pass through the stencil only in the passages provided by the cut pattern in the stencil.

The preferred photoconducting screen 30 consists of a photoconductor coated on a fine metal screen. An imaging system 31 will create areas charged in such a manner as to repel ion flow and other areas uncharged or discharged in an image pattern to allow the passage of the ions produced by the corona device 32. These devices are known and are mentioned only as examples.

The stencil screen 30 is moved into position over the upper run of the belt 10 and the corona device 32 caused to emit a pattern of ion particles through the screen to the belt surface to neutralize those charges produced by the uniform deposition of the corona device 20. This results in a field of toner particles in which the background is uniformly adhering to the belt surface by means of the electrostatic charge, and an image area within the field wherein the toner is loose because of a discharge of the image-holding field.

Thus, the belt 10 is advanced to a station 34 where a pressure roller 36 presses a previously prepared master shown in FIG. 3 against the surface 14 and causes the loose image area toner to adhere to the polysiloxane surface. If necessary or desirable, a field device may be established behind the master sheet to help attract the toner from the surface 14 to the polysiloxane surface.

After transfer of the image to the master sheet, the master may be treated by any device for fixing the toner in a known manner. Pressure, heat and/or solvent fixing are devices well-known in the art.

After the image has been lifted from the surface of the belt 10, the belt then proceeds around the end of the roller 16 and the areas previously neutralized are re-flooded with a new charge from the corona device 20 and if the charge on the balance of the background has become weak, the strength of the charge is reinforced. Then the belt is retoned in the manner described, and prepared for a second imprint.

The prepared master is used in any suitable lithographic or electrostatic printing apparatus whether offset or direct image. Although usually not necessary, some moisture may be employed in the lithographic mode if that is believed desirable to improve and assure quality.

At the end of the use of the prepared master, rather than discarding the master, the surface may be flooded with a solvent for the toner resin binder in order to dissolve the image and restore the polysiloxane master surface to a clean state for reuse. Toner mixes usually employ carbon and a fusable resin which holds the carbon particles in position. Such resins are soluble in a number of petroleum and alcohol solvents, and are thus removable.

FIG. 4 is an alternative method of producing masters by the principles of this invention, and also illustrates a means for making a negative master wherein the background is ink-receptive and the image is ink-rejecting.

The apparatus of FIG. 4 is essentially the same as that in FIG. 1 except that the belt, designated herein as belt 50, is not an electrostatic belt but is designed only to carry masters represented by symbols 52 and 53in FIG. 4. A looped endless belt is not essential but is in harmony with FIG. 1 and will illustrate the principles. A vacuum belt, mechanical adhesion or any other means is employed to carry the masters 52 and 53 on belt 50.

The masters pass the corona discharge station and are then blanketed-toned by the brush 22. Thereafter the stencil screen operates as described with respect to FIG. 1 to release a pattern of the toner particles.

This embodiment differs in that the image area is lifted from the surface of the masters rather than the background. Hence, the masters are caused to run under a roller 60. Roller 60 could operate either as a mechanical adhesion device to attract the particles, or may be assisted by a field effect produced from within the roller to help lift away the loosened toner material. The result is a master with a uniformly toned background and a non-toned image area. This master may be used to produce an inked background with a blank image area, or printing areas may be provided which are negative working and will adhere to the image area in preference to the background.

In either event, whether the master is made by the process and apparatus of FIG. 1 or FIG. 4, conventional fusing is employed to bind the image to the surface of the master, and after use, the toner material may then be dissolved in a suitable solvent for reuse of the master.

EXAMPLE l An endless belt of aluminized mylar was uniformly charged to +700v with a positive corona and toned uniformly with a bias electroded cascade developer, using Xerox 914 developer mix. The toned belt was then imaged with a negative corona directed through the stencil to the toner layer. The negative image charge leaked through the toner and neutralized the positive charge on the belt, loosening the toner in an imagewise fashion.

The imagewise loosened toner was then transferred to a polysiloxane surface. This was accomplished by placing the polysiloxane in contact with the imaged belt and running them between conducting pressure rollers biased to keep the charged background toner on the mylar belt. The loosened toner transferred by pressure to the polysiloxane sheet.

The toned polysiloxane sheet was then fused and used to print lithographic copies.

After use, the polysiloxane sheet was scrubbed with acetone which dissolved the toner but did not dissolve the polysiloxane. After drying, the polysiloxane sheet was ready to receive another image.

EXAMPLE 2 A thin sheet of Teflon (tetrafluoroethylene) with an aluminum backing was uniformly toned using a mag netic brush of Addressograph-Multigraph Type D Electrostatic Developer Mix. The brush was biased to +l00v relative to the aluminum backing and deposited toner on the initially uncharged Teflon.

The toner layer was then uniformly charged with a positive corona and then imagewise charged with a negative corona directed through a stencil modulator to the belt. The magnitude of the deposited image negative charge density was several times that of the uni form positive charge density.

The imagewise charged toner was then transferred to a receiving roller which was biased positively to the alu' minum backing to pick up the image charged toner and repel the background toner.

The background toner remaining on the Teflon sheet was heat-fused to the sheet and negative lithographic copies printed from it.

After use, the Teflon sheet was scrubbed with methylene chloride which dissolved the toner but did not dissolve the Teflon. After drying, the Teflon sheet was ready to receive another image.

EXAMPLE 3 A receiving surface was toned as in Example 2. It was a polyethylene surface for the lithographic master and a metal surface for the dry electrostatic master case.

In one test, the uniformly toned surface was then imagewise charged by a negative corona directed through an ion modulator to the toner and in another test, a positive corona was used. Enough image charge was deposited to pin-down the toner on the sheet and the loosely bound background toner removed with a blast of air.

The remaining image toner was then heat-fused to the receiving surface and copies printed from the master. Lithographic copies were made from the toned polyethylene plate and dry electrostatic copies from the toned metal plate.

What is claimed is:

l. The method of making a lithographic master, comprising the steps of:

1. providing a flexible carrier support sheet having an oleophobic layer adhered thereto which is highly repellent to oil based ink, said oleophobic layer having an adhesive release value, when dry, of less than about grams per square inch and being an electrically insulated material selected from the class of ink release surface materials consisting of a cured elastomeric organopolysiloxane, tetrafluoroethylene, and polyethylene;

2. creating a blanket electrostatic charge on said carrier support sheet and uniformly toning said sheet with a triboelectric toner;

3. thereafter, subjecting said toned support sheet to a pattern of electrostatic charge to neutralize the electrostatic holding power thus forming loose toner in a pattern formation;

4. providing a transfer surface having a mechanical affiliation for said loose toner in the pattern formation, and placing said transfer surface against said toned support sheet bearing the loose toner pattern to separate the toner into one surface with a negative image and the other with a positive image; and

5. finally, fixing the image to the carrier to produce a lithographic master.

2. In the method defined in claim 1, the carrier support sheet being a continuous belt, and the transfer surface picking up a positive image.

3. In the method of claim 2, said transfer surface being a dry, semi-conducting electrostatic master.

4. In the method of claim 1, the oleophobic layer being polysiloxane having a low adherence for grease lithographic ink.

5. [n the method of claim 1, the final step of dissolving the fixed image to reuse the carrier support sheet.

6. In the method of claim I, producing the pattern of electrostatic charge by use of ion modulators.

7. The method of making a lithographic master, comprising the steps of:

1. providing an electrically insulating flexible carrier support sheet having an oleophobic layer adherent thereto which is highly repellent to oil-based ink, said oleophobic layer being further characterized as comprising a cured elastomeric organopolysiloxane having an adhesive release value, when dry, of less than about lOO grams per inch;

2. creating a blanket electrostatic charge on said carrier sheet and applying a uniform coating of a triboelectric toner thereon held by said charge;

3. thereafter, subjecting said toned surface to a pattern of electrostic charge to neutralize the electrostatic holding power thus forming loose toner in a pattern formation;

4. separating said loose toner in said pattern formation from said toned surface to create a remainder pattern of toner which may be transferred to a surface having an olephobic layer adherent thereto which is highly repellent to oil-based ink, said olephobic layer being selected from the class of ink release surface materials consisting of a cured elas tomeric organopolysiloxane, tetrafluoroethylene, and polyethylene, having an adhesive release value, when dry, of less than about lOO grams per square inch; and

5. finally fixing the toner on the carrier support to produce an oleophobic master.

8. In the method of claim 7, said transfer surface being a dry electrostatic master.

9. [n the method of claim 7, the method of producing the pattern of electrostatic charge by use of ion modu-

Claims (22)

1. PROVIDING A FLEXIBLE CARRIER SUPPORT SHEET HAVING AN OLEOPHOBIC LAYER ADHERED THERETO WHICH IS HIGHLY REPELLENT TO OIL-BASED INK, SAID OLEOPHOBIC LAYER HAVING AN ADHESIVE RELEASE VALUE, WHEN DRY, OF LESS THAN ABOUT 100 GRAMS PER SQUARE INCH AND BEING AN ELECTRICALLY INSULATED MATERIAL SELECTED FROM THE CLASS OF INK RELEASE SURFACE MATERIALS CONSISTING OF CURED ELASTOMERIC ORGANOPOLYSILOXANE, TETRAFLUOROETHYLENE, AND POLYETHYLENE;

1. THE METHOD OF MAKING A LITHOGRAPHIC MASTER, COMPRISING THE STEPS OF:

2. CREATING A BLANKET ELECTROSTATIC CHARGE ON SAID CARRIER SUPPORT SHEET AND UNIFORMLY TONING SAID SHEET WITH A TRIBOELECTRIC TONER;

2. creating a blanket electrostatic charge on said carrier sheet and applying a uniform coating of a triboelectric toner thereon held by said charge;

2. In the method defined in claim 1, the carrier support sheet being a continuous belt, and the transfer surface picking up a positive image.

2. creating a blanket electrostatic charge on said carrier support sheet and uniformly toning said sheet with a triboelectric toner;

3. In the method of claim 2, said transfer surface being a dry, semi-conducting electrostatic master.

3. thereafter, subjecting said toned surface to a pattern of electrostic charge to neutralize the electrostatic holding power thus forming loose toner in a pattern formation;

3. THEREAFTER, SUBJECTING SAID TONED SUPPORT SHEET TO A PAT TERN OF ELECTROSTATIC CHARGE TO NEUTRIALIZE THE ELECTROSTATIC HOLDING POWDER THUS FORMING LOOSE TONER IN A PATTERN FORMATION;

3. thereafter, subjecting said toned support sheet to a pattern of electrostatic charge to neutralize the electrostatic holding power thus forming loose toner in a pattern formation;

4. PROVIDING A TRANSFER SURFACE HAVING A MECHANICAL AFFILIATION FOR SAID LOOSE TONER IN THE PATTERN FORMATION, AND PLACING SAID TRANSFER SURFACE AGAINST SAID TONER SUPPORT SHEET BEARING THE LOOSE TONER PATTERN TO SEPARATE THE TONER INTO ONE SURFACE WITH A NEGATIVE IMAGE AND THE OTHER WITH A POSITIVE IMAGE; AND

4. separating said loose toner in said pattern formation from said toned surface to create a remainder pattern of toner which may be transferred to a surface having an olephobic layer adherent thereto which is highly repellent to oil-based ink, said olephobic layer being selected from the class of ink release surface materials consisting of a cured elastomeric organopolysiloxane, tetrafluoroethylene, and polyethylene, having an adhesive release value, when dry, of less than about 100 grams per square inch; and

4. providing a transfer surface having a mechanical affiliation for said loose toner in the pattern formation, and placing said transfer surface against said toned support sheet bearing the loose toner pattern to separate the toner into one surface with a negative image and the other with a positive image; and

4. In the method of claim 1, the oleophobic layer being polysiloxane having a low adherence for grease lithographic ink.

5. In the method of claim 1, the final step of dissolving the fixed image to reuse the carrier support sheet.

5. finally, fixing the image to the carrier to produce a lithographic master.

5. FINALLY, FIXING THE IMAGE TO THE CARRIER TO PRODUCE A LITHOGRAPHIC MASTER.

5. finally fixing the toner on the carrier support to produce an oleophobic master.

6. In the method of claim 1, producing the pattern of electrostatic charge by use of ion modulators.

7. The method of making a lithographic master, comprising the steps of:

8. In the method of claim 7, said transfer surface being a dry electrostatic master.

9. In the method of claim 7, the method of producing the pattern of electrostatic charge by use of ion modulators.

Images