US3490368A

US3490368A - Printing by particulate images

Info

Publication number: US3490368A
Application number: US422235A
Authority: US
Inventors: Lloyd F Bean
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1964-12-30
Filing date: 1964-12-30
Publication date: 1970-01-20
Anticipated expiration: 1987-01-20
Also published as: FI47145C; NL145056B; DE1496169C3; FI47145B; CH446906A; GB1128173A; DE1496169B2; DE1496169A1; BE674293A; DK117303B; NO130551C; NO130551B; FR1464987A; AT281875B; SE355681B; NL6517071A

Description

Jan. 20, 1970 F. BEAN 3,490,368

PRINTING BY PARTICULATE IMAGES Filed Dec. 30, 1964 2 Sheets-Sheet l L INVENTOR.

LLOYD F. BEAN m@ a I f OM? Jan. 20, 1970 L. F. BEAN PRINTING BY PARTICULATE IMAGES 2 Sheets-Sheet 2 Filed Dec. 30, l196@ FIG.

INVENTOR. L LOYD F'. B E AN United States Patent O 3,490,368 PRINTING BY PARTICULATE IMAGES Lloyd F. Bean, Rochester, N.Y., assignor to Xerox Corporation, Rochester, N.Y., a corporation of New York Filed Dec. 30, 1964, Ser. No. 422,235 Int. Cl. B41m 1/10 U.S. Cl. 101-170 13 Claims ABSTRACT OF THE DISCLOSURE This application relates to a printing master wherein -a thermoplastic particle image in imagewise configuration 1s partially fused to a thermoplastic substrate in such a manner that large numbers of interstitial spaces remain among the partially fused particles, said interstitial spaces acting as means for the acceptance and retentio-n of liquid material added thereto. The application also relates to the method of preparation of the printing master and the method for producing graphic representations therewith.

This invention relates generally to printing by means of xerographically prepared plates, and more particularly, to such printing wherein the xerographically formed particulate image itself comprises the ink-bearing member.

A number of techniques are known whereby the art of Xerography may be utilized to produce master plates for subsequent use in printing processes. For example, lithogaphie masters may be prepared by a xerographic process which ultimately leads to the deposition of a toner in image configuration upon a hydrophyllic surface. The differential surface wetting characteristics of the toner and the base hydrophyllic surface are then utilized in the conventional techniques of lithography. Xerography has also been used to deposit in image configuration an etching resist upon a metallic plate which is subsequently etched to form a letterpress master. More recently, in the application of Kenneth W. Gunther and Robert W. Gundlach, Ser. No. 193,277, filed May 8, 196-2, and entitled Electrostatic Frosting, now U.S. Patent No. 3,196,011, a technique for frost gravure printing has been disclosed wherein the minute depressions present in frosted image configurations are utilized to hold quantities of ink which are subsequently transferred to a sheet of paper brought into pressure contact with the frosted image.

While these .and other Xerographic processes and techniques for producing printing plates represent considerable advancement in the printing art, yet they have generally been found less than satisfactory in one or the other of two respects. In particular, either the technique for production of the master is itself overly complex and expensive; or else, the technique-although itself acceptableresults in a master that is difficult to use or that gives inferior printing results. In the case of the letterpress master, for example, the etching technique previously alluded to is considerably involved and time-consuming. On the other hand, the referenced lithographie master and the frost gravure techniques, while simplifying production of masters, result in masters having relatively poor background printing characteristics and less than desirable ink density control qualities. In addition, in offset lithography, especially, critical adjustments are necessary in the use of the masters, which makes necessary the presence of a highly skilled operator in order to achieve consistently satisfactory printing results.

Now in accordance with the present invention, a new process is disclosed whereby one may xerographically prepare by relatively Asimple techniques new, unusual, and easily used printing plates, which are capable of producing long runs of copy of the highest quality on ordinary printing papers. By means of the new process simple xerographic toners can be utilized in image configurations as highly effective and enduring transfer media for ordinary inks to ordinary papers.

It is therefore the principal object of the present invention to provide a process whereby relatively simple Xerographic toners may be formed into irnage configuration area capable of effectively holding and. transferring ink to unprinted papers.

More particularly, it is an object of the present invention to provide a process whereby Xerographic -toners in image configurations may be so treated and affixed to a surface as to thereby posses abilities to accept and retain quantities of ink tendered, until subsequent contact with a sheet of ordinary paper effects release. p

It is a further object of the present invention to provide novel and long-wearing printing plates in which the printing elements comprise partially fused xerographic toners.

It is still further object of the present invention to provide novel printing plates which are adaptable to simple, automatic machine printing.

It is yet another object of the present invention to provide novel, xerographically prepared printing plates which are capable of reproducing copy with exceedingly little objectionable background.

Briefly stated, these and other objects of the present invention are attained by depositing a particulate toner image upon a suitable substrate and thereafter fusing the toner -to a degree sufficient to obtain a high order of adherence between the mass of toner and the underlying substrate while yet attaining but a limited degree of coherence between individual particles comprising the toner. More specifically, the heat fusing is so limited that melting in and about the toner particles is sufficient to tack toner particles one to the other, but yet not so great as to coalesce the individual particles into a smooth glazed mass. As a result of this limited fusing, there is retained within the mass of partially fused toner, large numbers of intersticial spaces, which act as ink retention means in subsequent use of the toner as an ink transfer media. The desired high degree of adhesion between the toner lmage and the underlying substrate is obtained in the present invention by depositing the toner image upon a suitable thermoplastic base, or by utilizing a toner of such composition as will provide its own adherent bond to a relatively inert substrate without itself glazing over into a coalesced mass.

Printing plates formed in accordance with the processes and techniques herein disclosed may be inked and utilized much in the manner of a conventional gravure plate and in fact, as will be subsequently pointed out, the properties of these new plates are in many respects quite similar to such gravure plates.

A more thorough understanding of the objects of the present invention and of the manner in which such objects are achieved may now be had by reference to the following detailed specification, especially when read in conjunction with the attached drawings, in which:

FIGURE l diagrammatically illustrates a plate about to be prepared in accordance with the practice of the present invention.

FIGURE 2 illustrates the partial fusing of a toner image to the plate of FIGURE l in the practice of the present invention.

FIGURES 3-6 illustrate the use of a plate prepared pursuant to the present invention in the printing of a sheet of paper.

FIGURE 7 is an enlarged View of a section of toner bonded to a thermoplastic base according to the present invention, and illustrates the physical nature of the bonding among the toner particles and between these particles and the underlying substrate.

FIGURE 8 illustrates the inkng action upon the toner section of FIGURE 7.

FIGURE 9 shows the enlarged toner section of FIG- URE 8 as the ink is Withdrawn during printing.

FIGURE 10 diagrammatically illustrates an alternate mode of obtaining a toner image upon a suitable substrate.

FIGURE 11 diagrammatically illustrates a section through `a toner particle particularly adapted for use in the present invention.

FIGURE 12 illustrates the bonding action that occurs when an aggregate of toner particles as in FIGURE 11 is utilized in the present invention.

FIGURE 13 diagrammatically illustrates a complete rotogravure-type press utilizing a printing plate prepared pursuant to the present invention.

In FIGURE l, plate 3 is shown as comprising a conductive supporting layer 5 which may, for example, -be aluminum foil, upon which is coated a photoconductive thermoplastic layer 7. The thermoplastic layer 7 in a preferred embodiment consists of a mixture of a polyvinyl chloride-acetate copolymer resin such as, for example, VYNS 3 (Union Carbide) and an organic photoconductor, such as for example, TO 1920 by Kalle & Company. A latent charge image 9 is shown formed upon the thermoplastic surface by the usual techniques of xerography, as for example, by charging the photoconductive surface in darkness and thereafter exposing to a light pattern. The latent image-bearing plate is thereafter developed by dusting with a toner which in a preferrred embodiment may comprise a polystyrene base composition such as is described in U.S. Patent No. 3,079,342.

In FIGURE 2, plate 3 now carrying the toner developed image 13 is partially fused by heat from heat source 11. The latter may comprise a hot plate positioned under supporting surface 5, with an intervening layer of water 1S inserted to assure good thermal contact. As will be more fully explained below, the fusing is allowed to proceed only to a point where both softening of the thermoplastic overcoating 7, and partial melting of the toner image 13 occurs. Heat source 11 is then removed, the thermoplastic layer and adherent toner image are permitted to harden, and the plate is now ready for use in printing.

In FIGURES 3-6, the image-bearing plate is used to print a sheet of white paper. Specifically, in FIGURE 3 a water base ink 17 from a source 15 is uniformly coated upon the surface of plate 3. In FIGURE 4, excess ink iS removed from the plate surface by the rubber blade 19 of a squeegee 21 which passes over the plate surface. Next, in FIGURE 5, a plain sheet of White paper 23 is brought into contact with the inked printing plate 3 by pressure from a roller 25. The printed sheet is then removed as in FIG- URE 6. The plate 3 is now ready for another use in the printing cycle.

FIGURE 7 diagrammatically illustrates on an enlarged scale the action that occurs upon `application of a limited degree of heat fusing to the toner-thermoplastic base com- Ibination of FIGURE 2. Individual toner particles are shown at 27. The toner as previously indicated, may suitably comprise a polystyrene base composition such as is described in U.S. Patent No. 3,079,342. Thermoplastic layer 7 may-as also previously indicatedcomprise the resin vinylite VYNS 3, manufactured by the Union Carbide Corporation. Although layer 7 may also carry a photo-conductive constituent, the photoconductive nature of the material is irrelevant to the action now -being considered. The materials comprising toner particles 27 and the thermoplastic layer 7 are intentionally chosen to have appropriately related melting points. Preferably, the thermoplastic layer should have a melting point slightly lower than that of the toner material so that upon `application of heat, the layer 7 will soften slightly in advance of the toner, thereby assuring that formation of a bond between toner and support layer will not depend critically on the duration of heating of the toner. This is, for example, the

case with the toner composition and thermoplastic material cited. That is to say, the melting point of the VYNS 3 and photoconductor mixture-which melting point is essentially that of the VYNS 3 binder-is in the range of C., while the melting point of the toner composition described in U.S. Patent No. 3,079,342, is somewhat higher. A limited degree of adherence between the bottom layer 31 of toner particles and the thermoplastic layer 7 will thus begin to occur somewhat before any melting in the toner itself. Shortly thereafter, slight melting begins within the toner mass proper. The first result of this initiation of toner melting is to tack the toner particles one to the other at their points of mutual contact, as for example, at 33. If application of heat to the plate is continued, fusing of the toner particles will proceed beyond this point and general overall coalescence of the toner mass will result, with an accompanying general overall glazing of the image that is very apparent even to the unaided eye. If fusing is allowed to proceed to Such a point, it will be found that the toner may not be effectively utilized as a printing element. Accordingly, in the practice of the present invention, the heating process is cut off at a point corresponding to the limited fusing shown in the figure. Solidification at this point thus results in (l) cohesive tacking of toner particles at mutual contact points 33, and (2) rm adherence of the bottom layer of toner 31 to the substrate 7.

The net important result of the preceding partial fusing action is to include within the mass of semi-consolidated toner large numbers of intersticial spaces as at 35, and these are in fact, the means by which ink is retained in the subsequent use of the plate in printing. Upon application of ink to the toner surface, capillary action draws the liquid into these interstices much as if the toner image were a sort of sponge. The result of this action is clearly shown in FIGURE 8 wherein an enlarged view of the rubber blade 19 of the squeegee is shown passing over the prepared and inked plate. The rubber blade here is compressed against the irregular surface of the toner so as to enclose and wipe clean the irregular high points as the blade passes over. The blade leaves in its wake a multitude of minute inked reservoirs much like the tiny reservoirs that remain in a conventional gravure plate upon passage of the doctor blade.

Upon subsequent pressure application of a sheet of paper to the toner bearing plate, ink contained in the intersticial spaces 33 is drawn out by capillary action and into the paper. This subsequent action is illustrated in FIGURE 9 where the arrows indicate ink flowing out of the toner-retained interstices and into the fibers of paper 23, as the roller 28 passes over the paper.

In practicing the present invention heating parameters can be completely specified for suitable degrees of fusing. For example, using the polystyrene base toner composition of U.S. Patent No. 3,079,342 upon a substrate comprising-either entirely or as a binder in combination with an organic photoconductorthe polyvinyl chlorideacetate copolymer VYNS 3 (available from the Union Carbide Corporation), it 'was found that heating at a temperature of C. for ten seconds gave excellent results.

Yet while it might be supposed that formation and retention of a configuration such as is shown in FIGURE 7 would depend very critically upon a precise cut-off of of heating, it has been found in practice that the range of tolerable heating has a sufficient spread to readily control the process. Thus, using the same materials as indicated in the previous paragraph, it has been found that by heating at C. satisfactory printing images will result anyhwhere in the time duration range of 2 to 16 seconds. If heating is sustained to about 32 seconds, the ink retaining properties of the image begin to seriously diminish, and overall glazing of the toner image begins; by the time 64 seconds pass, the ink retaining properties are entirely lost, and the image has become completely glazeda fact that can be observed even with the unaided eye. At the other end of the effective time duration range exemplified for t-he invention, it was found that heating at 100 C. for less than about 2 seconds resulted in an image configuration with high ink retention characteristics, but one readily removable by abrasion, and therefore unsuited for sustained printing runs. The explanation of lthis latter result is simple-withfsuch a brief period of heating, an adequate bond to the substrate could not be formed.

Since the printing capabilities of the present invention are derived through the presence of multiple intersticial spaces which act as tiny reservoirs for the printing ink, it will be appreciated that a collection of a certain minimum number of particles will be necessary before any ink retention at all is possible. This turns out to be one of the outstanding advantages of the present printing technique; for in many other processes for xerographically p preparing masters-or for that matter, in preparation of copies by conventional xerography itself-stray toner particles are deposited at various unintended jpoints upon the light sensitive master or transfer agent for the master and such points will cause random background marking in copy produced from such masters. In the present process, however, such background toner will not ultimately affect copies printed from the master because isolated toner particles as they appear on the master will not provide intersticial cavities to hold quantities of ink.

It will be appreciated that the present invention may be practiced with a variety of substrates other than as shown in FIGURE l. The principal requirement in practicing the invention is merely that the combination of toner and substrate be so chosen that the two essential results of the invention may be carried out; namely, the tacking by cohesion, each to the other,of toner particles, and the forming, by adhesion, of a bond between the mass of partially fused toner and the substrate. There is, accordingly, no requirement that the substrate be photoconductive in nature, or that it form part of a permanent combination with a metallic supporting layer.

For example, in FIGURE 10, a printing master 37 is shown being prepared by transfer of an unfixed toner image 13 from a conventional xerographic plate 39. The latter comprises the usual conductive metallic plate 41 upon which is adherent a photoconductive layer, as for example, of selenium at 43. The material comprising the thermoplastic base `45 of printing master 37 may suitably be almost any thermoplastic sheet material which has a melting point related to the toner used, in the manner previously indicated. With the polystyrene-base toner previously indicated, for example, sheet Mylar (polyethylene terephthalate) has been found yq'uite effective. After the unfused toner image is electrostatically transferred with the aid of corotron I60 to the thermoplastic base 45, the base together with its adherent toner image is stripped away from the

xerographic plate

3,9 and partially heat fused in the Imanner previously discussed. The resulting printing master may then be used much as the printing plate of IFIGUR-ES 3-6, except that it will usually be desirable because of the flexible nature-of the printing master to first secure it to a rigid supporting structure, such as, for example, the face of a rotary cylinder.

In FIGURE 11, a greatly enlarged section is shown through a toner particle particularly adapted for use in the present invention. The particle consists of a refractory spherical center 47 which may, for example, comprise a glass bead having a diameter of the order of 5-50 microns, upon which is coated a uniform thermoplastic shell of several microns thickness. An aggregate of such toner particles is shown in FIGURE l2 in the process of bond formation between an image configuration of the toner and a substrate. The substrate 53 may now comprise any of a very large number of rigid or non-rigid materials, since the formation of an adhesive bond between the toner image and the substrate no longer depends upon the thermoplastic properties of the substrate itself. Thus, the substrate 53 might, for example, comprise a metallic aluminum plate, or a glass or rigid plastic plate. Flexible but high melting plastic surfaces might also be employed. Upon subjection to heating, the thermoplastic shell 49 gradually lmelts, fusing the toner particles to each other and to the substrate 53. It will be noted in FIGURE 12 that as in the embodiments of the invention previously considered, intersticial spaces 35 remain in great numbers to now act as the ink holding means for subsequent use of the deposited toner as a printing member. It will be appreciated, however, that use of the modified toner composition in the instant embodiment has resulted in a number of advantages as compared. with use of the more conventional type of toners. In particular overfusing of the toner is now virtually impossible since melting can only take place to the extent of the shells contained on the refractory particles and the thickness of the fusible shell 49 is preadjusted to give substantially less resin volume than the total intersticial volume between toner cores 47. In addition, the substrate as indicated, `may now be chosen with great fiexibility, since adhesion of the toner image to the substrate is achieved by means of the thermoplastic shells carried by the toner itself, rather than by means of the thermoplastic nature of the substrate'.

It is instructive in connection with this consideration of inert substrates to note that a conventional xerographic toner image formed upon or transferred to a relatively inert substrate and fused by conventional xerographic techniques is found to `be entirely unsuitable for the present printing method. Under the action of heating or the application of solvent vapors, the conventional image particles are found to first coalesce, and only subsequent to the occurrence of this cohesive fusion is an adhesive bond established to the inert substrate. The cited combination is therefore fundamentally inoperative for utilization With the present printing method because even if fusion is arrested While the image is still porous the adhesive bond to the substrate is at that point in time insufficient to withstandard the abrasive operations of subsequent inking and printing. On the other hand, if fusion is extended in order to improve the adhesive bond of the image to its supporting surface the image fuses to a high gloss, losing its porosity and ink retaining properties.

Irrespective of whether the toner material comprises a conventional xerographic toner such as the polystyrenebase composition described in U.S. Patent No. 3,079,342, or the modified refractory-centered toner of FIGURE l2, i-t will be found advantageous in the practice of the present invention to utilize an aggregate of toner particles having as narrow a size distribution as possible. That is to say, all toner particles should preferably be of substantially the same diameter. The reason for this will become clear upon consideration of the mechanism by which the present printing technique functions. In particular, since the ability of the partially fused toner mass to effectively hold ink depends upon the presence of large numbers and total volume of interstices, it will be clear that the maxim-urn` number and/or size of such inclusions is best assured by an aggregate of spherical particles of approximately the same size. For if the size distribution is wide, small particles will tend to fill in the interstices` betwen large ones With a corresponding reduction of ink holding capacity.

In FIGURE 13 a complete rotogravure type press is diagrammatically illustrated which utilizes a printing plate prepared pursuant to the present invention. For purposes of illustration only, the printing plate is considered to be shown at 37 as a printing master similar to that described in connection with FIGURE 10. Thus, for example, the master may comprise a partially fused toner image 87 of the polystyrene based toner previously alluded to, upon a Mylar (polyethylene terephthalate) base 89. The master 37 is clamped to a rigid rotating cylinder 61 by clamping means 63. As the cylinder rotates in the direction indicated, ink from reservoir 65 is forced by pump 67 through conduit 69 and inking means 71 to discharge from orifice 91 upon the rotating master-bearing cylinder. The inkcoated master then rotates through secondary ink bath 73, formed within

base

9,3 in consequence of the limited drainage from ink exit conduit 75. The ink coated master then passes under blade holder 95. This blade holder is quite similar to the doctor plate holder of a conventional rotogravure press, except that the steel blade of the usual rotogravure press is here replaced by rubber. Thereafter, in the continuing rotation of the cylinder, the ink master passes under impression cylinder 77 where it contacts and prints upon paper web 79.

Web rollers

81 and 83 guide the paper web through the compression cylinder and maintain the desired degree of tautness.

It will be appreciated that in preparing printing plates in accordance with the present invention, it is not essential that xerographic techniques be utilized to deposit the particulate image configuration. While the invention is particularly adapted to the techniques of xerography, yet many other known techniques could be utilized to deposit such particulate configurations on suitable substrates. Thus, for example, it is possible to selectively deposit compositions analogous to the toners that have been described for use in the invention, by dusting such compositions through a stencil onto a surface of the type described in this specification.

While the present invention has been particularly described in connection with fusing techniques utilizing heat, it will be understood by those skilled in the art that vapor fusing techniques may readily be used to achieve similar results. Thus, by analogy, a toner image configuration may be affixed to a substrate to form a printing master in accordance with the present invention by limited vapor fusing of suitable particulate toner compositions upon suitable substrates. The choice of particulate composition and substrate is dictated by the same considerations as with the heat fusing-viz, that both be fusible by the solvent vapors, and that the substrate be in particular, somewhat more readily fusible than the particulate composition. By way of illustration, such a combination can be achieved by utilizing the toner composition which is the subject of U.S. Patent No. 2,753,308 upon a substrate of the polyvinyl chloride-acetate copolymer resin VYNS 3 previously referenced, and fusing such combination with the vapors of the solvent trichloroethylene.

Having thus described the present invention, it will become apparent that numerous modifications and departures as explained above may now be made by those skilled ni the art, and yet such modifications and departures will yet fall within the scope of this invention. Consequently, the invention herein disclosed is to be construed as limited only by the spirit and scope of the appended claims.

What is claimed is:

1. A method for printing upon an ink receptive medium comprising:

(a) depositing heat fusible xerographic toner particles in image configuration upon a thermoplastic surface having a melting point approximately equal to the melting point of said particles;

(b) heating said particles and said thermoplastic surface sufiiciently to initiate melting` thereof;

(c) cooling said thermoplastic surface and said particles before identity of individual particles is lost by -substantial coalescence thereof;

(d) applying ink to said surface and said particles;

(e) removing ink from portions of said surface not bearing said particles in said image configuration;

(f) firmly contacting said surface and said particles with a plane ink receptive medium to be printed.

2. A printing method comprising:

(a) depositing heat fusible xerographic toner' particles in image configuration areas upon a thermoplastic surface, said surface having a melting point slightly lower then said particles;

(b) heating said particles and said thermoplastic surface sufficiently to initiate melting;

(c) cooling said thermoplastic surface and said particles before substantial coalescence of said particles occurs;

(d) applying ink to said image configuration areas;

(e) bringing said surface and said particles in said image configuration areas in contact with an ink receptive medium to be printed.

3. A printing process comprising:

(a) depositing minute thermoplastic particles in image configuration upon a thermoplastic surface;

(b) heating said particles and said thermoplastic surface, sufficiently to soften said thermoplastic surface and said particles;

(c) cooling said thermoplastic surface and said particles to permit mechanical bonding between at least a portion of said particles and said surface, and among said particles;

(d) applying ink to said surface and said particles;

(e) removing ink from portions of said surface not contacting said particles;

(f) contacting said surface and said particles with an ink receptive medium to be printed.

4. A method for xerographically reproducing a graphic pattern comprising:

(a) charging a photoconductive thermoplastic surface in darkness;

(b) light projecting said graphic pattern upon said surface to produce a latent electrostatic image of said pattern upon said surface;

(c) developing said-latent electrostatic image by dusting said surface with a heat fusible xerographic toner, said toner having a melting point at least as high as the melting point of said surface;

(d) heating said surface and said toner sufficiently to initiate melting thereof;

(e) cooling said surface and said toner before identity of individual toner particles is lost by substantial coalescence;

(f) applying ink to said surface and said toner;

(g) removing ink from portions of said surface not bearing said toner;

(h) contacting said surface and said toner with a plane ink receptive medium',

' (i) removing said medium from contact with said surface and said toner.

5. A method for reproducing graphic representations comprising:

(a) electrostatically charging a xerographic plate in darkness;

(b) exposing said plate to a light image of said graphic representation tovform a latent electrostatic image of said representation;

(c) developing said latent electrostatic image by dusting said plate with a xerographic toner;

(d) transferring said toner developed image from said plate to a thermoplastic surface having a melting point slightly lower than the melting point of said toner;

(e) lheating said thermoplastic surface bearing said toner developed image sufficiently to initiate melting of said surface and said toner;

(f) cooling said thermoplastic surface and said toner before identity of individual toner particles is lost by substantial coalescence thereof;

(g) applying ink to said surface and said toner image;

(h) removing ink from portions of said surface not bearing said toner;

(i) contacting said surface and said toner image with an ink receptive media.

6. A method for producing graphic representations upon ink receptive media comprising:

(a) depositing minute spheroidical thermoplastic particles in the configuration of said graphic representation upon a thermoplastic surface;

(b) physically bonding said particles which contact said thermoplastic surface to said surface and physically bonding said particles to each other at their points of mutual contact;

(c) depositing ink in the intersticial voids among the said particles;

(d) contacting said particles in said graphic representation with an ink receptive transfer media whereby said ink is withdrawn from said voids onto said media.

7. A process according to claim 6 in which said bonding is brought about by heat softening of said surface and said particles.

8. A process according to claim 6 in which said bonding is brought about by solvent vapor softening of said surface and said particles.

9. A method for reproducing a graphic representation upon an ink receptive medium comprising:

(a) depositing minute thermoplastic coated refractory particles in the configuration of said graphic representation upon a thermoplastic surface;

(b) heating said particles and said thermoplastic surface sufficiently to soften said surface and said coating of said particles whereby interfusing occurs at -contacting points of adjacent particles and at points of contact between said particles and said surface;

(c) permitting said particles and said surface to cool;

(d) applying ink to said configuration upon said surface;

(e) contacting said 'conliguration with an ink receptive media.

10. A method for printing upon ink receptive media comprising:

(a) depositing minute thermoplastic coated refractory particles in image configuration upon a plane surface;

(b) fusing said particles to each other at points of mutual contact and fusing particles adjacent to said plane to the plane;

(c) applying ink to the intersticial voids among said particles;

(d) contacting said ink receptive media with said configuration.

11. A method according to claim 10 in which said fusing is brought about by heating said particles.

12. A method according to claim 10 in which said fusing is brought about by solvent vapor softening the thermoplastic coating of said particles.

13. A method for printing upon ink receptive media comprising:

(a) depositing minute thermoplastic coated refractory centered spheroids in image configuration upon a plane Surface;

(b) physically bonding said particles which contact said surface to the surface, and physically bonding said particles to one another at their points of closest mutual approach, including heating said coated particles to interfuse the said coating at said points of mutual approach and cause said thermoplastic coating at points of said particles which contact said surface to soften and wet said surface;

(c) cooling said particles and said surface so as to solidify said thermoplastic at said mutual approach points and at said points of said particles which contact said surface;

(d) depositing ink in the interstical voids among the said particles forming said graphic representation upon said surface;

(e) contacting said particles in said image configuration with an' ink receptive medium, whereby said ink is withdrawn from said voids onto said receptive medium.

References Cited UNITED STATES PATENTS GEORGE F. LESMES, Primary Examiner C. E. VAN HORN, Assistant Examiner U.S. C1. X.R.

96-1; lOl-401.1; 1l7--17.5