CA1199233A

CA1199233A - Laminated thermal transfer medium for correction

Info

Publication number: CA1199233A
Application number: CA000426925A
Authority: CA
Inventors: Hugh T. Findlay; Keith A. Jones
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1982-06-15
Filing date: 1983-04-28
Publication date: 1986-01-14
Also published as: AU7319587A; ES523231A0; DE3365259D1; AU1487583A; JPS58220795A; EP0096740B1; EP0096740A1; US4453839A; AU593106B2; JPH0452240B2; AU567878B2; ES8504560A1; BR8303140A

Abstract

LAMINATED THERMAL TRANSFER MEDIUM
FOR CORRECTION

Abstract A thermal ribbon particularly suited to be used once for printing at one temperature and for lift-off correction at a lower temperature. The bottom, resistive layer is a blend of an aliphatic polyurethane and a urethane acrylic copolymer with conductive carbon black. The next layer is 1000 angstroms thick aluminum. The next layer is the release layer, of an ethylene organic acid copolymer, a low-melting material. The top layer is an ink layer containing ethylene vinyl acetate and polyethyacrylate. The resistive layer has a light dusting of graphite. Low print currents for both printing and lift-off correction are achieved.

Description

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LAMINATED THERMAL TRANSFER MEDIUM
FOR CO~RECTION

Description Cross Reference to Related Application 5 Canadian Application No. 426,926, filed .~pril 28, 1983, entitled "Modified Resistive Layer In Thermal Transfer Medium," by Patsy A. Bowlds, Rex D. Fathergill, David P. Dunn, Hugh T. Findlay and Donald W. Stafford, and assigned to the same assignee to which this application is assigned, is directed to graphite at the side of the resistive layer upon which printing electrodes are applied duri.ng printing. The preferred embodiment of the inven-tion of this application includes dusted-on graphite, which is the same preferred modification of the resistive layer described ~nd claimed in that application.

Technical Field This invention relates to thermal printing, particularly to lift-off correction and -to a resistive layer blend of resins with conductive filler.

Thermal printing of the kind involved is in the nature of non-impact typewriting. Printing is by flow of melted material from a transfer medium which appears similar to a one-use typewriter ribbon. A lower lamination : 25 is resistive and the ribbon is contacted by electrodes, for example with point electrodes and a broad area contact electxode. High current densities in the resistive layer at the po.int electrodes during an applied voltage pulse produce intense local heating.
Ink is t.ranser.red from the ribbon to paper at localized areas at which heat is generated. Lift off correction is the physical stripping of a printed character from the paper or other surface on which it is printed.

Background Art Canadian Application Serial No. 406,400, filed June 30, 1982, entitled "Laminated Element, Thermal Printer and Process for Lift-Off Correction"
and assigned to International Business '~achines Cor~oration describes and claims lift-off correction using a thermal printer employing intermediate heat for correction. That application discloses a transfer medium which prints in the normal manner having a resistive layer of polycarbonate, an intermediate lamination of aluminum, and a transfer layer formulated to print at normal printing temperatures and to correct at temperatures less than the printing temperatures.

This invention employs the same transfer layer formulation as that application, while achieving printing and correction at substantially lower temperatures. This is achieved by employing a layer which facilitates release between the aluminum and the transfer layer.
-United States patent 4,320,170 to Hugh ~. Findlay, Issued March 1982, entitled "~olyurethane Ribbon For Non-Impact Printing" and assigned to the same assignee to which this application is assigned describes and claims a thermal ribbon havlng a xesistive layer of polyurethane. The best-made embodiment of this invention employs essentially the same resistive layer except that the urethane is blended as a copolymer with ethyl acrylate to provide greater thermal s-tability.

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The essential element of this invention which permits printin~ and lift-off correction at lower temperatures is the release layer. Such a release layer is disclosed in an article entitled "Release-Adhesive InterlayPrs For Lift-Off Correction" in IBM Technical Disclosure Bulletin, Vol. 24, No. 5 (October 1981), page 2247 by C. W. Anderson et al. That article discloses ethylene acrylic acid copolymer as one interlayer material, which material is believed to be essentially identical with the material of the preferred embodiment of this invention. The basic difference between that article and the invention here described and claimed is in the characteristics of the ink layer. That ink layer was a polyamide (misspelled polyamid in the publication), carbon blackl and a plasticizer blended to be of high viscosity under heat. That ink material does not function at intermediate heat to become tacky for lift-off correction of characters printed from the ink.
Lift-off correction of the polyamide ink is by a separate adhesive element, such as by a conventionally used adhesive tape. The subject invention improves a prior art ribbon which both prints at normal temperature and corrects at a lower temperature.

An interlayer in a thermal printing system employing an adhesive top layer is disclosed in an article entitled "Delayed Tuck Ribbon for Laser Transfer and Other Printing," in IBM Technical Disclosure Bulletin, Vol.
19, No. 2 (July 1976) page 672 by C. A. Bruce and C. E.
Stratton. Release layers in conventional transfer mediums are shown in U. S. patent nos. 3,337,361 to La Count and 3,170,809 to Barbour. Polymers as th~ resistive layer in a thermal ribbon having urethane and non-urethane major parts are shown in the prior art in U. S. patent no. 4,~69,892 to Shat-tuck et al.

9~33 LE9~82-005 Disclosure of the Invention In accordance with this invention a transfer medium fox thermal printing has a release layer of low-melting material between the ink layer contain marking material and the support layer for ~he marking material. In certain embodiments the material of the release layer is primarily or entirely a polymeric alkane. The material of the marking layer preferably is that formulated for lift~off correction of printing from the same ribbon at intermediate temperatures, and the intermediate layer permits both printing and correction to be accomplished at substantially lower temperatures.
In a still more specific aspect of the preferred embodiment the electrically resistive su~strate layer comprises a pol~meric urethane and polymeric ethyl acrylate.

The effectiveness of the lift-off correction at intermediate heat is bo-th unexpected ~nd a siynificant advantage in that injury to the ribbon during printing for heat is dramatically reduced. Print-current reduction of 40%
or more is realized while lift-off correction at lower temperatures remains effective. This results because the release layer permits printing at lower temperatures.

Heat injury to thermal ribbons duriny printing can be a major-problem. Some degradation Qf the ribbon may be tolerable where the ribbon is to be used only once, but in any case the ribbon usuaily must remain physically united sufficient to be moved from the printing area during printing. Typically, the ribbon must be wound on a takP-up spool. For many ribbons, desired printing requires temperatures which melt or burn holes in the resins of the resistive layer. With -the intermediate layer of this invention, equivalen-t functioning is ~9~3~;~

achieved at lower currents and correspondingly lower temperatures. Degradation of the ribbon within tolerable limits might still be accepted with the use of this invention when currents and corresponding temperatures are increased to increase overall printing speed. In the speciric embodiment, temperature resistance is further enhanced by the resistant characteristics of the ethyl acrylate part of the resistive layer.

Brief Description of Drawings The details Qf this invention will be described in connection with the accompanying drawing, which illustrates the manner of graphite coating.

Best Mode For Carrying Out The Invention The preferred and best embodiment of this invention is a four-layer lamination of regular cross-section particularly suited to be used once for printing at one temperature and for lift-off correction using the same ribbon at a lower temperature. The bottom layer is a blend of an aliphatic polyurethane and a urethane acrylic copolymer with conductive, particulate carbon black, which acts as a resistive layer. The xesistive layer is 17 microns in thickness. The next layer is a 1000 angstroms thick layer of vacuum-deposited aluminum The next layer is the release layer, which is 2 microns in thickness.
Finally, on the release layex is a 4 microns thick ink layer flowable in response to heat created by electric current applied from the outside of the resistive layer. The outside of the resistive layer carries graphite which has been dusted on and hurnished, resulting in an outer deposit of graphite too small to ~uantify by conventional measurirlg techniques.

LE9~82-005 --6~

Printing is effected by known techniques in which the resistive layer is contacted with point electrodes.
The aluminum layer (or, alt~rnatively, the resistive layer~ is contacted with a broad area electrode. The point electrodes are selectively driven in the form of the images desired with sufficient current to produce local heating which causes transfer of ink from the ri~bon to a paper or other substrate in contact with the ribbon.

Lift-off correction is as described in CA Ap~l~ication No.
406,400, Filed June 30, 1982. The erase operation is effected over an incorrect character in the manner of printing, but with the currents being at a predetermined amourlt which is less than that to cause printing. The ribbon is not stripped away until after a cooling period. The correction operation may be in a manner otherwise identical with ordinary printing of the incorrect character or it may be with the activation of all printing electrodes (block erase~ where the return to the incorrec-t character may be slightly out of registration. During correction the printing speed may be reduced, but this is a non-essential design alternative.

The graphite applied by dusting is as described and claimed in the application discussed under the heading "Cross Reference to Related Application" above. The graphite does not function to greatly reduce printing current but does reduce damage from interface effects between the electrodes and the resistive layer. The graphite is believed to form a low resistance electrical, sparking-millimlzing connection between the electrodes of the printhead and the body of the polyurethane-ethyl acrylate r~sistive layer or other resistive layer. The graphite also functiorls as a solid lubricant to reduce frictiorl. It also functions -to loosen material which builds-up at the printhead. The substantial advantages of the intermediate layer in reducing current have been observed in ribbons not having the graphite.

The Resistive Layer The dry inyredients of the resistive layer by weight are as follows.

Resistive Layer - Dry Ingredients Material % By Weight 1) Aliphatic Polyurethane 37.5 10 2~ Urethane Ethyl Acrylake 37.5 ~Copolymer 3) Conductive Carbon Black 25.0 The-aliphatic polyurethane is the dry ingredient of Neorez R-960, trademark of Polyvinyl Chemical Industries.
The ure-thane appears to have few polar or reactive functional groups other than the urethane linkages.
Nevertheless, the material is described by its mamlfacturer as suited to be cross linked at carboxyl func-tional groups in the urethane.

The copolymer is the dry ingredient of UXP102, trademark of Polyvinyl Chemical Industries. That is a copolymer of 50~O by molecule weight urethane and 50% by molecule weigh-t ethyl acrylate.

The preerred resistive layer is cast from a predominantly water borne dispersion. The following formula for -the dispersion is prepaxed by mixing and grinding the ingredients together in a standard, hic3h-shear mixer until particle wetting is comple-te, typically one hour for small bakches.

~C~9;~33 Resistive Layer - Dispersion Formula Ingredient ~ By W~ight 1) Neorez R-960* (Polyvinyl Chemical34.6 Industries aliphatic urethane dispersion)

2) XC72R (Cabot Co. conductive carbon 34.6 black) ~100% solid particles with exceptionally high surface area)

3) UXP102** (Polyvinyl Chemical 34.5 Industries copolymer of urethane and ethyl acrylate)

4) Water (additional to water in above) 23.0 *Neorez R-960 consists of the followin~, by weight:
33% aliphatic urethane; 15% N-methyl-2-pyrrolidone;
1.2% ethylamine; and 50.8% water.

**U~P102 consists of the following by weight: 33%
copolymer of 50% by molecule weight urethane and 50% by molecule weiyht ethyl acrylate; 1.2% ethylamine; and 65,8% water.

The resistive layer dispersion is cast by a reverse roll coater onto a temporary release substrate. This may be a 4 millimeter thick polypropylene or polyethylene terephthalate (Imperial Chemical Industries) film.
Dryin~ is then conducted by forced hot ~ir. The upper surface is then metalized by vacuum deposition of aluminum to a thickness of 1000 angstxoms.

The intermediate, release layer is then deposited on the aluminum. This i5 also applied as a water-borne dispersion from a reverse roll coater.

Release Layer The preferred xelease layer is e-thylene organic acid copolymer of 95% by weight ethylene and 5% by weight organic acid. This material is cast from an emulsion.

The material used is commercially obtained as Esi-Cryl 2540-N, a product of Emulsion System Inc. This is a 25% solids emulsion of water and a non~ionic surfactant.
The organic acid part of the polymer appears to be acrylic acid. The copolymer is of molecular weight of 3000 to 3500 and has a softening point of 108C.

The Esi-Cryl 2540-N is coated without modification on the aluminum using a reverse rod coater. Drying i5 then conducted by forced hot air.

Very satisfactory results have been achieved by using a linear crystalline polyethylene as the intermediate layer material.

The material used is commercially obtained as Poly - Emulsion 316 N30 a product of Chemical Corporation of America. This is an aqueous emulsion of the polyethylene, which is characterized by a high degree of slip and hardness, and by a high melt viscosity.

It is coated and used as the release layer as described for the preferred ethylene organic acid copolymer.

Ink Layer Formula Parts by Component Weight % Solids Adcote 37JD610 6 73.4 (An ethylene vinyl acetate copolymer of 6300 weight avexage molecular weight;
approximately 90~ by weight being the polyethylene component; with about 6% by weight rosin acids as dispersants; 40% total solids in water; trademark product of Morton Chemical Co.) Hycar 2600X120 1 15.3 (Polyethylacrylate, with about 4% by weight poly-acrylonitrile, some dispersant;
50% solids in water; trademark product of B. F. Goodrich Chemical Co.) Aquablack 140 1 11.3 (~arbon black, 7% by weight naphthalene sulonic acid ~ispersant; 37% solids in water; trademark product of Bordon Chemical, Division of Bordon Inc.) Water ~distilled, additional 1 --to water in foregoing) The foregoi.n~ intermediate layer is overcoated using a reverse roll coater with the ink layer formula in an amount to produce the desired dry thickness. Drying by evaporation of the water vehicle is then conducted using forced hot air. The co~)ined polyurethane-acrylate resistive layer with intermediate layexs and top ink layer is stripped from the temporary substrate. This is a bulk ribbon to which a minute graphite coating is then applied to the outer sur~ace of the resistive layer. After the graphite application, the bulk ribbon is sli-t to the desired width and wound into a spool.

Graphite Application The graphite is an outer layer on the resistive layer and may be applied prior to the application of other parts of the ribbon. Typically, it will be applied last, and this discussion assumes the ribbon is otherwise finished when the graphite is applied. The graphite applied is a powder.

The graphite used is the Micro-850 product of Asbury Graphite Mills, Asbury, New Jersey. This is understood to be the cleanest and smallest in particle size graphite sold commercially by that company, which company is unders-tood to ~e a representative range of graphite products. The particle size is understood to be 0.5 to O.6 micron in average diameter. The graphite is natural as opposed to synthetic and is understood to have a ash content of 1% by weight maximum. (The ash would be primarily silicon oxides and metal oxides and the like, and it essentially the residual extraneous materials from processing.~

The drawing illustrates significant elements of the preferred station to apply the dusted-on graphite.
Mechanical details to turIl the mechanisms and direct the bulk ribbon are not specifically indicated as they are not exceptional and may be conventional. The supply roll l in a commercial process is an otherwise 3~
LE9~82-005 -12~
finished bulk roll as just described. This is fed to a back-up roll 3 with the resistive layer outward.

Back-up roll 3 is situated in applicator tank 5, which is closed except for felt-sealed, small openings to receive ribbon 7 and roll 3. Applicator roll 9 is a paint roll of soft, artificial cloth. Roll 9 rotates continuously during graphite application and physically rubs against ribbon 7. It dips into the graphite powder 11 on the floor of tank 5 and carries graphite in its fibers in the manner of painting. Graphite transfers to ribbon 7 as roll 9 rubs against it. The direction of movement of roll 9 is not important.

Ribbon 7 exits tank 5 having the transferred graphite on its surface. It immediately enters cleaning tank 13. Tank 13 also is closed except for small felt-sealed openings tc receive ribbon 7 on roll 3. Cleaning brush 15 in tank 13 rotates in the direction of travel of ribbon 7. The direction of rota-tion, however, i5 not important. Brush 15 is also a paint roll of soft cloth, which tends to capture excess graphite. Vacuum line 17 pulls graphite from the air in tank 13. After an area of brush 15 leaves the ribbon 7 it encounters beater bar 19, ~ stationary bar which is positioned to disturb the cloth of brush 15. This shakes loose graphite from brush 15, which is then removed by vacuum line 17.

Ribbon ~ then leaves tank 13 and is guided past one upper, sharp scraper blade 2Q and two longitudinally spaced, sharp scraper blades 21 and 23. Blades 20, 21 and 23 may be or have the characteristics of razor blades. Where the operation o cleani.ng brush 15 or othex cleaners is sufficient, scraper blades 20, 21 and 23 may be wholly eliminated. The top blade 20 is or 3'~3 scraping off graphite which settles from the atmosphere rom tank 5 around the edges of ribbon 7. Where the bulk ribbon 7 is wide, these edges may be trimmed off.
In any event, tension on scraper blades 20, 21 a.nd 23 is very light.

Ribbon 7 is guided around a roll 25 of tissue 27.
Tissue 27 may be or have the characteristics of toilet tissue. The resistive layer side of ribbon 7 covers most of one side of the curved surface of roll 25.
Roll 25 moves in the direction of ribbon 7 and at slightly greater velocity (the direction movement is not critical). Tissue 27 is fed away from roll 25 so that the outer surface of roll 25 is continuously renewed. Where the operation of cleaning brush 15 or other cleanexs is sufficient, tissue 27 may be wholly eliminated.

The foreyoiny manufacture results in a fi.nal dusting and polishing of graphite which leaves a coating so minute as not to be measureable by ordinary techniques.
The graphite remains by inherent surface effects between the graphite and the surface of the resistive layer~
The silver appearance of graphite does appear on the surface.

The complete ribbon is rolled into a take-up spool 2~. `
That is a bulk roll ready to be slit to the desired width and would into a spool.

It will be apparent that var.ious moditications can be made in the foregoing without departing from the basic inventive concepts described. Accordingly, pat.ent coverage claimed is as follows.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A transfer medium for thermal printing comprising a layer of marking material which is non-tacky and cohesive at ordinary room temperatures and which forms a bond for lift-off correction of thermal printing made from said transfer medium after having been raised to temperatures above ordinary room temperatures and below temperatures at which thermal printing by said transfer medium normally is effected, and a support layer upon which said marking material is supported, said transfer medium having a release layer comprising a low-melting material between said marking material and said support layer.

2. The transfer medium as in claim 1 in said release layer is predominantly an alkane.

3. The transfer medium as in claim 1 in which said release layer has a softening point of about 108°C.

4. The transfer medium as in claim 1 in which said marking material is a blend comprising ethylene vinyl acetate copolymer, a compatible acrylic polymer, and carbon black.

5. The transfer medium as in claim 2 in which said marking material is a blend comprising ethylene vinyl acetate copolymer, a compatible acrylic polymer, and carbon black.

6. The transfer medium as in claim 3 in which said marking material is a blend comprising ethylene vinyl acetate copolymer, a compatible acrylic polymer, and carbon black.

7. The transfer medium as in claim 4 in which said support layer comprises a solid polymer with conductive particles dispersed in said polymer and in which said release layer and said polymer are separated by an aluminum layer of thickness in the order of mangitude of 1000 angstroms.

8. The transfer medium as in claim 5 in which said support layer comprises a solid polymer with conductive particles dispersed in said polymer and in which said release layer and said polymer are separated by an aluminum layer of thickness in the order of magnitude of 1000 angstroms.

9. The transfer medium as in claim 6 in which said support layer comprises a solid polymer with conductive particles dispersed in said polymer and in which said release layer and said polymer are separated by an aluminum layer of thickness in the order of magnitude of 1000 angstroms.

10. The transfer medium as in claim 4 in which said marking material is a blend of about 69 parts by weight ethylene vinyl acetate copolymer, about 15 parts by weight of a compatible acrylic polymer, and about 11 part by weight carbon black.

11. The transfer medium as in claim 5 in which said marking material is a blend of about 69 parts by weight ethylene vinyl acetate copolymer, about 15 parts by weight of a compatible acrylic polymer, and about 11 part by weight carbon black.

12. The transfer medium as in claim 6 in which said marking material is a blend of about 69 parts by weight ethylene vinyl acetate copolymer, about 15 parts by weight of a compatible acrylic polymer, and about 11 part by weight carbon black.

13. The transfer medium as in claim 7 in which said marking material is a blend of about 69 parts by weight ethylene vinyl acetate copolymer, about 15 parts by weight of a compatible acrylic polymer, and about 11 part by weight carbon black.

14. The transfer medium as in claim 8 in which said marking material is a blend of about 69 parts by weight ethylene vinyl acetate copolymer, about 15 parts by weight of a compatible acrylic polymer, and about 11 parts by weight carbon black.

15. The transfer medium as in claim 9 in which said marking material is a blend of about 69 parts by weight ethylene vinyl acetate copolymer, about 15 parts by weight of a compatible acrylic polymer, and about 11 part by weight carbon black.

16. The transfer medium as in claim 11 in which said release layer consists essentially of a linear crystalline polyethylene.

17. The transfer medium as in claim 12 in which said release layer consists essentially of a copolymer of 95% by weight ethylene and 5% by weight organic acid of molecular weight of about 3000 to 3500.

18. The transfer medium as in claim 14 in which said release layer consists essentially of a linear crystalline polyethylene.

19. The transfer medium as in claim 15 in which said release layer consists essentially of a copolymer of 95% by weight ethylene and 5% by weight organic acid of molecular weight of about 3000 to 3500.

20. A transfer medium for thermal printing comprising a layer of marking material, a support layer upon which said marking material is supported, said marking material being meltable to effect printing by heat supplied from said support layer, said transfer medium having a release layer consisting essentially of a.
polymeric alkane in contact with said marking material and said support layer.

21. The transfer medium as in claim 20 in which said alkane is a linear crystalline polyethylene.

22. The transfer medium as in claim 21 in which said support layer comprises a solid polymer with conductive particles dispersed in said polymer and in which said release layer and said polymer are separated by an aluminum layer of thickness in the order of magnitude of 1000 angstroms.

23. The transfer medium as in claim 21 in which said marking material is a blend comprising ethylene vinyl acetate copolymer, a compatible acrylic polymer, and carbon black.

24. The transfer medium as in claim 22 in which said marking material is a blend comprising ethylene vinyl acetate copolymer, a compatible acrylic polymer, and carbon black.

25. The transfer medium as in claim 23 in which said marking material is a blend of about 69 parts by weight ethylene vinyl acetate copolymer, about 15 parts by weight of a compatible acrylic polymer, and about 11 parts by weight carbon black.

26. The transfer medium as in claim 24 in which said marking material is a blend of about 69 parts by weight ethylene vinyl acetate copolymer, about 15 parts by weight of a compatible acrylic polymer, and about 11 parts by weight carbon black.

27. A transfer medium for thermal printing comprising a layer of marking material comprising a blend a polymeric alkane and a compatible polymeric acrylic, said marking material being sufficiently cohesive at a first temperature for lift-off correction of thermal printing made from said marking material, said marking material forming a bond for lift-off correction with said printing at a second temperature, said second temperature being higher than said first temperature, a support layer upon which said marking material is supported, and a release layer consisting essentially of a polymer which is predominantly an alkane between said marking material and said support layer.

28. The transfer medium as in claim 27 in which said release layer consists essentially of a copolymer of 95% by weight ethylene and 5% by weight organic acid of molecular weight of about 3000 to 3500.

29. The transfer medium as in claim 27 in which said release layer consists essentially of a linear crystalline polyethylene.

30. The transfer medium as in claim 28 in which said support layer comprises a solid polymer with conductive particles dispersed in said polymer and in which said release layer and said polymer are separated by an aluminum layer of thickness in the order of magnitude of 1000 angstroms.

31. The transfer medium as in claim 29 in which said support layer comprises a solid polymer with conductive particles dispersed in said polymer and in which said release layer and said polymer are separated by an aluminum layer of thickness in the order of magnitude of 1000 angstroms.

32. The transfer medium as in claim 30 in which said marking material is a blend of about 69 parts by weight ethylene vinyl acetate copolymer, about 15 parts by weight of a compatible acrylic polymer, and about 11 parts by weight carbon black.

33. The transfer medium as in claim 31 in which said marking material is a blend of about 69 parts by weight ethylene vinyl acetate copolymer, about 15 parts by weight of a compatible acrylic polymer, and about 11 parts by weight carbon black.

34. A transfer medium for non-impact thermal transfer printing having a thermal transfer layer and an electrically resistive substrate layer, said resistive substrate layer comprising a polymeric urethane, a polymeric acrylate, and an electrically significant amount of conductive, particulate material.

35. The transfer medium as in claim 34 in which said polymeric urethane and said polymeric acetate comprise a blend of an aliphatic polyurethane and a urethane ethyl acrylate copolymer.

36. The transfer medium as in claim 35 in which said aliphate polyurethane and said copolymer are in about equal part by weight and said copolymer is about equal part by molecular weight in urethane and ethyl acrylate.

37. The transfer medium as in claim 34 in which said particulate material is carbon black.

38. The transfer medium as in claim 35 in which said particulate material is carbon black.

39. The transfer medium as in claim 36 in which said particulate material is carbon black.

40. The transfer mediumas in claim 38 having an aluminum layer of thickness in the order of magnitude of 1000 angstroms on the side of said substrate layer between said substrate layer and said thermal transfer layer.

41. The transfer medium as in claim 39 having an aluminum layer of thickness in the order of magnitude of 1000 angstroms on the side of said substrate layer between said substrate layer and said thermal transfer layer.

42. The transfer medium as in claim 40 in which the thickness of said substrate layer is the order of magnitude of 17 microns.

43. The transfer medium as in claim 41 in which the thickness of said substrate layer is the order of magnitude of 17 microns.