CA2053739A1

CA2053739A1 - Donor element for thermal imaging containing infra-red absorbing squarylium compound

Info

Publication number: CA2053739A1
Application number: CA002053739A
Authority: CA
Inventors: Reid E. Kellogg; Evan D. Laganis; Sheau-Hwa Ma
Original assignee: Individual
Current assignee: EIDP Inc
Priority date: 1990-10-25
Filing date: 1991-10-18
Publication date: 1992-04-26
Also published as: EP0482595A1; JP2502228B2; JPH04263992A; KR920007839A; AU8673691A; US5019549A

Abstract

DONOR ELEMENT FOR THERMAL IMAGING CONTAINING
INFRA-RED ABSORBING SQUARYLIUM COMPOUND

These is disclosed donor elements dor laser-induced thermal imaging processes containing infra-red absorbing squarylium dyes of the following structure:

Description

2~3~3~

IT~E
DONOR ELEMENT FOR THERMAL IMAGING CONTAINING
INFRA-~ED ABSORBING SQUARYLIUM COMPOUND

~ his invent~on relates to ~hermal imaglng. More particularly this in~ention rela~es ~o Aonor element~
for laser-induced thermal imaging processes ~n which the donor element contains certain lnfra-red abs~rbing sguarylium compounds.

Thermal imaging processes are well-known. In the~e processes a donor element comprising a colorant is heated, by, for example, a thermal head or an infra-xed laser, causing the colorant to be transferred to a receptor sheet. Depending on the process, the colorant may be a dye or pigment or a mixture of dyes and/or pigments. Imagewise heating of the donor element reproduces the corresponding image on the receptor sheet. Trans~er in register to the 8~me reCeptor 3heet from several dif~erently colored donor elements produces a mul~icolored image. Different slngle colored donor elements or a multicolor donor ~lement carrying d~erent colors in dif~erent regions which can be brought into po~ition ~n turn can be used for transEer.
~ hen an infra-red laser ls used for thermal transfer, only a single, 3mall, ~elected area ~ heate~
~t one time. Since only ~ ~mall region of colorant i~
heated and transferred, the image can be built up p~xel by pixel. Computer control of such proce8se5 allows multicolor images of h~gh definltio~ to be produced at h~gh ~peed. Thi~ proces~ ls di~closed 1D Baldock, UX
Pa~ent 2,083,72~.

'il 2~3 In the laser-induced thermal dye transfer process, the donor element comprlses a heat transferabl~ dye, sometimes called a thermal trans~er dye, usually ln a formulation with a binder, supported on a substrate.
~he dye donor element is contacted with a receptor sheet, and the ~urface of the substrate irradiated with an infra-red laser to transfer thP dye to the receptor sheet. For ~he heat transferable dye to be directly heated by the laser, a dye wh~ch strongly absorbs the wavelength of the exciting laser ~s requlred. This need to match the infra-red ahsorption of the dye ~o the emission of the laser gr~atly restr~cts the number of dyes which can be use~ in the laser-induced thermal transfer process. ~
As an alternative, the dye may be heated indirectly by incorporating a sep rate radiatlon absorber, such as carbon black, into the dye layer. HoweYer, carbon black has a tendency to aggregate or a~glomerate when coated 50 that the absorber ls not uniformly distributed in the donor element. In addition, small carbon black particles tend to b~ carried over with the dye, contaminating the image.
Alt~rnatlvely, an infra-red absorbing comp~und can b~ added to the dye layer. Dye donor layerq contalning infra-red absorbing matexials have been disclosed by, for example, Barlow, U.S. Patent 4,778,128, which di~closes thermal printing media comprising infra-red ~bsorbing poly~substltuted)phthalocyanine comp~unds;
DeBoer, EP0 Applicatlon 0 321 923, ~hich discl~ses infxa-red absorb$ng donor element~ which contain cyanine dyes; and DeBoer, ~.S. Patent 4,942,141, w~ich di close~
lnfra-r~d absorbing donor element which contain selected squarylium dyeQ. However, there is a continuin~ need for infra-red absorbing materials which 2~373~

may be used to advantaqe i~ laser-induc~d thermal transfer processes.

This invention ~s a donor element for a laser-induced thermal transfer process, ~id donor elemen~
comprising a support bearing thereon a colorant layer, said colorant layer c:omprising a coloran~c and an infra-red absorbing material, said infra-red ab~orbt~cJ
materlal having the structure:
R1 ~ R3 S ~ CH ~ CH ~ 5 wherein each Rl, R2, R3, and R4 is independently an alkyl group sf ~rom one to eight car~on atoms.
In a preferred embc~diment of thi~ vent~on, the colorant layer also comprises a bislder. In a mor13 preferred embodiment of this invention, Rl, R2~ R3, and R4 are each ~-butyl.
~0 The invention is a donor element for thermal tran fer proc~sses particularly adapted for use ~n laser-induc~d thermal transfer imaging. The donor element comprises a colorant layer and a support.

The coloran~ layer compri~e~ ~ heat-trancferable oolorant, an lnfra-red absorblng mater~alr and, preferably, a ~inder.

L ~I
2 ~ 3 The infra-red absorbing material must have a strong absorption in the emlssion region of the exciting laser and should have good thermal stability 80 that it 15 not decomposed by the incident radiation. The mater~al ls preferably sub~ antlally non-transferable 80 it i~ not tran~ferred during ~maging. It l~ preferred ~hat lt be es~entially non-absorbing in the visible so that small amounts, if transferred, wlll not af~ect the image. It is also preferred that the material be ~oluble ln a solvent which can be used to coat the colorant layer onto the support.
Infra-red absorbing materials of the following ~tructure are used in the colorant layer of the instant invention:
R~ 1I R3 S~=~)=CH W--CH-~S

0~ ~

R1, R2, R3, an~ R4 are each independently alkyl groups o~ ~rom one to eight carbon atoms. It is pr~ferred that Rl, R2, R3, and R4 be the ~ame.
The most preferred in~ra-red ~b~rblng material is SQS, in which Rl, R2, R3, and R4 are each e~ual to ~
butyl. 5QS is readily ~oluble ln ~he usual non-reac~ive organic solvents, such as, for ex~mple, alcohols, 2~ ketones, acetonitrile, chlorinated hydrocarbons, such as dichloromethane, and hydrGcar~ons, such ~s toluene. It has ~trong ab~orptlon in the infra-red and l~ttle or no ~bsorption ln the ~isible. The absorpti~n maximum, ~l4 nm (measured in dichloromethane3 coincides with the .. .. . . . .. . . . ..

L ,i 2 ~ 3 wavelength of emlssion o~ readily av~llable in~ra-xed diode lasers ~750 to B70 nml.
The infra-red absorbing materlals may be prepared by con~entional synthet~o methods. A procedure for the synthesis of SQS ls given in Gravesteijn, U.S. Patent 4,508,811, the disclo~ure of which is incorporated by reference.
The infra-sed absorblng m~terial~ may be present in the donor lay~r ln any conGentrat1On which is effective for ~he intended purpose. In general, Goncentratlons of 0.1 to 10% of the total coating weight have been found to be effectlve. A pre~erred concentration i3 1 to 5%

of the total coatlng welght.

The colorant layer compr~ses a heat-transferable colorant or a mixture of heat-transferable colorants. A
heat-transferrable colorant is a colorant, such as, for example, a dye or a pigment, ~hlch is transferred from the donor element to ~he recept~r sheet by the action o~
heat. On transfer it produce~ the desired color on the receptor sheet. Important crlteria for the select.ton vf a heat-transferable colorant are its thermal properties, brightness of shade, light and heat ~astness, and facility o~ ~ppllcation to the .qupport. For suitabla perforrnance, the colorant ~hould transfer e~enly, in a predetermined relationship to ~he heat appliedr ~o that the lntensity of color on the receptor -~heet 1~ smsothly related to the ~eat applied and go~d density gradatiQn ls ~ttained. The colo~ant must be migrate from ~he - donor element to the receiver sheet at the lm~ging energies employed, generally 0.2 to 2 J/cm2.
Useful heat~-tran~ferable colorants include: ~a) pigment.~ dispersed ln polymeric ~atrice~ ~hlch will ~often or m~l on heating, and (b~ dyes, ~uch as, for example, sublim~ble dye3. U~eful ~ubllmable dyes, !i avallable ~rom Crompton and ~owles ~Readlng/ PA~, lnclude: I~tratherm~ Dark Brown (azo ~ype, Disperse Brown 27), Intratherm~ Pink 1335NT (anthraquinone type~;
Intratherm~ Brilliant Red P-1314NT (anthraquinone type, Disperse Red 60); Intratherm~ Red P-1339 (anthraquinone type, Disper~e ~iolet ~7); Intratherm~ ~lue P~1305NT
(an~hraguinone type, Disper~e Blue 359); ~nd ~n~ratherm~
Yellow 343NT (quinoline type, Disperse Yellow 54 ~epresen~at~ve sublimable dye~ are disclosed ln:
0 ~regory, U.S. Patent 4,764,17a; ~otta, U.S. Patent 4,541,830; ~oore, U.S. Patent 4,698,651; Evans, U~S.
Patent 4,695,2B7; Wea~er, U.S. Patent 4,701,439; DeBoer, U.S. Patent 4,772,582; and DeBoer, U.S. Patent 4,942,141.
1~ The heat-transfexable colorant and infra-red absorbing material are preferably di~persed in a polymeric binder. Typic~l binders include, but are not limited to: cellulose derivati~es, such as, cellulose acetate, cellulose tr~acetate, cellulose acetate butyrate, cellulose ~cetate propionate, cellulose ac~ta~e hydrogen phthalate; poly~cetals~ such as polyvinyl butyral; waxes having a so~tening or melting point o~ about 60G~ to about 150C; acrylate and methacrylate polym~rs and copolymer~; polycarbon~te;
copolymers of ~tyrene and acrylonitrile; poly~ulfones;
and poly(phenylene oxide). The blnder may be ~ed at a coatln~ weight of about 0.1 ~o ~bou~ 5 g~
It wlll b~ recognized .hat the lnfra-r0d absorbing mater~al and the h~at-transferable colorant may be present tn separate layers on ~he support. Such an arxangements 1~ cvnsldered to be equ$~alent to that described hereln.

7 ~ 7 3 ~

~k Any material which i~ dimensionally stable, capable of transmitting the radiatl~n from the infra-red laser to the colorant layer, and not adver~ely affected by this radiation can be used as ~he support. Such ma~erials include, but are not limlt~d ~o: polyes~er~, such ~s, for example, polyethylene ~erephthalate;
polyamides; polycarbonates; ~lassine paper; cellulose esters; fluoropolymer~; polyethers; polyacetals;
polyolefins; etc. A preferred ~upport materia:L i~
p~lyethylene terephthalate film. The support typically ~as a thickness of from ~bout 2 to about 250 microns and may comprise a subbing layer, if desired. A preferred thickness i~ about ~0 microns to ab~ut 75 microns.
~lthough the colorant layer can be applied to the support as a dispersion in a suitable 301vent, applicat~on from solution ls preferred. Any suitable solvent may be used to coat the colorant layer. The colorant layer may be coated onto the support u~ing conventional ooating technl~u~s or it may ~e printed thereon by a printing technique, such as, for example, gravure pr$nting. 7 B~hg~;
The receptor ~heet typlcally comprises ~ 3upport and an ima~e~rece~ving layer. Th~ ~upport i9 CompriBed o~ a dimensionally stable ~h~et material. It may be a tran~parent film, such as, for example, polyethyle~e terephthalate, polyether sulfone, a polyimide, a poly(vinyl alcohol-co-~cet~l), or a cellulose ester~
3 D suc~ as for example, cellulose ace ate. The support may also be opaque, such as, ~or example, polye~hylene tereph~halate ~illed wlth a white pigment ~uch as t~tanium divxide, lvory paper, or synth~tic paper, such ~s Tyvek~ spunbonded olef~n.

. 8 ~ 7 3 ~

The image recelving layer may compri~e a coatlng of, for example, a polycarbonate, a polyurethane, a polyester, polyvinyl chloride, styrene/acrylvnltrlle copolymer, poly(caprolactone), ~nd mixtures thereof.
The image recelving layer may be present ln any amount which is effec~lve for the intended purpose. In general, good reaults have been ~bt2ined at coating ~elghts of 1 to 5 g/m2.
~ol~rant ~rans~Q~
The donor elements are used to form a colored image by thermal colorant transfer. This process compri~es lmagewise exposure of the donor element with an infra-red laser so that colorant is transferred to the receptor sheet to form a colored image.
The donor element may be used in sheet form or in the form of a continuous roll or ribbon. The donor el~ment may comprise a single c~lor or lt may comprlse alternating areas of different colors, such ~s, for example, cyan, magenta, yellow, and ~lack.
Although various types of l~sers may be used to effect transfer of the heat-transferable colorant from the donor ~lement to the recelver sh~et, dlode las~rs emittiny in the region of 750 to 870 nm offer ~ubstantial advantage ln terms of thelr 8mall slze, low cost, stability, rellabillty, ruggedness, and ~a~e of modulatlon. Diode laser~ emltting ln the range of 800 to 830 nm are pre~exred for u~e with the donor ~lements of this invention. Such laser~ are commercially avallable from~ for example~ ~pectra D~ ode Lab~ratories (San Jose, CA3.
A transfer asqemblage comprises ~ donor element and a rec iver sheet in which the color~nt layer of the donox element 1~ contiguou~ to the lma~e receiving l~yer of the rece~ver sheet. Th$s as~e~blsge ~ay be preassembled as an integral unit when a slngle colored image is desired. This may be done by reversi~ly adhexing the donor element ~nd the receiver sheet together at their margins. After lmagewise exposu~e, S the they are separated to reYeal ~he image on the reCeiver sheet.
When a multicolor image is to be produced, ~he assemblage is formed a plurality Of time~. After the first colored image is ~ran~ferred, the ~s3embl~ge is separated and a second do~or ele~ent (or ~nother area of the same donor element which comprises a dl~ferently colored heat-transferable rolorant) is brought in contact with the receiver sheet and imagewi~e exposed in register with the first image. The process i~ repeated ~5 with donor elements containing dlffexently colored heat-transferable colorants as many times as desired. A
preferred process consists of transferriny cyan, yellow, and magenta lmag~s to produce a thxee colored image.
The do~or element of this inventlon is adapted for the production of both ~ingle color and multicolor colored lmage by a la~er-induced th~rmal transfer process. It can be u~ed to obta~n prints of images which have been recorded el~ctronically by v~riou~
electronic devices, ~uch as color video cameras. I~ can also be used to generate hard copy output in varlous proofing appllcations.
The advantageous properties of thl~ invention can be observed by refer~nc~ to the followlny ~xamples ~hich lllustrate, but do not llmit, the lnvention.

1 o 2 ~ ~ 3 7 3 9 ~E~
g~Y
Butvar~ B-90 Polyvinyl butyral; CAS 63148-65-2;
Monsanto, St. Louis, ~O

CAB Celllllo~e ace~ate bu~yra~e (17% butyl~;
Aldrich, ~ilwaukee, WI

Joncryl~9 682 Solid acryllc re~ln; molecul2~r weigh'c 1,700, actd number 235; John30n Wax, Ra cine, WI

Lexan~ 1500 Polycarbonate; General Electric Co., Pittsfield, MA
1~
Lithol Rubine Yellow ~hade Llthol Rubi~e flushed ~n Polyver~yl mult~purpoqe Yehicle; 50%
pigment, 50~ vehlcle, ~3% solids; C.I.
15850:1; Sun C~emtcal Corp., Cincinnati~ O~

Red P-1339 Intra~herm~ Red P-1339; C.I. Di~per~e Vlolet 17; l-amlno 2-bromo-q-hydroxyanthraquinone; CAS 12217-92-4;
Crompton ~ Knowle~ Corp., Reading, PA

SQS 4-[[3-[[2,6~Bls~l,l-dime hylethyl) 4H-~hiopyran~4-yli~ene]methyl]-2-hydroxy-4-oxo-2-cyclobuten-1-ylidene3methyl-2,6-bi~(l,l-d~methy~ethyl~th~opyrlium hydrox~de, lnner 3alt; CAS 8887~-49-3 1~

t 3~3~

Vybar 260 pol ymerized alpha-~lkenes of great~r the ten carbon atoms; Petrolite Speclalty Polymer Group, Tulsa, OK

WB-17 Petroli~e WB-17: Ox~ :lized great~r than C10 z~lpha-alkene reaction product wlth ethanolamine ~nd 2, 4 toluene dilsocyanate;
P~trolite Specialty Polymers Group, Tulsa, OK
In the examples which ~ollow, ncoatlng ~olution"
refers to the mixture of solvent and additives W}l~ ch ls coated on the support, even though some of the additives may be in suspension rather ~han in solution. Amounts 15 are expressed in parts by weight.

~m~
A coating solution colltaining the following ingred$ents, expressed in parts by weight, was made up:
20 Red P-1339, O.lB8; CAB, 0.188; SQS, 0.0075; and dichloromethane, 9.6~. The composition wa~ 3tl.rred to completely di solve the solids and coated on c~ona discharge treated 3 mil (about 75 m~cron) polyethylerle ~erephthalate ~ilm wlth ~ doc~or kni~e ~n about 2 mil 2 5 ~about 50 micron~ ~7et gap and air drled to form the donor element w~.thln a coating th~ cknes~ o~ about O . 55 mic:ron .
The coated S1 de of the donor element wa3 con~act~d with a receptor sheet of Thermaco~ or~ video prlnt paper 3 0 ~astman Rodak Company~ Rochestert NY~ by tight ly tapin~
th~m together on a 'c25t drum to forrn a thermal transfer ~ssembl~ge. The uncoated ~lde of ~he donor eleme~t wa~
exposed on a rotatlng drum with a 100 mM infr~-red laser eml . ~lng at 830 E~n (Spectra D~ode Laboratorie~, Inc. 9 ~ 12 San Jose, CA). At 0.33 J/cm21 ~ery inte~se mag~nka lines about 8 micron wide were obtained on the reCeptQr sheet.

E~am~LQ_~
A coating solution Containing the ~ollowing ingredien~s, was made up: Red P-1339, 0.188; Lexan~
1500; 0.188; SQS, O.aO75; and dichloromethane, 9.62.
The composit$on waS dissolved, coated, and imaged a3 in Example 1. ~t 0.33 ~/cm2, very intense m~genta lines about 8 micron wide were obtained on the receptor sheet.
~am~L
A coating solu~ion contain$ng the followin,g ingredients, was made up: Red P-1339, 0.75; Butvar~ 90, 0.75; SQS, 0.06; and dichloromethane, 18.44. The composition was dissolv d, coated, and imaged as ln ~xample l. At O.33 J/cm2, very inten~e magenta lines about 8 m~cron wide were obta~ned on the receptor shee~.
~L~
A coating solution contalning the ~ollowing ingredients, wa~ made up: ~ed P-1339, 0.75J Bu~var~ ~-90l 0.75; dichlorome~hane, 18.5. The c~mpositlon wa dls~olved, coat~d, and imaged ~ in ~xample 1. Mo image could ~e d~tected on ~he r~ceptor ~heet.

To form the donor elemeDt~ ~ coating ~olut~on c~ntaining the followi~ ingredients, was made up:
Li~hol ~ub~ne, 1.38; ~B-l7, lolO; SQS, 0.12; and toluene, 27c52. WB-17 was predissolved ln toluene with slight heating. Then the ingredlent were di~p~r~ed on a 2-roll ~ill o~ernight. The dispersion was coated on .'. I i 2a~337 corona discharge treated polyethyl~ne tereph'chalate using a doctor knife with an about 2 mil (about 50 microns ) wet gap .
After dry~ng, the donor element was contacted with S a sheet of the Thermacolor0 vides print paper ~Eastman Kodak Co., Roohester, NY~ or a sheet of the Tektronlx thermal transf~r paper (Te~tronix Co.~ WilQ~nv~lle, OR) as described in Example 1. The thermal transfer a~semblage was imaged as described in Example 1. At 0 . 38 J/cm2, very tntense bright red, 8 micron llnes were obtained on the receptor sheet (about 100% transfer~
with very little background stain.

~e~
A coating solution containing the following ingredients, was made up: ~ithol Rubine, 1.38; W~-17, 1.10; and toluene, 27.52. The di~persion was prepared, coated, and imaged a-~ in Example 4. No trsnsfer o~
colorant to the receptor ~heet was be observed.
~am~5~
A coating solution containing tha ~ollowing ingredients, was made up: Lithol,Rubine~ 1.66; Vybar 260, 0.50; SQS, 0.04; zlnd toluene, 17.80. Vybar 2~0 w~s 2 S predissolved in toluene with ~light heating. The composition was di~per~ed, cDated, and lmaged as ln Example 4. At 0.75 J/cm2, very intens~ red llne~ were obtained on the receptor ~he~. A control wi~h ~o SQS
showed no im~ge.
3~

A coating ~c~lu'cic)n co2ltalr~ing 'che follow~ng ingredients, was made up: Lltllol ~ubir~e, û~66, ;roncryl~
682, 0.50; SQS, 0.03; and tetrahydrofuranr 11.81. The ~ ~ ~ 3 7 3 ~

composition was dispersed, and coated on both corona discharge treated polyethylene terephthalate fi}m and plain polyethylene terephthal~te ~ilm. Both coatings were imaged as in Example 4 ~o give very ~ntense red lines ~n the receptor sheet at 0.75 J/cm2.

~4

Claims

1. A donor element for a laser-induced thermal transfer process, said donor element comprising a support bearing thereon 2 colorant layer, said colorant layer comprising a colorant and an infra-red absorbing material, said infra-red absorbing material having the structure:

wherein each of R1, R2, R3, and R4 is independently an alkyl group of from one to eight carbon atoms.

2. The donor element of claim 1 wherein R1, R2, R3, and R4 are the same.

3. The donor element of claim 1 wherein R1, R2, R3, and R4 are each t-butyl.

4. The donor element of claim 1 wherein the colorant is a sublimable dye.

5. The donor element of claim 1 wherein the colorant is a pigment.

6. The donor element of claim 1 wherein the colorant layer additionally comprises a binder.

7. The donor element of claim 6 wherein R1, R2, R3, and R4 are the same.

8. The donor element of claim 6 wherein R1, R2, R3, and R4 are each t-butyl.

9. The donor element of claim 6 wherein the colorant is a sublimable dye.

10. The donor element of claim 9 wherein R1, R2, R3, and R4 are the same.

11. The donor element of claim 9 wherein R1, R2, R3, and R4 are each t-butyl.

12. The donor element of claim 6 wherein the colorant is a pigment.

13. The donor element of claim 12 wherein R1, R2, R3, and R4 are the same.

14. The donor element of claim 12 wherein R1, R2 R3, and R4 are each t-butyl.

15. A thermal transfer assemblage for a laser-induced thermal transfer process, said thermal transfer assemblage comprising:
(a) a donor element comprising a support bearing thereon a colorant layer, said colorant layer comprising a colorant and an infra-red absorbing material, said infra-red absorbing material having the structure:
wherein each of R1, R2, R3, and R4 is independently an alkyl group of from one to eight carbon atoms; and (b) a receiver sheet comprising support and an image-receiving layer;

16

17 wherein said colorant layer of said donor element is contiguous to said image receiving layer of said receiver sheet.
16. The thermal transfer assemblage of claim 15 wherein R1, R2, R3, and R4 are the same.
17. The thermal transfer assemblage of claim 15 wherein R1, R2, R3, and R4 are each t-butyl.

18. The thermal transfer assemblage of claim 15 wherein the colorant is a sublimable dye.

19. The thermal transfer assemblage of claim 15 wherein the colorant is a pigment.

20. The thermal transfer assemblage of claim 15 wherein the colorant layer additionally comprises a binder.

21. The thermal transfer assemblage of claim 20 wherein R1, R2, R3, and R4 are the same.

22. The thermal transfer assemblage of claim 20 wherein R1, R2, R3, and R4 are each t-butyl.

23. The thermal transfer assemblage of claim 20 wherein the colorant is a sublimable dye.

24. The thermal transfer assemblage of claim 23 wherein R1, R2, R3, and R4 are the same.

25. The thermal transfer assemblage of claim 23 wherein R1, R2, R3, and R4 are each t-butyl.

26. The thermal transfer assemblage of claim 20 wherein the colorant is a pigment.

27. The thermal transfer assemblage of claim 26 wherein R1, R2, R3, and R4 are the same.

28. The thermal transfer assemblage of claim 26 wherein R1, R2, R3, and R4 are each t-butyl.

WHAT IS CLAIMED IS:
1. A donor element for a laser-induced thermal transfer process, said donor element comprising a support bearing thereon a colorant layer, said colorant layer comprising a colorant and an infra-red absorbing material, said infra-red absorbing material having the structure:

wherein each of R1, R2, R3, and R4 is independently an alkyl group of from one to eight carbon atoms.
2. The donor element of claim 1 wherein R1, R2, R3, and R4 are the same.
3. The donor element of claim 1 wherein R1, R2, R3, and R4 are each t-butyl.
4. The donor element of claim 1 wherein the colorant is a sublimable dye.
5. The donor element of claim 1 wherein the colorant is a pigment.
6. The donor element of claim 1 wherein the colorant layer additionally comprises a binder.
7. The donor element of claim 6 wherein R1, R2, R3, and R4 are the same.
8. The donor element of claim 6 wherein R1, R2, R3, and R4 are each t-butyl.
9. The donor element of claim 6 wherein the colorant is a sublimable dye.

10. The donor element of claim 9 wherein R1, R2, R3, and R4 are the same.
11. The donor element of claim 9 wherein R1, R2, R3, and R4 are each t-butyl.
12. The donor element of claim 6 wherein the colorant is a pigment.
13. The donor element of claim 12 wherein R1, R2, R3, and R4 are the same.
14. The donor element of claim 12 wherein R1, R2, R3, and R4 are each t-butyl.
15. A thermal transfer assemblage for a laser-induced thermal transfer process, said thermal transfer assemblage comprising:
(a) a donor element comprising a support bearing thereon a colorant layer, said colorant layer comprising a colorant and an infra-red absorbing material, said infra-red absorbing material having the structure:

wherein each of R1, R2, R3, and R4 is independently an alkyl group of from one to eight carbon atoms; and (b) a receiver sheet comprising support and an image-receiving layer;

wherein said colorant layer of said donor element is contiguous to said image receiving layer of said receiver sheet.
16. The thermal transfer assemblage of claim 15 wherein R1, R2, R3, and R4 are the same.
17. The thermal transfer assemblage of claim 15 wherein R1, R2, R3, and R4 are each t-butyl.
18. The thermal transfer assemblage of claim 15 wherein the colorant is a sublimable dye.
19. The thermal transfer assemblage of claim 15 wherein the colorant is a pigment.
20. The thermal transfer assemblage of claim 15 wherein the colorant layer additionally comprises a binder.
21. The thermal transfer assemblage of claim 20 wherein R1, R2, R3, and R4 are the same.
22. The thermal transfer assemblage of claim 20 wherein R1, R2, R3, and R4 are each t-butyl.
23. The thermal transfer assemblage of claim 20 wherein the colorant is a sublimable dye.
24. The thermal transfer assemblage of claim 23 wherein R1, R2, R3, and R4 are the same.
25. The thermal transfer assemblage of claim 23 wherein R1, R2, R3, and R4 are each t-butyl.
26. The thermal transfer assemblage of claim 20 wherein the colorant is a pigment.
27. The thermal transfer assemblage of claim 26 wherein R1, R2, R3, and R4 are the same.
28. The thermal transfer assemblage of claim 26 wherein R1, R2, R3, and R4 are each t-butyl.