Note: Descriptions are shown in the official language in which they were submitted.
SUBLI~ATION TRANSFER IMAGING SYSTEM
Field of the Invention
This invention relates to a method of forming
an imaye in which a sheet bearing a radiation-
sensitive image-forming layer is image-wise exposed to
record an image in said layer and thereafter the
image-forming components are transferred to a receptor
layer or sheet to form a permanent image. In
10 particular, the invention relates to a sublimation
transfer imaging process employing a
radiation-sensltive sheet comprising one or more
bleachable dyes.
Background of the Invention
Positive working non-silver systems in which
an originally coloured species is decolourised
(bleached) in an imagewise manner upon exposure to
light have received a considerable amount of
attention. A large variety of dyes and activators
2~ have been disclosed for such systems, see, for
example, .J. Kosar, ~ight Sensitive Systems, page 387,
Wiley, New ~ork 1965.
The reaction relies on the fact that the dye
absorption is sensitising the dye's own destruction or
25 decolourisation, for example a yellow dyes absorbs
blue light; the excited dye thus formed reacts with an
activator which releases the species to bleach the
dye. Similarly green light would destroy the magenta
and red light the cyan dyes.
This dye bleach-out process is thus capable of
producing colour images in a simple way. However, in
spite of its apparent simplicity, the bleach-out
process poses a number of problems. In particular,
the purity of the whites in the final image leaves
=2=
much to be desired, image stability may not be good
and a fixing step may be re~uired to stabilise the
image.
Our copending European Patent Application No.
5 84301156.0 (Serial No. 0 120 601) discloses a
radiation-sensitive element capable of recording an
image upon image-wise exposure to radiation of
selected wavelength, the element comprising, as the
image-forming components, an effective amount of a
10 bleachable dye in reactive association with an
iodonium ion.
The element is capable of recording a positive
image simply upon exposure to radiation of selected
wavelength; the radiation absorbed by the dye which is
15 in reactive association with an iodonium ion causes
the dye to bleach. The dyes are believed to sensitise
spectrally the reduction of the iodonium ion through
the radiation absorbed by the dyes associated with the
iodonium ion. Thereafter the element may be
20 stabilised to fix the image by destruction of the
iodonium ion or by separation of the dye relative to
the iodonium ion.
The dyes used may be of any colour and any
chemical class which i5 capable vf bleaching upon
25 exposure to radiation of selected wavelength in the
presence of an iodonium ion.
By a suitable selection of dye an element may
be prepared which is sensitive to radiation of a
selected wavelength band within the general range 300
30to 1100 nm, the particular wavelength and the width of
the band depending upon the absorption characteristics
of the dye. In general, where a dye has more than one
absorption peak it is the wavelength corresponding to
S~4
=3=
the longest wavelength peak at which one would choose
to irradiate the element.
Elements intended for the production of images
from radiation in the visible region (400 to 700 nm)
will contain dyes which will bleach from a coloured to
a substantially colourless or very pale state. In
practice, such bleachable dyes will undergo a change
such that the transmission optical density at the
~ max will drop from 1.0 or more to less than 0.09,
10 preferably less than 0.05. The dyes will generally be
coated on the support to provide an optical density of
about 3.0 or more.
In the case of elements sensitive to
ultraviolet radiation (300 to 400 nm) the dyes will
15 not normally b~ coloured to the eye and there may be
no visible change upon exposure to ultraviolet
radiation and bleaching. The image-wise exposed
elements may be used as masks for further ultraviolet
exposure after fixing.
Infrared sensitive elements contain dyes
having an absorption peak in the wavelength range 700
to 1100 nm. These dyes may also have absorption peaks
in the visible region before and/or after bleaching.
Thus, as well as providing a means for obtaining masks
?5 for subsequent infrared exposure in a similar manner
to the ultraviolet masks, infrared sensitive elements
may record a visible image upon image-wise exposure to
infrared radiation.
Exposure may be achieved with a wide variety
30 of sources including incandescent, gas discharge and
laser sources. For laser scanning applications the
laser beam may need to be focussed in order to achieve
sufficient exposure.
55~
=~=
The dyes used may be anionic, cationic or
neutral. Anionic dyes give very good photo-
sensitisation which is believed to be due to an
intimate reactive association betwean the negatively
charged dye and the positively charged iodonium ion.
Also anionic dyes may readily be mordanted to cationic
polymer binders and it is relatively simple to remove
surplus iodonium ions in an aqueous bath in a fixing
step if the mordanting polymer is cationic. However,
10 neutral dyes also give good results and are preferred
over cationic dyes for overall photosensitivity.
Cationic dyes are least preferred since it is more
difficult to achieve intimate reactive association
between the positively charged dye and iodonium ion,
15 and selective remcval of iodonium ion after imaging is
more difficult.
The bleachable dyes may be generically
referred to as polymethine dyes which term
characterises dyes having at least one electron donor
20 and one electron acceptor group linked by methine
groups or aza analoyues. The dyes have an oxidation
potential between 0 and +1 volt, preferably between
+0.2 and +0.8 volt. The bleachable dyes may be
selected from a wide range of known classes of dyes
25 including allopolar cyanine dye bases, complex
cyanine, hemicyanine, merocyanine, azine, oxonol,
streptocyanine and styryl.
The dye and iodonium system has its greatest
sensitivity at the lmax f the longest wavelength
30 absorbance peak. Generally, it is necessary to
irradiate the system with radiation of wavelength in
the vicinity of this ~max for bleaching to occur.
Thus, a combination of coloured dyes may be used, e.g.
~2~5~
=5-
yellow, magenta and cyan, in the same or different
layers in an element and these can be selectively
bleached by appropriate visible radiation to form a
full colour image. Monochromatic or polychromatic
images may be produced using the photosensitive
materials with relatively short exposure times in
daylight or sunlight or even artificial sources of
light (e.g. fluorescent lamps or laser beams). The
exposure time, for adequate results, for example when
10 using an 0.5 kW tungsten lamp at a distance of 0.7 m,
may be between 1 second to 10 minutes.
The iodonium salts used in the imaging system
are compounds consisting of a cation wherein a
positively charged iodine atom bears two covalently
15 bonded carbon atoms, and any anion. Preferably the
acid from which the anion is derived has a pKa ~ 5.
The preferred compounds are diaryl, aryl/heteroaryl or
diheteroaryl iodonium salts in which the carbon-to-
iodine bonds are from aryl or heteroaryl groups.
20 Aliphatic iodonium salts are not normally thermally
stable at temperatures above 0C. However, stabilised
alkyl phenyl iodonium salts such as those disclosed in
Chem. Lett. 1982, 65-6 are stable at ambient
temperatures and may be used.
The ~leachable dye and iodonium salt are in
reactive association on the support. Reactive
association is defined as such physical proximity
between the compounds as to enable a chemical reaction
to take place between them upon exposure to light. In
30 practice, the dye and iodonium salt are in the same
layer or in adjacent layers on the support.
In general, the weight ratio of bleachable dye
to iodonium salt in the element is in the range from
1:1 to 1:50, preferably in the range from 1:2 to 1:10.
~69~
=6=
The bleachable dye and iodonium salt may be
applied to the support in a binder. Suitable binders
are transparent or translucent, are generally
colourless and include natural polymers, synthetic
resins, polymers and copolymers, and other film
forming media. The binders may range from
thermoplastic to highly cross-linked, and may be
coated from aqueous or organic solvents or emulsions.
Suitable supports include transparent film,
10 e.g. polyester, paper e.g. baryta-coated photographic
paper, and metallised film. Opaque vesicular
polyester films are also useful.
The fixing of the radiation-sensitive elements
may be effected by destruction of the iodonium ion by
15 disrupting at least one of the carbon-to-iodine bonds
since the resulting monoaryl iodine compound will not
react with the dye. The conversion of the iodonium
salt to its non-radiation sensitive form can be
effected in a variety of fashions. Introduction of
20 ammonia and amines in reactive association with the
iodonium ion, or a reaction caused on heating, or UV
irradiation of a nucleophilic anion such as I~, Br~,
Cl~, BAr4~ (tetra-arylboronide), Ar~ (e.g.
phenoxide~, or 4-NO2C6H4CO2~, with the iodonium ion,
25 will effect the conversion.
An alternative method of achieving
post-imaging stabilisation or fixing is to remove the
iodonium ion from reactive association with the dye by
washing with an appropriate solvent. For example, in
30 the case of elements using mordanted oxonol dyes and
water soluble iodonium salts formulated in gelatinl
after imaging, the iodonium salt is simply removed by
an aqueous wash, which leaves the immobilised dye in
i9~
the binder. The dye stability to light is then
equivalent to that of the dye alone. An element in
which the dye and iodonium salt is formulated in
polyvinylpyridine may be treated with aliphatic
ketones to remove the iodonium salt and leave the dye
in the binder.
The elements may be used as transparencies for
use with overhead projectors, for making enlarged or
duplicate copies of colour slides and for related
10 graphics or printing applications, such as pre-press
colour proofing materials.
Dye diffusion transfer systems are known and
are becoming increasingly important in colour
photography (see C.C. Van de Sande in Angew Chem.
15 1983, 22, 191-209). These systems allow "rapid
access" colour images without a complicated processing
sequence. The construction of these colour materials
may be donor-receptor type (e.g. Ektaflex commercially
available from Kodak) integral peel-apart type (e.g.
20 Polaroid, E.H. Land, H.G. Rogers, V.X. Walworth in J.
Sturge Nebelette's Handbook o$ Photography and
Reprography, 7th Ed. 1977, Chapter 12), or integral
single sheet type (e.g. Photog. Sci. and Eng., 1976,
20~ 155)o Silver halide diffusion transfer systems
25 are also known (e.g. E.H. Land. Photog. Sci. and Eng.,
1977, _ , 225). Examples of diffusion transfer fixing
in non-silver, dye-forming reactions employing solvent
application to effect the transfer are disclosed in
United States Patent Specification Nos. 3 460 313 and
30 3 598 583. The latter patent also describes a
full-colour imaging element, applicable for
preparation of colour proofs, fixed by transfer of dye
precursors in register to a receptor. Other examples
~2i~ S~
of non-silver diffusion transfer imaging systems are
disclosed in British Patent Specification Nos.
1 0S7 703, 1 355 61~ and 1 371 898. The latter two
Patents also disclose the transfer of dye images under
the influence of dry heat.
It has now been found that certain dyes which
are bleachable upon exposure to radiation in the
presence of iodonium ion are susceptible to diffusion
or sublimation transfer and this property may be
10 utilised to separate such dyes from the iodonium ion
and produce a clean, stable image by transfer from a
radiation-sensitive layer to a receptor layer or
separate receptor element.
Brief Summary__f the Invention
According to the present invention there is
provided a process for ~orming an image which
comprises image-wise exposing to radiation of selected
wavelength a carrier element comprising, as image
forming cornponents, in one or more imaging layers
20 coated on a support a bleachable dye in reactive
association with iodonium ion thereby bleaching the
dye in exposed areas to form a positive image, and
thereafter transferring the positive d~e image to a
receptor which is either a receptor layer present on
25 the carrier or a separate receptor element by
heating the carrier element to a sufficient
temperature to allow the dye image to sublime to the
receptor thereby forming an image on the receptor.
S94
g
The process of the invention provides stable
dye images, optionally full colour images, of high
quality with low background fog. The imaging system
does not require the presence of silver halide.
Description of the Preferred Embodiments
In accordance with the invention the
bleachable dyes are sublimable and after image-wise
exposure the carrier element is placed in intimate
contact with a receptor and the resulting composite
10 heated for a sufficient time and to a sufficient
temperature to allow the dye to sublime across the
interface to the receptor thereby forming a laterally
reversed positive image on the receptor. Thereafter
the carrier element is separated from the receptor.
.
6~
=10=
The sublimation transfer allows the formation
of a stable dye image having high colour purity. The
process is entirely dry and takes only a few minutes
to give colour prints. A single transfer from the
carrier element to a receptor results in a mirror
image. If a true image; right-reading, is required a
double transfer process may be employed transferring
the dyes from the carrier element to an intermediate
receptor and thereafter transferring the dyes from the
10 intermediate receptor to the final receptor.
Alternatively, a true image may be formed by reversing
the transparency used for exposure.
The process may be used to achieve a
multi-colour print either by sequentially transferring
15 dyes from separate carrier elements or by utilising a
carrier element having two or more coloured dyes, e.g.
magenta, cyan and yellow, and transferring the dyes
simultaneously~
Suitable dyes for use in this system are those
20 which are both bleachable upon exposure to radiation
in the presence of an iodonium ion and are sublimable,
preferably in the temperature range 80 to 160C, more
preferably 100 to 150C. In general, the dyes are
electrically neutral (i.e. not charged) and have a
25 molecular weight of less than 400, preferably less
than 350. The dyes also generally possess a compact
or aball-like" structure; dyes having an elongate
structure, e.g. those having long methine chains, do
not readily sublime. The dyes are also selected such
30 that they do not fade or undergo a change in colour on
- sublimation. When more than one dye is employed it is
desirable to match the sublimation characteristics of
the dyes to ensure an even transfer rate for all the
dyes.
~26~5~
Suitable bleachable dyes may be generically
referred to as polymethine dyes which term
characterises dyes having at least one electron donor
and one electron acceptor group linked by methine
groups or a~a analogues. The dyes have an oxidation
potential between 0 and +1 volt, preferably between
~0.2 and ~0.8 voltO The bleachable dyes may be
selected from a wide range of known classes of dyes
including allopolar cyanine dye bases, complex
10 cyanine, hemicyanine, merocyanine, azine, oxonol,
streptocyanine and styryl.
In general, suitable dyes for use in the
invention will have the structure:
R2
.'~
in which:
n is 0, 1 or 2, and
~.z~
Rl to R4 are selected to provide an electron
donor moiety at one end of the conjugated chain and an
electron acceptor moiety at the other, and may be
selected from substituents including hydrogen,
halogen, cyano, carboxy, alkoxy, hydroxy, nitro,
alkyl, aryl groups or heterocyclic rings any of which
may be substituted. The skeletal structure of the
groups Rl to R4 generally contain up to 14 atoms
selected from C, N, O and S. When the skeletal
lO structure of a Rl to ~4 group is in the orm of a
linear chain there will usually be no more than 6
carbon atoms in the chain. When the skeletal
structure is cyclic there will be no more than 7 atoms
in any single ring. Cyclic structures may comprise
l5 two or more fused rings containing up to 14 atoms. If
the skeletal structure of a Rl to R~ group comprises
two unfused cyclic groups there will be no more than 3
atoms in the linear chain between the groups.
Alternatively, R1 and R2 and/or R3 and R4 may
20 represent the necessary atoms to complete optionally
substituted aryl groups or hetreocyclic rings,
generally containiny up to 14 atoms selected from C,
N, O and S and having a structure as defined above.
The conjugated chain is preferably composed of
25 carbon atoms but may include one or more nitrogen
atoms providing the conjugation is not disrupted. The
free valences on the chain may be satisfied by
hydrogen or any substituent of the type used in the
cyanine dye art including fused ring systems.
The particular selection of substituents Rl to
R4 effects the light absorbance properties of the dye
which may be varied to provide absorption peaks
ranging from the ultraviolet (300 to 400 nm), near
ILZ6~5'~
=13=
visible (400 to 50~ nm), far visible (500 to 700 nm)
and infrared (700 to 1100 nm).
Dyes of the above formula are well known
particularly in the silver halide photographic art and
S are the subject of numerous patents. Exemplary dye
structures are disclosed in The Theory of the
Photographic Process, T.H. James, Ed. MacMillan
Editions 3 and 4, and Encyclopaedia of Chemical
Technology, Kirk Othmer, 3rd Edition, Vol. 18, 1983.
Within the above general structure of dyes are
various classes of dye including:
1) Merocyanine dyes of the general formula:
R `B
in which:
q is an integer of 0 to 2,
R5 represents hydrogen or a substituent which
may be present in conventional cyanine dyes, e.g.
alkyl (preferably of 1 to 4 carbon atoms), etc.,
the groups A and B, which need not necessarily
complete a ayclic structure with the methine chain,
2S independently represent alkyl, aryl or heterocyclic
groups or the necessary atoms to complete heterocyclic
rings which may be the same or different.- The
skeletal structure of the groups A and B generally
contain up to 14 atoms selected from C, N, O and S.
30 When the skeletal structure of A or B is in the form
of a linear chain there will usually be no more than 6
carbon atoms in the chain. When the skeletal
structure completed by A or B is cyclic there will be
,
s~
=1~=
no more than 7 atoms in any single ring. Cyclic
structures may comprise two or more fused rings
containing up to 14 atom~. If the skeletal structure
complete by A or B comprises two unfused cyclic yroups
there will be no more than 3 atoms in the linear chain
between the groups. Additionally B may complete a
carbocyclic ring.
These dyes are well known in the silver halide
photographlc art and are described in The Theory of
10 the Photo~raphic Process, reEerred to above.
It is to be understood that these cyanine,
merocyanine, anionic and oxonol dyes may bear
substituents along the polymethine chain composed of
C, N, O and S, and that these substituents may
15 themselves join to form ~, ~ or 7 membered rings, or
may bond with rings A and B to form further rings,
possibly with aromatic character. Rings A and B may
also be substituted by C, N, H, O and S containiny
groups such as alkyl, substituted alkyl, alkoxy, amine
20 (primary, secondary and tertiary), aryl (e.g. phenyl
and substituted phenyl), halo, carboxyl, cyano, nitro,
etc. Exemplary substituents are well known in the
cyanine dye art.
2~ Benzylidene and cinnamylidene dyes of the
25 structure:
~ ~3 C ~1
R R
in which:
~4S~
=15=
A is as defined above, and may additionally be
cyano, or carboalkoxy or other carbonyl-containing
groups, e.g. ketone, or S=O containing groups, e.g.
S02Me,
n is 0 or 1,
R6 and R7 independently represent a hydrogen
atom or an alkyl group (optionally substituted) or
aryl group containing up to 12 carbon atoms,
R8 is H or CN or CO2R9, in which R9 is an
lOopticnally substituted alkyl group of up to 6 carbon
atoms, and
the Eree valences may be satisfied by hydrogen
or alkyl groups, or together may form a 6-membered
carbocyclic saturated or aromatic ring.
Examples of such dyes include:
CN
Me 2 ~ Me 2N~
3) Quinoline merocyanine dyes of the general
structures:
X
~3 CH) p=C~ ~ (CH-CH) p C~
~26~5~
=16 =
in which:
R6 is as defined above,
p is 0 or 1, and
at least one of X and Y is an electron
withdrawing group, e.g. cyano, nitro, carbonyl (in
aldehyde, ketone, carboxylic acid, ester or amide),
sulphonyl containing up to 6 atoms selected from C, N,
0 and S, or X and Y together form a 5 or 6 membered
ring with additional atoms selected from C, N, 0 and
S, and containing an electron withdrawing group ~e.g.
keto).
Examples of such dyes include:
CN CN H NO2
~ and
Et ~e
4) Phenoazine dyes of the general structure:
Z ~ Q ~ O
in which:
2 is an electron donor, e.g. NR6R7, in which
R6 and R7 are as defined above, and
Q represents 0, S, NH, NCH3, NC2H5, CH2,
e.g.
Me2N 5
~64~
-17=
5) A2amethine or indoaniline dyes of the general
structure:
, ~ NR6R
ll~N --
O `-B
in which:
r is 0 or 1, and
A, B, R6 and R7 are as deEined above.
The group NR6R7 may also be positioned in a
para-disposition to the chain, in addition to the
ortho-disposition shown. Simiariy the carbonyl group
may be in other dispositions on the ring.
These dyes have been used in chromogenic
photographic processes. Specific examples of such
dyes include:
~ M ~ ~ ~ 3
N and
~ ,,
NMe2
~Z64~
= l&
The iodonium ions used in the invention are
compounds consisting of a cation wherein a positively
charged iodine atom bears two covalently bonded carbon
atoms, and any anion. The preferred compounds are
diaryl, aryl/heteroaryl or diheteroaryl iodonium salts
in which the carbon-iodine bonds are from aryl or
heteroaryl groups and one of the aryl or heteroaryl
groups is substituted with an alkyloxy group.
Suitable iodonium salts may be represented by the
10 formula:
Ar
~ A~
Ar
15 in which~
Arl and Ar2 independently represent
carbocyclic or heterocyclic aromatic-type groups
generally having from 4 to 20 carbon atoms, or
together with the iodine atom complete a heterocyclic
20 aromatic ring.
These groups include substituted and unsubstituted
aromatic hydrocarbon rings, e.g. phenyl or naphthyl,
which may be substituted with alkyl groups, e.g.
methyl, alkoxy groups, e.g. methoxy, chlorine,
25 bromine, iodine, fluorine, carboxy, cyano or nitro
groups or any combination thereof~ Examples of
hetero-aromatic groups include thienyl, furanyl and
pyrazolyl which may be substituted with similar
substituents as described above. Condensed
3~ aromatic/hetero-aromatic groups, e.g. 3-indolinyl, may
also be present,
~ represents an anion which may be
incorporated into Arl or Ar2.
=19=
Preferably Arl and Ar2 do not have more than
two substituents at the alpha-positions of the aryl
groups. Most preferably Arl and Ar2 are both phenyl
groups.
The alpha-positions of the Arl and Ar2 groups
may be linked together to include the iodine atom
within a ring structure, e.g.
~ I ~ A~
in which z is an oxygen or sulphur atom. An example
of such an iodonium salt is:
=2~=
N02 I ~ No2
PF6~3
Other suitable iodonium salts include polymers
containing the unit:
/ -CH-CH2-
~J ~
\ A~ I~ -Ph /
in which Ph represents phenyl.
Examples of such polymers are disclosed in Yamada and
Okowara, Makromol. _hemie, 1972, 152, 61-6.
Any anion may be used as the counter-ion A~
20 provided that the anion does not react with the
iodonium cation under ambient temperatures. Suitable
inorganic anions include halide anions, HS04~, and
halogen-containing complex anions, e.g.
tetrafluoroborate, hexafluorophosphate,
25 hexafluoroarsenate and hexafluoroantimonate. Sultable
organic anions include those of the formulae:
Rl 7co~ or R17So3~
30 in which R17 is an alkyl or aryl group of up to 20
carbon atoms, e.g. a phenyl group, either of which may
be substituted. Bxamples of such anlons include
CH3CO ~ and CF3Cod3.
~Z6~L5~4f
=21=
A~ may be present in Ar1 or Ar2, e.g.
A
in which A~ represents cod~, etc.
Furthermore, A~ may be present in a molecule
containing two or more anions, e.g. dicarboxylates
10 containing more than 4 carbon atoms.
The most significant contribution of the anion
is its effect upon the solubility of the iodonium salt
in different solvents or binders.
Most of the iodonium salts are known, they ~ay
15 be readily prepared and some are commercially
available. The synthesis of suitable iodonium salts
is disclosed in F.M. Beringer et al, Journal of the
American Chemical Society, 80, 4279 (1958).
Suitable substrates for the donor (or carrier)
20 for use in sublimation transfer are plastics film,
paper (cellulosic or synthetic fibre), metallised
plastics film and plastic film to film or plastic film
to paper laminates.
The substrate should be unaffected by the
25 processing conditions. For example, the substrate
must be heat-stable and not possess undesirable
dimensional variation, nor degradation, nor tackiness
when subjected to the sublimation conditions. A
preferred substrate is a plastics film such as
3~ polycarbonate film, cellulose acetate film or most
pre~erably polyester, e.g. poly(ethylene
terephthalate~, which may be biaxially orientated.
~269~5~9~
=22=
The substrates may possess surface modifying
or other coatings to enhance adhesion of imaging
layers, to improve smoothness, etc. Resin coated
photographic grade paper is a suitable substrate. The
plastics film may specifically possess a subbing layer
which acts as a priming layer for gelatin and other
hydrophilic coating.
Binders suitable for use in preparing the
carrier element for use in sublimation transfer are
10 organic binders which dissolve readily in solvent and
afford on coating clear dispersions of the dyes and
iodonium salts described herein. Suitable binders
include poly(vinyl butyral)l polytvinyl acetate)
polymers and phenolic resins~ The preferred weight
15 range of iodonium ion to binder is from 3 to 15~. The
preferred weight range of dye to iodonium salt is 1:1
to 1:15, more preferably 1:1 to 1:5.
~69LS~
=~3=
The binder must allow the dyes to migrate on
heating to the processing temperature, thus allowing
transfer to the receptor layer. If more than one dye
is present, a general equivalence of sublimation
transfer rates is desirable.
A layer containing the above components is
coated preferably at 30 to 60 g/m2, wet deposition
onto the substrate. It is undesirable to have
overlayers as this hinders sublimation of the dyes,
10 unless the overlayer is very thin. It is also
preferred for all the bleachable dyes and iodonium
salts present in an element to be in a single layer.
Generally the element should be constructed so as not
to inhibit the ready sublimation transfer of the dye
15 from the carrier sheet. The topmost surface of the
element should allow good contact with the receptor
layer and not become tacky on heating to the transfer
temperature.
The carrier element is firstly exposed so as
20 to cause bleaching of the dyes by reaction with the
iodonium ion. Most frequently visible light will be
used, the actinic wavelengths corresponding to the
absorption charact~ristics of the dyes. A variety of
light sources may be used including continuous white
25 light and laser. Sufficient exposure must be given to
ensure full bleaching or decomposition of the dyesr as
residual, unreacted dye may transfer. Thereafter the
exposed precursor element is used to effect transfer
of the unreacted dyes. Exposure is normally
30 undertaken at ambient conditions of temperature
although mild heating is allowable generally up to
about 80Ct provided that this does not cause
sublimation.
L~
=24 =
on liyht exposure the dyes react with the
iodonium ions to give non-sublimable, charged
species. The dyes reported in Table l are believed to
react on exposure with iodonium salts to give charged
photo-products of the general structure as follows:
NMe2 ~NMe2 X
~ + I0 ~
The reaction products do not significantly
transfer on heating. After imaging at room
temperature, the unbleached dye is readily separated
by thermal transfer. Thus, the unbleached dye is
transferred by sublimation to the receptor, and the
20iodonium salt and the dye photoproduct remain
substantially in the imaging layer.
While the main purpose of this invention is to
achieve visible dye transfer, organic ultraviolet and
infrared absorbing molecules may also be transferred,
25 e.g. to make ultraviolet vr infrared masks.
The receptor material may be selected from a
wide range of materials as described above including
paper, particularly coated paper, e.g. poly(vinyl
chloride) coated paper, plastics film materials, e.g.
30pvlyester, such as poly(ethylene terephthalate) films,
including metallised films, woven and non-woven
materials such as textile fabric and cloth and
plastics paper.
~6~S~
=25=
The precursor and receptor should be capable
of conforming together to allow transfer. The
receptor material should absorb the transferred dyes
for permanence and may be coated with absorbing
pigments, mordants and organic polymers to improve dye
absorption and stability. The receptor should
withstand the transfer conditions and not exhibit
adverse loss of dimensional stability or tackiness.
Typical processing times are from 30 to 120
10 seconds, with heating from 100 to 150C. Thereafter
the receptor is separated giving a single or multiple
te.g. full) colour reproduction. Heat may be applied
through conduction or convection, contact with a
heated roller, drum, platen or other surface, or in an
15 oven or by an electrically heated layer or underlayer.
The short processing time and dry conditions
are particularly useful aspects of this invention.
The choice of receptor substrates is large and the
transfer leaves behind various species which
20 contribute to background fog levels. The backgrounds
on the receptors are much cleaner (e.g. low Dmin) and
there is a reduced tendency or the dye to degrade,
being removed from the proximity of iodonium ions.
Dyes transferred to a receptor substrate may
25 be further transferred from the receptor to yet
another receptor. Here if the transfer is to be
effected again, the first receptor should readily
release the dyes again on heating. Multiple transfers
of this kind will generally be accompanied by some
3~ loss in resolution and optical density. Single
transfer results in a reversed-reading image. Double
transfer results in a right-reading image.
Dyes may be transferred sequentially from
~2~i4~9~
=26=
separate substrates in order to achieve a multi~colour
print, but generally it is desirable to transfer
magenta, cyan and yellow dyes simultaneously from a
single substrate if a full-colour print is required.
Once transferred the dyes may be viewed by
reflection, as on paper, or by transmission. In
general, only the unreacted dyes are transferred,
however it is permissable for sublimable colourless
stabilising additives to be transferred. Preferably
1~ such additives are incorporated in the surface of the
receptor. Additives allowing maintenance of colour
density are particularly useful.
The invention will now be illustrated by the
following Examples.
In the following Examples the sensitivity of
the element was measured by the following technique.
A 2.5 cm s~uare piece of each sample was exposed over
an area of 2.5 mm2 with focussed light filtered, using
a Kodak narrow band filter (551.4 nm:power output =
2~ 2.36 x 10-3 W/cm2) and the change in the transmission
optical density with time was monitored usiny a Joyce
Loebl Ltd. microdensitometer. A plot of transmission
optical density versus time was made and the exposure
time tt) for the optical density to fall from DmaX to
25 (DmaX-l) was determined. The energy required (E) was
calculated as the exposure time (t) x power output
(- 2.36 x 10-3 wJcm2): this gives an indication of
the sensitivity of the elements.
In all cases a significant reduction of
3~ background density was achieved after transfer which
gave a much cleaner image. Typically the minimum
density before transfer and after exposure was
approximately 0.15, this reducing to approximately
0.05 or below after transfer.
~2~45~4~
=27=
Example 1
Single dye su~limation transfer
Dye No. 1 (0.06 g) in 3 ml ethanol was added
fr~ to Butvar B76 (1 g) in 7 ml butan-2-one.
~- Diphenyliodonium hexafluorophosphate (0.3 g) was added
to the resulting lacquer in red light. The mixture
was coated at 75 micron thickness on unsubbed
polyester base and dried at room temperature for 15
minutes in the dark. The following Table reports the
initial and transferred maxiJnum optical densities,
10 Dmax, achieved.
A strip of the sample was imaged through a
step wedge having an optical density differential
between adjacent steps of 0.15, with a tungsten halide
source ~1 kW, 0.5 m) for 120 seconds. The resulting
15 step image was contacted with a photographic, baryta
paper receptor coated with poly(vinyl chloride)
Bakelite Ltd. r type VYNS, in the dark. The
construction was covered with muslin and the composite
heated with an iron set at "cotton" ~temperature
20 l~O~C) for 2 minutes. Separation oE the construction
gives a Nmirror image" copy of the carrier filrn
transferred onto the PVC coated paper. The following
Table reports the reflected density after transfer.
The minimum background density was found to be
25 significantly less after the transfer process.
Resolution test
A strip of the sample was contacted with an
UGRA mask (the UGRA mask was an 1976 UGRA-Gretag-Plate
Control Wedge PCW) and this construction imaged as
above using a tungsten halide source. In the carrier,
the best resolution was 4 micron which is equivalent
to 25~ lines per millimetre. The imaye was
'r~ Q ~ rl~,
lZ6~S~
=28=
transferred to the PVC coated receptor by heating as
above described~ The best resolution was 17 micron
which is equivalent to 59 lines per millimetre.
Examples 2 to 6
Example 1 was repeated using the dyes reported
in the following Table, individually in the
proportions indicated. The Table reports the maximum
10 optical density by transmission achieved in the
original and by reflectance in the receptor and the
eneryy required at the max of the dye which gives a
measure of the photosensitivity of the composition. A
significant reduction in the minimum background
15 density was observed after sublimation transfer.
~Z~ ?4
=~gC
Table
Example Dye No. Structure Weight ~max in Density E
No. 9 ethanol Ini Tr (x106 mJ~m2)
nm
__ _ _ __ _ .
1 1 NMe2 0.06 475 1.5 1.0 1.9
CO 2
~'
CN
2 2IMe2 0.06 450 1.3 0.9 8
2Me
CN
3 3~ ez 0.06 550 1.3 1.3 6.2
ll ~
~0
~y
,~
-
Ini ~= Initial density (transmission)
Tr = Transferred density (reflected) after heating
2 mins/150~.
1~6~5~
=30=
Table (Contd.)
_ _
Example Dye No. Structure Weight ~max in Density E
No. g ethanol Ini TX (x106 mJ/m2)
nm
4 4 ~ 2 0.06 570 1.0 0.8 5.1
~3
o
NMe2 0.06 560 1.3 1.2 7.6
~ O
0~ '
6 6 ~ 2 0.06 503 0.9 0.5 6
,~
CN
CN
.
~'~64~
a31=
E~ o 14
Photothermographic imaging with sublimation fixin~
These Examples are for dyes which need light
and heat simultaneously to react with iodonium salts.
The samples were coated in Butvar as in
Example 1, but containing the dyes in the following
Table, in the reported amounts. These dyes do not
10 react with iodonium salts at room temperature, e.g.
the change in the dye absorbance is zero after 5
minutes exposure to filtered light
(2 mm2 spot/1.7 mW/cm2). On heating to above the Tg
of the binder, e.g. 70C for Butvar B76~ the
15 light-induced reaction occurs. In some cases, there
is an intermediate colour prior to bleaching.
In all cases a significant reduction in the
mioimum background optical density was observed.
~;~645~
=32=
Table
Example ~e No. Structure Weight ~max in Density E
r~o. g a) ethanol Ini Tr (x106 mJ/m2)
b) Butvar
nm
25C 80C
_
7 7 IMe2 0,04 430 a 3.0 1.8400 9
CN
8 8 CN CN 0.02 430 b 1.2 0,890 0.7
~3 '
I
C2H5
9 9 ¢~SN2 0.02 470 b 0.9 0.4 100 9
CH3
"
.
~z~
=33=
Table ~Contd.)
Example Dye No. Structure W~ight ~max in Den~ity E
No. g a) ethanol Ini Tr ~x106 mJ/m2)
b) ~utvar
nm
25C 80C
~Me2 0 04 550 a 0.5 0.6 100 80
CN
_ _ _ _ . _ _ _
11 11 0.02 S60 a 0.6 0.7 50
603 b
" ~ N~ ~
~S~O
NMe2
__ _ _ . _
~26~S~
=3~=
Table (Contd.)
Example Dye No. Structure Weight ~max in Density E
No. g a) ethanol Ini Ir (x106 mJ/m2)
b~ Butvar
rlm
25C ~0C
__ _ . _ _
12 12 ~ 2 0.02 660 a O.S 0.6 100 1.3
~ Cl
o
13 13 0.02 540 a 0.9 0.2 100 9
Ph
O ~ N ~ NMe2
14 14 0.10 530 a 1.8 1.2 1001.8
Me
O ~ N ~ NMe2
Ini = Initial density (transmitted)
Tr = Transferred density (reflected) after heating
2 mins/15QC.
~;~69LS~
=35=
Example 15
Light and heat imaging fixed b~ _transfer
The blue coating oE Example 12 was contacted
with a black on white photocopy and the composite put
through the 3M Thermofax ~odel 45CB processor at the
~medium" setting. The result was a negative copy of
the photocopy, bleaching had occurred in the regions
10 in contact with the black characters. This copy was
then stabilised by dye sublimation to a poly(vinyl
chloride) coated paper receptor by heating for 30
seconds at 100C. The result was a blue-coloured
negative print of the original. A significant
15 reduction in background density was observed on
transfer.
Example 16
This Example shows the single sheet
panchromatic capability of the invention.
A mixture of Dye No. 1 (0.06 g) and Dye No. 13
(0.06 g) in 3 ml EtOH was added to a lacquer of Butvar
B76 (1 g) in 7 ml butan-2-one. To the red mixture in
25 red light, was added diphenyliodonium hexafluoro-
phosphate (0.3 g). The resulting lacquer was
knife-edge coated at 75 micron, wet thickness onto
unsubbed polyester base (100 micron). The film was
dried for 15 minutes at room temperature in air.
A strip of this red film was subjected to a
spot of light filtered through a narrow cut filter at
551.4 nm for 100 seconds; in the area of light, a
yellow spot (5 mm diameter) formed. The imaged strip
:~z~s~
=36=
was then contacted with PVC coated paper and the
composite heated for 2 minutes at 150C to transfer
the dyes out of Butvar layer into the receptor. Good
resolution was obtained; there was no spread of
mayenta into the imaged yellow spot.
