U.S. patent application number 10/440689 was filed with the patent office on 2003-11-06 for laser addressable thermal transfer imaging element with an interlayer.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Chang, Jeffrey C., Chou, Hsin-Hsin, Jalbert, Claire A., Staral, John S., Tolbert, William A., Wolk, Martin B..
Application Number | 20030207198 10/440689 |
Document ID | / |
Family ID | 24534620 |
Filed Date | 2003-11-06 |
United States Patent
Application |
20030207198 |
Kind Code |
A1 |
Chang, Jeffrey C. ; et
al. |
November 6, 2003 |
Laser addressable thermal transfer imaging element with an
interlayer
Abstract
A thermal transfer donor element is provided which comprises a
support, a light-to-heat conversion layer, an interlayer, and a
thermal transfer layer. When the above donor element is brought
into contact with a receptor, and imagewise irradiated, an image is
obtained which is free from contamination by the light-to-heat
conversion layer. The construction and process of this invention is
useful in making colored images including applications such as
color proofs and color filter elements.
Inventors: |
Chang, Jeffrey C.; (North
Oaks, MN) ; Staral, John S.; (Woodbury, MN) ;
Tolbert, William A.; (Woodbury, MN) ; Wolk, Martin
B.; (Woodbury, MN) ; Jalbert, Claire A.;
(Cottage Grove, MN) ; Chou, Hsin-Hsin; (Woodbury,
MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
24534620 |
Appl. No.: |
10/440689 |
Filed: |
May 19, 2003 |
Related U.S. Patent Documents
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Application
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Filing Date |
Patent Number |
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10440689 |
May 19, 2003 |
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10219427 |
Aug 15, 2002 |
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6582877 |
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10219427 |
Aug 15, 2002 |
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09738775 |
Dec 18, 2000 |
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6296529 |
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09738775 |
Dec 18, 2000 |
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09553294 |
Apr 20, 2000 |
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6270934 |
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09553294 |
Apr 20, 2000 |
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09349329 |
Jul 8, 1999 |
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6099994 |
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09349329 |
Jul 8, 1999 |
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09031941 |
Feb 27, 1998 |
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5981136 |
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09031941 |
Feb 27, 1998 |
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08632225 |
Apr 15, 1996 |
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5725989 |
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Current U.S.
Class: |
430/200 ;
430/201; 430/271.1 |
Current CPC
Class: |
B41M 5/392 20130101;
B41M 5/465 20130101; G03F 3/108 20130101; B41M 2205/02 20130101;
B41M 2205/06 20130101; B41M 5/42 20130101; B41M 7/009 20130101;
B41M 2205/38 20130101; H01L 51/0013 20130101; B41M 5/265 20130101;
B41M 5/38214 20130101; G02F 1/133516 20130101; G02B 5/201 20130101;
B41M 5/44 20130101; B41M 5/46 20130101; Y10S 430/165 20130101; B41M
3/003 20130101; B41M 5/426 20130101; B41M 5/385 20130101 |
Class at
Publication: |
430/200 ;
430/201; 430/271.1 |
International
Class: |
G03F 007/11; G03F
007/34 |
Claims
What is claimed is:
1. A thermal transfer element comprising: a thermal transfer layer
capable of being selectively transferred from the thermal transfer
donor element when the thermal transfer donor element is exposed to
imaging radiation, wherein the thermal transfer layer comprises a
phosphor or fluorescent dye; a light-to-heat conversion layer
comprising a material that absorbs imaging radiation to convert the
radiation into heat; and an interlayer disposed between the
light-to-heat conversion layer and the transfer layer; wherein the
interlayer remains substantially intact when the thermal transfer
element is exposed to imaging radiation to selectively transfer the
thermal transfer layer.
2. The thermal transfer element of claim 1, wherein the thermal
transfer layer comprises a phosphor.
3. The thermal transfer element of claim 1, wherein the interlayer
comprises a pigment.
4. The thermal transfer element of claim 1, wherein the interlayer
does not visibly distort or decompose at temperatures below
150.degree. C.
5. The thermal transfer element of claim 1, further comprising a
second interlayer disposed between the interlayer and the transfer
layer.
6. The thermal transfer element of claim 5, wherein the second
interlayer remains substantially intact when the thermal transfer
layer is selectively transferred upon exposure of the thermal
transfer element to imaging radiation.
7. The thermal transfer element of claim 1, wherein the thermal
transfer layer comprises polymerizable or crosslinkable
material.
8. The thermal transfer element of claim 7, wherein the
polymerizable or crosslinkable material comprises monomers,
oligomers, or combinations thereof.
9. The thermal transfer element of claim 7, wherein the thermal
transfer layer further comprises a crosslinking agent.
10. The thermal transfer element of claim 7, wherein the thermal
transfer element further comprises a polymerization or crosslinking
initiator.
11. A thermal transfer element comprising: a thermal transfer layer
capable of being selectively transferred from the thermal transfer
donor element when the thermal transfer donor element is exposed to
imaging radiation, wherein the thermal transfer layer comprises
polymerizable or crosslinkable material; A light-to-heat conversion
layer comprising a material that absorbs imaging radiation to
convert the radiation into heat; and an interlayer disposed between
the light-to-heat conversion layer and the transfer layer; wherein
the interlayer remains substantially intact when the thermal
transfer element is exposed to imaging radiation to selectively
transfer the thermal transfer layer.
12. The thermal transfer element of claim 11, wherein the
polymerizable or crosslinkable material comprises monomers,
oligomers, or combinations thereof.
13. The thermal transfer element of claim 11, wherein the thermal
transfer layer further comprises a crosslinking agent.
14. The thermal transfer element of claim 11, wherein the thermal
transfer element further comprises a polymerization or crosslinking
initiator.
15. The thermal transfer element of claim 11, wherein the
interlayer does not visibly distort or decompose at temperatures
below 150.degree. C.
16. The thermal transfer element of claim 11, further comprising a
second interlayer disposed between the interlayer and the transfer
layer.
17. The thermal transfer element of claim 16, wherein the second
interlayer remains substantially intact when the thermal transfer
layer is selectively transferred upon exposure of the thermal
transfer element to imaging radiation.
18. A process for transferring an image onto a receptor comprising
the steps of: providing on a substrate a light-to-heat conversion
layer, a thermal transfer layer and an interlayer disposed between
the light-to-heat conversion layer and the thermal transfer layer,
wherein the thermal transfer layer comprises polymerizable or
crosslinkable material; placing the thermal transfer layer in
contact with a surface of the receptor; irradiating the
light-to-heat conversion layer in an imagewise pattern with a light
source to thermally transfer portions of the thermal transfer layer
corresponding to the imagewise pattern to the receptor without
transferring significant portions of the interlayer; and
polymerizing or crosslinking the polymerizable or crosslinkable
material of the portions of the thermal transfer layer transferred
to the receptor.
19. The process of claim 18, wherein the polymerizable or
crosslinkable material comprises monomers, oligomers, or
combinations thereof.
20. The process of claim 18, wherein the thermal transfer layer
further comprises a crosslinking agent.
21. The process of claim 18, wherein the thermal transfer layer
further comprises a polymerization or crosslinking initiator.
22. The process of claim 18, wherein polymerizing or crosslinking
the polymerizable or crosslinkable material comprises polymerizing
or crosslinking the polymerizable or crosslinkable material of the
portions of the thermal transfer layer transferred to the receptor
by radiation.
23. The process of claim 18, wherein polymerizing or crosslinking
the polymerizable or crosslinkable material comprises polymerizing
or crosslinking the polymerizable or crosslinkable material of the
portions of the thermal transfer layer transferred to the receptor
by heat.
24. The process of claim 18, wherein polymerizing or crosslinking
the polymerizable or crosslinkable material comprises polymerizing
or crosslinking the polymerizable or crosslinkable material of the
portions of the thermal transfer layer transferred to the receptor
by chemical curative.
25. The process of claim 18, wherein the transfer layer comprise
phosphor or fluorescent dye.
26. A process for transferring an image onto a receptor comprising
the steps of: providing on a substrate a light-to-heat conversion
layer, a thermal transfer layer and an interlayer disposed between
the light-to-heat conversion layer and the thermal transfer layer,
wherein the thermal transfer layer comprises a fluorescent dye or
phosphor; placing the thermal transfer layer in contact with a
surface of the receptor; and irradiating the light-to-heat
conversion layer in an imagewise pattern with a light source to
thermally transfer portions of the thermal transfer layer
corresponding to the imagewise pattern to the receptor without
transferring significant portions of the interlayer.
27. The process of claim 26, wherein the thermal transfer layer
comprises a phosphor.
Description
[0001] This is a continuation of Ser. No. 09/738,775, filed Dec.
15, 2000, which is a continuation of Ser. No. 09/553,294, now U.S.
Pat. No. 6,270,934, filed Apr. 20, 2000, which is a continuation of
Ser. No. 09/349,329, now U.S. Pat. No.6,099,994, filed Jul. 8,
1999, which is a continuation of Ser. No. 09/031,941, now U.S. Pat.
No. 5,981,136, filed Feb. 27, 1998, which is a divisional of Ser.
No. 08/632,225, now U.S. Pat. No. 5,725,989, filed Apr. 15,
1996.
FIELD OF INVENTION
[0002] This invention relates to thermal transfer imaging elements,
in particular, to laser addressable thermal transfer elements
having an interlayer between a radiation-absorbing/thermal
conversion layer and a transferable layer. In addition, the
invention relates to a method of using the thermal transfer element
in a thermal transfer system such as a laser addressable
system.
BACKGROUND
[0003] With the increase in electronic imaging information capacity
and use, a need for imaging systems capable of being addressed by a
variety of electronic sources is also increasing. Examples of such
imaging systems include thermal transfer, ablation (or
transparentization) and ablation-transfer imaging. These imaging
systems have been shown to be useful in a wide variety of
applications, such as, color proofing, color filter arrays for
liquid crystal display devices, printing plates, and reproduction
masks. The traditional method of recording electronic information
with, a thermal transfer imaging medium utilizes a thermal
printhead as the energy source. The information is transmitted as
electrical energy to the printhead causing a localized heating of a
thermal transfer donor sheet which then transfers material
corresponding to the image data to a receptor sheet. The two
primary types of thermal transfer donor sheets are dye sublimation
(or dye diffusion transfer) and thermal mass transfer.
Representative examples of these types of imaging systems can be
found in U.S. Pat. Nos. 4,839,224 and 4,822,643. The use of thermal
printheads as an energy source suffers several disadvantages, such
as, size limitations of the printhead, slow image recording speeds
(milliseconds), limited resolution, limited addressability, and
artifacts on the image from detrimental contact of the media with
the printhead.
[0004] The increasing availability and use of higher output compact
lasers, semiconductor light sources, laser diodes and other
radiation sources which emit in the ultraviolet, visible and
particularly in the near-infrared and infrared regions of the
electromagnetic spectrum, have allowed the use of these sources as
viable alternatives for the thermal printhead as an energy source.
The use of a radiation source such as a laser or laser diode as the
imaging source is one of the primary and preferred means for
transferring electronic information onto an image recording media.
The use of radiation to expose the media provides higher resolution
and more flexibility in format size of the final image than the
traditional thermal printhead imaging systems. In addition,
radiation sources such as lasers and laser diodes provide the
advantage of eliminating the detrimental effects from contact of
the media with the heat source. As a consequence, a need exists for
media that have the ability to be efficiently exposed by these
sources and have the ability to form images having high resolution
and improved edge sharpness.
[0005] It is well known in the art to incorporate light-absorbing
layers in thermal transfer constructions to act as light-to-heat
converters, thus allowing non-contact imaging using radiation
sources such as lasers and laser diodes as energy sources.
Representative examples of these types of elements can be found in
U.S. Pat. Nos. 5,308,737; 5,278,023; 5,256,506; and 5,156,938. The
transfer layer may contain light absorbing materials such that the
transfer layer itself functions as the light-to-heat conversion
layer. Alternatively, the light-to-heat conversion layer may be a
separate layer, for instance, a separate layer between the
substrate and the transfer layer. Constructions in which the
transfer layer itself functions as the light-to-heat conversion
layer may require the addition of an additive to increase the
absorption of incident radiation and effect transfer to a receptor.
In these cases, the presence of the absorber in the transferred
image may have a detrimental effect upon the performance of the
imaged object (e.g., visible absorption which reduces the optical
purity of the colors in the transferred image, reduced transferred
image stability incompatibility between the absorber and other
components present in the imaging layer, etc.).
[0006] Contamination of the transferred image by the light-to-heat
conversion layer itself is often observed when using donor
constructions having a separate light-to-heat conversion layer
contamination of the transferred image by such unintended transfer
of the light-to-heat conversion layer occurs and the light-to-heat
conversion layer possesses an optical absorbance that interferes
with the performance of the transferred image (e.g., transfer of a
portion of a black body light-to-heat conversion layer to a color
filter array color proof), the incidental transfer of the
light-to-heat conversion layer to the receptor is particularly
detrimental to quality of the imaged article. Similarly, mechanical
or thermal distortion of the light-to-heat conversion layer during
imaging is common and negatively impacts the quality of the
transferred coating. U.S. Pat. No. 5,171,650 discloses methods and
materials for thermal imaging using an "ablation-transfer"
technique. The donor element used in the imaging process comprises
a support, an intermediate dynamic release layer, and an ablative
carrier topcoat containing a colorant. Both the dynamic release
layer and the color carrier layer may contain an infrared-absorbing
(light to heat conversion) dye or pigment. A colored image is
produced by placing the donor element in intimate contact with a
receptor and then irradiating the donor with a coherent light
source in an imagewise pattern. The colored carrier layer is
simultaneously released and propelled away from the dynamic release
layer in the light struck areas creating a colored image on the
receptor.
[0007] Co-pending U.S. application Ser. No. 07/855,799 filed Mar.
23, 1992 discloses ablative imaging elements comprising a substrate
coated on a portion thereof with a energy sensitive layer
comprising a glycidyl azide polymer in combination with a radiation
absorber. Demonstrated imaging sources included infrared, visible,
and ultraviolet lasers. Solid state lasers were disclosed as
exposure sources, although laser diodes were not specifically
mentioned. This application is primarily concerned with the
formation of relief printing plates and lithographic plates by
ablation of the energy sensitive layer. No specific mention of
utility for thermal mass transfer was made.
[0008] U.S. Pat. No. 5,308,737 discloses the use of black metal
layers on polymeric substrates with gas-producing polymer layers
which generate relatively high volumes of gas when irradiated. The
black metal (e.g., black aluminum) absorbs the radiation
efficiently and converts it to heat for the gas-generating
materials. It is observed in the examples that in some cases the
black metal was eliminated from the substrate, leaving a positive
image on the substrate.
[0009] U.S. Pat. No. 5,278,023 discloses laser-addressable thermal
transfer materials for producing color proofs, printing plates,
films, printed circuit boards, and other media. The materials
contain a substrate coated thereon with a propellant layer wherein
the propellant layer contains a material capable of producing
nitrogen (N.sub.2) gas at a temperature of preferably less than
about 300.degree. C.; a radiation absorber; and a thermal mass
transfer material. The thermal mass transfer material may be
incorporated into the propellant layer or in an additional layer
coated onto the propellant layer. The radiation absorber may be
employed in one of the above-disclosed layers or in a separate
layer in order to achieve localized heating with an electromagnetic
energy source, such as a laser. Upon laser induced heating, the
transfer material is propelled to the receptor by the rapid
expansion of gas. The thermal mass transfer material may contain,
for example, pigments, toner particles, resins, metal particles,
monomers, polymers, dyes, or combinations thereof. Also disclosed
is a process for forming an image as well as an imaged article made
thereby.
[0010] Laser-induced mass transfer processes have the advantage of
very short heating times (nanoseconds to microseconds); whereas,
the conventional thermal mass transfer methods are relatively slow
due to the longer dwell times (milliseconds) required to heat the
printhead and transfer the heat to the donor. The transferred
images generated under laser-induced ablation imaging conditions
are often fragmented (being propelled from the surface as
particulates or fragments). The images from thermal melt stick
transfer systems tend to show deformities on the surface of the
transferred material. Therefore, there is a need for a thermal
transfer system that takes advantage of the speed and efficiency of
laser addressable systems without sacrificing image quality or
resolution.
SUMMARY OF THE INVENTION
[0011] The present invention relates to a thermal transfer element
comprising a substrate having deposited thereon (a) a light-to-heat
conversion layer, (b) an interlayer, and (c) a thermal transfer
layer. The thermal transfer layer may additionally comprise
crosslinkable materials.
[0012] The present invention also provides a method for generating
an image on a receptor using the above described thermal transfer
element. An image is transferred onto a receptor by (a) placing in
intimate contact a receptor and the thermal transfer element
described above, (b) exposing the thermal transfer element in an
imagewise pattern with a radiation source, and (c) transferring the
thermal transfer layer corresponding to the imagewise pattern to
the receptor, with insignificant or no transfer of the
light-to-heat conversion layer. When the thermal transfer layer
contains crosslinkable materials, an additional curing step may be
performed where the transferred image is subsequently crosslinked
by exposure to heat or radiation, or treatment with chemical
curatives.
[0013] The phrase "in intimate contact" refers to sufficient
contact between two surfaces such that the transfer of materials
maybe accomplished during the imaging process to provide a
sufficient transfer of material within the thermally addressed
areas. In other words, no voids are present in the imaged areas
which would render the transferred image non-functional in its
intended application.
[0014] Other aspects, advantages, and benefits of the present
invention are apparent from the detailed description, the examples,
and the claims.
DETAILED DESCRIPTION OF INVENTION
[0015] A thermal transfer element is provided comprising a light
transparent substrate having deposited thereon, in the following
order, a light-to-heat conversion (LTHC) layer, a heat stable inter
layer, and a thermal transfer layer. The substrate is typically a
polyester film, for example, poly(ethylene terephthalate) or
poly(ethylene naphthalate). However, any film that has appropriate
optical properties and sufficient mechanical stability can be
used.
Light-to-heat Conversion Layer
[0016] In order to couple the energy of the exposure source into
the imaging construction it is especially desirable to incorporate
a light-to-heat conversion (LTHC) layer within the construction.
The LTHC layer comprises a material which absorbs at least at the
wavelength of irradiation and converts a portion of the incident
radiation into sufficient heat to enable transfer the thermal
transfer layer from the donor to the receptor. Typically, LTHC
layers will be absorptive in the infrared region of the
electromagnetic spectrum, but in some instances visible or
ultraviolet absorptions may be selected. It is generally desirable
for the radiation absorber to be highly absorptive of the imaging
radiation, enabling an optical density at the wavelength of the
imaging radiation in the range of 0.2 to 3.0 using a minimum amount
of radiation absorber to be used.
[0017] Dyes suitable for use as radiation absorbers in a LTHC layer
may be present in particulate form or preferably substantially in
molecular dispersion. Especially preferred are dyes absorbing in
the IR region of the spectrum. Examples of such dyes may be found
in Matsuoka, M., Infrared Absorbing Materials, Plenum Press, New
York, 1990, and in Matsuoka, M., Absorption Spectra of Dyes for
Diode Lasers, Bunshin Publishing Co., Tokyo, 1990. IR absorbers
marketed by American Cyanamid or Glendale Protective Technologies,
Inc., Lakeland, Fla., under the designation CYASORB IR-99, IR-126
and IR-165 may also be used. Such dyes will be chosen for
solubility in, and compatibility with, the specific polymer and
coating solvent in question.
[0018] Pigmentary materials may also be dispersed in the LTHC layer
for use as radiation absorbers. Examples include carbon black and
graphite as well as phthalocyanines, nickel dithiolenes, and other
pigments described in U.S. Pat. Nos. 5,166,024 and 5,351,617.
Additionally, black azo pigments based on copper or chromium
complexes of, for example, pyrazolone yellow, dianisidine red, and
nickel azo yellow are useful. Inorganic pigments are also valuable.
Examples include oxides and sulfides of metals such as aluminum,
bismuth, tin, indium, zinc, titanium, chromium, molybdenum,
tungsten, cobalt, iridium, nickel, palladium, platinum, copper,
silver, gold, zirconium, iron, lead or tellurium. Metal borides,
carbides, nitrides, carbonitrides, bronze-structured oxides, and
oxides structurally related to the bronze family (e.g. WO.sub.2.9)
are also of utility.
[0019] When dispersed particulate radiation absorbers are used, it
is preferred that the particle size be less than about 10
micrometers, and especially preferred that the particle size be
less than about 1 micrometer. Metals themselves may be employed,
either in the form of particles, as described for instance in U.S.
Pat. No. 4,252,671, or as films as disclosed in U.S. Pat. No.
5,256,506. Suitable metals include aluminum, bismuth, tin, indium,
tellurium and zinc.
[0020] Suitable binders for use in the LTHC layer include
film-forming polymers, such as for example, phenolic resins (i.e.,
novolak and resole resins), polyvinyl butyral resins,
polyvinylacetates, polyvinyl acetals, polyvinylidene chlorides,
polyacrylates, cellulosic ethers and esters, nitrocelluloses, and
polycarbonates. The absorber-to-binder ratio is generally from 5:1
to 1:100 by weight depending on what type of absorbers and binders
are used. Conventional coating aids, such as surfactants and
dispersing agents, may be added to facilitate the coating process.
The LTHC layer may be coated onto the substrate using a variety of
coating methods known in the art. The LTHC layer is coated to a
thickness of 0.001 to 20.0 micrometers, preferably 0.01 to 5.0
micrometers. The desired thickness of the LTHC layer will depend
upon the composition of the layer. A preferred LTHC layer is a
pigment/binder layer. A particularly preferred pigment based LTHC
layer is carbon black dispersed in an organic polymeric binder.
Alternatively, other preferred LTHC layers include metal or
metal/metal oxide layers (e.g. black aluminum which is a partially
oxidized aluminum having a black visual appearance).
Interlayer Construction
[0021] The interlayer may comprise an organic and/or inorganic
material. In order to minimize damage and contamination of the
resultant transferred image, the interlayer should have high
thermal resistance. Preferably, the layer should not visibly
distort or chemically decompose at temperatures below 150.degree.
C. These properties may be readily provided by polymeric film
(thermoplastic or thermoset layers), metal layers (e.g., vapor
deposited metal layers), inorganic, layers (e.g., sol-gel deposited
layers, vapor deposited layers of inorganic oxides [e.g., silica,
titania, etc., including metal oxides]), and organic/inorganic
composite layers (thermoplastic or thermoset layers). Organic
materials suitable as interlayer materials include both thermoset
(crosslinked and thermoplastic materials. In both cases, the
material chosen for the interlayer should be film forming and
should remain substantially intact during the imaging process. This
can be accomplished by the proper selection of materials based on
their thermal and/or mechanical properties. As a guideline, the
T.sub.g of the thermoplastic materials should be greater than
150.degree. C., more preferably greater than 180.degree. C. The
interlayer may be either transmissive, absorbing, reflective, or
some combination thereof at the imaging radiation wavelength.
[0022] The surface characteristics of the interlayer will depend on
the application for which the imaged article is to be used.
Frequently, it will be desirable to have an interlayer with a
"smooth" surface so as not to impart adverse texture to the surface
of the thermally transferred layer. This is especially important
for applications requiring rigid dimensional tolerances such as for
color filter elements for liquid crystal displays. However, for
other applications surface "roughness" or "surface patterns" may be
tolerable or even desirable.
[0023] The interlayer provides a number of desirable benefits. The
interlayer is essentially a barrier against the transfer of
material from the light-to-heat conversion layer. The interlayer
can also prevent distortion of the transferred thermal transfer
layer material. It may also modulate the temperature attained in
the thermal transfer layer so that more thermally unstable
materials can be transferred and may also result in improved
plastic memory in the transferred material. It is also to be noted
that the interlayer of the present invention, when placed over the
LTHC layer, is incompatible with propulsively ablative systems like
those of U.S. Pat. Nos. 5,156,938; 5,171,650; and 5,256,506 because
the interlayer would act as a barrier to prevent propulsive forces
from the LTHC layer from acting on the thermal transfer layer. The
gas-generating layers disclosed in those patents also would not
qualify as interlayers according to the present invention, as those
layers must be thermally unstable at the imaging temperatures to
decompose and generate the gas to propel material from the
surface.
[0024] Suitable thermoset resins include materials which may be
crosslinked by thermal, radiation, or chemical treatment including,
but not limited to, crosslinked poly(meth)acrylates, polyesters,
epoxies, polyurethanes, etc. For ease of application, the thermoset
materials are usually coated onto the light-to-heat conversion
layer as thermoplastic precursors and subsequently crosslinked to
form the desired crosslinked interlayer.
[0025] In the case of thermoplastic materials, any material which
meets the above-mentioned functional criteria may be employed as an
interlayer material. Accordingly, the preferred materials will
possess chemical stability and mechanical integrity under the
imaging conditions.,Classes of preferred thermoplastic materials
include polysulfones, polyesters, polyimides, etc. These
thermoplastic organic materials may be applied to the light-to-heat
conversion layer via conventional coating techniques (solvent
coating, etc.).
[0026] In the cases of interlayers comprised of organic materials,
the interlayers may also contain appropriate additives including
photoinitiators, surfactants, pigments, plasticizers, coating aids,
etc. The optimum thickness of an organic interlayer is material
dependent and, in general, will be the minimum thickness at which
transfer of the light-to-heat conversion layer and distortion of
the transferred layer are reduced to levels acceptable for the
intended application (which will generally be between 0.05 .mu.m
and 10 .mu.m).
[0027] Inorganic materials suitable as interlayer materials include
metals, metal oxides, metal sulfides, inorganic carbon coatings,
etc., including those which are highly transmissive or reflective
at the imaging laser wavelength. These materials may be applied to
the light-to-heat-conversion layer via conventional techniques
(e.g., vacuum sputtering, vacuum evaporation, plasma jet, etc.).
The optimum thickness of an inorganic interlayer will again be
material dependent. The optimum thickness will be, in general, the
minimum thickness at which transfer of the light-to-heat conversion
layer and distortion of the transferred layer are reduced to an
acceptable level (which will generally be between 0.01 .mu.m and 10
.mu.m).
[0028] In the case of reflective interlayers, the interlayer
comprises a highly reflective material, such as aluminum or
coatings of TiO.sub.2 based inks. The reflective material should be
capable of forming an image-releasing surface for the overlying
colorant layer and should remain intact during the colorant coating
process. The interlayer should not melt or transfer under imaging
conditions. In the case where imaging is performed via irradiation
from the donor side, a reflective interlayer will attenuate the
level of imaging radiation transmitted through the interlayer and
thereby reduce any damage to the resultant image that might result
from interaction of the transmitted radiation with the transfer
layer and/or receptor. This is particularly beneficial in reducing
thermal damage to the transferred image which might occur when the
receptor is highly absorptive of the imaging radiation. Optionally,
the thermal transfer donor element may comprise several
interlayers, for example, both a reflective and transmissive
interlayer, the sequencing of which would be dependent upon the
imaging and end-use application requirements.
[0029] Suitable highly reflective metallic films include aluminum,
chrome, and silver. Suitable pigment based inks include standard
white pigments such as titanium dioxide, calcium carbonate, and
barium sulfate used in conjunction with a binder. The binder may be
either a thermoplastic or thermoset material. Preferred binders
include high T.sub.g resins such as polysulfones, polyarylsulfones,
polyarylethersulfones, polyetherimides, polyarylates, polyimides,
polyetheretherketones, and polyamideimides (thermoplastics) and
polyesters, epoxies, polyacrylates, polyurethanes,
phenol-formaldehydes, urea-formaldehydes, and
melamine-formaldehydes (thermosets), etc.
[0030] Polymerizable or crosslinkable monomers, oligomers,
prepolymers and polymers may be used as binders and crosslinked to
form the desired heat-resistant, reflective interlayer after the
coating process. The monomers, oligomers, prepolymers and polymers
that are suitable for this application include known chemicals that
can form a heat resistant polymeric layer. The layer may also
contain additives such as crosslinkers, surfactants, coating aids,
and pigments.
[0031] The reflective layer thickness can be optimized with respect
to imaging performance, sensitivity, and surface smoothness.
Normally the thickness of the interlayer is 0.005 to 5 microns,
preferably between 0.01 to 2.0 microns. Optionally, the reflective
interlayer may be overcoated with a non-pigmented polymeric
interlayer to allow a better release of color image.
Thermal Transfer Layer
[0032] The transfer layer is formulated to be appropriate for the
corresponding imaging application (e.g., color proofing, printing
plate, color filters, etc.). The transfer layer may itself be
comprised of thermoplastic and/or thermoset materials. In many
product applications (for example, in printing plate and color
filter applications) the transfer layer materials are preferably
crosslinked after laser transfer in order to improve performance of
the imaged article. Additives included in the transfer layer will
again be specific to the end-use application (e.g., colorants for
color proofing and color filter applications, photoinitiators for
photo-crosslinked or photo-crosslinkable transfer layers, etc.,)
and are well known to those skilled in the art.
[0033] Because the interlayer can modulate the temperature attained
in the thermal transfer layer, materials which tend to be more
sensitive to heat than typical pigments may be transferred with
reduced damage using the process of the present invention. For
example, medical diagnostic chemistry can be included in a binder
and transferred to a medical test card using the present invention
with less likelihood of damage to the medical chemistry and less
possibility of corruption of the test results. A chemical or
enzymatic indicator would be less likely to be damaged using the
present invention with an interlayer compared to the same material
transferred from a conventional thermal donor element.
[0034] The thermal transfer layer may comprise classes of materials
including, but not limited to dyes (e.g., visible dyes, ultraviolet
dyes, fluorescent dyes, radiation-polarizing dyes, IR dyes, etc.),
optically active materials, pigments (e.g., transparent pigments,
colored pigments, black body absorbers, etc.), magnetic particles,
electrically conducting insulating particles, liquid crystal
materials, hydrophilic or hydrophobic materials, initiators,
sensitizers, phosphors, polymeric binders, enzymes, etc. For many
applications such as color proofing and color filter elements, the
thermal transfer layer will comprise colorants. Preferably the
thermal transfer layer will comprise at least one organic or
inorganic colorant (i.e., pigments or dyes) and a thermoplastic
binder. Other additives may also be included such as an IR
absorber, dispersing agents, surfactants, stabilizers,
plasticizers, crosslinking agents and coating aids. Any pigment may
be used, but for applications such as color filter elements,
preferred pigments are those listed as having good color permanency
and transparency in the NPIRI Raw Materials Data Handbook, Volume 4
(Pigments) or W. Herbst, Industrial Organic Pigments, VCH, 1993.
Either non-aqueous or aqueous pigment dispersions may be used. The
pigments are generally introduced into the color formulation in the
form of a millbase comprising the pigment dispersed with a binder
and suspended into a solvent or mixture of solvents. The pigment
type and color are chosen such that the color coating is matched to
a preset color target or specification set by the industry. The
type of dispersing resin and the pigment-to-resin ratio will depend
upon the pigment type, surface treatment on the pigment, dispersing
solvent and milling process used in generating the millbase.
Suitable dispersing resins include vinyl chloride/vinyl acetate
copolymers, poly(vinyl acetate)/crotonic acid copolymers,
polyurethanes, styrene maleic anhydride half ester resins,
(meth)acrylate polymers and copolymers, poly(vinyl acetals),
poly(vinyl acetals) modified with anhydrides and amines, hydroxy
alkyl cellulose resins and styrene acrylic resins. A preferred
color transfer coating composition comprises 30-80% by weight
pigment, 15-60% by weight resin, and 0-20% by weight dispersing
agents and additives.
[0035] The amount of binder present in the color transfer layer is
kept to a minimum to avoid loss of image resolution and/or imaging
sensitivity due to excessive cohesion in the color transfer layer.
The pigment-to-binder ratio is typically between 10:1 to 1:10 by
weight depending on the type of pigments and binders used. The
binder system may also include polymerizable and/or crosslinkable
materials (i.e., monomers, oligomers, prepolymers, and/or polymers)
and optionally an initiator system. Using monomers or oligomers
assists in reducing the binder cohesive force in the color transfer
layer, therefore improving imaging sensitivity and/or transferred
image resolution. Incorporation of a crosslinkable composition into
the color transfer layer allows one to produce a more durable and
solvent resistant image. A highly crosslinked image is formed by
first transferring the image to a receptor and then exposing the
transferred image to radiation, heat and/or a chemical curative to
crosslink the polymerizable materials. In the case where radiation
is employed to crosslink the composition, any radiation source can
be used that is absorbed by the transferred image. Preferably the
composition comprises a composition which may be crosslinked with
an ultraviolet radiation source.
[0036] The color transfer layer may be coated by any conventional
coating method known in the art. It may be desirable to add coating
aids such as surfactants and dispersing agents to provide an
uniform coating. Preferably, the layer has a thickness from about
0.05 to 10.0 micrometers, more preferably from 0.5 to 2.0
micrometers.
Receiver
[0037] The image receiving substrate may be any substrate suitable
for the application including, but not limited to various papers,
transparent films, LCD black matrices, active portions of LCD
displays, metals, etc. Suitable receptors are well known to those
skilled in the art. Non-limiting examples of receptors which can be
used in the present invention include anodized aluminum and other
metals, transparent plastic films (e.g., PET), glass, and a variety
of different types of paper (e.g., filled or unfilled, calendered,
coated, etc.). Various layers (e.g., an adhesive layer) may be
coated onto the image receiving substrate to facilitate transfer of
the transfer layer to the receiver.
Imaging Process
[0038] The process of the present invention may be performed by
fairly simple steps. During imaging, the donor sheet is brought
into intimate contact with a receptor sheet under pressure or
vacuum. A radiation source is then used to heat the LTHC layer in
an imagewise fashion (e.g., digitally, analog exposure through a
mask, etc.) or to perform imagewise transfer of the thermal
transfer layer from the donor to the receptor.
[0039] The interlayer reduces the transfer of the LTHC layer to the
receptor and/or reduces distortion in the transferred layer.
Without this interlayer in thermal mass transfer processes
addressed by radiation sources, the topography of the transfer
surface from the light-to-heat conversion layer may be observably
altered. A significant topography of deformations and wrinkles may
be formed. This topography may be imprinted on the transferred
donor material. This imprinting of the image alters the
reflectivity of the transferred image (rendering it less reflective
than intended) and can cause other undesirable visual effects. It
is preferred that under imaging conditions, the adhesion of the
interlayer to the LTHC layer be greater than the adhesion of the
interlayer to the thermal transfer layer. In the case where imaging
is performed via irradiation from the donor side, a reflective
interlayer will attenuate the level of imaging radiation
transmitted through the interlayer and thereby reduce any
transferred image damage that may result from interaction of the
transmitted radiation with the transfer layer and/or the receptor.
This is particularly beneficial in reducing thermal damage which
may occur to the transferred image when the receptor is highly
absorptive of the imaging radiation.
[0040] A variety of light-emitting sources can be utilized in the
present invention. Infrared, visible, and ultraviolet lasers are
particularly useful when using digital imaging techniques. When
analog techniques are used (e.g., exposure through a mask) high
powered light sources (e.g, xenon flash lamps, etc.) are also
useful. Preferred lasers for use in this invention include high
power (>100 mW) single mode laser diodes, fiber-coupled laser
diodes, and diode-pumped solid state lasers (e.g. Nd:YAG and
Nd:YLF). Laser exposure dwell times should be from about 0.1 to 5
microseconds and laser fluences should be from about 0.01 to about
1 Joules/cm.sup.2.
[0041] During laser exposure, it may be desirable to minimize
formation of interference patterns due to multiple reflections from
the imaged material. This can be accomplished by various methods.
The most common method is to effectively roughen the surface of the
donor material on the scale of the incident radiation as described
in U.S. Pat. No. 5,089,372. This has the effect of disrupting the
spatial coherence of the incident radiation, thus minimizing self
interference. An alternate method is to employ the use of an
antireflection coating on the second interface that the incident
illumination encounters. The use of anti-reflection coatings is
well known in the art, and may consist of quarter-wave thicknesses
of a coating such as magnesium fluoride, as described in U.S. Pat
No. 5,171,650. Due to cost and manufacturing constraints, the
surface roughening approach is preferred in many applications.
[0042] The following non-limiting examples further illustrate the
present invention.
EXAMPLES
[0043] Materials used in the following examples are available from
standard commercial sources such as Aldrich Chemical Co.
(Milwaukee, Wis.) unless otherwise specified. The preparation of
hydantoin hexacrylate used in Example Compound A in U.S. Pat. Nos.
4,249,011 and 4,262,072.
Laser Imaging Procedure A
[0044] The colorant coating side of a thermal transfer donor was
held in intimate contact with a 75 mm.times.50 mm.times.1 mm glass
slide (receptor) in a vacuum chuck such that the laser was incident
upon the substrate (PET) side of the donor and normal to the
donor/receptor surface. The vacuum chuck was attached to an X-Y
translation stage such that it could be scanned in the plane of the
donor/receptor surface, allowing laser exposure over the entire
surface. A CW(continuous wave) N:YAG laser system was used for
exposure, providing up to 14.5 Watts at 1064 nm in the film plane.
The laser had a Gaussian spatial profile with the spot size
tailored using external optics. An acoustic-optic modulator allowed
control of the laser power from .about.0 to 80%, the laser pulse
width from .about.20 ns to CW. The X-Y stage and laser power, pulse
width and repetition rate were computer controlled allowing
programmed patterns to be imaged.
Laser Imaging Procedure B
[0045] The colorant coating side of a thermal transfer donor was
held in intimate contact with a 75 mm.times.50 mm.times.1 mm glass
slide (receptor) in a vacuum chuck such that the laser was incident
upon the substrate (PET) side of the donor. The vacuum chuck was
attached to a one dimensional translation stage such that it could
be scanned in plane of the donor/receptor surface, allowing laser
exposure over the entire surface. An optical system comprised of a
CW Nd:YAG laser, acousto-optic modulator, collimating and beam
expanding optics, an optical isolator, a linear galvanometer and an
f-theta scan lens was utilized. The ND:YAG laser was operating in
the TEM 00 mode, and produced a total power of 7.5 Watts on the
image plane. Scanning was accomplished with the high precision
linear Cambridge Technology Galvonometer. The laser was focused to
a Gaussian spot with a measured diameter of 140 microns at the
1/e.sup.2 intensity level. The spot was held constant across the
scan width by utilizing an f-theta scan lens. The laser spot was
scanned across the image surface at a velocity of 7.92
meters/second. The f-theta scan lens held the scan velocity uniform
to within 0.1%, and the spot size constant to within .+-.3
microns.
Example 1
Comparative Example
[0046] This example demonstrates the preparation and use of a
thermal transfer donor without an interlayer.
[0047] A black aluminum (partially oxidized Al, AlO.sub.x)
light-to-heat conversion layer with a transmission optical density
(TOD=-logT, where T is the measured fractional transmission) of
0.53 at 1060 nm was coated onto a 4 mil poly(ethylene
terephthalate) (PET) substrate via reactive sputtering of Al in an
Ar/O.sub.2 atmosphere in a continuous vacuum coater according to
the teachings of U.S. Pat. No. 4,430,366. This AlO.sub.x
light-to-heat conversion layer was then overcoated with a red color
ink with 26.5 weight % total nonvolatiles content (CRY-S089,
produced by Fuji-Hunt Electronics Technology Co., LTD, Tokyo,
Japan) using a #5 coating rod and dried to produce a thermal
transfer donor.
[0048] This donor was then tested for transfer of the thermal
transfer layer to a glass slide receptor, which had been precoated
with a vinyl acrylic copolymer (Wallpol 40148-00, Reichhold
Chemicals, Inc. Research Triangle Park, N.C.). The above-described
Laser Imaging Procedure A was employed, the laser spot size
diameter (1/e.sup.2) was 100 .mu.m the power at the film plane was
8.4 Watts, and exposures were performed at pulse widths of 4, 6, 8
and 10 microseconds.
[0049] The results showed that, although color images were formed
on the receptor at the four different pulse widths, the images were
discolored. A microscopic examination of the images revealed that
the red color images were contaminated with the black aluminum
light-to-heat conversion layer which had transferred from the
donor.
Example 2
[0050] This example demonstrates the preparation and use of a
thermal transfer donor with a thermoset interlayer.
[0051] The same black aluminum light-to-heat conversion layer
referenced in Example 1 was coated with a 5 weight % solution of
hydantoin hexacrylate (49 parts by weight), 1,6-hexanediol
diacrylate (49 parts by weight) and
2,2-dimethoxy-2-phenylacetophenone (2 parts by weight) in
2-butanone using a #5 coating rod, dried and then radiation
crosslinked via exposure in a Radiation Polymer Corporation
(Plainfield, Ill.) UV Processor Model No. QC 1202AN3TR. (medium
pressure uv lamp, total, exposure ca. 100 millijoules/cm.sup.2,
N.sub.2 atmosphere) to produce an interlayer. The cured interlayer
was smooth, non-tacky, and resistant to many organic solvents
including 2-butanone. The cured interlayer was then overcoated with
the same red color ink employing the same coating procedures as
described in Example 1.
[0052] The resulting donor was tested for transfer of the thermal
transfer layer to a glass slide receptor employing laser imaging
conditions identical to those described in Example 1.
[0053] A microscopic examination of the images on the receptor
clearly indicated that the red color images were free of black
aluminum contamination. The same microscopic examination of the
imaged area of the donor showed that the interlayer and black
aluminum light-to-heat conversion layer remained intact on the
thermal transfer donor.
Example 3
[0054] This example demonstrates the preparation and use of a
thermal transfer donor with a thermoplastic interlayer.
[0055] The same black aluminum light-to-heat conversion layer
referenced in Example was coated with a 10 weight % solution of
Radel A-100 polysulfone resin (Amoco Performance Products, Inc.,
Alpharetta, Ga.) in 1,1,2-trichloroethane using a #12 coating rod.
The Kadel A-100 interlayer was then overcoated with the same red
color ink and employing the same coating procedures as described in
Example 1.
[0056] The resulting donor was tested for transfer of the thermal
transfer layer to a glass slide receptor employing laser imaging
conditions identical to that described in Example 1. The results
again showed that the color images were formed on the receptor at
the four different pulse widths. A microscopic examinations of the
images on the receptor clearly indicated that the red color images
were free of black aluminum contamination. The same microscopic
examination of the imaged area of the donor showed again that the
interlayer and black aluminum light-to-heat conversion layer
remained intact on the thermal transfer donor.
Example 4
[0057] This example demonstrates the preparation and use of a
thermal transfer donor with an inorganic interlayer.
[0058] A black aluminum (AlO.sub.x) coating was deposited onto 4
mil poly(ethylene terephthalate) (PET) substrate via evaporation
oral in a partial O.sub.2 atmosphere according to the teachings of
U.S. Pat. No. 4,430,366. The transmission and reflection spectra of
the resultant coating on PET were measured from both the black
aluminum coating side and the substrate (PET) side using a Shimadzu
MPC-3100 spectrophotometer with an integrating sphere (Shimadzu
Scientific Instruments, Inc., Columbia, Md.). The transmission
optical densities (TOD=-logT, where T is the measured fractional
transmission) and reflection optical densities (ROD=-logR, where R
is the measured fractional reflectance) at 1060 nm are listed in
Table 1. The thickness of the black aluminum coating was determined
to be 1100 .ANG. by profilometry after masking and etching a
portion of the coating with 20 percent by weight aqueous sodium
hydroxide.
1 TABLE 1 Side of TOD ROD Incident Beam (at 1060 nm) (at 1060 nm)
Coating 1.047 0.427 Substrate 1.050 0.456
[0059] An alumina interlayer (approximately 1000 .ANG. thick) was
coated onto the black aluminum surface by evaporation of
Al.sub.2O.sub.3 in a vacuum coater.
[0060] A colorant coating solution was prepared by combining and
mixing 2 grams of 10 weight % Heucotech GW3451 Lot 3F2299 PG 7
binderless pigment dispersion (Heucotech Ltd., Fairless Hills,
Pa.), 0.917 grams deionized H.sub.2O, 0.833 grams of 18 weight %
Elvacite.RTM. 2776 in water (prepared by mixing 0.8 g of a 25%
ammonia solution and 22 g water, and 5 g of Elvacite.RTM. 2776 from
ICI Acrylics, Wilmington, Del.) and 10 drops of a 1 weight %
solution of FC-170C fluorochemical surfactant (3M, St. Paul,
Minn.). This green coating solution was coated onto the alumina
surface using a #4 coating rod. The resultant green donor media was
dried at 50.degree. C. for 2 minutes. The same green solution was
coated onto the black aluminum (AlO.sub.x) surface of the
light-to-heat conversion film that did not have the alumina
interlayer using #4 coating rod. The resultant green donor media
was dried at 50.degree. C. for 2 minutes.
[0061] These two donors, one with an alumina interlayer and the
other without, were imaged onto glass receptors to make color
filter elements for a liquid crystal display via laser induced
thermal transfer imaging (LITI) utilizing the above-described Laser
Imaging Procedure A. For these experiments, the laser spot diameter
size (1/e.sup.2) was 100 .mu.m, the power at the film plane was 4.2
Watts, and the pulse width was 8 .mu.sec. The amount of black
aluminum contamination of the resultant color filters was then
quantified via digitizing micrographs of the corresponding color
filters and subsequent image analysis with IPLAB Spectrum-NV (Siga
Analytics Corp., Vienna, Va.). The analyses indicate that the
average area of the black aluminum light-to-heat conversion layer
transferred to the receptor per imaged spot was 4 .mu.m.sup.2 black
aluminum contamination per spot for the sample with the alumina
interlayer vs. 125 .mu.m.sup.2 for the sample with no
interlayer.
[0062] These results demonstrate the efficacy of the interlayer in
improving transferred image quality and preventing image
contamination with the light-to-heat conversion
Example 5
[0063] This example demonstrates the preparation and use of a
thermal transfer donor with a thermoset interlayer and a
crosslinkable transfer layer.
[0064] A carbon black light-to-heat conversion layer was prepared
by coating an aqueous dispersion of carbon black in a radiation
curable resin onto a 2 mil PET substrate with a Yasui Seiki Lab
Coater, Model CAG-150 (Yasui Seiki Co., Bloomington, Ind.) using a
microgravure roll of 90 helical cells per lineal inch. The coating
was subsequently in-line dried and uv-cured on the coater before
windup. The coating solution consisted of 16.78 weight % of a
urethane-acrylate oligomer (Neorad NR-440 from Zeneca Resins,
Wilmington, Mass.), 0.84 weight % of
2-hydroxy-2-methyl-1-phenyl-1-propanone photoinitiator (Darocur
1173, Ciba-Geigy, Hawthorne, N.Y.), 2.38 weight % of carbon black
(Sunsperse Black 7, Sun Chemical, Amelia, Ohio), a 80 weight % of
water having a pH of ca. 8.5.
[0065] The light-to-heat conversion layer was then overcoated with
an interlayer coating utilizing the above-described coater with a
microgravure roll of 110 helical cells per lineal inch. After the
interlayer was coated, it was in-line dried and uv-cured. The
interlayer coating solution consisted of 19.8 weight % of a
urethane-acrylate oligomer (Neorad NR-440 from Zeneca Resins,
Wilmington, Mass.), 1.0 weight % of 2-hydroxy-2
methyl-1-phenyl-1-propanone photoinitiator (Darocur 1173,
Ciba-Geigy, Hawthorne, N.Y.), and 79.2 weight % of water having a
pH of 8.5.
[0066] The colorant transfer layer was a 15 weight % nonvolatiles
content aqueous dispersion prepared by Penn Color, Doylestown, Pa.,
and consisted of Pigment Green 7 and Elvacite 2776 (ICI Acrylics,
Inc., Wilmington, Del.) neutralized with dimethylethanolamine at a
3:2 pigment/binder ratio, containing 4 weight % Primid XL-552 (EMS
American Grilon, Sumter, S.C.) relative to the polymer, and 1
weight % Triton X-100 relative to the total nonvolatiles content.
This dispersion was coated onto the interlayer using a #3 coating
rod and the resultant coating was dried at 80.degree. C. for 3
minutes.
[0067] The colorant layer was then transferred to two glass slides
using imaging conditions employing Laser Imaging Procedure B to
produce LCD color filter elements. The colorant transferred to the
glass slides (lines ca. 90 micrometers wide with a line-to-line
spacing of ca. 150 micrometers) with no contamination of the carbon
black layer. Microscopic examination of the donor sheet showed the
carbon black composite light-to-heat conversion layer and the
protective clear interlayer were intact. One of the color filter
elements was then placed in an oven and heated at 2000.degree. C.
in a nitrogen atmosphere for one hour in order to activate the
crosslinking-chemistry between the Primid XL552 and the Elvacite
2776. The other color filter element was not heated, but maintained
at ambient temperature. Each of the resultant color filter elements
was then cut into three ca. 25 mm.times.37 mm sections. One of the
sections derived from each of these color filter elements was then
immersed in 10 ml of 1-methyl-2-pyrrolidinone for 10 minutes. The
color filter elements were then removed from the immersion
solvents. The visible spectra of the solutions resulting from
extractions of these color filter elements were then obtained in a
quartz cuvette with a 1 cm path length on a Shimadzu MPC-3100
spectrophotometer. These spectra indicated the .lambda..sub.max of
the color cell array extracts to be at ca. 629 nm, with good
chemical resistance of each of the color cell array elements
corresponding to low absorbance of its 1-methyl-2-pyrrolidinone
extract at 629 nm. The corresponding results of the chemical
resistance testing of the crosslinked and uncrosslinked color
filter element are provided in Table 2.
2TABLE 2 Color Filter Element Absorbance of Corresponding
1-Methyl-2- Designation Pyrrolidinone Extract (629 nm)
uncrosslinked color array 0.53 crosslinked color array 0.04 neat
solvent (1-methyl-2- 0.04 pyrrolidinone)
[0068] The above results demonstrate the efficacy of the interlayer
in improving the quality of the transferred image, and the
effectiveness of crosslinking the transferred coating to improve
its corresponding solvent resistance.
Example 6
Comparative Example
[0069] This example demonstrates the preparation and use of a
thermal transfer donor without an interlayer.
[0070] A carbon black light-to-heat conversion with an absorbance
of 1.35 at 1064 nm, was prepared by coating an aqueous dispersion
of carbon black in a radiation curable resin onto a 2 mil PET
substrate with a Yasui Seiki Lab Coater, Model CAG-X150 (Yasui
Seiki Co., Bloomington, Ind.) using a microgravure roll of 90
helical cells per lineal inch. The coating was subsequently in-line
dried and uv-cured on the coater before windup. The coating
solution consisted of 1 part of carbon black (Sunsperse black, Sun
Chemical, Amelia, Ohio), 7 parts of NR-440 (a crosslinkable
urethane acrylate oligomer from Zeneca Resins, Wilmington, Mass.),
and 0.35 part of a photoinitiator (Darocur 1173 from Ciba-Geigy,
Hawthorne, N.Y.) at 35 wt % total solid in water to give a
light-to-heat conversion coating with a 4.5 .mu.m dry
thickness.
[0071] The light-to-heat conversion layer was overcoated with a
clear interlayer, followed by a colorant layer. Using a #5 coating
rod, an aqueous solution containing 12.5 wt % NR-440 and 0.6 wt %
Darocur 1173 was coated, dried at 80.degree. C. for 2 minutes and
UV crosslinked to provide a color topcoat with a heat stable,
smooth release surface. The color transfer layer was applied by
coating the green color ink of Example 5 at 15 wt % total solid
using a #5 coating rod and drying for 3 min at 60.degree. C. to
give a 1 .mu.m thick colorant layer.
[0072] The donor thus prepared was tested for imagewise transfer of
the thermal transfer layer to a black chrome coated glass receptor,
which had an absorbance of 2.8 at 1064 nm. The color donor sheet
was imaged with a line pattern and transferred onto the glass
receptor (75 mm.times.50 mm.times.1.1 mm). Imaging was performed in
a flat-bed imaging system, using a Nd:YAG laser operating at 7.5 W
on the donor film plane with a 140 .mu.m laser spot size (1/e.sup.2
diameter). The laser scan rate was 4.5 m/s. Image data were
transferred from a mass-memory system and supplied to an
acoustic-optic modulator which performed the imagewise modulation
of the laser. During the imaging process, the donor sheet and the
receptor were held in intimate contact with vacuum assistance.
[0073] A microscopic inspection of the resultant image on the
receptor indicated that the imaged lines possessed a uniform line
width of 89 .mu.m. Damage (e.g., roughened surface, cracks,
bubbles, color variation, etc.) was observed to be present at the
central portion of each of the transferred colorant lines.
Example 7
[0074] This example demonstrates the preparation and use of a
thermal transfer donor with a vapor-coated aluminum reflective
interlayer coated over a LTHC layer comprising carbon black
dispersed in a crosslinked organic binder.
[0075] The donor used in this example was the same as that used in
Example 6, except that a vapor-coated aluminum reflective
interlayer was coated on the light-to-heat conversion layer prior
to coating the color transfer layer. The aluminum coating was
determined to have 85.8% reflection at 1064 nm.
[0076] The donor was tested for imagewise transfer of the thermal
transfer layer to a black chrome coated glass receptor using the
same method described in Example 6. A microscopic inspection of the
resultant image indicated that the image lines were of good overall
quality with a uniform line width of 82 .mu.m. No obvious sign of
thermal damage was observed in the central portion of the
transferred lines.
Example 8
[0077] This example demonstrates the preparation and use of a
thermal transfer donor with a white reflective interlayer.
[0078] The donor used in this example was the same as that used in
Example 6, except that a white reflective interlayer was coated on
the light-to-heat conversion layer prior to the other coatings. The
white reflective layer was prepared by coating a white correction
ink at 17.3 wt % total solid (Pentel Correction Pen.TM. ink) with a
#3 coating rod, followed by drying at 80.degree. C. for 2 min. The
coating was determined to have a reflectivity of 22.5% at 1064
nm.
[0079] The donor was tested for imagewise transfer of the thermal
transfer layer to a black chrome coated glass receptor using the
same method described in Example 6. A microscopic inspection of the
resultant image indicated that the image lines were of good overall
quality with a uniform line width of 82 .mu.m. No obvious sign of
thermal damage was observed in the central portion of the
transferred lines.
Example 9
[0080] The donors used in this example were the same as those used
in Examples 6-8, except that a carbon black light-to-heat
conversion layer with an absorbance of 0.94 at 1060 nm was used.
This light-to-heat conversion layer was prepared by the same method
as described in Example 6, except that the coating solution
contained 27 wt % total solids instead of 35 wt %.
[0081] The donors were tested for imagewise transfer of the thermal
transfer layer to a black chrome coated glass receptor using the
same method described in Example 6.
[0082] The results of a microscopic inspection of the resultant
images on the receptors are summarized in Table 3.
3TABLE 3 Effect of Reflective Interlayer on Image Quality (5.3
m/sec Scan Speed) Donor Linewidth (.mu.m) Damage to transferred
line Control 90 some A1 Interlayer 97 some White Interlayer 100
none
[0083] The results indicate that images transferred from the donor
with a white interlayer (22.5% R, 46% T) suffered the least
damage.
[0084] These results demonstrate the efficacy of a reflective
interlayer in the improvement of transferred image quality and the
prevention of thermal damage of the transferred material.
Example 10
[0085] This example demonstrates the preparation and use of a
thermal transfer donor with a reflective aluminum interlayer coated
over a black aluminum LTHC layer. A black aluminum (partially
oxidized Al, AlO.sub.x) light-to-heat conversion layer of
approximately 800 .ANG. was coated onto a 4 mil poly(ethylene
terephthalate) (PET) substrate via reactive sputtering of Al in an
Ar/O.sub.2 atmosphere in a continuous vacuum coater according to
the teachings of U.S. Pat. No. 4,430,366. Approximately 100 .ANG.
of Al was then sputtered onto the AlO.sub.x light-to-heat
conversion layer in an Ar atmosphere with the same continuous
vacuum coater. The resultant material containing the reflective
aluminum interlayer was then overcoated with an aqueous color ink
of the composition shown in Table 4 using a #4 coating rod and
dried at 60.degree. C. to produce a thermal transfer donor.
4TABLE 4 Composition of Aqueous Green Ink Coating Solution Coating
Component Percent by Weight PG-7 Pigment* 9.1 ICI Elvacite 2776*
5.3 Triethyl-O-acetyl-citrate 0.3 Dimethylethanolamine 1.1 3M
FC-430 Surfactant 0.04 H.sub.2O 84.2 *A dispersion of PG-7 pigment
in Elvacite 2776 was obtained from Penn Color, Doylestown, PA.
[0086] This donor was then tested for thermal transfer to a glass
slide receptor to produce a color filter element for a liquid
crystal display. The above-described Laser Imaging Procedure A was
employed and the laser spot diameter was 100 .mu.m (1/e.sup.2), the
power at the film plane was 8.4 Watts, and exposures performed at
pulse widths of 4, 6 and 8 microseconds.
[0087] The results showed that the transferred images were
essentially free from black aluminum contamination under the
above-described imaging conditions.
[0088] Reasonable variations and modifications are possible from
the foregoing disclosure without departing from either the spirit
or scope of the present invention as recited in the claims.
* * * * *