BACKGROUND
[0001] This invention relates to aluminum base lithographic printing plates and to the preparation
of such plates.
[0002] Albuminum base lithographic printing plates such as described in US Pat. No. 3,181,461,
issued May 4, 1965, have come into wide use in the printing industry and especially
in offset printing and direct lithographic printing by newspapers using converted
letterpress printing presses.
[0003] Time is often a factor in making lithographic printing plates and this is especially
critical in the case of newspapers. The present day technique involves making a full
size photographic negative of a paste-up of each page for the newspaper, exposing
a wipe-on or pre-sensitized lithographic plate through the negative, developing the
plate 1 and mounting it on the printing press. This process is time consuming and
becomes even less efficient where duplicate plates are required for a multiple press
operation which is common in the newspaper industry.
[0004] In order to improve the time element, it has been proposed to eliminate the use of
a light-sensitive substrate, and, instead, to directly reproduce the printing surface
on the substrate via electrostatics or laser transfer. US Pat. No. 2,862,815 issued
December 2, 1958, describes an electrostatic reproduction process and US Pat. No.
3,962,513 issued June 8, 1976, and US Pat. No. 3,964,389 issued June 22, 1976, describe
forming the printing surface via laser transfer. However, these proposals have not
met with much success because the images formed using these direct reproduction techniques
lacks the integrity and durability required for good quality, dependable lithographic
printing.
[0005] It has also been proposed to print on anodized aluminum surfaces by heat transferring
a minor image from a pre-printed carrier sheet followed by sealing of the anodized
surface by prolonged immersion in boiling water (cf. US Pat. No. 3,484,342, issued
Dec. 16, 1969). This transfer of a pre-printed image is for decorative purposes and
sealing closes the pores over the transferred image for light fastness.
SUMMARY
[0006] The present invention provides a high quality, dependable aluminum base lithographic
printing plate and method. The printing plate comprises an aluminum substrate having
a hydrophilic porous anodic oxide layer thereon and a durable and reinforceable oleophilic
sublimated image in and on the porous anodic oxide layer. Heat transferable dyes are
preferred and the use of wet photochemical and wet photographic processing is eliminated.
[0007] The process of the invention for making a lithographic printing plate includes the
steps of providing an aluminum substrate with a hydrophilic, porous anodic oxide layer
and depositing or transferring an oleophilic image in and on the porous layer by sublimation.
The second step can be carried out in a number of ways. For example, a carrier with
a sublimatable oleophilic image can be placed face down on the aluminum substrate
and heated to sublimate the image in and onto the porous layer. The image can be formed
on the carrier using electrostatic techniques such as xerography, zinc oxide imaging
and charge transfer imaging (electrostatography) and an electrostatic toner composition
containing a sublimatable material such as a disperse dye.
[0008] Another way of carrying out the second step of the process is to place a carrier
which is transparent to laser radiation having a laser responsive coating containing
a sublimatable oleophilic material thereon face down on the lithographic substrate
and depositing the oleophilic image by selected irradiation with a laser.
[0009] Another approach involves coating the substrate with a sublimatable material such
as a dispersion of a disperse dye in a water soluble film former such as polyvinyl
alcohol, carboxymethyl cellulose, gelatin and the like. A solution of a sublimatable
material such as a disperse dye dissolved in acetone or other suitable sc
lent can be used in the same fashion for coating the substrate. With his approach,
two techniques are available to transfer an image to the underlying substrate via
sublimation. The first involves selected irradiation of the coated substrate followed
by removal of the unirradiated non-image portions. If a water soluble film former
is used in the coating this can be done simply by washing the laser imaged plate with
water. The second technique involves using a mask such as a black image on white paper.
The latter is placed image up on the coated substrate and flasher with. infrared.
This causes the material in the coating under the image to sublimate onto the substrate.
The process is completed by removing the non-image portions.
DESCRIPTION OF THE DRAWING
[0010] The present invention will be more fully understood from the following description
taken in conjunction with the accompanying drawing wherein:
Fig. 1 is a cross-sectional diagrammatic view illustrating one embodiment of the present
invention;
Fig. 2 is a cross-sectional diagrammatic representation of a lithographic printing
plate formed according to the embodiment illustrated in Fig. 2;
Figs.3 and 4 are cross-sectional diagrammatic representations illustrating another
embodiment of the invention utilizing laser transfer techniques;
Figs.5 a and 5 b are cross-sectional diagrammatic views illustrating a further embodiment
using a coated substrate and laser image for the transfer; and
Figs. 6 a and 6 b are cross-sectional diagrammatic views illustrating another embodiment
using a coated substrate and a mask.
DESCRIPTION
[0011] Fig. 1 of the drawing provides a simple illustration of the present invention wherein
an anodized aluminum substrate 10 is in contact with a carrier 12 having a sublimatable
image 14 thereon. Heat from the source causes the image 14 to sublimate in and onto
the pores of the substrate 10 producing oleophilic image 14' thereon (Fig. 2). The
image 14 for transfer to the substrate 10 is preferably formed on the carrier 12 using
direct imaging such as electrostatic copying of an original or composite using a toner
containing, for example, a sublimatable disperse dye. The image 14 can also be formed
by incorporating a sublimatable material into ribbons used in typewriters, telexes,
teletypes and other mechanical and automatic typing devices. Normal typing will transfer
the sublimatable material from the ribbon to paper which can then be used as the imaged
carrier 12 in the manner described herein. There are also known image transmission
systems that employ electrostatics or other means to convert sound or electrical impulses
into visible images. These can be employed in tie invention by incorporating a sublimatable
material such as disperse dye into the toner or toner medium used to produce a visible
image on a carrier such as paper. The imaged paper can then be used as the imaged
carrier 12 in the manner described herein.
[0012] Figs. 3 and 4 illustrate another embodiment of the invention wherein a laser transfer
technique is employed. A laser transparent film 16 having thereon a laser responsive
sublimatable coating 18 is placed face down on the substrate 10. A laser is employed
to transfer portions of the sublimatable coating 18 from the film 16 onto the substrate
10. Using known techniques, a "reading" laser causes the "writing" laser to transfer
the laser coating 18 in the image areas illustrated by reference numeral 14'. If desired
the film 16 can have a dark or black coating on the side facing the laser to facilitate
heat transfer through to the coating 18.
[0013] The laser transparent film 16 with the portions 15 (Fig. 4) remaining after the laser
transfer operation can be used as a negative itself to produce duplicate lithographic
printing plates using conventional sensitized substrates.
[0014] Figs. 5 and 6 show a coating 50 on the substrate 10. The coating 50 is or can contain
a sublimatable material such as a disperse dye. The coating can be a disperse dye
in a water soluble film former or it can be deposited from a solution of a disperse
dye, as described above.
[0015] Direct imaging with a laser forms image portions 52 and non-image portions 54. The
portions 54 are removed, for example by dissolving with water leaving the plate shown
in Fig. 5 b.
[0016] Imaging through a paper mask 60 with black (or dark) image 62 via an IR flash or
exposure is shown in Fig. 6. The image 62 readily transmits heat to the underlying
coating 50 while the non-image portions of paper 60 reflect the heat. In both Figs.
5 and 6 a transparent cover such as glass and/or a vacuum can be used to assist in
the sublimation transfer.
[0017] In all of the embodiments shown in Figs. 1 - 6, a heated platten can be used in contact
with the back or underside of the substrate 10 to approach (but not exceed) the sublimation
temperature. This means that the transferring heat source need only add a small increment
of heat energy to cause sublimation rather than having to bring the temperature up
from ambient.
[0018] An essential feature of the invention involves the transfer by sublimation of a material
placed in contact with (Figs. 1 - 4) or coated on an aluminum substrate (Figs. 5 and
6). In the transfer process, the image becomes firmly affixed in and on the porous
anodic layer on the substrate via sublimation through most likely a combination of
physical and chemical forces although this is not fully understood.
[0019] The aluminum substrate must be capable of holding a sublimated image and is provided
with a porous anodic oxide layer for this purpose. The aluminum substrate can be pretreated
(e. g. grained) bevore anodizing and/or posttreated such as described in US Pat. No.
3,181,461 with sodium silicate, provided the substrate retains sufficient residual
porosity so as to be substantive toward the sublimatable material. The term "porous"
thus includes anodized and unsealed aluminum as well as anodized aluminum that has
been posttreated in such a way that it retains sufficient residual porosity.
[0020] Tempered aluminum is generally used to make anodized substrates which are suitable
for use in the present invention. Tempered aluminum generally has a temper rating
of between H-12 and H-19 where direct cold reduction is employed or between H-22 and
H-27 where a combination of cold reduction and back annealling are employed. See the
American Aluminum Association publication entitled Aluminum Standards and Data.
[0021] Unlike decorative printing on anodized aluminum, the porous anodic layer of the substrate
of the invention must remain unsealed after image transfer via sublimation in order
for the image to form the oleophilic printing area which itself comes in contact with
the printing ink or is reinforced with known lacquers which do the printing.
[0022] The oleophilic sublimatable image 14 can be deposited on the carrier 11 using known
electrostatic techniques such as xerography, zinc oxide imaging and charge transfer
imaging. US Patent 2,862,815 referred to previously and US Patents 3,671,119 and 3,671,230
both issued June 20, 1972, are examples of such electrostatic techniques and are incorporated
herein by way of reference. Charge transfer imaging (e. g. Minolta Camera Co.) is
preferred because of the character of the image formed.
[0023] Basically, what is involved in using a laser transfer technique to form the image
14' (Fig. 4) is to employ a laser transparent film such as a polyester film coated
with a material 18 that can be sublimated by laser energy. If necessary or desired,
oxidizable or explosive constituents may be used to encourage transfer or increase
sensitivity of the coating 18. Nitrocellulose, peroxides, azides and nitrates are
examples of these constituents. To transfer selected portions of coating to form image
14' on the substrate, a beam of energy from a laser which produces wave lengths in
the infrared region such as a YAG (Yttrium-Aluminum-Garnet) laser which has an effective
wave length of about 1.06 microns, or an Argon laser which has an effective wave length
in the range of from about 0.48 to about 0.52 microns, is focused by means known in
the art through the laser transparent film to the interface between the coating and
the film. The energy provided by the laser beam causes sublimation leaving a clear
area on the laser transparent film 16 (see Fig. 4).
[0024] Imaging with a laser as described herein can also be used to advantage for making
nameplates, dials and signs on unsealed or porous anodized aluminum which can be sealed,
if desired or necessary, after image transfer. This has real advantages over current
systems since it eliminates preprinting prior to image transfer and permits one-step,
direct imaging.
[0025] The plate of the invention (e. g. as shown in Figs. 2, 4, 5 b and 6 b) can be treated
using conventional techniques to reinforce the image 14' for example ,by applying
a lacquer composition containing gum arabic.
[0026] A sublimatable material is one that will under proper conditions of temperature and
pressure) pass directly from the solid state without ever going through the liquid
state. Temperatures will generally be in the range of 60° C to 260° C and pressures
in the range of 1 to 10 psi, depending on the character of the material being worked
with. Suitable materials have a sublimation half-life (the time required for one-
half of a given amount of material to pass from the solid to the vapor state) in this
temperature range of from O.5 to 75 seconds. The preferred temperature range is 82°
C to 232
0 C and the more preferred range is 121
0 C to 219° C. Suitable sublimation materials are described in US Patents 3,484,342,
3,707,346, 3,792,968 and 3,829,286 and need not produce a visible image so long as
it is oleophilic and will accept ink or a reinforcing lacquer.
[0027] Heat transfer dyes commonly used in dry heat transfer printing of textiles can be
used to form sublimated oleophilic images according to the invention. Many of these
Materials are known as disperse dyes examples of which are as follows:
YELLOW
ORANGE
[0029]

RED
VIOLET
BLUE
BROWN
[0033]

[0034] Disperse type inks generally contain from 5 - 20 % by weight disperse dye, preferably
about 10 % such inks are commercially available and the following (Manufactured by
Crompton and Knowles Corp. of Fair Lawn, New Jersey) are useful in practicing the
invention:
Intratherm Yellow P-345 NT
Intratherm Yellow P-340 NT
Intratherm Yellow P-342
Intratherm Yellow P-343 NT
Intratherm Yellow P-346
Intratherm Brilliant Yellow P-348
Intratherm Brilliant Orange P-365
Intratherm Orange P-367
Intratherm Orang P-368
Intratherm Pink P-335 NT
Intratherm Brilliant Red P-314 NT
Intratherm Red P-334
Intratherm Red P-336
Intratherm Red P-339
Intratherm Scarlet P-355
Intratherm Scarlet P-358
Intratherm Violet P-344 NT
Intratherm Blue P-304 NT
Intratherm Blue P-305 NT
Intratherm Blue P-306 NT
Intratherm Brilliant Blue P-308
Intratherm Blue P-310 NT New
Intratherm Dark Blue P-311 NT
Intratherm Brown P-301
Intratherm Dark Brown P-303
Transfer Black XB-6
Transfer Black XB-8
[0035] Heat transfer dyes can be formulated into coating containing from 5 - 20 % by weight
(preferably about 10 % by weight) disperse dye and applied to a carrier such as paper,
plastic or the like for later transfer to a lithographic substrate using a laser transfer
technique. Formulations based on conventional wet or dry toners can be used to form
an image on a carrier using electrostatic copying techniques such as xerography, zinc
oxide or charge transfer imaging. Toners containing 5 - 60 % weight disperse dye,
preferably 10 - 40 % by weight, can be employed.
[0036] The following examples are intended to illustrate the invention without limiting
same:
Example 1:
[0037] Sublimable dyes such as the disperse dyes mentioned above may be incorporated into
inks, one example being Black NY 83779, sold by Sinclair and Valentine Co. for heat
transfer textile printing. The ink is coated onto a film substrate with a Meyer rod
or Bird applicator. Suitable films for this are Mylar (tm, DuPont), acetate and polystyrene.
After drying, the coated film is put coated-side down in contact with an anodized
aluminum offset plate which, in turn, is placed on a curved stepping platen. Es- posure
of the film is via an Argon laser (5 W., Spectra-Physics 165) using the 4800 line
only. Scanning is achieved by means of a single-facet, rotating 45° mirror. Input
is provided via magnetic tape. After imaging, the film which is lifted from the aluminum
substrate retains a negative dye image, while the highdensity, positive, dye image,
which had transferred (sublimated) to the aluminum plate, readily accepts lacquer
and ink. Abrasion tests, made on a Gardner Abrasion Machine, indicate that the sublimed
dye image is capable of long runs on an offset press.
Example 2:
[0038] Inks normally used for heat transfer printing of textiles containing red, blue and
yellow sublimable dyes as described above are obtained from Sinclair and Valentine
Co. and coatet on Mylar film (TM DyPont). These inks are designated Red NY 83983,
Blue NY 83982, and Yellow NY 83777. Films made with these inks are exposed as in Example
1, with similar results of dye image transfer and retention, and abrasion testing.
Example 3:
[0039] Crompton & Knowles' 8 % intratherm Red P-399, incorporated into a gravure ink, is
printed onto conventional paper. The paper is placed printed- side down onto a rained
anodized aluminum substrate, which is then placed in a Simplex, Slide-O-Mat, Transfer
Press sold by Archie Solomon & Associates. Heat (204
0 C) cand pressure are applied for 10 seconds. Upon separation a dense image of the
print was on the plate. This transferred (sublimated) image accepted ink and lacquer
readily.
Example 4:
[0040] 40 % Intratherm Red P-339 is incorporated into a conventional liquid toner for electrostatic
imaging. The toner is placed in a Minolta electrostatic copier. The copy produced
is placed face-down on an aluminum anodized surface. Transfer is accomplished as in
Example 3. The transferred sublimated image is a perfect facsimile which accepted
lacquer and ink readily.
Example 5:
[0041] A coating is formulated as follows (Parts by weight):
57 - Water
5 - Pluronic F-38 (non-ionic sufucant)
38 - Intratherm Red P-339
100 Total Slurry
[0042] These are mixed for 5 minutes in a blender.
Coating (Parts by Weight)
[0043] 26.3 - slurry as above 73.7 - (5 %) Polyvinyl Alcohol (Monsanto 40-20)
[0044] This is mixed for 5 minutes in a blender.
[0045] The coating is applied to an anodized aluminum plate. The coated plate is then imaged
with a YAG Laser as in Example 1. After exposure, the plate is washed in water to
remove the non-image area leaving asu- blimated disperse dye image on the anodized
plate.
Example 6:
[0046] A coated plate, prepared as in Example 5, is covered with a mask (black image upon
an opaque, white background). The masked plate is exposed to a source of infrared
radiation. The image areas absorb the radiation, heating the coated plate image-wise
underneath. The dye sublimates into the substrate forming an image. Water was removed
from the non-image area leaving a sublimated image on the anodized plate.
Example 7:
[0047] A film of polyester is sub-coated with a 5 % solution of nitrocellulose (RS 1/2 sec.
Hercules Corp.). The subbed film is then coated with a disperse dye coating as in
Example 5. The coated film is the used to image an anodized aluminum plate as in Example
1.
Example 8:
[0048] Intratherm Red P-339 is incorporated into a 5 % solution of nitrocellulose (RS 1/2
sec. Hercules Corp.). This material is coated onto a polyester film and coated film
is used to image an anodized plate as in Example 1.
[0049] Other sublimable materials that are of use in this invention are naphthalene, iodine,
anthracene, adipic acid, anthraquinone, benzophenone, caprolactam, lauric acid, sebacic
acid and other componds as listed in Handbook of Cem. & Physics, page C-716, Ed. 52,
1971 - 1972.
1. Lithographic printing plate comprising an aluminum substrate having a hydrophilic,
porous anodic oxide layer thereon and an oleophilic sublimated image in and on said
layer of anodic oxide.
2. Plate of claim 1 wherein the image area is reinforced.
3. Plate of claim 1 wherein the sublimated material comprises a disperse type heat
transfer dye.
4. Process for making a lithographic printing plate which comprises:
(a) providing an aluminum substrate having a hydrophilic, porous anodic oxide layer
thereon; and
(b) depositing an oleophilic image in and on the porous lyer by sublimation.
5. Process of claim 4 wherein an oleophilic image comprising a sublimatable material
is formed on a carrier, said carrier is placed face down on said lithographic substrate
and said oleophilic image is transferred to said substrate by sublimation.
6. Process of claim 5 wherein the image is formed on the carrier electrostatically.
7. Process of claim 6 wherein the image is formed on the carrier by charge transfer
imaging.
8. Process for making a lithographic printing plate which comprises:
(a) providing an aluminum substrate having a hydrophilic porous anodic oxide layer
thereon;
(b) forming an oleophilic image on an carrier by charge transfer imaging using a toner
comprising a sublimatable material; and
(c) contacting the imaged carrier with the porous layer and transferring the image
in and onto the porous layer by sublimation.
9. Process of claim 8 wherein the toner contains a disperse type heat transfer dye.
10. Process of claim 4 wherein a laser responsive coating containing a sublimatable
oleophilic material is applied to a carrier which is transparent to laser radiation
and said oleophilic image is transferred to said porous layer via sublimation by selected
irradiation with a laser.
11. Process of claim 4 wherein a laser responsive coating containing a sublimatable
oleophilic material is applied to said substrate, an oleophilic image is transferred
in and onto said porous layer via sublimation by selected irradiation with a laser
and the non-image portion of the coating is removed.
12. Process of claim 4 wherein a coating containing a sublimatable oleophilic material
is applied to said substrate, an oleophilic image is transferred in and onto said
porous layer via sublimation by the application of heat through a mask and the non-image
portion of the coating is removed.
13. Electrostatic toner composition comprising a sublimatable material.
14. Composition of claim 13 wherein the composition is oleophilic.
15. Composition of claim 13 wherein the sublimatable material is a disperse type heat
transfer dye.
16. Process for imaging aluminum having a porous anodic oxide layer thereon which
comprises contacting said layer with a laser responsive material containing a sublimatible
material and selectively irradiating said aluminum with a laser to transfer the desired
image by sublimation in and onto said porous layer.
17. Process of claim 16 wherein the laser responsive material is applied to a carrier
that is transparent to laser radiation.
18. Process of claim 16 wherein the laser responsive material is coated onto the aluminum.