Laser imageable direct-write printing member

A laser imageable direct write printing member for use with a laser producing laser infrared radiation comprising a flexible sheet of plastic having first and second surfaces serving as a film substrate. A vacuum-deposited laser ablative coating is carried by said first surface formed of a metal selected from a group consisting of titanium, zirconium, hafnium and alloys thereof.

This invention relates to a lithographic laser imageable direct-write film 
and a printing member incorporating the same. 
Heretofore aluminum plates have typically been utilized to provide the 
dimensional stability required for multiple plate registration in color 
printing applications and to achieve the durability required for long 
printing press runs. Aluminum substrates typically 5 to 20 mils in 
thickness required treatment such as graining and anodizing to provide 
adhesion for the subsequent coatings of light sensitive layers of organic 
compounds or emulsions for improved ink retention. In certain 
applications, polyester plates have been utilized typically only in black 
and white or spot color printing because of the lack of dimensional 
stability required for process color printing. Although polyester plates 
are inexpensive to produce and can be handled in raw form for surface 
coating processes, such plates are limited to short printing press runs. 
There is therefore a need for a new and improved printing member which 
overcomes these disadvantages. 
In general, it is an object of the present invention to provide a 
lithographic laser imageable printing member which does not require the 
preparation of metal surfaces for printing. 
Another object of the invention is to provide a printing member of the 
above character in which laser imageable coatings are carried by a thin 
film substrate which can be adhered to or laminated to a thicker substrate 
to provide the desired dimensional stability. 
Another object of the invention is to provide a printing member of the 
above character in which a laser ablative coating is carried by the thin 
film substrate. 
Another object of the invention is to provide a film of the above character 
in which the laser ablative coating is a vacuum-deposited metal selected 
from the group of titanium, zirconium, aluminum, hafnium and alloys 
thereof. 
Another object of the invention is to provide a film of the above character 
in which an image coating has a different affinity from that of the film 
substrate for at least one printing liquid selected from the group 
consisting of ink and an abhesive fluid for ink to provide the desired 
image areas. 
Another object of the invention is to provide a film substrate of the above 
character in which the film substrate after formation of the 
vacuum-deposited laser ablative coating and the image coating thereon can 
be adhered to a base substrate. 
Another object of the invention is to provide a film substrate and printing 
member of the above character which makes it possible to substantially 
reduce costs of production.

In general, the laser imageable direct write film of the present invention 
is for use with a laser producing infrared radiation and is comprised of a 
flexible film of a plastic having first and second surfaces. A 
vacuum-deposited laser ablative coating is carried by the first surface 
and is formed of a material selected from a group of metals consisting of 
titanium, zirconium, and hafnium and alloys thereof. 
More specifically as shown in FIG. 1 of the drawings, the lithographic 
laser imageable direct-write film 11 consists of a flexible film substrate 
12 in sheet form having upper and lower parallel spaced-apart surfaces 13 
and 14. The film substrate 12 can be formed of a suitable material such as 
a polyester or a polymer and can have a thickness ranging from 0.2 to 10 
mils and preferably a thickness ranging from 1-2 mils. It is desirable 
that the sheet 12 have good dimensional stability to serve as a film 
substrate which is provided by PET (polyethyleneterephthalate). By way of 
example, ICI 442 (2 mil thickness) and H 3930 (7 mil thickness) can be 
used. It should be appreciated that the quality of the surface desired for 
the printing application in which the film substrate is to be used is 
determined by the quality of the surface 13. 
After the desired film substrate 12 has been selected, the film substrate 
12 in sheet form typically is placed in rolls so that the sheet material 
can be advanced through a vacuum chamber in a conventional roll coater. 
During advancement through the roll coater, a laser ablative coating 16 is 
vacuum-deposited onto the surface 13. By way of example, rolls of sheet 
film substrate 12 having a width ranging from 3 to 6 feet and having a 
length of 10,000 linear feet and greater can be used. 
In connection with the present invention, a metal is selected from the 
group of titanium, zirconium, aluminum, hafnium and alloys thereof. These 
metals have been selected to be efficient laser ablative or laser energy 
absorption thin films. Such metals should have large h and k values so 
that they are good laser energy absorbers at the laser wavelength. 
Typically a single ablative or laser energy absorption metal layer is 
deposited. However, additional layers can be used as hereafter described. 
The deposition can take place by sputtering or thermal vaporization. The 
vacuum-deposited laser ablative or laser energy absorption coating 16 is 
typically deposited to a thickness ranging from about 5 .ANG. to 400 .ANG. 
and preferably a thickness of less than 200 .ANG.. The metal ablative or 
laser energy absorption metal coating 16 can be vacuum-deposited to the 
desired thickness in a single pass or multiple passes through the roll 
coater by resistive heating, electron beam heating or sputtering of the 
metal. 
When an ablative or laser energy absorption metal coating is desired to be 
formed of multiple layers, a bilayer such as shown in FIG. 2 or a trilayer 
as shown in FIG. 3 can be utilized. Such multiple layers are desired when 
a highly reactive metal forms a part of the ablative or laser energy 
absorption coating. Highly reactive metals, as for example, zirconium and 
hafnium are more sensitive to infrared laser energy and thus their use is 
desirable in the present invention. As shown in the direct-write film 21 
in FIG. 2, a highly reactive metal such as zirconium or hafnium is 
vacuum-deposited onto the surface 13 of the sheet 12 in a roll coater by 
resistive heating, electron beam heating or sputtering to form a reactive 
metal layer 22 having a thickness ranging from 50-200 .ANG.. Thereafter, a 
protective layer 23 of a metal such as titanium is vacuum-deposited in the 
roll coater over the layer 22 to a thickness ranging from 5 to 50 .ANG. 
and preferably 5 to 20 .ANG. to provide a bilayer. The layer 23 prevents 
oxidation of the reactive metal layer 22. 
When additional protection is desired for the reactive metal layer 22, a 
direct-write film 31 as shown in FIG. 3 can be utilized in which a thin 
metal layer 32 is vacuum-deposited in the roll coater onto the surface 13 
of the film substrate 12 prior to the deposition of the thicker reactive 
metal layer 22. It is deposited to a suitable thickness of from 5-50 .ANG. 
and preferably a thickness of 5-20 .ANG.. Although the film substrate 12 
provides some protection to the adjacent side of the reactive metal layer 
22, the additional protective layer 32 provides additional protection from 
oxidation and thus serves as a surface passivation layer. Thus, it can be 
seen that at least one of the first and second surfaces of the reactive 
metal layer 22 is covered by a layer of titanium as shown in FIG. 2 and 
both the first and second surfaces of the reactive metal layer 22 are 
covered by titanium layers 23 and 32 as shown in FIG. 3. It should be 
appreciated that the use of titanium is exemplary and the protective layer 
may be comprised of other metals which have resistance to oxidation as for 
example nickel, chromium, alloys thereof, stainless steel and like 
materials. 
After the vacuum-deposited laser ablative or laser energy absorption 
coating has been applied in the manner hereinbefore described, the film 
substrate 12 can be removed in roll form from the roll coater after which 
the film substrate 12 is subjected to a conventional coating process which 
typically is a wet process at atmospheric pressure and thus typically is 
carried out at another location or facility. Since the film substrate is 
in roll form, the organic material coating process also is accomplished in 
a roll-coating operation in which the organic material is applied to the 
exposed surface of the vacuum-deposited laser ablative coating 16 (FIG. 1) 
coating 23 and 22 (FIG. 2) and coating 23, 22 and 32 (FIG. 3). Thus, as 
shown in FIG. 4, an organic coating 36 is applied to the layer 16 to form 
an image coating. Such organic coatings are applied in a manner well known 
to those skilled in the art in which a thin organic coating 36 is applied 
to the surface of the ablation coating 16. Solvents therein are evaporated 
by ultraviolet or thermal heating until the organic coating 36 has dried. 
Alternatively, if desired, the organic coating 36 can be applied by 
lamination of a solidified layer of the organic material coating 36 to the 
ablative coating 16 by suitable means such as an adhesive applied to the 
surface of the ablation coating 16 or the coating 36 and thereafter 
laminating the organic coating 36 onto the ablative coating 16. This 
provides a direct-write film 41. Similar direct-write films can be 
prepared by the application of organic material coatings for layers 36 to 
the structures shown in FIGS. 2 and 3. 
The organic material coating 36 is prepared so that it has hydrophilic or 
hydrophobic and oleophillic or oleophobic characteristics with respect to 
the printing ink or inks to be utilized with the direct-write films of the 
present invention. By way of example, the organic material coating can be 
in the form of an oleophobic material such as a silicone polymer that 
repels ink. Alternatively it can be in the form of hydrophilic material 
such as polyvinyl alcohol which absorbs water. The coating 36 is typically 
deposited to a thickness of 0.5 to 5 microns and preferably a thickness of 
1 to 3 microns. The organic coating 36 can also be characterized as an 
image coating which exhibits an affinity different from that of the thin 
film substrate 12 for at least one printing liquid selected from the group 
consisting of ink and an abhesive fluid for ink. 
After the organic coating 36 has been dried, the coated film 41 as shown in 
FIG. 5 can be adhered to a base or base substrate 46 having an upper 
surface 47 to form a laser imageable direct-write printing member 51. The 
substrate 46 is formed of a suitable material such as aluminum or a 
polyester and has a thickness ranging from 5 to 20 mils. The lower surface 
14 of the film substrate 12 is adhered to the surface 47 of the base 
substrate 46 by suitable means such as an adhesive (not shown) which can 
be disposed either on the surface 14 or on the surface 47 so that it is 
secured or laminated in a dimensionally stable configuration on the 
surface 47 of the substrate or base 46. The substrate or base 46 
preferably should be dimensionally stable so that it will not have a 
maximum excursion in excess of 0.2 mil. 
The composite printing member 51 shown in FIG. 5 can then be utilized and 
loaded directly into the printing press to be imaged or into an image 
setting machine where it can be imaged by lasers emitting energy at 
typically 850 nanometers to create images on the composite film 31. The 
image creation occurs because an ablation mechanism which is accomplished 
by the decomposition or gasification of the organic layer formed by the 
sheet 12 which results in ejection of the overlying laser energy absorbing 
layer 16. The polymeric layer 12 is heated to decomposition at 
temperatures as for example 265.degree. C. (538 K) below the melting or 
vaporization temperature of the laser absorbing layer 16. It is 
advantageous that the laser absorbing layer not melt or vaporize since 
such a phase transition consumes laser energy without a corresponding 
temperature rise which would reduce ablation sensitivity. This is a very 
important consideration because laser diodes utilized in such applications 
typically have low power outputs. 
Stated in another manner, the present invention can be characterized as one 
providing a lithographic printing member directly imageable by laser 
discharge. The member can be considered as being comprised of a top-most 
or first layer 36 (see FIG. 4) which is polymeric and a thin metal layer 
16 underlying the first layer 36. A substrate 12 underlies the metal layer 
16. Metal layer 16 is formed of a material which is subject to ablative 
absorption of imaging infrared radiation while the first layer 36 is not. 
The first layer 36 and the substrate 12 exhibit different affinities for 
at least one printing liquid selected from the group consisting of ink and 
an abhesive fluid for ink. The metal used for the thin metal layer can be 
titanium. The substrate 12 is laminated to a metal support 46 (see FIG. 
5). 
From the foregoing, it can be seen that the present invention consists of a 
laser imageable composite coating on a thin PET film substrate which is 
laminated to a backing sheet or substrate which can be formed of a metal 
such as aluminum, a plastic such as polyester, or even paper. The surface 
quality and printing action as well as the laser imaging coatings are 
carried by the surface of the thin PET film substrate. The 
vacuum-deposited laser ablative coating as well as the organic coating are 
thin film structures which absorb energy at the laser wavelength. These 
thin film structures absorb laser energy in very small volumes resulting 
in local heating causing modification of the imaging surface which affects 
the ability of the surface to hold ink or reject ink. This invention makes 
it possible to eliminate the need to perform graining or other 
conditioning steps needed to prepare an aluminum surface for printing. It 
also provides the ability to utilize a low cost light weight thin 
substrate for deposition of the laser imageable coating. The use of the 
lightweight thin polymer film as for example PET film results in a greater 
coating capability in thin film roll coating machines which are used to 
produce the imageable coating of the present invention because longer 
rolls can be loaded into the roll coating machines. The use of the very 
thin polymer substrates has other advantages such as less deflection or 
indentation during printing leading to a longer plate life. By the use of 
thin absorbing metal layers coated onto polymer film substrates for 
imaging, a laminated structure is provided which gives the durability and 
dimensional stability of a conventional aluminum printing plate.