Patent Application
20080087181
For a better understanding of the invention with regard to the embodiments thereof, reference is made to the accompanying drawings, in which like numerals designate corresponding elements or sections throughout and wherein:
a,
3
b,
3
c illustrate a general process for the production of a negative mold relief and a positive flexo plate in a preferred embodiment of the present invention;
a and 4b illustrate the use of machining the bulk relief at a course layer prior to laser imaging at a finer layer;
A laser beam 14 is passed through a focusing lens 16 to form a convergence cone 18 which is focused on the final depth of an ablative polymer material 12 to the non-ablative level, that is, at the upper surface of a non-ablative substrate 10. Substrate 10 is made of a plate of thin aluminum or any other non-ablative material as is known to those skilled in the art. The convergence cone 18 produces natural shoulder reliefs 19 in the inverse cone 20 formed in the curative material 12, such as ablative, liquid polymer material.
The method utilizes multi-focusing on the bottom of each ablatable layer. Laser beam 14 is passed through focusing lens 16 to form convergence cone 18. In technique A shown performed on one side of
In technique B shown on the other side of
a,
3
b,
3
c illustrate a general process for the production of a negative mold relief and a positive flexo plate in a preferred embodiment of the present invention.
A mold is provided as shown in
In
To obtain different physical properties, such as hardness or resiliency, of the final plate, resin can optionally be filled layer by layer and different curing regimes applied. For example, a thin, low viscosity printing layer can be poured onto the mold relief. Low viscosity and thin layer will ensure good pits filling, preventing air bubbles. After that, a higher viscosity resin can be poured in without a risk of air bubbles forming to affect the printing quality. Finally, still another, backing resin can be added to fill in the mold to provide toughness to the flexo plate.
The same mold can be used for more than one flexo plate casting, provided the mold is made of durable material. Cured resin removal does not require any pattern breakages as the bumps profile will always be of conical or stepped shape that allows mold-flexo separation without undercuts.
Resin curing can be done in any technique as is known to those skilled in the art, such as UV curing. There are other non-UV curable materials in which the reaction is initiated by heat or humidity. In accordance with the principles of the present invention, a preferred method involves the use of UV curable liquid resins.
For subtractive laser imaging, a thin aluminum sheet, a few tenths of a millimeter thick, surface treated by black sulfuric anodization, is plated with a polymer containing black carbon additives for radiation absorption, 0.5-1.0 mm thick and nitrocellulose for enhanced laser ablation characteristics. The anodized aluminum serves as the fine layer media, whereas the polymer serves as the coarse layer media. The prefabricated sandwich is placed in a laser image setter device (not shown). The layers are laser ablated and imaged by one or more passes, depending on the power density applied to the mold, for creating negative reliefs with shoulders into which curable material 26 can be cast (see
To ensure that the bottom, printing level will have the same relief depth, the ablation is done until the black, anodized layer is removed by laser beam 11 passed through focusing lens 16 to form convergence cone 18. The final focus level should be approximately on the bottom of the anodized layer. For the non-printing layers, the focus position can be either on the corresponding ablation layer or the final print layer. In either case, the printing layer resolution will not be damaged by a defocused beam. The focused beam diameter is the smallest of all, thus providing for the best printing humps resolution. To further ensure the quality of the mold printing layer and optimize the throughput of the coarse layers, the reliefs can be imaged with power modulation as a function of screen density. The higher the laser power is, the larger the spots that will be produced due to the media non-linearity response.
To further enhance the throughput of material removal in the coarse mold layers, the material used, in a preferred embodiment of the present invention, consists of porous, foam-like media with additives of black carbon for improved radiation absorption, and some nitrocellulose that magnifies laser power. The major advantage of this method over direct flexo engraving is that the ablated mold materials need not have expensive and high quality mechanical properties: need not have flexibility for prints, nor stress durability. These low-level demands allow a drastic reduction in laser power and a reduction of fumes, allowing use of lower-cost, non-functional materials and, most importantly, achieve superior image quality.
The ceramic quality of the black sulfuric anodization layer provides for sharp image boundaries, impossible to achieve by either direct flexo engraving or photochemical flexo etching process as in the prior art.
a and 4b illustrate the use of machining to remove the bulk reliefs prior to laser imaging. Large mold areas that do not require high resolution can be produced by machining. Throughput vs. resolution is traded off by removing the hard mold media with a milling head having several cutting tools 28 of various diameters. The machined areas can then be inkjet or laser imaged for producing negative reliefs of printing quality.
In
In
Layers 35 of a polymer powder 36 are spread over a non-ablative substrate 10, such as aluminum. Heat 42 is applied to the substrate 10 to raise the temperature of polymer powder 36 to reduce the amount of power required from convergence cone 18. A laser beam 14 is passed through a laser focusing lens 16 to form convergence cone 18 used to selectively fuse the melted polymer material 38 which then forms cured printing areas (shown by darker fused particles). Residues of unfused powder particles 37 are removed, for example, by being suctioned off by a suction device 40.
The disposable recyclable mold media—the media consisting of melted media and solid particles can be re-melted and re-circulated after producing the flexo plate. This feature can reduce user's costs and allow a clean process. In addition to that, the “suction” particles and melted material can also be reused.
The melted polymer material 38 which forms the mold media does not have to be homogenous—it can contain solid, non-melting, particles of sub-pixel size (e.g., black, light-absorbing particles) bonded together by easily melted media, such as ice or wax. When such a particle gets energy from laser beam, it heats up and liquefies the bonding media. Vacuum suction force applied in a vicinity of heated particles will lift the unattached particles and leave the bonded ones inside the mold.
Referring now to
Since a high-resolution image is not needed, drop placement accuracy of >10 microns can be achieved by using, for example, Spectra/Dimatix (www.dimatix.com) Nova or Galaxy ink jet printing heads. To create layer 45 to dimensions of 0.6 mm high and one square meter will take less than ten minutes while using only three suggested printing heads.
The ink used for build up can be a melted wax or any other rapid prototyping material as is known to those skilled in the art. There is also an option of ink-jetting liquid droplets 44 and freezing them down on the image surface to create the relief. The flexo “shoulders” are built using an algorithm developed for this purpose as is known to those skilled in the art.
Of course the mold preparation process can be done in reverse order, i.e., first a lower resolution relief is produced by ink-jetting, then fine details are added by laser engraving. In this case the laser beam ablates both mold layer and some parts of the inkjet relief (the part which covers the image area).
When using inkjet to produce an imaged mold, high-resolution border walls can be built using small nozzle heads and then filled in by using larger nozzle heads with much higher throughput (a combination of throughput and high resolution).
The heated, unattached particles can optionally be removed by using electrostatic forces. In an alternative embodiment of the present invention, suction device 40 is electrostatic. By charging bonding media 48 and an electrostatic suction device 40 with opposite electric charges, an electrostatic force will be applied to all the solid particles 50 in the vicinity of suction device 40. Only those that were heated and melted by bonding media 48 will be released and will be pulled out of the mold, creating voids.
Alternatively, substrate 10 is coated with a physical mixture of easily melted bonder 48, e.g., wax, containing solid particles 50 used as a filler. Solid particles 50 are not intended to melt, but rather to heat as a result of laser beam 14 heating. The heating melts the bonding media 48 around solid particles 50 so the freed particles 52 can be easily removed with suction, thus creating a relief. The solid particles 50 can be made of plastic, ceramic or metallic materials. The main advantage of this method is low power required to melt wax and no burning products. The filler material, such as solid particles 50, is optimized for the lowest thermal capacity and for the lowest thermal conductivity for cross-talk prevention.
Variable resolution particles can also be used. Only the final, fine resolution should be at the bottom side of the mold. Thus the mold can be made of several layers of filler particles, each layer having particles of different sizes. This may be useful for throughput enhancement.
Optionally, the image is ink-jetted onto the base level and powder 36 is spread onto the surface which is previously wetted.
Alternatively, a mixed method of laser melting/ablating and inkjet printing can be used (see
Having described the present invention with regard to certain specific embodiments thereof, it is to be understood that the description is not meant as a limitation, since further modifications may now become apparent to those skilled in the art, and it is intended to cover such modifications as fall within the scope of the appended claims.
| Number | Date | Country | |
|---|---|---|---|
| 60852129 | Oct 2006 | US |
