Reference is made to commonly-assigned copending U.S. patent application Ser. No. 13/622,385, filed Sep. 19, 2012, entitled SYSTEM FOR FORMING STRUCTURED MICRODOTS, by Anderson; U.S. patent application Ser. No. 13/622,386, filed Sep. 19, 2012, entitled METHOD OF FORMING SECURITY MARKINGS, by Anderson; and U.S. patent application Ser. No. 13/622,387, filed Sep. 19, 2012, entitled SYSTEM FOR FORMING SECURITY MARKINGS USING STRUCTURED MICRODOTS; the disclosures of which are incorporated herein.
This invention relates in general to flexographic printing and in particular to using microdots for plate registration.
The flexographic industry has developed over the years from hand carved rubber plates with no expectations of register control between colors, to use of a photopolymer plate 100, shown in
Flexographic printing was the least of the print processes in terms of capabilities and the lowest cost compared to the traditional offset, letterpress and rotogravure printing processes used for package printing. Since the introduction of the photopolymer plate making systems, the growth in use of flexography has been significant, becoming the largest printing process used in packaging, and in some regions, like North America gaining over 80 percent of market share.
Throughout the development process, registration systems have steadily improved as the flexographic printing process has improved. The flexographic plate is selectively exposed to ultra violet light and unwanted areas washed away leaving a raised printing surface 103, shown in
The plates 110, shown in
To enable greater productivity and accuracy, video mounting systems were developed, shown in
As demand for flexographic printing process grows, it is moving to process printing, that is, building images and colors out of four (CMYK), six, or seven process colors. It is important for process printing that the colors are in accurate registration to each other. With the printed dots being as small as 10-20 microns, any shift in registration can cause color shifts, image errors, or interference patterns with a negative impact on the final image. This has driven the industry to smaller register marks, shown in
As applications for functional printing develop for very small lines and circuits as small as five microns in width, and the need for accurate layer to layer registration, on printing register, and the mounting of the plates accurately on the print cylinders and sleeves increases, there is a further need for improvement in microdots. The current state of the art is to place 2 or more microdots on each of the plates, 115, 116, shown in
Current microdots are typically 200-250 microns in size. A recent publication, U.S. Publication No. 2011/0265676, describes a registration system employing a scattered microdot pattern with each dot about 200 microns. Such large dots are objectionable when visible in the printed product. Smaller registration features are desired to ensure invisibility. In the printing of functional materials, such as electronic circuits, component sizes of five microns or less are desirable. When printing multiple layers, registration accuracy must be improved.
Traditionally the size of the microdots in flexo is limited to the size of a separate stand alone dot made of a group of pixels that can be consistently and independently formed on the plate. These are described as the minimum isolated dot size. In the majority of the flexoplate market this is presently between 120 and 250 microns.
Traditional digital flexo imaging technology uses Gaussian lasers, 140, shown in
Briefly, according to one aspect of the present invention a method of making microdots for printing plate registration includes forming a first plurality of square spots less than or equal to 11 microns, 156. A first group of the first plurality of square spots 157 is formed in a first pattern and the first pattern is less than or equal to 66 microns and comprises a first microdot.
The invention provides a shaped dot with an equivalent circular diameter of about 33 to 66 microns on the printing plate surface 161, which is significantly smaller than traditional microdots 160. The shaped spot comprises a pattern of six or more square pixels each less than 11 microns edge length arranged in a contiguous manner 170, shown in
Pixel for pixel imaging allows the combination of unique patterns of pixels or additional image components to make an identifier for brand owners, 180, shown in
The invention and its objects and advantages will become more apparent in the detailed description of the preferred embodiment presented below.
The present invention will be directed in particular to elements forming part of or in cooperation more directly with the apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art.
Referring to
A limitation of flexographic plate making with the existing plate manufacturers at the time was a minimum size for an isolated dot, which was 200-250 microns in size due to the manufacturing constraints. A smaller dot would not hold on the plate. (The standard industry specification today for the microdot size is 200-250 microns in diameter.)
The flexographic printing industry is now capable of matching or beating competitive printing processes in terms of print capabilities for resolution, density, and production speeds. It is now normal for flexographic printing to use process printing to build colors out of two or more screens instead of traditional spot colors, raising the flexographic printing capabilities even further. One issue in the transition from single spot colors to process printing, is that the demands on holding register are more critical than ever, with mis-register between two or more colors potentially causing a shift in the color and visible print defects.
Process printing today uses minimum dot sizes of 10-30 microns depending on application and print capabilities, so the use of a standard 200 micron registration mark is large and causes severe challenges on registration as print capabilities and expectations continue to rise.
Video mounting equipment has been improving significantly for manual and automatic registration control, yet registration remains controlled by a general 200 micron round dot, limited by the minimum isolated dot capabilities of traditional plate making.
All traditional lasers, see
Square spot imaging systems such as Kodak Flexcel NX, image flexographic plates, as shown in
The structured microdot solution 154 allows a much higher level of process printing to be used because of the benefits of imaging accuracy. See
In March 2012 a panel of industry speakers at the FFTA Forum in San Antonio stated that “flexographic printing can match or better offset and rotogravure printing on all items, except register, and this remains the greatest limitation for process printing in flexography.” The current microdots used in flexographic printing are limited to 200 microns in size by the minimum isolated dots capabilities of the plates, while the structured microdot solution can form 50 microns minimum isolated dots.
Current microdots are basically round dots of photopolymer without shape or structure to provide data other than basic location. The present invention uses the pixel for pixel imaging capabilities of the structured microdot system to produce a new structured microdot to supply greater accuracy in register, but also to provide additional data in terms of plate position, direction, and inversion.
The present invention uses structured microdots that are 66 microns or less in dimension, and are a combination or a series of imaged pixels to produce a structured shape allowing straight edges for register along with image components that will indicate direction, rotation, or inversion issues, for use with manual or automatic video mounting systems. The present invention allows use of a single pair of microdots on either side of the plate, as shown in
The present invention provides a smaller microdot compared to the prior art, with clear structure. See
There are several options for the structured microdot as shown in
The inner section 172 provides the ability to register to an even finer level with suitable equipment, or for more challenging demands. The inner section also provides a clear indication if the plate is rotated or inverted, and can act as a check point to ensure the plate is mounted in the correct orientation. These features combine to enhance the register capabilities of the flexographic plate system in mounting before coming to the printing press, allowing reduced adjustments on press, greater image accuracy, and production efficiencies.
The benefits of using structured microdots for the flexographic printing industry have enhanced benefits for specific markets. For example, moving from a broad round microdot with no straight edges or corners, to a structure in the present invention, with right angle corners, provides benefits in registration measurement and control. Reducing the size of the microdot from 200 microns to the structure microdot of 66 microns or less also provides a significant opportunity to reduce registration errors and increase accuracy.
Changing from traditional Gaussian imaging with or without oxygen inhibition in plate making, with its inherent errors in size and variability, to pixel for pixel imaging accuracy, enhances register capabilities and reduces significantly the plate making tolerances on the microdot and register accuracy. A square outer structure with straight edges and a right angle corner also allows greater accuracy in two perpendicular directions.
Having an inner component allows higher accuracy on registration if the application requires it. Having an inner structure that is not consistent in all directions allows any rotation of the plate to be identified and rejected or corrected, relevant to manual and automatic mounting systems. An inner structure on the structured microdot, allows identification if the plate is inverted with the non-imaged side up instead of down, which is particularly useful when using automatic mounting systems.
Functional printing applications tend to rely on the printing of lines and circuits more than dots and process on the final substrate. There exists a need to obtain the highest level of accuracy in mounting relates to the need to print circuits and lines of down to five microns in position to the next conductive or resistive material, and achieve the required electronic conductive or resistive properties and circuit function.
When printing, a 200 micron microdot is too large to truly provide the tolerances required. The reduction in size and increase in accuracy for the structured microdot suits the demands of industry and the inner structure allows the highest level of accuracy, especially with automated mounting systems. The clear and immediate identification of any rotation and inversion of the plate is important where the layers of the circuits and their direction may not be obvious, and costs in the components mean errors are extremely expensive.
Although all of the applications of the structured microdot have focused on registration benefits, in the discussion above there are also opportunities to utilize the structured microdot in new ways when it is printed. One opportunity is in covert security to identify the pre-press provider, printer, or both, which is especially useful for brands that use several prepress and printers for the same product range.
The use of the microdot for a covert security feature may be feasible depending on the print and resolution capabilities of the flexo printing process. In its simplest form it could be a series of 66 micron full blocks, half blocks, and triangles in a set combination in one or more of the eight possible locations around the structured microdot. See
The ability of the microdot to be used in a covert security manner, with patterns only known or understood by the brand owners and their prepress providers gives a strong tool for identification of illegal or incorrect actions. The structured microdot, when using all security areas as solid blocks, similarly to the areas shown in
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention.
Number | Name | Date | Kind |
---|---|---|---|
5576830 | O'Brien et al. | Nov 1996 | A |
5626076 | Ireton | May 1997 | A |
5633676 | Harley et al. | May 1997 | A |
6079806 | Wen et al. | Jun 2000 | A |
6103353 | Gasper et al. | Aug 2000 | A |
RE38065 | Bravenec et al. | Apr 2003 | E |
7123384 | Koifman | Oct 2006 | B2 |
8102282 | Wei et al. | Jan 2012 | B2 |
20110265676 | Golan et al. | Nov 2011 | A1 |
Entry |
---|
“Don't over think it” by John Anderson, Sep. 2009; http://www.packageprinting.com/article/flexo-platemaking-complex-only-if-you-let-become-so-405055/2#; 4 pages. |
Number | Date | Country | |
---|---|---|---|
20140076184 A1 | Mar 2014 | US |