WO2001009679A1

WO2001009679A1 - Method for producing photomasks

Info

Publication number: WO2001009679A1
Application number: PCT/IL2000/000461
Authority: WO
Inventors: Yosef Kamir
Original assignee: Creoscitex Corporation Ltd.
Priority date: 1999-08-02
Filing date: 2000-08-02
Publication date: 2001-02-08
Also published as: IL131202A0; WO2001009679B1

Abstract

An inexpensive processless method using a laser plotter for producing photomasks which are useful in other pre-press processes such as the preparation of offset plates and silk screens. The method provides additional uses for expensive plotters, and is useful in creating pre-press proof-reading for digitally imaged flexography plates. In a preferred embodiment, exposed conventional negative film which is completely blackened by silver deposits and has been conventionally processed is placed in a laser plotter, and imaged by ablating away the silver. The resulting film needs no further processing. Alternatively, positive film, which is already black may be processed and imaged without exposure. The ablated exposed film is useful as a mask for any type of printing plate which uses film as an intermediate material, including preparation of offset plates, silk screens, PCBs (printed circuit boards), or even conventional flexography plates. Additionally, the ablated exposed film may then be used for other purposes, making the laser plotter even more economical. The film can be used either to inspect the image visually or to produce a proof color copy.

Description

METHOD FOR PRODUCING PHOTOMASKS

FIELD OF THE INVENTION The present invention relates to a novel processless method of producing photomasks, in particular a method of producing photomasks using a laser plotter.

BACKGROUND OF THE INVENTION

Flexography is one of the four major methods of printing used today. In flexography, the printing plates have a raised surface that accepts the ink, the background being the recessed surface. Digitally imaged flexography plates consist of a polyester base coated with a thick layer of photosensitive material which polymerizes upon exposure to UV light, as disclosed in US Patent No. 5,262,275 to Fan. The photosensitive material is blocked by a black UV-opaque, infrared-sensitive overlayer. In order to image the plate, a plate setter equipped with an infrared laser ablates away the black layer in the image areas. The remaining unablated black layer acts as a mask for the non-image areas during the UV exposure of the thick photosensitive layer. The UV exposure causes the polymers to become cross-linked in the photosensitive layer in the image areas that have been exposed by ablation. After UV exposure the remaining black layer and the unpolymerized material of the non-image areas are washed away.

The photosensitive material in the flexography plate must be thick to create the surface height differential necessary for flexography. Therefore, the black overlayer needs a correspondingly high optical density in order to withstand the high exposure power of the UV source necessary to cure the thick layer of photosensitive material. Because of this high optical density, approximately 2 to 4 joules/cm² are required to ablate the black overlayer so as to create the image.

Digital flexography plates are imaged on a laser plotter (or plate setter) for this purpose, such as the Lotem Flexo commercially available from Scitex Corporation, Herzliya, Israel. Plotters of this type are quite expensive and it would be desirable to be able to use the plotter for additional purposes, so as to justify its cost.

US Patent No. 3,314,075 to Becker discloses a system for recording data at high density employing a film having a black coating and a laser arranged to project modulated thermal energy onto the film and cause the removal of bits of the coating. Becker describes various techniques for producing coated films of this type. The Becker film is designed for microfilm applications with the preferred exposure being UV. UV is an inefficient method of ablation as compared to modern IR sources.

In production of photographic materials, there is a certain amount of waste due to inadvertent exposure of photosensitive materials to light. It would be desirable to find a method of use for this material which recognizes a value in this waste. In laser plotters, the use of inexpensive materials, many of which would normally be thrown away, such as exposed film, has not been explored by prior art techniques. Normally laser plotters employ digital flexography plates that are relatively expensive, up to 10 times the price of a regular flexography plate. It would be desirable to find an additional use for a laser plotter, and additionally to recycle an inexpensive material such as exposed film. SUMMARY OF THE INVENTION Accordingly, it is a broad object of the present invention to overcome the problems of the prior art and provide an inexpensive processless method of producing photomasks using a laser plotter, which are useful in other pre-press processes such as the preparation of offset plates and silk screens. This would provide additional uses for expensive plotters such as the Lotem Flexo. The same method is helpful in creating pre-press proof-reading for digitally imaged flexography plates.

In accordance with a preferred embodiment of the present invention there is provided a processless method for producing photomasks using a laser plotter, said method comprising the steps of: preparing a black-coated film; ablating said film on the laser plotter, in accordance with image information supplied from an image data source; and illuminating said ablated film for purposes of retrieving said image information. In a preferred embodiment, exposed conventional negative film which is completely blackened by silver deposits and has been conventionally processed is placed in the plotter, preferably a Lotem Flexo, by way of example, and imaged by ablating away the silver The resulting film needs no further processing. (Alternatively, positive film, which is already black may be processed and imaged without exposure.) . The ablated exposed film is useful as a mask for any type of printing plate which uses film as an intermediate material, including preparation of offset plates, silk screens, PCBs (printed circuit boards), or even conventional flexography plates. Additionally, the ablated exposed film may then be used for other purposes, making the laser plotter even more economical The film can be used either to inspect the image visually or to produce a proof color copy such as a Cromalin by using four separation films, as known in the art Once the image has been inspected and approved, the more expensive digitally imaged flexography plate may be produced

The process of ablation in the laser plotter has been shown to create cells of a depth of approximately 8 to 12 microns in the ablated exposed film. These cells can be used as gravure cells and the ablated exposed film may then function as a short run polymer gravure plate

These additional uses of the ablated exposed film increase the versatility of the Lotem Flexo Plotter, giving it the ability to produce processless films for many types of plate making, an economical proof copy or short run polymer processless gravure plates.

In this way, an inexpensive item which was previously considered not useful, namely, exposed conventional film, or such film beyond its expiration date, is "recycled" for a productive use, and provides an economical way to produce a photomask for varied printing processes

Other featuies and advantages of the invention will become apparent from the following drawings and descriptions

BRIEF DESCRIPTION OF THE DRAWINGS

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 in which Fig 1 is a flow chart showing the prior art method of imaging digital flexography plates,

Fig 2 is a flow chart showing the method of the present invention for imaging exposed film, and

Figs 3a-b show, respectively, an image and a cross-sectional drawing of the gravure cells produced in negative film exposures

DETAILED DESCRIPTION OF THE INVENTION

Referring now to Fig 1 , there is a flow chart showing the prior art method of imaging digital flexography plates, as per image data 8, as known in the art In block 10, a digital flexography plate is provided The digital flexography plate is comprised of three layers a base of a flexible material, a photosensitive polymer layer which is cross-linked upon exposure to UV light, and an infrared (IR)-sensitive, UV-opaque black layer (available, for example, as type Cyrel, DPH-45 by DuPont, Germany) In block 12, digital flexography plate 10 is placed in a laser plotter for exposure at a specific wavelength and laser power, generally to IR light, so as to cause ablation of the black layer in the areas which are to be imaged By way of example, the wavelength may be 830nm with an exposure power of 500mW The ablation of the black layer exposes the photosensitive polymer layer so that after exposure to U V light in block 14, the exposed areas of the photosensitive layer become cross-linked The plate is then processed to wash away uncross-linked areas of the photosensitive layer and the remaining black layer, in block 16 The plate may then be visually checked, in block 18, to see that the image is correct If it is correct the plate is then used for printing in block 20. If not, the plate is discarded and the image data must be edited and corrected, in block 22, and a new digital flexography plate must be taken and the process begun again This results in the waste of an expensive digital flexography plate

In Fig 2, there is shown a flow chart of the method of the present invention for imaging exposed film used for proofing the data to be exposed on the flexography plate In block 24, exposed and processed conventional negative film (for example Kodak, Rochester, NY, USA, Catalog #3650363), in which the film is blackened by silver deposits, is taken The film is placed in a laser plotter for ablation, in block 26 The laser plotter used here is the same laser plotter that will be used later for exposing the flexography plate Ablation is done, according to image data 8, at a wavelength of 830 nm and a laser power of 500 mW, by way of example The resulting ablated exposed film may then be used for any of three possible uses

In block 28, the ablated film, representing one color separation, is visually proof-read The ablation process evaporates the black layer of exposed negative film 24 leaving the transparent base layer intact This renders the ablated film suitable for visual proofing and other processes Optionally, a Cromalin image (block 30) may be created, as known in the art, from the film for proof-reading, if desired Creating a Cromalin (color proofing device made by Dupont) requires preparation of four separation films (cyan, magenta, yellow and black) making up the image data, which means that the process of blocks 24 and 26 must be repeated four times If the image is approved, a digital flexography plate 32 may be placed in the plotter and ablated according to image data 8 as in block 26, as described in Fig 1 Blocks 32 and 26 in Fig 2 are identical to blocks 10 and 12 in Fig 1 , respectively Block 26 may therefore be followed by blocks 14, 16 and 20 of Fig 1, without the need to proofread as in block 18, Fig. 1. The laser plotter is used, therefore, for both the proofing step and for the later step of exposure of the flexography plates, which makes the entire operation extremely efficient and economical

If the image needs editing (block 34), it is edited and another set of proof copies may be produced by returning to blocks 24 and 26.

The processes demonstrated in blocks 24 and 26 of Fig. 2 can be used in applications other than proofing and exposing flexography plates. For example, the exposed film 24 ablated by the plotter in block 26 may be used as a photomask for various printing processes, as shown in block 36 It may be used to produce offset plates, screens for screen printing or conventional flexography plates, as known in the art. Also, it could be used for PCB layout fabrication, which requires film as a photomask. It may be used in any printing process which uses a photomask This represents a flexible exploitation of the original plotter used mainly to expose flexography plates. The use of film with a matte surface is advantageous in the masking process

The process of ablation performed by laser plotter 26 creates an ablation depth of approximately 8-12 microns which can then be used as cells for holding ink in the gravure printing process In block 38, the ablated exposed film is used as an inexpensive short run polymer processless gravure plate

In Fig 3a, there is shown a negative film exposure in which the plotter ablates the imaged areas 42, creating areas on the film which are shown in white, corresponding to the image. The non-imaged areas 44 are shown in black. For this process, Kodak Film #3650363 (Kodak Corp , Rochester, NY, USA) may be used, by way of example Fig. 3b is a cross-sectional drawing corresponding to Fig. 3a, showing the imaged areas 42 which are recessed (ablated) and act as ink cells for the gravure printing process, as known in the art. Areas 44 are the non-imaged areas which are not ablated.

In this way, the use of exposed and processed film, which previously may have been discarded, as "beyond date", for example, is shown to be used in an economical way to produce a photomask, with the added benefit of also being able to be used to proof-read digital flexography plates or as a short run gravure plate. This saves the expense of wasted flexography plates due to editing errors, and creates new uses for the expensive laser plotting machine.

Having described the 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 suggest themselves to those skilled in the art, and it is intended to cover such modifications as fall within the scope of the appended claims.

Claims

1 A processless method for producing photomasks using a laser plotter, said method comprising the steps of preparing a black-coated film, ablating said film on the laser plotter, in accordance with image information supplied from an image data source, and illuminating said ablated film for purposes of retrieving said image information

2 1 he method of claim 1 wherein said ablation step is accomplished using a laser light source

3 The method of claim 2 wherein said laser light source is provided as an infrared laser

4 The method of claim 1 wherein said retrieving of said image information includes using said ablated film as a photomask

5 The method of claim 4 wherein said illumination step includes illuminating said ablated film for use as a photomask in a printing process

6 The method of claim 5 wherein said printing process is one of the group of offset printing, screen printing, printed circuit fabrication and flexography 7 The method of claim 1 wherein said illumination step includes illuminating said ablated film for proofreading purposes

8 The method of claim 1 further comprising the steps of ablating a digital flexography plate on said laser plotter according to said information; and using said ablated plate in a flexographic printer

9 T he method of claim 1 wherein said black coated film is an exposed and processed negative film

10 The method of claim 1 wherein said black coated film is a processed positive film

1 1 The method of claim 1 further comprising the step of examining said ablated film for purposes of proof-reading said image information

12 The method of claim 1 1 wherein said step of examining includes visual examination

1 The method of claim 1 1 wherein said step of examining includes color proofing

14 The method of claim 1 1 further comprising the step of editing said image information after said examining step

15. The method of claim 1 wherein said ablation step creates cells of a depth appropriate for use in a gravure printing process.

16. The method of claim 14 further comprising the step of using said ablated film as a processless polymer gravure printing plate.

17. A method for processless proof-reading of digital flexography plates substantially as described herein by way of example and with reference to the drawings.