Printing – Stenciling – Stencils
Reexamination Certificate
2001-08-14
2003-04-01
Evanisko, Leslie J. (Department: 2854)
Printing
Stenciling
Stencils
C101S128400, C347S103000
Reexamination Certificate
active
06539856
ABSTRACT:
BACKGROUND TO THE INVENTION
1. Field of the Invention
The present invention relates to the production of stencils for screen printing.
2. Related Background Art
The production of screen printing stencils is generally well known to those skilled in the art.
One method, referred to as the “direct method” of producing screen printing stencils involves the coating of a liquid light-sensitive emulsion directly onto a screen mesh. After drying, the entire screen is exposed to actinic light through a film positive held in contact with the coated mesh in a vacuum frame. The black portions of the positive do not allow light to penetrate to the emulsion which remains soft in those areas. In the areas which are exposed to light, the emulsion hardens and becomes insoluble, so that, after washing out with a suitable solvent, the unexposed areas allow ink to pass through onto a substrate surface during a subsequent printing process.
Another method, referred to as the “direct/indirect method” involves contacting a film, consisting of a pre-coated unsensitised emulsion on a base support, with the screen mesh by placing the screen on top of the flat film. A sensitised emulsion is then forced across the mesh from the opposite side, thus laminating the film to the screen and at the same time sensitising its emulsion. After drying, the base support is peeled off and the screen is then processed and used in the same way as in the direct method.
In the “indirect method” a film base is pre-coated with a pre-sensitised emulsion. The film is exposed to actinic light through a positive held in contact with the coated film. After photochemical hardening of the exposed emulsion, the unexposed emulsion is washed away. The stencil produced is then mounted on the screen mesh and used for printing as described above for the direct method.
In the “capillary direct method” a pre-coated and pre-sensitised film base is adhered to one surface of the mesh by the capillary action of water applied to the opposite surface of the mesh. After drying, the film is peeled off and the screen then processed and used as described for the direct method.
In addition to the above methods, hand-cut stencils can be used. These are produced by cutting the required stencil design into an emulsion coating on a film base support. The cut areas are removed from the base before the film is applied to the mesh. The emulsion is then softened to cause it to adhere to the mesh. After drying, the base is peeled off. The screen is then ready for printing. This method is suitable only for simple work.
One problem generally associated with all the prior art methods is that many steps are necessary to produce the screen, thus making screen production time-consuming and labour-intensive.
Another problem is that normal lighting cannot be used throughout the screen production process in any of the methods except hand cutting. This is because the stencil materials are light-sensitive. In addition, it is necessary to provide a source of actinic (usually UV) light for exposing the stencil. This usually incurs a penalty of initial cost, space utilisation and ongoing maintenance costs.
Other methods of preparing printing screens are available. CA-A-2088400 (Gerber Scientific Products, Inc.) describes a method and apparatus in which a blocking composition is ejected directly onto the screen mesh surface in a pre-programmed manner in accordance with data representative of the desired image. The blocking composition directly occludes areas of the screen mesh to define the desired stencil pattern.
EP-A-0492351 (Gerber Scientific Products, Inc.) describes a method where an unexposed light-sensitive emulsion layer is applied to a screen mesh surface and a graphic is directly ink-jet printed on the emulsion layer by means of a printing mechanism to provide a mask through which the emulsion is exposed before the screen is further processed.
Both the above methods require the use of very specialised equipment (because of the need to handle large complete screens) which incurs a certain cost as well as imposing restrictions arising from the limitations of the equipment, in particular in terms of the size of screen and its resolution.
Ink-jet printers operate by ejecting ink onto a receiving substrate in controlled patterns of closely spaced ink droplets. By selectively regulating the pattern of ink droplets, ink-jet printers can be used to produce a wide variety of printed materials, including text, graphics and images on a wide range of substrates. In many ink-jet printing systems, ink is printed directly onto the surface of the final receiving substrate. An ink-jet printing system where an image is printed on an intermediate image transfer surface and subsequently transferred to the final receiving substrate is disclosed in U.S. Pat. No. 4,538,156 (AT&T Teletype Corp.). Furthermore, U.S. Pat. No. 5,380,769 (Tektronix Inc.) describes reactive ink compositions containing at least two reactive components, a base ink component and a curing component, that are applied to a receiving substrate separately. The base ink component is preferably applied to the receiving substrate using ink-jet printing techniques and, upon exposure of the base ink component to the curing component, a durable, crosslinked ink is produced.
One object of the present invention is to make screen-printing stencil production less time-consuming and labour-intensive.
Another object is to allow normal lighting to be used throughout the stencil production process and to avoid both the problems of prior art stencil materials which are light-sensitive and also the need to provide a source of actinic (usually UV) light for exposing the stencil.
SUMMARY OF THE INVENTION
The present invention provides a method of producing a screen-printing stencil having open areas and blocked areas for respectively passage and blocking of a printing medium, the method comprising:
providing a receptor element comprising an optional support base and a stencil-forming layer which is capable of reacting with a chemical agent applied thereto to produce areas of lower solubility where application takes place and to leave higher solubility areas elsewhere, the areas of lower solubility being sufficiently adherent for attachment of the receptor element to a screen-printing screen after washing away of the areas of higher solubility from the receptor element;
applying the said chemical agent imagewise to the stencil-forming layer in areas corresponding to the blocked stencil areas;
washing away the stencil-forming layer in the higher solubility areas;
bringing the receptor element into contact with the screen in order to attach it to the screen by the adherency thereto of the areas of lower solubility; and
removing any remaining part of the receptor element in order to produce the screen-printing stencil.
In the method of the invention, the stencil is formed by chemical means without the need to use either special lighting conditions or actinic radiation.
Also, it is possible to carry out the method at reduced expenditure of time. and labour, compared with the known processes.
Advantageously, the chemical agent is applied dropwise to the stencil-forming layer.
Conveniently, the dropwise application is by use of an ink-jet device, for example an ink-jet printer or plotter. The device may have one or more ejection heads.
If desired, the chemical agent may be produced in situ by reaction between two or more precursor materials, separately applied to the stencil-forming layer, prior to contact with the stencil forming agent, at least one of which is applied in the said areas corresponding to the blocked areas of the stencil to be produced. This may conveniently be achieved by use of a plurality of drop-ejection heads.
When dropwise application is employed, the application is preferably controlled according to data encoding the desired pattern of blocked and open areas of the stencil to be produced. This control is conveniently by a computer, for example a personal computer. Thus, data representative of the desired output patter
Foster David Joseph
Jones John W.
Autotype International Limited
Evanisko Leslie J.
Wall Marjama & Bilinski LLP
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