Autotype International Limited

Hartwell Dosimeters Limited

David Joseph Foster

John William Jones

Anna Jane Harris

John Steel

Dennis D Maguire

Stuart A Falconer

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 includes providing a receptor element having an image-receiving layer capable of receiving a first chemical agent in areas corresponding to the blocked areas of the stencil to be produced. A first chemical agent is applied to the image-receiving layer of the receptor element in the corresponding areas. A second, stencil-forming chemical agent is then applied to a screen printing screen and the image-receiving layer fo the receptor element brought into contact with the stencil-forming agent to allow the first and second chemical agents to react to produce on the screen a stencil-forming layer having areas of lower solubility corresponding to the said blocked areas and areas of higher solubility in areas corresponding to the open stencil areas. Any remaining unreacted part of the receptor element is removed and the second chemical agent washed away in the higher solubility areas thereby producing the screen-printing stencil.

Screen printing stencil production

Screen printing stencils are produced by a positive-working method which involves no light-sensitive materials and does not require the use of safe lights. A coated receptor film having a coating layer and a support layer is imaged using an ink-jet printer or plotter in areas corresponding to the open stencil areas. The film is then applied to a mesh and an emulsion applied. Chemical hardening of the emulsion takes place in the non-imaged areas. The stencil is then produced by removing the support layer of the film and washing away the unhardened emulsion. The receptor film may include a layer which is incorporated into the stencil layer to form a profile. In addition to screen production methods, coated films, coating compositions and compositions for imagewise application are disclosed.

A coated film product comprises a support base, a stencil-forming layer and an intermediate release layer. The stencil-forming layer is a blend of two grades of polyvinyl alcohol having different degrees of hydrolysis. The stencil-forming layer is imaged by dropwise application (for example using an ink-jet printer or plotter) of a cross-linking agent which hardens the stencil-forming layer to resist washing out with water. The hardened areas remaining after washing out are however sufficiently tacky for the washed-out film to adhere to the screen mesh by application of pressure and, after removal of the support base, form the stencil layer of a screen-printing screen.

Method of screen printing stencil production

A gamma radiation dosimeter comprises a polyester film substrate, of which a central circular region is coated with a gamma-radiation sensitive layer which is covered by an overlayer. The radiation-sensitive layer is formed from styrene-acrylonitrile copolymer and contains 1-bromoadamantane and a leuco dye. The overlayer is formed from an acrylic resin binder containing a UV-absorber. The central region is surround by an annular region which is divided into six equally-sized sections, each of which is printed in a color which corresponds to the color developed in the central region when it has been exposed to successive increasing amounts of gamma radiation. After exposure of the device, the amount of radiation to which the device has been exposed can be determined by comparing the color generated in the region with the colors of the six sections. The color of the section most closely corresponding to that of the central region indicates the dose of gamma radiation which the device, and any other object similarly exposed, has received.

Gamma radiation detection

Masking films, having the advantageous properties of both those masking films having an intermediate adhesive layer and those masking films having a high-adhesion masking layer without an intermediate adhesive layer, include a masking layer which incorporates a cellulose ester component, a polyurethane and one or more colorants selected from dyes and pigments.

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Swindon, United Kingdom

David Joseph Foster