FR2507788A1 - Process for sensitising screens for screen printing - uses photographic enlarger with UV lamp condenser and adjustable condenser - Google Patents

Abstract

The process for sensitising screen printing screens uses a photographic enlarger (1) to enlarge the document or film. This is subjected to a strong source of ultra violet light which is condensed and focussed across an adjustable objective (9), before enlarging. The screen emulsions are lit directly, without film contact. The enlarger can be horizontal or vertical and has an ultra violet lamp (2). The condenser has two plano-convex lenses (6a,6b). Very small films are used.

Description

 the current screen printing enlargers are used for the production of documents to be copied, that is to say enlarged films which will subsequently be brought into contact with a screen printing screen (fabric).

For this, use is made of exposure frames also called vacuum frames, or # contact frames, which have the function of strongly and regularly pressing the document to be copied onto the photosensitive emulsion layer of the emulsified screen print.

 The reproduction of the original, which is small, is therefore done on an ili scale between the document to be copied (enlargement film of the original) and the screen screen applied by pressing against it in the pneumatic exposure frame. .

 The appropriately insulated screen printing screen is used later, according to a known technique, for the final printing, for example of a commercial poster, this work being done on "printing tables" of the traditional type.

 Currently, it is therefore necessary, starting from an original document of which a small format film has been produced, to obtain a second enlargement film of the first, in a dimension equal to that of the screen printing screen that is desired. sunstroke, screen which will then be used to obtain the final impressions.

 Before being brought into contact with the screen printing screen, the enlarged film impressed from the small original document must be developed.

 It is only after development that it is brought into pressure contact with the screen printing screen. It is then exposed to the emission of a strong light source in ultraviolet radiation and the sensitive layer carried by the screen printing screen is impressed by this source through the image of the enlarged film, film in close contact with said screen.

 This traditional process therefore requires obtaining enlarged films, therefore gelatinous surfaces carrying emulsrons, of large surface area, an expensive raw material, a large labor force, and expensive equipment, in this case the pneumatic frame which is used to apply the enlarged film under pressure against the screen printing screen; vacuum plating also requires precise and expert handling.

 When we also know that a 3 m X 4 m poster obtained by screen printing is produced in 7 juxtaposed pieces requiring the production of 7 contact films, of lm20 X lm60 and this for a single color, and that 4 X 7 = 28 is required if the poster is in four colors, one can easily imagine the very high cost price of implementing this classic process.

 The plaintiff has tackled this problem in an attempt to reduce handling and colts in significant proportions. Experience has shown that this can be achieved in at least 50% of the time.

 What is surprising is that the inventor succeeded against all of the preconceived assumptions and theories of trades people, the solution seeming so little obvious that even tests in the sense of the invention had not attempted, the researchers considering a priori that the path discovered by the inventor would inevitably lead to failure. Experience and perseverance in a "prohibited" direction has surprisingly proved the opposite, which gives the invention its originality.

 The inventor deliberately rejected the enlargers of the screen printing benches used in the field of graphic arts, and which generally use frosted glasses for the operation of exposure to ultraviolet light.

 The process according to the invention essentially consists in using a photographic type enlarger, to enlarge the document or negative film of small format to be reproduced, in subjecting this document to the emission of a relatively powerful source of ultraviolet radiation, to condense and focus the light through an adjustable objective in order to project the enlargement, and to directly insulate the emulsified serigraphic screen without passing through a traditional contact film.

 The great originality of the process therefore lies in the direct awareness of the emulsified layer of the screen printing screen from an enlarged image transmitted by ultra-violet radiation.

 A vertical or horizontal photographic enlarger using an ultraviolet lamp as a light source therefore makes it possible to obtain an enlarged projection capable of insolation, that is to say of attacking the sensitive emulsified layer of the screen printing screen.

 Since, according to this new method, direct and enlarged sunshine is produced on the screen, it is therefore no longer necessary to manufacture intermediate contact films, at high cost and representing a significant workforce. As a corollary, since it no longer passes through these fiE # s # contact, this eliminates the necessary pneumatic chassis and the manipulations relating to bringing in contact and under vacuum pressure of the films enlarged with the screens. serious graphics.

 It has been proven by experience, it seemed like a challenge to tradespeople, that the ultra-vio # ets rays still retained enough power when passing through all the elements of the optical system of the photographic enlarger to have the capacity to realize an enlarged projection generating direct sunlight on a screen-printed screen.

The presumed loss of ultraviolet radiation is compensated for by the combined effect in the enlarger of an additional lens and an optical capacitor, for example two plano-convex lenses with face to face connectivity, and by the total suppression of all frosted glass. These lenses can be of any suitable material, optical glass or synthetic resin,
The ultraviolet light source can be of any known type (halogen metal, Arc, Xenon, etc.). The adaptation of any enlarger to the reproduction bench is extremely easy with this new type of lighting for the recommended purpose.

 Finally, it will be noted that the exposure time with this new method of projection by direct enlargement is substantially the same as by the conventional method.

 It will also be noted that the production of pictures to obtain the "printed circuits" can be carried out according to the same process as that of screen printing screens.

 By way of illustrative example and without this having any limiting character, an apparatus for implementing the invention will be described below.

 The single figure of the accompanying drawing shows an elevation in vertical section of an enlarger according to the invention.

 In this drawing, we see at 1 the chamber of the device, at 2 the source of ultraviolet radiation, at 3 the mechanism for adjusting the source, at 4 a converging lens with its cooling fan 5, at 6a and Gb the two plane-corvex lenses forming an optical capacitor, at 7 their cooling fan, at 8 the negative format film or document holder chassis constituting the original to be reproduced, at 9 the objective and at 10 the adjustment mechanism of the objective.

 It goes without saying that one can, without departing from the scope of the present invention, make any modification to the embodiments which have just been described.

 In particular, it will be possible, using the same apparatus as that described, to insulate or print daylight films or papers by the same UV lamps in enlargement or reduction or reproduction with opaque or transparent documents.

Claims (2)

 1 - Process for raising awareness of screen printing, essentially characterized by the fact that it consists in using a photographic type enlarger, to enlarge the negative document or film - of small format to be reproduced, to submit this document to the emission a relatively powerful source of ultraviolet radiation, to condense and focus the light through an adjustable objective in order to project the enlargement, and to directly insulate the emulsified serigraphic screen without passing through a traditional contact film.  2 - Apparatus for implementing the method according to claim 1 characterized in that it comprises - an enlarger of the horizontal or vertical photographic type - an ultraviolet emission lamp - a converging lens in any event - an optical capacitor advantageously composed of two planconvex lenses - and an adjustable objective, to obtain a projection and an enlargement on a screen print screen exposed directly.