US2572930A - Exposure apparatus for contact printing - Google Patents

Description

Oct. 30, 1951 P. H. HELDENS EXPOSURE APPARATUS FOR CONTACT PRINTING Filed Dec. 16, 1948 Patented Oct. 30, 1951 EXPOSURE APPARATUS FOR CONTACT PRINTING Peter Henrikus Heldens, Venlo, Netherlands, assignor to Chemische Fabriek L. Van Der Grinten, Venlo, Netherlands, a company of the Netherlands Applicationneeember 16, 1948, serial No. 65,638, In the Netherlands July 17, 1946 sclaims. (c1. sis- 73) This invention relates to apparatus for making exposures in photographic contact printing, in which exible sheets such as lms, papers or the like, are exposed to light transmitted through a supporting cylinder. The flexible sheets comd prise a light sensitive layer in contact with an original. While the invention is useful invarious kinds of photographic contact printing, it is particularly suitable and serves important needs in diazotype contact printing processes.

An object of this invention is to provide an apparatus of the nature mentioned that enables Vaccurate determination of the duration of exposure and yet accommodates iiexible sheet material having any of a Wide variety of dimensions, and which is operated and controlled inv a simple and. reliable manner, so that the apparatus may A serve general uses in oflices or vthe like. and may be operated eiiciently even by unskilled persons.

The exposure apparatus here employed is ofy the type utilizing a hollow rotary cylinder of lightpervious material upon which to wrap the sheet material for exposure and through which to expose it from a light source inside the cylinder, together with a iiexible apron for wrapping and 'holding the material over the cylinder. 'I'his apron may approach the cylinder` tangentially and pass further over it in a position in which the apron is movable back and forth in its own plane, with rotation of the cylinder, so as to wrap and unwrap itself about the cylinder in supporting relation to sheet material laid upon the apron. Thus in the initial position of the apparatus the portion of the apron approaching the cylinder .may receive the material to be exposed, and when vthe apron is next moved into the working or exposing position of the apparatus, at which it is wrapped about the cylinder, it will overlie and hold the material properly against the cylinder. Inrthis way the sheet material to be exposed can have nearly any shape or surface area that may be accommodated Within the surface area of the cylinder available to be lapped by the apron, and simple apparatus and manipulations serve for positioning and exposing the material. kBut the desired control `of the exposure-proper, especially determination of the proper duration of exposure in relation to the moment of full penetration or transmission of eiective light through the material, is not accomplished. This presents difficulty because the effective light may becomposed largelyv of invisible Wave lengths, the apron is generally a :fabric either entirely impervious or lacking a uniform degree of perviousness to the light, and the surface area and disposition ofthe material to be exposed are subiect to variations.

To achieve this desiredcontrol, according to the present invention, at least a local area of the apron is made pervious to the effective light, and this area is located s0 that in the normal position of the apparatus,4 whenever sheet material to be exposed is placed upon the apron, at least a part of the material will be laid over the light pervious area. In the working or exposing position of the apparatus the light pervious area of the apron assumes a denite radial location with respect. to the axis of the cylinder and it overlies part of the. material to be exposed; and at or along a radius of that location a photoelectric cell is arranged outside the cylinder so that it will be acted-upon by rays transmitted from the light source through the cylinder, the sheet material held upon it and the light pervious area of the apron` in the course of eachr exposure. Accordingly, when radiation from the light source penetrates through the material being exposed the photoelectric cell is energized correspondingly, and its response may be utilized` for accurate control or indication of the duration of exposure by causing itV to activate a connected exposure control means, for example, a galvanometer orl an electric control apparatus that inactivates the light source.

The light pervious area of the apron may be formed of inset material that is translucent or transparent to the effective light, or it may be merely an opening in the apron fabric. Unless the photoelectric cell itself is sensitive only to the light effective in thev exposing process, and not to ineffective` rays thatmay pass freely through sheet material beim exposed, a light lter should be provided between the photoelectric cell and the light source. The light lter should be one transmitting vonly rays that penetrate increasingly through the light-sensitive sheet material as the exposing process progresses. The filter may be integral or combined with thelight pervious area of the apron, or it may be a part of the. photoelectric cell unit.

In embodiments of the invention adapted for use in diazotype contact printing a light lter that absorbs rays having wave lengths in excess of 4500 A. may be used effectively, since diazotype films, papers or the like absorb especially rays of shorter wave lengths than 4500 A. The exposure of diazotype sheet material results after a certain period in a fairly sudden penetration of, the effective light through the diazo layer, and from the course of this penetration a desirable end point for the exposurel can be deducted. The 4course of this penetration can be ascertained readily through action of the photoelectric cell. In connection with a galvanometer, for example, the photoelectric cell causes the light transmitting analysis of the diazotype material and the progress of the exposure to be indicated continuously by the galvanometer so that, through observation of its pointer, the exposure may be discontinued in each instance at the right moment.

Other objects, features and advantages of this invention may be apparent from the followingk detailed description of an illustrative embodiment and from the accompanying schematic drawing thereof. It is to be understood that the improvements or combinations hereinafter claimed as this invention may be embodied in various other forms and ways.

In the drawing:

Fig. 1 is a schematic perspective view of the illustrative embodiment;

Fig. 2 is a schematic vertical cross section through the light pervious cylinder, showing its relationship to the light source, the flexible apronand the photoelectric cell in the initial or non-exposing position of the apparatus; and

Fig. 3 is a vertical cross section similar to Fig. 2 in the working or exposing position of the apparatus, in which sheet material for exposure is held against. the cylinder by the apron Wrapped thereover.

t 4Referring more particularly toFig. 1, the apparatus has a frame or casing I formed by side walls 2 and 3 and front and back Walls 4 and 5, respectively. A pivoted hood 6 to cover the cylinder is hinged at 'I to the upper edge of back wall 5. in the frame for rotation about a horizontal axis, this cylinderbeing supported rotatably on rollers 9. There are three of these rollersat each end of the cylinder, having their axes xed at I0 in the respective side walls 2 and 3 of theframe. A tubular lamp II, preferably a high pressure mercury vapor lamp', is mounted inside the cylinder 8 at a central position along its axis so that radiation from this lamp will pass uniformly through the wall of the cylinder to material held against its surface. i

A flexible 'apron I2V is arranged with one end xed to the glass cylinder along a generating line near I3. This apron extends over part of the surface of the cylinder and thence tangentially forward in a horizontal plane to a roller I4 mounted between side walls 2 and 3 near the front wall 4. The portion I5 of the 'apron approaching cylinder 8 from roller I4 thus forms, in its initial position, a 4kind of table upon which suitable sheet material may be placed for exposure. From the front of this portion the apron passes over roller I4 downward and thence backward inside the frame, as an extension I6 which may be kept stretched by tension springs I'l connected thereto and to the frame.

As seen in Figs. 1 and 2, the fabric of the apron has an opening or similar light-pervious area I8 on the apron the material and the apron are Wrapped about the cylinder, through rotation of the cylinder in any suitable manner, such as by putting the hand on its surface and pushing it to a working or exposing position substantially as illustrated in Fig. 3. The springs I1 keep the apron tightened although being not strong enough to rotate the cylinder automatically back.

A hollow glass cylinder 8 is mounted formed in it, through which the apron may transmit the effective light from tube II. This area may be left unobstructed or provided with an inset piece I9 of transparent material, but it preferably is inset with a light lter at I9. The light-pervious area is arranged in table portion I5 of the apron that receives the sheet material to be exposed, and it preferably is disposed centrally near to cylinder 8 so that upon placing any usual size of such material on the apron up to its line of tangency with the cylinder a part of the material will be sure lto overlie the lightpervious area.

l After the'sheet material has been Vplaced thus As there shown, the sheet material to be exposed may consist of an original 20 to be copied and a light sensitive diazotype sheet 2I, and the original lies next to the surface of cylinder 8 with the diazotype sheet in contact and the assembled sheet material held in proper position by apron portion I5 wrapped about it. At this exposing position of the apparatus the light-pervious area I8 has been displaced to a definite radial location with respect to the axis of cylinder 8, and it overlies part of the sheet material'between it and light source I I.

. A photoelectric cell 22 is mounted at that radial location, outside the cylinder and the orbit o f the apron Wrapped thereon, so that the photo.. electric cell will receive and respond to 4light transmitted through the material lbeing exposed and the light-pervious area. The photoelectric cell 22 may be mounted, for example, o n a bracket 23 held by a crossbar 24, so as to be stationary and separate from the cylinder assembly. The photoelectric cell is connected byvwiring 25 with a galvanometer 26 so that the galvanoineter is energized according to the intensity of light striking the photoelectric cell and thus indicates the progress of the exposing process.

In `embodiments of the apparatus adapted for diazotype contact printing, a light filter is used that absorbs wave lengths in excess of 4500 A. The light filter in anyv case may be part of the photoelectric cell unit'22 instead of being applied as at I9 tothe opening or light-pervious area of the apron.

While exposing material in the apparatus the hood 8 preferably is kept closed. `It has a recess 21 to accommodate the photoelectric cell unit'22 in closed position. The progress of the exposing process is determined by watching the galvanometer 26. When the effective light from tube II breaks with increasing intensity through the material being exposed, the photoelectric cell and the galvanometer respond accordingly, and the person attending the apparatus then may discontinuethe exposure when the highest intensity has been reached or has been nearly reached with assurance that a satisfactoryprint may beA obtained.

I claim:

1. In an exposure apparatus for photographic contact printing comprising a hollow rotatable exposure member having a cylindrically `curved panel of light-pervious material, a light source within said member, and a flexible apron engaging and movable with the surface of the panel and having a portion of its length extending away from the panel in one position to permit the insertion of an original sheet and a contacting sensitized diazotype sheet between the apron and said surface, the apron moving upon rotation of said member to move sheets so inserted to an exposing position at which it is wrapped and holds such sheets about said surface, alight-pervious area provided at least in' a part of `said apron portion that overlies such sheets in exposing position, a photoelectric cell mounted adjacent to but outside the path of said apron on a'radius from said light source that passes through said light-pervious area and a sensitized sheet thereunder when the apron is at exposing position, and means connected with said cell and responsive to its activation as light penetrates through such sensitized sheet for indicating the progress of an exposure.

2. An exposure apparatus as described in claim 1, said exposure indicating means being a galvanometer visible to an attendant of the apparatus.

3. In an exposure apparatus for photographic contact printing comprising a hollow rotatable exposure member having a cylindrically curved panel of light-pervious material, a light source within said member, and a flexible apron engaging and movable with the surface of the panel and having a portion of its length extending away from the panel in one position to permit the insertion of an original sheet and a contacting sensitized diazotype sheet between the apron and said surface, the apron moving upon rotation of said member to move sheets so inserted to an exposing position at which it is wrapped and holds such sheets about said surface, a lightpervious area provided at least in a part of said apron portion that overlies such sheets in exposing position, a photoelectric cell mounted adjacent to but outside the path of said apron on a radius from said light source that passes through said light-pervious area and a sensitized sheet thereunder when the apron is at exposing position, a light filter disposed on said radius between the photoelectric cell and the light source, said filter transmitting only light that penetrates increasingly through such sensitized sheet as antact printing comprising a hollow rotatable exposure member having a cylindrically curved panel of light-pervious material, a source of actinic light within the said member, and a ilexible apron engaging and moving with the surface of the panel and'having a portion of its length `extending away from the panel in one position to permit the insertion of contacting original and sensitized diazotype sheets between the apron and said surface, the apron moving upon rotation of the member to move sheets so inserted to an exposing position -at which it is wrapped and holds such sheets about said surface, a light-pervious area provided at least in a part of said apron portion that overlies such sheets in exposing position, a photoelectric cell mounted adjacent to but outside the path of said apron on a radius from said light source that passes through said light-pervious area and a sensitized sheet thereunder when the apron is at exposing position, a light filter that absorbs Wave lengths in excess of 4500 A. disposed on said radius between the photoelectric cell and said light source, and means connected with said cell and responsive to its activation as light penetrates through such sensitized sheet for indicating the progress of an exposure.

5. An exposure apparatus as described in claim 4, said light lter being in said light-pervious area of the apron.

PETER HENRIKUS HELDENS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 601,883 Schwarz Apr. 5, 1898 1,966,322 Tuttle July 10, 1934 1,973,469 Denis Sept. 11, 1934 1,973,470 Denis Sept. 11, 1934 2,024,678 Brunk Dec. 17, 1935 2,138,445 Dantzenberg Nov. 29, 1938 2,222,961 Szasz Nov. 26, 1940 2,238,762 Whitaker Apr. 15, 1941 2,364,580 Young Dec. 5, 1944 2,386,856 Houston Oct. 16, 1945 FOREIGN PATENTS Number Country Date 231,309 Germany Feb. 20, 1911 194,524 Great Britain Mar. 15, 1923

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