US2141103A - Manufacture and development of light-sensitive coated paper - Google Patents

Description

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Patented Dec. 20, 1938 unirso 'rrrr ATENT OFFECE MANUFACTURE AND DEVELGIMENT 0 LIGHT-SENSKTIVE COATED lPAPER No Drawing. Application July 27, 1936, Serial No. 92,930

2 Claims.

Our invention relates to improvements in the manufacture and development of light sensitive, coated paper.

Positive prints, so-called, have been made by various processes in which a tracing of a drawing, or other transparent positive is placed over a sheet of material, usually paper, having a sensitized coating thereon. After exposure to light the print is subjected to a developing operation which develops the parts screened from the light, causing the lines (in the case of a mechanical drawing) to-stand out in contrast with a lighter background. The advantage of such a positive print is that explanatory words or figures, subsequently written on the background with pen or pencil are more legible than where they are written on a dark background, as in the case of a blue print. Also, such positive prints are less trying on the eyes where the proper colors are employed. Certain kinds of positive print paper are now available whereon the sensitized coating consists of diazo compounds. Such compounds are decomposed when subjected to light, so that the formation of an azodyestuif with a coupling com- The areas screened from the light, however, as for example by the lines on a tracing, remain unchanged and may react with a coupling component to form an azodyestuif. Where the sensitized coating comprises both the azo component and the diazo component, the same may be developed by an alkali such as gaseous ammonia. Where the ammonia fume de veloper has been used, the two ingredients have een applied as a coating to one side of the paper. In using the developer, specially constructed apparatus must be provided to prevent the escape of ammonia fumes. The process requires a substantial amount of time and the contrast between the lines and the background is not as well defined in many cases as is desired.

Another method of employing diazo compounds has been to apply one of the ingredients to the surface of the paper, the other ingredient and an alkali being applied as a developing solution. Such developer is costly due to said ingredient, and its application calls for certain knowledge and skill on the part of the operator to obtain prints uniform in color. For example, water graduallyevaporates from the supply of the de veloping solution thus changing its effectiveness unless the concentration is maintained constant by the operator. As a result, the color of successive prints changes.

Our invention overcomes these difiiculties and makes possible the production of diazo positive prints in which a strong color contrast is obtained, in less time, and at a lower cost of developing solution than heretofore.

In using the method in which the reaction is caused by the application of an alkali, as for example by ammonia fumes, it has not been practical to apply the alkali in the form of a liquid, as the liquid causes the chemicals on the exposed and unexposed areas to intermingle, more or less, resulting in a blurred print, 1. e, causing so-called bleeding". Therefore, the alkali has been applied in the form of a gas, which is much less convenient to control than a liquid.

One of the objects of our invention is to provide an improved process whereby the developer for prints of this character may be applied in the form of a liquid but without causing bleeding.

Another object is to improve the process in which fumes of an alkali liquid are used, by greatly accelerating said process.

A further object is to provide a process in which one side of the sheet is coated with an azo' component and a diazo light-sensitive salt, and the print thereafter developed by applying an alkaline solution to the opposite side of the sheet.

Where the sheet is of paper, 1. e. of a cellulosic material, the reaction is more effective and the resulting prints are greatly improved.

The invention will be understood readily by reference to certain observations and experiments. We have discovered that when the paper is coated with the azo component and diazo compounds, a liquid developer containing an alkali can be applied to the back of the paper and better results obtained than are obtained with the fume method of development and also without experiencing the running of the chemicals or bleeding. We have also discovered that an application of moisture to the back of the paper just prior to subjecting the coated side thereof to the action of the ammonia fumes, very greatly accelerates the rate of development. Any aqueous solution which will not react with the ammonia fumes may be used. In the prior process the damp fumes to which the dry printed sheets are subjected arise from concentrated ammonium hydroxide solution. If this same solution is applied to the front side in the form of a liquid a very weak color development takes place in addition to the objectionable bleeding referred to. Under our improved method, however, a comparatively weak solution, for example a 5% ammonia solution, applied to the rear surface of the paper causes rapid development and gives the deepest colored lines possible. Without limiting ourselves to any particular theory we beiieve that this improvement in color contrast is due to some relation or reaction between the two constituents, i. e, the light sensitive diazo compound and the azo component, with the cellulose fibers of the paper stock. It does not appear to be caused by any other agent or ingredient in the diazo salt, the azo component or thepaper stock. We have found that certain agents may be incorporated in the diazo salt, the azo component or the paper stock that-suspend either or both, separately or mixed, with or without alkali, which agents retard or accelerate the well known color forming reaction between these two materials.

The following test will illustrate certain phases of the invention. For the light sensitive diazo compound the following may be used:

l-diazo-2-naphthol*4-sulphonic acid This may be prepared as an aqueous solution of almost any concentration after which a small quantity of an azo component, for instance, resorcinol, (convenient in solid form) is placed directly into this diazo solution and the solution stirred rapidly to dissolve all the azo component in the least possible time. The solution will color by coupling within several minutesafter the addition of the resorcinol, thus ruining it for the test. Hence said solution should be poured out quickly upon a thick piece of one hundred per cent rag unsized paper stock. Filter paper which is one hundred per cent rag is used for this test. This paper is allowed to dry in air, or at a low heat until thoroughly dried. On this sensitized paper about ten drops of any alkali solution may be dropped on the same spot (5% ammonium carbonate is satisfactory). Color development takes place immediately, the most intense color appearing not at the central point but at the fringes of the spot which spreads from the center, i. efwhere the solution is absorbed by the fibers as it spreads to the outer edge of the circle. If a second piece of filter paper, saturated with the same 5% ammonium carbonate solution, is placed over a different area on the same sensitized sheet, so that it just dampens the said area, the color development is intense and uniform throughout said area. Although this peculiarity of dye stufis in solution to stratify when placed upon porous filter papers has been known heretofore, it has not been applied to the development of sensitized papers of the diazo type.

Our invention then, when back-side development of positive diazotype papers with an alkali solution alone is considered, arises out of an observation that if an alkali solution approach a dried coating consisting of a mixture of a nonsubstantive diazo compoundand an azo component in an acidified, latent or inhibited state, through a layer of pure cellulose fiber, then on contact of the alkali with such a coating, the dye produced will immediately be substantive on the fiber, i. e. it adheres thereto. The cellulose fibers alone have thus acted, in efiect, as a mordant. Also, substantiveness is maintained when diazo compounds that are innately substantive are used in the coating under the same conditions.

The formula given in connection with the above mentioned test is by way of illustration only, as practically all of the formulae used heretofore in making diazo prints may be used in connection with the processes of our invention. Particularly do we wish to stress the fact that we have found that those diazo derivatives which usually give dark to black colors, couple rapidly with azo components, and are characterized byhaving a tertiary bound nitrogen atom in a para position to the diazo group, function well in most of the processes described herein.

The following example illustrates our invention:

The azo component is present in the light sensitive layer, together with the diazo compound. An alkali solution is applied to the back of such sensitized paper to eifect the color development and cause the coupling to take place.

In applying the liquids in the foregoing example, the paper may be caused to travel over a roller dipping in the liquid or the latter may be supplied in the form of a spray, in either case somewhat similar to the equipment used in continuous blue print machines.

In accordance with the present invention, the developing compounds which are most suitable are aqueous solutions of alkalies or alkaline-reacting substances and ammonia and its compounds are included under the term alkaline-reacting substances. In addition to ammonia and ammonium carbonate as suitable alkali compounds, sodium carbonate and potassium carbonate may also be used.

We claim:

1. The process of developing light-exposed, positive diazotype prints having a diazo compound and an azo component applied to one side thereof, which consists in applying an alkali solution to the other side thereof exclusively to effect the coupling.

2. The process ofmaking non-bleeding prints which consists in applying a diazo compound and an azo component to one side of a sheet of paper,

' exposing the same to light and thereafter developing the print by applying an alkali solution to the other side only thereof to efiect the coupling by the penetration of said solution through the material of said sheet.

HAROLD J. BRUNK. MORRIS DICKASON.