US2317521A

US2317521A - Sensitizer containing gel-forming colloidal clay

Info

Publication number: US2317521A
Application number: US416046A
Authority: US
Inventors: Clyde A Crowley; John B Mullen
Original assignee: HUEY Co
Current assignee: HUEY Co
Priority date: 1941-10-22
Filing date: 1941-10-22
Publication date: 1943-04-27
Anticipated expiration: 1960-04-27
Also published as: USRE22579E

Description

Patented Apr. 27, 1943 umrso STATES PATENT OFFICE SENSITIZER CONTAINING GEL-FORMING COLLOIDAL CLAY 9 Claims.

This invention relates to improvements in the sensitized layers of photosensitive papers, and to means oi accomplishing these improvements. An object of this invention is the formation of sensitized layers with improved properties, particularly sensitized layers which have higher printing speed, which can be washed more rapidly, and which will give images at greater shapness, better definition, and improved clarity.

Among the types of sensitizers to which our invention can be applied are so-called "blueprint sensitizers, either of the negative or direct positive type; diazo" sensitizers: and direct line iron sensitizers, whch are cited merely as examples of specific types of sensitizers with which our invention can be used. In general, our invention can be used with any type of sensitized layer which is applied to a base of paper, cloth, or the equivalent from a solution in water, whatever the active light sensitive chemicals may be.

In the ordinary process oi preparing blueprint papers, paper or other suitable base is coated with a solution which comprises light-sensitive ferric compounds such as ammonium ierrioxslate, a ferricyanide salt, and usually so-called solubilizing" or buflering agents such as potassium oxalate, which are used primarily to improve the keeping and washing quality of the sensitized paper. The customary practice is to pass the paper stock over coating rollers, which apply the sensitizing, solution, after which the paper is dried. It is common practice to apply two coats of the sensitizing solution before drying. The papers are subsequently exposed to light under a design, washed to remove unreacted chemicals, developed in a solution of an oxidizing agent such as potassium dlchromate, and rinsed before drying. The resulting prints are negatives of the original design, with white lines on a blue background.

This process suflers from a number of disadvantages. In the flrst place, the sensitizer penetrates into the paper below the surface for a considerable distance. This has two undesirable effects: First, it slows down the action oi light on the sensitive chemicals appreciably, since these chemicals are partially concealed in the paper matrix; and secondly-for the same reason, it makes washing slower than is desirable and often less thorough. In addition, partially because washing must be protracted, some chemicals may wash or bleed irom the exposed to the unexposed areas. causing indistinct lines and images. The contrast is also reduced thereby.

In other types oi sensitive papers of the gen- A. Crowley and m... B. Mullen, Chicago, asaignors to The Huey 00., Chicago,

No Drawing. Application October 22, 1941, Serial No. 416,046

eral type described above, the same difliculties occur also, in greater or less degree. The disadvantages generally tound in processes in which an aqueous sensitizing solution is applied to pa- 5 per 01 similar base, and arising largely from penetration of the sensitizer into the paper, can be summarized briefly as follows:

(1) The speed is reduced by penetration; (2) the ease, speed, and completeness of washing are lowered; and (3) the possibility of bleeding and of indistinct lines is increased. All or some of these difllculties are found in blueprint papers, whether of the ordinary lemon-yellow type containing ierricyanide, or the blue-blue" type containing i'errocyanide; in diazo papers; in silver negative or brown print papers; and in the various direct line iron papers.

Various means have been tried to eliminate these troubles By increasing the concentration of the sensitizer, it is possible to increase its viscosity and, therefore, to reduce penetration. However, this method causes great difllculty in the coating plant, since the highly concentrated solutions are subject to crystallization when slight evaporation or change in temperature occurs, and will, therefore, change in composition (affecting the nature of the sensitized layer), and may even deposit crystals on the paper web. The use of a hard-surfaced paper has also been tried, which reduces penetration and actually makes 'it possible to eliminate the loss in speed and slowness of washing caused by penetration. However, in practice it is not possible to use a paper with a sufllciently hard-sized, non-absorbent surface to eliminate these effects entirely, since to do so would mean that the sensitized layer on the paperwould be so thin that it would give grossly insufllcient pigmentation. Also, since with a paper of this type of surface there is no means of bonding the sensitizing chemicals to the paper,and they are actually laid on the surface, bleeding is actually increased rather than reduced.

Some mean of attaching the sensitized layer firmly to the paper is required, and no better method for use with aqueous solution sensitizers has been found than penetration into the paper. The best that has been done to date is to attempt to control the penetration by means of the surface size on the paper.

A We have discovered a method whereby aqueous solution sensitizers of the types described above and other types of sensitizers in aqueous solution can be applied to paper or similar base, which liminates in whole or in part these objectionable features found hitherto. Our invention consists in the use of a sensitizing solution which contains bentonite or an equivalent type oi gelforining colloidal clay, which is coated onto the paper or other base. By the use or such a sensitizer, it is possible to obtain a sensitized coating which is substantially on the surface of the paper, so that itis in a position to react most rapidly with the light; soluble unreacted chemicals can be washed out more readily and completely, and as the bentonite (or its equivalent) serves to bind the chemicals to the paper, reaction products are less likely to be washed into the unexposed areas.

In the practice of this invention, an aqueous sensitizing solution or suspension containing the light-sensitive chemicals and bentonite is applied to the surface of the paper, cloth, or other base by any suitable means. One method of application is the use of coating rollers similar to those ordinarily used with aqueous sensitizers: by adjusting the tension on the paper as it passes over the coating rollers, it is possible to lay down a satisfaeio: y film, which is smoothed, and excess material removed if necessary, by use of a squeegee rod or a doctor's knife. Other methods of application can also be used, and will readily suggest themselves to those skilled in the art; and our invention is not limited to any method of application of the sensitized layer.

The amount of bentonite required varies with the nature of the paper or other base and with the nature of the sensitizing solution. The quantity of bentonite should be sutllcient to increase the viscosity of the sensitizer, and .to prevent substantially all penetration into the paper, With relatively hard-surfaced papers, or papers with a relatively impervious size, this will hat-- urally require less bentonite than with softer, more porous papers. Also, the nature and amounts of ions present and also the relative order of mixing of the components of the sensitizer affect the viscosity and other character'- istics of the final sensitizer. In general, it has been found that from 1% to by weight of bentonite will give satisfactory effects.

In practicing this invention, it is preferable to use a relatively hard-surfaced paper which has a low tendency to absorb water. Such a paper can be prepared by use of a glue size which is subsequently tanned by formaldehyde or other agents, by sizing with resins such as urea-iormaldehyde type, by use of other types of surface sizes, or by supercalenderlng, or by combinations of these means or by other means. However, it is possible by proper control of the sensitiaer to obtain good results even on papers of more open or porous structure, and our invention is notlimited to any particular type of paper.

We have mentioned the fact that bentonite increases the viscosity of the sensitlzer; however, this is not believed to be the sole explanation of its effect in reducing penetration into the paper. If such were the case, it would be possible simply by increasing the content 01' dissolved solids, for example by the addition of sugar, to increase the viscosity suiiiciently to reduce penetration. However, although this has been attempted in the past, it is possible to achieve the eflect desired only to a limited extent by this method.

Bentonite and other gel-forming colloidal clays are hydrophllic colloids, and when dispersed in water they reduce the amount oi free or available water. By so doing bentonite increases the viscosity of the solution. but its eifects are not ascribable to the increased viscosity alone. but rather to the reduction in the free water, since all or a large part of the water is linked to the bentonite (or to the ions) as water by hydration. While this is believed to be the true explanation of the action of bentonite, our invention is not limited to this explanation.

Example I A. Bentonite g 10 Water ml 96 B. Ammonium oxalate ..g.. 6 Citric acid g 6 Ferric ammonium oxalate g- 39 Potassium ferricyanide g.. 5 Water to make ml 244 (Density l3 B.)

Example I! A. Bentonite -g 16.00 Water ml 145.00 B. Oxalic acid (H2C2O42H2O) g 6.00

Potassium carbonate (KZCOJ-2H20) g 13.31 Potassium ierrocyanide g 15.00 Potassium ferricyanide g 0.375 Ferric ammonium oxalate g 30.00

Water to make -ml 314 (Density 13.2 B.)

Example III A diazo sensitizer is prepared as follows:

A. Diazo sensitizer g 70.0 B. Bentonite g 3.0

Water A is added to B and mixed thoroughly. The mixture is coated on to paper, and the paper is exposed under a design to light. Development is efiectecl with an alkaline solution or a coupling agent consisting of phloroglucinol, resoreinol, sodium carbonate, and water.

Diazo papers can also be prepared under this invention by incorporating in the sensitize: the coupling compounds; the sensitizer must then be acid to prevent coupling. Such papers are developed after exposure by treatment with a solution oi an alkali or by exposure to a moist atinosphere containing ammonia or other alkaline vapor.

. The term bentonite is intended to describe the colloidal clay round almost exclusively in Wyoming. The term is not a trade name, but a generic name descriptive of the clay round in the Fort Benton area. There are other similar colloidal clays found in other parts or the United states and known as subbentonite clays and available for use. although with less eflectiveness in the use outlined in the foregoing description.

It will be understood that this invention is not restricted to the particular sensitizers shown, nor to the types oi. sensitizers shown, which are cited merely as examples; and no unnecessary restrictions are to be assumed therefrom.

We claim:

1. A sensitizer comprising light-sensitive chemicals and a gel-forming colloidal clay.

2. A sensitizer comprising an aqueous solution of light-sensitive chemicals and a gel-iorming colloidal clay.

3. A sensitizer comprising light-sensitive chemicals and gel-forming bentonite. A

4. A sensltizer comprislna an aq eous solution of light-sensitive chemicals'and gel-forming bentonite.

5. A sheet containing a layer 01' light-sensitive chemicals and gel-forming bentonite.

B. A sheet having a composite layer includin a sensitize'r and gel-forming bentonite, said bentonite acting to inhibit penetration of the chemicals into the structure.

7. A sheet having a composite layer including a sensitizer and gel-forming bentonite in the proportion or 1 to 10% by weight of the sensitizcr. said bentonite'acting to inhibit penetration of the sensitizer into the body of the sheet.

8. A sensitizer tor blueprint paper including a light-sensitive i'erric compound and a minor proportion of a geldorming colloidal clay.

9. Blueprint paper comprising a sheet having a composite layer including a sensitizer comprisin: light-sensitive ferric compound and a minor proportion 01 a gel-forming colloidal clay, said clay acting to inhibit penetration or the sensitizer chemicals into the body oi the sheet.

CLYDE A. CROWLEY. JOHN B. MULLEN.