USRE22579E - Sensitizer containing a gel-forming - Google Patents

Description

Reisaued Dec. 19, 1944 I SENSITIZER CONTAINING A GEL-FORMING COLLOIDAL CLAY Clyde A. Crowley, Chicago, and John B. Mullen, Elgin, Ill., assignors to The Huey 00., Chicago, Ill., a corporation of Illinois No Drawing. Original No. 2,317,521, dated April 27, 1943, Serial No. 416,046, October 22, 1941. Application for reissue September 18, 1944, Se-

rial No. 554,599%

9 Claims.

This invention relates to improvements in the sensitized layers of photosensitive papers, and to means of accomplishing these improvements. An object of this invention is the formation of advantages generally found in processes in which an aqueous sensitizing solution is applied to paper or similar base, and arising largely from penetration of the sensitizer into the paper, can

sensitized layers with improved properties, parbe summarized briefly as follows: ticularly sensitized layers which have higher (1) The speed is reduced by penetration; (2) printing speed, which can be washed more rapidthe ease, speed, and completeness of washing ly, and which will give images of greater sharpare lowered; and (3) the possibility of bleeding ness, better definition, and improved clarity. and of indistinct lines is increased. All or some The types of sensitizers to which our invention of these iflle lties are found in l epri p pers. is applied are so-called "b1ueprint .sensitizers, whether of the ordinary e w type either of the negative or direct positive type; Containing fel'rieyanide, e yp diazo sensitizers; and direct line iron sensitizers, containing ferrocyanide; in diazo papers; and in In general, our invention can be used with any the Various direct line iron p p such type of sensitized layer which is applied to Va means have been tried eliminate a base bi paper, cloth, or the equivalent from these troubles. By increasing the concentration solution in water, whatever the active light sen- 0f the sensitizel. it is Possible to increase its sitive chemicals thereof may be. viscosity and, therefore, to reduce penetration. In the ordinary process of preparing blueprin However, this method causes great diiiiculty in papers, paper or other suitable base is coated the coating P since the h y concentrated with a solution which comprises light-sensitive solutions e subjecttocrystalliz ion e sl ferric compounds such as ammonium ferri-oxaevap r ion C e in temperature Occurs, and late, a ferricyanide salt, and usually so-called will, th re. n e in composition (affectin "solubilizing or buffering agents such as potasthe nature of the sensitized layer), and may even slum oxalate, which are used primarily to imdepos t c y t 0 t e Paper The use Of a prove the keeping and washing quality of the hard-surfaced paper has also been tried, which sensitized paper. The customary practice is to reduces Penetration and actually makes it P pass the paper stock over coatin rollers, which sible to eliminate the 85 in pe and s ow apply the sensitizing solution, after which the of washing caused by pe t t o e in paper is dried. It is common practic'e to apply practice it is not Po e o use a p p W a two coats of the sensitizin solution before drysumciently hard-sized, non-absorbent surfaceto ing. The papers are subsequently exposed to eliminate these eflects entirely, since to do so lightunder a design, washed to remove unreacted would mean that the sensitized a r o the P pe chemicals, developed in a solution of an oxidizing would be so thin t t it would give gro agent such as potassium dichromate, and rinsed ffi i nt pi m n ion Al since w p ner before drying. The resulting prints arev negaof this type of surface there is no means 01' bondtives of the original design, with white lines on sensitizing chemicals o e e and a blue background. they are actually laid on the surface, bleeding is This process suffers from a number of disadactually increased rat e t e vantages. In the first place, the sensitizer penedo some means tt g the sensitized layer trates into the paper below the surface for a firmly t0 e P p s required. and no better considerable distance. This has two undesirable method for use w th aqu us s uti n s nsitizers efl'ects: first, it slows down the action of li ht has been found then ati n int h pap r. on the sensitive chemicals appreciably, since these The best that has been done o date i to at mp chemicals are partially conc d i th paper to control the penetration by means of the surface matrix; and secondly, for the same reason, it Size on the P makes washing slower than is desirable and often We have discovered met od whereby aqueless thorough. In addition, partially because ous solution sensitizers of the types described washing must be protracted, some chemicals may above in aqueOlls Solution can be app to P p wash or bleed from th exposed t th or similar base, which eliminates in whole or in exposed areas, causing indistinct lines and part these objectionable features found hitherto. images. The contrast is also reduced thereby. Our invention consists in the use of a sensitiz- In other types of sensitive papers of the gening solution which contains bentonite or an era] type described above, the same difficulties equivalent p f gel-forming colloidal clay. occur also in greater or less degree. The dis- M whi h is coated onto the paper or other base. By

the use of such a sensitizer, it is possible. to

obtain a sensitized coating which is substantially on the surface of the paper, so that it is 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'e'quivalent) 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 ap-.

plied 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 satisfactory 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 oi bentonite, our invention is not limited to this explanation.

Example I A. Bentonite 10 Water ml 96 B. Ammonium oxalate g.. 6

Citric a I I 6. Ferric ammonium oxalate g 39 Potassium ferricyanide g Water to make ..ml 244 I (Density 13 B.)

The B solution is added to the bentonite suspension A while stirring. The paper sensitized with this solution is exposed under a design to light, washed, developed with an oxidizing agent,

- and again washed. Paper coated with this sensisuggest themselves-to those skilled in the art;

. and our invention is not limited to any method of applicat on 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 sufilcient to increase the viscosity of the sensitizer," and to prevent substantially all penetration into the paper.

tizer is faster and washes better giving clearer prints than paper sensitized with a sensitizer identical in composition except for the omission of the bentonite.

Example II A. Bentonite ...g 16.00 Water e ml 145.00 B. Oxaiic acid (HzCzOiBHzO) g 6.00 Potassium, carbonate (K130321120) g 13.31 Potassium ferrocyanide ..g 15.00 Potassium ferricyanide ..-g 0.375 Ferric ammonium oxalate g 30.00

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

Solution B is added to the bentonite dispersion A while stirring. The paper sensitized with this solution is exposed under a design to light, washed to remove excess or unreacted chemicals, treated with an oxidizing agent, washed again. and dried.

use a relatively hard-surfaced paper which has a low tendency to absorb water. Such a paper can be prepared by use ofa glue size which .is subsequently tannedby-formaldehyde or other agents, by sizing with resins such as urea-dormaldehyde type, by use of other types of surface sizes, or by super calendering, or by combinations of these means or by other means. However, it is possible by proper control of the sensitizer to obtain good results even on papers of more open or porous structure, and our invention is not limited to any particular type of paper.

.We have mentioned the fact that bentonite increases the viscosity of the-sensitizer; however, this is not believed to be the sole explanation of its eflect in reducing penetration into the paper. If: such were the case, its-.wo'uld be possible simply by increasing the content of dissolved solids, for example by the addition of sugar, to increase the viscosity sufliciently to reduce penetration. However, although this has been attempted in the past, it is possible to achieve the eiiect desired only to a limited extent by this method. vBentonite and other geliorming colloidal clays are hydrophilic colloids, and when dispersed in water they reduce the amount of free or available water. By so' doing bentonite increases the viscosity of the solu-, tion, but its effects 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 The paper so sensitized gives higherprinting speed, easier washing and sharper prints than paper prepared with the same sensitizer with bentonite omitted.

Erample m a 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 eilected with an alkaline solution of a coupling agent consisting of 'phloro-glucinol, resorcinol, sodium carbonate, and water.

Diazo papers can also be prepared under this invention by incorporating in the sensitizer the coupling compounds; the sensitizer must then be acidto prevent coupling. Such papers are developed after exposure by treatment with a solution of an alkali or by exposure to a moist atmosphere containing ammonia or other alkaline The term "bentonite" is intended to describe the .colloidal clay found almost exclusively in Wyoming. The term is not a trade name, but a generic name descriptive of the clay found in the Fort Benton area. There are other si ar colloidal clays found in other parts of the United States and known as subbentonite clays and available for use, although with less effectiveness in the use outlined inthe foregoing description.

It will be understood that this invention is not restricted to the particular sensitizers shown which are cited merely as examples of the type with which our invention is concerned; and no -ite and light-sensitive chemicals selected from the group consisting of 1) blueprint sensitizers. (2) diazo sensitizers, and (3) direct line iron sensitizers.

4. A sensitizer comprising gel-forming bentonite and an aqueous solution of light-sensitive chemicals selected from the group consisting of (1) blueprint sensitizers, (2) diazo sensitizers and (3) direct line iron sensitizers.

5. A sheet containing a layer of gel-forming bentonite and light-sensitive chemicals selected from the group consisting of (1) blueprint sensi- I tizers, (2) diazo sensitizers and (3) direct line iron sensitizers,

v gel-forming bentonite and light-sensitive chemicals selected from the group consisting of (1) blueprint sensitizers. (2) diazo sensitizers and (3) direct line iron sensitizers, said bentonite acting r to inhibit penetration of the sensitizer into the body of the sheet.

7. A sheet having a composite layer including gel-forming bentonite and light-sensitive chemicals, said gel-forming bentonite acting to inhibit penetration of the light-sensitive chemicals into the body of the sheet, said gel-forming bentonite being present in the proportion of 1 to 10% by weight of the light-sensitive chemicals, said lightsensitive chemicals being selected from the group consisting of (1) blueprint sensitizers, (2) diazo sensitizers and (3) direct line iron sensitizers.

8. A sensitizer for blueprint paper including a light-sensitive ferric compound and a minor proportion of a gel-forming colloidal clay.

9. Blueprint paper comprising-a sheethaving a composite layer including a sensitizer comprising light-sensitive ferric compound and a minor proportion of a gel-forming colloidal'clay, said clay acting to inhibit penetration of the sensitizer chemicals into the body of the sheet.

CLYDE A. CROWLEY.

JOHN B. MULLER.