US2154506A - Manufacture of blue-print sheets - Google Patents

Description

April 18, 1939.

UNDER COAT.

W. M. HINMAN ET AL Filed March 8, 1937 TOP COAT.

CONTAINING SALT FROM GROUP: SOLUBLE FERRICYANIDE AND FERROCYANIDE SALTS; AND OPTIONAL CONTENTS OF SIMPLE OXALATE SALT AND BODY LIKE CONTAINING LIGHT-SENSITIVE FERRIOXALATE SALT AND SOLUBLE FERRICYANIDE SALT; AND OPTIONAL CONTENTS OF REDUCING AGENT LIKE OXALATE SALT AND A BODY LIKE GELATINE.

GELATINE CARRIER LIKE PAPER fflyeizars. Zfla/fi'er" J6 flaw/mm Patented Apr. I8, 1939 UNITED STATES PATENT OFFICE.

2,154,506 mum-Acme or nrLUn-rnm'r sans-rs Walker M. Hinman, Winnetka. and Walter G. Hollmann, Chicago, Ill., assignors to The Frederlck Post Company, Chicago, Ill., a corporation of Illinois Application March a, 1937, Serial No. 129,040

Claims.

The present invention relates to blue print papers and the like of the type in which light is used to produce a blue background of complex iron cyanogen compounds from appropriate 3 light-sensitive chemicalmixtures, followed by a the increase in the speed of printing a paper without sacrifice of depth of blue color, and

15 another aspect of the same problem, an increase in the depth of color of a given speed" of paper. Attempts to solve these problems by increased concentrations of sensitizing solutions and increased thicknesses of sensitive coatings have reached a limited success, and then other dlfiiculties are encountered.

The object of the present invention is to make a sensitized blue-printing sheet which has when developed an improved depth of blue at a given printing speed, or a speedier paper for a desired depth of blue.

A particular object of the invention'is to use initially in the sensitive coating a product which is formed ordinarily inthe light-printing operation.

Still another object 'of the invention is to thicken the coating by dividing it into two different but contiguous bodies or layers, and to use in one body or layer materials which need not be struck by light, while reserving for the other body or layer, materials which must be struck by light.

Various other and ancillary objects and advantages of the invention will become apparent invention and of several ways of carrying it out.

The invention can best be understood by a brief reference to the fundamental chemistry of blue-print papers. Blue-print papers are. dry

ferrioxalate salt and potassium ferricyanide. The principle of operation holds that on exposing the sensitized paper to light the ferrioxalate salt is reduced forming ferrous oxalate. This 50 is an insoluble compound which is fixed inp'osition in the paper and forms the pattern of the print, and is changed later in situ to an insoluble blue compound. In the presence of water the ferrous oxalate and the potassium ferri- 55 cyanide react to form insoluble blue ferrous from the following detailed explanation of the sensitized sheets usually containing a suitable ferricyanide. Where light does not strike the sheet the ferrioxaiate remains unchanged and the original unchanged sensitizing mixture is washed out. Thus the developed sheet contains no chemical where it is protected from light, and contains blueinsoluble ferrous ferricyanide where it is struck by light.

Howeven'the practical operations are not fully in accordance with this main principle, partly because there are side or additional reactions. The first of these is a minor chemical reduction which takes place, principally during exposure, by action of the oxalate content of the coating on the ferricyanide, forming some theoretically undesired potassium ferrocyanide in the lightstruckportion, and leaving a portion of the theoretically desirable unchanged potassium ferricyanida. Therefore on wetting the exposed print there follows another side reaction whereby the newly formed ferrous oxalate combines also with the newlyformed potassium ferrocyanide to form ferrous ferrocyanide, which is a white insoluble compound. It is thus seen that where theory calls for transformation of the insoluble ferrous oxalate to a blue pigment, a white pigment also may be formed by the secondary reaction. Mixtures from blue to white may result. If the exposure to light is weak, the secondary reaction is .less and more blue pigment forms. If the exposure to light is strong the secondary reaction is greater and muchmore white pigment forms. In commercial practice there are mixed white and blue pigments having a a greyish blue appearance at this stage' In fact, it ,is a practice to encourage the photochemical reduction of ferricyanide salt to ferrocyanide salt by having present additional reducing agent such as an oxalate, a citrate or a tartrate; but preferably an excess of some soluble oxalate salt.

Theory at this stage calls for complete washing out of soluble material, largely solubleoxalate salts, so as to leave only these mixed white and blue pigments. Then, practice calls for oxidation whereby the insoluble white ferrous ferrocyanide is converted to insoluble blue ferric ferrocyanide. Air will oxidize it, but this is too slow. Hence a chemical oxidizer is used, and such use in more perfected form is set forth in the copending. application of applicant Hinman, Serial No. 727,248, filed May 24, 1934, the inventionof which is applicable to the paper made by the present invention.

Referring'to .the above description, it should be stated that it describes what occurs in blueprint papers having a sensitizing mixture of ferrioxalate and ferricyanide as appropriate salts. The ferrioxalate is essentially the one compound which must be decomposed or altered by light to produce ferrous oxalate. At the same time the ferricyanide is only incidentally but desir-' ably altered, and that occurs because it is usually present with some form of reducing agent, usually the ferrioxalate or other oxalate, which furnishes the reducing power whereby a ferro cyanide is formed. But this incidental reduction utilizes some of the actinic energy which should be directed toward forming ferrous oxalate; As

a result the paper is slower printing for a given depth of blue, or else the blue is weaker for a given time of printing.

According to the present invention this incidental waste of actinic energy in the light-printing period is minimized. The manner in which this is done may be presented in several aspects, but generally it may be said that the essential light-sensitive ferrioxalate is more effectively concentrated near the surface of the sensitizedsheet, and the ferricyanide content which ordinarily goes with it is lessened. Not only is this accompanying ferricyanide content, lessened by shifting its location, but the shifted portion is in whole or in part replaced by ferrocyanide and located below the top surface but contiguous thereto.

And in addition, to maintain more or less distinct but contiguous bodies or layers, a sizing, or matrix, or body, or vehicular substance 'of suitable sort may be used in one or both bodies or layers, to maintain a certain degree of isolation, at least until after the light-exposure has been made.

Thus, it has been found that more of the light energyin printing may be used to form a deeper field or image of insoluble ferrous oxalate. Upon development by wetting, the chemicals of the inner and outer layers readily diffuse to meet with each other. Thus the insoluble ferrous oxalate' formsthe blue insoluble ferrous ferricysnide, and also forms the white insoluble ferrous ferrocyanide, which latter is oxidizable in development to insoluble blue ferric ferrocyanide.

At this point it is pertinent to state that a dried I paper coated only with a solution of ammonium speed.".

In the practice of the present invention it has been found that the prior art practice of having ferrioxalate and ferricyanide intimately associated, must still beobservedmnd the ratio of these may vary greatly as in the prior art. .It has not been found possible to make a complete separation as the general discussion might lead the reader up to this point to suspect. Hence, since ferricyanide must be used in the surface coat, body or layer, it is preferred to use in the lower coat, body or layer ferrocyanide without ferri- 'cyanide, and to reduce the ferricyanide content of the surface coat, body or layer. In practice thetotal quantity of iron cyanides thus employed in both bodies orlayers maybe'less thanhas in place in developing the sheet.

been needed heretofore when there has been no separation into two portions.

In creating the coats, bodies or layers it becomes necessary to use something to define the same and to maintain some line of demarcation between them. This may be accomplished simply by using a gum or colloid. or other coating substance which will contain the chemicals, and which when wet will permit .the release or the difiusion of such chemicals from the colloid. Many film-forming substances are known and may be used such as: glue, gelatine, starch, dextrine, oxidized starch, other converted or soluble starches and starch derivatives, certain cellulose derivatives, regenerated cellulose, gum .arabic,

gum tragacanth, and a large number of gums and substances which may generally bedesignated as hydrophilic colloids or substances. Preferably they are used in solution form and are dried after application. Of course a paper'base itself may constitute a medium to define the first residue, and a second residue may be formed thereon. But usually the paper base for blue-print papers is highly sized or finished so that its surface is not at all or not very absorptive of coating solutions, thus to form more nearly true coatings rather than impregnated paper surfaces. It is customary in the ordinary coating of blue-print paper to use a coating solution containing an agent of the character above specified, such as glue or 'gelatine, partly in order to facilitate spreading of the sensitizing composition with even distribution over the sheet, and to hold it The present invention therefore contemplates using such agent in either or in both compositions to be applied in creating bodies or layers. It is also to be considered that a body or layer may be formed in two operations as well as in one, by first applying a suitable asent such as gelatine, or even regenerated cellulose, which may be dried in whole or in part, and then wetted with a solution which may contain the chemicals and may be lacking in a glue-like substance. I

In practical operations under this invention a well sized paper is used. This is coated with an under-coating composition containing hydrophilic substance and certain chemicals, and then dried. The driedcoating may be covered immediately or later with the surface-coating composition. and this likewise contains hydrophilic body substance by preference and the light-sensitive chemicals. If the hydrophilic body is omitted and the coating composition contains only chemicals, these enter the surface of the socalled-dried under-coating to a degree, but yet contiguous superimposed coats are present, although not sharply defined. By preference therefore, an agent such as selatine is included in eachcoating composition to maintain more eomplete-separation. Also, it is preferred to dry the first coating and to coat immediately, to form the second coating, since this assures uniform surface conditions on the undercoat for receiving the second coat, whereby the dual coatings present a uniform product when continuous production is employed. Actually, one drying oven is employed for a continuous web of paper. There aretwo' coating baths and devices, one positioned drying oven. An oven temperature of I".

is suitable for all the-solutions hereinafter .dis-

closed, but it is to be understood that this tem-' perature is not critical, nor is heat necessary for the process. Ordinary coating devices known to the art suflice for each coating composition.

Exmu: I

Under coat. Water to gallons 1 Pounds Sodium ferrocyanide 1 Ammonium oxalate 32 Potassium ferricyanidm 6 Powdered glue (adhesive grade) 26 Surface coat. Water to 100 gallons Pounds Ammonium ferrioxalate Ammonium oxalate 32' Potassium ferricyanide 18 Exmnn II Under coat. Water to 100 gallons Pounds Potassium ferrocyanide 6 Ammonium oxalate 32 Gelatin 6.5 Surface coat. Water to 100 gallons 1 Pounds Ammonium ferrioxaiate 175 Ammonium oxalate 8 Potassium ferricyanide 18 Gelatin 0.5

Under coat. Water to 100 gallons Pounds Sodium ferrocyanide 6.00 Oxalic acid 31.25 onia (26 Be.) 16.25 Anhydrous potassium carbonate.- 12.00 Powdered glue 14.25 Monosodium phosphate 3.50

Surface coat. Water to 100 gallmts Ammonium ferrioxalate lbs 189 Ammonia (26 es.) do 7.38 lvionosodium phosphate do 8.25 Qxalicacid do 7.00 Photoengraving glue ml 630 Potassium ferricyanide lbs 23.25

under the influence of light. The mono-sodium phosphate has also a retarding function, but doubtlessly through the difierent mechanism of hydrogen ion control by its bufier action. In Examples I and II the oxalate salts are employed as such in compounding the formula, and the ammonium salt alone is'used', since it is fairly insoluble and does not so readily transfer from the dried under coat in applying the surface coating composition. lmExample 111 these oxalate salts are built up from formative components, such as oxalic acid,.ammonia, and potassium carbonate, forming both ammonium oxalate and potassium oxalate. Slight excess of any such component is not harmful in the presence of the bufier salt monosodium phosphate, and this gives some latitude for variations of the formula by carelessness, error, or variations in material.

The accompanying drawing illustrates the invention showing particularly the arrangement of the bodies. In the drawing III illustrates the carrier base, which is preferably a well-sized sheet of paper as commonly used in the blueprint field, which can receive a liquid coating composition and form a residual coat when dried. Numeral ll represents the position of the resulting dried coat, as may be readily produced from the solutions designated Under coat in the examples. Numeral 12 represents the position of the residue formed by coating onto the dry body ii a composition such as that designated Surface coat in the examples, and drying the'same; The

legends on the parts indicate briefly the variations discussed hereinabove.

Returning to. the pertinent phases of the invention it may be noted that some of the oxalate content of the prior art, as well as some of the iron cyanide content, has been transferred from the light-sensitive surface coat I! to the undercoat ll. Since some reducing agent in addition to the oxalate content of ferrioxalate is desirable for transforming ferricyanide to ferrocyanide, it is desirable not to move all of the oxalate or other reducing agent (citrates and tartrates being also used), into the under coat. However, the lessened concentrations of such reducing agent and of ferricyanide salt is efiective to lessen the tendency for the ferricyanide to use up actinic energy in being reduced to ferrocyanide. Thus there is left a greater opportunity for the preponderating quantity of ferrioxalate to be reduced to the fleld-image-forming ferrous oxalate, without collateral loss caused by the presence of chemicals necessary for the later reactions of development.

From the foregoing it will be readily understood how the invention may be modified and changed from the preferred exples given. It is appreciated that difierent manufacturers of blue-print papers use variations of many basic formulas, and employ difierent combinations of potassium and ammonium salts. All those de perturesand modifications naturally occurring to those skilled in the art, and suggested herein.

sheet having two contiguous water permeable coats containing chemical ingredients, one coat being light-sensitive and located for positioning it between the other and a source of 'actinic light and containing light-sensitive ferrloxalate salt,

a soluble ferricyanide salt and a reducing agent therefor capable of converting the ferricyanide to ferrocyanide by the action of actinic light,-and the other coat containing a soluble complex salt of the group consisting of ferricyanide and ferrocyanide-which is adapted to difluse to the first coat upon wetting for reaction with the insoluble ferrous oxalate formed in the light-sensitive coat by the action of light.

. 2. A sensitized blue-print sheet comprising a sheet having two contiguous water-permeable various salts, usually selecting from sodiumf coats containing chemical ingredients, one coat being light-sensitive and located for positioning it between the other and a source of actinic light and containing light-sensitive ferrioxalate salt, I. a soluble ferricyanide salt and a reducing agent therefor capableof converting the fen'icyanide to ferrocyanide by the action of actinic light, and the other coat containing a soluble ferrocyanide salt which is adapted to diffuse to the first coat 1. upon wetting for reaction with the insoluble ferrous oxalate formed in the light-sensitive coat by the action of light.

3. A sensitized blue-print sheet comprising a sheet having two contiguous water-permeable 1 coats containing chemical ingredients, one coat therefor capable of convertingtthe ferricyanide to ferrocyanide by the action of actinic light, and the other coat, containing ,a soluble ferrocyanide salt and a soluble fer'ricyanide salt both of which are adapted to diffuse to the first coat upon wetting for reaction with the insoluble ferrous oxalate formed in the light-sensitive action of light. L A sensitized blue-print'sheet comprising a sheet having two contiguous water-permeable coats containing chemical ingredients, one coat being light-sensitive and located for positioning it between the other and a source of actinic light and containing light-sensitive ferrioiutlate salt, a soluble ferricyanide salt and a reducing agent therefor capable of converting the ferricyanide to ferrocyanide by the action of actinic light, and the other cost containing a soluble oxalate salt, and also a soluble ferrocyanide salt and a soluble fen'icyanidesaltboth of which are adapted to difiuse to the first coat upon wetting for reaction with the insoluble ferrous oxalate formed in the light-sensitive coat by the action of light.

5. A sensitized blue-print sheet comprising a sheet having two contiguous water-permeable coats containing chemical ingredients, one coat being light-sensitive and located for positioning it between the other and a source of actinic light and containing light-sensitive ferrioxalate salt and a soluble fen'iiiyanide salt as the essential ingredients for reaction under the influence of actinic light to produce insoluble ferrous oxalate,

being 'light -sensitive and located for positioning; 4 it between the'other and a source of actinic light and containing light-sensitive ferrioxalate. salt,

and asoluble ferricyanide salt as the essential ingredients for reaction under'the influence of and the other coat containing a supply of soluble salt of the group consisting of ferricyanideand ferrocyanide essential forthe development of. an insoluble pigmert upon application of water, by diffusion torand reaction with the ferrous oxalate,

"each of said coats being more or less definite and containing a body of hydrophilic substance housing the respective chemical ingredients,

7. A light-sensitive sheet for blue-printing I. I comprising a light-sensitive material in extended coat by the actinic light to produce insoluble ferrous oxalate,

. of light and containing essentially a light-sensitive mixture of soluble salts-of ferrioxalate and ferricyanide, and contiguous material in like form positioned in .the sheet to be more remote from said source. of actinic light than said first form, said second form containing a soluble ferrocyanide salt, both materials being permeable to water to cause difiusion of ferrocyanide from thesecond form to the first form for development of a light-exposed print.

8. A sensitized blue-print body comprising a carrier base having two contiguous water-permeable layers thereon containing chemical ingredients, one layer being light-sensitive and located for positioning it between the other and a source of actinic light and containing light-sensitive ferrioxalate salt, a soluble ferricyanide salt and a reducing agent therefor-capable of converting the ferricyanide to ferrocyanide by the action of actinic light, and the other layer containing a soluble complex salt of the group" consisting of ferricyanide and ferrocyanide which is adapted to diffuse to the first layer upon wetting for reaction with the insoluble ferrous oxalate formed in the light-sensitive layer by the action of light.

9. A sensitized blue-print body comprising a carrier base'having two contiguous water-permeable layers thereon containing chemical ingredients, one layerbeing light-sensitive and located for positioning it between the other and a source of, actinic light 'and containing light-sensitive ferrioxalate salt, a soluble ferricyanide salt and a reducing agent therefor capable of converting the ferricyanide to ferrocyanide by the action oi actinic light, and the other layer containing a soluble ferrocyanide salt and a soluble ferri cyanide salt both of which are adapted to diffuse sensitive layer by the action of light.

10. A sensitized blue-print body comprising a carrier base having two contiguous water-permeable layers thereon containing chemical ingredients, one layer being lint-sensitive and located for positioning it between the other and a source of actinic light and containing lightsensitive ferrioxalate salt, and a soluble ferricyanide salt as the essential ingredients for re- 4 action under the influence of actinic light to produce insoluble ferrous oxalate, and the other layer containing a supply of soluble salt of the groupconsisting of ferricyanide and ferrocyanide essential for the development of an insoluble pigment upon application of water, by diffusion to and reaction with the ferrous oxalate, each of 'said layers being more or less definite and containing a body of hydraphilicsubstance housing the respective chemical ingredients.

'11. The process of making sensitized bodies for blue-prints of the type in which a lightsensitive ferrioxalate salt is altered by light to produce insoluble ferrous oxalate and in which a soluble complex salt of the group consisting of 'ferricyanide and ferrocyanide unites with the ferrous oxalate to form an insoluble complex iron iron-cyanide when water is'applled, the steps of coating a carrier body with an aqueous coating composition containing salt from said abovementioned group. drying the application to a coat on said body, then applying to said heat a second aqueous-coating composition carrying a light-sensitizing substance including essentially light-sensitive ferrloxalate salt, a lesser quantity of soluble ferricyanide salt, and a reducing agent which is capable of converting the last-mentioned ferricyanide salt to a ierrocyanide salt by the action of actinic application to a coat overlying the first coat. while preserving the light sensitive character of the resultingoverlying coat.

12. The process of claim 11 in which the first coating composition includes a simple oxalate salt.

13. The process of claim 11 in which at least one of the coating compositions contains a dimiorming hydrophiiic substance as a body defining the resulting coat.

14. The process of making sensitized bodies for blue-prints of the type in which a light-sensitive terrioxalate salt is altered by light to produce insoluble ferrous oxalate and in which a soluble complex salt of the group of ferricyanide and ferrocyanide unites with the ferrous light, and drying said second 4 oxalate to form an insoluble cyanide when water is applied, the steps of coatin: a carrier body with an aqueous coating, composition containing salt from said above-mentioned group, drying the application to a coat on said body, then applying to said coat a second aqueous coating composition carrying a lightsensitizing substance including essentially lightsensitive ierrioxalate salt and a. lesser quantity oi soluble ierrlcyanide salt, and drying said secand application to a coat overlying the first'coat.

while preserving the light-sensitive character of the resulting overlying coat.

15. The process of claim 14 in. which at least one o! the coating compositions contains a dimiorming hydrophilic substance as a bodydeflning the resulting coat.

- WALKER M.

complex iron ironmm. WALTER G. HOI..1MANH. v

Images